Effect of molecular weight and polydispersity on kinetics of dissolution and release from pH/temperature-sensitive polymers

Abstract

N-isopropylacrylamide (NIPAAm) polymers exhibit a lower critical solution temperature (LCST). Aqueous solutions of these polymers are soluble below their LCST and precipitate above their LCST. The LCST is dependent on pH for polymers with ionizable groups because of a change in hydrophilicity with ionization and electrostatic repulsion that cause a shift in the LCST. We have designed a novel polymeric delivery system that utilizes linear, pH/temperature-sensitive terpolymers of NIPAAm, butyl methacrylate (BMA) and acrylic acid (AA). This system allows the aqueous loading of drugs in polymeric beads with high loading efficiency while preserving the bioactivity of the protein drug. Furthermore, the unique properties of the pH/temperature-sensitive polymeric bead make it a potential system for oral drug delivery of peptide and protein drugs to different regions of the intestinal tract. This study aims at investigating the effect of polydispersity and molecular weight (MW) of terpolymers of poly(NIPAAm-co-BMA-co-AA) with feed mol ratio of NIPAAm/BMA/AA 85/5/ 10 on the polymer dissolution rate and on the release kinetics of a model protein, namely insulin. Varying the weight average MW (M_w) and polydispersity of the polymer modulated the polymer dissolution rate and the release rate of insulin from pH/temperature-sensitive polymeric beads. An increase in the polydispersity of the polymer through the addition of high MW polymer chains caused a decrease in the release rate of insulin and in the polymer dissolution rate. High MW polymer chains impose a certain degree of interaction between polymer chains due to chain entanglement. There is a limiting value of MW above which chain entanglement has no effect on drug release rate.

Keywords:

• pH/temperature-sensitive polymer
• N-isopropylacrylamide
• molecular weight
• polydispersity