Culture of chondrocytes in alginate surrounded by fibrin gel: Characteristics of the cells over a period of eight weeks

Abstract

Objective - To produce tissue engineered cartilage by human articular chondrocytes in vitro for further use in in vivo manipulations for the treatment of cartilage defects. Methods - Human articular chondrocytes were cultured in 0.5%, 1.0%, and 2.0% of alginate for up to four weeks. The optimal concentration of an alginate matrix for cell replication and for aggrecan synthesis by chondrocytes was determined. DNA content in the different culture conditions was measured after two and four weeks. Aggrecan synthesis rates and accumulation in the surrounding extracellular matrix were assessed by [35S]sulphate incorporation after the same periods of culture. To follow the outgrowth of chondrocytes from the alginate beads, chondrocytes were cultured for four weeks in 0.5 or 1.0% alginate surrounded by 0.25 or 0.5% fibrin gel. DNA content of each culture was measured after different culture periods. Finally, human chondrocytes in 1.0% alginate beads were embedded in 0.5% fibrin gel for eight weeks. Immunohistochemical analysis for aggrecan, type I and II collagen was performed weekly. Results - At two weeks the DNA content in each culture significantly increased in 0.5 and 1.0% alginate cultures in comparison with baseline values. This increase continued until week 4 at the three alginate concentrations. Aggrecan synthesis at two weeks was highest in 0.5 and 1.0% alginate cell cultures. At four weeks aggrecan synthesis rates decreased independently of the alginate concentrations. Aggrecan mainly accumulated in the interterritorial matrix. Proliferation of chondrocytes in alginate and outgrowth of these cells in the surrounding fibrin gel were evident throughout the culture period. The accumulation of aggrecan and type II collagen around the cells, in alginate as well as in fibrin gel, gradually increased over the culture period. Type I collagen appeared after six weeks in alginate and in the surrounding fibrin. Conclusion - Human chondrocytes proliferate in this culture system, show an outgrowth into the surrounding fibrin, and synthesize a cartilage-like matrix for up to eight weeks.