Biologic behavior of an in vitro hydrated collagen gel-human tenocyte tendon model

An in vitro human tenocyte-collagen gel model was developed to study tenocyte-mediated Type I collagen fibril reorganization, proliferation, and Type I collagen gene expression. Human tenocytes, obtained from extrasynovial forearm flexor tendons from children 5 to 10 years of age were cultured on plastic or in a cylinder of hydrated Type I collagen gel. Collagen solution was seeded with human tenocytes at 5 x 10(5) cells/mL and gelled in cylinder molds; gel cylinders without human tenocytes served as controls. Gel cylinders were pinned to troughs to create noncompliance. The gel cylinders were analyzed for collagen birefringence and cell shape at 7 and 21 days and for proliferation and gene expression for Type I collagen at 7 days. Under conditions of noncompliance, human tenocytes reoriented Type I collagen into longitudinal bundles resembling the parallel organization of collagen in native tendons. Tenocyte shape became fusiform between the collagen bundles which mimics the morphologic features of a tenocyte in vivo. The structural changes in the tenocytes and matrix are accompanied by downregulation of human tenocyte proliferation and Type I collagen gene expression. When released from the gel cylinder and grown again on plastic, human tenocytes resume proliferation and Type I collagen gene expression. The human tenocytes in this in vitro gel cylinder model system control fibril reorganization and proliferation, resembling their behavior during the development and repair of native tendons.