Swelling and disintegration of multi-component polymeric structures

This thesis aims to develop an understanding about swelling and disintegration of multi-component polymeric structures such as pharmaceutical tablets. The thesis presents a model for the diffusion-driven water uptake, swelling deformation and subsequent disintegration of polymer matrix drug-delivery devices. Hygroscopic swelling occurs when a dry tablet enters a humid environment and absorbs water molecules. The modification of tablet structures changes the release profile of the drug in the desired manner. The previous research mostly focused on transport problems related to drug release. This study contributes an understanding of the mechanical behaviour of hydrophilic polymer release matrix materials which are treated as continuum. Modelling of the swelling problem involves concurrent large deformation of the polymer network and diffusion of the solvent through the network. A coupled diffusion-deformation model was created to study the relation between both physics. The coupled diffusion-deformation model was utilised to consider disintegration of polymer matrix through the inclusion of swelling agents. Two cases were presented to illustrate the application of the model: swelling-controlled and immediate-release drug delivery systems. This study used COMSOL Multiphysics®, a finite element commercial software to perform the analysis. Various physical modules: structural mechanics, chemical transport and mathematics were combined for solving coupled diffusion-deformation-damage boundary value problems. The numerical results were validated using existing experimental data from the literature. The model parameters were varied to investigate their sensitivity to the solution. Higher solvent concentration gradient in the matrix produced higher swelling strain, thus increased local stress. Disintegrability was measured by the time taken for the maximum principal stress to reach a given failure. Higher coefficient of water diffusion allows higher amount of water ingression into the matrix. Higher coefficient of hygroscopic swelling generates higher local swelling strain. This study facilitates in understanding the complex phenomena in the application of drug release formulation.