Hydroxyapatite Coatings Research Articles

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.

Bioinspired Hydroxyapatite Coating Infiltrated with a Graphene Oxide Hybrid Supramolecular Hydrogel Orchestrates Antibacterial and Self-Lubricating Performance.

Hydroxyapatite (HA) bioceramic coating has been extensively applied for the modification of metallic implants to improve their biocompatibility and service life after implantation. Unfortunately, HA coating often suffers from high friction, severe wear, and bacterial invasion, which restrict its application in artificial joints. According to a bioinspired soft/hard combination strategy, a novel HA composite coating that is infiltrated with a vancomycin-loaded graphene oxide (GO) hybrid supramolecular hydrogel is developed via vacuum infiltration and a subsequent host-guest interaction-induced self-assembly process. The holes of textured HA ceramic coating act just like a "magic pocket", offering a stable container to form and store GO hybrid hydrogels and even to recycle wear debris as well. The drug-loaded hybrid hydrogels stored in textured HA coating possess a unique shear force and/or frictional heat triggered gel-sol transition and sustained drug release behavior, acting like the extrusion of synovial fluid during articular cartilage movement, leading to a remarkable self-lubrication, anti-wear performance, and promising antibacterial property against Staphylococcus aureus. The friction coefficient and wear rate of composite coating reduced by nearly five times and three orders of magnitude compared with textured HA coating, respectively, which benefited from the synergistic lubricate effect of cyclodextrin-based pseudopolyrotaxane supramolecular hydrogel and GO lubricants.

Electrodeposition of Hydroxyapatite Coating on Ti6Al4V Alloy: Mechanistic Investigation of the Substrate Crystallographic Texture Effect

Hydroxyapatite (HAp) coating electrodeposition was performed on three orthogonal surfaces of duplex-annealed Ti6Al4V alloy. This approach made it possible to investigate the effect of substrate crystallographic texture on hydroxyapatite coating properties exclusively from its microstructure. The coating characteristics were evaluated by scanning electron microscopy, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), laser surface profilometry, and potentiodynamic polarization test. The results showed that the presence of low-surface energy planes leads to smaller HAp deposits of 39 ± 4 μm due to the higher nucleation rate during electrodeposition. The highest surface roughness value of 75 ± 1 μm, as well as the lowest degree of crystallinity, equal to 23.5%, belonged to the surface in which and planes of high-surface energy placed in parallel to the surface. The electrochemical test results showed that the protective efficiency of HAp coatings was the highest for the surface with planes in parallel. This was attributed to the increased thickness and the low porosity content of the coating.

Antibacterial Properties and Biocompatibility of Hydroxyapatite Coating Doped with Various Cu Contents on Titanium

Antibacterial Properties and Biocompatibility of Hydroxyapatite Coating Doped with Various Cu Contents on Titanium

Morphology of Hydroxyapatite Coatings Formed on VT1-0 Titanium as a Result of Combined Treatment

Morphology of Hydroxyapatite Coatings Formed on VT1-0 Titanium as a Result of Combined Treatment

PERFORMANCE OF THERMALLY SPRAYED HYDROXYAPATITE COATINGS FOR BIOMEDICAL IMPLANTS: A COMPREHENSIVE REVIEW

Metallic bioimplant are widely used now-a-days to replace a part of human body in a physiologically accepted manner. However, the bio-compatibility of the metallic bioimplant was mainly achieved by the incorporation of a bio-compatible coating on its surface through suitable surface modifications techniques. In surface modifications techniques, the thermal spraying is widely used for modification of metallic bioimplant due to its versatile nature. In thermal spraying, the hydroxyapatite (HAp)-based coatings are mainly preferred because this coating responses to physiochemical environment and adapts itself accordingly. But bulk of the HAp coating give out due to less adhesion strength of the HAp coating and its poor mechanical properties. The properties of HAp-based coatings can be designed as per requirements by reinforcing this coating through hard particulates in suitable proportions. In this paper, the various thermal sprayed (TS) coatings used for performing HAp-based coatings on bioimplant were discussed. The influence of reinforcements on the mechanical and bio-compatible properties of the coatings is also discussed in detail. Lastly, the challenges in the TS HAp coatings along-with the future perspective of TS coating in fabricating of 3D biomedical implants by using cold spray (CS) has also been summarized.

Optimization of formation of phase pure hydroxyapatite and fabrication of electrochemically stable HAP coatings on 316L SS for orthopedic applications

AbstractImpact of sintering temperature and aging time was investigated on purity and phase of hydroxyapatite powders synthesized through sol–gel process. Phase, composition, and morphology of the prepared hydroxyapatite powders were characterized using X‐ray diffraction (XRD), Fourier transform infrared (FT‐IR), and scanning electron microscopy (SEM)/energy dispersive spectroscopy (EDS). Plausible mechanism respective to the formation of HAP from the precursors Ca(NO3)2·4H2O and triethyl phosphite (TEP) by sol–gel process was determined from 31P NMR analysis. Further, the development of hydroxyapatite coatings on 316L SS metallic surfaces was done by varying the spin coating parameters such as spin speed, spin time, and sintering atmosphere, and their corrosion resistance behavior in SBF solution was evaluated by electrochemical impedance spectroscopy (EIS) and TAFEL polarization analysis. From the results, we inferred that the HAP coatings deposited on 316L SS surfaces at 3000 rpm/min under nitrogen atmosphere sintering have shown improved corrosion resistivity. The effect of aging time, sintering atmosphere, and spin speed was evaluated in terms of corrosion resistance behavior.

Effect of carbon interface on adhesion and anti-corrosion properties of hydroxyapatite coating on AZ31 magnesium alloy

In order to improve the adhesion and anti-corrosion properties of hydroxyapatite coating (HA) on the surface of implant magnesium alloy, carbon interface (C) was successfully introduced by resin carbonization method. The adhesion and anti-corrosion properties of the coatings were characterized. After introducing PyC interface, the adhesion of the coating increased by 173%. The corrosion current in the polarization curve decreased by three orders of magnitude, meaning that the corrosion resistance was improved significantly. The microcracks on carbon interface layer surface provided enough bonding strength between the hydroxyapatite coating and carbon coating, due to forming the mortise and tenon embedding structure. The introduction of PyC interface layer improved the overall density of the coating and effectively isolated the contact between the corrosion solution and the magnesium alloy matrix, resulting in that the corrosion resistance was significantly improved.

Survival of Hydroxyapatite-Coated Versus Non-hydroxyapatite-Coated Total Hip Arthroplasty Implants in a Veteran Population.

Hydroxyapatite (HA) coatings were introduced to improve uncemented implant osteointegration and to prevent loosening and osteolysis. However, data regarding these implants have been inconsistent. We studied the effect of HA coating of femoral stems and acetabular cups on component revision after primary total hip arthroplasty (THA) in the veteran population. We identified patients who underwent uncemented primary THA at any Veterans Health Administration (VHA) hospital from 2000 to 2017 and who had implants that were available as either HA-coated or non-HA-coated models. The endpoint was removal of the component of interest for any reason. For each individual stem and shell, unadjusted and adjusted (for age and body mass index) Cox proportional hazards models were used to estimate hazard ratios for the risk of explantation between HA-coated and non-HA-coated implants of the same type. A total of 262 HA-coated cups, 4580 non-HA-coated cups, 4767 HA-coated stems, and 9397 non-HA-coated stems were available for analysis. The mean follow-up time was 9.01 years (43,627 total implant-years) for cups and 7.13 years (101,004 total implant-years) for stems. One of the two shells reviewed had significantly lower survivorship and an elevated hazard ratio for explantation with HA coating. Among the five implant pairs of stems, and the other shell, implant survival and hazard ratios for explantation were not affected by HA coating. HA coating did not improve THA implant survival in our veteran population. Although HA-coated versions of hip implants tend to be more costly than their noncoated counterparts, these results do not support their general use.

Corrosion and wear performances of hydroxyapatite and boron-containing TiO2 composite coatings on Ti6Al7Nb alloy

Plasma electrolytic oxidation coupled with hydrothermal treatment is a relatively new technique to form a hydroxyapatite/TiO2 layer on titanium alloys for biomedical applications. Hence the process allows achieving a bioactive and bactericidal surface by using electrolytes that contain ions (such as calcium-phosphorus and boron) necessary for desired properties. The coating properties are controllable by adjusting the parameters in the PEO process. In the present study, an electrolyte that contains both calcium, phosphorus, and boron ions was used to form a rough and porous oxide layer on Ti6Al7Nb which is known to be less toxic than the most widely used Ti alloy for biomedical applications, Ti6Al4V. A hydroxyapatite and boron-containing oxide layer was obtained after plasma electrolytic oxidation and hydrothermal treatment. Coatings were examined by XRD, XPS, SEM, contact angle measurement system, micro-hardness tester, wear tester, and corrosion measurement system. The results showed that the wear and the corrosion properties of all coated samples increased. Especially boron doping enhanced both the wear and corrosion resistance. Relatively the best corrosion resistance was achieved from CaP-B and the best wear resistance was from HA-B samples. The hardness values and mean surface roughness of all coated samples also increased while the average friction coefficients decreased. The hardness increased from 323 ± 5 HV0.1 to 1084 ± 16 HV0.1 where the coefficient of friction decreased from 0.5672 ± 0.01 to 0.4697 ± 0.03.

Cold Spraying of Thick Biomimetic and Stoichiometric Apatite Coatings for Orthopaedic Implants

Ceramic coatings have a long history in the orthopaedic field, with plasma sprayed coatings of hydroxyapatite as leading standard in the manufacturing process; however, these coatings can contain secondary phases resulting from the decomposition of hydroxyapatite at high temperatures, which limit the lifetime of implants and their osseointegration. This work aims to produce coatings that can maximize bone osseointegration of metallic implants. In order to preserve the raw characteristics of hydroxyapatite powders that are thermally unstable, coatings were deposited by cold spray onto Ti6Al4V alloy substrates. In contrast with other thermal spray technologies, this process presents the advantage of spraying particles through a supersonic gas jet at a low temperature. On top of hydroxyapatite, carbonated nanocrystalline apatite was synthesized and sprayed. This biomimetic apatite is similar to bone minerals due to the presence of carbonates and its poor crystallinity. FTIR and XRD analyses proved that the biomimetic characteristics and the non-stoichiometric of the apatite were preserved in the cold spray coatings. The cold spray process did not affect the chemistry of the raw material. The adhesion of the coatings as well as their thicknesses were evaluated, showing values comparable to conventional process. Cold spraying appears as a promising method to preserve the characteristics of calcium phosphate ceramics and to produce coatings that offer potentially improved osseointegration.

Nano Hydroxyapatite for Biomedical Applications Derived from Chemical and Natural Sources by Simple Precipitation Method.

In the past, bone fractures due to accidents were rectified by surgery and reconstruction of bone structure. In recent times, researchers have been made to find a solution by producing alternate biomaterials. Hydroxyapatite (HAp) is one of the most important bioactive materials used as a substitute for human hard tissue because of its composition being very similar to human bones and teeth. A study has proved that HAp has been used for bone regeneration in clinical trials in the mid-1980. HAp has been used as implant coatings and graft materials and also used as granules, cement, and pastes for bone regenerative applications. HAp coatings on bioimplants improved biocompatibility, bioactivity, and biological fixation. Moreover, some of the deposition methods can be employed to increase the cellular responses of bone regeneration such as sputtering, spraying, electrodeposition, and pulsed layer deposition. The researcher has prepared hydroxyapatite from chemical and natural sources. The surface area and intrinsic properties of the HAp play a vital role in bone-related applications. This can be achieved by synthesizing the HAp from natural sources rather than synthetic materials. The HAp obtained from the chemical source is not fulfilling the requirements of the natural bone. A variety of biowaste materials such as eggshell, crab shell, snail shell, bovine bone, fishbone, and fish scales are available in nature and can be converted to useful calcium source for HAp. The present study is to produce the HAp from biowaste materials like eggshell and chemical sources using the wet precipitation method. The synthesized HAp is coated on the Ti6Al4V alloy using the electrodeposition method, and it is immersed in SBF solution at 37°C for corrosion testing. The coated samples are investigated by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), electrochemical study, field emission scanning electron icroscopy (FESEM), energy dispersive X-ray analysis (EDAX), AFM, and antibacterial activity with two different microorganisms. FTIR and XRD confirm the functional groups and crystallinity of the HAp. The good antibacterial activity of the HAp is observed against two bacterial strains. The corrosion studies reveal that the HAp derived from a natural source is eco-friendly and nontoxic and has excellent corrosion resistivity and cell adhesion properties. A strong bond is formed between the naturally derived HAp with bone tissue which is involved in the bio-resorption process and does not pose any side effect to the human body compared to synthetically derived HAp. In addition, the biowaste materials are converted to useful biomaterials and can reduce environmental pollution.

A novel method for the formation of bioceramic nano-calcium hydroxyapatite coatings using sol-gel and dissolution-precipitation processing

The wet chemistry route has been developed to prepare calcium hydroxyapatite (Ca10(PO4)6(OH)2, (HA)) thin films on a silicon substrate using the novel low-temperature sol-gel and dissolution-precipitation approach. The calcium carbonate thin films on the silicon substrate were obtained by spin-coating technique when substrates were repeatedly coated with 10, 20 and 30 layers of sol-gel solution. The composites formed of crystalline and amorphous CaCO3 were obtained by calcination of the coatings for different time at 600°C. A dissolution-precipitation procedure was used for the preparation of calcium hydroxyapatite thin films on silicon substrate at 80°C. The obtained synthesis products were characterised by X-ray powder diffraction (XRD) analysis, scanning electron microscopy (SEM) and Raman spectroscopy.

Osteoblast Attachment on Titanium Coated with Hydroxyapatite by Atomic Layer Deposition.

Background: The increasing demand for bone implants with improved osseointegration properties has prompted researchers to develop various coating types for metal implants. Atomic layer deposition (ALD) is a method for producing nanoscale coatings conformally on complex three-dimensional surfaces. We have prepared hydroxyapatite (HA) coating on titanium (Ti) substrate with the ALD method and analyzed the biocompatibility of this coating in terms of cell adhesion and viability. Methods: HA coatings were prepared on Ti substrates by depositing CaCO3 films by ALD and converting them to HA by wet treatment in dilute phosphate solution. MC3T3-E1 preosteoblasts were cultured on ALD-HA, glass slides and bovine bone slices. ALD-HA and glass slides were either coated or non-coated with fibronectin. After 48h culture, cells were imaged with scanning electron microscopy (SEM) and analyzed by vinculin antibody staining for focal adhesion localization. An 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) test was performed to study cell viability. Results: Vinculin staining revealed similar focal adhesion-like structures on ALD-HA as on glass slides and bone, albeit on ALD-HA and bone the structures were thinner compared to glass slides. This might be due to thin and broad focal adhesions on complex three-dimensional surfaces of ALD-HA and bone. The MTT test showed comparable cell viability on ALD-HA, glass slides and bone. Conclusion: ALD-HA coating was shown to be biocompatible in regard to cell adhesion and viability. This leads to new opportunities in developing improved implant coatings for better osseointegration and implant survival.

Sol–gel derived hydroxyapatite coating on titanium implants: Optimization of sol–gel process and engineering the interface

AbstractSol–gel derived hydroxyapatite coatings on metallic implants are important to promote their osseointegration and biocompatibility. However, such coatings generally suffer from drawbacks that limit implant longevity. In this study, the sol gel process to prepare hydroxyapatite was optimized and used to deposit a hydroxyapatite layer on Ti6Al4V. Samples were pretreated by thermal oxidation, sol–gel coating, and anodization to produce titanium dioxide interlayers with various structures. The results of structural and thermal analysis have determined the optimal preparation parameters to produce monophasic and crystalline hydroxyapatite. The introduction of titanium dioxide intermediate layers produced crack-free hydroxyapatite films and promoted the adherence and integrity of the coating, where the adhesive strength was remarkably improved. Furthermore, potentiodynamic polarization tests in simulated body fluid revealed low corrosion rates and high protection property of the hydroxyapatite/titania coated samples, making these structures promising for the coatings of bone replacements. Graphical abstract

Development of Hydroxyapatite Coating on Titanium Alloy for Orthopedic Applications

Biomaterials are synthetic materials that are utilized to restore or replace damaged or diseased human body parts, allowing them to regain their original form and function to improve the quality and longevity of human life. Titanium and its alloys have long been employed in biomedical applications due to its remarkable features, such as good biocompatibility, resistance to bodily fluid effects, tremendous tensile strength, flexibility, and high corrosion resistance. Titanium and its alloys have a unique combination of strength and biocompatibility that makes them suitable for medical or recreational purposes. If these materials are used as bio-implant, it releases toxic ions like aluminium and vanadium in the body fluid environment after implantation. [1-3] To overcome the problem, Ti6Al4V alloy was coated with hydroxyapatite (HAp), which provides better bioactivity, osteocompatibility, and antibacterial activity. This layer prevents the further passing of ions from the biomaterial and improves the tissue growth on the bone. The present work is to synthesize HAp from snail shells using a simple wet precipitation method.[4] The waste material of snail shells can be utilized for the development of the HAp, which was non-toxic, eco-friendly, and also to improve bioactivity and biocompatibility of the biomaterials. The prepared HAp was coated on the Ti6Al4V alloy by using the electro-deposition method.[5] Thermal analysis of obtained CaO powder was investigated by TG–DTA analysis. The coated alloy was characterized by various techniques such as FTIR, XRD, TG-DTA, FESEM, EDAX, AFM, and antibacterial activity.

Correction to: Boron-Doped Hydroxyapatite Coatings on NiTi Alloys Using the Electrophoretic Deposition Method: Enhanced Corrosion and Adhesion Performances

Correction to: Boron-Doped Hydroxyapatite Coatings on NiTi Alloys Using the Electrophoretic Deposition Method: Enhanced Corrosion and Adhesion Performances

Microstructure and Properties of Hydroxyapatite Coatings Made by Aerosol Cold Spraying–Sintering Technology

Hydroxyapatite is a widely used material used for the bioactivation of an implant’s surface. A promising hydroxyapatite coating approach is the kinetic deposition of powder particles. The possibility of solid-state deposition improvement through the merging of Aerosol Deposition and Low Pressure Cold Spraying techniques is a promising prospect for improving the deposition efficiency and the quality of coatings. The objective of the paper is to study the possibilities of hydroxyapatite coating structure modification through changes in the coating process and post-heat treatment. The novel Aerosol Cold Spraying system joining Low Pressure Cold Spraying and Aerosol Deposition was used for the deposition of coatings. The coating’s post-processing was conducted using two techniques: Spark Plasma Sintering and Pressureless Sintering. The coating’s structure was examined using scanning, transmission, and light microscopy, and X-ray diffraction. Substrate–coating bond strength was assessed using a tensile test. Homogenous buildup using Aerosol Cold Spraying of hydroxyapatite was achieved. Various pores and microcracks were visible in the sprayed coatings. The deposition process and the thermal post-processing did not lead to significant degradation of the hydroxyapatite phase. As a result of the Spark Plasma Sintering and Pressureless Sintering at 800 °C, an increase in tensile adhesion bond strength and crystal size was obtained.

Antibacterial Longevity of a Novel Gallium Liquid Metal/Hydroxyapatite Composite Coating Fabricated by Plasma Spray.

Hydroxyapatite (HAp)-coated metallic implants are known for their excellent bioactivity and osteoconductivity. However, infections associated with the microstructure of the HAp coatings may lead to implant failures as well as increased morbidity and mortality. This work addresses the concerns about infections by developing novel composite coatings of HAp and gallium liquid metal (GaLM) using atmospheric plasma spray (APS) as the coating technique. Five weight percent Ga was mixed into a commercially supplied HAp powder using an orbital shaker; then, the HAp-Ga particle feedstock was coated onto Ti6Al4V substrates using the APS technique. The X-ray diffraction results indicated that Ga did not form any Ga-related phases in either the HAp-Ga powder or the respective coating. The GaLM filled the pores of the HAp coating presented both on the top surface and within the coating, especially at voids and cracks, to prevent failures of the coating at these locations. The wettability of the surface was changed from hydrophobic for the HAp coating to hydrophilic for the HAp-Ga composite coating. Finally, the HAp-Ga coating presented excellent antibacterial efficacies against both initial attachments and established biofilms generated from methicillin-resistant Staphylococcus aureus and Pseudomonas aeruginosa after 18 h and 7 days of incubation in comparison to the control HAp coating. This study shows that GaLM improves the antibacterial properties of HAp-based coatings without sacrificing the beneficial properties of conventional HAp coatings. Thus, the HAp-Ga APS coating is a viable candidate for antibacterial coatings.

In vitro assessment of plasma-sprayed reinforced hydroxyapatite coatings deposited on Ti6Al4V alloy for bio-implant applications

In vitro assessment of plasma-sprayed reinforced hydroxyapatite coatings deposited on Ti6Al4V alloy for bio-implant applications