Figure 2

Miniaturized NiTi springs fabricated copper hypotubes yielding nitinol springs with diameters 1.1 mm in (a-1) a coil of copper/NiTi structure, (a-2) heat treated, and (a-3) released by etching. Another spring with diameter 0.75 mm is formed in (b-1) a coil of copper/NiTi that is (b-2) heat treated, (b-3) is gradually etched in ammonium persulfate solutions, and is (b-4) fully released. (c) SEM image of another spring with OD ~ 0.7 mm.