Controlled enzymatic degradation of poly(ε-caprolactone)-based copolymers in the presence of porcine pancreatic lipase

摘要

Poly(ε-caprolactone) (PCL) has been extensively studied for biomedical use due to its outstanding biocompatibility. Well-defined random and block copolymers based on PCL such as poly(ε-caprolactone-r-2,2-dimethyltrimethylene carbonate) (PCD), poly[(ε-caprolactone-r-2,2-dimethyltrimethyIene carbonate)-b-PEG-b-(ε-caprolactone-r-2,2-dimethyltrimethylene carbonate)] (PECD) and poly[MPEG-b-(ε-caprolactone-r-2,2-dimethyltrimethylene carbonate)] (MPECD) containing 5.0-8.5 mol% 2,2-dime-thyltrimethylene carbonate (DTC) and 15.9-18.3 mol% polyethylene glycol (PEG) or polyethylene glycol monomethyl ether (MPEG) have been synthesized by using lanthanum tris(2,6-di-tert-butyl-4-methyl-phenolate) as catalyst. Their crystallization properties, thermal behaviors, hydrophilicities and degradation properties depend on the tunable microstructures and morphologies. It is found for the first time that porcine pancreatic lipase (PP lipase) can effectively catalyze the degradation of PCD electrospun mats (Ems) with 92.0% weight loss within 7 days while it shows no detectable effect on PCL Ems. Surface erosion mechanism is proposed in the enzymatic degradation systems, and the high proportion of amorphous domain of PCD contributes to its fast degradation rate according to the degradation product analyses. The enzymatic degradation rates of PCD Ems with porous structures and huge surface areas are higher than those of compression molding films (CMFs). Introducing PEG segment improves the hydrophilicity of PCD but decreases the degradation rate. A PEG segment enrichment process on the surface is addressed, which prevents the contact of PP lipase with PCD segments in the PEG-involved electrospun fiber. PECD and MPECD exhibit different mechanical strengths and contact angles, but similar degradation profiles. This study provides a practical example for tunable biodegradation of polyesters by designing the materials' bulk structures and/or surface morphologies.