Investigation of surface and structural properties of coated niTi alloy as a biomaterial

In this study, the coatability of NiTi alloys, which are shape memory materials used in the biomedical field, and the effects of the coating on surface and structural properties were investigated. A comparison of different coating processes was also conducted. For this purpose, the surfaces of NiTi shape memory alloys were coated using different coating methods and materials to extend their retention in the body and minimize Ni release. The coated samples were then examined to evaluate their biocompatibility. In this study, NiTi samples with dimensions of 10x10 mm and 1.5x70 mm, conforming to ASTM F2063-18 standards, were used. Coating materials included suspensions of 1 wt.% hydroxyapatite, 3 wt.% chitosan, and 3 wt.% sodium alginate, prepared from pure powders. The coating methods employed were dipping and spin coating. Optimal coating parameters were determined using optical microscopy. During the HAp coating process, the samples were coated, then left at room temperature for 24 hours, followed by drying at 100°C for 24 hours. The dried samples were sintered in a quartz glass tube furnace, heated from room temperature to 900°C at a rate of 5°C/min, under an argon atmosphere for 8 hours, and then allowed to cool in the furnace. Chitosan and sodium alginate coatings were applied at various spin speeds, and the samples were dried at 60°C for 24 hours. The surface topography and elemental analysis of the coated samples were examined using optical microscopy, FESEM-EDS, and XRD, and then they were immersed in simulated body fluid for 7, 14, and 21 days. The immersion fluids were analyzed for Ni release using ICP-MS, and the results were compared. As a result of the conducted studies, a Ni release test was performed on NiTi samples coated with optimal parameters. The Ni release levels of the raw and coated samples were compared, and it was determined that the Ni release decreased in the coated samples. By reducing the release of Ni ions from the NiTi alloy used as a biomaterial, its biocompatibility was improved.