Effects of directed gel degradation and collagenase digestion on the integration of neocartilage produced by chondrocytes encapsulated in hydrogel carriers.

Chondrocytes were encapsulated in non-degrading and partially degrading poly(ethylene glycol) (PEG) gels in apposition to native cartilage layers in order to examine the effects of gel degradation on the integration of regenerated cartilaginous matrix with native tissue. In addition, the effect of collagenase predigestion of the native cartilage surfaces on this integration was examined in studies with partially degrading co-polymer gels. Integration was quantitatively assessed by mechanical measurements of adhesive strength, and visualized by histological staining and non-destructive ultrasound analysis. Constructs with encapsulated chondrocytes and a non-degrading gel layer had significantly higher adhesive strength than partially degrading gel constructs and non-degrading gel constructs without cells. In addition, better maintenance of proper cell morphology was observed near the gel-cartilage interface in non-degrading gel constructs than in partially degrading gel constructs after 8 weeks of in vitro culture. Facile collagen distribution in the degrading gels appeared to have a significant effect on mechanical adhesion measurements only when the native cartilage surface was predigested with collagenase. Ultrasound analysis provided qualitative evidence of cartilaginous matrix evolution and non-destructive imaging of developing constructs and the interface between newly formed matrix and existing cartilage tissue.