Investigation of Cell Sources and Surface Modification Strategies for Hybrid and Tissue Engineered Heart Valves

Bioprosthetic heart valve replacements often calcify and fail, particularly when used to treat pediatric patients. Even recent advances in processing methods have been insufficient to completely address the risk of complications in the pediatric population. Fully synthetic tissue engineered heart valve (TEHV) replacements have been suggested as an ideal replacement, as they can be seeded with autologous cells to form a viable tissue that is capable of somatic growth and hemostasis. However, this technology is still in development, and will not be available to patients within a short (5-10 year) time period. In the interim, some studies have investigated coating methods for current valve replacements to try to improve their biocompatibility in the short term. However, many of these proposed mechanisms face many regulatory issues because of the processing steps involved. In this work, we investigated the characteristics of pediatric valvular interstitial cells (VICs) and their comparability to a potential surrogate cell source, dermal fibroblasts, for long-term TEHV development. We found that these cells behave similarly, particularly when cultured on collagen type I substrates. This study provides additional guidance for the development of TEHVs specifically for pediatric patients and expands current knowledge about pediatric VICs, a previously understudied cell population. The next studies focused on advancing short-term solutions for biocompatibility in bioprosthetic heart valve replacements. Due to the individual variability and difficulty analyzing bioprosthetic tissue, a model surface was developed to aid the optimization of surface coating methods for tissue valves. The bioprosthetic valve surface model (BVSM) was shown to have comparable surface mechanical properties, residual toxicity from glutaraldehyde fixation, and content of reactive groups for surface coating. Additionally, the BVSM was easy to construct, highly reproducible, and allowed for fine-tuning of the surface characteristics which could be altered for future studies of cellular interactions with the surface. In general, the BVSM developed in this work can be applied to optimize and analyze surface coating methods quickly and easily and to answer questions related to cell behavior in response to the surface coatings. Finally, the BVSM was applied in a final study to optimize our proposed two-step surface coating method for bioprosthetic heart valve replacements. This two-step coating method involves non-toxic, mild reactants and conditions which create a thin, polyethylene glycol (PEG)-based hydrogel coating on the surface. This coating can also include other molecules of interest without changes to the reaction protocol. Through the optimization on the BVSM, we demonstrated the formation of a thin, continuous surface coating that successfully repelled protein adsorption and did not significantly affect the BVSM surface mechanical properties. Based on this success, the coating method was translated directly to bioprosthetic tissue samples. Results showed areas of coating formation of the coating on the tissue, confirmed by both SEM and XPS analysis, and that the areal coverage of the coating could be improved with an increase in catalyst concentration. This work demonstrates the feasibility of this proposed coating method for modifying the surface of bioprosthetic heart valve tissue, which could improve the biocompatibility of these devices. In future studies, this coating can be easily modified with molecules to encourage in situ endothelialization for even better hemocompatibility, particularly for pediatric patients. The cell characterization, optimization tools, and coating method developed here could lead to breakthroughs in current device biocompatibility and will support the long-term development of TEHVs as an ideal pediatric valve replacement