Hydroxyapatite Coatings Research Articles

The Influence of rhBMP-7 Associated with Nanometric Hydroxyapatite Coatings Titanium Implant on the Osseointegration: A Pre-Clinical Study.

Background: Bioceramic nanometer coatings have been regarded as potential substitutes for plasma-sprayed hydroxyapatite coatings, and the association with bone morphogenetic protein (BMP) is an attempt to achieve faster osseointegration to hasten oral rehabilitation. Objective: This study aimed to investigate the effect of recombinant human bone morphogenetic protein-7 (rhBMP-7) on the osseointegration of titanium implants coated with a thin film surface of hydroxyapatite (HA). Methods: Two implants (n = 24) were placed in each white New Zealand rabbits’ femur (n = 6). Implants were placed in the right femur after standard instrumentation (A and B) and in the left femur after an over-instrumentation (C and D), preventing bone-implant contact. The distal implants were installed associated with rhBMP-7 (groups B [regular instrumentation] and D [over-instrumentation]) and, also, in the absence of without BMP (control groups A [regular instrumentation] and C [over-instrumentation]). After 4 weeks, the animals were euthanized. The bone blocks containing the implants were embedded in methyl methacrylate and sectioned parallel to the long axis of the implant, which were analyzed by image segmentation. The data were analyzed using a nonparametric statistical method. Results: We observed that Group A had a mean bone formation of 35.6% compared to Group B, which had 48.6% (p > 0.05). Moreover, this group showed 28.3% of connective tissue compared to Group A, with 39.3%. In the over-instrumented groups, rhBMP-7 (Group D) showed an enhanced and significant increase in bone formation when compared with the group without rhBMP-7 (Group C). Conclusion: We concluded that the association of rhBMP-7 to thin nanostructure HA-coated implants promoted greater new bone area than the same implants in the absence of rhBMP-7, mainly in cases of over-instrumented implant sites.

The correlation between osseointegration and bonding strength at the bone-implant interface: In-vivo & ex-vivo investigations on hydroxyapatite and hydroxyapatite/titanium coatings

This study investigated the effects of hydroxyapatite (HA) and hydroxyapatite/titanium (HA/Ti) coatings on osseointegration and bonding strength at the bone-implant interface. The coatings were made using air plasma spray (APS), and three study groups were examined: 1) Uncoated commercial pure titanium (CP-Ti) rods; 2) HA-coated CP-Ti rods, and 3) Composite of 50 %wt HA + 50 %wt Ti coated CP-Ti rods. The rods were implanted into the distal femurs and proximal tibias of fifteen New Zealand white rabbits, and 8 weeks after the implantation, the samples were harvested. The results of pull-out tests showed that the ultimate strength of HA and HA/Ti coatings were significantly greater than the uncoated samples (P < 0.05). Moreover, even though the histological evaluations showed significantly greater osseointegration of HA/Ti composite coatings compared with HA coatings (P < 0.05), nonetheless, the composite of HA/Ti offers no significant increase in the ultimate strength, stiffness, and bonding strength at the bone-implant interface, compared with the HA group (P > 0.05). Thus, in an eight-week study, there was no linear correlation between the osseointegration and the bonding strength at the bone-implant interface. The results of this work may imply that the extent of osseointegration at the bone-implant interface does not necessarily determine the value of the bonding strength at the bone-implant interface. It is speculated that, in a longer-term study, a greater quality of bone formation may occur during osseointegration, between the implant and its adjacent bone, which can lead to a more enhanced bonding strength, compared with the 8-weeks post-surgery follow up.

In vivo evaluation of osseointegration ability of sintered bionic trabecular porous titanium alloy as artificial hip prosthesis.

Hydroxyapatite (HA) coatings have been widely used for improving the bone-implant interface (BII) bonding of the artificial joint prostheses. However, the incidence of prosthetic revisions due to aseptic loosening remains high. Porous materials, including three-dimensional (3D) printing, can reduce the elastic modulus and improve osseointegration at the BII. In our previous study, we identified a porous material with a sintered bionic trabecular structure with in vitro and in vivo bio-safety as well as in vivo mechanical safety. This study aimed to compare the difference in osseointegration ability of the different porous materials and HA-coated titanium alloy in the BII. We fabricated sintered bionic trabecular porous titanium acetabular cups, 3D-printed porous titanium acetabular cups, and HA-coated titanium alloy acetabular cups for producing a hip prosthesis suitable for beagle dogs. Subsequently, the imaging and histomorphological analysis of the three materials under mechanical loading in animals was performed (at months 1, 3, and 6). The results suggested that both sintered bionic porous titanium alloy and 3D-printed titanium alloy exhibited superior performances in promoting osseointegration at the BII than the HA-coated titanium alloy. In particular, the sintered bionic porous titanium alloy exhibited a favorable bone ingrowth performance at an early stage (month 1). A comparison of the two porous titanium alloys suggested that the sintered bionic porous titanium alloys exhibit superior bone in growth properties and osseointegration ability. Overall, our findings provide an experimental basis for the clinical application of sintered bionic trabecular porous titanium alloys.

Plasma-Sprayed Hydroxyapatite Coatings and Their Biological Properties

Air plasma spraying (APS) is a common method of producing hydroxyapatite (HA) coatings for alloprosthetic implants. Modification of HA spraying potentially may diminish the risk of inflammation and local infection during bone implantation. Titanium implants were HA coated with different deposition process parameters. HA powder was deposited using APS with axial powder injection at three different distances (100, 120, and 140 mm). The surface morphology of each implant was examined and the direct contact cytotoxicity of each HA coating was evaluated according to norm ISO 10993 5:2009. The response of monocytes to HA was assessed via the activation of transcription nuclear factor. All coatings had a lamellar structure. HA sprayed at a distance of 120 mm showed the highest roughness and little phase change. The analysis of the results of the conducted research showed that plasma-spraying distance during the HA coating process had a negligible impact on biocompatibility. The results obtained for a distance of 120 mm showed a slight increase in the biological properties tested. Moreover, HA coatings sprayed at different distances were not cytotoxic and did not stimulate the NF-kB. Bare titanium was less susceptible to colonization by Staphylococcus aureus than HA-coated surfaces. HA constitutes a potentially good, low-cost, non-cytotoxic material for joint prostheses.

A study on biological properties of titanium implants coated with multisubstituted hydroxyapatite

In this work, it was found that the composition of hydroxyapatite coatings deposited on a titanium substrate depends on the temperature of detonation products and on the composition of the initial explosive mixture. Depending on the detonation mode, it was possible to obtain a coating of oxyhydroxyapatite containing or not containing an admixture of other calcium orthophosphates. It was shown for the first time that the structure of multisubstituted Zn–Si-hydroxyapatite and Ag–Zn–Si-hydroxyapatite with substitution degree x(Zn) = x(Si) = 0.2 and x(Ag) = 0.1 has lower thermal stability as compared to unsubstituted hydroxyapatite. The formation of a small amount of the α-Ca3(PO4)2 phase upon detonation deposition of the multisubstituted hydroxyapatites was obviously due to structural transformations that occurred when the material was heated by the detonation products. In vivo biological testing of titanium implants coated or not coated with hydroxyapatite revealed that the coating significantly accelerates osteogenesis in the gap between native bone and the implant; this acceleration improved implant fixation. In animals with the uncoated plates, fibrogenesis processes significantly outstripped the osteogenesis. The presence of Zn and Si ions in the apatite coating had a potentiating influence on the osteoinduction caused by hydroxyapatite. Osteogenesis in this case was more complete and characterized by pronounced processes of mineralization of the bone plates. The addition of Ag ions to the Zn–Si-hydroxyapatite at a concentration of 1 at.% did not impair its osteogenic activity and did not have a toxic effect on bone tissue, while imparting antibacterial properties to the material.

Experimental Study of Nano-Structural Coatings Formed by Microwave Plasma

A novel microwave plasma (MP) torch on a rectangular waveguide with two magnetron sources 2.45 GHz and an experimental setup are designed to perform hydroxyapatite (HA) coatings on metallic and dielectric substrates. Operating regimes of a such torch are investigated. Experimental studies have proved the advantages of this method of HA coating in comparison with analogous techniques. The proposed design is suitable for application in other technologies of different materials processing. Results obtained in the present study help to better understand the processes of nano-structural layer formation on solid substrates.

Robust Superhydrophobic Brass Mesh with Electrodeposited Hydroxyapatite Coating for Versatile Applications.

A robust superhydrophobic brass mesh was fabricated based on a low-energy surface and a roughness on the nano/micro-meter scale. It was carried out by the forming of hydroxyapatite (HP) coatings on its surface through a constant current electro-deposition process, followed by immersion in fluoroalkylsilane solution. Surface morphology, composition and wetting behavior were investigated by field-emission scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), high speed camera, and contact angle goniometer. Under optimal conditions, the resulting brass mesh exhibited superhydrophobicity, excellent anti-corrosion (η = 91.2%), and anti-scaling properties. While the surfactant liquid droplets of tetradecyl trimethyl ammonium bromide (TTAB) with different concentration were dropped on the superhydrophobic surface, maximum droplet rebounding heights and different contact angles (CAs) were observed and measured from side-view imaging. The plots of surfactant-concentration−maximum bounding height/CA were constructed to determine its critical-micelle-concentration (CMC) value. Close CMC results of 1.91 and 2.32 mM based on the determination of maximum rebounding height and CAs were obtained. Compared with its theoretical value of 2.1 mM, the relative errors are 9% and 10%, respectively. This indicated that the novel application based on the maximum rebounding height could be an alternative approach for the CMC determination of other surfactants.

Deposition of Fluoresceine-Doped HAp Coatings via High-Velocity Suspension Flame Spraying

In current medicine, joint revision surgery plays an important role in the treatment of degenerative joint diseases. Infections of the artificial joints are an iatrogenic, accompanying symptom after joint replacement procedures. A new approach is to functionalize the bioactive coatings of the implants by infiltrating them with anti-inflammatory drugs. This work aims at a one-step approach in manufacturing drug-doped, porous hydroxyapatite coatings by high-velocity suspension flame spraying (HVSFS). Thermal exposure of the temperature-sensitive drugs is critical. Therefore, a new process setup, combining one axial and one radial suspension line, is used for coating deposition. The lower dwell time of the suspension in the flame through radial injection helps in controlling the temperature exposition of the contained drug to the flame. Additionally, the influence of the powder morphology, used as a carrier for the drug in the suspension, is investigated by carrying out spray experiments with suspensions from three different granule types. To analyze the temperature exposition within the coating process, fluoresceine was used as a model drug, as the decomposition of the organic, fluorescing molecules can be easily controlled by fluorescence intensity measurements. It could be shown that the deposition of temperature-sensitive organic molecules is possible without degrading the molecular structure by a modified HVSFS process. This knowledge offers new possibilities in the cost-effective one-step manufacturing of functionalized, anti-inflammatory bioceramic coatings on orthopaedic implants.

Development of TiO2–HA Coatings by PEO on Titanium Scaffolds Fabricated by Direct Ink Writing

Development of TiO2–HA Coatings by PEO on Titanium Scaffolds Fabricated by Direct Ink Writing

Effects of silver/selenium/chitosan doped hydroxyapatite coatings on REX-734 alloy: Morphology, antibacterial activity, and cell viability

The goal of this study was to improve the antibacterial activity and cell viability of the Rex-734 alloy in biomedical applications. Various biocomposite coatings, such as single-layer hydroxyapatite (HAp), HAp/silver(Ag), and HAp/selenium(Se)/chitosan(Chit), were applied to Rex-734 alloy at various film thicknesses. The surface coatings were characterized by scanning electron microscopy, SEM, EDX, XRD and coating thickness and hardness of surface coatings were measured. The in vitro antibacterial activities of the coated and uncoated substrates were tested against Esherichia coli JM 103 and Staphylococcus aureus ATCC29293. In vitro cell–material interactions using Saos-2 osteoblast cells were characterized by the 3-(4,5-dimethylthiazol2-yl)− 2,5-diphenyltetrazolium bromide (MTT) assay for cell viability. The post-coating sintering parameters were shown to have a significant effect on the surface morphology. When compared to single HAp and HAp/Ag coatings, Se and Chit additions to HAp powders revealed good crack-free coating surfaces. Crack-free coating morphologies were achieved with a sintering speed of 3 °C/min. While single-HA coatings had an antimicrobial efficiency of 83% against E. coli, this value increased to 94% with Ag additive and to 85% with Se additive. Similarly, Ag and Se additives improved HAp's antimicrobial efficiency against Staphylococcus aureus. Cell viability decreased in the HAp/Ag coating at 86.5% and 90.93%, but increased significantly (p < 0.05) in the HA/Se-Chit coating at 137,43% and 158.23% at the end of the first and seventh days of incubation, respectively. The addition of Ag/Se/Chit to HAp increased the viability of the Rex-734 cells. Furthermore, it was revealed that the HAp-doped Se/Chit duplex biocomposite coating groups increased bone cell viability at much higher rates than the single-layer HAp coatings.

Microstructural designed S58 bioactive glass/ hydroxyapatite composites for enhancing osteointegration of Ti6Al4V-based implants

Novel bioactive glass (BG)/hydroxyapatite (HAP) composites were successfully manufactured by electrostatic spray deposition (ESD) to improve the overall osteointegration of Ti6Al4V-based implants. Herein, we combined the high bioactivity of the S58 formulation with the long-term stability of HAP. Highly porous coral-like S58 BG coatings with different thicknesses (6 and 30 μm) were deposited on the top of a thin (150 nm) and dense nanocrystalline HAP layer starting from homogeneous liquid precursor solutions by ESD. In vitro studies were carried out by immersion in simulated body fluid (SBF) solution and compared with single-layered coatings of S58 and HAP. The SBF test revealed that the presence of the BG-topcoat layer significantly improves the reactivity in terms of mineralization response compared to single-layered HAP coating. Furthermore, the S58 coating thickness was found to influence the biological response. The thinner composite is suggested to have a better mineralization performance than the thicker one.

Hydroxyapatite coating processes with EPD method and investigation of mechanical properties of coatings

This paper reports on electrophoretic deposition of hydroxyapatite coatings on 316L stainless steel and Ti6Al4V alloy. Coatings were carried out at 60 sec. deposition time and voltage values of 40, 80, 120, 160 Voltage. Suspension: It was prepared by using Ethanol, Hydroxyapatite, Polyvinyl Alcohol, Sodium dodecyl sulfate, N-N-Dimethylformamide chemicals. The findings and results acquired at the end of the study have been presented and discussed. When the Ca/P values calculated in the study are examined, it was seen that there are values close to the ideal Ca/P ratio (1.67) in all parameters. When the roughness values are examined, it was seen that coatings close to the ideal surface roughness value (1-1.5 µm) are obtained. When the nano indentation test results were evaluated, it was observed that coatings suitable for shell bone implants were obtained.

Effect of Hydroxyapatite Coating by Er: YAG Pulsed Laser Deposition on the Bone Formation Efficacy by Polycaprolactone Porous Scaffold.

Composite scaffolds obtained by the combination of biodegradable porous scaffolds and hydroxyapatite with bone regeneration potential are feasible materials for bone tissue engineering. However, most composite scaffolds have been fabricated by complicated procedures or under thermally harsh conditions. We have previously demonstrated that hydroxyapatite coating onto various substrates under a thermally mild condition was achieved by erbium-doped yttrium aluminum garnet (Er: YAG) pulsed laser deposition (PLD). The purpose of this study was to prepare a polycaprolactone (PCL) porous scaffold coated with the hydroxyapatite by the Er: YAG-PLD method. Hydroxyapatite coating by the Er: YAG-PLD method was confirmed by morphology, crystallographic analysis, and surface chemical characterization studies. When cultured on PCL porous scaffold coated with hydroxyapatite, rat bone marrow-derived mesenchymal stem cells adhered, spread, and proliferated well. The micro-CT and staining analyses after the implantation of scaffold into the critical-sized calvaria bone defect in rats indicate that PCL porous scaffold coated with hydroxyapatite demonstrates accelerated and widespread bone formation. In conclusion, PCL porous scaffold coated with hydroxyapatite obtained by the Er: YAG-PLD method is a promising material in bone tissue engineering.

Modification of hydroxyapatite coating in the presence of adipic acid for Mg-based implant application

This study investigated the role of adipic acid (AA) in improving the anti-corrosion performance and in-vitro bioactivity of hydroxyapatite coating applied on AZ31 Mg alloy. Firstly, hydroxyapatite (HA) coating was applied on the AZ31 Mg alloy. In the next step, the optimized hydroxyapatite-based coating, modified with adipic acid by direct addition and post-treatment methods. Corrosion behavior of uncoated sample and different coated samples were studied by Electrochemical Impedance Spectroscopy (EIS) and Direct Current (DC) Polarization techniques. Surface characterization was examined by Field Emission Scanning Electron Microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDXS), X-ray diffraction (XRD) and contact angle measurements. According to the contact angle results, all coated samples reveal high hydrophilic behavior. Additionally, the XRD analysis confirms the formation of hydroxyapatite crystals in all coated samples and the presence of the AA in HA + AA and HA − AA coatings does not change the crystal structure of the hydroxyapatite. Electrochemical studies display that the Rp value of HA coating is increased from 3630 Ω.cm2 to 10784 Ω.cm2 by the direct addition method also by the post-treatment method the polarization resistance reached 10294 Ω.cm2. In addition, an in-vitro bioactivity assessment was performed in a simulated body fluid (SBF). Based on FE-SEM studies, a protective layer of AA is formed on HA coating by the post-treatment method which improves the anti-corrosion behavior efficiently. The results showed that the adipic acid-modified hydroxyapatite coatings by direct addition and post-treating methods display better anti-corrosion properties and bioactivity compared to the optimal hydroxyapatite coating.

Wear-resistant ceramic coatings deposited by liquid thermal spraying

As a surface strengthening and surface modification technology of materials, liquid thermal spray technology has been used in many fields, such as wear and friction reduction, corrosion resistance, and high-temperature oxidation resistance. This article reviews the progress of liquid thermal sprayed coating in wear resistance as well as friction reduction in recent years. The influences of microstructure, composition, phase structure and mechanical properties on the tribological properties of typical coatings (including ceramic coatings and multiphase composite coatings) are investigated. The tribological properties of the coating are determined by the coating characteristics (including microstructure, porosity, mechanical properties, etc.) and the service conditions (working temperature, lubrication state, etc.). Typical ceramic wear-resistant coatings include Al2O3, YSZ, HA coatings, etc. The tribological properties of the coating can be significantly improved through process optimization and heat treatment. The comparison of nanostructured and microstructured ceramic-based coating reveals that nanostructured coating reduces wear by absorbing stress. The interaction between different constituent phases improves wear resistance and reduces wear in composite coatings. Finally, various challenges faced by liquid thermal spray are pointed out, and future research focuses are proposed.

Influence of Magnesium Content on the Physico-Chemical Properties of Hydroxyapatite Electrochemically Deposited on a Nanostructured Titanium Surface

The aim of this research was to obtain hydroxyapatite (HAp)-based coatings doped with different concentrations of Mg on a Ti nanostructured surface through electrochemical techniques and to evaluate the influence of Mg content on the properties of HAp. The undoped and doped HAp-based coatings were electrochemically deposited in galvanostatic pulsed mode on titania nanotubes with a diameter of ~72 nm, being designed to enhance the adhesion of the HAp coatings to the Ti substrate. The obtained materials were investigated by Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), X-Ray Diffraction (XRD), and Fourier-Transform Infra-Red spectroscopy (FTIR). The adhesion of the coatings to the substrate was also evaluated with the help of the “tape-test” and the micro-scratch test. The morphology (SEM) of all the coatings is made of very thin and narrow ribbon-like crystals, with some alterations with respect to the Mg amount in the coatings. Thus, a concentration of 1 mM of Mg in the electrolyte leads to wider and thicker ribbon-like crystals, while a concentration of 1.5 mM in the electrolyte generated a morphology that resembles the undoped HAp. Both phase composition (XRD) and chemical bonds (FTIR) analysis proved the formation of HAp in all coatings. Moreover, according to XRD, all coatings have a strong orientation toward the (002) plane. Irrespective of the Mg content, all coatings registered an average roughness between approx. 500 and 600 nm, while the coating thickness increased after addition of Mg, from a value of 9.6 μm, for the undoped HAp, to 11.3 μm and ~13.7 μm for H/Mg1 and H/Mg2, respectively. In terms of adhesion, it was shown that the coatings a H/Mg2 had a poorer adhesion when compared to H/Mg1 and the undoped HAp (H), which registered similar adhesion, indicating that a concentration of 1.5 mM of Mg in the electrolyte reduces the adhesion of the Hap-based coatings to the nanostructured surface. The obtained results indicated that Mg concentrations up to 1 mM in the electrolyte can enhance the properties of HAp-based coatings electrochemically deposited on a nanostructured surface, while even a slightly higher concentration of 1.5 mM can negatively impact the characteristics of HAp coatings.

Biological characterization of the zinc-modified hydroxyapatite coated by a pulsed laser deposition method

Pure Hydroxyapatite (Ca10(PO4)6(OH)2) and Zn-HA nanoparticles were successfully deposited on steel substrates, and laser ablation was performed by the pulsed laser deposition (PLD) technique using an Nd: YAG laser (λ = 532 nm, τ = 12 ns). The bioactivity of the thin film was investigated by its immersing in a simulated body fluid solution of pH 7.4 at 37 °C for incubation of 14 days. The growth of the apatite layer after immersion was studied. The analysis showed the formation of needle-like crystals after immersion in solution. Wettability angles decreased for the HA coating after post-deposition compared to pure HA coatings at room temperature and ion substitutions in bioceramics lead to wettability modification. The findings confirm that Zn doping with different concentrations improved antibacterial activity. The results demonstrate that coating the surface with bioactive materials modified with metal ions, yields good biological responses, and varied compositions differentially affect the water contact angles as well as HA layer growth.

Role of Hydroxyapatite (HA) Coatings in Implants : A Review

Biomaterials are the materials that are used for the restoration and reorganization of various tissues as well as organs. Some of the common materials presently used are organic, metallic, and composites. To increase the biocompatibility of these materials, some types of coatings are regularly applied. Hydroxyapatite is one of the materials which is mostly used for coating these materials. Hydroxyapatite acquires the same structural and chemical characteristics as human bone. In the present review, we discussed the various aspects of hydroxyapatite coatings that consist of rationale, coating process, various techniques, and coating failures.

Effects of hydroxyapatite coatings on enhanced corrosion protection and cytocompatibility of high-purity magnesium

Effects of hydroxyapatite coatings on enhanced corrosion protection and cytocompatibility of high-purity magnesium

Influence of the thermal treatment of a hydroxyapatite powder on the characteristics of coatings deposited by cold gas spraying

Usually deposited by air plasma spraying, hydroxyapatite (HAP) is widely employed as coatings for biomedical applications thanks to its biocompatibility. Over the past decades, cold gas spraying (CS) technology is of growing interest because it allows avoidance of oxidation or phase transition of materials due to lower deposition temperatures. However, spraying ceramics by CS is highly challenging and the mechanisms responsible for the deposition are not clearly described in the literature even if HAP has already been successfully sprayed by CS. In this article, the approach consists both in developing suitable HAP coatings devoted to functionalizing medical prostheses and in explaining the different steps of the deposit buildup by CS. The properties of the starting powder such as its morphology influence the quality of the final coating without any real chemical reaction with the substrate. Here it is shown how a simple preliminary thermal pre-treatment of the powder significantly affects the deposit formation and quality. The conclusions drawn in this paper demonstrate that the obtaining of a HAP coating compatible with the targeted biomedical applications requires compromises especially between the powder crystallinity and deposition efficiency.