Degradation models for polyesters and their composites

Intensive studies are being carried out to use devices made of bioresorbable polymers inside the human body to provide various temporary functions. Typical examples include scaffolds for tissue engineering, fixation screws for broken bones and drug-loaded matrices for controlled-release. The development is entirely based on trial and error. The degradation rate strongly depends on the shape and size of the devices, making it difficult to transfer experience from one device to another. The degradation time ranges from weeks to years; animal and ultimately human trials have to be carried out, making the trial and error approach time-consuming and expensive. The entire field would benefit enormously from mathematical models capable of predicting the degradation and property change of the devices. This PhD project will develop such models as following: a) A multi-scale model for degradation of bioresorbable polyesters was developed. Events that occur at the molecular scale are modelled at the molecular scale using the kinetic Monte Carlo schemes while events that occur at the device scale are modelled using macroscopic diffusion model. b) A phenomenological model for simultaneous crystallisation and biodegradation of biodegradable polymers was developed. This model completed the degradation theory developed by Wang et al. at University of Leicester. c) The model in (b) was improved and applied to the analysis of accelerated degradation data. Temperature effects were taking into account by using Arrhenius relations. d) A model for the biodegradation of composite materials made of polyesters and calcium phosphates was developed. A calcium phosphate effectiveness map is established to show the conditions under which incorporating calcium phosphates into polyesters is effective, saturated or ineffective. f) A phase field model was developed for drug release from a swelling Hydroxypropyl methylcellulose matrix. This model can be readily extended to full three dimensional problems.