Modification of Drug Release Profiles of Poly(L-Lactide) Using Palmitic Acid

Palmitic acid was added into drug-loaded poly(L-lactide) (PLLA) to modify the drug release profiles of the polymer. The acid was added in different concentrations and gradients across the thickness of the polymer. Drug release was monitored using a UV spectrometer over a period of 90 days. Degradation was studied using gel permeation chromatography and differential scanning calorimetry (DSC) to follow the change in the molecular weight and glass transition temperature respectively. Addition of palmitic acid was found to accelerate the degradation of PLLA and resulted in an accelerated release of the drug as expected. Modification of release profiles by designing the acid gradient was also attempted. It was found that the total acid concentration is still the dominant factor over the gradient design in affecting the degradation and subsequently the release profiles. Different drug concentrations also played a role in the different release profiles exhibited. Surprisingly the sample with lower drug concentration (2wt%) showed a much higher initial burst than the 5wt% loaded samples. This was due to the induced nucleation of the polymer by the drug at low concentration resulting in higher crystallinity of the polymer and consequently overall lower solubility of the drug.