The releasing rates of Ni in porous NiTi SMA in simulated body fluid and physiological saline are much higher than those of the dense NiTi SMA with same nominal surface area. The releasing rate of Ni under bending strain will further increase. After immersion in 4 mol/L NaOH aqueous solution at 60 degrees C for 24 h and subsequent heating at 600 degrees C for 1 h, a oxidation layer formed on the surface of the porous NiTi alloy, which prevented the porous NiTi alloy from contacting the immersion solution and greatly decreased the amount of nickel releasing from the porous NiTi alloy.
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