The effects of crosslinking density on cartilage formation in photocrosslinkable hydrogels

Photoencapsulation of chondrocytes to produce tissue engineered cartilage provides many benefits including rapid polymerization times, the ability to fabricate complex architectures in vivo, and spatial and temporal control during polymerization. Recently, we have examined the cytocompatibility of several photoinitiation schemes and found that low photoinitiator concentrations and light intensities in the ultraviolet and visible range are cytocompatible. In this work, we are currently investigating photocrosslinkable hydrogels based on poly(vinyl alcohol) (PVA) and poly(ethylene oxide) (PEO) as scaffolds for tissue engineering cartilage. In particular, the influence of the network crosslinking density, swelling ratio, and chemical composition on the ability of encapsulated chondrocytes to form extracellular matrix is examined. The cartilage produced in these hydrogels will be quantified using biochemical assays that measure DNA content and the amount of sulfated glycosaminoglycans and total collagen in the extracellular matrix. We have demonstrated that chondrocytes encapsulated in a polymer scaffold made from a 20 wt% solution of PEODM/PEO (40 wt% dimethacrylated PEO (MW 3400)/60 wt% PEO (MW 100 K)) form cartilage, and after four weeks the results based on the wet weight of cartilage were approximately 0.03 million cells/mg cartilage, approximately 1.5% glycosaminoglycans and approximately 4.5% total collagen.