In vitro assessment of zinc apatite coatings on titanium surfaces

In this paper, coatings of hydroxyapatite partially substituted with zinc (ZnHA) were produced on titanium substrates by a two-step hydrothermal process using a precursor solution rich in calcium, phosphate and zinc. Activation of titanium surfaces was performed by oxidation with an acidic HF/HNO₃ solution. The coated substrates were then converted into HA by immersion in an alkali 0.1 M NaOH solution. The ZnHA samples were characterized by several techniques and their in vitro behavior was studied in comparison to hydroxyapatite (HA) and titanium (Ti-control) samples. A uniform and homogeneous calcium-deficient carbonate apatite coating was obtained for all samples, both doped and undoped with zinc. The percentage of zinc incorporated in the coatings is 7 at%, and the Ca/P ratio is 1.61(±0.01) for both types of samples, suggesting that Zn is incorporated substitutionally, replacing Ca atoms into the HA structure. The incorporation of Zn in the HA structure changed the crystals morphology, reduced crystals sizes and decreased the deposition rate showing that zinc is an inhibitor of the growth of HA crystal. X-ray diffraction showed that HA is the single crystalline phase present after alkali treatment. The coating adhesion strength was evaluated in terms of the critical load (Lc) obtained from scratch tests and no significant difference was found between the two tested groups, indicating the good adhesion of ZnHA to Ti substrates. The in vitro response of human osteoblasts (HOB) exposed to the surfaces of HA and ZnHA coatings was evaluated. The results of Live/Dead tests showed cell viability for all samples surfaces, but the adhesion and proliferation tests showed that ZnHA samples presented better adhered and spread cells compared with HA. ZnHA coatings presented cells with elongated or polygonal shapes and clearly more spread than HA. Quantitative analysis showed that there was a significantly higher number of cells adhered to ZnHA coatings compared to HA, indicating the zinc incorporation stimulates osteoblast proliferation.     

Systematic optimization of corrosion,bioactivity, and biocompatibility behaviors of calcium-phosphate plasma electrolytic oxidation (PEO) coatings on titanium substrates

To optimize the corrosion, bioactivity, and biocompatibility behaviors of plasma electrolytic oxidation (PEO) coatings on titanium substrates, the effects of five process variables including frequency, current density, duty cycle, treatment time, and electrolyte Ca/P ratio were evaluated. In our systematic study, a Taguchi design of experimental based on an L16 orthogonal array was used. For this, the coatings characteristics such as the surface roughness, wettability, rutile to anatase and Ca/P ratios, and corrosion polarization resistance were investigated. After determining the optimum process variables for each response, the apatite forming ability in SBF (bioactivity behavior) and MG63 cell attachment and flattening (biocompatibility behavior) for two groups of coatings were examined. The first group was optimized based on the maximum corrosion polarization resistance and the variables were set as the frequency of 2000 Hz, the current density of 5 A/dm², the duty cycle of 30%, the treatment time of 5 min, and the Ca/P ratio of 0.65 at. % in the electrolyte. For the second group, the maximum surface roughness, greatest Ca/P ratio, and highest wettability as well as the minimum rutile to anatase ratio in coatings, could be obtained when the variables were set as the frequency of 10 Hz, the current density of 12.5 A/dm², the duty cycle of 50%, the treatment time of 12.5 min, and the Ca/P ratio of 1.70 at. % in the electrolyte. The results showed that while both groups of coatings indicated a significant apatite forming ability and can serve as bioactive coatings, a proper attachment and flattening of cells and consequently, the favorable biocompatibility properties were seen only in the first group.     

Microstructures,mechanical properties and corrosion resistance of sprayed Ca–P coating for micropatterning carbon/carbon substrate surface

Carbon/carbon (C/C) surface micropatterning is a method of modifying the surface into the complete and regular geometry. In this work, we introduce a positive effect on bonding strength between sprayed Ca–P coating and surface micropatterning C/C substrate. Interestingly, C/C substrate coated by Ca–P coating provides textured surface for a new bone ingrowth. The sprayed Ca–P coating is then subjected to microwave-hydrothermal (MH) treatment with the aim of eliminating surface defects and obtaining a uniform purity phase. These objectives were achieved in our previous study by the MH method. The molar ratio of Ca/P in the coatings is nearly close to 1, which is far below that of Ca/P for hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂, HA, 1.67). The purpose of this article is to transform the phases in the sprayed Ca–P coating, which owns the better bioactivity and high corrosion resistance. In order to raise the molar ratio of Ca/P, the coatings are treated under high-temperature (around 700 °C). They are analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and a fourier transform infrared spectra (FTIR). The bonding strength (coating/substrate), biological activity and corrosion resistance of the coatings are investigated. The resulting coatings own the different microstructures and phase compositions from the original sprayed Ca–P coating. Especially, results show that the shear strength of the sprayed Ca–P coating deposited on surface micropatterning C/C substrate increases by 61% which is more than that of the coating on non-surface micropatterning C/C substrate. Additionally, high-temperature treated coating presents a good biological activity and an excellent corrosion resistance of current density (1.3078 × 10^-6 A/cm²) and potential (−0.17 V_SCE).     

A novel apatite-inspired Sr5(PO4)2SiO4 plasma-sprayed coating on Ti alloy promoting biomineralization,osteogenesis and angiogenesis

Osteoconductive, osteoinductive, anti-infection, and controlled ionic release properties are crucial for the long-term clinical success of orthopedic and dental metallic implants. In this study, we have successfully synthesized apatite chemical structure mimic Sr₅(PO₄)₂SiO₄ (SPS) nanopowder by sol-gel method to be used as a novel bioactive ceramics coatings on medical-grade titanium alloy by plasma-spray deposition technique. The deposited SPS coatings were analytically characterized by XRD and SEM-EDS analysis and confirmed that the coating possessed a pure crystalline phase of SPS without any other secondary phases, and exhibited a sharp needle-like morphology with the existence of Sr, P, O, Si elements. The cross-sectional view proved that the deposition of dense SPS layer with a thickness of 116 μm. The in vitro ionic dissolution behavior of SPS coatings was detected by ICP-OES analysis and confirmed their controlled releasing profile of ions such as Sr (120–55 ppm) and Si (0.14–9.86 ppm). In vitro biomineralization study demonstrated that the SPS coatings were remarkably encouraged the ball likes apatite crystals growth on their surface with a Ca/P ratio (1.677) similar to natural bone minerals. The SPS coatings exhibited notable cellular interactions with human umbilical card-derived mesenchymal stem cells (HUMSCs) in terms of cell proliferation, early-stage differentiation, and calcium nodule accumulation in ECM, also the osteogenic differentiation was found to be prominent for SPS coated Ti64 than sandblasted Ti64. Furthermore, the angiogenic property of SPS coated Ti64 was evaluated by Human umbilical vein endothelial cells (HUVECs) and confirmed their tremendous cell viability with non-toxicity and nominal angiogenic differentiation. Therefore, our study proved that the apatite-inspired SPS bioactive ceramics coatings could improve the biofunctional activities of orthopedic and dental implants for their better clinical success.     

Correlation between microstructure and properties of biocomposite coatings

A SiO₂–CaO–Na₂O (SCN) based bioactive glass was used to prepare glass–matrix/Ti particle composite coatings (SCNT). The coatings were obtained by vacuum plasma spray (VPS) on Ti–6Al–4V substrates. Two different deposition methods have been compared: (a) VPS of powders obtained by ball milling of sintered composites; (b) in situ plasma spray of mixed titanium and glass powders. For comparative purposes, pure SCN glass coatings were produced. The coating morphology and microstructure were observed by optical and scanning electron microscopy, compositional analyses by energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). Comparative mechanical tests were carried out by shear tests and by Vickers indentations at the interface between the substrate and the coatings. The bioactivity of glass- and composite coatings was investigated in vitro by soaking them in a simulated body fluid (SBF) with the same ion concentration of the human plasma. All the layers retain their starting composition. The composite coatings obtained by VPS of the powdered presintered composites showed a better mechanical behaviour with respect both to the composite coatings obtained by the in situ method and to the pure glass coatings. Both the glass- and the two kind of composite coatings revealed to be bioactive by the growth of a thick apatite layer after 30 days of soaking in SBF. The electrochemical behaviour of the SCNT coatings was evaluated by means of potentiodynamic anodic polarization curves and free corrosion potential measurements in Ringer solution at 25 °C. For comparative purposes the same analyses were performed on analogous bioactive glass-matrix/Ti particle composite coated samples, based on the system TiO₂–SiO₂–CaO–B₂O₃ (TSCB), and obtained both by the in situ and by presintering method as well. The results of the electrochemical tests showed a better corrosion behaviour of the samples coated by VPS of powdered sintered composites with respect to those coated by in situ VPS composites.     

Biomimetic Preparation and Characterization of Bioactive Coatings on Alumina and Zirconia Ceramics

For the preparation of bioactive coatings on alumina and zirconia ceramic surfaces a fast biomimetic method using a supersaturated solution containing Na⁺, Ca²⁺, Cl⁻, HCO₃⁻, and PO₄³⁻ ions was used. The coatings were analysed with the use of an X-ray diffraction spectrometer and a transmission electron microscope equipped with an energy-dispersive spectroscopy detector. After the precipitation both coatings were composed of poorly crystallized, nanosized, plate-like particles with the octacalcium phosphate (OCP) crystal structure. The adhesion of the coatings was improved by a heat treatment at 1050°C for 1 h. During this heat treatment the calcium phosphate layer, deposited from a supersaturated solution onto the surface of the substrates, was sintered to form a dense coating. At the same time the OCP crystal structure was transformed into that of hydroxyl apatite, the coating's crystallinity was increased, and the particles grew isotropically up to 300 nm in size. The bioactivity of the coated ceramic was confirmed before and after the heat treatment using a simple simulated body fluid test.     

Effect of carbonate content on the in vitro bioactivity of carbonated hydroxyapatite

The effect of carbonate content on the apatite-forming ability of carbonated hydroxyapatite (CHA) in simulated body fluid (SBF) has been investigated. Five different nanocrystalline B-type CHA with carbonate content ranged from 2.01 to 5.25 wt% were prepared, sintered, and assessed for their in vitro bioactivity in SBF solution for 7-weeks under static conditions at 36.5 °C. The formation of the apatite layer and the surface morphology of CHA were examined by using a scanning electron microscope (FESEM) at week 1, 3, and 7 of SBF immersion, respectively. The Ca/P molar ratio of the CHA was determined by X-ray fluorescence (XRF). In addition, the sample weight changes and the pH of the SBF solution were measured. The results show that the formation of apatite layer depends on the carbonate content of CHA. Increasing the carbonate content caused significant increases in the surface area of CHA and the rate of apatite formation. Weight loss was observed for all CHA samples during the first week of SBF immersion, and thereafter followed by weight regain weekly until week 7. The changes in the pH of SBF and the Ca/P molar ratio were proportional to the carbonate content of CHA. This study thus highlights the importance of determining carbonate content aspect that govern the bioactivity of CHA.     

TiCN and metallic coatings for corrosion protection of separator plates in MCFCs

Stainless steel 304 substrates were coated with different materials in order to find a suitable coating material for corrosion protection of separator plates in molten-carbonate fuel cells (MCFCs). Five titanium carbonitride coatings differing in composition and morphology and a titanium monoxide coating were deposited with chemical vapour deposition techniques. Also double-layer coatings of TiN/Au and TiN/Ni were prepared. The coatings were tested on their corrosion protection of separator plates in four different environments: under MCFC-cathode or anode gas, at load or at open circuit conditions. The corrosion behaviour was characterized using cyclic voltammetry. Corrosion rates were determined with electrochemical methods and cross-section analyses of corrosion layers. Titanium nitride coatings showed the best corrosion protection. The titanium carbide and titanium monoxide coating showed respectively less and no protection. The thin gold and Ni-coatings were unstable. Under cathode gas, the most important corrosion protection is given by keeping the cell at load, and then a titanium nitride coating might provide lifetime protection. Under anode gas, corrosion is most severe at load conditions. A titanium nitride coating also gives corrosion protection, but not enough for lifetime protection.     

热处理对钛基体表面电泳沉积GO/HA生物活性涂层的影响

采用电泳沉积法在钛基体表面制备氧化石墨烯(GO)/羟基磷灰石(Ca₁₀(PO₄)₆(OH)₂, HA)复合涂层,通过XRD和SEM等测试手段对不同热处理条件下得到的GO/HA涂层进行表征。研究结果表明,热处理有助于促进涂层中HA结晶度的提高,600℃和800℃的热处理温度并没有导致HA发生热分解,但有可能破坏了涂层中GO的有序晶体结构。GO/HA涂层具有优异的生物活性,但随热处理温度的升高,涂层的润湿性和生物活性下降。热处理过程有利于涂层致密,加强涂层与基体的结合,800℃热处理后的涂层结合强度高达25.31 MPa。     

Coupling sol-gel with electrospray deposition: Towards nanotextured bioactive glass coatings

For the first time, the sol-gel method was coupled with electrostatic spray deposition (ESD) to fabricate nanotextured bioactive glass (BG) coatings with a controlled microstructure in a one-pot-process. Three BG compositions belonging to the SiO₂-CaO-P₂O₅ system (S85, S75, and S58) were homogeneously deposited on metallic Ti6Al4V substrates starting from the atomization of precursor solutions. All coatings displayed an amorphous character, as confirmed by XRD. A wide variety of innovative BG morphologies were obtained, tuning the key parameters of ESD, leading from highly porous coral-like to compact reticular-type coatings. The bioactivity, in terms of apatite formation, of as-deposited coatings was tested by immersion in simulated body fluid solution. Textural properties were found to play an important impact in its biological performance. Highly porous ESD-coatings exhibited remarkable bioactivity for S75 and S58 compositions, compared with more compacted ones of equal formulations. S85 composition was found extremely reactive regardless of the coating microstructure.     

Hydroxyapatite Coating on Thermally Oxidized Titanium Substrates

Titanium substrates were oxidized in oxygen or air at temperatures of 600°–800°C, then immersed in solutions of 2.0m M – 20.7m M CaCl₂ and 1.2m M –12.4m M KH₂PO₄ for aging periods of 0.5–10 d. The titanium surface was successfully coated with hydroxyapatite (HAP) when the substrates were oxidized in oxygen gas at 610°C for 1 h and then aged in a solution of 2.00m M Ca²⁺ and 1.20m M PO₄³⁻. The Ca/P ratio of the surface coating increased toward its stoichiometric HAP value (return 10/6) as the aging time increased; the Ca/P ratio attained a value of 1.66 after 10 d.     

Preparation of Chitosan-based nanocomposites and biomedical investigations in bone tissue engineering

Chitosan (CS)/Bioglass (BG)/Hydroxyapatite (HA)/Halloysite nanotube (HNT) nanocomposites were deposited on titanium (Ti) by electrophoretic deposition (EPD). The nanostructures with the uniform distribution of ceramic particles into CS polymer were yielded. In vitro experiment depicted CS/BG/HA/HNT is precipitated with apatite particles by immersion into corrected simulated body fluid (C-SBF) at 37?°C. Furthermore, In vitro bioactivity, biomineralization, and cell attachment indicated that all of the coatings have a desirable apatite induced ability and cell compatibility. Finally, biodegradability of CS-BG-HA/HNT nanocomposite verified the degradation ratio of CS-BG-HA-HNT is 4 times more than that of CS-BG-HA.     

Structural evaluation,preliminary in vitro stability and electrochemical behavior of apatite coatings on Ti6Al4V substrates

Medical-grade alloys, such as Ti-6Al-4V, have been used for fixation of fractured bone and for the total replacement of defective bone. Their bioactivity could be improved by applying a bone-like apatite layer onto their surfaces. This, in turn, enhances their integration with the surrounding tissues upon implantation. In addition, the presence of a bioactive bone-like coating minimizes the likelihood of corrosion. Various methods are known for the formation of apatite coating onto Ti-6Al-4V, among which sputtering has shown its promise as a simple direct method. In the current work, a sputtering technique was used to develop a 300 nm-thick bone-like apatite layer onto Ti-6Al-4V. Structural composition, integrity and morphology of the as-coated and thermally treated coatings were investigated. Coated substrates were further evaluated after soaking them in a simulated body fluid (SBF) for up to 14 days. Results showed the formation of an amorphous apatite layer onto the alloy, that was further shown to partially crystallize upon heat treatment. As a result of SBF treatment, the apatite layer was found to remodel through a dissolution-precipitation mechanism due to its amorphous and non-stoichiometric nature, forming a smooth layer with better homogeneity and decreased surface roughness. Electrochemical analysis of the coated alloys showed the enhanced corrosion protection of the alloy surfaces by coating them with apatite. In addition, pre-grinding of the alloy surfaces before the formation of the coating was also found to improve the corrosion inhibition of the alloy surfaces in aqueous media.     

Preparation and characterization of hydroxyapatite coating by magnetron sputtering on Mg–Zn–Ag alloys for orthopaedic trauma implants

The aim of the present paper was to evaluate the effect of hydroxyapatite coatings on the two types of Mg–Zn–Ag alloys as a possible solution to control magnesium alloy degradation. The coatings were prepared by the radio frequency magnetron sputtering method at a deposition temperature of 300 °C. To perform this evaluation, the coated alloys were immersed in a simulated body fluid solution at body temperature (37 ± 0.5 °C) to determine the corrosion resistance through electrochemical and immersion tests. Moreover, the investigation also consisted of the evaluation of microchemical, mechanical, and morphological properties. The deposition temperature of 300 °C was enough to obtain a crystalline hydroxyapatite structure with a Ca/P ratio close to the stochiometric one. The adhesion of coatings was not influenced by the nature of Mg–Zn–Ag alloys, so similar values for both coated alloys were found. The results showed that the coating was homogonous deposited on the Mg–Zn–Ag alloys and the corrosion resistance of uncoated magnesium alloys was improved.     

How bone marrow-derived human mesenchymal stem cells respond to poorly crystalline apatite coated orthopedic and dental titanium implants

Due to the delayed and weak bone-implant integration in dental and orthopedic devices, there have been several attempts to enhance implant–bone interactions for rapid osseointegration. In this paper, the interactions of human bone marrow-derived stromal (mesenchymal) stem cells (hMSCs) with uncoated and coated titanium alloy implants with poorly crystalline apatite are studied. First the configuration and chemical composition of the apatite coatings and their deposition progress in different experimental conditions are investigated and discussed. Then, hMSCs are cultured on different substrates and cell attachment and proliferation are monitored and evaluated for different time intervals. Although the uncoated and coated substrates indicate good cell attachment, the differences in proliferation and morphology of the cells spread over the coated samples are significant. It is concluded that the coated samples improve the capability for accepting the cells in three-dimensional and slender shapes. The migration of hMSCs on both substrates are discussed. As such cell migration is directly associated to the osteoconduction, the findings confirm the hypothesis of enhancement in bone formation on the surface of biomimetically poorly crystalline apatite coated titanium implants. This in vitro study demonstrates that the coated samples are nontoxic and biocompatible enough for ongoing osteogenic studies in bone or dental defects in animal models in vivo.     

Improving the stability and bioactivity of micro-arc oxidized calcium phosphate/titania porous coatings by high energy shot peening pretreatment

Micro-arc oxidation (MAO) is one of the conventional methods for surface modification of titanium (Ti)-based dental materials. However, in the process of MAO, the surface porous titania (TiO₂) coating is prone to micro-crack, which affects the stability of coating and the long-term service life of the implant. In this work, high-energy shot peening (HESP) pretreatment would be used to improve the stability and bioactivity of the MAO coatings and increase the effective doping of calcium and phosphorus (Ca & P) elements in surfaces. We verified that the MAO specimens pretreated by HESP (S-MAO) had larger pore size (~ 4.0 μm), coating thickness (~ 8.5 μm) and critical load (~ 11.1 N) than the samples without pretreatment (MAO, ~ 3.1 μm, 6.2 μm & 6.2 N); and the content of Ca and P in S-MAO group (Ca: ~ 6.3 wt%; P: ~ 9.4 wt%) was higher than that of MAO group (Ca: ~ 5.8 wt%; P: ~ 6.7 wt%. Meanwhile, it was also proved that compared with Ti and MAO groups, MC3T3-E1 cells on S-MAO substrates had better spreading, viability, ALP activity, and osteogenic gene expression. All the above results indicate that the HESP pretreatment has excellent potential to improve the coating stability and bioactivity of MAO-treated substrates.     

Cerium-doped hydroxyapatite/collagen coatings on titanium for bone implants

The novelty of the present research consists in the possibility of obtaining cerium-doped hydroxyapatite/collagen coatings on the titanium support, to improve the performance of the bone implants. These coatings were deposited on the titanium surface by biomimetic method using a modified supersaturated calcification solution (SCS) additionally containing a cerium source and collagen. Prior to the deposition of the apatite layer, an alkali ÷ thermal oxidation pretreatment has been applied to ensure an increase in the bioactivity of the titanium surface. The coatings were examined by scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and Fourier transformed infrared (FTIR) spectroscopy. The EDX and XRD investigations of the coatings indicated that cerium was incorporated in the hydroxyapatite lattice. The collagen presence in the coatings was confirmed by FTIR analysis. The cerium-doped hydroxyapatite/collagen coatings showed good antibacterial efficacy against Escherichia coli and Staphylococcus aureus bacteria, being more effective against Escherichia coli. These coatings have a significant potential to be used in the dental and orthopedic implants, as the osseointegration depends on much more factors than simple formation of hydroxyapatite.     

Low-Temperature Preparation of Anatase and Rutile Layers on Titanium Substrates and Their Ability To Induce in Vitro Apatite Deposition

Surface modification of titanium and its alloys to induce apatite deposition within a short period is of practical importance in clinical applications. In this study, titanium substrates were treated with hydrogen peroxide solutions at low temperatures to yield titania layers consisting of anatase and rutile. Those titania layers, regardless of the fraction of anatase and rutile, were bioactive to induce deposition of apatite in Kokubo's simulated body fluid within 24 h. The bioactivity was attributed to both the epitaxial effect and the abundant Ti–OH group of the titania layer.     

Synthesis,characterization and in-vitro biocompatibility of electrophoretic deposited europium-doped calcium silicate on titanium substrate

Europium (Eu) has attracted attention to be incorporated as biologically active ions to achieve different biological and functional properties of biomaterials. In this study, calcium silicate (CS) coatings doped with different amount of Eu (up to 10 mol%) were successfully formed on titanium substrates via electrophoretic deposition. A low amount of Eu (2.5 mol%) gave a relatively denser coating and improved coating adhesion strength (～3.3 N). All Eu–CS coatings provided good apatite forming ability, yet lower degradation rate, as compared to CS coating. Moreover, it was observed that the human fetal osteoblast (hFOB) cells could attach and proliferate on all Eu–CS coatings, suggesting their biocompatible nature. Eu2.5CS not only showed comparable cell proliferation with CS, but also enhanced the osteogenic activity of the CS coating. All results suggested that Eu2.5CS coatings are promising coating materials for biomedical implants, particularly bone tissue engineering applications.     

Electrophoretic deposition of bioactive wollastonite and porcelain–wollastonite coatings on 316L stainless steel

Wollastonite and porcelain–wollastonite coatings on stainless steel were obtained by electrophoretic deposition using acetone as dispersive medium. A direct electric current of 800 V for 3 min was used for obtaining the single wollastonite coating. A well-sintered layer was observed after heat treatment at 1050 °C for 1 h in air. The two-layer coating was obtained by depositing dental porcelain at 400 V for 30 s followed by the deposition of wollastonite at 400 V for 3 min. After forming the two layers, this complex coating was heat treated at 800 °C for 5 min. Under these conditions, strong bonds of both the interface wollastonite–porcelain and that of porcelain–metallic substrate were observed. The in vitro bioactivity assessment of the coatings was performed by immersing the deposited substrates in simulated body fluid (SBF) for 21 days. All the materials showed to be highly bioactive through the formation of a homogeneous apatite layer.