Novel Dynamic Bioreactor and PEGDA Hydrogel Scaffolds for Investigation and Engineering of Aortic Valve Tissues
Grande-Allen, K. Jane
Doctor of Philosophy thesis
Tissue engineered heart valves (TEHV) will allow clinicians to have a highquality prosthesis for patients that could eliminate many drawbacks of currently available treatments. Although there is great promise for TEHV, the field is still in its infancy; proper scaffolding materials and dynamic culture regimens that produce TEHV suitable for implantation in the aortic valve (A V) position have not yet been identified. Novel systems to apply biomechanical stimuli to developing engineered tissues and materials development and characterization will be necessary to progress towards an aortic TEHV. This thesis work aimed to address these issues in a parallel manner. The thesis begins by describing the design and physical characterization of a bioreactor system capable of both AV organ culture and biomechanical conditioning of engineered A V tissues. This work demonstrated that the newly developed bioreactor system allows A V to be cultured dynamically in a simple system that scales to accommodate varying sample sizes. Evaluation of this bioreactor system showed that dynamic culture of A V maintained normal tissue phenotype for durations of up to seven days, which is to-date the longest ex vivo maintenance of normal A V tissue phenotype in a dynamic bioreactor system. This thesis work also investigated the suitability ofpoly(ethylene glycol) diacrylate hydro gels to be used as a TEHV scaffold. These studies showed that flexural stiffness of the resulting scaffolds could be modulated by varying the formulation parameters chosen, and that valvular interstitial cells embedded and cultured within these gels (also containing incorporated bioactive moieties) maintained expression of several characteristic phenotypic markers. The thesis also describes studies in which advanced iii hydrogel scaffolds were fabricated using anatomically-inspired composite strategies, resulting in scaffolds that possessed unique material properties (anisotropic behavior and altered bending stiffness) compared to standard single component hydrogels. These studies were the first to show a biphasic, trilayered quasilaminate structure in a photopolymerized system. Additionally, these studies demonstrated the development of new anatomically-inspired patterns of reinforcement that allow hydrogels material behavior to more closely mimic tissue. The thesis closes with a description of the implications of these studies on heart valve tissue engineering and potential future directions using these techniques.