Abstract
The treatment for Coronary Heart Diseases - caused by the deposition of plaque on
arterial walls - which has been the deployment of metal stent in the blocked artery, poses
serious complications in the form of accumulation of blood clots due to the permanent
and rigid nature of metals. Meanwhile, Bioresorbable Vascular Scaffolds (BVSs) - made
up of poly l-lactide (PLLA) - are transient implants offering support to artery for 6-9
months and leaving no trace behind once dissolved after 2 years. PLLA, however, has
lower strength compared to metals and thus requires a higher thickness to make it useful
for transplants. Thermal annealing, which can alter the microstructure of PLLA to
make it thinner and stronger, is a good solution for this problem. In order to implement
thermal annealing, experimentation and simulations are required to study the behavior
of the microstructure during the process. In general, its behavior below glass transition
temperature and at short time-scale is glassy, while above glass transition temperature
and at long time scale is rubbery. With constitutive models available for other polymers,
such as polyethylene terephthalate (PET) - not only a significant polymer due to its
extensive industrial use but also a polymer that is temperature and strain-rate sensitive
- it is intended to develop a constitutive model for PLLA accordingly. In this regard,
the well-known Buckley model is implemented and extended. The model allows to study
the microstructural behaviour in PLLA at the temperatures of interest during thermal
annealing. Numerical results will be presented and compared for neat PLLA samples
for different strain rates and temperatures.
