Preparation, Characterization, and Corrosion Behavior of Calcium Phosphate Coating Electrodeposited on the Modified Nano
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RECENTLY, NiTi alloy has found a variety of applications in implants due to its unique properties such as superelasticity, shape memory effect, and good bio-compatibility.[1–4] NiTi represents the most similarity to the bone tissues including a recoverable strain up to 10 pct and an elastic constant close to that of the bone. The small difference between the elastic modulus of the NiTi alloy and bone tissues results in an appropriate distribution of stress through the conjunction and its surroundings, which is a beneficial factor accelerating the bone growth.[5–8] However, the NiTi alloy shows a poor corrosion resistance to the localized corrosion in body environments.[9] In addition, the high nickel content of NiTi (about 50 at. pct) may lead to the
SEYED OMID REZA SHEYKHOLESLAMI, JAFAR KHALILALLAFI, and LEILA FATHYUNES are with the Faculty of Materials Engineering, Research Center for Advanced Materials, Sahand University of Technology, 5133511996, Tabriz, Iran. Contact e-mail: jallafi@yahoo.de Manuscript submitted March 31, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
higher release of toxic Ni ions during long-term implantation, causing some health problems as well as the weakening of bone-building cells.[8,10–14] Moreover, formation of a non-adherent layer of the connective tissue on the bio-inert surface of NiTi can eliminate the integrity between this alloy and the surrounding bone, which results in failure of implantation.[15–17] Therefore, it is necessary to avoid the release of Ni ions[6,18] and increase in the bioactivity of the NiTi surface by applying bio-compatible coatings such as calcium phosphate (Ca-P).[19,20] Among all of the Ca-P bio-ceramics, stoichiometric hydroxyapatite [HA; Ca10(PO4)6(OH)2] with the Ca/P molar ratio of 1.67 is the most stable phase during the healing period.[21,22] HA, with the structural and compositional similarity to the inorganic compounds of the natural bone, is well known as an appropriate candidate to promote the activity of osteoblastic bone cells.[21] Therefore, suitable mechanical properties of the metal as well as the bioactivity and corrosion resistance of the Ca-P compounds can be achieved by applying the HA coating on the surface of the metallic implants.[22–24] Nowadays, the electrochemical deposition (ECD) method for applying the Ca-P coatings has attracted much attentions,[22] due to the possibility of forming a
uniform layer on the porous substrate, high efficiency, low equipment cost, low temperature, and its high ability to control the morphology and thickness of the coating by the processing parameters.[20,25–28] In this method, different types of Ca-P ceramics could be deposited. However, due to the probable instability at the interface between the bone and the implant, deposition of HA as the most stable phase is preferred more than the other Ca-P phases.[29–31] It should be noted that the poor adhesion of HA to the metallic implants can limit its application as a coating, especially under mechanical tensions.[21] In addition, the Ca-P coatings c
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