Injection moulding process: CFD evaluation on the orientation of polymeric chains for manufacturing heart valves.

Introduction: Polymeric Heart Valve (PHV) prostheses aim at combining the hemodynamic advantages of biological valves with the durability of mechanical valves. Styrene Block Polymers (SBPs) appear to be the best materials for this application, because of their excellent biocompatibility, chemical stability and fatigue resistance. SBPs can be processed by injection moulding, allowing controlling the alignment of the polystyrene micro-chains. Aim of this work is to simulate the injection moulding process to analyse polymer chains orientation within the PHV leaflets and optimise manufacturing. Material and methods: Small Angle X-ray Scattering Analysis was performed on a thin membrane made of poly-(Styrene-Isoprene-Butadiene-Styrene) with 19% styrene (SI/BS19) manufactured by injection moulding, to visualise the polymer chains orientation in the material. Based on these data a total of six numerical models (Fluent®14.0, ANSYS Inc., Canonsburg, PA, USA) of the PHV mould differing in the polymer injection inlets and outlets were developed. A hexahedral mesh, including approximately 1,000,000 cells was used. The Carreau Model was used to describe SI/BS19 rheology. Data from the computational analysis were used to calculate the directions along which the polymer chains were aligned. Results: SI/BS19 chains orientation along the leaflets is mainly perpendicular to the flow direction of the polymer. Polymer chains orientation along the leaflets does not change significantly when different locations of the injectors are considered. Also different polymer mass flow rates exerts negligible effects on the polymer chains orientation. Discussion: The numerical model allowed a reliable simulation of the injection moulding process showing that a different location of the injectors do not affect polymer chains orientation as well as different mass flow rates of the polymer. These results allow the optimisation of the moulding process in terms of minimisation of the manufacturing time duration.