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Polymer 3D printing has is used in a wide range of applications in the medical field. Polyamide 12 (PA12) is a versatile synthetic polymer that has been used to reconstruct bony defects. Coating its surface with calcium phosphate compounds, such as hydroxyapatite (HA), could enhance its bonding with bone. The aim of this study was to coat 3D-printed polyamide 12 specimens with hydroxyapatite by a simple innovative surface treatment using light-cured resin cement. Polyamide 12 powder was printed by selective laser sintering to produce 80 disc-shaped specimens (15 mm diameter × 1.5 mm thickness). The specimens were divided randomly into two main groups: (1) control group (untreated), where the surface of the specimens was left without any modifications; (2) treated group, where the surface of the specimens was coated with hydroxyapatite by a new method using a light-cured dental cement. The coated specimens were characterised by both Fourier transform infrared spectroscopy (FTIR) and Transmission Electron Microscopy (TEM), (n = 10/test). The control and treated groups were further randomly subdivided into two subgroups according to the immersion in phosphate-buffered saline (PBS). The first subgroup was not immersed in PBS and was left as 3D-printed, while the second subgroup was immersed in PBS for 15 days (n = 10/subgroup). The surfaces of the control and treated specimens were examined using an environmental scanning electron microscope (SEM) and energy dispersive X-ray analysis (EDXA) before and after immersion in PBS. Following the standard American Society for Testing and Materials (ASTM D3359), a cross-cut adhesion test was performed. The results of the FTIR spectroscopy of the coated specimens were confirmed the HA bands. The TEM micrograph revealed agglomerated particles in the coat. The SEM micrographs of the control 3D-printed polyamide 12 specimens illustrated the sintered 3D-printed particles with minimal porosity. Their EDXA revealed the presence of carbon, nitrogen, and oxygen as atomic%: 52.1, 23.8, 24.1 respectively. After immersion in PBS, there were no major changes in the control specimens as detected by SEM and EDXA. The microstructure of the coated specimens showed deposited clusters of calcium and phosphorus on the surface, in addition to carbon, nitrogen, and oxygen, with atomic%: 9.5, 5.9, 7.2, 30.9, and 46.5, respectively. This coat was stable after immersion, as observed by SEM and EDXA. The coat adhesion test demonstrated a stable coat with just a few loose coating flakes (area removed <5%) on the surface of the HA-coated specimens. It could be concluded that the 3D-printed polyamide 12 could be coated with hydroxyapatite using light-cured resin cement. [ABSTRACT FROM AUTHOR]

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]

Carbon fiber (CF) is one of ideal reinforcements to hydroxyapatite (HA) owing to its unique structure, excellent biocompatibility and high mechanical properties. However, the mechanical property of CF reinforced HA (CF/HA) composites cannot be effectively improved due to the mismatch in surface properties and thermal expansion coefficients between CF and HA. In order to solve the problems, nano-hydroxyapatite (nHA) coating with different thickness was fabricated on the CF surface. The effect of the coating thickness on mechanical property of nHA-coated CF/HA composites was studied by finite element analysis. The CF with proper nHA coating thickness was subsequently used to reinforce HA. The compressive strength of nHA-coated CF/HA composites was approximately 97.3 % and 164.6 % higher than those of the uncoated CF/HA composites and pure HA ceramics, respectively. The interface properties and crack propagation were analyzed by cohesive element in the finite element analysis. The toughening mechanism of the composites included interfacial debonding, crack deflection, crack branching, and crack bridging. The mechanical properties of nHA-coated CF/HA composites were enhanced due to the strong interfacial bonding strength and reducing cracking in HA matrix. The prepared nHA-coated CF/HA composites satisfy the requirement of the mechanical properties of human load-bearing bone. It can be used to prepare cages, plates, screws, pins and other compact bone substitute parts in bone grafting. The study provided a method for construction of nHA-coated CF/HA composites with the designed properties by adjusting the nHA coating on the fiber and can be used to design other fibers reinforced ceramic matrix composites. [Display omitted] [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]

Despite of possessing very high biocompatibility and osteointegrating properties, HAp exhibits poor mechanical strength and cannot be used in high load-bearing areas. To improve the drawbacks of HAp, it can be either doped with polymeric material or can be coated on some substrate having high mechanical strength. Polymeric substances are known for their mechanical strength and non-toxicity. Addition of polymers in the HAp matrix enhances the properties of HAp. Poly methyl methacrylate (PMMA) is used as bone cement and possesses excellent antimicrobial properties. It is doped inside the HAp matrix to modify some of the drawbacks of HAp, such as brittleness, degeneration, the growth and spread of microbes and bacteria over time. α-Al2O3 was chosen because of its chemical inertness, high mechanical strength, resistant to corrosion, wear and tear. The present study focuses on the comparison of doping of PMMA in HAp and PMMA-doped HAp coating on α-Al2O3, which is being studied first time. The changes in the phase, surface morphology, corrosion resistance, optical contact angle and mechanical behaviour of both the coated and doped samples were studied. The hardness of the coated samples and the doped samples was found to be higher than the pure HAp samples. The dielectric properties of both the samples were studied, and it was observed that initially at lower frequency, the impedance of doped samples was lower in comparison to coated samples. Coated samples showed higher contact angle in comparison to doped samples. Clotting behaviour was studied using whole blood clotting method. [ABSTRACT FROM AUTHOR]

In this study, pure and 10% wt. Titania-Stabilised Zirconia (TiSZ) -reinforced Hydroxyapatite (HA) coatings were deposited on magnesium substrate using plasma spray as a single layer and double layer with an HVOF sprayed Ti bond coat. The coated specimens were characterised by X-ray diffraction (XRD) analysis, and scanning electron microscopy equipped with energy dispersive spectroscopy (SEM, EDS). Rockwell-C adhesion and scratch tests were performed. The corrosion behaviours in simulated body fluid (SBF) of coatings were investigated by an electrochemical corrosion test. Analyses confirmed successful coating with a dense titanium buffer layer. The double-layered HA-titanium combination offered superior corrosion resistance compared to single layers. While adding TiSZ enhanced adhesion, it compromised scratch resistance. The titanium bond coat had minimal impact on adhesion and cohesion behaviour of coatings. [ABSTRACT FROM AUTHOR]

This work studies the influence of the composition of an acetylene–oxygen explosive O2/C2H2 mixture on the structure and properties of hydroxyapatite coatings obtained by detonation spraying. The molar ratios of O2/C2H2 were 2.61; 3.03 and 3.35; the explosive charge was between 73 and 77%. The results of X-ray phase analysis showed partial conversion of the hydroxyapatite (HA) phase to the tricalcium phosphate (α-TCP) phase and formation of the amorphous phase during detonation sputtering. The formation of a small amount of the α-TCP phase during detonation spraying of HA is obviously due to structural transformations occurring during the heating of the material by detonation products. In addition, very rapid cooling of molten particles leads to the formation of the amorphous phase. The study results of the microstructure of the cross sections of the formed coatings, conducted using scanning electron microscopy, indicate that an increase in the O2/C2H2 ratio leads to increased porosity in the coatings. Additionally, an increase in the explosive charge by 77% results in the appearance of transverse cracks in the coating. [ABSTRACT FROM AUTHOR]

Low-modulus β-type Ti-45Nb alloy is a promising implant material due to its good mechanical biocompatibility, non-toxicity, and outstanding corrosion resistance. Its excellent chemical stability brings new challenges to chemical surface modification treatments, which are indispensable for both osteogenesis and antibacterial performance. Coatings containing metal ions as anti-microbial agents can be an effective way to reduce implant-associated infections caused by bacterial biofilm. Gallium ion (Ga3+) has the potential to reduce bacterial viability and biofilm formation on implant surfaces. In this study, a novel two-step process has been proposed for Ga3+ incorporation in hydroxyapatite (HAP) to develop bioactive and antibacterial surfaces on Ti-45Nb alloy. For the generation of bioactive surface states, HAP electrodeposition was conducted, followed by wet chemical immersion treatments in gallium nitrate (1 mM). Different buffers such as phosphate, sodium bicarbonate, ammonium acetate, and citrate were added to the solution to maintain a pH value in the range of 6.5–6.9. Coating morphology and HAP phases were retained after treatment with gallium nitrate, and Ga3+ ion presence on the surface up to 1 wt.% was confirmed. Combining Ga and HAP shows great promise to enable the local delivery of Ga3+ ions and consequent antibacterial protection during bone regeneration, without using growth factors or antibiotics. [ABSTRACT FROM AUTHOR]

Due to their biodegradable nature and enhanced adhesive strength at the interface, poly– (lactic acid) (PLA) based coatings are frequently used in biomedical alloys. But it is unable to create metal-tissue interaction because of its very hydrophobic surface feature. Researchers are therefore looking at composite coatings that are reinforced with hydroxyapatite (HA). In this study, the effect of halloysite nanotube (HNT) was investigated to hydroxyapatite (HA) reinforced PLA coatings synthesized on Ti–6Al–4V (Ti64) biomedical alloy. Investigations were conducted on the hybrid coatings' characterization such as SEM/EDS, FTIR, contact angle tests, and XRD analyses. Adhesion tests at alloy-coating interface were revealed with ASTM D3359–09 standards. In-vitro electrochemical corrosion tests (ASTM–G59) and immersion tests (ISO-23317) were conducted on coatings for reveal both biodegradability and osteoconductivity behaviours of coatings. SEM morphologies revealed that surfaces have micron-sized pores on both coatings. But HA/HNT reinforced coatings have more homogenous morphology with decreased pore size. The elemental distribution of coatings was confirmed by the EDS analyses. While FTIR research demonstrated a variation in the influence of HNT on the coating of PLA depending on the bond status, XRD results showed that there were no phase changes in the coatings. It was found that coatings with HNT reinforcement, have higher adhesion strength at the substrate-coating interface (1B for HA and 4B for HA/HNT reinforced coatings). Following in-vitro electrochemical corrosion experiments, it was discovered that the corrosion current density (Icorr) value reduced even more with the PLA/HA-HNT coating (1.784, 0.245, and 0.032 µA cm–1) than it did with the PLA/HA coating alone. The results of the impedance spectroscopy (Nyquist curves) confirmed that the coatings' corrosion resistance increased as the Icorr value decreased. Possible corrosion mechanism was discussed with equivalent circuit model which consist two–constant elements. It was found that both coatings exhibited a characteristic that induced calcium phosphates (CaPs) on their surfaces after in-vitro immersion tests. The contact angle tests revealed that the high hydrophobic effects of coatings would have a positive effect on the alloy–tissue interaction in the long term due to the bioactive compounds that they have. The dense and homogeneous CaPs in the PHH coatings increased with HNT reinforcement, leading to more effective interaction with surrounding tissues during in-vitro tests. The findings led to the conclusion that the hybrid coatings produced with the reinforcement of HA/HNT will not readily delaminate during application and will improve the interaction between the alloy and the tissue under prolonged physiological conditions. [ABSTRACT FROM AUTHOR]

The purpose of this review paper is to describe a noble approach, called Growing Integration Layers (GIL) method, for the application of biocompatible oxide ceramics layers coating on bulk metallic alloys. Since these oxides are utilizing component(s) of the alloy then formed by mostly electrochemical reactions at low temperatures, they are well adhered on the alloy substrate. The GIL strategy differs significantly from so-called layer-by-layer integration, layers are deposited from top-to-top. In the GIL, the oxide layers are produced and grown on the substrate alloy from the bottom. Therefore those layers on metallic substrate is chemically and structurally continuous thus shows excellent adhesion. Using GIL method, a variety of functional and structural ceramic layers can be processed mostly in aqueous solutions, thus they are typical soft and green processes, consuming low energy. These methods can be applied in the preparation of dense/porous and graded intermediate layers of ceramics for a wide variety of applications, including thermal, mechanical, chemical and biomedical. This review concentrate on successful ceramics coating on Titanium based metallic alloys via GIL strategy. The GIL technology improves the adhesion of ceramic layers and introduces bioactivity to bulk metallic alloys. Since bulk metallic glasses and alloys generally contain active components like titanium, it can be used in the formation of titanium oxide and/or hydroxides which are bioactive. During this oxidation/hydroxidation, widely diffused interfaces and continuously graded layers are formed from bulk substrate, even at ambient temperature and pressure. One of the most notable examples of GIL method is the coating of bio-active hydroxyapatite (HA) ceramics on Ti alloys. We have exhibited here with (1) Bioactive ceramic layers on bulk metallic glasses, (2) Hydroxyapatite-like coating on Ti–Cu–Sn alloy and (3) Sr doped apatite-like coating on the same alloy. [ABSTRACT FROM AUTHOR]

BACKGROUND: High density polyethylene has been widely used as a repair material for cranial and maxillofacial bone defects, but its preparation method and surface activity still need further improvement. OBJECTIVE: To optimize the preparation method of high density polyethylene and improve the surface activity of high density polyethylene. METHODS: The high density polyethylene scaffolds were prepared by extrusion 3D printing technology, and the scaffolds were immersed in dopamine solution and simulated body fluid successively to be coated with polydopamine and hydroxyapatite. The microstructure, hydrophilicity and compression modulus of the scaffolds before and after coating were characterized. Mouse embryonic osteogenic precursor cells (MC3T3-E1) and human umbilical vein endothelial cells were inoculated on the surface of the scaffold to evaluate the cytocompatibility and early osteogenic and angiogenic differentiation of the scaffold before and after coating. RESULTS AND CONCLUSION: (1) The 3D printed high density polyethylene scaffold’s fibers were arranged regularly and pores were uniform. Characterization results showed that polydopamine and hydroxyapatite coatings were successful on the surface of the scaffolds. Compared with the unmodified scaffold, the surface water contact angle of the scaffold modified with polydopamine coating and polydopamine + hydroxyapatite coating decreased significantly (P < 0.05), and the compressive modulus did not change significantly. (2) Compared with the unmodified scaffold, the modified scaffold with polydopamine coating and polydopamine + hydroxyapatite coating could promote the adhesion of MC3T3-E1 cells and human umbilical vein endothelial cells (P < 0.05). The cell adhesion promoting effect of double coating modified group was better than that of single coating modified group (P < 0.05). Compared with the unmodified scaffold, the modified scaffold with polydopamine coating and polydopamine + hydroxyapatite coating could promote the proliferation of MC3T3-E1 cells and human umbilical vein endothelial cells (P < 0.05). The proliferation promoting effect of double coating modified group was better than that of single coating modified group (P < 0.05). Compared with unmodified scaffolds, the scaffolds modified with polydopamine coating and polydopamine + hydroxyapatite coating could promote the osteogenic differentiation of MC3T3-E1 cells (P < 0.05), and increase the expression of angiogenic factor CD31 in human umbilical vein endothelial cells. The double-coating modified group was more obvious. (3) The results showed that the high density polyethylene scaffolds coated with polydopamine and hydroxyapatite based on 3D printing technology have good cytocompatibility and early osteogenic and angiogenic differentiation ability. [ABSTRACT FROM AUTHOR]

In this review paper, different methods of hydroxyapatite‐based coatings on external fixation pins with improvement in the adhesion strength are explained. Different coating methods such as dip coating, surface‐induced mineralization, plasma spraying, physical vapor deposition magnetron sputtering, micro‐arc oxidation, electrophoretic deposition, chemical vapor deposition, ion beam assisted deposition, sol‐gel dip coating, pulsed laser deposition, and electrohydrodynamic coating are investigated. The micro‐arc oxidation method showed high degradation delaying of the substrate with a high‐voltage electrolyte solution. Moreover, controlling the coating porosity by applying the gas is a good feature of the physical vapor deposition magnetron sputtering method. The comparison of the hydroxyapatite (HA) coatings method showed that the plasma spraying method leads to better coating features between the coating methods on the implant pins. [ABSTRACT FROM AUTHOR]

In order to improve the interfacial bonding at coating-substrate, a graphene oxide-hydroxyapatite (GH) coating was designed and constructed. The microstructure, bonding strength and in vitro bioactivity of the coating were analyzed. The results showed that GH coating presented uniform and crack-free structure with a flake morphology. The bonding strength of GH coating was 7.81 MPa, which is about 1.2 times that of pure hydroxyapatite coating. In vitro bioactivity test using simulated body fluid exhibited that GH coating processes the ability to induce apatite formation. The GH coating should have potential application in surface modification for biomedical materials. [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]

Hydroxyapatite coatings were deposited for 1, 2, and 3 h on NiTi substrates using plasma-assisted radio frequency sputtering. The matrix consisted of NiTi B2 and NiTi B19' phases and Ti2Ni, Ni3Ti, and Ni4Ti3 intermetallic compounds. The surface coating was monoclinic hydroxyapatite. Increasing the deposition time to 3 h made it possible to form a dense hydroxyapatite layer without visible defects. The phase contrast maps showed that the coating consisted of round grains of different fractions, with the smallest grains in the sample deposited for 3 h. The wettability tests showed that the coating deposited for 3 h had the highest surface energy, reflected in the proliferation density of the MCF-7 cell line. [ABSTRACT FROM AUTHOR]

Titanium (Ti) implants are widely used in medicine. Meanwhile, surface modification of Ti can strengthen the osseointegration of implants. In this study, we modified Ti implant surfaces, which was coated with GO, HA, HA-2wt%GO and HA-5wt%GO via electrophoresis deposition, to investigate their mechanisms and biological activity. Uncoated Ti was used as the control. Further, we examined the biological behavior and osteogenic performance of mouse bone marrow mesenchymal stem cells (BMSCs) cultured on coatings in vitro. We found that the HA-GO nanocomposite coating improved the roughness and hydrophilicity of the Ti surface. Compared with the uncoated Ti or Ti modified by HA or GO alone, cell adhesion and diffusion were enhanced on HA-GO-modified Ti surfaces. In addition, the proliferation and osteogenic differentiation of BMSCs in vitro were significantly improved on HA-GO-modified surfaces, whereas osteogenesis-related gene expression and alkaline phosphatase activity were slightly enhanced. Furthermore, we noted that bone regeneration was improved in the HA-2wt%GO group in vivo. Thus, the HA-2wt%GO nanocomposite coating might have potential applications in the field of dental implants. [ABSTRACT FROM AUTHOR]

Titanium (Ti) implants are widely used in medicine. Meanwhile, surface modification of Ti can strengthen the osseointegration of implants. In this study, we modified Ti implant surfaces, which was coated with GO, HA, HA- 2wt%GO and HA-5wt%GO via electrophoresis deposition, to investigate their mechanisms and biological activity. Uncoated Ti was used as the control. Further, we examined the biological behavior and osteogenic performance of mouse bone marrow mesenchymal stem cells (BMSCs) cultured on coatings in vitro. We found that the HA-GO nanocomposite coating improved the roughness and hydrophilicity of the Ti surface. Compared with the uncoated Ti or Ti modified by HA or GO alone, cell adhesion and diffusion were enhanced on HA-GO-modified Ti surfaces. In addition, the proliferation and osteogenic differentiation of BMSCs in vitro were significantly improved on HAGO- modified surfaces, whereas osteogenesis-related gene expression and alkaline phosphatase activity were slightly enhanced. Furthermore, we noted that bone regeneration was improved in the HA-2wt%GO group in vivo. Thus, the HA-2wt%GO nanocomposite coating might have potential applications in the field of dental implants. [ABSTRACT FROM AUTHOR]

Ti6Al4V substrates were electrochemically deposited with nano-crystalline hydroxyapatite (HA) from aqueous electrolytes. Cathodic HA coatings were obtained when the electrolyte was stirred using ultrasonic vibration. Two current densities of 20 mA/cm2 and 50 mA/cm2 were employed. Polarization and electrochemical impedance spectroscopy (EIS) were the techniques used to estimate the corrosion of coatings in simulated body fluid (SBF). The results indicate good corrosion resistance for the coating obtained at 50 mA/cm2 from ultrasonic stirring of the electrolyte. [ABSTRACT FROM AUTHOR]

The coating of hydroxyapatite (HAP) on the surface of bio-inert metallic implants to augment their bioactivity is in use for the last two decades. Substitution of various materials in HAP further improves the functionality of these coatings. We demonstrate coating of Ti6Al4V alloy sheets with strontium and niobium reinforced HAP using microwave (MW) irradiation technique. Physical characterization revealed, uniform semicrystalline hydroxyapatite coating with enhanced surface roughness and microhardness. The increased surface roughness was accompanied by higher wettability and more protein adsorption. Electrochemical corrosion assessment showed a dramatic increase in corrosion potential and a noticeable decline in corrosion current density suggesting an enhanced anticorrosive behaviour. These implants also exhibited improved hemocompatibility and bacteriostatic properties. Cell viability and confocal microscopy studies of the coated samples showed enhanced cell attachment on the surface. We propose microwave irradiation as a fast and hassle-free alternative for one-pot synthesis and deposition of ionic substituted HAP on metallic implants. [ABSTRACT FROM AUTHOR]

Ti-6Al-4V-ELI titanium alloy is useful in biomedical applications due to its mechanical characteristics. To improve properties, alloy surfaces was coated with various methods. In this work, titanium–hydroxyapatite(Ti-HA) composite coatings were deposited on Ti-6Al-4V-ELI through mechanical milling(MM). Coatings’ phase analysis, surface morphology, wear, corrosion, and in vitro performance were examined. The results show that average coating thickness varied between 190 and 305 µm. The substrate has a specific wear rate of 7.22×10−4 mm3/Nm, while Ti5HA has the lowest rate among composite coatings at 2.7×10−4 mm3/Nm. Coated surfaces demonstrated better corrosion resistance than bare substrate in electrochemical tests conducted in Ringer's and phosphate buffered saline (PBS) physiological solutions. Ti5HA has the lowest Icorr (0.119 μA/cm2) in Ringer's solution, while Ti10HA has the lowest Icorr (0.245 μA/cm2) in PBS solution. Apatite layer development was seen on all coated surfaces following 7 and 14 days of in vitro experiments. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hydroxyapatite (HA) coating was fabricated by flame spray technique (FS). • Synthesized nanohydroxyapatite powder was used directly without any granulation. • Hydroxyapatite and tricalcium phosphate (TCP) were present in the coatings. • Nano-sized hydroxyapatite formed after simulated body fluid (SBF) test for 7 days. • Porous structure enhanced bioactivity as resorption and nucleation rate increased. This research involves fabrication and characterization of flame sprayed hydroxyapatite (HA) coatings on 316 stainless steel substrates where the desirable structure with high porosity can be obtained. Nano-sized HA powder was synthesized and calcined at 600 °C. The subsequent powder was used as feedstock powder for flame spray technique (FS). In-flight particles of HA were spherical with the range of particle size between 3–37 µm. The average coating thickness was 128 µm and the crystalline phases were a mixture of HA and tricalcium phosphate (TCP). Simulated body fluid (SBF) test showed that HA layer was formed after 7 days. Highly bioactive properties were due to high surface area from rough coating and porous structure, which would be beneficial from the flame spray technique. The coating is promising for applications in biomedical field. [ABSTRACT FROM AUTHOR]

This work intended to elucidate, in an in vitro approach, the cellular and molecular mechanisms occurring during the bone healing process, upon implantation of a tailored degradable multifunctional Mg-based alloy. This was prepared by a conjoining anodization of the bare alloy (AZ31) followed by the deposition of a polymeric coating functionalized with hydroxyapatite. Human endothelial cells and osteoblastic and osteoclastic differentiating cells were exposed to the extracts from the multifunctional platform (having a low degradation rate), as well as the underlying anodized and original AZ31 alloy (with higher degradation rates). Extracts from the multifunctional coated alloy did not affect cellular behavior, although a small inductive effect was observed in the proliferation and gene expression of endothelial and osteoblastic cells. Extracts from the higher degradable anodized and original alloys induced the expression of some endothelial genes and, also, ALP and TRAP activities, further increasing the expression of some early differentiation osteoblastic and osteoclastic genes. The integration of these results in a translational approach suggests that, following the implantation of a tailored degradable Mg-based material, the absence of initial deleterious effects would favor the early stages of bone repair and, subsequently, the on-going degradation of the coating and the subjacent alloy would increase bone metabolism dynamics favoring a faster bone formation and remodeling process and enhancing bone healing. [ABSTRACT FROM AUTHOR]

Magnesium is a candidate metal for biodegradable implant applications for its biodegradation tendency and excellent biocompatibility. Unfortunately, the high degradation rate of magnesium and also its localized degradation in physiological conditions are the main issues for its successful implant applications. The degradation rate of magnesium has been reduced to some degree via alloying, but the localized degradation susceptibility is a great concern. For many years, hydroxyapatite (HAp), a biocompatible ceramic material, has been extensively used for bio-implant applications. Recently, a substantial amount of research has been carried out on coating HAp on magnesium-based materials for improved degradation resistance in particular and also to enhance the biocompatibility. This review article focuses on the different methods of HAp coating on magnesium-based materials and also the recent cutting-edge advancements made in the coating process for improved degradation resistance and biocompatibility. The mechanical stability of the HAp coated magnesium-based materials is also discussed. [ABSTRACT FROM AUTHOR]

The present study explores how the hydroxyapatite (HAp) nanoparticles could influence the surface properties of the electrophoretic ZnO/HAp composite coating on stainless steel SS316L substrate. Various weight dispersion of HAp nanoparticles (1.0 g/l, and 1.5 g/l) and applied voltage of 40 V and 50 V were applied during the deposition of the composite coatings. The ZnO/HAp composite coatings were characterized using field emission scanning electron microscopy (FESEM), x-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), contact angle, Vicker's hardness, surface profilometer, scratch tester, and atomic force microscopy (AFM) analyser. The composite coating with 1.5 g/l of HAp with an applied voltage of 40 V has exhibited a homogeneous distribution with higher coating thickness of 11.17 μm, and importantly, low porosity (< 0.94 %, which is <1 %). Crystal sizes increases from 19.2 to 28 nm when the applied voltage and weight dispersion of HAp is increased. FTIR analysis confirmed the higher deposition of polymeric groups in ZnO/HAp composite coatings irrespective to the weight dispersion and voltages. Furthermore, the higher dispersion of HAp has decreased the surface energy and roughness with optimum coating hardness. However, the better adhesion strength was achieved in comparison to the other composite coatings. The failures that occurred during the scratch test were further detailed in this study using the AFM and SEM. [Display omitted] • Electrophoretic deposition of ZnO/HaP composites on Stainless Steel 316L • Uniform deposition, compactness, and increased coating hardness • Increased hydrophilicity with lower surface energy is obtained. • The adhesive strength of ZnO/HaP composite coating is increased. [ABSTRACT FROM AUTHOR]

Upon implantation of biomaterials in human body, the risk for electrochemical corrosion within the surrounding environment becomes a critical factor affecting implant biocompatibility. This study endeavors to develop a biofunctionalized and corrosion-resistant TiO 2 /hydroxyapatite coating using a cost-effective one-step plasma electrolytic oxidation (PEO) process. Initially, magnesium and zinc substituted hydroxyapatite (HA) particles were synthesized to enhance bioactivity and antibacterial properties compared to pure HA. The synthesized particles underwent characterization using X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). Subsequently, these synthesized particles were utilized in the Plasma Electrolytic Oxidation (PEO) coating process. Polarization and electrochemical impedance spectroscopy (EIS) tests, in addition to bioactivity and antibacterial activity assessments, were conducted to examine the corrosion resistance and biological response of the coatings. The results of biological tests on particle-containing PEO coatings on titanium demonstrated a significant improvement in the bioactivity and antibacterial activity of the biofunctionalized coatings caused by ion-substituted HA particles. Furthermore, polarization and EIS results indicated superior corrosion resistance in the biofunctionalized coatings. Electrochemical tests after one week of immersion in simulated body fluid (SBF) revealed the positive influence of apatite formation on the long-term corrosion behavior of coatings with ion-substituted particles. [Display omitted] • Successful incorporation of Mg and Zn-substituted HA particles in the PEO coating. • Development of a biofunctionalized PEO coating using inexpensive DC power source. • A biofunctionalized coating improves corrosion resistance and biological response. • Improved long-term corrosion resistance of the PEO coating. [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]

BACKGROUND: With its excellent biocompatibility and osteoconductivity, hydroxyapatite is widely used as a material coating in tissue engineering, and its biological properties are strongly associated with the morphology caused by the manufacturing process. OBJECTIVE: To investigate the effects of plasma spraying and electrochemical deposition on the stent of hydroxyapatite coating on the proliferation, adhesion and osteogenic differentiation of bone marrow mesenchymal stem cells. METHODS: Hydroxyapatite coating was prepared on titanium stent using plasma spraying and electrochemical deposition. The titanium stent without coating was used as a control. Rat bone marrow mesenchymal stem cells were cocultured with three kinds of stents for 1, 3, 5, and 7 days. Cell proliferation was detected using CCK-8 assay for 5 days. Cell adhesion was observed using scanning electron microscope and confocal laser microscope. At 14 days, alkaline phosphatase staining was conducted; at 21 days, alizarin red staining was performed. At 14 and 21 days, real-time quantitative fluorescent polymerase chain reaction was conducted to analyze osteogenic differentiation of bone marrow mesenchymal stem cells. RESULTS AND CONCLUSION: (1) With the extension of the culture time, the cell proliferation rate of each group increased. The cell proliferation rate of the plasma spraying group was higher than that of the electrochemical deposition group and the control group (P < 0.05). (2) Scanning electron microscopy showed that cell adhesion was seen on the stents in the three groups. The plasma spraying group had the largest cell spreading area, and the control group had the smallest cell spreading area. The laser confocal microscope showed that the actin fibers in the plasma spraying group were the densest and the cells were in good extension; the electrochemical deposition group was relatively dense and the cells were in normal extension. In the control group, cytotactin was relatively sparse and the cells were not fully extended. (3) The alkaline phosphatase activity of the plasma spraying group was higher than that of the electrochemical deposition group and the control group, and calcium nodules were formed more than that of the electrochemical deposition group and the control group. (4) Real-time quantitative fluorescent polymerase chain reaction showed that the expression levels of osteopontin, type I collagen, osteocalcin and Runx2 mRNA in plasma spraying group were higher than those in electrochemical deposition group at the same time except that there was no difference between osteocalcin mRNA expression at 7 days and Runx2 mRNA expression at 14 days (P < 0.05). (5) The results showed that the morphology of plasma sprayed hydroxyapatite coating is more conducive to proliferation, adhesion and osteogenic differentiation of bone marrow mesenchymal stem cells. [ABSTRACT FROM AUTHOR]

Hydroxyapatite (HA) coating has been carried out on a titanium alloy Ti–29Nb–13Ta-4.6Zr (TNTZ) to improve the biocompatibility and bioactivity of the alloy in order to attain a high degree of osseointegration and low inflammatory reactions in bone tissue after implantation in orthopedic implant applications. The coating process was carried out using the electrophoretic deposition (EPD) method. TNTZ implants with and without HA coating were installed in the tibia of the Rattus norvegicus Wistar test rats; the test animals were then terminated after two weeks. The degree of osseointegration was measured using a removal torque tester, the Tumor Necrosis Factor-Alpha (TNF-α) level was measured by using the Enzyme-Linked Immunosorbent Assay (ELISA) method, and a histopathological analysis was carried out on the implanted tissue. TNTZ implants with HA coating exhibit significantly higher osseointegration compared to those without HA coating, whereas TNTZ implants without HA coating can trigger significantly higher TNF-α levels. Greater osteogenesis occurs in a bone tissue fitted with TNTZ implants with HA layers. The HA coating on the surface of the TNTZ implant can reduce excessive inflammation, enhance the osteogenesis process, and then improve osseointegration in the bone tissues of test animals. It is also expected to be suitable for orthopedic implant applications. [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]

In this research, the cell viability is tested on the surface-modified implants. Electrochemical setup is used for coating the hydroxyapatite (HA) powder and nano zinc particle (Zn)n on the Ti-6Al-4 V alloy. The electrolyte is prepared by mixing the HA and (Zn)n of varying quantity, and the effect of electrochemical parameter on surface coating thickness, surface quality and cell viability was studied. Based on the study, the cell viability is observed to be maximum at HA and (Zn)n concentration of 6 g/L and 0.8 g/L, respectively. The (Zn)n concentration in the range of 0.8 to 1.2 g/L and voltage of 12–13 V is suitable for obtaining the controlled coating thickness. During the electrochemical process, the nanopores HA structures with a pore size of 215–786 nm are obtained attributes for better cells attachment on the surface. The cell viability is found high (0.366) at 6 g/L HA and 1.6 g/L of (Zn)n concentration at 14 V. [ABSTRACT FROM AUTHOR]

The aim of this work was to synthesize hydroxyapatite (HAp) by sol–gel route using eggshell and triethyl phosphite as calcium and phosphorus precursors, respectively. After the preparation of homogeneous solution with aging period for 24 h, hydroxyapatite (HAp) sol–gel coatings were made on Ti6Al4V substrate. Polyethylene glycol (PEG) and triethanolamine (TEA) were added to HAp solution to enhance morphological structure of coatings. PEG- and TEA-added solutions and coatings were labeled as P-Hap and T-Hap, respectively. The coating process was carried out by spin coating method, and the coated samples were heated up to 600 °C for 1 h. Phase development of coatings and dried powder and morphologies of coatings upon heat treatment were detected by XRD and SEM, respectively. Thermal behavior of obtained powder were investigated with DTA/TGA. Surface roughness was determined by XP2 surface profilometer. It was found that all the samples at RT showed amorphous structure and transformed at 600 °C to well-crystallized HAp-phase with no β-TCP. Morphological results indicated that T-HAp coating showed the best morphology with crack-free uniform porous structure, which is necessary for biocompatible implants. P-HAp coating showed non-uniform porous structure with large cracks, whereby HAp coatings had similar structure to T-HAp coatings but with much less porosity. [ABSTRACT FROM AUTHOR]

Generally, the coating properties of polymeric compounds are enhanced by using nanomaterials as fillers which are non-biobased. In this project, the hydroxyapatite (HAP) was obtained from waste fish scales and the biobased hyperbranched polyol (HyBP) was synthesized from castor oil. The series of nanocomposites were prepared by adding various amounts of HAP (0.5% wt, 1% wt, and 2% wt) in HyBP along with isophorone diisocyanate (IPDI) (maintaining the NCO:OH, ratio at 1.2:1). These mixtures were coated on mild steel panels and glass plates. The synthesized HyBP was characterized by FTIR, 1HNMR, and 13CNMR techniques. The HAP was characterized by FTIR, FESEM, and XRD techniques. The surface morphology of prepared nanocomposites was studied by FESEM, XRD, and AFM techniques. The nanoparticle size was determined by TEM technique. The thermal behavior of nanocomposites was studied by TGA technique. The coating properties were determined by impact strength, crosscut adhesion, and flexibility test. The corrosion properties of the coatings were determined by the immersion test as well as electrochemical test. [ABSTRACT FROM AUTHOR]

Purpose: Recently, titanium (Ti) and its alloys have been widely used in dental and surgical implants in the last few decades. However, there is a loosening effect over a long period usage. Therefore, the present study aimed to increase life of an implant by its surface modification. Methods: In present study, sol-gel process has been applied to create tantalum pentoxide (Ta2O5) layer coating on Ti-substrate. In this technique, polyethylene glycol (PEG) plays an important role to form uniform porous coating, which can have potential application in formation of strong bonding to the natural bone. Results: Microstructural, elemental, structural and binding energy results showed that the material with 100% PEG-enhanced sol-gel Ta2O5 with spin coating onto Ti substrate followed by an optimized sintering temperature (500 °C) has better porous structure than that of 5% PEG-enhanced sol-gel Ta2O5 coating, and would be suitable for tissue in-growth properties. Conclusions: Therefore, it was concluded that the present spin coated 100% PEG-enhanced Ta2O5 coating onto Ti, having the most suitable morphology with enhanced roughness, could be noteworthy for potential tissue in-growth and it could provide desired bonding at the interface of Ti-implant coating and host tissues in biomedical applications. [ABSTRACT FROM AUTHOR]

Bone quality around dental endosseous implants is a key factor in implant prognosis. Surface coatings represent an important method to increase osseointegration in oral implantology. Newer titanium alloys such as Ti6Al7Nb are under research in order to replace the commonly used Ti6Al4V, for a better osseointegration, with lower risks. Hydroxyapatite (HA) is the most commonly used coating, but others such as SiO2-TiO2 are under development in search for a better biological response. In this study, screw-type Ti6Al7Nb, Ti6Al7Nb-HA, and Ti6Al7Nb-SiO2-TiO2 implants were placed into the femur of six New Zealand White Rabbits. Three months later, the samples were harvested and examined using Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDX). The results showed a better osseointegration of surface coated Ti6Al4Nb implants. No differences could be found between hydroxyapatite and SiO2-TiO2 coatings. These Ti6Al7Nb alloy coatings could be considered in the future for implant manufacturing. [ABSTRACT FROM AUTHOR]

Magnesium (Mg) as a potential material for biodegradable implants is attractive due to its mechanical similarity to the bone tissue and nontoxic corrosion products. However, the rapid corrosion rate of bare magnesium is associated with hydrogen release, which may complicate the healing process. The corrosion rate may be reduced by suitable alloying, but concurrently the biocompatibility of such alloy might be deteriorated. Another way of reduction of the corrosion rate is coating. Hydroxyapatite (HA)‐based coating is considered to improve biocompatibility as well as decrease the corrosion rate by the barrier effect. In this study, ultrathin (150 nm) HA and HA containing Sr coatings are deposited via pulsed electron ablation technique on pure Mg. The microstructure of the coating was assessed by scanning electron microscopy. Electrochemical methods were used to investigate the corrosion properties of prepared coatings. The materials covered by this layer were characterized by superior corrosion behavior, with corrosion rates of coated samples up to five times lower as compared with the uncoated ones. Such coating is the thinnest coating found in the literature sources. [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]

Bone and tooth enamel surface are made up of different crystallographically hydroxyapatite (HA), whereby bone comprises a(b)-planes of HA whilst tooth enamel comprises c-planes of HA. The reason behind the difference between HA orientations in both tissues are still yet to be discovered. We report the fabrication of anisotropic coatings of a-plane oriented HA according to the following process: (i) synthesis of a-plane oriented HA powders via a hydrothermal reaction and (ii) fabrication of a-plane oriented HA coatings via a Drop-on-Demand (DoD) micro-dispensing technique. Two types of HAs with high a-plane orientation degree of 72.2 and 75.6% (HA10 and HA84, respectively) was synthesised for the DoD coatings. The HA84 coating demonstrated more uniform and flatter surface than HA10 coating. The heat treatment of HA10 and HA84 coatings prepared with mesh-sieved particles led to a low adhesion strength for the substrates. However, the orientation degrees of those coatings (96.0 and 94.6%, respectively) were higher than the coatings without mesh-sieving. [ABSTRACT FROM AUTHOR]

A series of nanocomposite coatings was produced, comprising a hydrogel polymer, poly(2-hydroxyethyl methacrylate)/poly(ε-caprolactone) (PHEMA/PCL) matrix with nanoscale carbonated hydroxyapatite (nCHA) filler particles. The weight fraction of the filler was varied from 0 to 20% and the composites were applied as coatings onto Ti-6Al-4V substrates. The filler distribution and surface morphology were investigated by AFM, and the mechanical stability of the coatings was characterised using nanoindentation in both dry and wet conditions. The cellular response to the coatings was also examined in vitro using human osteoblast (HOB) cells. It was found that interfacial cracking occurred for composites containing greater than 10 wt.% nCHA and that 10 wt.% nCHA composite coatings appear to offer the greatest coating stability and bioactivity compared with the other composite coatings. It was concluded that the nCHA-containing PHEMA/PCL composite coatings had the potential to provide a soft, low modulus interface between metal implants and bone. [ABSTRACT FROM AUTHOR]

Investigating the effects of rhBMP2 (recombined human bone morphogenetic protein-2) release kinetics on bone formation is important to optimize the use of rhBMP2 in tissue-engineered bone. However, there is still no direct evidence regarding how the release kinetic of rhBMP2 has effects on mesenchymal stem cells homing and differentiation during bone regeneration. In this study, we construct control and non-control released rhBMP2 coatings within the pores of 3D printed hydroxyapatite scaffold, and investigate how the release kinetic of rhBMP2 affects bone inductivity of tissue-engineered bone. We show that control released rhBMP2 has better effects on enhancing mesenchymal stem cells proliferation and migration than non-control released rhBMP2. Control released rhBMP2 promotes mesenchymal stem cells differentiation to a better extent than non-control released rhBMP2. Those findings are in consistent with the results of quantitative rhBMP2 stimulation for mesenchymal stem cells proliferation, migration and differentiation. The histological results after in vivo implantation also reveal that control released rhBMP2 coating can induce more bone formation than non-control released rhBMP2. Our data provide a basis for optimizing the rhBMP2 delivery modes in tissue-engineered bone and improving the bone inductivity of rhBMP2. [ABSTRACT FROM AUTHOR]

Coating on prostheses and implantable devices is one of the ways to increase the osseointegration of these products. However, plasma spray techniques, that are normally used, present high complexity and high cost. In this work, a new methodology for coating with nanometric hydroxyapatite is presented, with a low cost and ease of production. The technique proposed involves the formation of a suspension of hydroxyapatite (HAp) and oil of turpentine (OT) and its application, with a paintbrush, on the titanium substrate. In order to qualify the process for medical devices, the properties of the titanium substrate, before and after the coating process, the calcium phosphate phases present and the adhesive bond of the coating were evaluated. The results indicated that thermal treatment does not affect the properties of ASTM F67 titanium in order to compromise the properties and the analyses, by X-ray diffraction and Raman spectroscopy, proved that no formation of second phases of calcium phosphate occurred. The adhesive bond assay showed that the coating behaved according to ISO 13779–2, i.e., it had adhesive bond values higher than 15 MPa. The proposed new coating method proved promising for the titanium coating and is an alternative to the complex and high cost processes normally used in metal implants. [ABSTRACT FROM AUTHOR]

Abstract In the past decades, weak adhesive strength and thin thickness are headaches existed between carbon/carbon (C/C) composite and hydroxyapatite (HA) coating by one-step electrochemical deposition. To solve this problem, a monetite precursor coating was first synthesized on (NH4) 2 S 2 O 8 treated C/C (N-C/C) by hydrothermal electrochemical deposition, and then hydrothermally treated in a sodium silicate solution to transform into a SiO 2 /HA composite coating. The morphology, microstructure, in-vitro bioactivity and biocompatibility of the SiO 2 /HA coating were investigated. The distribution of spherical nano SiO 2 in the HA coating was homogeneous with uniform grain size of about 100 nm. The composite coating had a rod shaped morphology and a compact microstructure. For comparison, another HA coating was prepared on N-C/C under the same processing conditions except for sodium silicate addition in the hydrothermal system. Scratch and nano-indentation tests showed that this SiO 2 /HA composite coating presented an adhesive strength of a critical load of 31.63 N, was nearly 1.5 times as high as one of the HA coating on N-C/C, and its modulus and hardness were 58.3 Gpa and 2.93 Gpa, far higher than those of the HA coating. In-vitro bioactivity and cell biocompatibility tests showed that the SiO 2 /HA coating could induce apatite growth and had superior abilities of cell attachment and cell proliferation to naked C/C and the HA coating. Graphical abstract A procedure to prepare SiO 2 reinforced hydroxyapatite coating in this article is described as following. Image 1 Highlights • A SiO 2 /HA coating was successfully synthesized through a low temperature process. • The adhesive strength of the SiO 2 /HA coating can reach a critical load of 31.63 N. • The SiO 2 /HA coating owned higher hardness and elastic modulus than HA coating without SiO 2. [ABSTRACT FROM AUTHOR]

Magnesium (Mg) and its alloys have attracted a great deal of attention as next-generation biomaterials due to their highly appealing properties. However, the high corrosion kinetics and inadequate hemocompatibility have limited their widespread acceptance as implant materials. In this study, an attempt was made to improve the corrosion resistance and hemocompatibility of Mg alloy ZK60 by coating it with niobium (Nb)-reinforced hydroxyapatite (HA). The Nb-reinforced HA (HA-Nb) coating was obtained through plasma spray technique by varying weight percent (wt%) of Nb-reinforcement in HA at three levels (10 wt%, 20 wt%, and 30 wt%). Nb-reinforcement had a more pronounced effect on the microhardness and wettability as compared to the surface roughness of the coating. The corrosion investigation revealed that the HA-Nb coatings were more effective than the pure HA and Nb coatings for inhibiting the rapid corrosion of the Mg alloy. With the progressive increment of the Nb-content in HA, protection efficiency (P e) for HA-Nb coatings increased (∼4%, 12% and 18% for HN1, HN2, and HN3, respectively) in comparison to pure HA coating. The HA-Nb coatings exhibited no adverse effects on the erythrocytes and the hemolysis rate (HR) was within the domain of safe value (<5%) for implant materials. • Plasma spray method was used to coat Mg alloy ZK60 with HA, Nb and HA-Nb coatings. • The hardness of surface increased with the progressive increment of Nb-content HA. • The surface of HA and HA-Nb coatings revealed hydrophilic nature. • Nb-reinforcement in HA increased the degree of protection offered by the surface. • HA-Nb coatings revealed better hemocompatibility than Mg Alloy ZK60. [ABSTRACT FROM AUTHOR]

Highlights • The corrosion behaviors of PCL-gelatin composite coatings were significantly higher than that of AISI 316L SS. • The AISI 316L SS was modified as a biocompatible substrate for inhibition of ion release in simulated body fluid. • SEM results show a uniform adherent PCL-gelatin coating on the surface of 316Lss via utilizing dip coating method. • The adhesion results show that the PCL-gelatin composite coating has a convenient adhesion to the metallic substrate. Abstract Currently, stainless steel is the material on which extensive research interest is being focused for the purpose of using it as bone implant in biomedical application. In order to improve the corrosion resistance of 316L AISI substrates, surface coating is extensively utilized. In the present research, to improve the corrosion resistance of 316L in PBS solution, a PCL-Gelatin composite was coated on the surface of 316L substrates using dip coating method. The coating 316L substrates were tested for their corrosion behavior in PBS solution at room temperature The corrosion current density was reported to be 0.62 μA/cm2 for uncoated 316L substrate, whereas, in the samples coated with PCL-Gelatin composite containing 50, 70 and 90 wt.% PCL coating had the corrosion current density of 0.403, 0.228 and 0.045 μA/cm2, respectively. The electrochemical impedance spectroscopy (EIS) results have been substantiated by the results obtained using potentiodynamic polarization curve. Scanning electron microscope (SEM), Fourier transformation infrared spectroscopy (FTIR) was utilized for characterization studies. SEM micrographs show that PCL-Gelatin coating is a smooth uniform coating. Laser surface profile meter measurement indicates PCL-Gel coating as a convenient candidate for increasing the surface roughness. Generally, the PCL-Gelatin composite coating could be a good choice for surface modification of 316L to improve the corrosion resistance and bioactivity of 316L. [ABSTRACT FROM AUTHOR]

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

To suit a target application, the machining mechanism of electro discharge machining (EDM) process has been hybridized to powder mixed EDM (PM-EDM) by adding various substances in the form of additives into the dielectric fluid. In this study, the application of PM-EDM to fabricate Lakargiite (CaZrO3) coating on Zr-Cu-Ni-Ti-Be substrate surface for potential orthopedic application, using hydroxyapatite (HA) powder as dielectric additive was proposed. The effect of various HA powder concentrations on deposition of CaZrO3 on Zr-Cu-Ni-Ti-Be surface was investigated. Zr-Cu-Ni-Ti-Be bulk metallic glass (BMG) has exceptional mechanical and chemical properties compared to its crystalline counterpart. It is expected that, the formation of a nanoporous bioactive CaZrO3 coating on the BMG surface will enhance its bioactivity. The FESEM investigation presents the formation of various interconnected shallow craters, nanopores, and few nanocracks and the energy dispersive X-ray spectroscopy results depict the presence of about 50% Lakargiite phase on the HA-deposited BMG surface. The X-ray powder diffraction characterization identified the phases includes ZrC, ZrO, TiC, and CaTiO3 formed on the PM-EDMed surface. The Rockwell hardness testing revealed the rise of BMG surface hardness to about 42%. The roughness of EDMed surface reduced from 6.22 nm to 2.00 nm after HA powder suspended in the dielectric fluid. [ABSTRACT FROM AUTHOR]

Fluoridated hydroxyapatite (FHA) coatings were prepared on a Ti substrate using a suspension plasma spraying technique. The crystalline phases and chemical compositions of the coatings were characterized using x-ray diffraction, Fourier transform infrared spectroscopy, and x-ray photoelectron spectroscopy. The analysis confirmed that the coating consisted of an FHA phase. The corrosion behavior in simulated body fluid was studied using potentiodynamic polarization tests, and the results indicated that the FHA coating greatly enhanced the corrosion resistance of the Ti substrate. The chemical stability of the FHA coatings was assessed by evaluating the release of Ca2+ ions. The results indicated that the substitution of fluorine into the hydroxyapatite (HA) structure had a positive effect on the dissolution resistance of the HA. The antibacterial activity was investigated using a surface-plating method; the results revealed that the antibacterial activity of the FHA coating was greater than that of the pure HA coatings. During cell culture tests, the FHA coating did not exhibit cytotoxicity toward the osteoblast cell line, and the cell proliferation was comparable with that of the HA coatings. The antibacterial activity and cell culture results suggested that the plasma-sprayed FHA coating possesses good antibacterial qualities, but is biocompatible with osteoblasts. The promising features of the FHA coating render it suitable for orthopedic and dental applications. [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]

Hydroxyapatite (HA)-containing Al 2 O 3 coatings were prepared on NiTi alloys through a cathodic plasma electrolytic deposition (CPED) process, followed by hydrothermal treatment (HT). The surface morphology, elemental distribution and phase composition of each coating were studied by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and X-ray diffraction (XRD). SEM observations revealed that the coatings exhibited a “crater-like” porous structure, and that the thickness of the coating could be up to 100 μm. The results of EDS demonstrated that the Ca and P concentrations in the Al 2 O 3 coatings could be increased to 8.2% and 4.7%, respectively, and that the Ca/P ratio could reach 1.72, which was close to that of natural HA. The results of XRD analysis showed that the CPED coating mainly comprised α-Al 2 O 3 and γ-Al 2 O 3 , and that HA crystallization was induced by the subsequent HT. The corrosion resistance of the samples was investigated by potentiodynamic polarization tests and electrochemical impedance spectroscopy (EIS). The results showed that the corrosion resistance of the sample with the CPED-HT coating was enhanced by more than two orders of magnitude compared to that of the uncoated NiTi alloy. Ni ion release in simulated body fluid (SBF) was characterized by inductively coupled plasma-atomic emission spectroscopy, and the results showed a significant drop in the concentration of released Ni ions from 18.0 μg/mL for the uncoated NiTi alloy to 0.7 μg/mL for the CPED-HT coating. In addition, the SBF soaking test showed that HA precipitated on the CPED-HT coating and that the HA layer became thicker and larger with increasing soaking time, indicating that the CPED-HT coating exhibited excellent apatite-inducing ability. Thus, the introduced CPED-HT treatment provides a new and effective route for the surface modification of NiTi alloys for use as biomedical materials. [ABSTRACT FROM AUTHOR]

High-frequency magnetron sputtering (HFMS) at various plasma powers has been applied to obtaining hydroxyapatite (HA) coating with amorphous and crystalline structure on VT1-0 titanium. The results concerning the influence of thermal treatment on the coating under isothermal holding for 1 h at 700-1000°C are presented. Structure, phase composition, topography and morphology of the formed hydroxyapatite coatings have been analyzed by X-ray phase analysis, scanning electron microscopy, energy-dispersive spectroscopy, atomic-force microscopy, and IR spectrometry. It is found that, depending on discharge power and temperature of isothermal annealing, molecular bonds are formed that are typical for HA accompanied by variations in phase and elemental compositions. [ABSTRACT FROM AUTHOR]

This article examines the substrate/coating interface of a coating deposited onto mild steel and stainless steel substrates using an ambient temperature blast coating technique known as CoBlast. The process uses a coincident stream of an abrasive blast medium and coating medium particles to modify the substrate surface. The hypothesis for the high bond strength is that the abrasive medium roughens the surface while simultaneously disrupting the passivating oxide layer of the substrate, thereby exposing the reactive metal that then reacts with the coating medium. The aim of this study is to provide greater insight into the coating/substrate bonding mechanism by analysing the interface between a hydroxyapatite coating on both mild and stainless steel substrates. The coating adhesion was measured via a tensile test, and bond strengths of approximately 45 MPa were measured. The substrate/coating interface was examined using transmission electron microscopy and selected area diffraction. The analysis of the substrate/coating interface revealed the presence of ultrafine grains in both the coating and substrate at interface associated with deformation at the interface caused by particle impaction during deposition. The chemical reactivity resulting from the creation of these ultrafine grains is proposed to explain the high adhesive strength of CoBlast coatings. [ABSTRACT FROM AUTHOR]