NiTi coated with oxide and polymer films in the in vivo healing processes

Plates of NiTi chemically etched, electro-polished, and sol–gel coated with XO2 (X = Ti, Si, Zr), or coated with oxides and dip-coated polymers of Dextro-Levo-lactide-co-glycolide (DL-PLG, 0.4 μm thickness), Dextro-Levo-lactic acid (DL-PLA, 1.3 μm) or poly methyl methacrylate polymer (PMMA, 1.7 μm) were obtained. Smooth and uniform NiTi surfaces without significant pitting, as revealed by AFM, were prepared for chemical etching of 120 s in HF:HNO3:H2O = 1:5:4, followed by electropolishing 120 s in H2SO4:CH3OH:H2O = 1:4:5 electrolyte and using a potential of 9 V. Dip-coated layer of PMMA has shown cracks and large pores and was eliminated from further experiments. Samples of pristine and coated NiTi were in vivo implanted into rabbits and extracted after 10 and 60 days. Clinically, all implants are biocompatible; all rabbits survived and a recovery process was observed for all cases. NiTi covered with SiO2, DL-PLG and SiO2/DL-PLG have shown the best healing evolution. For 10 and 60 days good recovery was found also for NiTi coated with TiO2. Coatings of ZrO2 and ZrO2/DL-PLG have shown the poorest results. The oxide coating and the roughness RZJIS that contains information on the ‘deep’ large areas in the coatings show the strongest influence on the healing processes. Work indicates the possibility of space- and time- scale controlled variation of the functional properties. Keywords: NiTi alloy, Coating of TiO2, SiO2, ZrO2, DL-PLG, DL-PLA, PMMA, Roughness, In vivo test