A collagen-glycosaminoglycan co-culture model for heart valve tissue engineering applications

In order to develop efficient design strategies for a tissue-engineered heart valve, in vivo and in vitro models of valvular structure and cellular function require extensive characterisation. Collagen and glycosaminoglycans (GAGs) provide unique functional characteristics to the heart valve structure. In the current study, type I collagen-GAG hydrogels were investigated as biomaterials for the creation of mitral valve tissue. Porcine mitral valve interstitial cells (VICs) and endothelial cells (VECs) were isolated and co-cultured for 4 weeks in hydrogel constructs composed of type I collagen. The metabolic activity and tissue organisation of mitral valve tissue constructs was evaluated in the presence and absence of chondroitin sulphate (CS) GAG, and comparisons were made with normal mitral valve tissue. Both collagen and collagen-CS mitral valve constructs contracted to form tissue-like structures in vitro. Biochemical assay demonstrated that over 75% of CS was retained within collagen-CS constructs. Morphological examination demonstrated enhanced VEC surface coverage in collagen-CS constructs compared to collagen constructs. Ultrastructural analysis revealed basement membrane synthesis and cell junction formation by construct VECs, with an increased matrix porosity observed in collagen-CS constructs. Immunohistochemical analyses demonstrated enhanced extracellular matrix production in collagen-CS constructs, including expression of elastin and laminin by VICs. Both native valve and collagen-CS construct VECs also expressed the vasoactive molecule, eNOS, which was absent from collagen construct VECs. The present study demonstrates that collagen gels can be used as matrices for the in vitro synthesis of tissue structures resembling mitral valve tissue. Addition of CS resulting in a more porous model was shown to positively influence the bioactivity of seeded valve cells and tissue remodelling. Collagen-GAG matrices may hold promise for a potential use in heart valve tissue engineering and improved understanding of heart valve biology.