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NiTi alloys are actively used in medicine as implants because of their mechanical properties. At the same time, however, the NiTi surface is not biologically active, which has a negative effect on osteogenesis. In addition, Ni is capable of causing various toxic reactions in the human body. It is therefore necessary to create a composite coating that is both bioactive and prevents the release of Ni ions. It has been shown that by changing the modes of plasma assisted RF sputtering of a calcium phosphate target, it is possible to obtain coatings with different contents of the amorphous phase. The coatings formed consist of hydroxyapatite and amorphous calcium phosphate. On the surface of a sample not treated with argon plasma, there are no phases containing calcium or phosphorus, although these elements are present on the surface. The different ways in which the CaP coatings were applied also affected their structure. It was found that the CaP coatings of samples M2 and M3 have mediocre corrosion resistance, dissolving quickly. This has a positive effect on the ability to osteogenesis, which was discovered as a result of in vitro tests. These tests have shown that the sample obtained at I discharge = 30 A and U bias = 30 V has the highest bioactivity and produces the lowest percentage of dead cells. [ABSTRACT FROM AUTHOR]

In this study, hydroxyl apatite (HA) as a bio-ceramic is coated on the TiNi shape memory. In this approach, Tri-ethanolamine and butanol were used as suspensions. To set up Electrophoretic Deposition (EPD) process, voltages of 20, 30 and 40 volts were applied on the cathode for 1-5 minutes. The sintering process was done in the Ar atmosphere for two hours at 800°C. SEM and XRD were used to investigate surface morphologies and phases. Obtained results showed that higher electrical currents led to generation of thicker coatings registering 105% and 12.3% improvement for weight and thickness after 6 minutes, respectively. Moreover, Transformation of HA to other calcium phosphate phases doesn’t happen at a sintering temperature of 800°C. Moreover, a uniform, homogeneous and crackles coating can be reached in the voltage of 30 volts at low sintering temperatures. This process can be utilized an alternative technique for bioactive coatings. [ABSTRACT FROM AUTHOR]

As a result of hydroxyapatite's (HAp) similarity to the mineral component of bone, it has been extensively investigated for biomedical application. To mimic the non-stoichiometric hydroxyapatite of bone or add positive features to it, different cationic and anionic substitutions have been studied. In this study, the nanocomposite coating of strontium (Sr) and silver (Ag) substituted HAp was deposited on a rarely investigated β type titanium alloy with low Young's modulus to investigate its morphological and chemical features, crystallographic structure, thickness, biocompatibility, and hydrophilicity. The coating was deposited via a little reported electrochemical method which has the advantages of both electrolytic and electrophoretic deposition. The process is simple and can be conducted under mild experimental conditions to prevent potential high-temperature induced-thermal stress complications. The chemical, morphological and crystallographic features were characterised using EDAX, FE-SEM, and XRD analysis. The coating thickness was measured using a profilometry test. The biocompatibility and wetting behaviour were evaluated by MTT assay and the sessile drop technique, respectively. The coatings have shown rod-shaped, homogenous, and nano-sized HAp particles, with a close Ca/P ratio to stoichiometric apatite; meanwhile, Sr and Ag nanosphere particles are capable of modifying its surface. The coating can support cell growth and proliferation and shows a superhydrophilic surface. [ABSTRACT FROM AUTHOR]

This study is the second part of a two-part study whereby supersaturated solutions of calcium and phosphate ions generate well-defined hydroxyapatite coatings for orthopaedic implants. An 'ideal' process solution is selected from Part 1, and the detailed characterisation of films produced from this solution is undertaken here in Part 2. Analysis is presented on the hydroxyapatite produced, in both powder form and as a film upon titanium substrates representative of orthopaedic implants. From thermal analysis data, it is shown that there is bound and interstitial water present in the hydroxyapatite. Nuclear magnetic resonance data allow for the distinction between an amorphous and a crystalline component of the material. As hydroxyapatite coatings are generated, their growth mechanism is tracked across repeated process runs. A clear understanding of the growth mechanism is achieved though crystallinity and electron imaging data. Transmission electron imaging data support the proposed crystal growth and deposition mechanism. All of the data conclude that this process has a clear propensity to grow the hydroxyapatite phase of octacalcium phosphate. The investigation of the hydroxyapatite coating and its growth mechanism establish that a stable and reproducible process window has been identified. Precise control is achieved, leading to the successful formation of the desired hydroxyapatite films. [ABSTRACT FROM AUTHOR]

This study introduces and explores the use of supersaturated solutions of calcium and phosphate ions to generate well-defined hydroxyapatite coatings for orthopaedic implants. The deposition of hydroxyapatite is conducted via several solutions of metastable precursors that precipitate insoluble hydroxyapatite minerals at a substrate–solution interface. Solutions of this nature are intrinsically unstable, but this paper outlines process windows in terms of time, temperature, concentration and pH in which coating deposition is controlled via the stop/go reaction. To understand the kinetics of the deposition process, comparisons based on ionic strength, particle size, electron imaging, elemental analyses and mass of the formed coating for various deposition solutions are carried out. This comprehensive dataset enables the measurement of deposition kinetics and identification of an optimum solution and its reaction mechanism. This study has established stable and reproducible process windows, which are precisely controlled, leading to the successful formation of desired hydroxyapatite films. The data demonstrate that this process is a promising and highly repeatable method for forming hydroxyapatites with desirable thickness, morphology and chemical composition at low temperatures and low capital cost compared to the existing techniques. [ABSTRACT FROM AUTHOR]

Hydroxyapatite (Ca10(PO4)6(OH)2) coatings are often made in a two-step process, where hydroxyapatite is firstly synthesized, and then applied as a coating for different applications. One way to make the process more efficient, is to combine the synthesis and coating processes into a single step. Plasma spray is a common method used to apply hydroxyapatite as a coating, as it is a fast and controlled method of coating materials. The aim of the present study was to investigate the inflight reaction of calcium carbonate (CaCO3) and brushite (CaHPO4·2H2O) to synthesize hydroxyapatite using plasma spray. Various plasma spray parameters were used to observe their effect on the quantity of hydroxyapatite produced in the coating. Phase analysis was carried out using XRD, and the morphology of the coatings was observed using SEM. Plasma spray coatings containing hydroxyapatite, tetracalcium phosphate (Ca4(PO4)2O) and calcium oxide (CaO) were successfully made from the reaction between the precursor powders. The plasma spray parameters which influenced the particle velocity were found to have the largest effect on the quantity of hydroxyapatite produced in the coating. The plasma temperature was also found to affect the amount of hydroxyapatite produced. [ABSTRACT FROM AUTHOR]

Calcium phosphate-based coatings are widely studied in orthopedics and dentistry for their similarity to the mineral component of bone and their capability to promote osseointegration. Different calcium phosphates have tunable properties that result in different behaviors in vitro, but the majority of studies focus only on hydroxyapatite. Here, different calcium phosphate-based nanostructured coatings are obtained by ionized jet deposition, starting with hydroxyapatite, brushite and beta-tricalcium phosphate targets. The properties of the coatings obtained from different precursors are systematically compared by assessing their composition, morphology, physical and mechanical properties, dissolution, and in vitro behavior. In addition, for the first time, depositions at high temperature are investigated for the further tuning of the coatings mechanical properties and stability. Results show that different phosphates can be deposited with good composition fidelity even if not in a crystalline phase. All coatings are nanostructured and non-cytotoxic and display variable surface roughness and wettability. Upon heating, higher adhesion and hydrophilicity are obtained as well as higher stability, resulting in better cell viability. Interestingly, different phosphates show very different in vitro behavior, with brushite being the most suitable for promoting cell viability and beta-tricalcium phosphate having a higher impact on cell morphology at the early timepoints. [ABSTRACT FROM AUTHOR]

In this research, hydroxyapatite powder particles were coated on a Ti-6Al-4V alloy substrate by the plasma spraying method to create bone implants by benefitting from titanium's mechanical properties and hydroxyapatite's biological properties. Hydroxyapatite prepared by the plasma spraying method suffers from decomposition, formation of other calcium phosphate phases, weak adhesion to the substrate, and microcrack formation in the coating due to residual stresses initiated by the high temperature of the coating process. To improve the hydroxyapatite coating properties, the Ti-6Al-4V alloy was preheated, and then hydroxyapatite coating took place. The results showed that residual stress in the interface decreased, and adhesion improved by preheating the substrate. However, formation of an amorphous phase on coating was observed, resulting in a higher dissolution rate in the biological environment and weak mechanical properties compared to crystalline hydroxyapatite. Experimental results showed that heat treatment after the coating process decreased the amount of this amorphous phase and heightened the crystallinity of the coating by up to more than 60%. [ABSTRACT FROM AUTHOR]

Ion-substituted calcium phosphate (CP) coatings have been extensively studied as promising materials for biomedical implants due to their ability to enhance biocompatibility, osteoconductivity, and bone formation. This systematic review aims to provide a comprehensive analysis of the current state of the art in ion-doped CP-based coatings for orthopaedic and dental implant applications. Specifically, this review evaluates the effects of ion addition on the physicochemical, mechanical, and biological properties of CP coatings. The review also identifies the contribution and additional effects (in a separate or a synergistic way) of different components used together with ion-doped CP for advanced composite coatings. In the final part, the effects of antibacterial coatings on specific bacteria strains are reported. The present review could be of interest to researchers, clinicians, and industry professionals involved in the development and application of CP coatings for orthopaedic and dental implants. [ABSTRACT FROM AUTHOR]

The hydroxyapatite coating on the metallic implant is preferred to improve biocompatibility and faster bone integration. The reliability of the coating during fixation and after surgery is important to achieve the expected bone growth. The micromotion between the implant and bone due to patient movement causes fretting and deteriorates the coating. New coating techniques are attempted to improve the strength of the HAp coating. The suspension plasma spray (SPS) process is a new process where fine grain-structured coating with controlled porosity can be developed. The fretting wear behavior of titanium (Ti) substrate and SPS-coated HAp on Ti substrate fretted against alumina are discussed in this paper. The relative displacement expected in the bone and stem interface is estimated using numerical studies, and fretting wear experiments are carried out with the maximum relative displacement estimated. Fretting wear tests are performed using the ball-on-flat configuration at different contact stresses. The fretting friction coefficient variation in the coated samples during the initial contact period is different compared to the uncoated samples. A high friction coefficient during the early stages of fretting influences the reliability of the coating, although the steady-state friction coefficient is nearly the same as that of the uncoated titanium. The friction force vs. displacement loops obtained from the tests revealed 'gross-slip' conditions. The wear scar observations using a scanning electron microscope and 3D-profilometer revealed significant damage in coated samples compared to the uncoated titanium samples. The porous nature of the SPS coating and fine wear particles facilitates a smooth layer formation in longer run. [ABSTRACT FROM AUTHOR]

With the objective of enhancing the stability of scorodite, its encapsulation with hydroxyapatite (Ca5(PO4)3OH) (HAP) and fluorapatite (Ca5(PO4)3F) (FAP) surface coatings, the two most stable of the calcium phosphates, inert to pH and redox potential variations, are presented in this work. The experimental work includes: (1) determination of the metastable zone for HAP and FAP precipitation, (2) the synthesis of crystalline scorodite under atmospheric conditions using hydrothermal scorodite seed and its characterization, (3) the coating of scorodite with hydroxyapatite and fluorapatite with supersaturation-controlled heterogeneous crystallization, and (4) the long-term stability of the encapsulated scorodite solids. Hydroxyapatite and fluorapatite were prepared with homogeneous precipitation from a metastable solution to which reagents were added at a controlled flow rate. Crystalline scorodite was produced with seeding precipitation and encapsulated with a direct apatite (HAP or FAP) deposition that was controlled by adjusting the pH and reagent addition. The stability tests in oxic and anoxic environments over the pH range of 5–9 showed the release of arsenic from the apatite-coated scorodite to be much lower than from naked scorodite, thereby demonstrating that apatite-based encapsulation of hazardous materials is technically feasible and merits further consideration for development into an arsenic stabilizing technology. [ABSTRACT FROM AUTHOR]

Globally, vast research interest is emerging towards the development of biodegradable orthopedic implants as it overcomes the toxicity exerted by non-degradable implants when fixed in the human body for a longer period. In this context, magnesium (Mg) plays a major role in the production of biodegradable implants owing to their characteristic degradation nature under the influence of body fluids. Also, Mg is one of the essential nutrients required to perform various metabolic activities by the human cells, and therefore, the degraded Mg products will be readily absorbed by the nearby tissues. Nevertheless, the higher corrosion rate in the biological environment is the primary downside of using Mg implants that liberate H 2 gas resulting in the formation of cavities. Further, in certain cases, Mg undergoes complete degradation before the healing of damaged bone tissue and cannot serve the purpose of providing mechanical support. So, many studies have been focused on the development of different strategies to improve the corrosion-resistant behavior of Mg according to the requirement. In this regard, the present review focused on the limitations of using pure Mg and Mg alloys for the fabrication of medical implants and how the calcium phosphate conversion coating alters the corrosive tendency through the formation of hydroxyapatite protective films for enhanced performance in medical implant applications. [ABSTRACT FROM AUTHOR]

TA6V (Ti‐6Al‐4V) titanium alloy is commonly used in implantology due to its biocompatibility and interesting mechanical properties. However, its lack of bioactivity is responsible for orthopedic implants loosening, eventually leading to the necessity for a revision surgery. In this study, inorganic coatings are developed with the aim of improving osteo‐integration of TA6V implants. To this end, a carbonated calcium phosphate apatite, already reported to be osteo‐conductive and naturally present in bone tissue, is shaped in the form of micro‐sized filaments, via the electrospinning process, in order to mimic the architecture of the collagen fibrils naturally present in the bone extracellular matrix. The process is then adapted to coat complex, 3D implants. Cellular assays with MG‐63 highlight that cell viability and proliferation are promoted on the coated implant, as a result of both its chemical and morphological properties. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

[Display omitted] • Rapid coating of orientation-controlled hydroxyapatite layer on human tooth in 30 s. • Rapid protection and repair of tooth surface in dental practice using hydroxyapatite. • Laser-assisted novel crystallization using viscous light-absorber paste. • The method is applicable to all tissues of tooth using medically approved equipment. • Finding of hydroxyapatite nanofibers as the constituent of enamel, like as bone. Functionalization of teeth surfaces has attracted much attention from the perspective of preventive dentistry. Laser irradiation (30 s) of the viscous light-absorber paste coated on the tooth substrate enabled ultrafast coating of orientation-controlled fluoride-substituted hydroxyapatite (HAP) rod layers, 150–500 nm thick, in a calcium phosphate solution. On enamel, the layers perfectly inherited orientations and structures of the crystals in the substrate, exhibiting two types of hierarchies at different scales. One was a submicron-scale hierarchy, in which an approximately 60-nm-wide rod comprised multiple thinner rods, approximately 20-nm wide, oriented along the c -axis. The 20-nm-wide rods exhibited another type of nanoscale hierarchy comprising incompletely assembled nanofibers < 5-nm wide. In dentin and cementum, c -axis-elongated HAP rods grown on the substrates displayed less arrangement in their elongation direction than those grown on enamel. Most rods on dentin were single crystals, unlike those grown on enamel. On the cementum, each polycrystalline rod (100–150 nm wide) comprised multiple single-crystal rods approximately 60-nm wide, forming a sub-micron hierarchy similar to that observed in enamel. The developed method may be useful in dental practice for protecting teeth surfaces and repairing microdefects in enamel, dentin, and cementum. [ABSTRACT FROM AUTHOR]

[Display omitted] The present work reports the adsorption, release, antibacterial properties, and in vitro cytotoxicity of sodium fusidate (SF) associated with a carbonated calcium phosphate bone cement. The adsorption study of SF on cement powder compared to stoichiometric hydroxyapatite and nanocrystalline carbonated apatite was investigated to understand the interaction between this antibiotic and the calcium phosphate phases involved in the cement formulation and setting reaction. The adsorption data revealed a fast kinetic process. However, the evolution of the amount of adsorbed SF was well described by a Freundlich-type isotherm characterized by a low adsorption capacity of the materials toward the SF molecule. The in vitro release results indicated a prolonged and controlled SF release for up to 34 days. The SF amounts eluted daily were at a therapeutic level (0.5–2 mg/L) and close to the antibiotic minimum inhibitory concentration (0.1–0.9 mg/L). Furthermore, the release data fitting and modeling suggested that the drug release occurred mainly by a diffusion mechanism. The antibacterial activity showed the effectiveness of SF released from the formulated cements against Staphylococcus aureus. Furthermore, the biological in vitro study demonstrated that the tested cements didn't show any cytotoxicity towards human peripheral blood mononuclear cells and did not significantly induce inflammation markers like IL-8. [ABSTRACT FROM AUTHOR]

Although calcium‑magnesium phosphate cements (CMPCs) have been widely applied to treating critical-size bone defects, their repair efficiency is unsatisfactory owing to their weak surface bioactivity and uncontrolled ion release. In this study, we lyophilized alginate sodium (AS) as a coating onto HAp/K-struvite (H@KSv) to develop AS/HAp/K-struvite (AH@KSv), which promotes bone regeneration. The compressive strength and hydrophilicity of AH@KSv significantly improved, leading to enhanced cell adhesion in vitro. Importantly, the SA coating enables continuous ions release of Mg2+ and Ca2+, finally leading to enhanced osteogenesis in vitro/vivo and different patterns of new bone ingrowth in vivo. Furthermore, these composites increased the expression levels of biomarkers of the TRPM7/PI3K/Akt signaling pathway via an equilibrium effect of Mg2+ to Ca2+. In conclusion, our study provides novel insights into the mechanisms of Mg-based biomaterials for bone regeneration. • Novel scaffold (AH@KSv) with improved surface bioactivity were successfully prepared via the lyophilization method. • AH@KSv enhances in vitro / in vivo osteogenesis in bone regeneration. • Regulatory mechanisms of TRPM7/PI3K/Akt signaling pathway are related to equilibrium effect of Mg2+ to Ca2+. [ABSTRACT FROM AUTHOR]

The use of artificial biomaterials has been acclaiming potential therapeutic scope in diverse clinical applications. This review started with the description of the basics of biomaterials, and desirable properties, which are the prerequisites to understand biomaterials. The orthopedic biomaterials, their classification and the importance of calcium phosphate (CaP) materials for hard-tissue applications were utterly discussed. Furthermore, among the various CaP biominerals, the importance of hydroxyapatite (HAP) and its synthesis techniques was comprehensively reviewed. The sol–gel route for the synthesis of HAP nanoparticles and deposition of coatings were systematically studied. Among the metallic substrates, Ti6Al4V alloy remained the focus of this study. Moreover, several film pre-preparation methods were also given due importance. The importance of other surface modification techniques, especially in the context of Ti6Al4V substrates, was also discussed. Among several coating techniques to deposit CaP coatings, special attention was paid to the spin and dip coating techniques. In addition to monolithic HAP coatings, reinforced and antimicrobial HAP coatings were also reviewed from broad perspectives. Therefore, this review provides an in-depth insight into the preparation and properties of apatitic nanoparticles and their coatings for orthopedic and dental applications. [ABSTRACT FROM AUTHOR]

This review summaries more than three decades of scientific knowledge on electrodeposition of calcium phosphate coatings. This low-temperature process aims to make the surface of metallic bone implants bioactive within a physiological environment. The first part of the review describes the reaction mechanisms that lead to the synthesis of a bioactive coating. Electrodeposition occurs in three consecutive steps that involve electrochemical reactions, pH modification, and precipitation of the calcium phosphate coating. However, the process also produces undesired dihydrogen bubbles during the deposition because of the reduction of water, the solvent of the electrolyte solution. To prevent the production of large amounts of dihydrogen bubbles, the current density value is limited during deposition. To circumvent this issue, the use of pulsed current has been proposed in recent years to replace the traditional direct current. Thanks to breaking times, dihydrogen bubbles can regularly escape from the surface of the implant, and the deposition of the calcium phosphate coating is less disturbed by the accumulation of bubbles. In addition, the pulsed current has a positive impact on the chemical composition, morphology, roughness, and mechanical properties of the electrodeposited calcium phosphate coating. Finally, the review describes one of the most interesting properties of electrodeposition, i.e., the possibility of adding ionic substituents to the calcium phosphate crystal lattice to improve the biological performance of the bone implant. Several cations and anions are reviewed from the scientific literature with a description of their biological impact on the physiological environment. [ABSTRACT FROM AUTHOR]

The eclipse type pulsed-laser deposition (PLD) scheme as a droplet-eliminated method with irradiation on a β-tricalcium phosphate (β-TCP) slab target was employed to achieve high density without holes, high purity, and high crystallinity hydroxyapatite (HAp) coating on a zirconia substrate with a low annealing temperature under an H2O vapor pressure. An obstacle ball was set between the target and the substrate so that ablated droplets would collide with the ball and be eliminated, while other ablated atoms went around the ball and were deposited on the substrate. A flat, transparent, and high-density coating layer was deposited on the substrate in an H2O vapor atmosphere at 0.1 Torr for different substrate surface temperatures from 20 °C to 650 °C. The phase of the coating layers was significantly changed from amorphous calcium phosphate to crystalline HAp when the temperature was set to over 360 °C, as determined from Raman microscopy measurements. Raman spectroscopy also showed that the HAp crystal size became larger as the temperature was increased to over 360 °C. It was concluded that the eclipse type PLD method with irradiation on a β-TCP target would improve the quality of HAp coatings and allow effective lowering of the annealing temperature. [ABSTRACT FROM AUTHOR]

Type AISI 316 L Stainless Steel (316 L SS) plays a crucial role in bone replacement surgery due to its excellent mechanical features, availability at low cost, and ease of fabrication, but its performance is low when in contact with the aggressive conditions of the human body fluids. Chitosan (CTS) is a biopolymer that blended with hydroxyapatite (HAp) could form coatings to improve surface properties of a metallic orthopedic prosthesis, i.e., corrosion-resistance to the base metal and biocompatibility of the ceramic on the metal surface. This work aims to obtain and evaluate HAp/CTS composite coatings deposited on the surface of AISI 316 L SS substrate by electrophoretic deposition (EDP) technique. The influence of the time of deposition on the coating's characteristics and properties was characterized and discussed. The coatings were structural, elemental, and chemically characterized using X-Ray diffraction and Raman spectroscopy. HV values in a range of 64.7 to 111.5 were observed, showing the lowest HAp/CTS-30.0 coating values for all the loads applied. The lowest HV value was nearby to the reported value for human bone's hardness, around 47HV; considering that the coating will be in constant contact motion with the bone surface, the contact with a softer surface could decrease the wear on the human bone. The hardness decreases with the coating thickness's increment because the coating presented a higher plastic deformation than the 316 L SS surfaces. A decrease in the roughness average (Ra) was well noticed as the deposition time increased; meanwhile, the thickness increased as the deposition time increased. [ABSTRACT FROM AUTHOR]

We have studied the feasibility of improving the functionality of composite titanium implants by modifying their oxidized surface with the aim of imparting it bioactive properties. The growth of a structured calcium silicophosphate layer on an oxidized titanium surface by a sol–gel process has been shown to significantly change its morphology, ensuring porosity and a specific surface area as large as 18.0 ± 0.5 m2/g. Owing to the sol–gel derived film, the surface of the titanium coating acquires hydrophilicity, as well as adsorption and chemical activity, due to surface centers having an excess charge: SiO–Hδ+ and Si–OHδ–. Interaction of the surface with an SBF solution leads to the formation of amorphous and crystalline calcium phosphates on it. Our results suggest that oxidized titanium implants coated with a sol–gel derived film will exhibit bioactive behavior under the conditions of a living organism. [ABSTRACT FROM AUTHOR]

Purpose: Titanium dental implants have a high success rate; however, there are instances when a modified surface may be desirable. The aim of this article was to systematically review the different types of implant coatings that have been studied clinically, in vivo and in vitro, and the coating techniques being implemented. Materials and Methods: The literature was searched electronically and manually through The Cochrane Library, Medline, and PubMed databases to identify articles studying dental implant surfaces and coating techniques. The database search strategy revealed 320 articles, of which 52 articles were considered eligible--40 in relation to implant coatings and 12 to the coating technique. An additional 30 articles were retrieved by hand search. Results: Several materials were identified as possible candidates for dental implant coatings; these include carbon, bisphosphonates, bone stimulating factors, bioactive glass and bioactive ceramics, fluoride, hydroxyapatite (HA) and calcium phosphate, and titanium/titanium nitride. HA coatings still remain the most biocompatible coatings even though the more innovative bioglass suggests promising results. The most common coating techniques are plasma spraying and hydrocoating. More recent techniques such as the nanoscale technology are also discussed. Conclusions: Several implant coatings have been proposed, and some appear to give better clinical results and improved properties than others. Clinical trials are still required to provide compelling evidence-based results for their long-term successful outcomes. [ABSTRACT FROM AUTHOR]

A firm connection of the bone-implant-fixation system is of utmost importance for patients with cranial defects. In order to improve the connection reliability, the current research focuses on finding the optimal fixation method, as well as selection of the implant manufacturing methods and the used materials. For the latter, implementation of bioactive materials such as hydroxyapatite or other calcium phosphates has also been considered in the literature. The aim of this study was to investigate the effect of gradual osseointegration on the biomechanical performance of cranial Ti6Al4V implants with a deposited HA coating as the osseointegration agent. This effect was assessed by two different computational approaches using finite element method (FEM) modeling. The values of key input parameters necessary for FEM were obtained from experimental plasma spray deposition of HA layers onto Ti6Al4V samples. Immediately upon implantation, the HA layer at the bone-implant contact area brought only a slight decrease in the values of von Mises stress in the implant and the micro-screws when compared to a non-coated counterpart; importantly, this was without any negative trade-off in other important characteristics. The major benefit of the HA coatings was manifested upon the modeled osseointegration: the results of both approaches confirmed a significant reduction of investigated parameters such as the total implant displacements (reduced from 0.050 mm to 0.012 mm and 0.002 mm while using Approach I and II, respectively) and stresses (reduced from 52 MPa to 10 MPa and 1 MPa) in the implanted components in comparison to non-coated variant. This is a very promising result for potential use of thermally sprayed HA coatings for cranial implants. [ABSTRACT FROM AUTHOR]

Phosphate coatings have been produced by plasma-spraying hydroxyapatite (HA) and tricalcium phosphate (TCP) powders onto Ti substrates at initial temperatures of 20, 300, and 550°C, followed by hydrothermal treatment (HTT) at 650°C, and the variation in the phase composition of the coatings has been examined in relation to the phase composition of the plasma-sprayed powders: 100 wt % HA, 100 wt % α‑TCP, and 100 wt % β-TCP. The as-prepared coatings produced by plasma-spraying the HA powder consisted of 87–91 wt % HA and 9–13 wt % CaO, and after HTT their phase composition was 89–93 wt % HA and 7–11 wt % CaO. The coatings produced by plasma-spraying the α-TCP powder at initial substrate temperatures from 20 to 550°C consisted entirely of a crystalline α-TCP phase. The coatings produced by plasma-spraying the β-TCP powder consisted of both β-TCP and α-TCP, and the content of the latter phase decreased from 100 to 80% as the substrate temperature was raised from 20 to 550°C. After HTT, the coatings contained 26–28% HA, independent of the phase composition of the starting TCP powders. [ABSTRACT FROM AUTHOR]

Hydroxyapatite (HAP) is one of the most attractive calcium phosphates which is used for different applications. While HAP has been mostly synthesized using wet methods, recently solid‐state synthesis methods have attracted more attention. Many efforts have been made to better understand the solid‐state synthesis mechanism. In this study, the kinetics of the solid‐state reaction between hydroxide calcium (Ca(OH)2) and phosphorus pentoxide (P2O5) was studied under nonisothermal conditions using isoconversional methods. The phase analysis revealed that HAP is the main product of this process with no impurity. Thermogravimetric (TG) curves were recorded at four heating rates (β = 5, 10, 12 and 15°C⋅min−1) and analyzed by several well‐known isoconversional methods. Activation energy values were determined for each extent of reaction, which varied from ∼139 to 100 kJ/mol at the reaction extent of 0.1–0.9. Comparison between activation energy values obtained by isoconversional methods revealed that Flynn–Ozawa–Wall and Vyazovkin's method are more accurate than other. The preexponential factor and the reaction model were determined through model‐free methods. The obtained results indicated that the reaction mechanism was chemically controlled or ordered‐based model. Furthermore, the results showed that formation of HAP does not depend on the heating rate; however, it proceeds with increasing temperature. [ABSTRACT FROM AUTHOR]

Objectives: The aim of this study is to evaluate the effect of pH treatment on the formation of hydroxyapatite (HA) coating layer and the biodegradation rate of hydroxyapatite coated AZ31 alloy for applications in biodegradable implants. Methods: HA was grown on the surface of AZ31 substrate at three different pH solutions of 7.5, 9.0, and 10.5 respectively by chemical solution treatment method. The coated samples were evaluated their biodegradation behavior by immersion test in the simulated body fluid (SBF) for 14 days. The biodegradation rate of the samples during immersion test was observed by Mg2+ ion quantification method and measuring the increase of pH of the medium. Results: HA coatings were successfully grown on the AZ31 substrate at three different pH conditions. The sample coated at pH 7.5 showed its uniform and dense coating layer resulted in highest corrosion resistance. While the highest biodegradation rate was observed for the sample coated at pH 10.5 due to many micro-cracks formed in the HA layer. After 14 days of immersion, Mg(OH)2 and calcium phosphate were corrosion products on the surface of the specimens coated at pH 10.5 and pH 9.0 respectively. While HA almost remained on the surface of sample coated at pH 7.5. Conclusion: AZ31 alloy coated with HA at pH 7.5 has lowest biodegradation rate and become suitable for applications in biodegradable implants. [ABSTRACT FROM AUTHOR]

A possibility in principle is determined for the titanium surface functionalization by oblique sputtering of nanostructured bioactive calcium phosphate coatings. The coatings are deposited by the RF magnetron sputtering of the targets based on hydroxyapatite and antibacterial zinc-substituted hydroxyapatite. The coating morphology and their growth characteristics are studied as a function of such process parameters as the specimen tilt angle with respect to the particle flux from the source, the supplied power, and the distance from the target plane to the specimen surface. As the tilt angle is increased, the coating surface morphology significantly changes and represents nanosized structural elements oriented towards the particle source and ordered in accordance with the substrate surface morphology prior to sputtering. The inner coating structure consists of columnar elements tilted to the substrate plane. [ABSTRACT FROM AUTHOR]

Biphasic hydroxyapatite/β-tricalcium phosphate foams were prepared using the replication technique starting from a precipitated hydroxyapatite (Ca 10 (PO 4) 6 (OH) 2 : HAP) powder, and sodium glycerophosphate (GP). The effect of the grinding time, solid loading, dispersant amount, and etching, replication, and sintering processes were investigated. The SEM, OEM and FTIR analyses proved that the surface of the polyurethane template must be treated with NaOH solution to make it more hydrophilic prior to the coating process. With a solid loading of 40 wt-%, the slurries prepared from the precipitated hydroxyapatite presented a shear thinning behavior, which was useful for the coating process. The SEM analysis of the foams showed that the optimum number of coating layers to obtain foam with an identical structure with the template was limited to three. The use of GP and the optimized preparation parameters helped to decrease the consolidation temperature of the ceramic foams to 1000 °C. The XRD and FTIR analyses of the prepared foams showed that the thermal treatment of the GP and the HAP mixture led to a partial decomposition of the HAP to tricalcium phosphate. The fitting of the XRD patterns and the obtained lattice parameters proved that the decomposition was accompanied by the insertion of sodium from GP toward the lattice of tricalcium phosphate and the formation of Na-β-tricalcium. The results of the SEM analysis, the pore size distribution and the mechanical strength showed that the presence of the Na-β-tricalcium reduced the pore size distribution from 500-2700 to 100–1700 μm, decreased slightly the total porosity from 80 vol-% to 70 vol-%; and improved the mechanical strength of the obtained foam from 1.56 MPa to 2.60 MPa. [ABSTRACT FROM AUTHOR]

The prospect of modifying the surface properties of the substrate (or base) material to enhance its corrosion and wear resistance as well as its reliability, performance, and more importantly its bioactivity is made possible using nanocoatings. An effective technique of synthesizing high purity nanocoatings in addition to nanopowders and fibers is to utilize the sol‐gel approach. It is an attractive and versatile method that can be carried out with relative ease. Ceramic coatings, such as hydroxyapatite (HAp), can be fabricated through chemical means from solutions and consequently complex shapes can be coated economically. Given the fact that mixing takes place on the atomic scale, one of the key advantages of the sol‐gel technique is its capacity to produce homogeneous materials, and it has been shown that the mechanical properties of sol‐gel coatings are enhanced due to the presence of nanocrystalline grain structures. This review covers a brief insight into the recent application of HAp nanocoatings derived from sol‐gel technique. [ABSTRACT FROM AUTHOR]

Polymer-based scaffolds have already gained popularity in many biomedical applications due to convenient routes for fabrication and favourable structural, physicochemical and functional characteristics. However, polymeric scaffolds lack osteoconductivity and some synthetic polymers carry the risk of inflammatory response caused by degradation by-products. Those facts limit their practical use in bone tissue engineering. In this study, three-dimensional (3D) porous scaffolds from naturally derived polymer, namely regenerated cellulose, were prepared using a non-hydrolytic sol-gel and lyophilization techniques. To induce osteoconductive properties of the polymeric scaffolds, cuttlebone microparticles were immobilized and the surface coating was achieved via in vitro mineralization using 10-fold concentrated simulated body fluid (10x SBF). Biogenic activity of cuttlebone is explained by its chemical composition, which includes polysaccharide β -chitin and macro-, micro- and trace elements favourable for mineralization. Parallel the scaffolds were examined during long-term (24 weeks) in vitro mineralization in 1x SBF for the purpose to investigate apatite-forming ability of the scaffolds. A nice cauliflower-like structures and needle-like dents of the spherical aggregates, which are characteristic to hydroxyapatite precursors, were observed on the surface of cellulose/cuttlebone scaffolds by SEM. 10x SBF coating enhanced cell attachment to the scaffolds because SBF elements are known to increase bioactivity by inducing re-deposition of carbonate apatite crystallites on scaffold surface. Additionally, calcium and phosphate depositions were clearly observed on the developed scaffolds using von Kossa and Alizarin Red S staining. Proliferative and osteoconductive effects on the osteoblast-like MG-63 cells demonstrate the cellulose/cuttlebone scaffolds soaked in 10x SBF as a favourable material for bone tissue engineering. [ABSTRACT FROM AUTHOR]

Additive manufactured, porous bone implants have the potential to improve osseointegration and reduce failure rates of orthopaedic devices. Substantially porous implants are increasingly used in a number of orthopaedic applications. HA plasma spraying–a line of sight process—cannot coat the inner surfaces of substantially porous structures, whereas electrochemical deposition of calcium phosphate can fully coat the inner surfaces of porous implants for improved bioactivity, but the osseous response of different types of hydroxyapatite (HA) coatings with ionic substitutions has not been evaluated for implants in the same in vivo model. In this study, laser sintered Ti6Al4V implants with pore sizes of Ø 700 μm and Ø 1500 μm were electrochemically coated with HA, silicon-substituted HA (SiHA), and strontium-substituted HA (SrHA), and implanted in ovine femoral condylar defects. Implants were retrieved after 6 weeks and histological and histomorphometric evaluation were compared to electrochemically coated implants with uncoated and HA plasma sprayed controls. The HA, SiHA and SrHA coatings had Ca:P, Ca:(P+Si) and (Ca+Sr):P ratios of 1.53, 1.14 and 1.32 respectively. Electrochemically coated implants significantly promoted bone attachment to the implant surfaces of the inner pores and displayed improved osseointegration compared to uncoated scaffolds for both pore sizes (p<0.001), whereas bone ingrowth was restricted to the surface for HA plasma coated or uncoated implants. Electrochemically coated HA implants achieved the highest osseointegration, followed by SrHA coated implants, and both coatings exhibited significantly more bone growth than plasma sprayed groups (p≤0.01 for all 4 cases). SiHA had significantly more osseointegration when compared against the uncoated control, but no significant difference compared with other coatings. There was no significant difference in ingrowth or osseointegration between pore sizes, and the bone-implant-contact was significantly higher in the electrochemical HA than in SiHA or SrHA. These results suggest that osseointegration is insensitive to pore size, whereas surface modification through the presence of an osteoconductive coating plays an important role in improving osseointegration, which may be critically important for extensively porous implants. [ABSTRACT FROM AUTHOR]

Calcium phosphate (CP)-based biomaterials, especially nanostructured ones, show a high biocompatibility and increased biological properties. The coatings composed of stoichiometric hydroxyapatite have been extensively used to improve integration of metallic implants in the host bone. However, these coatings exhibited several drawbacks that limited their successful application. It was concluded in numerous articles that the sol-gel derived coatings can undergo cracking and delamination and are scarcely uniform. In this review article the recent advances on the sol-gel synthesis of different phosphate coatings and thin films are summarized. The attention is paid to coatings and thin films of calcium hydroxyapatite (CHAp), other phosphates, bioglasses and different composite materials. The state of the art, limitations, potentialities, open challenges, and the future scenarios for the application of CP bioceramics are highlighted in this study. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study was to investigate and compare bone formation on titanium implant surfaces coated with biomimetically deposited calcium phosphate (BDCaP) or electrochemically deposited hydroxyapatite (EDHA). Materials and Methods: The implants were separated into three groups: a control group, a BDCaP group, and an EDHA group. Surface analysis was performed by field-emission scanning electron microscopy, x-ray diffractometry, and Fourier transform infrared spectroscopy. Implants were inserted in a randomized arrangement into rabbit tibiae. After 2, 4, and 8 weeks, the tibiae were retrieved and prepared for histomorphometric evaluation. Results: Field-emission scanning electron microscopy showed that the BDCaP crystals were flakelike and the EDHA crystals were rodlike with a hexagonal cross section. X-ray diffractometric patterns and Fourier transform infrared spectroscopy spectra showed that the BDCaP coating consisted of HA and octacalcium phosphate, whereas the EDHA coating consisted of HA. Histologic observation showed that new bone on the EDHA-coated implant became mature after 4 weeks, while new bone on the control and BDCaP-coated implants was mature after 8 weeks. The EDHA implant showed significantly greater BIC and bone area compared to the control and BDCaP implants during 4 to 8 weeks. The BDCaP coating failed to show increased bone formation during the test period. Conclusion: The present EDHA coating has good bone formation properties, while the BDCaP coating has weaker bone formation properties. [ABSTRACT FROM AUTHOR]

Purpose: The aim of this study was to evaluate the formation of a hydroxyapatite coating on titanium plate by discharging in typical and modified artificial body fluids. Materials and Methods: Japanese Industrial Standard Grade 2 titanium plates were used as specimens. Discharging was performed on the specimens in each solution, and the surface topography of each coating was observed with a scanning electron microscope. The Ca/P atomic ratio and surface characterization of each coating were evaluated by x-ray photoelectron spectroscopy, and crystal phases of each coating were analyzed by Fourier transform infrared spectroscopy and x-ray diffraction. Results: Tricalcium phosphate formed on the titanium surface in a 1.5 Ca/P solution with high ion concentrations of calcium (2.5 mmol/L) and phosphorous (1.67 mmol/L). Crystalline HA was formed on the titanium surface in a 1.5 Ca/P solution (Hanks' balanced salt solution without organic molecules) with low ion concentrations of calcium (1.26 mmol/L) and phosphorus (0.83 mmol/L). Discussion: A solution containing organic pH buffer was insufficient to form stable coatings on the titanium surface. Coating properties strongly depended on the Ca/P chemical ratio of the applied solution. A Ca/P ratio of 1.5 was appropriate for preparing a calcium phosphate coating on a titanium surface, whereas a Ca/P ratio of 2.5 was excessively high. Conclusion: These findings suggest that Hanks' balanced salt solution without organic molecules is the most suitable solution for forming crystalline hydroxyapatite coatings on titanium surfaces by the discharging method. [ABSTRACT FROM AUTHOR]

Purpose: The objective of this study was to evaluate the effect of radiofrequency- (RF) sputtered calcium phosphate (CaP) coating of titanium implants on bond strength at the bone-implant interface and percent bone contact length. Materials and Methods: Cylindric sputtered CaP-coated and plasma- sprayed hydroxyapatite- (HA) coated implants (4.0 mm diameter and 8 mm length) were implanted in dog mandibles. Half the sputtered CaP-coated implants were heat-treated. Results: Twelve weeks after implant placement, no statistical differences in the mean ultimate interfacial strengths were observed between as-sputtered CaP-coated, sputtered CaP-coated heat-treated, and control plasma-sprayed HA-coated implants. Histomorphometric evaluation indicated that the percent bone contact lengths for the plasma-sprayed HA-coated implants and the as-sputtered CaP-coated implants were similar and significantly greater than that for the sputtered CaP-coated heat-treated implants. Differences in the ultimate interfacial strength and percent bone contact length between different implant sites in the mandible were not observed. Discussion: The results of this study, considered together with the results of previous studies, suggest that once early osseointegration is achieved, biodegradation of the thin CaP coatings is not detrimental to bone-coating-implant fixation, and does not compromise bone responses to the coated implant surfaces. Conclusion: The interfacial strength and histomorphometric data suggest that the CaP coatings applied using the sputtering process produce bone responses similar to those of HA coatings applied using plasma spraying. [ABSTRACT FROM AUTHOR]

• Hydroxyapatite and brushite coatings are prepared by temperature substrate deposition. • Ti6Al4V substrate was pretreated by the plasma electrolytic oxidation (PEO). • PEO coatings have high corrosion resistance, strong bond with the surface. • Hydroxyapatite and brushite provide the bioactivity of the coatings. Hydroxyapatite (HA) and brushite (DCPD) coatings were prepared on plasma electrolytic oxidation (PEO)-treated Ti6Al4V substrates using thermal substrate deposition (TSD) technology. For the deposition of calcium phosphate (CaP) coatings of different phase compositions, the temperature-dependent solubility phenomenon of calcium orthophosphates at a fixed solution pH was used. DCPD and calcium-deficient HA (Ca/P = 1.64) coatings were obtained at substrate temperatures of 85 °C and 140 °C, respectively. For 30 min of deposition, a 300 μm thick HA coating consisting of both needle- and plate-shaped crystals of 4 μm and a 50 μm thick DCPD coating with needle-like crystals of 7 μm were obtained. Porous morphologies were characteristic of both coatings. [ABSTRACT FROM AUTHOR]

Hydroxyapatite (HA) is widely used as surface coatings on biomedical metal implants because of its excellent biocompatibility and osteoconductivity. In this study, HA coatings were deposited onto Ti-6Al-4V substrates by micro-plasma spraying and then heat treated at 650 °C in a muffle furnace for 3 h and 6 h. XRD results showed that, the HA peaks were sharper than those of corresponding as-sprayed coatings and the amorphous diffuse background was reduced after heat treatment. The transformation from impurity phases such as tetra-calcium phosphate (TTCP) and tri-calcium phosphate (TCP) and amorphous calcium phosphate (ACP) to crystalline HA occurred during the heat treatment. Moreover, the texture intensity was not increased during the re-crystallization of ACP and the transformation of impurity phases into HA. The SEM results showed that nanograins were formed on the coating surface. In addition, with the increase of the holding time, the nanograins become coarse. • Three kinds of HA coatings with different phase structure were fabricated by micro-plasma spraying. • The effect of heat treatment on the crystallinity, microstructure and surface morphology of HA coatings was investigated. • After heat treatment, nanograins of HA were formed on the coating surface and the nanograins became coarse with the increase of the holding time. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Coatings based on ion-substituted calcium phosphate (Ca-P) have attracted great attention in the scientific community over the past decade for the development of biomedical applications. Among such Ca-P based structures, hydroxyapatite (HA) has shown significant influence on cell behaviors including cell proliferation, adhesion, and differentiation. These cell behaviors determine the osseointegration between the implant and host bone and the biocompatibility of implants. This review presents a critical analysis on the physical vapor deposition magnetron sputtering (PVDMS) technique that has been used for ion-substituted Ca-P based coatings on implants materials. The effect of PVDMS processing parameters such as discharge power, bias voltage, deposition time, substrate temperature, and post-heat treatment on the surface properties of ion-substituted Ca-P coatings is elucidated. Moreover, the advantages, short comings and future research directions of Ca-P coatings by PVDMS have been comprehensively analyzed. It is revealed that the topography and surface chemistry of amorphous HA coatings influence the cell behavior, and ion-substituted HA coatings significantly increase cell attachment but may result in a cytotoxic effect that reduces the growth of the cells attached to the coating surface areas. Meanwhile, low-crystalline HA coatings exhibit lower rates of osteogenic cell proliferation as compared to highly crystalline HA coatings developed on Ti based surfaces. PVDMS allows a close reproduction of bioapatite characteristics with high adhesion strength and substitution of therapeutic ions. It can also be used for processing nanostructured Ca-P coatings on polymeric biomaterials and biodegradable metals and alloys with enhanced corrosion resistance and biocompatibility. Statement of Significance Recent studies have utilized the physical vapor deposition magnetron sputtering (PVDMS) for the deposition of Ca-P and ion-substituted Ca-P thin film coatings on orthopedic and dental implants. This review explains the effect of PVDMS processing parameters, such as discharge power, bias voltage, deposition time, substrate temperature, and post-heat treatment, on the surface morphology and crystal structure of ion-substituted Ca-P and ion-substituted Ca-P thin coatings. It is revealed that coating thickness, surface morphology and crystal structure of ion-substituted Ca-P coatings via PVDMS directly affect the biocompatibility and cell responses of such structures. The cell responses determine the osseointegration between the implant and host bone and eventually the success of the implants. [ABSTRACT FROM AUTHOR]

Abstract In this study, a high power fibre laser was used to synthesize titanium hydroxyapatite composite coating over biomedical-grade Nitinol surface through laser in-situ formation, cladding and alloying processes. The laser fluence is varied in the range of 2 kJ/cm2 to 8 kJ/cm2 in view of establishing a relationship between various in-situ phase-formation characteristics along with the rate of diffusion of the base material in the cladding zone with molten pool temperature. The alloying with base Nitinol material and subsequent diffusion of titanium to the in-situ formed calcium phosphate cladding layer are observed in the samples treated with laser fluence of 4 kJ/cm2 or above. Double layer configuration of the solidified molten pool is mostly found in all the cladding samples. At the fluence of 6 kJ/cm2 or above, the top layer primarily comprises segregated titanium-hydroxyapatite phase along with diffusion of titanium from the base material. Whereas, the bottom part of the molten pool is dominated with titanium-rich nickel–titanium intermetallic reinforced with nano particles. The steady-state variations of calcium and elemental presence of titanium through the cladding cross-section along with no nickel or oxide presence are confirmed through EDS line scans. The spherical and lamellar structures of formation of titanium-hydroxyapatite on the top surface also help to improve the overall corrosion resistance properties as compared to the bare surface. The modulus of elasticity is controlled by the variation of the top layer and intermediate layer composition and thickness, which varies with laser fluence. It falls in the range of 6–30 GPa which is similar to natural bone. Thus this nickel-free alloying and cladding layer of titanium-hydroxyapatite can serve as one of the potential candidates for use as a coating over the load bearing Nitinol implants to arrest the nickel release phenomena. Graphical abstract Unlabelled Image Highlights • Nickel free titanium–calcium phosphate coating developed through laser cladding • Layer composition and microstructure directly dependent on input laser fluence • Migration of titanium from base layer to clad layer is observed. • Clad surface exhibits high corrosion resistance compared to bare Nitinol. • Surface modulus of elasticity is found in 6–30 GPa range, similar to natural bone. [ABSTRACT FROM AUTHOR]

The bioactivity of zirconia in osseous-implant applications has been debated widely. Acid etching, grit blasting, etc. , were employed to improve the microroughness and osseointegration. Coating of calcium phosphate minerals, which are established for metals like titanium is not compatible with zirconia and suffers delamination. Here ceramic dough processing-based composite slurry having HAp and zirconia was explored to form a thin (~10 μm) gradient coating on a zirconia dental screw implant. The coating has a homogeneous distribution of secondary phase without affecting the fine machined features like threads. Further, the matrix is porous with increased roughness, but a minimal compromise on strength. During the scratch test, the coating survived a normal load >70 N using a diamond indenter without any significant spalling or delamination. Given the simplicity and versatility, this approach is compatible and a promising solution for currently available bio-inert zirconia implants. • Functional gradient coating of HAp + zirconia composite on zirconia dental implants fabricated by ceramic dough technique. • Uniform coating of <10 μm thickness, without disturbing the fine threads on root form dental implant. • Porous nature of the coating with minimal negative effect on the strength of the prosthesis. • Excellent scratch resistance owing to adherence by sintering to the substrate as well as retention of HAp's bioactivity. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Surface functionalization of teeth with fluoride-incorporated apatite layers displays great potential in treatments and prevention of dental disorders. In this study, we used a sintered hydroxyapatite (sHA) substrate as a model material of teeth, and established a rapid and area-specific coating technique of fluoride-incorporated apatite layers by using a laser-assisted biomimetic (LAB) process. In this technique, a sHA substrate was irradiated on the surface with a Nd:YAG pulsed UV laser for 30 min in supersaturated calcium phosphate (CaP) solutions with various fluoride concentrations. The fluoride concentration in the CaP solution was varied to control morphology, crystalline structure, and fluoride content of the resulting layers. Without fluoride in the CaP solution, an octacalcium phosphate (OCP) layer with a flake-like structure was formed on the laser-irradiated surface of the substrate. The addition of fluoride (1000 µM and 3000 µM) to the CaP solution led to the formation of fluoride-incorporated apatite layers with an enamel-like needle-like nanostructure. The fluoride-incorporated apatite layers adhered firmly to the sHA surface and reduced acid dissolution of the sHA substrate by acting as a protective covering. Additionally, the layers released fluoride ions for more than 24 h, and exhibited antibacterial activity relative to a caries-causing bacterium, namely Streptococcus mutans. Thus, our LAB process can potentially act as a new tool for functionalization of tooth surfaces. Statement of Significance We used a sintered hydroxyapatite (sHA) substrate as a model material of teeth, and established a rapid and area-specific coating technique of fluoride-incorporated apatite layers on the sHA surface by using our laser-assisted biomimetic (LAB) process. In this process, pulsed laser was utilized to accelerate seeded crystal growth in supersaturated calcium phosphate solutions supplemented with NaF. The thus-fabricated fluoride-incorporated apatite layers consisted of enamel-like needle-like nanocrystals with c -axis orientation. These fluoride-incorporated apatite layers adhered firmly to the sHA surface, reduced acid dissolution of the sHA substrate by acting as a protective covering, and exhibited antibacterial activity against Streptococcus mutans through the fluoride release. Thus, our LAB process can potentially act as a new tool for functionalization of tooth surfaces. [ABSTRACT FROM AUTHOR]