Remarkable biocompatibility enhancement of porous NiTi alloys by a new surface modification approach: In-situ nitriding and in vitro and in vivo evaluation

Department of Physics & Materials Science, City University of Hong Kong, Kowloon, Hong KongReceived 25 November 2010; revised 5 June 2011; accepted 7 June 2011Published online 20 September 2011 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/jbm.a.33198Abstract: An in-situ nitriding method has been developed tomodify the outer surface and the pore walls of both openand closed pores of porous NiTi shape memory alloys(SMAs) as part of their sintering process. XRD and XPSexaminations revealed that the modified layer is mainly TiN.The biocompatibility of the in-situ nitrided sample has beencharacterized by its corrosion resistance, cell adherence, andimplant surgery. The in-situ nitrided porous NiTi SMAs ex-hibit much better corrosion resistance, cell adherence, andbone tissue induced capability than the porous NiTi alloyswithout surface modification. Furthermore, the released Niion content in the blood of rabbit is reduced greatly by thein-situ nitriding. The excellent biocompatibility of in-situnitrided sample is attributed to the formation of the TiN layeron all the pore walls including both open and closedpores.