Design, fabrication and experimentation of a bifusiform retriever with two-way shape memory effects

A novel bifusiform thrombectomy device driven by the two-way shape memory effect (TWSME) was proposed for the therapeutic challenge of distal medium vessel occlusion (DMVO) in acute ischemic stroke (AIS). The retriever was constructed by intertwining NiTi shape memory alloy (SMA) wires into a bifusiform shape, and an analytical electro-thermal model of the SMA wire was established to predict its equilibrium temperature under different direct current (DC) powers. Moreover, finite element modeling and analysis were conducted for identification of expected temperature distribution across the SMA wire woven bifusiform retriever by electrical activation. Fabrication and experimental testing of the retriever prototype were completed, and an optimized annealing process of the raw SMA wire for the TWSME device was found: muffle furnace pretreatment at 500 °C for 180 min, followed by 5-cycle stretching at 125 MPa, primary limited aging at 350 °C for 30 min, and secondary unconstrained aging at 300 °C for 60 min. A physical cerebrovascular model and a blood clot made of glycerol and water were used for in vitro thrombectomy tests. The results showed that with a driving current of 0.22 A, the retriever achieved a contraction ratio of 38.89% and a contraction speed of 2.1 mm/s, successfully grasping, encapsulating, and retrieving the blood clot. This investigation confirms the great potential advantages of the bifusiform retriever in the cerebral thrombectomy.