A comparative study of apatite coating and apatite/collagen composite coating fabricated on NiTi shape memory alloy through electrochemical deposition

To improve bioactivity and long-term biocompatibility of NiTi shape memory alloys (SMAs), apatite and apatite/collagen composite coatings were formed at 37 degrees C on the metal through electrochemical deposition using double-strength simulated body fluid (2SBF) without and with dissolved collagen, respectively. Surface characteristics, wettability and chemical stability of the coatings were subsequently studied and comparisons were made between the apatite coating and apatite/collagen composite coatings. Surface morphology of the apatite/collagen coating revealed that many collagen fibers were embedded in apatite with flake-like structures. The phase composition and chemical composition analyses showed that calcium-deficient and carbonated hydroxyapatite with low crystallinity was formed in the apatite and apatite/collagen coatings. Moreover, the wettability of uncoated and coated NiTi SMA samples was investigated. Compared to both uncoated and apatite-coated NiTi SMA samples, apatite/collagen-coated samples were more chemically stable and exhibited higher corrosion resistance. (C) 2011 Elsevier B.V. All rights reserved.