Micro/nano-structured surface on titanium (Ti)-based implant gains great concern for its improvement on cell response and osteogenic ability. In this paper, a novel hierarchical structure combining microscale cavities and nanoscale steps was fabricated on Ti6Al4V, via sandblasting and ultrasonic-assisted acid-etching in mixed acids of HCl and H2SO4. Stepped structures are about 100-300 nm in width and 100-200 nm in height. The step density is increased with extension of acid-etching period, and significantly increased by ultrasonic treatment. It is supposed that the differences in etching rate of different crystal orientations are responsible for step formation. Moreover, ultrasonic and sandblasting treatments could increase acid-etching rate and promote the emergence of steps. The hierarchical surfaces exhibit similar microscale roughness to micro-rough surfaces without steps, but slightly higher contact angles.
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