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 Ph ₃ N/poly(L-lactic acid) (PLLA) (20:80wt.%) blend matrix (t ∼ 0.4μm on 1.0cm ² ) hydrolyzed in buffered conditions are simultaneously and independently analyzed in the low mass range for the surface accumulation profile of Ph ₃ N 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 Ph ₃ N 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 Ph ₃ N (pK _b = 0) from the blends, indicating that the initial rapid increase in surface concentration of Ph ₃ N is related to but not singularly dependent on the rate of PLLA degradation.