Poly (Vinyl Alcohol) Beads with Core-Shell Structure for Drug Delivery

Abstract

A new method of preparing large spherical poly(vinyl alcohol) (PVA) beads with a double-layer structure has been developed. The process involves a stepwise saponification of suspension polymerized PVAc beads and subsequent stepwise crosslinking of the PVA core and shell with glutaraldehyde. The resulting PVA beads have a thin, highly crosslinked outer shell and a lightly crosslinked inner core of different degrees of crosslinking. The kinetics of swelling and drug release from these beads in water were studied at 37°C using acetaminophen and proxyphylline as model drugs. The results show that the outer shell functions as a rate-controlling membrane upon increasing its crosslinking ratio, X, to about 0.5. This is reflected from the observed diffusional time-lags and the constant-rate regions during swelling and drug release. At lower shell crosslinking ratios (X < 0.35), the diffusional time-lags appear to be absent and the diffusional profiles are apparently first-order (Fickian) in nature, suggesting that the diffusion coefficients of both the drug and water have not been significantly affected by the small degrees of crosslinking in the shell. Based on the observed time-lags, the diffusion coefficient of water through the outer PVA shell with a high crosslinking ratio (X = 0.5) is estimated to be at least six times higher than that of acetaminophen and proxyphylline.