Surface hydrophilicity and enzymatic hydrolyzability of biodegradable polyesters: 1. Effects of alkaline treatment

Surface treatment using alkaline solutions was attempted to enhance the surface hydrophilicity and enzymatic hydrolyzability of hydrophobic poly(L-lactide) [ie poly(L-lactic acid) (PLLA) and poly(epsilon-caprolactone) (PCL). The alkaline treatment was performed by immersing the PLLA and PCL films in 0.01 and 4 N NaOH solutions, respectively, for various periods of time. The effects of the alkaline treatment on the hydrophilicity of the films were monitored by dynamic contact angle measurements, while the enzymatic hydrolyzability of the PLLA and PCL films after the alkaline treatment were evaluated by weight losses in the presence of proteinase K and Rhizopus arrhizus lipase, respectively. With the alkaline treatment the hydrophilicity of the PLLA and PCL films was controllable in the advancing contact angle (theta(a)) ranges of 84-108degrees and of 69-93degrees, respectively, by varying the alkaline treatment time. The enzymatic hydrolysis rates of the PLLA films became higher with decrease of the theta(a), irrespective of the crystallinity, strongly suggesting that the surface hydrophilicity or the surface molecular weight is crucial to determine their enzymatic hydrolyzability. In contrast, the enzymatic hydrolyzability of the PCL films remained unchanged even when the theta(a) decreased from 93degrees to 73degrees by alkaline treatment for 4 h. However, prolonged alkaline treatment for periods of time exceeding 4 h, which insignificantly altered the theta(a) but caused the formation of pores and cracks on the PCL film surface, accelerated the enzymatic hydrolysis of the PCL films. This indicates that the enzymatic hydrolyzability of the PCL film depends on the surface area per unit weight rather than the surface hydrophilicity. (C) 2003 Society of Chemical Industry.