Effect of serum and platelet-derived growth factor on chondrocytes grown in collagen gels

In this in vitro study, cell proliferation, viability, and morphology; proteoglycan (PG) synthesis; and gel contraction were assessed over a 15-day period (on days 3, 6, 9, 12, and 15) for mature bovine chondrocytes cultured in collagen gels. The environment within the gel was varied by changing the concentration of fetal bovine serum (1% and 10%) and platelet-derived growth factor-BB (PDGF; 0, 10, 50, 100 ng/ml) within the gel and incubation media. Our results showed that the amount of serum or PDGF added to the gels had no effect on cell viability, with >95% of cells remaining alive throughout the experiment. There was a significant increase in cell number over time in all groups, with a higher rate of cell proliferation in gels containing 10% serum and higher concentrations of PDGF. In addition, the amount of serum significantly affected gel contraction with or without PDGF. Gels containing 10% serum contracted on day 10-12, while none of the gels containing 1% serum contracted over the course of the experiment. The PG content within each gel increased with incubation time only for the gels containing 1% serum, and 10 or 100 ng/ml of PDGF. However, on a per cell basis, there was no change in the PG content with time when only serum was used and a significant decrease in the rate of PG production with the addition of PDGF (9.1-27.8 pgPG/cell/day). Cell morphology was also affected by PDGF, with the cells becoming more spindle shaped. Cell alignment within the gels appeared to be most affected by gel contraction. Collagen gels can act as cell carriers for the purpose of tissue engineering. These gels provide a three-dimensional environment in which chondrocytes can proliferate and produce matrix. We have shown how this environment can be controlled to affect gel contraction, rates of cell growth and PG production, and cellular morphology while maintaining cell viability. This information will be useful in determining the conditions in which chondrocytes can be grown within collagen gels and combined with cytokines to create an ideal tissue construct.