In vitro biomechanical and hydrodynamic characterisation of decellularised human pulmonary and aortic roots

Aortic Valve Engineering Advancements: Precision Tuning with Laser Sintering Additive Manufacturing of TPU/TPE Submillimeter Membranes

Synthetic biomaterials play a crucial role in developing tissue-engineered heart valves (TEHVs) due to their versatile mechanical properties. Achieving the right balance between mechanical strength and manufacturability is essential. Thermoplastic polyurethanes (TPUs) and elastomers (TPEs) garner significant attention for TEHV applications due to their notable stability, fatigue resistance, and customizable properties such as shear strength and elasticity. This study explores the additive manufacturing technique of selective laser sintering (SLS) for TPUs and TPEs to optimize process parameters to balance flexibility and strength, mimicking aortic valve tissue properties. Additionally, it aims to assess the feasibility of printing aortic valve models with submillimeter membranes. The results demonstrate that the SLS-TPU/TPE technique can produce micrometric valve structures with soft shape memory properties, resembling aortic tissue in strength, flexibility, and fineness. These models show promise for surgical training and manipulation, display intriguing echogenicity properties, and can potentially be personalized to shape biocompatible valve substitutes.

Mechanical failure analysis of patch materials used in aortic arch reconstruction: implications for clinical practice

OBJECTIVES

Thick-patch pulmonary homograft, autologous pericardium and CardioCel Neo are common patch materials for aortic arch reconstruction. Insufficient data exist on sutured patch strength and limits of use. We evaluated failure strength of these materials to develop a failure prediction model for clinical guidance.

METHODS

Patch failure strength was evaluated via sutured uniaxial and burst pressure testing. In sutured uniaxial testing, patches were sutured to aortic or Dacron tabs and pulled to failure. In burst pressure testing, patches were sewn into porcine aortas or Dacron grafts and pressurized to failure. Failure membrane tension was calculated. A prediction model of membrane tension versus vessel diameter was generated to guide clinical patch selection.

RESULTS

Combining sutured uniaxial and burst pressure test data, pulmonary homograft failure strength {0.61 [interquartile range (IQR): 0.44, 0.78] N/mm, n = 21} was less than half that of autologous pericardium [2.22 (IQR: 1.65, 2.78) N/mm, n = 15] and CardioCel Neo [1.31 (IQR: 1.20, 1.42) N/mm, n = 20]. Pulmonary homograft burst pressure [245 (IQR: 202, 343) mmHg, n = 7] was significantly lower than autologous pericardium [863 (IQR: 802, 919) mmHg, n = 6] and CardioCel Neo [766 (IQR: 721, 833) mmHg, n = 6]. Our model predicts failure limits for each patch material and outlines safety margins for combinations of aortic diameter and pressure.

CONCLUSIONS

Sutured failure strength of thick-patch pulmonary homograft was significantly lower than autologous pericardium and CardioCel Neo. Patient selection (predicted postoperative arch diameter and haemodynamics) and blood pressure management must be considered when choosing patch material for arch reconstruction. In older children and adolescents, autologous or bovine pericardium may be more suitable materials for aortic patch augmentation to minimize the risk of postoperative patch failure.

Pediatric pulmonary valve replacements: Clinical challenges and emerging technologies

Congenital heart diseases (CHDs) frequently impact the right ventricular outflow tract, resulting in a significant incidence of pulmonary valve replacement in the pediatric population. While contemporary pediatric pulmonary valve replacements (PPVRs) allow satisfactory patient survival, their biocompatibility and durability remain suboptimal and repeat operations are commonplace, especially for very young patients. This places enormous physical, financial, and psychological burdens on patients and their parents, highlighting an urgent clinical need for better PPVRs. An important reason for the clinical failure of PPVRs is biofouling, which instigates various adverse biological responses such as thrombosis and infection, promoting research into various antifouling chemistries that may find utility in PPVR materials. Another significant contributor is the inevitability of somatic growth in pediatric patients, causing structural discrepancies between the patient and PPVR, stimulating the development of various growth-accommodating heart valve prototypes. This review offers an interdisciplinary perspective on these challenges by exploring clinical experiences, physiological understandings, and bioengineering technologies that may contribute to device development. It thus aims to provide an insight into the design requirements of next-generation PPVRs to advance clinical outcomes and promote patient quality of life.

Biological Scaffolds for Congenital Heart Disease

Congenital heart disease (CHD) is the most predominant birth defect and can require several invasive surgeries throughout childhood. The absence of materials with growth and remodelling potential is a limitation of currently used prosthetics in cardiovascular surgery, as well as their susceptibility to calcification. The field of tissue engineering has emerged as a regenerative medicine approach aiming to develop durable scaffolds possessing the ability to grow and remodel upon implantation into the defective hearts of babies and children with CHD. Though tissue engineering has produced several synthetic scaffolds, most of them failed to be successfully translated in this life-endangering clinical scenario, and currently, biological scaffolds are the most extensively used. This review aims to thoroughly summarise the existing biological scaffolds for the treatment of paediatric CHD, categorised as homografts and xenografts, and present the preclinical and clinical studies. Fixation as well as techniques of decellularisation will be reported, highlighting the importance of these approaches for the successful implantation of biological scaffolds that avoid prosthetic rejection. Additionally, cardiac scaffolds for paediatric CHD can be implanted as acellular prostheses, or recellularised before implantation, and cellularisation techniques will be extensively discussed.

The effect of decellularisation on the real time mechanical fatigue of porcine aortic heart valve roots

Decellularised heart valve roots offer a promising option for heart valve replacement in young patients, having the potential to remodel and repair. Replacement heart valves have to undergo billions of opening and closing cycles throughout the patient’s lifetime. Therefore, understanding the effect of cyclic loading on decellularised heart valve roots is important prior to human implantation. The aim of this preliminary study was to investigate the influence of low concentration sodium dodecyl sulphate (SDS) decellularisation treatment on the in vitro real time mechanical fatigue of porcine aortic heart valve roots under physiological real time cyclic loading conditions. This required a specific real time in vitro method to be developed, since previous methods relied on accelerated testing, which is non-physiological, and not appropriate for valve replacement materials that exhibit time dependent characteristics. The effects of the real time fatigue on hydrodynamic function and mechanical properties of the heart valve roots were assessed. The mechanical fatigue of decellularised porcine aortic heart valve roots (n = 6) was assessed and compared to cellular porcine aortic heart valve roots (n = 6) in a modified Real time Wear Tester (RWT) at a physiological frequency and under cyclic pressure conditions for a maximum of 1.2 million cycles. Periodically, the heart valve roots were removed from the RWT to assess the influence of cyclic loading on valve competency (static leaflet closure). At the end of testing further hydrodynamic performance parameters were ascertained, along with determination of leaflet material properties. A real time mechanical fatigue assessment method was developed and applied; with two cellular and two decellularised porcine aortic leaflets in different heart valve roots showing tears in the belly region. The decellularised aortic heart valve roots exhibited comparative functionality to the cellular heart valve roots under in vitro static and pulsatile hydrodynamic conditions. However, the material properties of the decellularised aortic leaflets were significantly altered following cyclic fatigue assessment and showed increases in elastin and collagen phase slopes and ultimate tensile strength compared to the cellular porcine aortic leaflets in the circumferential direction. This preliminary study demonstrated that low concentration SDS decellularised porcine aortic heart valve roots can withstand physiological cyclic deformations up to 1.2 million cycles in a RWT whilst maintaining their overall hydrodynamic function and leaflet mechanical properties. This is the first full report of preclinical mechanical fatigue assessment of decellularised porcine aortic heart valve roots under physiological real time conditions.

Repopulation of decellularised porcine pulmonary valves in the right ventricular outflow tract of sheep: Role of macrophages

The primary objective was to evaluate performance of low concentration SDS decellularised porcine pulmonary roots in the right ventricular outflow tract of juvenile sheep. Secondary objectives were to explore the cellular population of the roots over time. Animals were monitored by echocardiography and roots explanted at 1, 3, 6 (n = 4) and 12 months (n = 8) for gross analysis. Explanted roots were subject to histological, immunohistochemical and quantitative calcium analysis (n = 4 at 1, 3 and 12 months) and determination of material properties (n = 4; 12 months). Cryopreserved ovine pulmonary root allografts (n = 4) implanted for 12 months, and non-implanted cellular ovine roots were analysed for comparative purposes. Decellularised porcine pulmonary roots functioned well and were in very good condition with soft, thin and pliable leaflets. Morphometric analysis showed cellular population by 1 month. However, by 12 months the total number of cells was less than 50% of the total cells in non-implanted native ovine roots. Repopulation of the decellularised porcine tissues with stromal (α-SMA+; vimentin+) and progenitor cells (CD34+; CD271+) appeared to be orchestrated by macrophages (MAC 387+/ CD163low and CD163+/MAC 387-). The calcium content of the decellularised porcine pulmonary root tissues increased over the 12-month period but remained low (except suture points) at 401 ppm (wet weight) or below. The material properties of the decellularised porcine pulmonary root wall were unchanged compared to pre-implantation. There were some changes in the leaflets but importantly, the porcine tissues did not become stiffer. The decellularised porcine pulmonary roots showed good functional performance in vivo and were repopulated with ovine cells of the appropriate phenotype in a process orchestrated by M2 macrophages, highlighting the importance of these cells in the constructive tissue remodelling of cardiac root tissues.

Transcatheter Heart Valves: A Biomaterials Perspective

Heart valve disease is prevalent throughout the world, and the number of heart valve replacements is expected to increase rapidly in the coming years. Transcatheter heart valve replacement (THVR) provides a safe and minimally invasive means for heart valve replacement in high-risk patients. The latest clinical data demonstrates that THVR is a practical solution for low-risk patients. Despite these promising results, there is no long-term (>20 years) durability data on transcatheter heart valves (THVs), raising concerns about material degeneration and long-term performance. This review presents a detailed account of the materials development for THVRs. It provides a brief overview of THVR, the native valve properties, the criteria for an ideal THV, and how these devices are tested. A comprehensive review of materials and their applications in THVR, including how these materials are fabricated, prepared, and assembled into THVs is presented, followed by a discussion of current and future THVR biomaterial trends. The field of THVR is proliferating, and this review serves as a guide for understanding the development of THVs from a materials science and engineering perspective.

Materials and manufacturing perspectives in engineering heart valves: a review

Valvular heart diseases (VHD) are a major health burden, affecting millions of people worldwide. The treatments for such diseases rely on medicine, valve repair, and artificial heart valves including mechanical and bioprosthetic valves. Yet, there are countless reports on possible alternatives noting long-term stability and biocompatibility issues and highlighting the need for fabrication of more durable and effective replacements. This review discusses the current and potential materials that can be used for developing such valves along with existing and developing fabrication methods. With this perspective, we quantitatively compare mechanical properties of various materials that are currently used or proposed for heart valves along with their fabrication processes to identify challenges we face in creating new materials and manufacturing techniques to better mimick ​the performance of native heart valves.