Cytocompatibility of UV and visible light photoinitiating systems on cultured NIH/3T3 fibroblasts in vitro

This work investigates the cytocompatibility of several photoinitiating systems for potential cell encapsulation applications. Both UV and visible light initiating schemes were examined. The UV photoinitiators included 2,2-dimethoxy-2-phenylacetophenone (Irgacure 651), 1-hydroxycyclohexyl phenyl ketone (Irgacure 184), 2-methyl-1-[4-(methylthio) phenyl]-2-(4-morpholinyl)-1-propanone (Irgacure 907), and 2-hydroxy-1-[4-(hydroxyethoxy)phenyl]-2-methyl-1-propanone (Darocur 2959). The visible light initiating systems included camphorquinone (CQ) with ethyl 4-N, N-dimethylaminobenzoate (4EDMAB) and triethanolamine (TEA) and the photosensitizer isopropyl thioxanthone. A cultured fibroblast cell line, NIH/3T3, was exposed to the photoinitiators at varying concentrations from 0.01% (w/w) to 0.1% (w/w) with and without the presence of initiating light. The results demonstrated that at low photoinitiator concentrations (6 0.01% (w/w)), all of the initiator molecules were cytocompatible with the exception of CQ, Irgacure 651, and 4EDMAB which had a relative survival ~ 50% lower than a control. In the presence of low intensity initiating light (~ 6 mW cm-2 of 365 nm UV light and ~ 60 mW cm-2 of 470-490 nm visible light) and initiating radicals, Darocur 2959 at concentrations 6 0.05% (w/w) and CQ at concentrations 6 0.01% (w/w) were the most promising cytocompatible UV and visible light initiating systems, respectively. To demonstrate the potential use of cytocompatible photoinitiating systems in cell encapsulation applications, chondrocytes were encapsulated in a photocrosslinked hydrogel using 0.05% (w/w) Darocur 2959 (cytocompatible) and 0.01% (w/w) Irgacure 651 (cyto-incompatible). After photopolymerizing for 10 minutes with ~ 8 mW cm-2 of 365 nm light, nearly all the chondrocytes survived the process with Darocur 2959 while very few of the chondrocytes survived the process with Irgacure 651.