Modelling of Drug Release from Biodegradable Polymers

Biodegradable polymers have highly desirable applications in the field of biomedical engineering, such as coronary stents, tissue engineering scaffolds and controlled release formulations. All these applications are primarily rely on the fact that the polymers ultimately disappear after providing a desired function. In this respect, the mechanism of their degradation and erosion in aqueous media has attracted great attention. There are several factors affecting the rate of degradation such as composition, molecular weight, crystallinity and sample size. Experimental investigations showed that the type of drug also plays a major role in determining the degradation rate of polymers. However, so far there is no theoretical understanding for the changes in degradation rate during the degradation in the presence of acidic and basic drugs. Moreover, there exists no model to couple the hydrolysis reaction equations with the erosion phenomena for a total understanding of drug release from biodegradable polymers. A solid mathematical framework describing the degradation of bioresorbable polymers has been established through several Ph.D. projects at Leicester. This Ph.D. thesis consists of three parts: the first part reviews the existing literature of biodegradable polymers and drug delivery systems. In the second part, the previous models are refined by considering the presence of acidic and basic drugs. Full interactions between the drug and polyesters are taken into account as well as the further catalyst effect of the species on polymer degradation and the release rates. The third part of this thesis develops a mathematical model combining hydrolytic degradation and erosion in order to fully understand the mechanical behaviour of the biodegradable polymers. The combined model is then applied to several case studies for blank polymers and a drug eluting stent. The study facilitates understanding the various mass loss and drug release trends from the literature and the underlying mechanisms of each study.