Current research projects
A. Modelling degradation of bioresorbable polymers
An intensive effort is being made worldwide to use devices made of bioresorbable materials 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. Through a series of PhD projects, a complete mathematical framework has been developed at Leicester for modelling the degradation of these devices. The mathematical equations were solved using the finite difference method. It was shown that the mathematical model is able to fit the experimental data obtained using simple plate samples that are available in the literature.
A 2-scale finite difference model for polymer degradation
Fitting of the mathematical model with experimental data
It has been demonstrated, through several MSc and undergraduate student projects, that the mathematical framework can be easily implemented (even by undergraduate students) in a commercial finite element package to predict degradation behavior of sophisticated devices such as screws and porous foams.
Current research is focused on understanding the degradation of mechanical properties as the polymer degrades. Atomic modelling techniques such as molecular dynamics and kinetic Monte Carlo methods are being used in this study.
An atomic model for degradation in mechanical properties
B. Modelling tablet swelling and controlled drug release
Controlled release of drugs from polymeric matrix is revolutionising medicine. The following figure shows schemetically a controlled release tablet made of multi-layered hydroxypropyl methylcellulose (HPMC).
A swelling tablet during controlled drug release
As water ingresses the polymer swells facilitating the release of the embedded drugs. The release profile can be manipulated by changing (a) the tablet design such as different geometries and layers of different polymers and (b) the polymer chemistry such as molecular weight, substitution degree and pattern of the methoxy and hydroxypropoxy groups within the glucose unit as well as along the cellulose backbone. A computer simulation technique based on the material points method is being developed at Leicester to optimise the material and tablet design for targeted release profiles.
C. Modelling sintering of advanced ceramics
Sintering is a process in which a powder compact is fired and consolidated into a strong solid. It is an ancient technique to make bricks, china and potteries. It is also a modern technology to fabricate a wide range of high-tech products. Almost all ceramic components are made by sintering. Solid oxide fuel cells and piezoelectric films are some recent examples of sintered systems. Supported by the EPSRC, we have two ongoing projects: (a) Finite element analysis of sintering deformation; (b) Modelling constrained sintering of solid oxide fuel cells, PZT films and industrial coatings.
Our predictive sintering technique starts with a model of green compacted ceramic (left) and then projects an anticipated post-sintering dimensions (mesh, right) in comparison to pre-sintering cross section (outside frame).
Computer simulated and observed (insert) cracking of a PZT film coated on a solid substrate during constrained sintering
D. Impact and penetration failure of ductile and brittle materials
Modelling penetration failure of either very ductile or very brittle materials is perhaps the most challenging problem in computational mechanics. At Leicester, major progress has been made to use the Material Points Method to model these sophisticated processes.
Computer simulated penetration of a skin and its supporting tissue