Analysis of in vitro drug dissolution from PCL melt extrusion

This study investigated the in vitro release of a model API (Nalidixic Acid) from a PCL bulk extrudate and determined how the extent and rate of drug release are affected by the addition of a pore former (PEG) and of a copolymer (PLLA) within the polymer matrix. Drug release and dissolution is a mass transport operation and therefore can rely on both molecular and bulk diffusion. Typical drug delivery systems are made up of three components; a matrix structure (which does not diffuse and hence, its diffusion coefficient is zero), solution (coming in from the external environment and moving inside the matrix structure) and drug (that usually diffuses from the inner matrix into the external release environment). The release from blends produced by both crash cooling and controlled cooling were considered, alongside those processed via both Single and Twin Screw Extrusion. From analysis of the extrusion process it was found that the polymer crystal size was smaller in blends prepared using a 100 °C/min cooling rate than those prepared using a 30 °C/min cooling rate. Furthermore, the solubility of NA in PCL was improved by a factor of 2 by increasing cooling rate which was attributed to higher percentage of amorphous regions. Moreover, a higher degree of NA release was observed in the faster cooling rate due to the increased solubility. The experimental kinetic drug release data were modelled using a number of simple approaches, and it was found that the Kosmeyer–Peppas model was best at describing the experimental data, with r2 ≥ 0.993. Finally, the hydrolytic degradation of the extrudates at 37 °C (under static aqueous conditions over the period of 6 months) was also analysed to determine degradation rates.