1
|
Kaiser AD, Haidar MA, Choi PS, Sharir A, Marsden AL, Ma MR. Simulation-based design of bicuspidization of the aortic valve. J Thorac Cardiovasc Surg 2024:S0022-5223(24)00009-6. [PMID: 38211896 DOI: 10.1016/j.jtcvs.2023.12.027] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/22/2023] [Revised: 12/05/2023] [Accepted: 12/21/2023] [Indexed: 01/13/2024]
Abstract
OBJECTIVE Severe congenital aortic valve pathology in the growing patient remains a challenging clinical scenario. Bicuspidization of the diseased aortic valve has proven to be a promising repair technique with acceptable durability. However, most understanding of the procedure is empirical and retrospective. This work seeks to design the optimal gross morphology associated with surgical bicuspidization with simulations based on the hypothesis that modifications to the free edge length cause or relieve stenosis. METHODS Model bicuspid valves were constructed with varying free edge lengths and gross morphology. Fluid-structure interaction simulations were conducted in a single patient-specific model geometry. The models were evaluated for primary targets of stenosis and regurgitation. Secondary targets were assessed and included qualitative hemodynamics, geometric height, effective height, orifice area, and billow. RESULTS Stenosis decreased with increasing free edge length and was pronounced with free edge length less than or equal to 1.3 times the annular diameter d. With free edge length 1.5d or greater, no stenosis occurred. All models were free of regurgitation. Substantial billow occurred with free edge length 1.7d or greater. CONCLUSIONS Free edge length 1.5d or greater was required to avoid aortic stenosis in simulations. Cases with free edge length 1.7d or greater showed excessive billow and other changes in gross morphology. Cases with free edge length 1.5d to 1.6d have a total free edge length approximately equal to the annular circumference and appeared optimal. These effects should be studied in vitro and in animal studies.
Collapse
Affiliation(s)
- Alexander D Kaiser
- Division of Pediatric Cardiology, Department of Pediatrics, Stanford University, Stanford, Calif; Cardiovascular Institute, Stanford University, Stanford, Calif
| | - Moussa A Haidar
- Division of Pediatric Cardiac Surgery, Department of Cardiothoracic Surgery, Stanford University, Stanford, Calif
| | - Perry S Choi
- Division of Pediatric Cardiac Surgery, Department of Cardiothoracic Surgery, Stanford University, Stanford, Calif
| | - Amit Sharir
- Division of Pediatric Cardiac Surgery, Department of Cardiothoracic Surgery, Stanford University, Stanford, Calif
| | - Alison L Marsden
- Division of Pediatric Cardiology, Department of Pediatrics, Stanford University, Stanford, Calif; Cardiovascular Institute, Stanford University, Stanford, Calif; Department of Bioengineering, Stanford University, Stanford, Calif; Institute for Computational and Mathematical Engineering, Stanford University, Stanford, Calif
| | - Michael R Ma
- Cardiovascular Institute, Stanford University, Stanford, Calif; Division of Pediatric Cardiac Surgery, Department of Cardiothoracic Surgery, Stanford University, Stanford, Calif.
| |
Collapse
|
2
|
Pedersen DD, Kim S, D'Amore A, Wagner WR. Cardiac valve scaffold design: Implications of material properties and geometric configuration on performance and mechanics. J Mech Behav Biomed Mater 2023; 146:106043. [PMID: 37531773 DOI: 10.1016/j.jmbbm.2023.106043] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2023] [Revised: 06/07/2023] [Accepted: 07/22/2023] [Indexed: 08/04/2023]
Abstract
Development of tissue engineered scaffolds for cardiac valve replacement is nearing clinical translation. While much work has been done to characterize mechanical behavior of native and bioprosthetic valves, and incorporate those data into models improving valve design, similar work for degradable valve scaffolds is lacking. This is particularly important given the implications mechanics have on short-term survival and long-term remodeling. As such, this study aimed to characterize spatially-resolved strain profiles on the leaflets of degradable polymeric valve scaffolds, manipulating common design features such as material stiffness by blending poly(carbonate urethane)urea with stiffer polymers, and geometric configuration, modeled after either a clinically-used valve design (Mk1 design) or an anatomically "optimized" design (Mk2 design). It was shown that material stiffness plays a significant role in overall valve performance, with the stiffest valve groups showing asymmetric and incomplete opening during systole. However, the geometric configuration had a significantly greater effect on valve performance as well as strain magnitude and distribution. Major findings in the strain maps included systolic strains having overall higher strain magnitudes than diastole, and peak radial-direction strain concentrations in the base region of Mk1 valves during systole, with a significant mitigation of radial strain in Mk2 valves. The high tunability of tissue engineered scaffolds is a great advantage for valve design, and the results reported here indicate that design parameters have significant and unequal impact on valve performance and mechanics.
Collapse
Affiliation(s)
- Drake D Pedersen
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, USA; McGowan Institute for Regenerative Medicine, University of Pittsburgh, PA, USA
| | - Seungil Kim
- McGowan Institute for Regenerative Medicine, University of Pittsburgh, PA, USA; Department of Surgery, University of Pittsburgh, PA, USA
| | - Antonio D'Amore
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, USA; McGowan Institute for Regenerative Medicine, University of Pittsburgh, PA, USA; Department of Surgery, University of Pittsburgh, PA, USA; Fondazione Ri.MED, Palermo, Italy; Clinical and Translational Science Institute, University of Pittsburgh, PA, USA
| | - William R Wagner
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, USA; McGowan Institute for Regenerative Medicine, University of Pittsburgh, PA, USA; Department of Surgery, University of Pittsburgh, PA, USA; Department of Chemical Engineering, University of Pittsburgh, PA, USA; Clinical and Translational Science Institute, University of Pittsburgh, PA, USA.
| |
Collapse
|
3
|
Kaiser AD, Schiavone NK, Elkins CJ, McElhinney DB, Eaton JK, Marsden AL. Comparison of Immersed Boundary Simulations of Heart Valve Hemodynamics Against In Vitro 4D Flow MRI Data. Ann Biomed Eng 2023; 51:2267-2288. [PMID: 37378877 PMCID: PMC10775908 DOI: 10.1007/s10439-023-03266-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2023] [Accepted: 05/31/2023] [Indexed: 06/29/2023]
Abstract
The immersed boundary (IB) method is a mathematical framework for fluid-structure interaction problems (FSI) that was originally developed to simulate flows around heart valves. Direct comparison of FSI simulations around heart valves against experimental data is challenging, however, due to the difficulty of performing robust and effective simulations, the complications of modeling a specific physical experiment, and the need to acquire experimental data that is directly comparable to simulation data. Such comparators are a necessary precursor for further formal validation studies of FSI simulations involving heart valves. In this work, we performed physical experiments of flow through a pulmonary valve in an in vitro pulse duplicator, and measured the corresponding velocity field using 4D flow MRI (4-dimensional flow magnetic resonance imaging). We constructed a computer model of this pulmonary artery setup, including modeling valve geometry and material properties via a technique called design-based elasticity, and simulated flow through it with the IB method. The simulated flow fields showed excellent qualitative agreement with experiments, excellent agreement on integral metrics, and reasonable relative error in the entire flow domain and on slices of interest. These results illustrate how to construct a computational model of a physical experiment for use as a comparator.
Collapse
Affiliation(s)
- Alexander D Kaiser
- Department of Pediatrics (Cardiology), Stanford University, Stanford, CA, USA
- Stanford Cardiovascular Institute, Stanford, CA, USA
| | - Nicole K Schiavone
- Department of Mechanical Engineering, Stanford University, Stanford, CA, USA
| | | | - Doff B McElhinney
- Department of Pediatrics (Cardiology), Stanford University, Stanford, CA, USA
- Stanford Cardiovascular Institute, Stanford, CA, USA
- Department of Cardiothoracic Surgery, Stanford University, Stanford, CA, USA
| | - John K Eaton
- Department of Mechanical Engineering, Stanford University, Stanford, CA, USA
| | - Alison L Marsden
- Department of Pediatrics (Cardiology), Stanford University, Stanford, CA, USA.
- Stanford Cardiovascular Institute, Stanford, CA, USA.
- Department of Mechanical Engineering, Stanford University, Stanford, CA, USA.
- Institute for Computational and Mathematical Engineering, Stanford University, Stanford, CA, USA.
- Department of Bioengineering, Stanford University, Stanford, CA, USA.
| |
Collapse
|
4
|
West TM, Howsmon DP, Massidda MW, Vo HN, Janobas AA, Baker AB, Sacks MS. The effects of strain history on aortic valve interstitial cell activation in a 3D hydrogel environment. APL Bioeng 2023; 7:026101. [PMID: 37035541 PMCID: PMC10076067 DOI: 10.1063/5.0138030] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2022] [Accepted: 03/13/2023] [Indexed: 04/05/2023] Open
Abstract
Aortic valves (AVs) undergo unique stretch histories that include high rates and magnitudes. While major differences in deformation patterns have been observed between normal and congenitally defective bicuspid aortic valves (BAVs), the relation to underlying mechanisms of rapid disease onset in BAV patients remains unknown. To evaluate how the variations in stretch history affect AV interstitial cell (AVIC) activation, high-throughput methods were developed to impart varied cyclical biaxial stretch histories into 3D poly(ethylene) glycol hydrogels seeded with AVICs for 48 h. Specifically, a physiologically mimicking stretch history was compared to two stretch histories with varied peak stretch and stretch rate. Post-conditioned AVICs were imaged for nuclear shape, alpha smooth muscle actin (αSMA) and vimentin (VMN) polymerization, and small mothers against decapentaplegic homologs 2 and 3 (SMAD 2/3) nuclear activity. The results indicated that bulk gel deformations were accurately transduced to the AVICs. Lower peak stretches lead to increased αSMA polymerization. In contrast, VMN polymerization was a function of stretch rate, with SMAD 2/3 nuclear localization and nuclear shape also trending toward stretch rate dependency. Lower than physiological levels of stretch rate led to higher SMAD 2/3 activity, higher VMN polymerization around the nucleus, and lower nuclear elongation. αSMA polymerization did not correlate with VMN polymerization, SMAD 2/3 activity, nor nuclear shape. These results suggest that a negative feedback loop may form between SMAD 2/3, VMN, and nuclear shape to maintain AVIC homeostatic nuclear deformations, which is dependent on stretch rate. These novel results suggest that AVIC mechanobiological responses are sensitive to stretch history and provide insight into the mechanisms of AV disease.
Collapse
Affiliation(s)
- Toni M. West
- James T. Willerson Center for Cardiovascular Modelling and Simulation, Oden Institute for Computational Engineering and Sciences and the Department of Biomedical Engineering, Austin, Texas 78711, USA
| | - Daniel P. Howsmon
- James T. Willerson Center for Cardiovascular Modelling and Simulation, Oden Institute for Computational Engineering and Sciences and the Department of Biomedical Engineering, Austin, Texas 78711, USA
| | - Miles W. Massidda
- Department of Biomedical Engineering, The University of Texas at Austin, Austin, Texas 78711, USA
| | | | | | - Aaron B. Baker
- Department of Biomedical Engineering, The University of Texas at Austin, Austin, Texas 78711, USA
| | - Michael S. Sacks
- James T. Willerson Center for Cardiovascular Modelling and Simulation, Oden Institute for Computational Engineering and Sciences and the Department of Biomedical Engineering, Austin, Texas 78711, USA
| |
Collapse
|
5
|
Bahadormanesh N, Tomka B, Abdelkhalek M, Khodaei S, Maftoon N, Keshavarz-Motamed Z. A Doppler-exclusive non-invasive computational diagnostic framework for personalized transcatheter aortic valve replacement. Sci Rep 2023; 13:8033. [PMID: 37198194 PMCID: PMC10192526 DOI: 10.1038/s41598-023-33511-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2022] [Accepted: 04/13/2023] [Indexed: 05/19/2023] Open
Abstract
Given the associated risks with transcatheter aortic valve replacement (TAVR), it is crucial to determine how the implant will affect the valve dynamics and cardiac function, and if TAVR will improve or worsen the outcome of the patient. Effective treatment strategies, indeed, rely heavily on the complete understanding of the valve dynamics. We developed an innovative Doppler-exclusive non-invasive computational framework that can function as a diagnostic tool to assess valve dynamics in patients with aortic stenosis in both pre- and post-TAVR status. Clinical Doppler pressure was reduced by TAVR (52.2 ± 20.4 vs. 17.3 ± 13.8 [mmHg], p < 0.001), but it was not always accompanied by improvements in valve dynamics and left ventricle (LV) hemodynamics metrics. TAVR had no effect on LV workload in 4 patients, and LV workload post-TAVR significantly rose in 4 other patients. Despite the group level improvements in maximum LV pressure (166.4 ± 32.2 vs 131.4 ± 16.9 [mmHg], p < 0.05), only 5 of the 12 patients (41%) had a decrease in LV pressure. Moreover, TAVR did not always improve valve dynamics. TAVR did not necessarily result in a decrease (in 9 out of 12 patients investigated in this study) in major principal stress on the aortic valve leaflets which is one of the main contributors in valve degeneration and, consequently, failure of heart valves. Diastolic stresses increased significantly post-TAVR (34%, 109% and 81%, p < 0.001) for each left, right and non-coronary leaflets respectively. Moreover, we quantified the stiffness and material properties of aortic valve leaflets which correspond with the reduced calcified region average stiffness among leaflets (66%, 74% and 62%; p < 0.001; N = 12). Valve dynamics post-intervention should be quantified and monitored to ensure the improvement of patient conditions and prevent any further complications. Improper evaluation of biomechanical valve features pre-intervention as well as post-intervention may result in harmful effects post-TAVR in patients including paravalvular leaks, valve degeneration, failure of TAVR and heart failure.
Collapse
Affiliation(s)
- Nikrouz Bahadormanesh
- Department of Mechanical Engineering, McMaster University, JHE-310, Hamilton, ON, L8S 4L7, Canada
| | - Benjamin Tomka
- Department of Mechanical Engineering, McMaster University, JHE-310, Hamilton, ON, L8S 4L7, Canada
| | | | - Seyedvahid Khodaei
- Department of Mechanical Engineering, McMaster University, JHE-310, Hamilton, ON, L8S 4L7, Canada
| | - Nima Maftoon
- Department of Systems Design Engineering, University of Waterloo, Waterloo, ON, Canada
- Centre for Bioengineering and Biotechnology, University of Waterloo, Waterloo, ON, Canada
| | - Zahra Keshavarz-Motamed
- Department of Mechanical Engineering, McMaster University, JHE-310, Hamilton, ON, L8S 4L7, Canada.
- School of Biomedical Engineering, McMaster University, Hamilton, ON, Canada.
- School of Computational Science and Engineering, McMaster University, Hamilton, ON, Canada.
| |
Collapse
|
6
|
Bahadormanesh N, Tomka B, Kadem M, Khodaei S, Keshavarz-Motamed Z. An ultrasound-exclusive non-invasive computational diagnostic framework for personalized cardiology of aortic valve stenosis. Med Image Anal 2023; 87:102795. [PMID: 37060702 DOI: 10.1016/j.media.2023.102795] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2021] [Revised: 02/27/2023] [Accepted: 03/06/2023] [Indexed: 03/30/2023]
Abstract
Aortic stenosis (AS) is an acute and chronic cardiovascular disease and If left untreated, 50% of these patients will die within two years of developing symptoms. AS is characterized as the stiffening of the aortic valve leaflets which restricts their motion and prevents the proper opening under transvalvular pressure. Assessments of the valve dynamics, if available, would provide valuable information about the patient's state of cardiac deterioration as well as heart recovery and can have incredible impacts on patient care, planning interventions and making critical clinical decisions with life-threatening risks. Despite remarkable advancements in medical imaging, there are no clinical tools available to quantify valve dynamics invasively or noninvasively. In this study, we developed a highly innovative ultrasound-based non-invasive computational framework that can function as a diagnostic tool to assess valve dynamics (e.g. transient 3-D distribution of stress and displacement, 3-D deformed shape of leaflets, geometric orifice area and angular positions of leaflets) for patients with AS at no risk to the patients. Such a diagnostic tool considers the local valve dynamics and the global circulatory system to provide a platform for testing the intervention scenarios and evaluating their effects. We used clinical data of 12 patients with AS not only to validate the proposed framework but also to demonstrate its diagnostic abilities by providing novel analyses and interpretations of clinical data in both pre and post intervention states. We used transthoracic echocardiogram (TTE) data for the developments and transesophageal echocardiography (TEE) data for validation.
Collapse
Affiliation(s)
| | - Benjamin Tomka
- Department of Mechanical Engineering, McMaster University Hamilton, ON, Canada
| | - Mason Kadem
- School of Biomedical Engineering, McMaster University, Hamilton, ON, Canada
| | - Seyedvahid Khodaei
- Department of Mechanical Engineering, McMaster University Hamilton, ON, Canada
| | - Zahra Keshavarz-Motamed
- Department of Mechanical Engineering, McMaster University Hamilton, ON, Canada; School of Biomedical Engineering, McMaster University, Hamilton, ON, Canada; School of Computational Science and Engineering, McMaster University, Hamilton, ON, Canada.
| |
Collapse
|
7
|
Salim MT, Villa-Roel N, Vogel B, Jo H, Yoganathan AP. HIF1A inhibitor PX-478 reduces pathological stretch-induced calcification and collagen turnover in aortic valve. Front Cardiovasc Med 2022; 9:1002067. [PMID: 36419483 PMCID: PMC9676244 DOI: 10.3389/fcvm.2022.1002067] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2022] [Accepted: 10/20/2022] [Indexed: 09/19/2023] Open
Abstract
HIF1A is significantly upregulated in calcified human aortic valves (AVs). Furthermore, HIF1A inhibitor PX-478 was shown to inhibit AV calcification under static and disturbed flow conditions. Since elevated stretch is one of the major mechanical stimuli for AV calcification, we investigated the effect of PX-478 on AV calcification and collagen turnover under a pathophysiological cyclic stretch (15%) condition. Porcine aortic valve (PAV) leaflets were cyclically (1 Hz) stretched at 15% for 24 days in osteogenic medium with or without PX-478. In addition, PAV leaflets were cyclically stretched at a physiological (10%) and 15% for 3 days in regular medium to assess its effect of on HIF1A mRNA expression. It was found that 100 μM (high concentration) PX-478 could significantly inhibit PAV calcification under 15% stretch, whereas 50 μM (moderate concentration) PX-478 showed a modest inhibitory effect on PAV calcification. Nonetheless, 50 μM PX-478 significantly reduced PAV collagen turnover under 15% stretch. Surprisingly, it was observed that cyclic stretch (15% vs. 10%) did not have any significant effect on HIF1A mRNA expression in PAV leaflets. These results suggest that HIF1A inhibitor PX-478 may impart its anti-calcific and anti-matrix remodeling effect in a stretch-independent manner.
Collapse
Affiliation(s)
- Md Tausif Salim
- School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA, United States
| | - Nicolas Villa-Roel
- The Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA, United States
| | - Booth Vogel
- School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA, United States
| | - Hanjoong Jo
- The Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA, United States
| | - Ajit P. Yoganathan
- School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA, United States
- The Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA, United States
| |
Collapse
|
8
|
Kaiser AD, Shad R, Schiavone N, Hiesinger W, Marsden AL. Controlled Comparison of Simulated Hemodynamics Across Tricuspid and Bicuspid Aortic Valves. Ann Biomed Eng 2022; 50:1053-1072. [PMID: 35748961 PMCID: PMC10775905 DOI: 10.1007/s10439-022-02983-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2021] [Accepted: 05/16/2022] [Indexed: 11/01/2022]
Abstract
Bicuspid aortic valve is the most common congenital heart defect, affecting 1-2% of the global population. Patients with bicuspid valves frequently develop dilation and aneurysms of the ascending aorta. Both hemodynamic and genetic factors are believed to contribute to dilation, yet the precise mechanism underlying this progression remains under debate. Controlled comparisons of hemodynamics in patients with different forms of bicuspid valve disease are challenging because of confounding factors, and simulations offer the opportunity for direct and systematic comparisons. Using fluid-structure interaction simulations, we simulate flows through multiple aortic valve models in a patient-specific geometry. The aortic geometry is based on a healthy patient with no known aortic or valvular disease, which allows us to isolate the hemodynamic consequences of changes to the valve alone. Four fully-passive, elastic model valves are studied: a tricuspid valve and bicuspid valves with fusion of the left- and right-, right- and non-, and non- and left-coronary cusps. The resulting tricuspid flow is relatively uniform, with little secondary or reverse flow, and little to no pressure gradient across the valve. The bicuspid cases show localized jets of forward flow, excess streamwise momentum, elevated secondary and reverse flow, and clinically significant levels of stenosis. Localized high flow rates correspond to locations of dilation observed in patients, with the location related to which valve cusps are fused. Thus, the simulations support the hypothesis that chronic exposure to high local flow contributes to localized dilation and aneurysm formation.
Collapse
Affiliation(s)
- Alexander D Kaiser
- Institute for Computational & Mathematical Engineering, Stanford University, Stanford, CA, USA
- Department of Pediatrics (Cardiology), Stanford University, Stanford, CA, USA
- Stanford Cardiovascular Institute, Stanford, CA, USA
| | - Rohan Shad
- Stanford Cardiovascular Institute, Stanford, CA, USA
- Department of Cardiothoracic Surgery, Stanford University, Stanford, CA, USA
| | - Nicole Schiavone
- Department of Mechanical Engineering, Stanford University, Stanford, CA, USA
| | - William Hiesinger
- Stanford Cardiovascular Institute, Stanford, CA, USA
- Department of Cardiothoracic Surgery, Stanford University, Stanford, CA, USA
| | - Alison L Marsden
- Institute for Computational & Mathematical Engineering, Stanford University, Stanford, CA, USA.
- Department of Pediatrics (Cardiology), Stanford University, Stanford, CA, USA.
- Stanford Cardiovascular Institute, Stanford, CA, USA.
- Department of Mechanical Engineering, Stanford University, Stanford, CA, USA.
- Department of Bioengineering, Stanford University, Stanford, CA, USA.
| |
Collapse
|
9
|
Kaiser AD, Shad R, Hiesinger W, Marsden AL. A design-based model of the aortic valve for fluid-structure interaction. Biomech Model Mechanobiol 2021; 20:2413-2435. [PMID: 34549354 PMCID: PMC10752438 DOI: 10.1007/s10237-021-01516-7] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2020] [Accepted: 08/22/2021] [Indexed: 11/27/2022]
Abstract
This paper presents a new method for modeling the mechanics of the aortic valve and simulates its interaction with blood. As much as possible, the model construction is based on first principles, but such that the model is consistent with experimental observations. We require that tension in the leaflets must support a pressure, then derive a system of partial differential equations governing its mechanical equilibrium. The solution to these differential equations is referred to as the predicted loaded configuration; it includes the loaded leaflet geometry, fiber orientations and tensions needed to support the prescribed load. From this configuration, we derive a reference configuration and constitutive law. In fluid-structure interaction simulations with the immersed boundary method, the model seals reliably under physiological pressures and opens freely over multiple cardiac cycles. Further, model closure is robust to extreme hypo- and hypertensive pressures. Then, exploiting the unique features of this model construction, we conduct experiments on reference configurations, constitutive laws and gross morphology. These experiments suggest the following conclusions: (1) The loaded geometry, tensions and tangent moduli primarily determine model function. (2) Alterations to the reference configuration have little effect if the predicted loaded configuration is identical. (3) The leaflets must have sufficiently nonlinear material response to function over a variety of pressures. (4) Valve performance is highly sensitive to free edge length and leaflet height. These conclusions suggest appropriate gross morphology and material properties for the design of prosthetic aortic valves. In future studies, our aortic valve modeling framework can be used with patient-specific models of vascular or cardiac flow.
Collapse
Affiliation(s)
- Alexander D Kaiser
- Institute for Computational and Mathematical Engineering, Stanford University, Stanford, CA, USA.
- Department of Pediatrics (Cardiology), Stanford University, Stanford, CA, USA.
- Stanford Cardiovascular Institute, Stanford, CA, USA.
| | - Rohan Shad
- Stanford Cardiovascular Institute, Stanford, CA, USA
- Department of Cardiothoracic Surgery, Stanford University, Stanford, CA, USA
| | - William Hiesinger
- Stanford Cardiovascular Institute, Stanford, CA, USA
- Department of Cardiothoracic Surgery, Stanford University, Stanford, CA, USA
| | - Alison L Marsden
- Institute for Computational and Mathematical Engineering, Stanford University, Stanford, CA, USA
- Department of Pediatrics (Cardiology), Stanford University, Stanford, CA, USA
- Stanford Cardiovascular Institute, Stanford, CA, USA
- Department of Bioengineering, Stanford University, Stanford, CA, USA
| |
Collapse
|
10
|
Park MH, Zhu Y, Imbrie-Moore AM, Wang H, Marin-Cuartas M, Paulsen MJ, Woo YJ. Heart Valve Biomechanics: The Frontiers of Modeling Modalities and the Expansive Capabilities of Ex Vivo Heart Simulation. Front Cardiovasc Med 2021; 8:673689. [PMID: 34307492 PMCID: PMC8295480 DOI: 10.3389/fcvm.2021.673689] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2021] [Accepted: 05/17/2021] [Indexed: 01/05/2023] Open
Abstract
The field of heart valve biomechanics is a rapidly expanding, highly clinically relevant area of research. While most valvular pathologies are rooted in biomechanical changes, the technologies for studying these pathologies and identifying treatments have largely been limited. Nonetheless, significant advancements are underway to better understand the biomechanics of heart valves, pathologies, and interventional therapeutics, and these advancements have largely been driven by crucial in silico, ex vivo, and in vivo modeling technologies. These modalities represent cutting-edge abilities for generating novel insights regarding native, disease, and repair physiologies, and each has unique advantages and limitations for advancing study in this field. In particular, novel ex vivo modeling technologies represent an especially promising class of translatable research that leverages the advantages from both in silico and in vivo modeling to provide deep quantitative and qualitative insights on valvular biomechanics. The frontiers of this work are being discovered by innovative research groups that have used creative, interdisciplinary approaches toward recapitulating in vivo physiology, changing the landscape of clinical understanding and practice for cardiovascular surgery and medicine.
Collapse
Affiliation(s)
- Matthew H Park
- Department of Cardiothoracic Surgery, Stanford University, Stanford, CA, United States.,Department of Mechanical Engineering, Stanford University, Stanford, CA, United States
| | - Yuanjia Zhu
- Department of Cardiothoracic Surgery, Stanford University, Stanford, CA, United States.,Department of Bioengineering, Stanford University, Stanford, CA, United States
| | - Annabel M Imbrie-Moore
- Department of Cardiothoracic Surgery, Stanford University, Stanford, CA, United States.,Department of Mechanical Engineering, Stanford University, Stanford, CA, United States
| | - Hanjay Wang
- Department of Cardiothoracic Surgery, Stanford University, Stanford, CA, United States
| | - Mateo Marin-Cuartas
- Department of Cardiothoracic Surgery, Stanford University, Stanford, CA, United States.,University Department of Cardiac Surgery, Leipzig Heart Center, Leipzig, Germany
| | - Michael J Paulsen
- Department of Cardiothoracic Surgery, Stanford University, Stanford, CA, United States
| | - Y Joseph Woo
- Department of Cardiothoracic Surgery, Stanford University, Stanford, CA, United States.,Department of Bioengineering, Stanford University, Stanford, CA, United States
| |
Collapse
|
11
|
Whelan A, O'Brien G, Szagdaj A, O'Reilly D, Lally C. Investigation into early stage fatigue-damage accumulation in glutaraldehyde-fixed bovine pericardium using a novel equibiaxial bulge inflation system. J Mech Behav Biomed Mater 2021; 121:104588. [PMID: 34091153 DOI: 10.1016/j.jmbbm.2021.104588] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2020] [Revised: 05/05/2021] [Accepted: 05/09/2021] [Indexed: 10/21/2022]
Abstract
A primary cause of bioprosthetic heart valve failure is premature degeneration of the pericardial leaflets, owing specifically to mechanical fatigue. There remains a paucity of experimental data and understanding of the fatigue-damage behaviour of this collagenous tissue under complex loading regimes. To meet this knowledge gap, a novel pressure inflation system was designed and built, to cyclically load circular samples of glutaraldehyde fixed bovine pericardium, under equibiaxial bulge conditions. A study up to 60 million cycles revealed new insights into the fatigue behaviour of pericardial tissue, where a statistically significantly higher level of permanent set was found in samples with high collagen fibre dispersion, in comparison to those with highly aligned fibres. Whilst permanent set is known to occur in the non-collagenous matrix of pericardium, this study demonstrates that at physiological loads, which elicit a matrix dominant mechanical response, permanent set and thus tissue-level damage, is still mediated by the underlying collagen fibres.
Collapse
Affiliation(s)
- Alix Whelan
- Trinity Centre for Biomedical Engineering, Trinity Biomedical Sciences Institute, Trinity College Dublin, Dublin 2, Ireland; Department of Mechanical, Manufacturing and Biomedical Engineering, School of Engineering, Trinity College Dublin, Dublin 2, Ireland; Structural Heart Division, Boston Scientific Corporation, Galway, Ireland
| | - Gordon O'Brien
- Department of Mechanical, Manufacturing and Biomedical Engineering, School of Engineering, Trinity College Dublin, Dublin 2, Ireland
| | - Anna Szagdaj
- Trinity Centre for Biomedical Engineering, Trinity Biomedical Sciences Institute, Trinity College Dublin, Dublin 2, Ireland; Department of Mechanical, Manufacturing and Biomedical Engineering, School of Engineering, Trinity College Dublin, Dublin 2, Ireland
| | - David O'Reilly
- Structural Heart Division, Boston Scientific Corporation, Galway, Ireland
| | - Caitríona Lally
- Trinity Centre for Biomedical Engineering, Trinity Biomedical Sciences Institute, Trinity College Dublin, Dublin 2, Ireland; Department of Mechanical, Manufacturing and Biomedical Engineering, School of Engineering, Trinity College Dublin, Dublin 2, Ireland; Advanced Materials and Bioengineering Research Centre (AMBER), Royal College of Surgeons in Ireland and Trinity College Dublin, Dublin, Ireland.
| |
Collapse
|
12
|
Nachlas ALY, Li S, Streeter BW, De Jesus Morales KJ, Sulejmani F, Madukauwa-David DI, Bejleri D, Sun W, Yoganathan AP, Davis ME. A multilayered valve leaflet promotes cell-laden collagen type I production and aortic valve hemodynamics. Biomaterials 2020; 240:119838. [PMID: 32092591 DOI: 10.1016/j.biomaterials.2020.119838] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2019] [Revised: 01/27/2020] [Accepted: 01/31/2020] [Indexed: 12/18/2022]
Abstract
Patients with aortic heart valve disease are limited to valve replacements that lack the ability to grow and remodel. This presents a major challenge for pediatric patients who require a valve capable of somatic growth and at a smaller size. A patient-specific heart valve capable of growth and remodeling while maintaining proper valve function would address this major issue. Here, we recreate the native valve leaflet structure composed of poly-ε-caprolactone (PCL) and cell-laden gelatin-methacrylate/poly (ethylene glycol) diacrylate (GelMA/PEGDA) hydrogels using 3D printing and molding, and then evaluate the ability of the multilayered scaffold to produce collagen matrix under physiological shear stress conditions. We also characterized the valve hemodynamics under aortic physiological flow conditions. The valve's fibrosa layer was replicated by 3D printing PCL in a circumferential direction similar to collagen alignment in the native leaflet, and GelMA/PEGDA sustained and promoted cell viability in the spongiosa/ventricularis layers. We found that collagen type I production can be increased in the multilayered scaffold when it is exposed to pulsatile shear stress conditions over static conditions. When the PCL component was mounted onto a valve ring and tested under physiological aortic valve conditions, the hemodynamics were comparable to commercially available valves. Our results demonstrate that a structurally representative valve leaflet can be generated using 3D printing and that the PCL layer of the leaflet can sustain proper valve function under physiological aortic valve conditions.
Collapse
Affiliation(s)
- Aline L Y Nachlas
- Wallace H Coulter Department of Biomedical Engineering, Emory University and Georgia Institute of Technology, Atlanta, GA, USA
| | - Siyi Li
- Wallace H Coulter Department of Biomedical Engineering, Emory University and Georgia Institute of Technology, Atlanta, GA, USA
| | - Benjamin W Streeter
- Wallace H Coulter Department of Biomedical Engineering, Emory University and Georgia Institute of Technology, Atlanta, GA, USA
| | - Kenneth J De Jesus Morales
- Wallace H Coulter Department of Biomedical Engineering, Emory University and Georgia Institute of Technology, Atlanta, GA, USA
| | - Fatiesa Sulejmani
- Wallace H Coulter Department of Biomedical Engineering, Emory University and Georgia Institute of Technology, Atlanta, GA, USA
| | - David Immanuel Madukauwa-David
- Bioengineering Graduate Program, Georgia Institute of Technology, Atlanta, GA, USA; George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA, USA
| | - Donald Bejleri
- Wallace H Coulter Department of Biomedical Engineering, Emory University and Georgia Institute of Technology, Atlanta, GA, USA
| | - Wei Sun
- Wallace H Coulter Department of Biomedical Engineering, Emory University and Georgia Institute of Technology, Atlanta, GA, USA
| | - Ajit P Yoganathan
- Wallace H Coulter Department of Biomedical Engineering, Emory University and Georgia Institute of Technology, Atlanta, GA, USA
| | - Michael E Davis
- Wallace H Coulter Department of Biomedical Engineering, Emory University and Georgia Institute of Technology, Atlanta, GA, USA; Children's Heart Research & Outcomes (HeRO) Center, Children's Healthcare of Atlanta & Emory University, Atlanta, GA, USA.
| |
Collapse
|
13
|
Raddatz MA, Madhur MS, Merryman WD. Adaptive immune cells in calcific aortic valve disease. Am J Physiol Heart Circ Physiol 2019; 317:H141-H155. [PMID: 31050556 DOI: 10.1152/ajpheart.00100.2019] [Citation(s) in RCA: 37] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Calcific aortic valve disease (CAVD) is highly prevalent and has no pharmaceutical treatment. Surgical replacement of the aortic valve has proved effective in advanced disease but is costly, time limited, and in many cases not optimal for elderly patients. This has driven an increasing interest in noninvasive therapies for patients with CAVD. Adaptive immune cell signaling in the aortic valve has shown potential as a target for such a therapy. Up to 15% of cells in the healthy aortic valve are hematopoietic in origin, and these cells, which include macrophages, T lymphocytes, and B lymphocytes, are increased further in calcified specimens. Additionally, cytokine signaling has been shown to play a causative role in aortic valve calcification both in vitro and in vivo. This review summarizes the physiological presence of hematopoietic cells in the valve, innate and adaptive immune cell infiltration in disease states, and the cytokine signaling pathways that play a significant role in CAVD pathophysiology and may prove to be pharmaceutical targets for this disease in the near future.
Collapse
Affiliation(s)
- Michael A Raddatz
- Department of Biomedical Engineering, Vanderbilt University , Nashville, Tennessee.,Vanderbilt University School of Medicine , Nashville, Tennessee
| | - Meena S Madhur
- Department of Medicine, Vanderbilt University Medical Center , Nashville, Tennessee.,Department of Molecular Physiology and Biophysics, Vanderbilt University , Nashville, Tennessee.,Division of Clinical Pharmacology, Vanderbilt University Medical Center , Nashville, Tennessee
| | - W David Merryman
- Department of Biomedical Engineering, Vanderbilt University , Nashville, Tennessee
| |
Collapse
|
14
|
miR-214 is Stretch-Sensitive in Aortic Valve and Inhibits Aortic Valve Calcification. Ann Biomed Eng 2019; 47:1106-1115. [PMID: 30671754 DOI: 10.1007/s10439-019-02206-3] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2018] [Accepted: 01/12/2019] [Indexed: 02/06/2023]
Abstract
miR-214 has been recently found to be significantly downregulated in calcified human aortic valves (AVs). ER stress, especially the ATF4-mediated pathway, has also been shown to be significantly upregulated in calcific AV disease. Since elevated cyclic stretch is one of the major mechanical stimuli for AV calcification and ATF4 is a validated target of miR-214, we investigated the effect of cyclic stretch on miR-214 expression as well as those of ATF4 and two downstream genes (CHOP and BCL2L1). Porcine aortic valve (PAV) leaflets were cyclically stretched at 15% for 48 h in regular medium and for 1 week in osteogenic medium to simulate the early remodeling and late calcification stages of stretch-induced AV disease, respectively. For both stages, 10% cyclic stretch served as the physiological counterpart. RT-qPCR revealed that miR-214 expression was significantly downregulated during the late calcification stage, whereas the mRNA expression of ATF4 and BCL2L1 was upregulated and downregulated, respectively, during both early remodeling and late calcification stages. When PAV leaflets were statically transfected with miR-214 mimic in osteogenic medium for 2 weeks, calcification was significantly reduced compared to the control mimic case. This implies that miR-214 may have a protective role in stretch-induced calcific AV disease.
Collapse
|
15
|
Quantitative Characterization of Aortic Valve Endothelial Cell Viability and Morphology In Situ Under Cyclic Stretch. Cardiovasc Eng Technol 2018; 10:173-180. [PMID: 30141125 DOI: 10.1007/s13239-018-00375-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/11/2018] [Accepted: 08/17/2018] [Indexed: 10/28/2022]
Abstract
Current protocols for mechanical preconditioning of tissue engineered heart valves have focused on application of pressure, flexure and fluid flow to stimulate collagen production, ECM remodeling and improving mechanical performance. The aim of this study was to determine if mechanical preconditioning with cyclic stretch could promote an intact endothelium that resembled the viability and morphology of a native valve. Confocal laser scanning microscopy was used to image endothelial cells on aortic valve strips subjected to static incubation or physiological strain regimens. An automated image analysis program was designed and implemented to detect and analyze live and dead cells in images captured of a live aortic valve endothelium. The images were preprocessed, segmented, and quantitatively analyzed for live/dead cell ratio, minimum neighbor distance and circularity. Significant differences in live/dead cellular ratio and the minimum distance between cells were observed between static and strained endothelia, indicating that cyclic strain is an important stimulus for maintaining a healthy endothelium. In conclusion, in vitro application of physiological levels of cyclic strain to tissue engineered heart valves seeded with autologous endothelial cells would be advantageous.
Collapse
|
16
|
Engineering a 3D-Bioprinted Model of Human Heart Valve Disease Using Nanoindentation-Based Biomechanics. NANOMATERIALS 2018; 8:nano8050296. [PMID: 29751516 PMCID: PMC5977310 DOI: 10.3390/nano8050296] [Citation(s) in RCA: 57] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/02/2018] [Revised: 04/18/2018] [Accepted: 04/24/2018] [Indexed: 01/18/2023]
Abstract
In calcific aortic valve disease (CAVD), microcalcifications originating from nanoscale calcifying vesicles disrupt the aortic valve (AV) leaflets, which consist of three (biomechanically) distinct layers: the fibrosa, spongiosa, and ventricularis. CAVD has no pharmacotherapy and lacks in vitro models as a result of complex valvular biomechanical features surrounding resident mechanosensitive valvular interstitial cells (VICs). We measured layer-specific mechanical properties of the human AV and engineered a three-dimensional (3D)-bioprinted CAVD model that recapitulates leaflet layer biomechanics for the first time. Human AV leaflet layers were separated by microdissection, and nanoindentation determined layer-specific Young’s moduli. Methacrylated gelatin (GelMA)/methacrylated hyaluronic acid (HAMA) hydrogels were tuned to duplicate layer-specific mechanical characteristics, followed by 3D-printing with encapsulated human VICs. Hydrogels were exposed to osteogenic media (OM) to induce microcalcification, and VIC pathogenesis was assessed by near infrared or immunofluorescence microscopy. Median Young’s moduli of the AV layers were 37.1, 15.4, and 26.9 kPa (fibrosa/spongiosa/ventricularis, respectively). The fibrosa and spongiosa Young’s moduli matched the 3D 5% GelMa/1% HAMA UV-crosslinked hydrogels. OM stimulation of VIC-laden bioprinted hydrogels induced microcalcification without apoptosis. We report the first layer-specific measurements of human AV moduli and a novel 3D-bioprinted CAVD model that potentiates microcalcification by mimicking the native AV mechanical environment. This work sheds light on valvular mechanobiology and could facilitate high-throughput drug-screening in CAVD.
Collapse
|
17
|
Capoulade R, Teoh JG, Bartko PE, Teo E, Scholtz JE, Tastet L, Shen M, Mihos CG, Park YH, Garcia J, Larose E, Isselbacher EM, Sundt TM, MacGillivray TE, Melnitchouk S, Ghoshhajra BB, Pibarot P, Hung J. Relationship Between Proximal Aorta Morphology and Progression Rate of Aortic Stenosis. J Am Soc Echocardiogr 2018; 31:561-569.e1. [DOI: 10.1016/j.echo.2017.12.008] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/20/2017] [Indexed: 10/18/2022]
|
18
|
Lam NT, Muldoon TJ, Quinn KP, Rajaram N, Balachandran K. Valve interstitial cell contractile strength and metabolic state are dependent on its shape. Integr Biol (Camb) 2017; 8:1079-1089. [PMID: 27713997 DOI: 10.1039/c6ib00120c] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
The role of valvular interstitial cell (VIC) architecture in regulating cardiac valve function and pathology is not well understood. VICs are known to be more elongated in a hypertensive environment compared to those in a normotensive environment. We have previously reported that valve tissues cultured under hypertensive conditions are prone to acute pathological alterations in cell phenotype and contractility. We therefore aimed to rigorously study the relationship between VIC shape, contractile output and other functional indicators of VIC pathology. We developed an in vitro model to engineer VICs to take on the same shapes as those seen in normal and hypertensive conditions. VICs with longer cellular and nuclear shapes, as seen in hypertensive conditions, had greater contractile response to endothelin-1 that correlated with increased anisotropy of the actin architecture. These elongated VICs also demonstrated altered cell metabolism through a decreased optical redox ratio, which coincided with increased cellular proliferation. In the presence of actin polymerization inhibitor, however, these functional responses were significantly reduced, suggesting the important role of cytoskeletal actin organization in regulating cellular responses to abnormal shape. Overall, these results demonstrate the relationship between cell shape, cytoskeletal and nuclear organization, with functional output including contractility, metabolism, and proliferation.
Collapse
Affiliation(s)
- Ngoc Thien Lam
- Cell and Molecular Biology Program, University of Arkansas, Fayetteville, AR 72701, USA
| | - Timothy J Muldoon
- Department of Biomedical Engineering, University of Arkansas, 122 John A. White Jr. Engineering Hall, Fayetteville, AR 72701, USA.
| | - Kyle P Quinn
- Department of Biomedical Engineering, University of Arkansas, 122 John A. White Jr. Engineering Hall, Fayetteville, AR 72701, USA.
| | - Narasimhan Rajaram
- Department of Biomedical Engineering, University of Arkansas, 122 John A. White Jr. Engineering Hall, Fayetteville, AR 72701, USA.
| | - Kartik Balachandran
- Department of Biomedical Engineering, University of Arkansas, 122 John A. White Jr. Engineering Hall, Fayetteville, AR 72701, USA.
| |
Collapse
|
19
|
A study of extracellular matrix remodeling in aortic heart valves using a novel biaxial stretch bioreactor. J Mech Behav Biomed Mater 2017; 75:351-358. [PMID: 28783560 DOI: 10.1016/j.jmbbm.2017.07.041] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2017] [Revised: 07/10/2017] [Accepted: 07/26/2017] [Indexed: 11/22/2022]
Abstract
In aortic valves, biaxial cyclic stretch is known to modulate cell differentiation, extracellular matrix (ECM) synthesis and organization. We designed a novel bioreactor that can apply independent and precise stretch along radial and circumferential directions in a tissue culture environment. While this bioreactor can be used for either native or engineered tissues, this study determined matrix remodeling and strain distribution of aortic cusps after culturing under biaxial stretch for 14 days. The contents of collagen and glycosaminoglycans were determined using standard biochemical assays and compared with fresh controls. Strain fields in static cusps were more uniform than those in stretched cusps, which indicated degradation of the ECM fibers. The glycosaminoglycan content was significantly elevated in the static control as compared to fresh or stretched cusps, but no difference was observed in collagen content among the groups. The strain profile of freshly isolated fibrosa vs. ventricularis and left, right, and noncoronary cusps were also determined by Digital Image Correlation technique. Distinct strain patterns were observed under stretch on fibrosa and ventricularis sides and among the three cusps. This work highlights the critical role of the anisotropic ECM structure for proper functions of native aortic valves and the beneficial effects of biaxial stretch for maintenance of the native ECM structure.
Collapse
|
20
|
Lam NT, Lam H, Sturdivant NM, Balachandran K. Fabrication of a matrigel-collagen semi-interpenetrating scaffold for use in dynamic valve interstitial cell culture. ACTA ACUST UNITED AC 2017; 12:045013. [PMID: 28484097 DOI: 10.1088/1748-605x/aa71be] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
The study of heart valve homeostatic and disease mechanisms are often limited by the challenges in simulating the in vivo milieu, where valve cells are surrounded by the extracellular matrix in a three-dimensional (3D) environment and experience multiple dynamic mechanical forces. Type I collagen is typically the most common 3D matrix used to culture valve cells in vitro. Unfortunately, this material has poor mechanical behavior due to an inherent propensity to compact significantly, unlike native valve leaflets. We hypothesized that incorporation of matrigel, which contains other heart valve-relevant matrix components such as type IV collagen and sulfated proteoglycans, to type I collagen would provide an appropriate physiological milieu for in vitro valve interstitial cell culture. Different semi-interpenetrating mixtures of collagen type I and matrigel were prepared and a thorough characterization of their physical, mechanical and biocompatibility properties was performed. We observed that the matrigel-collagen hydrogel was porous and degradable with tunable swelling behavior. Incorporation of matrigel not only enhanced the mechanical behavior of the composite hydrogel but also presented the cultured valve interstitial cells with a more enriched extracellular matrix network for in vitro culture. We showed that cells cultured in the composite hydrogel had comparable viability, proliferation and cell phenotype as compared with those in a collagen only gel. Importantly, the composite hydrogel was also amenable to in vitro cyclic stretching culture for 48 h. Overall, we report here the potential use of the matrigel-collagen hydrogel as a three dimensional scaffold for the dynamic mechanical culture of valve interstitial cells in vitro.
Collapse
Affiliation(s)
- Ngoc Thien Lam
- Cell and Molecular Biology Program, University of Arkansas, Fayetteville, AR 72701, United States of America
| | | | | | | |
Collapse
|
21
|
Cao K, Sucosky P. Computational comparison of regional stress and deformation characteristics in tricuspid and bicuspid aortic valve leaflets. INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING 2017; 33:e02798. [PMID: 27138991 DOI: 10.1002/cnm.2798] [Citation(s) in RCA: 43] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/19/2015] [Revised: 03/22/2016] [Accepted: 04/20/2016] [Indexed: 06/05/2023]
Abstract
The bicuspid aortic valve (BAV) is the most common congenital valvular defect and a major risk factor for secondary calcific aortic valve disease. While hemodynamics is presumed to be a potential contributor to this complication, the validation of this theory has been hampered by the limited knowledge of the mechanical stress abnormalities experienced by BAV leaflets and their dependence on the heterogeneous BAV fusion patterns. The objective of this study was to compare computationally the regional and temporal fluid wall shear stress (WSS) and structural deformation characteristics in tricuspid aortic valve (TAV), type-0, and type-I BAV leaflets. Arbitrary Lagrangian-Eulerian fluid-structure interaction models were designed to simulate the flow and leaflet dynamics in idealized TAV, type-0, and type-I BAV geometries subjected to physiologic transvalvular pressure. The regional leaflet mechanics was quantified in terms of temporal shear magnitude (TSM), oscillatory shear index (OSI), temporal shear gradient (TSG), and stretch. The simulations identified regions of WSS overloads and increased WSS bidirectionality (174% increase in temporal shear magnitude, 0.10 increase in OSI on type-0 leaflets) in BAV leaflets relative to TAV leaflets. BAV leaflets also experienced larger radial deformations than TAV leaflets (4% increase in type-0 BAV leaflets). Type-I BAV leaflets exhibited contrasted WSS environments marked by WSS overloads on the non-coronary leaflet and sub-physiologic WSS levels on the fused leaflet. This study provides important insights into the mechanical characteristics of BAV leaflets, which may further our understanding of the role played by hemodynamic forces in BAV disease. Copyright © 2016 John Wiley & Sons, Ltd.
Collapse
Affiliation(s)
- K Cao
- Department of Aerospace and Mechanical Engineering, University of Notre Dame, 365 Fitzpatrick Hall, Notre Dame, IN, 46556, USA
| | - P Sucosky
- Department of Mechanical and Materials Engineering, Wright State University, 3640 Colonel Glenn Highway, Dayton, OH, 45435, USA
| |
Collapse
|
22
|
Perez J, Diaz N, Tandon I, Plate R, Martindale C, Balachandran K. Elevated Serotonin Interacts with Angiotensin-II to Result in Altered Valve Interstitial Cell Contractility and Remodeling. Cardiovasc Eng Technol 2017; 9:168-180. [PMID: 28247311 DOI: 10.1007/s13239-017-0298-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/24/2016] [Accepted: 02/22/2017] [Indexed: 01/30/2023]
Abstract
While the valvulopathic effects of serotonin (5HT) and angiotensin-II (Ang-II) individually are known, it was not clear how 5HT and Ang-II might interact, specifically in the context of the mechanobiological responses due to altered valve mechanics potentiated by these molecules. In this context, the hypothesis of this study was that increased serotonin levels would result in accelerated progression toward disease in the presence of angiotensin-II-induced hypertension. C57/BL6 J mice were divided into four groups and subcutaneously implanted with osmotic pumps containing: PBS (control), 5HT (2.5 ng/kg/min), Ang-II (400 ng/kg/min), and 5HT + Ang-II (combination). Blood pressure was monitored using the tail cuff method. Echocardiography was performed on the mice before surgery and every week thereafter to assess ejection fraction. After three weeks, the mice were sacrificed and their hearts excised, embedded and sectioned for analysis of the aortic valves via histology and immunohistochemistry. In separate experiments, porcine valve interstitial cells (VICs) were directly stimulated with 5HT (10-7 M), Ang-II (100 nM) or both and assayed for cellular contractility, cytoskeletal organization and collagen remodeling. After three weeks, average systolic blood pressure was significantly increased in the 5HT, Ang-II and combination groups compared to control. Echocardiographic analysis demonstrated significantly reduced ejection fraction in Ang-II and the combination groups. H&E staining demonstrated thicker leaflets in the combination groups, suggesting a more aggressive remodeling process. Picrosirius red staining and image analysis suggested that the Ang-II and combination groups had the largest proportion of thicker collagen fibers. VIC orientation, cellular contractility and collagen gene expression was highest for the 5HT + Ang-II combination treatment compared to all other groups. Overall, our results suggest that 5HT and Ang-II interact to result in significantly detrimental alteration of function and remodeling in the valve.
Collapse
Affiliation(s)
- Jessica Perez
- Department of Biomedical Engineering, University of Arkansas, 122 John A. White Jr. Engineering Hall, Fayetteville, AR, 72701, USA
| | - Nancy Diaz
- Department of Biomedical Engineering, University of Arkansas, 122 John A. White Jr. Engineering Hall, Fayetteville, AR, 72701, USA
| | - Ishita Tandon
- Department of Biomedical Engineering, University of Arkansas, 122 John A. White Jr. Engineering Hall, Fayetteville, AR, 72701, USA
| | - Rachel Plate
- Department of Biomedical Engineering, University of Arkansas, 122 John A. White Jr. Engineering Hall, Fayetteville, AR, 72701, USA
| | - Christopher Martindale
- Department of Biomedical Engineering, University of Arkansas, 122 John A. White Jr. Engineering Hall, Fayetteville, AR, 72701, USA
| | - Kartik Balachandran
- Department of Biomedical Engineering, University of Arkansas, 122 John A. White Jr. Engineering Hall, Fayetteville, AR, 72701, USA.
| |
Collapse
|
23
|
Huang S, Huang HYS. Biaxial stress relaxation of semilunar heart valve leaflets during simulated collagen catabolism: Effects of collagenase concentration and equibiaxial strain state. Proc Inst Mech Eng H 2016; 229:721-31. [PMID: 26405097 DOI: 10.1177/0954411915604336] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Heart valve leaflet collagen turnover and remodeling are innate to physiological homeostasis; valvular interstitial cells routinely catabolize damaged collagen and affect repair. Moreover, evidence indicates that leaflets can adapt to altered physiological (e.g. pregnancy) and pathological (e.g. hypertension) mechanical load states, tuning collagen structure and composition to changes in pressure and flow. However, while valvular interstitial cell-secreted matrix metalloproteinases are considered the primary effectors of collagen catabolism, the mechanisms by which damaged collagen fibers are selectively degraded remain unclear. Growing evidence suggests that the collagen fiber strain state plays a key role, with the strain-dependent configuration of the collagen molecules either masking or presenting proteolytic sites, thereby protecting or accelerating collagen proteolysis. In this study, the effects of equibiaxial strain state on collagen catabolism were investigated in porcine aortic valve and pulmonary valve tissues. Bacterial collagenase (0.2 and 0.5 mg/mL) was utilized to simulate endogenous matrix metalloproteinases, and biaxial stress relaxation and biochemical collagen concentration served as functional and compositional measures of collagen catabolism, respectively. At a collagenase concentration of 0.5 mg/mL, increasing the equibiaxial strain imposed during stress relaxation (0%, 37.5%, and 50%) yielded significantly lower median collagen concentrations in the aortic valve (p = 0.0231) and pulmonary valve (p = 0.0183), suggesting that relatively large strain magnitudes may enhance collagen catabolism. Collagen concentration decreases were paralleled by trends of accelerated normalized stress relaxation rate with equibiaxial strain in aortic valve tissues. Collectively, these in vitro results indicate that biaxial strain state is capable of affecting the susceptibility of valvular collagens to catabolism, providing a basis for further investigation of how such phenomena may manifest at different strain magnitudes or in vivo.
Collapse
Affiliation(s)
- Siyao Huang
- Department of Mechanical & Aerospace Engineering, North Carolina State University, Raleigh, NC, USA
| | - Hsiao-Ying Shadow Huang
- Department of Mechanical & Aerospace Engineering, North Carolina State University, Raleigh, NC, USA
| |
Collapse
|
24
|
Gunning PS, Saikrishnan N, Yoganathan AP, McNamara LM. Total ellipse of the heart valve: the impact of eccentric stent distortion on the regional dynamic deformation of pericardial tissue leaflets of a transcatheter aortic valve replacement. J R Soc Interface 2016; 12:20150737. [PMID: 26674192 DOI: 10.1098/rsif.2015.0737] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Transcatheter aortic valve replacements (TAVRs) are a percutaneous alternative to surgical aortic valve replacements and are used to treat patients with aortic valve stenosis. This minimally invasive procedure relies on expansion of the TAVR stent to radially displace calcified aortic valve leaflets against the aortic root wall. However, these calcium deposits can impede the expansion of the device causing distortion of the valve stent and pericardial tissue leaflets. The objective of this study was to elucidate the impact of eccentric TAVR stent distortion on the dynamic deformation of the tissue leaflets of the prosthesis in vitro. Dual-camera stereophotogrammetry was used to measure the regional variation in strain in a leaflet of a TAVR deployed in nominal circular and eccentric (eccentricity index = 28%) orifices, representative of deployed TAVRs in vivo. It was observed that (i) eccentric stent distortion caused incorrect coaptation of the leaflets at peak diastole resulting in a 'peel-back' leaflet geometry that was not present in the circular valve and (ii) adverse bending of the leaflet, arising in the eccentric valve at peak diastole, caused significantly higher commissure strains compared with the circular valve in both normotensive and hypertensive pressure conditions (normotension: eccentric = 13.76 ± 2.04% versus circular = 11.77 ± 1.61%, p = 0.0014, hypertension: eccentric = 15.07 ± 1.13% versus circular = 13.56 ± 0.87%, p = 0.0042). This study reveals that eccentric distortion of a TAVR stent can have a considerable impact on dynamic leaflet deformation, inducing deleterious bending of the leaflet and increasing commissures strains, which might expedite leaflet structural failure compared to leaflets in a circular deployed valve.
Collapse
Affiliation(s)
- Paul S Gunning
- Biomechanics Research Centre, Biomedical Engineering, College of Engineering and Informatics, National University of Ireland Galway, Galway, Republic of Ireland
| | - Neelakantan Saikrishnan
- Cardiovascular Fluid Mechanics Laboratory, Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA, USA
| | - Ajit P Yoganathan
- Cardiovascular Fluid Mechanics Laboratory, Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA, USA
| | - Laoise M McNamara
- Biomechanics Research Centre, Biomedical Engineering, College of Engineering and Informatics, National University of Ireland Galway, Galway, Republic of Ireland
| |
Collapse
|
25
|
Schoen FJ, Gotlieb AI. Heart valve health, disease, replacement, and repair: a 25-year cardiovascular pathology perspective. Cardiovasc Pathol 2016; 25:341-352. [PMID: 27242130 DOI: 10.1016/j.carpath.2016.05.002] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/31/2016] [Revised: 05/04/2016] [Accepted: 05/05/2016] [Indexed: 01/24/2023] Open
Abstract
The past several decades have witnessed major advances in the understanding of the structure, function, and biology of native valves and the pathobiology and clinical management of valvular heart disease. These improvements have enabled earlier and more precise diagnosis, assessment of the proper timing of surgical and interventional procedures, improved prosthetic and biologic valve replacements and repairs, recognition of postoperative complications and their management, and the introduction of minimally invasive approaches that have enabled definitive and durable treatment for patients who were previously considered inoperable. This review summarizes the current state of our understanding of the mechanisms of heart valve health and disease arrived at through innovative research on the cell and molecular biology of valves, clinical and pathological features of the most frequent intrinsic structural diseases that affect the valves, and the status and pathological considerations in the technological advances in valvular surgery and interventions. The contributions of many cardiovascular pathologists and other scientists, engineers, and clinicians are emphasized, and potentially fruitful areas for research are highlighted.
Collapse
Affiliation(s)
- Frederick J Schoen
- Department of Pathology, Brigham and Women's Hospital, Harvard Medical School, 75 Francis Street, Boston, MA 02115; Pathology and Health Sciences and Technology (HST), Harvard Medical School, 75 Francis Street, Boston, MA 02115.
| | - Avrum I Gotlieb
- Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada; Faculty of Medicine, University of Toronto, Toronto, Ontario M5S 1A8, Canada; Laboratory Medicine Program, University Health Network, Medical Sciences Building, 1 King's College Circle, Rm. 6275A, Toronto, Ontario M5S 1A8, Canada.
| |
Collapse
|
26
|
Heide-Jørgensen S, Kumaran Krishna S, Taborsky J, Bechsgaard T, Zegdi R, Johansen P. A Novel Method for Optical High Spatiotemporal Strain Analysis for Transcatheter Aortic Valves In Vitro. J Biomech Eng 2016; 138:4032501. [DOI: 10.1115/1.4032501] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2015] [Indexed: 11/08/2022]
Abstract
The transcatheter aortic valve implantation (TAVI) valve is a bioprosthetic valve within a metal stent frame. Like traditional surgical bioprosthetic valves, the TAVI valve leaflet tissue is expected to calcify and degrade over time. However, clinical studies of TAVI valve longevity are still limited. In order to indirectly assess the longevity of TAVI valves, an estimate of the mechanical wear and tear in terms of valvular deformation and strain of the leaflets under various conditions is warranted. The aim of this study was, therefore, to develop a platform for noncontact TAVI valve deformation analysis with both high temporal and spatial resolutions based on stereophotogrammetry and digital image correlation (DIC). A left-heart pulsatile in vitro flow loop system for mounting of TAVI valves was designed. The system enabled high-resolution imaging of all three TAVI valve leaflets simultaneously for up to 2000 frames per second through two high-speed cameras allowing three-dimensional analyses. A coating technique for applying a stochastic pattern on the leaflets of the TAVI valve was developed. The technique allowed a pattern recognition software to apply frame-by-frame cross correlation based deformation measurements from which the leaflet motions and the strain fields were derived. The spatiotemporal development of a very detailed strain field was obtained with a 0.5 ms time resolution and a spatial resolution of 72 μm/pixel. Hence, a platform offering a new and enhanced supplementary experimental evaluation of tissue valves during various conditions in vitro is presented.
Collapse
Affiliation(s)
- Simon Heide-Jørgensen
- Department of Engineering, Faculty of Science and Technology, Aarhus University, Aarhus 8000, Denmark
| | | | - Jonas Taborsky
- Department of Engineering, Faculty of Science and Technology, Aarhus University, Aarhus 8000, Denmark
| | - Tommy Bechsgaard
- Department of Cardiothoracic Surgery, Aarhus University Hospital, Aarhus N8200, Denmark
| | - Rachid Zegdi
- Hôpital Européen Georges Pompidou, Service de Chirurgie Cardiovasculaire, Paris 75015, France
| | - Peter Johansen
- Department of Engineering Faculty of Science and Technology, Aarhus University Aarhus 8000, Denmark e-mail:
| |
Collapse
|
27
|
Pierce EL, Bloodworth CH, Naran A, Easley TF, Jensen MO, Yoganathan AP. Novel Method to Track Soft Tissue Deformation by Micro-Computed Tomography: Application to the Mitral Valve. Ann Biomed Eng 2015; 44:2273-81. [PMID: 26553575 DOI: 10.1007/s10439-015-1499-9] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2015] [Accepted: 10/31/2015] [Indexed: 11/29/2022]
Abstract
Increasing availability of micro-computed tomography (µCT) as a structural imaging gold-standard is bringing unprecedented geometric detail to soft tissue modeling. However, the utility of these advances is severely hindered without analogous enhancement to the associated kinematic detail. To this end, labeling and following discrete points on a tissue across various deformation states is a well-established approach. Still, existing techniques suffer limitations when applied to complex geometries and large deformations and strains. Therefore, we herein developed a non-destructive system for applying fiducial markers (minimum diameter: 500 µm) to soft tissue and tracking them through multiple loading conditions by µCT. Using a novel applicator to minimize adhesive usage, four distinct marker materials were resolvable from both tissue and one another, without image artifacts. No impact on tissue stiffness was observed. µCT addressed accuracy limitations of stereophotogrammetry (inter-method positional error 1.2 ± 0.3 mm, given marker diameter 1.9 ± 0.1 mm). Marker application to ovine mitral valves revealed leaflet Almansi areal strains (45 ± 4%) closely matching literature values, and provided radiographic access to previously inaccessible regions, such as the leaflet coaptation zone. This system may meaningfully support mechanical characterization of numerous tissues or biomaterials, as well as tissue-device interaction studies for regulatory standards purposes.
Collapse
Affiliation(s)
- Eric L Pierce
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, 387 Technology Circle NW, Suite 200, Atlanta, GA, 30313, USA
| | - Charles H Bloodworth
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, 387 Technology Circle NW, Suite 200, Atlanta, GA, 30313, USA
| | - Ajay Naran
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, 387 Technology Circle NW, Suite 200, Atlanta, GA, 30313, USA
| | - Thomas F Easley
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, 387 Technology Circle NW, Suite 200, Atlanta, GA, 30313, USA
| | - Morten O Jensen
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, 387 Technology Circle NW, Suite 200, Atlanta, GA, 30313, USA
| | - Ajit P Yoganathan
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, 387 Technology Circle NW, Suite 200, Atlanta, GA, 30313, USA.
| |
Collapse
|
28
|
Masoumi N, Howell MC, Johnson KL, Niesslein MJ, Gerber G, Engelmayr GC. Design and testing of a cyclic stretch and flexure bioreactor for evaluating engineered heart valve tissues based on poly(glycerol sebacate) scaffolds. Proc Inst Mech Eng H 2014; 228:576-586. [PMID: 24898445 DOI: 10.1177/0954411914534837] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Cyclic flexure and stretch are essential to the function of semilunar heart valves and have demonstrated utility in mechanically conditioning tissue-engineered heart valves. In this study, a cyclic stretch and flexure bioreactor was designed and tested in the context of the bioresorbable elastomer poly(glycerol sebacate). Solid poly(glycerol sebacate) membranes were subjected to cyclic stretch, and micromolded poly(glycerol sebacate) scaffolds seeded with porcine aortic valvular interstitial cells were subjected to cyclic stretch and flexure. The results demonstrated significant effects of cyclic stretch on poly(glycerol sebacate) mechanical properties, including significant decreases in effective stiffness versus controls. In valvular interstitial cell-seeded scaffolds, cyclic stretch elicited significant increases in DNA and collagen content that paralleled maintenance of effective stiffness. This work provides a basis for investigating the roles of mechanical loading in the formation of tissue-engineered heart valves based on elastomeric scaffolds.
Collapse
Affiliation(s)
- Nafiseh Masoumi
- Department of Bioengineering, The Pennsylvania State University, University Park, PA, USA
| | - M Christian Howell
- Department of Bioengineering, The Pennsylvania State University, University Park, PA, USA
| | - Katherine L Johnson
- Department of Bioengineering, The Pennsylvania State University, University Park, PA, USA
| | - Matthew J Niesslein
- Department of Bioengineering, The Pennsylvania State University, University Park, PA, USA
| | - Gene Gerber
- Department of Bioengineering, The Pennsylvania State University, University Park, PA, USA
| | - George C Engelmayr
- Department of Bioengineering, The Pennsylvania State University, University Park, PA, USA
| |
Collapse
|
29
|
Moore B, Dasi LP. SPATIO-TEMPORAL COMPLEXITY OF THE AORTIC SINUS VORTEX. EXPERIMENTS IN FLUIDS 2014; 55:1770. [PMID: 25067881 PMCID: PMC4106046 DOI: 10.1007/s00348-014-1770-0] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
The aortic sinus vortex is a classical flow structure of significant importance to aortic valve dynamics and the initiation and progression of calific aortic valve disease. We characterize the spatio-temporal characteristics of aortic sinus voxtex dynamics in relation to the viscosity of blood analog solution as well as heart rate. High resolution time-resolved (2KHz) particle image velocimetry was conducted to capture 2D particle streak videos and 2D instantaneous velocity and streamlines along the sinus midplane using a physiological but rigid aorta model fitted with a porcine bioprosthetic heart valve. Blood analog fluids used include a water-glycerin mixture and saline to elucidate the sensitivity of vortex dynamics to viscosity. Experiments were conducted to record 10 heart beats for each combination of blood analog and heart rate condition. Results show that the topological characteristics of the velocity field vary in time-scales as revealed using time bin averaged vectors and corresponding instantaneous streamlines. There exist small time-scale vortices and a large time-scale main vortex. A key flow structure observed is the counter vortex at the upstream end of the sinus adjacent to the base (lower half) of the leaflet. The spatio-temporal complexity of vortex dynamics is shown to be profoundly influenced by strong leaflet flutter during systole with a peak frequency of 200Hz and peak amplitude of 4 mm observed in the saline case. While fluid viscosity influences the length and time-scales as well as the introduction of leaflet flutter, heart rate influences the formation of counter vortex at the upstream end of the sinus. Higher heart rates are shown to reduce the strength of the counter vortex that can greatly influence the directionality and strength of shear stresses along the base of the leaflet. This study demonstrates the impact of heart rate and blood analog viscosity on aortic sinus hemodynamics.
Collapse
Affiliation(s)
- Brandon Moore
- Department of Mechanical Engineering, Colorado State University, Fort Collins, Colorado 80523-1374
| | - Lakshmi Prasad Dasi
- Department of Mechanical Engineering, Colorado State University, Fort Collins, Colorado 80523-1374
| |
Collapse
|
30
|
Gunning PS, Saikrishnan N, McNamara LM, Yoganathan AP. An in vitro evaluation of the impact of eccentric deployment on transcatheter aortic valve hemodynamics. Ann Biomed Eng 2014; 42:1195-206. [PMID: 24719050 DOI: 10.1007/s10439-014-1008-6] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2013] [Accepted: 03/31/2014] [Indexed: 10/25/2022]
Abstract
Patients with aortic stenosis present with calcium deposits on the native aortic valve, which can result in non-concentric expansion of Transcatheter Aortic Valve Replacement (TAVR) stents. The objective of this study is to evaluate whether eccentric deployment of TAVRs lead to turbulent blood flow and blood cell damage. Particle Image Velocimetry was used to quantitatively characterize fluid velocity fields, shear stress and turbulent kinetic energy downstream of TAVRs deployed in circular and eccentric orifices representative of deployed TAVRs in vivo. Effective orifice area (EOA) and mean transvalvular pressure gradient (TVG) values did not differ substantially in circular and eccentric deployed valves, with only a minor decrease in EOA observed in the eccentric valve (2.0 cm(2) for circular, 1.9 cm(2) for eccentric). Eccentric deployed TAVR lead to asymmetric systolic jet formation, with increased shear stresses (circular = 97 N/m(2) vs. eccentric = 119 N/m(2)) and regions of turbulence intensity (circular = 180 N/m(2) vs. eccentric = 230 N/m(2)) downstream that was not present in the circular deployed TAVR. The results of this study indicate that eccentric deployment of TAVRs can lead to altered flow characteristics and may potentially increase the hemolytic potential of the valve, which were not captured through hemodynamic evaluation alone.
Collapse
Affiliation(s)
- Paul S Gunning
- Biomechanics Research Centre, Department of Biomedical Engineering, National University of Ireland Galway, Galway, Ireland
| | | | | | | |
Collapse
|
31
|
Jackson MS, Igo SR, Lindsey TE, Maragiannis D, Chin KE, Autry K, Schutt R, Shah DJ, Valsecchi P, Kline WB, Little SH. Development of a Multi-modality Compatible Flow Loop System for the Functional Assessment of Mitral Valve Prostheses. Cardiovasc Eng Technol 2014. [DOI: 10.1007/s13239-014-0177-7] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
|
32
|
Myles V, Liao J, Warnock JN. Cyclic pressure and angiotensin II influence the biomechanical properties of aortic valves. J Biomech Eng 2013; 136:011011. [PMID: 24240552 DOI: 10.1115/1.4026041] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2013] [Indexed: 11/08/2022]
Abstract
Hypertension is a known risk factor for aortic stenosis. The elevated blood pressure increases the transvalvular load and can elicit inflammation and extracellular matrix (ECM) remodeling. Elevated cyclic pressure and the vasoactive agent angiotensin II (Ang II) both promote collagen synthesis, an early hallmark of aortic sclerosis. In the current study, it was hypothesized that elevated cyclic pressure and/or angiotensin II decreases extensibility of aortic valve leaflets due to an increase in collagen content and/or interstitial cell stiffness. Porcine aortic valve leaflets were exposed to pressure conditions of increasing magnitude (static atmospheric pressure, 80, and 120 mmHg) with and without 10−6 M Ang II. Biaxial mechanical testing was performed to determine extensibility in the circumferential and radial directions and collagen content was determined using a quantitative dye-binding method at 24 and 48 h. Isolated aortic valve interstitial cells exposed to the same experimental conditions were subjected to atomic force microscopy to assess cellular stiffness at 24 h. Leaflet tissue incubated with Ang II decreased tissue extensibility in the radial direction, but not in the circumferential direction. Elevated cyclic pressure decreased extensibility in both the radial and circumferential directions. Ang II and elevated cyclic pressure both increased the collagen content in leaflet tissue. Interstitial cells incubated with Ang II were stiffer than those incubated without Ang II while elevated cyclic pressure caused a decrease in cell stiffness. The results of the current study demonstrated that both pressure and Ang II play a role in altering the biomechanical properties of aortic valve leaflets. Ang II and elevated cyclic pressure decreased the extensibility of aortic valve leaflet tissue. Ang II induced direction specific changes in extensibility, demonstrating different response mechanisms. These findings help to provide a better understanding of the responses of aortic valves to mechanical and biochemical changes that occur under hypertensive conditions.
Collapse
|
33
|
Pham T, Sun W. Material properties of aged human mitral valve leaflets. J Biomed Mater Res A 2013; 102:2692-703. [PMID: 24039052 DOI: 10.1002/jbm.a.34939] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2013] [Revised: 08/01/2013] [Accepted: 08/26/2013] [Indexed: 11/08/2022]
Abstract
This study aimed to characterize the mechanical properties of aged human anterior mitral leaflets (AML) and posterior mitral leaflets (PML). The AML and PML samples from explanted human hearts (n = 21, mean age of 82.62 ± 8.77-years-old) were subjected to planar biaxial mechanical tests. The material stiffness, extensibility, and degree of anisotropy of the leaflet samples were quantified. The microstructure of the samples was assessed through histology. Both the AML and PML samples exhibited a nonlinear and anisotropic behavior with the circumferential direction being stiffer than the radial direction. The AML samples were significantly stiffer than the PML samples in both directions, suggesting that they should be modeled with separate sets of material properties in computational studies. Histological analysis indicated the changes in the tissue elastic constituents, including the fragmented and disorganized elastin network, the presence of fibrosis and proteoglycan/glycosaminoglycan infiltration and calcification, suggesting possible valvular degenerative characteristics in the aged human leaflet samples. Overall, stiffness increased and areal strain decreased with calcification severity. In addition, leaflet tissues from hypertensive individuals also exhibited a higher stiffness and low areal strain than normotensive individuals. There are significant differences in the mechanical properties of the two human mitral valve leaflets from this advanced age group. The morphologic changes in the tissue composition and structure also infer the structural and functional difference between aged human valves and those of animals.
Collapse
Affiliation(s)
- Thuy Pham
- Tissue Mechanics Laboratory, Department of Mechanical Engineering, Biomedical Engineering Program, University of Connecticut, Storrs, Connecticut, 06269
| | | |
Collapse
|
34
|
Gould ST, Srigunapalan S, Simmons CA, Anseth KS. Hemodynamic and cellular response feedback in calcific aortic valve disease. Circ Res 2013; 113:186-97. [PMID: 23833293 DOI: 10.1161/circresaha.112.300154] [Citation(s) in RCA: 89] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
This review highlights aspects of calcific aortic valve disease that encompass the entire range of aortic valve disease progression from initial cellular changes to aortic valve sclerosis and stenosis, which can be initiated by changes in blood flow (hemodynamics) and pressure across the aortic valve. Appropriate hemodynamics is important for normal valve function and maintenance, but pathological blood velocities and pressure can have profound consequences at the macroscopic to microscopic scales. At the macroscopic scale, hemodynamic forces impart shear stresses on the surface of the valve leaflets and cause deformation of the leaflet tissue. As discussed in this review, these macroscale forces are transduced to the microscale, where they influence the functions of the valvular endothelial cells that line the leaflet surface and the valvular interstitial cells that populate the valve extracellular matrix. For example, pathological changes in blood flow-induced shear stress can cause dysfunction, impairing their homeostatic functions, and pathological stretching of valve tissue caused by elevated transvalvular pressure can activate valvular interstitial cells and latent paracrine signaling cytokines (eg, transforming growth factor-β1) to promote maladaptive tissue remodeling. Collectively, these coordinated and complex interactions adversely impact bulk valve tissue properties, feeding back to further deteriorate valve function and propagate valve cell pathological responses. Here, we review the role of hemodynamic forces in calcific aortic valve disease initiation and progression, with focus on cellular responses and how they feed back to exacerbate aortic valve dysfunction.
Collapse
Affiliation(s)
- Sarah T Gould
- Department of Chemical and Biological Engineering, The Biofrontiers Institute, University of Colorado, Boulder, CO 80303, USA
| | | | | | | |
Collapse
|
35
|
Pham T, Martin C, Elefteriades J, Sun W. Biomechanical characterization of ascending aortic aneurysm with concomitant bicuspid aortic valve and bovine aortic arch. Acta Biomater 2013; 9:7927-36. [PMID: 23643809 DOI: 10.1016/j.actbio.2013.04.021] [Citation(s) in RCA: 80] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2012] [Revised: 03/20/2013] [Accepted: 04/11/2013] [Indexed: 11/25/2022]
Abstract
Studies have shown that patients harboring bicuspid aortic valve (BAV) or bovine aortic arch (BAA) are more likely than the general population to develop ascending aortic aneurysm (AsAA). A thorough quantification of the AsAA tissue properties for these patient groups may offer insights into the underlying mechanisms of AsAA development. Thus, the objective of this study was to investigate and compare the mechanical and microstructural properties of aortic tissues from AsAA patients with and without concomitant BAV or BAA. AsAA (n=20), BAV (n=20) and BAA (n=15) human tissues were obtained from patients who underwent elective AsAA surgery. Planar biaxial and uniaxial failure tests were used to characterize the mechanical and failure properties of the tissues, respectively. Histological analysis was performed to detect medial degenerative characteristics of aortic aneurysm. Individual layer thickness and composition were quantified for each patient group. The circumferential stress-strain response of the BAV samples was stiffer than both AsAA (p=0.473) and BAA (p=0.152) tissues at a low load. The BAV samples were nearly isotropic, while AsAA and BAA samples were anisotropic. The areal strain of BAV samples was significantly less than that of AsAA (p=0.041) and BAA (p=0.004) samples at a low load. The BAA samples were similar to the AsAA samples in both mechanical and failure properties. On the microstructural level, all samples displayed moderate medial degeneration, characterized by elastin fragmentation, cell loss, mucoid accumulation and fibrosis. The ultimate tensile strength of BAV and BAA sampleswere also found to decrease with age. Overall, the BAV samples were stiffer than both AsAA and BAA samples, and the BAA samples were similar to the AsAA samples. The BAV samples were thinnest, with less elastin than AsAA and BAA samples, which may be attributed to the loss of extensibility of these tissues at a low load. No apparent difference in failure mechanics among the tissue groups suggests that each of the patient groups may have a similar risk of rupture.
Collapse
|
36
|
Arjunon S, Rathan S, Jo H, Yoganathan AP. Aortic valve: mechanical environment and mechanobiology. Ann Biomed Eng 2013; 41:1331-46. [PMID: 23515935 DOI: 10.1007/s10439-013-0785-7] [Citation(s) in RCA: 79] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2012] [Accepted: 03/02/2013] [Indexed: 01/11/2023]
Abstract
The aortic valve (AV) experiences a complex mechanical environment, which includes tension, flexure, pressure, and shear stress forces due to blood flow during each cardiac cycle. This mechanical environment regulates AV tissue structure by constantly renewing and remodeling the phenotype. In vitro, ex vivo and in vivo studies have shown that pathological states such as hypertension and congenital defect like bicuspid AV (BAV) can potentially alter the AV's mechanical environment, triggering a cascade of remodeling, inflammation, and calcification activities in AV tissue. Alteration in mechanical environment is first sensed by the endothelium, which in turn induces changes in the extracellular matrix, and triggers cell differentiation and activation. However, the molecular mechanism of this process is not understood very well. Understanding these mechanisms is critical for advancing the development of effective medical based therapies. Recently, there have been some interesting studies on characterizing the hemodynamics associated with AV, especially in pathologies like BAV, using different experimental and numerical methods. Here, we review the current knowledge of the local AV mechanical environment and its effect on valve biology, focusing on in vitro and ex vivo approaches.
Collapse
Affiliation(s)
- Sivakkumar Arjunon
- The Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Room 2119 U. A. Whitaker Building, 313 Ferst Drive, Atlanta, GA 30332-0535, USA
| | | | | | | |
Collapse
|
37
|
Dellimore K, Kemp I, Rodriguez R, Scheffer C. In vitro characterization of an aortic bioprosthetic valve using Doppler echocardiography and qualitative flow visualization. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2013; 2012:6641-4. [PMID: 23367452 DOI: 10.1109/embc.2012.6347517] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
A 19 mm diameter prototype bioprosthetic valve mounted in a cardiac pulse duplicator was characterized using Doppler echocardiography and qualitative flow visualization at a heart rate of 72 bpm. Analysis of the flow visualization images revealed that the prototype and control valve leaflets open symmetrically but close asymmetrically. The asymmetry in the closing of the valves is likely due to the large pressure gradients across the valves and may have implications for the long term mechanical failure of the valves. The relatively high peak systolic velocity of 309.9 cm/s, which was measured in the prototype 19 mm valve, can be attributed to the small valve diameter and the high cardiac output used in the current study.
Collapse
Affiliation(s)
- Kiran Dellimore
- Biomedical Engineering Research Group, Department of Mechanical and Mechatronic Engineering, Stellenbosch University, South Africa
| | | | | | | |
Collapse
|
38
|
Sugimoto H, Sacks MS. Effects of Leaflet Stiffness on In Vitro Dynamic Bioprosthetic Heart Valve Leaflet Shape. Cardiovasc Eng Technol 2013; 4:2-15. [PMID: 23646095 DOI: 10.1007/s13239-013-0117-y] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Advances in the development of replacement heart valves require a deeper understanding of the valve dynamics. In the present study, dynamic aortic valve (AV) leaflet geometries were quantified in vitro using a structured laser-light imaging system (Iyengar et al., ABME 29(11):963-973, 2001). Native AV leaflets were first imaged under simulated physiological flow conditions within a rigid glass conduit with simulated anatomic sinuses. Next, the valve/glass conduit combination was removed from the loop and immersed in a 0.625% aqueous glutaraldehyde solution at room temperature for 24 h to produce a bioprosthetic heart valve (BHV). The BHV leaflets were then re-imaged under identical flow conditions while kept in the same position in the glass conduit to minimize artifacts associated with removal/reinsertion of the valve. We observed that: (1) the native leaflet exhibited small, high frequency shifts in shape; (2) the BHV leaflet demonstrated a more stabile shape, as well as focal regions of prolonged, high curvature; (3) the BHV leaflet opened and closed faster by ~10 ms compared to native leaflet; (4) in both the BHV and native states, the AV opened from basal region leading to free edge (5) when closing, both the native and BHV close with both free edge and circumferential together. The high bending observed in the BHV leaflet correlated with known locations of tissue deterioration previously reported in our laboratory. Thus, in order to minimize leaflet tissue damage, methods of chemical modification utilized in BHVs that maintain leaflet flexibility are necessary to minimize the onset and progression of tissue damage. We conclude that leaflet stiffness can have a considerable effect on dynamic valve motion, and can induce deleterious bending behaviors that may be associated with tissue breakdown and valve failure. Moreover, these unique data can provide much needed quantitative information for computational simulation of heart valve leaflet stiffness on heart valve function.
Collapse
Affiliation(s)
- Hiroatsu Sugimoto
- Center for Brand and Product Management, University of Wisconsin, Madison, WI, USA
| | | |
Collapse
|
39
|
Ferdous Z, Jo H, Nerem RM. Strain Magnitude-Dependent Calcific Marker Expression in Valvular and Vascular Cells. Cells Tissues Organs 2013; 197:372-83. [DOI: 10.1159/000347007] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/08/2013] [Indexed: 11/19/2022] Open
|
40
|
Saleeb A, Kumar A, Thomas V. The important roles of tissue anisotropy and tissue-to-tissue contact on the dynamical behavior of a symmetric tri-leaflet valve during multiple cardiac pressure cycles. Med Eng Phys 2013; 35:23-35. [DOI: 10.1016/j.medengphy.2012.03.006] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2011] [Revised: 01/28/2012] [Accepted: 03/12/2012] [Indexed: 10/28/2022]
|
41
|
Gould RA, Chin K, Santisakultarm TP, Dropkin A, Richards JM, Schaffer CB, Butcher JT. Cyclic strain anisotropy regulates valvular interstitial cell phenotype and tissue remodeling in three-dimensional culture. Acta Biomater 2012; 8:1710-9. [PMID: 22281945 DOI: 10.1016/j.actbio.2012.01.006] [Citation(s) in RCA: 85] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2011] [Revised: 12/20/2011] [Accepted: 01/05/2012] [Indexed: 01/05/2023]
Abstract
Many planar connective tissues exhibit complex anisotropic matrix fiber arrangements that are critical to their biomechanical function. This organized structure is created and modified by resident fibroblasts in response to mechanical forces in their environment. The directionality of applied strain fields changes dramatically during development, aging, and disease, but the specific effect of strain direction on matrix remodeling is less clear. Current mechanobiological inquiry of planar tissues is limited to equibiaxial or uniaxial stretch, which inadequately simulates many in vivo environments. In this study, we implement a novel bioreactor system to demonstrate the unique effect of controlled anisotropic strain on fibroblast behavior in three-dimensional (3-D) engineered tissue environments, using aortic valve interstitial fibroblast cells as a model system. Cell seeded 3-D collagen hydrogels were subjected to cyclic anisotropic strain profiles maintained at constant areal strain magnitude for up to 96 h at 1 Hz. Increasing anisotropy of biaxial strain resulted in increased cellular orientation and collagen fiber alignment along the principal directions of strain and cell orientation was found to precede fiber reorganization. Cellular proliferation and apoptosis were both significantly enhanced under increasing biaxial strain anisotropy (P<0.05). While cyclic strain reduced both vimentin and alpha-smooth muscle actin compared to unstrained controls, vimentin and alpha-smooth muscle actin expression increased with strain anisotropy and correlated with direction (P<0.05). Collectively, these results suggest that strain field anisotropy is an independent regulator of fibroblast cell phenotype, turnover, and matrix reorganization, which may inform normal and pathological remodeling in soft tissues.
Collapse
Affiliation(s)
- Russell A Gould
- Department of Biomedical Engineering, Cornell University, Ithaca, NY 14850, USA
| | | | | | | | | | | | | |
Collapse
|
42
|
Spinner EM, Buice D, Yap CH, Yoganathan AP. The effects of a three-dimensional, saddle-shaped annulus on anterior and posterior leaflet stretch and regurgitation of the tricuspid valve. Ann Biomed Eng 2011; 40:996-1005. [PMID: 22130636 DOI: 10.1007/s10439-011-0471-6] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2011] [Accepted: 11/09/2011] [Indexed: 11/30/2022]
Abstract
Tricuspid regurgitation (TR) is present in trace amounts or more in 82-86% of the population and is greater than mild in 14% of the population. In severe cases, it can contribute to right heart failure and adversely affect mitral valve repair durability. One major cause of TR is the dilation of the tricuspid annulus, which alters the geometry of the annulus from a saddle-shape to a more planar profile. Another cause of TR is the displacement of the papillary muscles (PMs), which results from right ventricular dilation. The objective of this study was to identify the effect of a saddle-shaped annulus on native tricuspid leaflet stretch mechanics and TR. In addition, the effects of geometric alterations, including annular dilatation and PM displacement, on leaflet stretch was investigated. Fresh porcine tricuspid valves (TVs) (n = 8) were excised and sutured to an adjustable three-dimensional annulus plate (allowing for dilatation and saddle-shape) and three PM attachment rods. The valve was then placed in the in vitro Georgia Tech right heart simulator. Dual-camera photogrammetry, was used to quantify the stretch ratio experienced by the valve leaflets at peak systole for the following conditions: physiologically normal, 100% annular dilatation, displaced PMs, and a combination of annular dilatation and PM displacement. In addition, a saddle and flat annulus were implemented for each of the four conditions. PM displacement was simulated by displacing all PMs by 10 mm in all directions (laterally, apically, posteriorly/anteriorly). The physiologically normal condition-normal annulus area, saddle-shaped annulus with PMs in a normal position, was used as a control. The results showed that the posterior leaflet exhibited significantly (p ≤ 0.05) higher major and areal stretch ratios as compared to the anterior leaflet at peak systole for all conditions tested. No significant difference was seen in stretch when a flat annulus was compared to saddle for the anterior or posterior leaflet for normal or disease conditions. Investigation of the impact of disease found a significant increase (p ≤ 0.10) in stretch in the posterior leaflet with a combination of annular dilatation and PM displacement (2.01 ± 0.68) as compared to the normal condition with a saddle annulus (1.43 ± 0.20). In addition displacement of the PMs resulted in a significant (p ≤ 0.01) reduction in TR, although the actual volume reduced was minimal (1.2 mL). Stretch values were measured for the anterior and posterior leaflet under both physiologic and pathologic conditions for the first time. Further, these results provide an understanding of the effects of geometric parameters on valve mechanics and function, which may lead to improved TV repairs.
Collapse
Affiliation(s)
- Erin M Spinner
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA 30332-0535, USA
| | | | | | | |
Collapse
|
43
|
Cyclic strain induces dual-mode endothelial-mesenchymal transformation of the cardiac valve. Proc Natl Acad Sci U S A 2011; 108:19943-8. [PMID: 22123981 DOI: 10.1073/pnas.1106954108] [Citation(s) in RCA: 120] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Endothelial-mesenchymal transformation (EMT) is a critical event for the embryonic morphogenesis of cardiac valves. Inducers of EMT during valvulogenesis include VEGF, TGF-β1, and wnt/β-catenin (where wnt refers to the wingless-type mammary tumor virus integration site family of proteins), that are regulated in a spatiotemporal manner. EMT has also been observed in diseased, strain-overloaded valve leaflets, suggesting a regulatory role for mechanical strain. Although the preponderance of studies have focused on the role of soluble mitogens, we asked if the valve tissue microenvironment contributed to EMT. To recapitulate these microenvironments in a controlled, in vitro environment, we engineered 2D valve endothelium from sheep valve endothelial cells, using microcontact printing to mimic the regions of isotropy and anisotropy of the leaflet, and applied cyclic mechanical strain in an attempt to induce EMT. We measured EMT in response to both low (10%) and high strain (20%), where low-strain EMT occurred via increased TGF-β1 signaling and high strain via increased wnt/β-catenin signaling, suggesting dual strain-dependent routes to distinguish EMT in healthy versus diseased valve tissue. The effect was also directionally dependent, where cyclic strain applied orthogonal to axis of the engineered valve endothelium alignment resulted in severe disruption of cell microarchitecture and greater EMT. Once transformed, these tissues exhibited increased contractility in the presence of endothelin-1 and larger basal mechanical tone in a unique assay developed to measure the contractile tone of the engineered valve tissues. This finding is important, because it implies that the functional properties of the valve are sensitive to EMT. Our results suggest that cyclic mechanical strain regulates EMT in a strain magnitude and directionally dependent manner.
Collapse
|
44
|
Balachandran K, Bakay MA, Connolly JM, Zhang X, Yoganathan AP, Levy RJ. Aortic valve cyclic stretch causes increased remodeling activity and enhanced serotonin receptor responsiveness. Ann Thorac Surg 2011; 92:147-53. [PMID: 21718840 DOI: 10.1016/j.athoracsur.2011.03.084] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/06/2011] [Revised: 03/14/2011] [Accepted: 03/15/2011] [Indexed: 10/18/2022]
Abstract
BACKGROUND Increased serotonin (5-hydroxytryptamine [5HT]) receptor (5HTR) signaling has been associated with cardiac valvulopathy. Prior cell culture studies of 5HTR signaling in heart valve interstitial cells have provided mechanistic insights concerning only static conditions. We investigated the hypothesis that aortic valve biomechanics participate in the regulation of both 5HTR expression and interrelated extracellular matrix remodeling events. METHODS The effects of cyclic stretch on aortic valve 5HTR, expression, signaling, and extracellular matrix remodeling were investigated using a tensile stretch bioreactor in studies which also compared the effects of adding 5HT and (or) the 5HT-transporter inhibitor, fluoxetine. RESULTS Cyclic stretch alone increased both proliferation and collagen in porcine aortic valve cusp samples. However, with cyclic stretch, unlike static conditions, 5HT plus fluoxetine caused the greatest increase in proliferation (p<0.0001), and also caused significant increases in collagen (p<0.0001) and glycosaminoglycans (p<0.0001). The DNA microarray data demonstrated upregulation of 5HTR2A and 5HTR2B (>4.5-fold) for cyclic stretch versus static (p<0.001), while expression of the 5HT transporter was not changed significantly. Extracellular matrix genes (eg, collagen types I, II, III, and proteoglycans) were also upregulated by cyclic stretch. CONCLUSIONS Porcine aortic valve cusp samples subjected to cyclic stretch upregulate 5HTR2A and 2B, and also initiate remodeling activity characterized by increased proliferation and collagen production. Importantly, enhanced 5HTR responsiveness due to increased 5HTR2A and 2B expression results in a significantly greater response in remodeling endpoints (proliferation, collagen, and GAG production) to 5HT in the presence of 5HT transporter blockade.
Collapse
Affiliation(s)
- Kartik Balachandran
- The Wallace H. Coulter School of Biomedical Engineering, Georgia Institute of Technology, Atlanta, Georgia, USA
| | | | | | | | | | | |
Collapse
|
45
|
Balachandran K, Hussain S, Yap CH, Padala M, Chester AH, Yoganathan AP. Elevated cyclic stretch and serotonin result in altered aortic valve remodeling via a mechanosensitive 5-HT(2A) receptor-dependent pathway. Cardiovasc Pathol 2011; 21:206-13. [PMID: 21865058 DOI: 10.1016/j.carpath.2011.07.005] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/28/2010] [Revised: 05/29/2011] [Accepted: 07/06/2011] [Indexed: 11/26/2022] Open
Abstract
INTRODUCTION Serotonin/5-hydroxytryptamine (5-HT) has been implicated in valve disease and in the modulation of valve mechanical properties. Several 5-HT receptor subtypes are also known to be mechanosensitive in other cell types, but this has not been studied in the context of the valve. In this study, we sought to understand the effects of elevated 5-HT levels and stretch overload on aortic valve remodeling and the dominant 5-HT receptor subtype that regulates these processes. METHODS AND RESULTS Collagen biosynthesis and tissue mechanical properties of porcine aortic valve cusps were evaluated after 10% (physiologic) and 15% (pathologic) dynamic stretch. These studies were performed in normal medium or medium supplemented with 5-HT (1, 10, 100 μM) in the absence and presence of 5-HT(2A) or 5-HT(2B) receptor antagonists. Fresh valves served as controls. Valve collagen content was maximal at the 10-μM 5-HT concentration for both 10% and 15% stretch. The 5-HT(2A) receptor antagonist reduced collagen synthesis, cell proliferation, and hsp47 expression under elevated and normal stretch, whereas the 5-HT(2B) receptor antagonist was effective only at normal stretch. The pretransition stiffness of the valve cusps was also increased in response to 5-HT via a stretch-sensitive 5-HT(2A) mechanism, with the post-transition stiffness unaltered. CONCLUSIONS Combined elevated stretch and 5-HT resulted in increased valve collagen biosynthesis, cell proliferation, and tissue stiffness. These responses were inhibited by a 5-HT(2A) antagonist. This strongly suggests that the 5-HT(2A) receptor subtype is sensitive to elevated stretch.
Collapse
Affiliation(s)
- Kartik Balachandran
- The Wallace H. Coulter School of Biomedical Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0535, USA
| | | | | | | | | | | |
Collapse
|
46
|
Warnock JN, Nanduri B, Pregonero Gamez CA, Tang J, Koback D, Muir WM, Burgess SC. Gene Profiling of Aortic Valve Interstitial Cells under Elevated Pressure Conditions: Modulation of Inflammatory Gene Networks. Int J Inflam 2011; 2011:176412. [PMID: 21876831 PMCID: PMC3159021 DOI: 10.4061/2011/176412] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2011] [Revised: 06/06/2011] [Accepted: 06/16/2011] [Indexed: 11/20/2022] Open
Abstract
The study aimed to identify mechanosensitive pathways and gene networks that are stimulated by elevated cyclic pressure in aortic valve interstitial cells (VICs) and lead to detrimental tissue remodeling and/or pathogenesis. Porcine aortic valve leaflets were exposed to cyclic pressures of 80 or 120 mmHg, corresponding to diastolic transvalvular pressure in normal and hypertensive conditions, respectively. Linear, two-cycle amplification of total RNA, followed by microarray was performed for transcriptome analysis (with qRT-PCR validation). A combination of systems biology modeling and pathway analysis identified novel genes and molecular mechanisms underlying the biological response of VICs to elevated pressure. 56 gene transcripts related to inflammatory response mechanisms were differentially expressed. TNF-α, IL-1α, and IL-1β were key cytokines identified from the gene network model. Also of interest was the discovery that pentraxin 3 (PTX3) was significantly upregulated under elevated pressure conditions (41-fold change). In conclusion, a gene network model showing differentially expressed inflammatory genes and their interactions in VICs exposed to elevated pressure has been developed. This system overview has detected key molecules that could be targeted for pharmacotherapy of aortic stenosis in hypertensive patients.
Collapse
Affiliation(s)
- James N Warnock
- Department of Agricultural and Biological Engineering, Mississippi State University, Mississippi State, MS 39762, USA
| | | | | | | | | | | | | |
Collapse
|
47
|
Balachandran K, Sucosky P, Yoganathan AP. Hemodynamics and mechanobiology of aortic valve inflammation and calcification. Int J Inflam 2011; 2011:263870. [PMID: 21760982 PMCID: PMC3133012 DOI: 10.4061/2011/263870] [Citation(s) in RCA: 110] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2011] [Accepted: 04/29/2011] [Indexed: 01/22/2023] Open
Abstract
Cardiac valves function in a mechanically
complex environment, opening and closing close to
a billion times during the average human lifetime,
experiencing transvalvular pressures and pulsatile
and oscillatory shear stresses, as well as bending
and axial stress. Although valves were originally thought to be
passive pieces of tissue, recent evidence points
to an intimate interplay between the hemodynamic
environment and biological response of the valve.
Several decades of study have been devoted to
understanding these varied mechanical stimuli and
how they might induce valve pathology. Here, we
review efforts taken in understanding the valvular
response to its mechanical milieu and key
insights gained from in vitro and
ex vivo whole-tissue studies in
the mechanobiology of aortic valve remodeling,
inflammation, and calcification.
Collapse
Affiliation(s)
- Kartik Balachandran
- Wyss Institute for Biologically Inspired Engineering, School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA
| | | | | |
Collapse
|
48
|
Yap CH, Saikrishnan N, Tamilselvan G, Yoganathan AP. Experimental Technique of Measuring Dynamic Fluid Shear Stress on the Aortic Surface of the Aortic Valve Leaflet. J Biomech Eng 2011; 133:061007. [DOI: 10.1115/1.4004232] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Aortic valve (AV) calcification is a highly prevalent disease with serious impact on mortality and morbidity. The exact cause and mechanism of the progression of AV calcification is unknown, although mechanical forces have been known to play a role. It is thus important to characterize the mechanical environment of the AV. In the current study, we establish a methodology of measuring shear stresses experienced by the aortic surface of the AV leaflets using an in vitro valve model and adapting the laser Doppler velocimetry (LDV) technique. The valve model was constructed from a fresh porcine aortic valve, which was trimmed and sutured onto a plastic stented ring, and inserted into an idealized three-lobed sinus acrylic chamber. Valve leaflet location was measured by obtaining the location of highest back-scattered LDV laser light intensity. The technique of performing LDV measurements near to biological surfaces as well as the leaflet locating technique was first validated in two phantom flow systems: (1) steady flow within a straight tube with AV leaflet adhered to the wall, and (2) steady flow within the actual valve model. Dynamic shear stresses were then obtained by applying the techniques on the valve model in a physiologic pulsatile flow loop. Results show that aortic surface shear stresses are low during early systole (<5dyn/cm2) but elevated to its peak during mid to late systole at about 18–20 dyn/cm2. Low magnitude shear stress (<5dyn/cm2) was observed during early diastole and dissipated to zero over the diastolic duration. Systolic shear stress was observed to elevate only with the formation of sinus vortex flow. The presented technique can also be used on other in vitro valve models such as congenitally geometrically malformed valves, or to investigate effects of hemodynamics on valve shear stress. Shear stress data can be used for further experiments investigating effects of fluid shear stress on valve biology, for conditioning tissue engineered AV, and to validate numerical simulations.
Collapse
Affiliation(s)
- Choon Hwai Yap
- Wallace H. Coulter School of Biomedical Engineering, Georgia Institute of Technology and Emory University, 315 Ferst Drive, Atlanta, GA 30332
| | - Neelakantan Saikrishnan
- Wallace H. Coulter School of Biomedical Engineering, Georgia Institute of Technology and Emory University, 315 Ferst Drive, Atlanta, GA 30332
| | - Gowthami Tamilselvan
- Wallace H. Coulter School of Biomedical Engineering, Georgia Institute of Technology and Emory University, 315 Ferst Drive, Atlanta, GA 30332
| | - Ajit P. Yoganathan
- Wallace H. Coulter School of Biomedical Engineering, Georgia Institute of Technology and Emory University, 315 Ferst Drive, Atlanta, GA 30332
| |
Collapse
|
49
|
Yap CH, Saikrishnan N, Yoganathan AP. Experimental measurement of dynamic fluid shear stress on the ventricular surface of the aortic valve leaflet. Biomech Model Mechanobiol 2011; 11:231-44. [PMID: 21465260 DOI: 10.1007/s10237-011-0306-2] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2010] [Accepted: 03/21/2011] [Indexed: 12/20/2022]
Abstract
Aortic valve (AV) calcification is a highly prevalent disease with serious impact on mortality and morbidity. The exact causes and mechanisms of AV calcification are unclear, although previous studies suggest that mechanical forces play a role. It has been clinically demonstrated that calcification preferentially occurs on the aortic surface of the AV. This is hypothesized to be due to differences in the mechanical environments on the two sides of the valve. It is thus necessary to characterize fluid shear forces acting on both sides of the leaflet to test this hypothesis. The current study is one of two studies characterizing dynamic shear stress on both sides of the AV leaflets. In the current study, shear stresses on the ventricular surface of the AV leaflets were measured experimentally on two prosthetic AV models with transparent leaflets in an in vitro pulsatile flow loop using two-component Laser Doppler Velocimetry (LDV). Experimental measurements were utilized to validate a theoretical model of AV ventricular surface shear stress based on the Womersley profile in a straight tube, with corrections for the opening angle of the valve leaflets. This theoretical model was applied to in vivo data based on MRI-derived volumetric flow rates and valve dimension obtained from the literature. Experimental results showed that ventricular surface shear stress was dominated by the streamwise component. The systolic shear stress waveform resembled a half-sinusoid during systole and peaks at 64-71 dyn/cm(2), and reversed in direction at the end of systole for 15-25 ms, and reached a significant negative magnitude of 40-51 dyn/cm(2). Shear stresses from the theoretical model applied to in vivo data showed that shear stresses peaked at 77-92 dyn/cm(2) and reversed in direction for substantial period of time (108-110 ms) during late systole with peak negative shear stress of 35-38 dyn/cm(2).
Collapse
Affiliation(s)
- Choon Hwai Yap
- Wallace H. Coulter School of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA 30332-0535, USA
| | | | | |
Collapse
|
50
|
Regional analysis of dynamic deformation characteristics of native aortic valve leaflets. J Biomech 2011; 44:1459-65. [PMID: 21458817 DOI: 10.1016/j.jbiomech.2011.03.017] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2010] [Revised: 01/06/2011] [Accepted: 03/14/2011] [Indexed: 11/21/2022]
Abstract
BACKGROUND The mechanical environment of the aortic valve (AV) has a significant impact on valve cellular biology and disease progression, but the regional variation in stretch across the AV leaflet is not well understood. This study, therefore, sought to quantify the regional variation in dynamic deformation characteristics of AV leaflets in the native mechanical environment in order to link leaflet stretch variation to reported AV calcification patterns. METHODS Whole porcine AVs (n=6) were sutured into a physiological left heart simulator and subjected to pulsatile and physiologically normal hemodynamic conditions. A grid of ink dots was marked on the entire ventricular surface of the AV leaflet. Dual camera stereo photogrammetry was used to determine the stretch magnitudes across the entire ventricular surface over the entire diastolic duration. RESULTS Elevated stretch magnitudes were observed along the leaflet base and coaptation line consistent with previously reported calcification patterns suggesting the higher mechanical stretch experienced by the leaflets in these regions may contribute to increased disease propensity. Transient stretch overloads were observed during diastolic closing, predominantly along the leaflet base, indicating the presence of a dynamic fluid hammer effect resulting from retrograde blood flow impacting the leaflet. We speculate the function of the leaflet base to act in cooperation with the sinuses of Valsalva to dampen the fluid hammer effect and reduce stress levels imparted on the rest of the leaflet.
Collapse
|