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The precision of macroscale mechanical measurements is limited by the inherent structural heterogeneity of human stratum corneum. Acta Biomater 2021; 130:308-316. [PMID: 34087446 DOI: 10.1016/j.actbio.2021.05.035] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2020] [Revised: 05/18/2021] [Accepted: 05/20/2021] [Indexed: 12/18/2022]
Abstract
Biological tissues are structurally heterogenous mosaics at cellular and sub-cellular length scales. Some tissues, like the outermost layer of human skin, or stratum corneum (SC), also exhibit a rich topography of microchannels at larger mesoscopic length scales. Although this is well understood, modern studies continue to characterize the mechanical properties of biological tissues, including the SC, using macroscale techniques that assume these materials are homogenous in structure, thickness, and composition. Macroscale failure testing of SC is commonly associated with large sample to sample variability. We anticipate that microscale heterogeneities play an important role in defining the global mechanical response of the tissue. To evaluate the validity of the prevailing paradigm that macroscopic testing techniques can provide meaningful information about failure in soft heterogenous tissues, the macroscale work of fracture in isolated human SC samples is measured using conventional macroscale testing techniques and compared with the energy cost of creating new crack interfaces at the microscale, measured using a modified traction force microscopy technique. Results show that measured micro- and macroscale energy costs per unit crack path length are highly consistent. However, crack propagation is found to be guided by microscale topographical features in the tissue. This correlation reveals that macroscale mechanical sample to sample variability is caused by notable differences in crack propagation pathways. STATEMENT OF SIGNIFICANCE: Although designed to test homogeneous materials, macroscopic uniaxial tensometry is currently the gold standard for measuring the mechanical properties of biological tissues. All tissues, including human stratum corneum are structurally heterogeneous at the microscale and mechanical measurements are commonly highly variable, even for specimens from the same source. This study explores the fundamental causes of this disparity and evaluates the prevailing paradigm that macroscopic testing techniques can provide meaningful information about failure in soft heterogeneous tissues. Results conclude that the cause of large variability in mechanical work of fracture is due to inherent structural heterogeneities governing crack propagation pathways and altering the total crack length. Structural heterogeneities in tissue therefore limits the precision of macroscale biomechanical testing.
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A new model of passive muscle tissue integrating Collagen Fibers: Consequences for muscle behavior analysis. J Mech Behav Biomed Mater 2018; 88:29-40. [DOI: 10.1016/j.jmbbm.2018.07.042] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2018] [Revised: 07/26/2018] [Accepted: 07/30/2018] [Indexed: 02/02/2023]
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Golob MJ, Massoudi D, Tabima DM, Johnston JL, Wolf GD, Hacker TA, Greenspan DS, Chesler NC. Cardiovascular function and structure are preserved despite induced ablation of BMP1-related proteinases. Cell Mol Bioeng 2018; 11:255-266. [PMID: 30123369 DOI: 10.1007/s12195-018-0534-y] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Introduction Bone morphogenetic protein 1 (BMP1) is part of an extracellular metalloproteinase family that biosynthetically processes procollagen molecules. BMP1- and tolloid-like (TLL1) proteinases mediate the cleavage of carboxyl peptides from procollagen molecules, which is a crucial step in fibrillar collagen synthesis. Ablating the genes that encode BMP1-related proteinases (Bmp1 and Tll1) post-natally results in brittle bones, periodontal defects, and thin skin in conditional knockout (BTKO) mice. Despite the importance of collagen to cardiovascular tissues and the adverse effects of Bmp1 and Tll1 ablation in other tissues, the impact of Bmp1 and Tll1 ablation on cardiovascular performance is unknown. Here, we investigated the role of Bmp1- and Tll1-ablation in cardiovascular tissues by examining ventricular and vascular structure and function in BTKO mice. Methods Ventricular and vascular structure and function were comprehensively quantified in BTKO mice (n=9) and in age- and sex-matched controls (n=9). Echocardiography, cardiac catheterization, and biaxial ex vivo arterial mechanical testing were performed to assess tissue function, and histological staining was used to measure collagen protein content. Results Bmp1- and Tll1-ablation resulted in maintained hemodynamics and cardiovascular function, preserved biaxial arterial compliance, and comparable ventricular and vascular collagen protein content. Conclusions Maintained ventricular and vascular structure and function despite post-natal ablation of Bmp1 and Tll1 suggests that there is an as-yet unidentified compensatory mechanism in cardiovascular tissues. In addition, these findings suggest that proteinases derived from Bmp1 and Tll1 post-natally have less of an impact on cardiovascular tissues compared to skeletal, periodontal, and dermal tissues.
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Affiliation(s)
- Mark J Golob
- Department of Biomedical Engineering, University of Wisconsin-Madison College of Engineering, Madison, WI 53706 USA
| | - Dawiyat Massoudi
- Department of Cell and Regenerative Biology, University of Wisconsin-Madison School of Medicine and Public Health, Madison, WI 53706 USA
| | - Diana M Tabima
- Department of Biomedical Engineering, University of Wisconsin-Madison College of Engineering, Madison, WI 53706 USA
| | - James L Johnston
- Department of Biomedical Engineering, University of Wisconsin-Madison College of Engineering, Madison, WI 53706 USA
| | - Gregory D Wolf
- Department of Biomedical Engineering, University of Wisconsin-Madison College of Engineering, Madison, WI 53706 USA
| | - Timothy A Hacker
- Department of Medicine, University of Wisconsin School of Medicine and Public Health, Madison, WI 53706 USA
| | - Daniel S Greenspan
- Department of Cell and Regenerative Biology, University of Wisconsin-Madison School of Medicine and Public Health, Madison, WI 53706 USA
| | - Naomi C Chesler
- Department of Biomedical Engineering, University of Wisconsin-Madison College of Engineering, Madison, WI 53706 USA.,Department of Medicine, University of Wisconsin School of Medicine and Public Health, Madison, WI 53706 USA
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Modeling the effect of collagen fibril alignment on ligament mechanical behavior. Biomech Model Mechanobiol 2017; 17:543-557. [PMID: 29177933 DOI: 10.1007/s10237-017-0977-4] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2017] [Accepted: 10/30/2017] [Indexed: 01/08/2023]
Abstract
Ligament mechanical behavior is primarily regulated by fibrous networks of type I collagen. Although these fibrous networks are typically highly aligned, healthy and injured ligament can also exhibit disorganized collagen architecture. The objective of this study was to determine whether variations in the collagen fibril network between neighboring ligaments can predict observed differences in mechanical behavior. Ligament specimens from two regions of bovine fetlock joints, which either exhibited highly aligned or disorganized collagen fibril networks, were mechanically tested in uniaxial tension. Confocal microscopy and FiberFit software were used to quantify the collagen fibril dispersion and mean fibril orientation in the mechanically tested specimens. These two structural parameters served as inputs into an established hyperelastic constitutive model that accounts for a continuous distribution of planar fibril orientations. The ability of the model to predict differences in the mechanical behavior between neighboring ligaments was tested by (1) curve fitting the model parameters to the stress response of the ligament with highly aligned fibrils and then (2) using this model to predict the stress response of the ligament with disorganized fibrils by only changing the parameter values for fibril dispersion and mean fibril orientation. This study found that when using parameter values for fibril dispersion and mean fibril orientation based on confocal imaging data, the model strongly predicted the average stress response of ligaments with disorganized fibrils ([Formula: see text]); however, the model only successfully predicted the individual stress response of ligaments with disorganized fibrils in half the specimens tested. Model predictions became worse when parameters for fibril dispersion and mean fibril orientation were not based on confocal imaging data. These findings emphasize the importance of collagen fibril alignment in ligament mechanics and help advance a mechanistic understanding of fibrillar networks in healthy and injured ligament.
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Golob MJ, Tabima DM, Wolf GD, Johnston JL, Forouzan O, Mulchrone AM, Kellihan HB, Bates ML, Chesler NC. Pulmonary arterial strain- and remodeling-induced stiffening are differentiated in a chronic model of pulmonary hypertension. J Biomech 2017; 55:92-98. [PMID: 28262286 DOI: 10.1016/j.jbiomech.2017.02.003] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2016] [Revised: 01/30/2017] [Accepted: 02/11/2017] [Indexed: 02/06/2023]
Abstract
Pulmonary hypertension (PH) is a debilitating vascular disease that leads to pulmonary artery (PA) stiffening, which is a predictor of patient mortality. During PH development, PA stiffening adversely affects right ventricular function. PA stiffening has been investigated through the arterial nonlinear elastic response during mechanical testing using a canine PH model. However, only circumferential properties were reported and in the absence of chronic PH-induced PA remodeling. Remodeling can alter arterial nonlinear elastic properties via chronic changes in extracellular matrix (ECM) content and geometry. Here, we used an established constitutive model to demonstrate and differentiate between strain-stiffening, which is due to nonlinear elasticity, and remodeling-induced stiffening, which is due to ECM and geometric changes, in a canine model of chronic thromboembolic PH (CTEPH). To do this, circumferential and axial tissue strips of large extralobar PAs from control and CTEPH tissues were tested in uniaxial tension, and data were fit to a phenomenological constitutive model. Strain-induced stiffening was evident from mechanical testing as nonlinear elasticity in both directions and computationally by a high correlation coefficient between the mechanical data and model (R2=0.89). Remodeling-induced stiffening was evident from a significant increase in the constitutive model stress parameter, which correlated with increased PA collagen content and decreased PA elastin content as measured histologically. The ability to differentiate between strain- and remodeling-induced stiffening in vivo may lead to tailored clinical treatments for PA stiffening in PH patients.
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Affiliation(s)
- Mark J Golob
- Department of Biomedical Engineering, University of Wisconsin-Madison College of Engineering, Madison, WI 53706, United States
| | - Diana M Tabima
- Department of Biomedical Engineering, University of Wisconsin-Madison College of Engineering, Madison, WI 53706, United States
| | - Gregory D Wolf
- Department of Biomedical Engineering, University of Wisconsin-Madison College of Engineering, Madison, WI 53706, United States
| | - James L Johnston
- Department of Biomedical Engineering, University of Wisconsin-Madison College of Engineering, Madison, WI 53706, United States
| | - Omid Forouzan
- Department of Biomedical Engineering, University of Wisconsin-Madison College of Engineering, Madison, WI 53706, United States
| | - Ashley M Mulchrone
- Department of Biomedical Engineering, University of Wisconsin-Madison College of Engineering, Madison, WI 53706, United States
| | - Heidi B Kellihan
- Department of Veterinary Medicine, University of Wisconsin-Madison, Madison, WI 53706, United States
| | - Melissa L Bates
- Department of Physiology, University of Iowa, Iowa City, IA 52242, United States
| | - Naomi C Chesler
- Department of Biomedical Engineering, University of Wisconsin-Madison College of Engineering, Madison, WI 53706, United States.
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Chen Q, Wang Y, Li ZY. Re-examination of the mechanical anisotropy of porcine thoracic aorta by uniaxial tensile tests. Biomed Eng Online 2016; 15:167. [PMID: 28155705 PMCID: PMC5259859 DOI: 10.1186/s12938-016-0279-6] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Objective Considering past studies on the orthotropic anisotropy of arteries in the circumferential and axial directions, this work aims to experimentally study the anisotropic behaviour of arteries by tensioning multi-directional strips of porcine thoracic aorta. Methods Histology is first analyzed by staining arterial sections of three orthotropic (axial, circumferential, and radial) planes. 168 stripped samples from 21 aortas are categorized into three loading-rate groups to investigate the influence of loading rates on the Young’s modulus and ultimate stress. Basing on the Young’s modulus and ultimate stress, the degree of anisotropy is calculated. Moreover, 24 stripped samples from 3 aortas are tested to study the relaxation anisotropy of arteries by fitting the experimental data with a five-parameter Maxwell reduced relaxation function. Results Histological analysis shows the parallel orientation of crimpled collagen and elastin fibres. The Young’s modulus and ultimate stress reach the greatest in the circumferential direction, and the smallest in the axial direction, respectively, and the values in the other directions are in-between; moreover, the two parameters monotonously increase as the samples orientate from the axial to circumferential directions. The Young’s modulus is more sensitive to the loading rate than the ultimate stress. The degree of anisotropy calculated by the Young's modulus is similar to that by the ultimate stress, and it is independent of loading rates. Stress-relaxation also exhibits anisotropy, whose variation is consistent with those of the two parameters. Conclusions Due to the stress-growth rule, fibre preferably orientates in the circumferential direction, and the preferable orientation results in great mechanical parameters, anisotropy, and small relaxation behaviour of arteries. The work extends the studies on the arterial anisotropy instead of only the circumferential and axial directions, and could be useful to comprehensively understand the anisotropy of arteries.
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Affiliation(s)
- Qiang Chen
- Biomechanics Laboratory, School of Biological Science and Medical Engineering, Southeast University, Nanjing, 210096, People's Republic of China.
| | - Yan Wang
- Biomechanics Laboratory, School of Biological Science and Medical Engineering, Southeast University, Nanjing, 210096, People's Republic of China
| | - Zhi-Yong Li
- Biomechanics Laboratory, School of Biological Science and Medical Engineering, Southeast University, Nanjing, 210096, People's Republic of China. .,School of Chemistry, Physics and Mechanical Engineering, Queensland University of Technology, Brisbane, Australia.
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Latorre M, Peña E, Montáns FJ. Determination and Finite Element Validation of the WYPIWYG Strain Energy of Superficial Fascia from Experimental Data. Ann Biomed Eng 2016; 45:799-810. [PMID: 27600686 DOI: 10.1007/s10439-016-1723-2] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2016] [Accepted: 08/26/2016] [Indexed: 11/30/2022]
Abstract
What-You-Prescribe-Is-What-You-Get (WYPIWYG) procedures are a novel and general phenomenological approach to modelling the behavior of soft materials, applicable to biological tissues in particular. For the hyperelastic case, these procedures solve numerically the nonlinear elastic material determination problem. In this paper we show that they can be applied to determine the stored energy density of superficial fascia. In contrast to the usual approach, in such determination no user-prescribed material parameters and no optimization algorithms are employed. The strain energy densities are computed solving the equilibrium equations of the set of experiments. For the case of superficial fascia it is shown that the mechanical behavior derived from such strain energies is capable of reproducing simultaneously the measured load-displacement curves of three experiments to a high accuracy.
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Affiliation(s)
- Marcos Latorre
- Escuela Técnica Superior de Ingeniería Aeronáutica y del Espacio, Universidad Politécnica de Madrid, Plaza Cardenal Cisneros, 3, 28040, Madrid, Spain
| | - Estefanía Peña
- Aragón Institute of Engineering Research (I3A), Mechanical Engineering Department, University of Zaragoza, Zaragoza, Spain.,CIBER de Bioingeniera, Biomateriales y Nanomedicina (CIBER-BBN), Zaragoza, Spain
| | - Francisco J Montáns
- Escuela Técnica Superior de Ingeniería Aeronáutica y del Espacio, Universidad Politécnica de Madrid, Plaza Cardenal Cisneros, 3, 28040, Madrid, Spain.
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