Facile control of the surface property and hydrolytic degradation of poly(l-lactide) materials by coating poly(l-lactide)-based triblock copolymers with hydrophilic or hydrophobic block

Abstract

Diversifying the surface property and hydrolytic degradation rate is crucial to widen the applications of poly(L-lactide) (PLLA). In the present study, PLLA films were coated with PLLA-poly(ethylene glycol) (PEG)-PLLA (PLLA-b-PEG-b-PLLA) and PLLA-polybutadiene (PB)-PLLA (PLLA-b-PB-b-PLLA) as typical examples of block copolymers to prepare biodegradable materials with controlled surface property and hydrolytic degradation rate. These block copolymers had outer blocks whose chemical structure is identical to that of the base material and a center block of hydrophilic PEG or hydrophobic PB. The contact angle of PLLA films with water (85°) was decreased and increased by coating with PLLA-b-PEG-b-PLLA (71°) and PLLA-b-PB-b-PLLA (115°), respectively, revealing the facile and effective hydrophilization or hydrophobization by coating. Due to increased hydroxy and carboxyl groups on the film surface, the contact angle values decreased monotonously with increasing alkaline hydrolytic degradation time, irrespective of the presence of the coated polymer or the type of polymer coating. The hydrolytic degradation was decelerated by coated PLLA-b-PEG-b-PLLA and PLLA-b-PB-b-PLLA and the decelerating effect was intense for hydrophobic PLLA-b-PB-b-PLLA than for hydrophilic PLLA-b-PEG-b-PLLA. After hydrolytic degradation, the contact angle difference between the PLLA-b-PEG-b-PLLA-coated and non-coated films remained unchanged, whereas that between the PLLA-b-PB-b-PLLA-coated and non-coated films became larger. This indicates a higher hydrolytic degradation-resistance of the coated PLLA-PB-PLLA than that of the coated PLLA-PEG-PLLA and thereby the hydrophobization effects of the coated PLLA-PB-PLLA lasted for a longer time. Coating triblock copolymers composed of outer blocks whose molecular structure is same as that of base polymeric materials and a center block with high or low hydrophilicity is a facile method to prepare fully biodegradable materials with controlled surface property and hydrolytic degradation rate.