Effect of pH on salicylic acid-based poly(anhydride-ester): Implications for polymer degradation and controlled salicylic acid release

Salicylic acid (SA)-based poly(anhydride-esters) (SAPAEs) hydrolytically degrade to release SA in a controlled manner over extended time periods. While these polymers have been well investigated under in vivo conditions, this study is the first detailed, systematic assessment of in vitro polymer degradation over a range of pH values. To investigate the effect of pH conditions on SAPAE degradation, in vitro degradation studies were conducted on SAPAE disks over a wide pH range (2.0, 4.0, 6.0, 7.4, 8.0, 9.0, and 10.0) for 30 days. Several parameters were evaluated, including SA concentrations in the degradation media, polymer mass loss, water uptake in the polymer matrices, and SA solubility at different pH values to substantiate SA release results and characterize the in vitro polymer degradation process. Complete SA release was achieved at more basic conditions (pH 9.0 and 10.0) over 9 days, whereas less than 41% SA was released over the same time period at neutral pH conditions (pH 8.0 and 7.4). By comparison, SA release was minimal in acidic pH conditions. Overall, we present quantitative data of polymer degradation as defined by SA in vitro release, which increased with increasing pH values. More basic conditions promoted polymer degradation, whereas acidic conditions minimized polymer degradation.