IN-VIVO CHARACTERIZATION OF BIOLOGICAL CONTROLLED-RELEASE DEVICE FOR IN-SITU DELIVERY OF TGF-β₁ FOR ORTHOPEDIC TISSUE ENGINEERING

This study was to evaluate a biologically-based controlled-release device for human transforming growth factor-β₁(hTGF-β₁), in vivo, which has has significant potential in orthopedic tissue engineering, differentiatingchondrocyte precursors. Mouse and human fibroblast were genetically modified via viral transfection to express hTGF-β₁. Two viral constructs were used to induce synthesis of latent (wild-type) or active (mutant-type) forms of hTGF-β₁. Microcapsules were prepared by extrusion of a suspension of cells in a dilute alginate solution followed by precipitation in a Ca²⁺ solution. Microcapsules were collected, placed in nylon pouches (1x1.5 in.), and implanted into either subcutaneous or intraperitoneal spaces of mice. After 1 or 3 weeks, pouches were extracted from mice, and the viability of implanted cells were measured by MTT. Initial cell viability measured by MTT was consistently maintained ∼70% immediately following encapsulation and ∼50% after 1- or 3-week implant in vivo. Microcapsules were collected for a release study of hTGF-β₁in vitro. Release rates of hTGF-β₁ slightly declined following encapsulation, but they remained almost constant even after 1- or 3-week implant. Taken altogether, alginate encapsulation was sufficient to protect xenogeneic (human) and allogeneic (murine) cells against host immune response, and the cells were still biologically active to synthesize and secrete hTGF-β₁ at a therapeutically significant level.