The in vitro cell expansion of autologous chondrocytes is of high interest in regenerative medicine since these cells can be used to treat joint cartilage defects. In order to preserve chondrocyte differentiation/ phenotype, while optimizing proliferation and adhesion on microspheres, several processing parameters were varied. In this study three different polylactide-co-glycolides were used with differing lactide-glycolide ratios (85:15 and 50:50) and in case of the 50:50-polymer with differing residual monomer contents (0.83% and 0.9%). An emulsion route was established, where the polymer was dissolved in CHCl₃ and then injected in 30g of stirred 0.5% PVA/H₂O solution at different concentrations (0.05, 0.10, 0.15 g/ml) and different stirring velocities (200, 300, 400 rpm) to produce microspheres with varying diameters. The spheres were washed in 2-propanol and were UV irradiated for sterilization purposes. The sphere size distribution and morphology was analyzed using image analyzing software (NI Vision 7.1) on SEM pictures. Linking the size distribution to the cell cultivation experiments, three optimum samples were selected for further investigations. The degradation of the carriers was determined in a long term experiment in culture medium for 4 month by gathering the weight loss every 20 days. Adherent cells were characterized after 0.5h up to 5 days by FDA+EB staining and SEM.
In ongoing investigations we test these microspheres as carriers for prostaglandins, since these molecules have a proliferative effect on chondrocytes, this could open exciting possibilities to enhance the expansion of autologous chondrocytes.

Acknowledgments:
The authors would like to thank Dr. H. Liedtke of Boehringer Ingelheim Pharma for the polymer samples.

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