Cultivation of cell-polymer cartilage implants in bioreactors

Cartilage implants for potential use in reconstructive or orthopedic surgery can be created by growing isolated cartilage cells (chondrocytes) in vitro on synthetic, biodegradable polymer scaffolds. The scaffolds provide specific three-dimensional structures which support cell proliferation and biodegrade in a controlled fashion in parallel to cellular regeneration of cartilaginous tissue. Cartilage implants based on chondrocytes and fibrous polyglycolic acid scaffolds were recently shown to closely resemble normal cartilage histologically as well as with respect to cell density and matrix composition (collagen, glycosaminoglycan) [Freed et al., J Biomed Mater Res 27:11-23, 1993a]. These findings form the basis for developing straightforward procedures to obtain implants for clinical use from small, autologous cartilage specimens without any limitations in terms of availability of donor tissue or implant dimensions. Chondrocyte growth and cartilage matrix regeneration on polymer scaffolds are interdependent and also depend on in vitro tissue culture conditions. Under static culture conditions, cell growth rates are diffusionally limited due to increasing cell mass and decreasing effective implant porosity resulting from cartilage matrix regeneration. Optimization of the in vitro culture environment is thus essential for the cultivation of large, clinically useful cartilage implants. Preliminary studies indicate that major improvements can be achieved using bioreactors that provide efficient mass transfer and controlled shear rates at the cell and implant surfaces.