Zn- or Cu-Containing CaP-Based Coatings Formed by Micro-arc Oxidation on Titanium and Ti-40Nb Alloy: Part I—Microstructure, Composition and Properties

Abstract

Zn- and Cu-containing CaP-based coatings, obtained by micro-arc oxidation process, were deposited on substrates made of pure titanium (Ti) and novel Ti-40Nb alloy. The microstructure, phase, and elemental composition, as well as physicochemical and mechanical properties, were examined for unmodified CaP and Zn- or Cu-containing CaP coatings, in relation to the applied voltage that was varied in the range from 200 to 350 V. The unmodified CaP coatings on both types of substrates had mainly an amorphous microstructure with a minimal content of the CaHPO4 phase for all applied voltages. The CaP coatings modified with Zn or Cu had a range from amorphous to nano- and microcrystalline structure that contained micro-sized CaHPO4 and Ca(H2PO4)2·H2O phases, as well as nano-sized β-Ca2P2O7, CaHPO4, TiO2, and Nb2O5 phases. The crystallinity of the formed coatings increased in the following order: CaP/TiNb < Zn-CaP/TiNb < Cu-CaP/TiNb < CaP/Ti < Zn-CaP/Ti < Cu-CaP/Ti. The increase in the applied voltage led to a linear increase in thickness, roughness, and porosity of all types of coatings, unlike adhesive strength that was inversely proportional to an increase in the applied voltage. The increase in the applied voltage did not affect the Zn or Cu concentration (~0.4 at%), but led to an increase in the Ca/P atomic ratio from 0.3 to 0.7.

Costimulatory Effect of Rough Calcium Phosphate Coating and Blood Mononuclear Cells on Adipose-Derived Mesenchymal Stem Cells In Vitro as a Model of In Vivo Tissue Repair

“…The increase in the MAO voltage led to a coating structure transformation from X-ray amorphous to the amorphous-crystalline state. Thus, chemical features of microarc CaP coatings excluding, to some degree, the Ca/P atomic ratio were not depended on the increasing magnitudes of applied voltage [37].…”

“…Biocompatible microarc CaP coatings [35] with a fixed R a = 2-4 µm promote MSC osteogenic differentiation both in vitro [20] and in vivo [36]; therefore, these conditions were adopted in our experiments. The microstructure, phase, and elemental composition, as well as physicochemical and mechanical properties were described for microarc CaP coatings in [37], in relation to the applied voltage in the range from 200 to 350 V. According to these results, the microarc CaP coatings on titanium substrate had mainly an amorphous microstructure with the CaHPO 4 phase for all applied voltages. The increase in the MAO voltage led to a coating structure transformation from X-ray amorphous to the amorphous-crystalline state.…”

“…On the other hand, surface and bulk features (R a , mass and thickness) are very processible and connected closely with the applied voltages and biological reactions [6,20,[37][38][39]. Because some variations of calcium, phosphorus, oxygen, and titanium contents and phase compounds accompanied with surface and bulk indices [37], microarc CaP-coated samples with a fixed range of R a = 2-5 µm were used in the different series of experiment ( Tables 1-4, Tables S1-S6).…”

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“…The Microarc-3.0 installation (ISPMS SB RAS, Tomsk, Russia) was used to carry out the MAO process and consists of a pulsed DC power supply, titanium electrolytic bath as an electrode (cathode), sample holder as the counterelectrode (anode), and PC for process control. In order to synthesize the CaP coatings, the electrolyte contained 5 wt.% nanosized HA (Ca 10 (PO 4 ) 6 (OH) 2 ), 7 wt.% CaCO 3 , 27 wt.% H 3 PO 4 , and distilled water as a balance [43,44]. Stoichiometric HA powder consisting of aggregates of round-shaped nanocrystallites with a size less than 50 nm was produced by solid-phase mechanochemical synthesis [45].…”

“…An acidic suspension electrolyte (pH = 1-2) incorporating an undissolved nano-dispersed HA was obtained. The MAO process was carried out in an anodic potentiostatic regime with following parameters: pulse frequency of 50 Hz; pulse duration of 100 µs; time of 10 min; and varied applied voltage of 200, 250, and 300 V [39,43,44].…”