Simultaneous determination of drug surface concentration and polymer degradation kinetics in biodegradable polymer/drug membranes: a model drug delivery system

This paper reports new simultaneous ToF-SIMS analysis to determine both the earliest stage of polymer degradation and the surface concentration of a drug additive. The static SIMS spectra of a model Ph3N/poly(L-lactic acid) (PLLA) (20:80 wt.%) blend matrix (t 0:4 mm on 1.0 cm2) hydrolyzed in buffered conditions are simultaneously and independently analyzed in the low mass range for the surface accumulation profile of Ph3N and in the high mass for the hydrolytic degradation kinetics of PLLA, respectively. The rate of PLLA degradation at pH 10.0 is 2 times faster than that at pH 7.4, but the corresponding rate of Ph3N accumulation at the surface is accelerated by a factor of 10.5 times faster. The results provide new insight in evaluating the surface concentration of Ph3N (pKb ¼ 0) from the blends, indicating that the initial rapid increase in surface concentration of Ph3N is related to but not singularly dependent on the rate of PLLA degradation. # 2004 Elsevier B.V. All rights reserved