A thermodynamic framework for additive manufacturing of crystallizing polymers, Part II: Simulation of the printing of a stent

Abstract

We use the theory developed by [43] to simulate in Abaqus the printing of a drug-eluting bioresorbable stent (BRS), which is used to treat a stenosed renal artery, by fused deposition modeling (FDM). The stent is assumed to be printed using a semi-crystalline polylactic acid (PLA). We control the process parameters to architect the microstructure of the stent such that the stent has an amorphous glassy phase on a crystalline backbone, which would ensure sufficient strength along with the regulated release of the drug into the bloodstream. Through this simulation, we highlight those regions in the stent geometry that should adhere to strict quality control requirements during the fabrication process. In this regard, it is observed that a preexisting crack at the core of the third layer has a very high tendency to propagate along the ‘r’ or ‘z’ direction, whereas a preexisting crack at the core of the second layer has a very high tendency to propagate along the ‘r’ direction, thus increasing the probability of an intra-layer delamination process during service. Similarly, the stent has a high chance of inter-layer delamination between the second and third layers by the mode-I mechanism for cracking. Moreover, the final cup-like warped geometry of the stent could injure the arterial wall during deployment by balloon expansion and also during service, thus increasing the risk of neointimal hyperplasia.