Analysis of the transport phenomena in swelling devices for controlled release of drug

Systems for oral controlled delivery of drugs are usually obtained by using polymers able to swell, such as HPMC (Hydroxypropyl methylcellulose). Thus, the controlled release of the drug takes place by means of a series of complex interacting mechanisms: the diffusion of the water into the system, the plasticization of the polymer (by lowering its glass transition temperature), the dissolution and the counter-diffusion of the drug through the swollen layer, the erosion of the superficial layers of exhausted polymer. In this work, the swelling and the erosion kinetics of pure HPMC tablets have been investigated. The masses of the polymer and of the water have been monitored by weighting the tablet for several immersion times in water, whereas the swelling kinetics has been studied by image analysis. The data collected allowed a careful analysis of the transport phenomena involved. Furthermore, the parameter of a model previously proposed have been tuned by comparison with such data.