Properties of the hydroxyapatite obtained by electrochemical assisted deposition (ED) are dependent on several factors including deposition temperature, electrolyte pH and concentrations, applied potential. All of these factors directly influence the morphology, stoichiometry, crystallinity, electrochemical behaviour, and particularly the coating thickness. Coating structure together with surface micro- and nano-scale topography significantly influence early stages of the implant bio-integration. The aim of this study is to analyse the effect of pH modification on the morphology, corrosion behaviour and in vitro bioactivity and in vivo biocompatibility of hydroxyapatite prepared by ED on the additively manufactured Ti64 samples. The coatings prepared in the electrolytes with pH = 6 have predominantly needle like morphology with the dimensions in the nanometric scale (~30 nm). Samples coated at pH = 6 demonstrated higher protection efficiency against the corrosive attack as compared to the ones coated at pH = 5 (~93% against 89%). The in vitro bioactivity results indicated that both coatings have a greater capacity of biomineralization, compared to the uncoated Ti64. Somehow, the coating deposited at pH = 6 exhibited good corrosion behaviour and high biomineralization ability. In vivo subcutaneous implantation of the coated samples into the white rats for up to 21 days with following histological studies showed no serious inflammatory process.
Hydroxyapatite (HAP) coatings are applied on metallic implant materials to combine mechanical properties of metallic material with bioactivity abilities of HAP ceramic. In this study, HAP coatings with additions of Si and Mg are proposed to be deposited on Ti6Al4V substrates by RF magnetron sputtering. Chemical bonding, morphology, topography and corrosion resistance in simulated body fluids (SBF) of the coatings were investigated. Additionally, mechanical and biological properties of the coatings were evaluated. It was found that the addition of Si and Mg does not influence the formation of a HAP phase. All the coatings exhibited smooth surface and uniform growth, without defects or cracks. Both hardness and elastic modulus of the coated samples decrease with Mg addition in the HAP-Si structure. Both Mg and Si addition into HAP coatings were found to enhance the corrosion resistance of the Ti6Al4V alloy in the SBF solution. Coatings with low Mg content exhibited better corrosion performance. All the coatings investigated were biocompatible, as demonstrated by SaOS-2 bone cell attachment and growth. However, cell proliferation and morphology were inferior on samples with the highest Mg content.
In the current study, we have examined the possibility to improve the biocompatibility of the (TiZrNbTaHf)C through replacement of either Ti or Ta by Si. The coatings were deposited on Si and 316L stainless steel substrates by magnetron sputtering in an Ar+CH4 mixed atmosphere and were examined for elemental composition, chemical bonds, surface topography, surface electrical charge and biocompatible characteristics. The net surface charge was evaluated at nano and macroscopic scale by measuring the electrical potential and work function, respectively. The biocompatible tests comprised determination of cell viability and cell attachment to the coated surface. The deposited coatings had C/(metal+Si) ratios close to unity, while a mixture of metallic carbide, free-carbon and oxidized species formed on the film surface. The coatings’ surfaces were smooth and no influence of surface roughness on electrical charge or biocompatibility was found. The biocompatible characteristics correlated well with the electrical potential/work function, suggesting a significant role of surface charge in improving biocompatibility, particularly cell attachment to coating's surface. Replacement of either Ti or Ta by Si in the (TiZrNbTaHf)C coating led to an enhanced surface electrical charge, as well as to superior biocompatible properties, with best results for the (TiZrNbSiHf)C coating.
Considering the requirements of medical implantable devices, it is pointed out that biomaterials should play a more sophisticated, longer-term role in the customization and optimization of the material–tissue interface in order to ensure the best long-term clinical outcomes. The aim of this contribution was to assess the performance of silicon carbide–hydroxyapatite in various simulated biological fluids (Dulbecco’s modified Eagle’s medium (DMEM), simulated body fluid (SBF), and phosphate buffer solution (PBS)) through immersion assays for 21 days at 37 ± 0.5 °C and to evaluate the electrochemical behavior. The coatings were prepared on Ti6Al4V alloy substrates by magnetron sputtering method using two cathodes made of hydroxyapatite and silicon carbide (SiC). After immersion assays the coating’s surface was analyzed in terms of morphology, chemical and phase composition, and chemical bonds. According to the electrochemical behavior in the media investigated at 37 ± 0.5 °C, SiC addition inhibits the dissolution of the hydroxyapatite in DMEM acellular media. Furthermore, after adding SiC, the slow degradation of hydroxyapatite in PBS and SBF media as well as biomineralization in DMEM were observed.
Abstract:This study aims to analyze hydroxyapatite (HAP) coatings enriched with Mg and Ti prepared by a magnetron sputtering technique on Ti6Al4V substrate. For preparation of the coatings, three magnetron targets (HAP, MgO and TiO 2 ) were simultaneously co-worked. The concentration of Mg added was varied by modifying the power applied to the MgO target. In all coatings, the Ti concentration was maintained constant by keeping the same cathode power fed during the whole deposition. The influence of different Mg dopant contents on the formation of phase, microstructure and morphology of the obtained Ti-doped HAP coatings were characterized by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Moreover, the effects of Mg addition upon corrosion, mechanical and biological properties were also investigated. Mg-and Ti-doped HAP coating obtained at low radio-frequency (RF) power fed to the MgO target provided material with high corrosion resistance compared to other coatings and bare alloy. A slight decrease in hardness of the coatings was found after the Mg addition, from 8.8 to 5.7 GPa. Also, the values of elastic modulus were decreased from 87 to 53 GPa, this being an advantage for biomedical applications. The coatings with low Mg concentration proved to have good deformation to yielding and higher plastic properties. Biological test results showed that the novel surfaces exhibited excellent properties for the adhesion and growth of bone cells. Moreover, early adherent vital cell numbers were significantly higher on both coatings compared to Ti6Al4V, suggesting that Mg ions may accelerate initial osteoblast adhesion and proliferation.
The reactive cathodic arc deposition technique was used to produce Ti nitride and oxynitride coatings on 304 stainless steel substrates (SS). Both mono (SS/TiN, SS/TiNO) and bilayer coatings (SS/TiN/TiNO and SS/TiNO/TiN) were investigated in terms of elemental and phase composition, microstructure, grain size, morphology, and roughness. The corrosion behavior in a solution consisting of 0.10 M NaCl + 1.96 M H2O2 was evaluated, aiming for biomedical applications. The results showed that the coatings were compact, homogeneously deposited on the substrate, and displaying rough surfaces. The XRD analysis indicated that both mono and bilayer coatings showed only cubic phases with (111) and (222) preferred orientations. The highest crystallinity was shown by the SS/TiN coating, as indicated also by the largest grain size of 23.8 nm, which progressively decreased to 16.3 nm for the SS/TiNO monolayer. The oxynitride layers exhibited the best in vitro corrosion resistance either as a monolayer or as a top layer in the bilayer structure, making them a good candidate for implant applications.
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