Molecular analysis and experimental investigation of the dissolution mechanism of semicrystalline polymers

The dissolution of semicrystalline poly(vinyl alcohol) (PVA) in water was investigated using spectrophotometric and other techniques by studying the influence the polymer molecular weight and crystallization conditions on the rate of dissolution. Changes in the degree of crystallinity and the crystal site distribution during the dissolution process were measured using differential scanning calorimetry, x-ray diffraction, transmission electron microscopy and attenuated total reflectance Fourier transform infrared spectroscopy. We propose a mechanism of dissolution whereby the crystal chains unfold to join the amorphous region around them, which subsequently disentangles and dissolves. A mathematical model was developed to describe crystal unfolding by taking into account the free energy changes occurring during the process. We have incorporated the rate of unfolding into a continuum framework to predict the dissolution kinetics of a semicrystalline polymer slab. The model predictions showed reasonable agreement with experimental results. Applications of PVA dissolution to biomedical applications such as controlled drug delivery and tissue regeneration have been investigated. We have been able to optimize the delivery of antitrichomonal drugs such as metronidazole for vaginal release applications. Based on dissolving semicrystalline PVA carriers, such systems can exhibit release behavior that is controlled by the erosion, swelling and diffusion fronts observed during the dissolution process. We have also developed a mathematical model to predict the drug release rates from such systems. Feasibility of using soluble PVA films for growth of osteoblasts and regeneration of bone has also been demonstrated