Computational modeling of drug eluting stents: macro, meso and nano-scale analysis

Degradable materials have found a wide variety of applications in the biomedical field ranging from sutures, pins and screws for orthopedic surgery, local drug delivery, tissue engineering scaffolds, and endovascular stents. Polymer degradation is the irreversible chain scission process that breaks polymer chains down to oligomers and, finally, monomers. These changes, which take place at the molecular scale, propagate through the space/time scales and affect the capacity of the polymer to release drugs, and the overall mechanical behavior of the device, whose spatial scale is denoted as macro-scale. A bottom-up multiscale analysis is applied to model the degradation mechanism which takes place in PLA matrices. We applied a protocol based on atomistic simulations to predict the water diffusion as a function of the swelling degree of the PLA matrix. The diffusion coefficients are passed to the macroscale model. A shift between two different behaviors, surface or bulk erosion, is observed with the variation of a single nondimensional parameter measuring the relative importance of the two mechanisms. The mechanical and transport properties of such systems evolve with time according to the change of relevant indicators such as the water content of the system, and the molecular weight of the PLA matrix.