Photochemical Crosslinking of Methacrylated Collagen Hydrogels: Effect of I2959 vs. VA086 on Mechanics and Cellular Response
Watkins, Kori Elizabeth
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Irgacure 2959 (I2959) is widely used for photochemical crosslinking of a variety of different hydrogels. However, the free radicals generated from I2959 have been reported to be highly cytotoxic. Previous work has shown that photochemical crosslinking of alginate hydrogels using VA086 (water soluble azo initiator) resulted in significantly higher viability of chondrocytes compared to I2959. However, photochemical crosslinking of pure methacrylated collagen type I hydrogels using VA086 has not yet been investigated. The goal of the current study was to compare the effects of I2959 vs. VA086 on the physical properties of methacrylated collagen type I hydrogels and SAOS-2 osteoblast cell viability. We hypothesize that crosslinking conditions will impact hydrogel mechanical properties. Further, we hypothesize that the use of VA086 as a photoinitiator will result in significantly higher osteoblast cell viability compared to I2959. Photochemically crosslinked collagen hydrogels were synthesized by mixing methacrylated collagen type I solution with a photoinitiator agent (I2959 or VA086) and exposed to UV light. Different concentrations and crosslinking times were employed to assess the effect on hydrogel morphology, physical properties, and cellular response. SEM imaging showed that photochemical crosslinking resulted in the merging of collagen fibrils for I2959 and VA086. Uniaxial compression tests showed that compressive modulus of methacrylated collagen hydrogels photocrosslinked with I2959 and VA086 was comparable. Results from degradation study showed that with increasing crosslinking concentration and exposure time increased the stability of hydrogels, and photochemical crosslinking with I2959 produced more stable hydrogels than VA086. Photochemical crosslinking decreased the swelling ratio of hydrogels compared to uncrosslinked hydrogels. Results from Alamar Blue and live-dead assay showed that photochemical crosslinking of methacrylated collagen hydrogels with VA086 resulted in higher cell viability and proliferation compared to I2959. Alizarin Red S staining confirmed that SAOS-2 cell-mediated mineralization was more pronounced on VA086 photocrosslinked hydrogels. In conclusion, the results from this study suggest that photochemical crosslinking changes the physical properties methacrylated collagen hydrogels, and that VA086 is more cytocompatible compared to I2959 for photochemical crosslinking of methacrylated collagen hydrogels.