Medium osmolarity and PCM development improves chondrocyte survival when photoencapsulated in PEG hydrogels at low densities.
The ability to encapsulate cells over a range of cell densities is important towards mimicking cell densities of native tissues and rationally designing strategies where cell source and/or cell numbers are clinically limited. Our preliminary findings demonstrate that survival of freshly isolated adult bovine chondrocytes dramatically decreases when photoencapsulated in poly(ethylene glycol) hydrogels at low densities (4 million cells/ml). During enzymatic digestion of cartilage, chondrocytes undergo a harsh change in their microenvironment. We hypothesize that the absence of exogenous antioxidants, thehyposmotic environment, and the loss of a protective pericellular matrix increase chondrocytes’ susceptibility to free-radical damage during photoencapsulation. Incorporation of antioxidants and serum into the encapsulation medium improved cell survival 2-fold compared to phosphate buffered saline. Increasing medium osmolarity from 330 to 400 mOsm (physiological), improved cell survival by 40% and resulted in 2-fold increase in ATP production 24 hours post-encapsulation. However, cell survival was only temporary. Allowing cells to reproduce some PCM prior to photoencapsulation in 400 mOsm medium resulted in superior cell survival during and post-encapsulation for up to 15 days. In summary, the combination of antioxidants, physiological osmolarity and the development of some PCM result inan improved robustness against free radical damage during photoencapsulation.