oa Decellularized In-Vitro Tissue-Engineered Heart Valves - First In-Vivo Results

Decellularized xenogeneic and allogeneic heart valves are used as matrices for tissue regeneration. However, xenografts are associated with a risk of immunogenic reactions or disease transmission and homografts are sparse. Further, remodeling capacity of these matrices is questioned, as cell infiltration is limited. Alternatively, biodegradable synthetic materials are attractive as of their unlimited supply and freedom in valve geometry, with sufficient capacity for cell infiltration and neotissue formation and remodeling, but with cell-mediated leaflet retraction and thickening as common problem with in-vivo application. To overcome cell-mediated leaflet retraction and thickening and the limitations when using xenografts or homografts, we propose to decellularize in-vitro cultured tissue-engineered heart valves as off-the-shelf matrices for in-vivo regeneration. Tissue-engineered heart valves are grown based on ovine vascular cells seeded onto PGA/P4HB valvular shaped scaffolds and exposed to dynamic loading in bioreactors for 4 weeks. Decellularization of in-vitro cultured tissue-engineered heart valves is demonstrated feasible with efficient cell removal and preservation of the collagen architecture and tissue strength. Storage of these valves up to 18 months did not affect tissue properties. Decellularization strongly reduced leaflet retraction and, therewith, improved valvular function up to 24 hours in a valve tester. In-vivo performance of decellularized in-vitro cultured tissue-engineered heart valves after trans-apical implantation in pulmonary position in sheep was evaluated after 8 (n=1), 16 (n=1) and 24 (n=1) weeks. Complete cellular repopulation was demonstrated within 8 weeks with excellent in-vivo performance and no signs of tissue thickening. Moderate regurgitation developed after 16 weeks with leaflet prolapse after 24 weeks and a reduced leaflet area, likely due to minimal coaptation in the current valve design. Minimal coaptation makes the leaflets prone to prolapse with direct loss of coaptation when repopulating cells exert traction forces. Mechanical analyses demonstrated tissue remodeling with a trend towards the development of anisotropic tissue properties in time, demonstrating the promising nature of decellularized in-vitro cultured tissue-engineered heart valves for in-vivo regeneration. Efforts are ongoing to increase the number of samples and to optimize valve design and geometry to increase leaflet coaptation and maintain optimal valve performance. The European Union's Seventh Framework Program is acknowledged for funding this study