DESIGN AND DEVELOPMENT OF SHAPE MEMORY POLYMER-BASED MECHANICAL THROMBECTOMY DEVICE

In the biomedical industry, research and application of shape memory polymers (SMP) have mainly been focused on drug-delivery implants, stents, orthopaedic devices, tissue engineering, and wound closure. Little focus has been given to using SMP as delivery catheters or access devices, which can benefit from greater flexibility and larger deformation relative to metals. This work aims at designing and developing a thrombectomy device prototype using an SMP at the distal tip of a microcatheter, which would recover to a desired shape to act as a retrieval mechanism, removing a thrombus from an occluded artery in an acute ischemic stroke. The catheter was built using a polytetrafluoroethylene (PTFE) liner substrate, braided reinforcement, a Pebax jacket layer, and a coiled copper wire heating element. A shape memory polyurethane (SMPU) was extruded and reflowed over the copper coil. The SMPU was shape-set into a helical shape and was then formed into a temporary straight shape. Thermomechanical testing of the SMPU demonstrated the effect of temperature on the mechanical properties, as when the polymer was heated above the transition temperatures, the mechanical behaviour changed, resulting in a lower stress but a greater strain rate. Applying a direct current to heat the copper coil and cause a thermal stimulus in the SMPU successfully induced a shape recovery of the distal tip to its original helical shape. Within this frame of reference, this work describes an SMPU tubing material with a straight secondary shape that can recover its coiled primary shape once thermally stimulated. The prototype further strengthens the experimental success.