Nitinol Wire Permanent Shape Setting: Nitinol wire with 0.02 inch diameter was purchased from McMaster-Carr (Elmhurst, Illinois, USA). The Nitinol wire was then coiled onto a 5 mm metal hex wrench with a pitch of 5 mm. The two ends were fixed using copper wire. Then we kept it inside a furnace (Thermolyne FB1315M, Thermo Scientific, Waltham, Massachusetts, USA) preheated to 510 ℃ for 30 min. Quickly chill it into room temperature (~24 ℃) tap water until it’s cooled.