In vivo evaluation of injectable thermosensitive polymer with time-dependent LCST

The focus of this study was to examine the biocompatibility, time-dependent LCST, and bioerodable properties of a copolymer system composed of NIPAAm, dimethyl-gamma-butyrolactone (DMBL), and acrylic acid (AAc). Sprague Dawley rats were subcutaneously injected with 25 wt % solutions of poly(NIPAAm-co-DMBL-co-AAc). At predetermined times, animals were sacrificed and polymer implants were recovered for characterization via H-1-NMR. In addition, polymer-contacting tissue sections were harvested and processed for histology. The biocompatibility of the implants was assessed by counting the number of fibroblasts and leukocytes present at the tissue-implant interface. The LCST data obtained from the in vivo implants was shown to agree with that of in vitro findings. Implant mass was shown to decrease after 4 days, indicating accelerated diffusion rates with increased implant swelling, hydrolytic degradation was confirmed with H-1-NMR measurements. The cellular presence at the copolymer implant-tissue interface was shown to return to that of normal tissue 30 days postimplantation, which suggests a normal wound healing response. (C) 2008 Wiley Periodicals, Inc. J Biomed Mater Res 90A: 11861197, 2009