Importance of cell phenotype, matrix factor and mechanical stimulus on tissue-engineered mitral valve chordae

Repair of mitral valve chordae tendineae is limited by the availability of artificial materials possessing appropriate biomechanical properties. Collagen-based tissue engineering holds great promise for the development of rejection-free biomaterial substitutes for numerous applications in reconstructive surgery. Previously using the principal of directed collagen gel shrinkage, we have fabricated smooth muscle cell (SMC) embedded collagen constructs with fairly good mechanical properties, but these materials still have insufficient mechanical strength. We have explored three fundamentals aspects, which make up tissue engineering namely (i) cell selection, (ii) scaffold composition and (iii) mechanical conditioning to study their effect on the mechanical properties of cell seeded collagen constructs.;The "directed collagen gel shrinkage" involves initial mixing of acid solubilized collagen with appropriate SMCs. On neutralizing the cell-collagen suspension, soluble collagen reassembles into fibrils that interact with the integrin receptors on the cell surface. When the gel is mechanically constrained, the collagen fibrils and the cells align in the direction of constraint thereby forming highly compact collagenous constructs. Since the composition and organization of the extracellular matrix (ECM) likely contributes to the mechanical properties of tissues, we have evaluated in separate studies the effect of incorporation of fibronectin and controlled mechanical stimulation on the tensile properties in our tissue culture model. Also evaluation of different SMC populations was carried out in parallel to optimize fabrication of mechanically consistent collagen constructs.;Although the addition of fibronectin and applied static mechanical loading resulted in improved failure strength and stiffness of mature constructs, SMC populations had by far the greatest effect on structural and mechanical integrity of cultured constructs. The exhaustive classification performed by collecting information on the proliferation, migratory, morphological and gene expression characteristics of SMCs used for tissue culture have revealed and identified phenotype-specific dependence on fabrication of collagen constructs. The studies performed here have not only enabled us to evaluate the effect of relevant biochemical and biomechanical stimuli on collagen constructs but also provided a blueprint for future SMC culture isolations to eliminate or reduce cell dependant variations on the development of tissue-engineered substitutes.