In vivo implantation of 2,2′-bis(oxazoline)-linked poly-ɛ-caprolactone: Proof for enzyme sensitive surface erosion and biocompatibility

Previously, we have demonstrated that 2,2-bis(2-oxazoline) linked poly-ɛ-caprolactone (PCL-O) is degraded in vitro enzymatically by surface erosion which could enable the novel use of this material for drug delivery and other biomedical applications. In this study, degradation, erosion (weight loss) and toxicity of PCL-O poly(ester-amide)s were evaluated in vivo. PCL and three PCL-O polymers with different PCL block lengths (Mn: 1500, 3900, 7500 g/mol) were melt-pressed in the form of discs and implanted subcutaneously in Wistar rats (dose ∼340 mg/kg) for 1, 4 and 12 weeks. With implantation for 12 weeks, up to 16.5% weight loss of polymer discs was measured for the most extensively linked PCL-O polymer (block length 1500 g/mol) whereas practically no weight loss was observed with the other polymers. NMR, DSC and SEC studies as well as SEM micrographs before and after implantation and in vitro hydrolysis studies indicate that enzyme based surface erosion of PCL-O polymers occurred in vivo. The in vivo evaluation based on results from hematology, clinical chemistry and histology of the implantation area and main organs (i.e. heart, lung, liver, kidney, spleen and brain) demonstrated that PCL-O polymers are biocompatible and safe, enzyme sensitive biomaterials.