Tojo Razafiarison
In this dissertation, we investigated the effect of poly(ethylene glycol) hydrogel network structures on various cellular activities such as proliferation and matrix production using chondrocytes as a cell source. We have used various methods to alter the network structure, which involves utilizing precursors with varying molecular weight and changing the degree of polymerization. The latter was achieved by varying initiator concentrations, and duration of polymerization time. PEG hydrogels constituting PEG precursors of molecular weights 3.4kDa, 6kDa, 10kDa and 20KDa were synthesized, characterized and subsequently tested for their effects on chondrocytes biosynthetic activity. The structural parameters of the hydrogel network that varied due to our experimental differences were determined. Specifically, the hydrogel structures were characterized in terms of swelling ratio, the molecular weight between crosslinks, the mesh size, and the pore size. Swelling ratio of the hydrogels decreased while gel content increased with longer UV exposure and higher photo-initiator concentration. High compressive modulus was observed with PEG 3.4kDa whereas PEG 20kDa exhibited high ultimate stress, which was 37 times higher than the other hydrogels. Cells in hydrogels with a lower MW (PEG3.4) showed higher proliferation and more ECM synthesis in comparison with high molecular weight PEG hydrogels. This could be attributed to the bigger pore size of the high molecular weight PEG hydrogels, which could result in loss of cells. However, the amount of DNA observed after week 4 normalized to day 1 revealed that cells in hydrogels with a higher MW showed a higher proliferation and the amount of ECM synthesized per cell was larger. Histology revealed that proteoglycans were more diffused in the matrix with higher MW, indicating the presence of higher pore size. Cellular aggregation was observed after 2 weeks in all the hydrogels except for the 3.4kDa hydrogels; the aggregation of cells in 20kDa was also very minimal. A low degree of polymerization led to a high proliferation rate during the first week followed by enhanced ECM production. Conversely, a high degree of polymerization led the cells to a greater amount of protein synthesis during the first week, followed by proliferation. While the cells behaved in different ways at early time points of the culture, at the end of 4 weeks, there was no significant difference between the number of cells, nor ECM production in different hydrogels. This study clearly shows that the network structure has a temporal effect on chondrocyte functions
2009
