Collagen scaffolds and injectable biopolymer gels for cardiac tissue engineering

[摘要] Three-dimensional biomaterial scaffolds have begun to shown promise for cell delivery for cardiac tissue engineering. Although various polymers and material forms have been explored, there is a need for: injectable gels that meet certain design specifications; a more indepth characterization of the scaffold properties; and a deeper understanding of the relation of select properties to cellular behavior, to provide a rational basis for future in vivo studies. The first objective of this thesis was to develop and characterize novel injectable biopolymer hydrogels capable of safely undergoing covalent cross-linking in vivo to provide a mechanically tunable nanofibrillar scaffold. Soluble type I collagen gels with genipin and transglutaminase cross-linkers, and gelatin-hydroxyphenylpropionic acid (Gtn-HPA) gels, the cross-linking of which are modulated by horse radish peroxidase and hydrogen peroxide, were investigated. The gels were characterized on the basis of rheological properties, resistance to degradation, and effects on stem cell behavior. Another objective was to evaluate the simultaneous differentiation of embryonic carcinoma cells (ECCs) incorporated in the gels into the three cell types in cardiac tissue -- cardiomyocytes, neural cells, and vascular endothelial cells -- and to determine the effects of certain properties of the gels on the differentiation profile, using mesenchymal stem cells as a comparative control. The injectable collagen-genipin and Gtn-HPA gels were found to be mechanically tunable hydrogel systems that supported cell encapsulation and proliferation at safe concentrations of the respective cross-linking agents. ECCs cultured as embryoid bodies (EBs) incorporated in the collagen-genipin and Gtn-HPA gels differentiated into cardiac, neural, and endothelial cells and combinations thereof, demonstrating the capability of EBs to express multiple cell lineages within the same EB. EBs cultured in collagen gels without cross-linkers and collagen gels with 0.25 mM genipin exhibited the highest differentiation efficiency compared to those cultured in monolayer, sponge-like scaffolds, and Gtn-HPA gels. The differentiation medium and culture time also had significant effects on differentiation efficiency. Notable findings included: the increased expression of neural and endothelial markers in EBs cultured in in mixed medium conditions compared to those cultured in neural or endothelial differentiation medium alone, and the correlation between angiogenic and neurogenic differentiation in the EBs in the non-cross-linked collagen gels for all media. Collectively, these findings show promise in using collagen gels cross-linked with 0.25 mM genipin, incorporated with EBs, for cellular therapy in cardiac tissue engineering applications.

[发布机构] Massachusetts Institute of Technology