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Photopolymerization has been widely explored in biomedical and tissue engineering applications due to its widely held potentials in the biomedical field. Photoinitiators embedded within crosslinked scaffold materials could potentially serve as a more effective alternative to present uses of gamma radiation for sterilization of implants and biomaterials. The purpose of this study was to evaluate the cellular toxicity and the intracellular response of three ultraviolet (UV) sensitive photoinitiators including eosin Y, 2-hydroxy-1-[4-(hydroxyethoxy)phenyl]-2methyl-1-propanone (Irgacure 2959) and dimethoxyphenyl acetophenone (DMPA) as well as the subsequent degree of proliferation of free radicals on HN4 cells. WST-1 assay indicated that HN4 cells can tolerate a wide range of concentrations of eosin Y and low concentrations of Irgacure 2959 (≤ 1 mg/ml) but not DMPA. Consistent with these results, eosin Y displayed no effect on intracellular AKT inactivation, but both Irgacure 2959 and DMPA concentration-dependently induced intracellular AKT inactivation. To initiate free radicals, these photoinitiators were exposed to UV light at 365 nm with an intensity of 100 watts for 30 minutes. In all three photoinitiating systems, HN4 cells failed to maintain cell viability and intracellular AKT activity. To further demonstrate the stability of free radicals on cytocompatibility, cell culture medium was mixed with eosin Y to reach a final concentration of 25μl/ml, and this mixture was exposed to UV light for 30 min. The mixture was kept in the dark prior to exposure to the cells. The results illustrate that the free radicals can be stable up to 48 hours, and HN4 cells failed to maintain cell viability and intracellular AKT activity in the eosin Y photoinitiating system after UV exposure. In summary, these results suggest that eosin Y is able to stabilize intracellular AKT activity and cell viability in a wider range than Irgacure 2959 and DMPA. However, the free radicals introduced by UV light significantly inhibit intracellular AKT activation and induce cytotoxicity. Future studies will aim to overcome the cruciality of removing from or significantly limiting free radicals within the photopolymer before biomedical applications.
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Virginia Commonwealth University. Undergraduate Research Opportunities Program
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