Fabrication of mitral valve chordae by directed collagen gel shrinkage.

The principles of tissue engineering are being used to explore numerous applications in reconstructive surgery. Mitral valve chordae are one such potential area, as mitral valve repair is increasing in popularity and synthetic materials have not been used widely. The use of cells, combined with reconstituted type I collagen, is an attractive option for fabricating materials for the replacement of thin tendonous structures such as mitral valve chordae. We have been using the principle of directed collagen gel shrinkage to fabricate tendinous structures with good mechanical properties. In this study, our objective was to maximize the strength of the collagen constructs by choosing cell type and optimizing cell-seeding density, culture time, and initial collagen concentration. A collagen-cell suspension was cast into silicone rubber wells with microporous anchors at the ends and cultured in an incubator. The anchors allowed shrinkage to occur only transverse to the long axis of the wells, thus creating highly aligned collagenous constructs. Collagen gel contraction increased with higher cell-seeding density. The optimal value was 10(6) cells/mL. The rate of gel contraction decreased with the initial collagen concentration. Fibril density increased with culture time, as the gel contracted. After the system was optimized, the mechanical strength of the constructs increased to 1.1 MPa, a value at least an order of magnitude greater than previously published results with similar systems. This study has demonstrated that collagen-cell constructs, with material properties similar to those of native mitral valve chordae, can be developed using the principle of directed collagen gel shrinkage. These structures may have application in other areas that require small-diameter tendons.