Local Toxicity of Topically Administrated Thermoresponsive Systems: In Vitro Studies with In Vivo Correlation

Thermoresponsive materials have the ability to respond to a small change in temperature—a property that makes them useful in a wide range of applications and medical devices. Although very promising, there is only little conclusive data about the cytotoxicity and tissue toxicity of these materials. This work studied the biocompatibility of three Food and Drug Administration approved thermoresponsive polymers: poly(N-isopropyl acrylamide), poly(ethylene glycol)-poly(propylene glycol)-poly(ethylene glycol) tri-block copolymer, and poly(lactic acid-co-glycolic acid) and poly(ethylene glycol) tri-block copolymer. Fibroblast NIH 3T3 and HaCaT keratinocyte cells were used for the cytotoxicity testing and a mouse model for the in vivo evaluation. In vivo results generally showed similar trends as the results seen in vitro, with all tested materials presenting a satisfactory biocompatibility in vivo. pNIPAM, however, showed the highest toxicity both in vitro and in vivo, which was explained by the release of harmful monomers and impurities. More data focusing on the biocompatibility of novel thermoresponsive biomaterials will facilitate the use of existing and future medical devices.