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AbstractIn this manuscript, the application of hydroxyapatite coatings to total ossicular reconstruction prostheses (TORPs) using finite element modeling simulations was investigated to enhance the biocompatibility and mechanical performance of these prosthetic devices for middle ear implants. We focused on evaluating biocompatible materials, particularly polyetheretherketone (PEEK) and titanium, by analyzing their mechanical behavior under simulated conditions. The results revealed that PEEK demonstrates mechanical performance almost on par with titanium, exhibiting excellent stability and resilience within the middle ear environment. PEEK offers several key advantages over titanium, including easier fabrication, greater availability, and a simplified application process for hydroxyapatite coatings. These benefits suggest that PEEK could be a highly effective alternative to titanium for use in middle ear prostheses. The findings of this study highlight the potential of PEEK to improve the design and functionality of middle ear implants, providing a promising direction for future research and development in this field. By leveraging the advantages of PEEK, we can advance the effectiveness and accessibility of middle ear prosthetic devices, ultimately benefiting patients requiring such interventions. [ABSTRACT FROM AUTHOR]

Despite a long period of application of metal implants, carbon–carbon medical composites are also widely used for bone defect prosthesis in surgery, dentistry, and oncology. Such implants might demonstrate excellent mechanical properties, but their biocompatibility and integration efficiency into the host should be improved. As a method of enhancing, the electrophoretic deposition of fine-dispersed hydroxyapatite (HAp) on porous carbon substrates might be recommended. With electron microscopy, energy dispersion X-ray and Raman spectroscopy, and X-ray diffraction, we found that the deposition and subsequent heat post-treatment (up to the temperature of 400 °C for 1 h) did not lead to any significant phase and chemical transformations of raw non-stoichometric HAp. The Ca/P ratio was ≈1.51 in the coatings. Their non-toxicity, cyto- and biocompatibility were confirmed by in vitro and in vivo studies and no adverse reactions and side effects had been detected in the test. The proposed coating and subsequent heat treatment procedures provided improved biological responses in terms of resorption and biocompatibility had been confirmed by histological, magnetic resonance and X-ray tomographic ex vivo studies on the resected implant-containing biopsy samples from the BDF1 mouse model. The obtained results are expected to be useful for modern medical material science and clinical applications. [ABSTRACT FROM AUTHOR]

The porous hydroxyapatite coatings with a spherical structure were formed on commercially pure titanium (CP-Ti) by the micro-arc oxidation (MAO) in an alkaline electrolyte (hydroxyapatite + 1 M potassium hydroxide) at the applied voltage of 140, 160, 180 V and deposition time of 1 and 2 min. It was determined that by increasing voltage from 140 to 160 V the Ca/P ratio increases from 1.54 to 1.69, i.e., the composition of hydroxyapatite (HA) approaches to the biological one that accelerates formation of the interfacial bond between the implant and bone tissue. It was shown that increasing deposition time from 1 to 2 min at the voltage of 140 V promotes increasing Ca/P ratio. The corrosion resistance of CP-Ti with HA coatings was studied in Ringer's solution at a temperature of 37 °C. The best corrosion protection was observed for the coating deposited at 160 V, 1 min, when the thickness of the coating and HA formation is the highest. [ABSTRACT FROM AUTHOR]

Xinlin Li,1,2,* Baojuan Yang,3,4,* Mengfei Xu,1,2 Fangyi Li,3,4 Zhaoli Geng,1,2 Weiqiang Cui,3,4 Xingfu Sun,3,4 Yanle Li,3,4 Yi Liu1,2 1Department of Orthodontics, School and Hospital of Stomatology, Cheeloo College of Medicine, Shandong University, Jinan, Shandong, 250012, People’s Republic of China; 2Shandong Key Laboratory of Oral Tissue Regeneration, Shandong Engineering Laboratory for Dental Materials and Oral Tissue Regeneration, Shandong Provincial Clinical Research Center for Oral Diseases, Jinan, Shandong, 250012, People’s Republic of China; 3Key Laboratory of High Efficiency and Clean Mechanical Manufacture, Ministry of Education, School of Mechanical Engineering, Shandong University, Jinan, 250061, People’s Republic of China; 4National Demonstration Center for Experimental Mechanical Engineering Education, Shandong University, Jinan, 250061, People’s Republic of China*These authors contributed equally to this workCorrespondence: Yi Liu, Department of Orthodontics, School and Hospital of Stomatology, Cheeloo College of Medicine, Shandong University, No. 44-1 Wenhua Road West, Jinan, Shandong, 250012, People’s Republic of China, Tel +86-531-88381630, Email yiliu@sdu.edu.cn Yanle Li, Key Laboratory of High Efficiency and Clean Mechanical Manufacture, Ministry of Education, Shandong University School of Mechanical Engineering, No. 17923, Jingshi Road, Jinan, 250061, People’s Republic of China, Tel +86-531-88392208, Email yanle.li@sdu.edu.cnIntroduction: The lack of osteoinductive, angiogenic and antimicrobial properties of hydroxyapatite coatings (HA) on titanium surfaces severely limits their use in orthopedic and dental implants. Therefore, we doped SiO2, Gd2O3 and CeO2 nanoparticles into HA to fabricate a HASiGdCe coating with a combination of decent antibacterial, angiogenic and osteogenic properties by the plasma spraying technique.Methods: The HASiGdCe coating was analyzed by SEM (EDS), surface roughness tests, contact angle tests, XRD, FTIR spectroscopy, tensile tests and electrochemical dynamic polarization tests. Methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa (PAO-1) were used as representative bacteria to verify the antibacterial properties of the HASiGdCe coating. We evaluated the cytocompatibility and in vitro osteoinductivity of the HASiGdCe coating by investigating its effect on the cell viability and osteogenic differentiation of MC3T3-E1 cells. We assessed the in vitro angiogenic activity of the HASiGdCe coating by migration assay, tube formation assay, and RT‒PCR analysis of angiogenic genes in HUVECs. Finally, we used infected animal femur models to investigate the biosafety, antimicrobial and osteointegration properties of the HASiGdCe coating in vivo.Results: Through various characterization experiments, we demonstrated that the HASiGdCe coating has suitable microscopic morphology, physical phase characteristics, bonding strength and bioactivity to meet the coating criteria for orthopedic implants. The HASiGdCe coating can release Gd3+ and Ce4+, showing strong antibacterial properties against MRSA and PAO-1. The HASiGdCe coating has been shown to have superior osteogenic and angiogenic properties compared to the HA coating in in vitro cellular experiments. Animal implantation experiments have shown that the HASiGdCe coating also has excellent biosafety, antimicrobial and osteogenic properties in vivo.Conclusion: The HASiGdCe coating confers excellent antibacterial, angiogenic and osteogenic properties on titanium implants, which can effectively enhance implant osseointegration and prevent bacterial infections, and it accordingly has promising applications in the treatment of bone defects related to orthopedic and dental sciences.Graphical Abstract: Keywords: hydroxyapatite coatings, SiO2, Gd2O3, CeO2, osseointegration, antibacterial

Despite a long period of application of metal implants, carbon–carbon medical composites are also widely used for bone defect prosthesis in surgery, dentistry, and oncology. Such implants might demonstrate excellent mechanical properties, but their biocompatibility and integration efficiency into the host should be improved. As a method of enhancing, the electrophoretic deposition of fine-dispersed hydroxyapatite (HAp) on porous carbon substrates might be recommended. With electron microscopy, energy dispersion X-ray and Raman spectroscopy, and X-ray diffraction, we found that the deposition and subsequent heat post-treatment (up to the temperature of 400 °C for 1 h) did not lead to any significant phase and chemical transformations of raw non-stoichometric HAp. The Ca/P ratio was ≈1.51 in the coatings. Their non-toxicity, cyto- and biocompatibility were confirmed by in vitro and in vivo studies and no adverse reactions and side effects had been detected in the test. The proposed coating and subsequent heat treatment procedures provided improved biological responses in terms of resorption and biocompatibility had been confirmed by histological, magnetic resonance and X-ray tomographic ex vivo studies on the resected implant-containing biopsy samples from the BDF1 mouse model. The obtained results are expected to be useful for modern medical material science and clinical applications.

This experimental research focuses on the nanostructure analysis of three materials; polyether ether ketone (PEEK), African land giant snail shell (ALGSS), and sea snail shell (SSS) powder, for the formation of hydroxyapatite (HA) coatings in bone implant applications. The study aimed to evaluate these materials’ surface characteristics, furrow depth, density, and other relevant parameters to assess their suitability as bone implant materials. The nanostructure analysis revealed distinct characteristics for each material. PEEK exhibited shallow furrows and a high density of furrows, making it a favourable substrate for hydroxyapatite coating formation. The ISO 25178 roughness analysis further characterised surface roughness and topography. African land giant snail shell powder, displayed a high material ratio, indicating a potential for hydroxyapatite conversion for biomedical application. The sea snail shell powder demonstrated intermediate furrow depth and density, warranting further investigation for optimisation as a precursor for hydroxyapatite coatings. The findings emphasise the significance of nanostructure properties in bone implant materials. The tailored nanostructure of materials such as PEEK, the synthesized powder can influence their biocompatibility, osseointegration, and long-term performance. The novelty of this research lies in the comprehensive analysis of the nanostructure properties of these materials, contributing to the understanding of their potential for bone implant applications. Overall, this experimental research is significant and provides valuable insights into the nanostructure characteristics of PEEK, African land giant snail shell powder, and sea snail shell powder and they all demonstrated the potential of forming hydroxyapatite coatings. These findings contribute to advancements in bone implantology, paving enhancing innovative and improved bone implant materials

Atmospheric plasma spray (APS) remains the only certified industrial process to produce hydroxyapatite (Hap) coatings on orthopaedic and dental implants intended for commercialization. Despite the established clinical success of Hap-coated implants, such as hip and knee arthroplasties, a concern is being raised regarding the failure and revision rates in younger patients, which are increasing rapidly worldwide. The lifetime risk of replacement for patients in the 50–60 age interval is about 35%, which is significantly higher than 5% for patients aged 70 or older. Improved implants targeted at younger patients are a necessity that experts have been alerted to. One approach is to enhance their bioactivity. For this purpose, the method with the most outstanding biological results is the electrical polarization of Hap, which remarkably accelerates implant osteointegration. There is, however, the technical challenge of charging the coatings. Although this is straightforward on bulk samples with planar faces, it is not easy on coatings, and there are several problems regarding the application of electrodes. To the best of our knowledge, this study demonstrates, for the first time, the electrical charging of APS Hap coatings using a non-contact, electrode-free method: corona charging. Bioactivity enhancement is observed, establishing the promising potential of corona charging in orthopedics and dental implantology. It is found that the coatings can store charge at the surface and bulk levels up to high surface potentials (>1000 V). The biological in vitro results show higher Ca2+ and P5+ intakes in charged coatings compared to non-charged coatings. Moreover, a higher osteoblastic cellular proliferation is promoted in the charged coatings, indicating the promising potential of corona-charged coatings when applied in orthopedics and dental implantology. [ABSTRACT FROM AUTHOR]

There is a strong need to search for more effective compounds with bone anti-resorptive properties, which will cause fewer complications than commonly used bisphosphonates. To achieve this goal, it is necessary to search for new techniques to characterize the interactions between bone and drug. By studying their interaction with hydroxyapatite (HA), this study used three forms of ceramic materials, two of which are bone-stimulating materials, to assess the suitability of new active substances with anti-resorptive properties. In this study, three methods based on HA in loose form, polycaprolactone/HA (a polymer-ceramic materials containing HA), and polymer-ceramic monolithic in-needle extraction (MINE) device (a polymer inert skeleton), respectively, were used. The affinity of risedronate (a standard compound) and sixteen aminomethylenebisphosphonates (new compounds with potential antiresorptive properties) to HA was defined according to the above-mentioned methods. Ten monolithic materials based on 2-hydroxyethyl methacrylate/ethylene dimethacrylate are prepared and studied, of which one was selected for more-detailed further research. Simulated body fluids containing bisphosphonates were passed through the MINE device. In this way, sorption–desorption of bisphosphonates was evaluated using this MINE device. The paper presents the advantages and disadvantages of each technique and its suitability for assessing new active substances. All three methods allow for the selection of several compounds with potentially higher anti-resorptive properties than risedronate, in hope that it reflects their higher bone affinity and release ability.

Atmospheric plasma spray (APS) remains the only certified industrial process to produce hydroxyapatite (Hap) coatings on orthopaedic and dental implants intended for commercialization. Despite the established clinical success of Hap-coated implants, such as hip and knee arthroplasties, a concern is being raised regarding the failure and revision rates in younger patients, which are increasing rapidly worldwide. The lifetime risk of replacement for patients in the 50–60 age interval is about 35%, which is significantly higher than 5% for patients aged 70 or older. Improved implants targeted at younger patients are a necessity that experts have been alerted to. One approach is to enhance their bioactivity. For this purpose, the method with the most outstanding biological results is the electrical polarization of Hap, which remarkably accelerates implant osteointegration. There is, however, the technical challenge of charging the coatings. Although this is straightforward on bulk samples with planar faces, it is not easy on coatings, and there are several problems regarding the application of electrodes. To the best of our knowledge, this study demonstrates, for the first time, the electrical charging of APS Hap coatings using a non-contact, electrode-free method: corona charging. Bioactivity enhancement is observed, establishing the promising potential of corona charging in orthopedics and dental implantology. It is found that the coatings can store charge at the surface and bulk levels up to high surface potentials (>1000 V). The biological in vitro results show higher Ca2+ and P5+ intakes in charged coatings compared to non-charged coatings. Moreover, a higher osteoblastic cellular proliferation is promoted in the charged coatings, indicating the promising potential of corona-charged coatings when applied in orthopedics and dental implantology.

Minxun Lu,1,2 Hongjie Chen,2 Bo Yuan,2 Yong Zhou,1 Li Min,1 Zhanwen Xiao,2 Xiangdong Zhu,2 Chongqi Tu,1 Xingdong Zhang2 1Department of Orthopedics, West China Hospital, Sichuan University, Chengdu, People’s Republic of China; 2National Engineering Research Center for Biomaterials, Sichuan University, Chengdu, People’s Republic of ChinaCorrespondence: Xiangdong ZhuNational Engineering Research Center for Biomaterials, Sichuan University, No. 29 Wangjiang Road, Chengdu 610064, People’s Republic of ChinaTel +86-28-85470770Email zhu_xd1973@scu.edu.cnChongqi TuDepartment of Orthopedics, West China Hospital, Sichuan University, No. 37 Guoxue Street, Chengdu 610041, People’s Republic of ChinaTel +86-28-85422570Email Tuchongqi@yeah.netPurpose: The aim of research is to fabricate nanostructured hydroxyapatite (HA) coatings on the titanium via electrochemical deposition (ED). Additionally, the biological properties of the ED-produced HA (EDHA) coatings with a plate-like nanostructure were evaluated in vitro and in vivo by undertaking comparisons with those prepared by acid/alkali (AA) treatment and by plasma spray-produced HA (PSHA) nanotopography-free coatings.Materials and Methods: Nanoplate-like HA coatings were prepared through ED, and nanotopography-free PSHA coatings were fabricated. The surface morphology, phase composition, roughness, and wettability of these samples were investigated. Furthermore, the growth, proliferation, and osteogenic differentiation of MC3T3-E1 cells cultured on each sample were evaluated via in vitro experiments. Histological assessment and push-out tests for the bone–implant interface were performed to explore the effect of the EDHA coatings on the interfacial osseointegration in vivo.Results: XRD analysis showed that the strongest intensity for the EDHA coatings was at the (002) plane rather than at the regular (211) plane. Relatively higher surface roughness and greater wettability were observed for the EDHA coatings. Cellular experiments revealed that the plate-like nanostructured EDHA coatings not only possessed an ability, similar to that of PSHA coatings, to promote the adhesion and proliferation of MC3T3-E1 cells but also demonstrated significantly enhanced early or intermediate markers of osteogenic differentiation. Significant osseointegration enhancement in the early stage of implantation period and great bonding strength were observed at the interface of bone and EDHA samples. In comparison, relatively weak osseointegration and bonding strength of the bone–implant interface were observed for the AA treatment.Conclusion: The biological performance of the plate-like nanostructured EDHA coating, which was comparable with that of the PSHA, improves early-stage osteogenic differentiation and osseointegration abilities and has great potential for enhancing the initial stability and long-term survival of uncemented or 3D porous titanium implants.Keywords: electrochemical deposition, hydroxyapatite coatings, nanoscale, osteogenic activity, osseointegration

Changes in the structure and phase composition of the hydroxyapatite (HA) plasma coating were established during deposition at the initial temperatures of 20 and 550°C of the titanium substrate and a deposition distance of 95 and 150 mm. The structure of HA coatings was analyzed by SEM and optical microscopy. DSC analysis established the transition temperatures of HA coatings to the equilibrium state. When deposited on a substrate with an initial temperature of 20°C at a deposition distance of 95 mm, a nanostructure with a crystallite size of 21 nm is recorded in the HA coating. When the deposition distance increases to 150 mm, the nonequilibrium phase composition increases, the crystallite size decreases to 12 nm, the HA content decreases from 72 to 61%, the TTCP content decreases from 10 to 5%, and the α-TCP content increases from 17 to 30%. A nonequilibrium nanostructural state passes into a more equilibrium state with the release of heat at temperatures of 615–727°C in DSC studies. The high-temperature α-TCP phase is not recorded when the coating is deposited onto a substrate with an initial temperature of 550°C at a deposition distance of 95 mm, the TTCP content increases by two times, the size of the HA phase crystallites reaches 36 nm, and their size in the sprayed powder is 75 nm. The HA coating has a dendritic microstructure and has no thermal effect during DSC heating at an initial substrate temperature of 550°C. [ABSTRACT FROM AUTHOR]

Surface modification of three-dimensional (3D)-printed titanium (Ti) scaffolds with hydroxyapatite (HA) has been a research hotspot in biomedical engineering. However, unlike HA coatings on a plain surface, 3D-printed Ti scaffolds have inherent porous structures that influence the characteristics of HA coatings and osteointegration. In the present study, HA coatings were successfully fabricated on 3D-printed Ti scaffolds using plasma spray and electrochemical deposition, named plasma sprayed HA (PSHA) and electrochemically deposited HA (EDHA), respectively. Compared to EDHA scaffolds, HA coatings on PSHA scaffolds were smooth and continuous. In vitro cell studies confirmed that PSHA scaffolds have better potential to promote bone mesenchymal stem cell adhesion, proliferation, and osteogenic differentiation than EDHA scaffolds in the early and late stages. Moreover, in vivo studies showed that PSHA scaffolds were endowed with superior bone repair capacity. Although the EDHA technology is simpler and more controllable, its limitation due to the crystalline and HA structures needs to be improved in the future. Thus, we believe that plasma spray is a better choice for fabricating HA coatings on implanted scaffolds, which may become a promising method for treating bone defects.

[Display omitted] • An experimental study describing processing and phase degradation of hydroxyapatite (HAp) coatings during axial plasma spray. • Studied the influence of feedstock (suspension as well as powder) characteristics on coating microstructure & phases. • Discussed the in-flight particle treatment and subsequent phase degradation while injecting suspension and powder feedstock. • Investigated the interplay between microstructure, phases, and coatings hardness as well as adhesion strength. • Demonstrated the deposition of thin and adherent HAp coatings by axial suspension plasma spray with limited phase degradation. Axial plasma spray is one of the thermal spray techniques to deposit multifunctional advanced coatings. The present work explores the use of this process to deposit thin, continuous, and adherent Ca 5 (PO 4) 3 OH (hydroxyapatite, HAp) coatings and characterize its microstructure, phases, hardness and adhesion strength. Three different suspension-deposited HAp coatings were investigated and compared with powder-deposited HAp coating on a Ti6Al4V substrate. The effect of mean solute particle size and solid-loading in the suspension has been explored on the evolution of microstructure, phase content and mechanical properties of axial suspension plasma sprayed (ASPS) coatings. Phase-characterization has shown retention of hydroxyapatite phase and coating crystallinity in the deposited coatings, whereas the adhesion strength of the HAp coating decreased from ∼40 MPa to ∼13 MPa when bioglass was added to the feedstock material. The lower solid load content and lower mean solute particle size in the suspension were found to be beneficial in achieving porous, rougher, and well-adhering coatings. This work concludes that ASPS can potentially deposit thin HAp coatings (< 50 μm) with high adhesion strength. [ABSTRACT FROM AUTHOR]

There is a strong need to search for more effective compounds with bone anti-resorptive properties, which will cause fewer complications than commonly used bisphosphonates. To achieve this goal, it is necessary to search for new techniques to characterize the interactions between bone and drug. By studying their interaction with hydroxyapatite (HA), this study used three forms of ceramic materials, two of which are bone-stimulating materials, to assess the suitability of new active substances with anti-resorptive properties. In this study, three methods based on HA in loose form, polycaprolactone/HA (a polymer-ceramic materials containing HA), and polymer-ceramic monolithic in-needle extraction (MINE) device (a polymer inert skeleton), respectively, were used. The affinity of risedronate (a standard compound) and sixteen aminomethylenebisphosphonates (new compounds with potential antiresorptive properties) to HA was defined according to the above-mentioned methods. Ten monolithic materials based on 2-hydroxyethyl methacrylate/ethylene dimethacrylate are prepared and studied, of which one was selected for more-detailed further research. Simulated body fluids containing bisphosphonates were passed through the MINE device. In this way, sorption–desorption of bisphosphonates was evaluated using this MINE device. The paper presents the advantages and disadvantages of each technique and its suitability for assessing new active substances. All three methods allow for the selection of several compounds with potentially higher anti-resorptive properties than risedronate, in hope that it reflects their higher bone affinity and release ability. [Display omitted] • Three methods for assessing the suitability of new active substances with anti-resorptive properties. • Investigation of the interactions between antiresorptive drugs and hydroxyapatite. • Sorption and desorption of risedronate and sixteen aminomethylenebisphosphonates. [ABSTRACT FROM AUTHOR]

Hydroxyapatite (HA) coatings were sprayed by an arc plasma gun with argon-nitrogen plasma at the power of 25 kW from the powder with particle size of 25–63 μm at the distance of 95 mm. Before spraying of the coatings, the samples were preheated in a resistance furnace in air to the temperatures within the range from 20 to 600°C. Adhesion of the HA plasma coating to a titanium substrate was determined on pin samples. The maximum mean value of adhesion was observed when the titanium substrate was preheated to the temperature of 550°C. The results of the study were discussed by reference to the way of increase in activity of the titanium substrate at its preheating for increase in the HA coating adhesion and formation of an equilibrium phase state in the HA coating necessary for long-term usage of the implants. The obtained results will be used for formation of the optimal structure of the bioactive coating consisting of a three-dimensional capillary-porous titanium coating (3D CP Ti) in the form of crests and hollows with porosity of 50% and HA coating sprayed on its surface at the temperature of 550°C. Such mode of the spraying provides formation of a dense, strong, and stable HA coating on endosseous implants. [ABSTRACT FROM AUTHOR]

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Hydroxyapatite coating composed of hexagonal rods are modified with silver ions to improve their antibacterial activity. The coatings are irradiated at room temperature using 15 keV Ag+ ion source and three different ion doses up to 6 x 1016 ions/cm². Morphological and structural changes in the crystal structure of hydroxyapatite are followed as a function of Ag+ ion dose using scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, and the Raman spectroscopy. We observed that implantation did not produce any morphological changes in crystals. Based on the X-ray diffraction data, we show that lattice constant of hydroxyapatite remains unchanged for all samples irrespective of the Ag+ ion dose. However, ion-induced defects formation is evidenced by detailed X-ray diffraction line profile analysis and broadening of the diffraction maxima with increasing Ag+ ion dose. [ABSTRACT FROM AUTHOR]

The present study estimated the cracking phenomenon in as-plasma-sprayed hydroxylapatite coatings (HACs) after they were being subjected to the severe cutting conditions in the direction perpendicular to the coating/substrate interface. In order to evaluate the effects of substrate preheating on the occurrence of micro-cracks, the HACs were deposited at different initial substrate temperatures (TS = 20, 100 and 200°C). The changes in phase composition and HA splat morphology with TS were observed and were correlated with the cracking occurrence. The results showed that severe cutting conditions introduced a localized cracking in the regions of HACs dominantly attributed to the brittle hydroxyl-deficient amorphous calcium phosphate (ACP) phase. This effect was particularly observable in the HACs deposited without preheating of substrate. On the other hand, the preheating of substrate reduced the presence of micro-cracks and caused insignificant changes in the average local phase composition. In HACs deposited with preheating of substrate, the HA splats (of which HACs are composed) were thinner and recrystallized HA regions seemed smaller in size and more evenly distributed. These results implied potentially important roles of the HA splat formation mechanism on the distribution of ACP and recrystallized HA regions in the as-plasma-sprayed HACs and the cracking resistance of HACs. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. TR 34022]

Abstract We describe fabrication of hydroxyapatite coatings consisting of micrometric hexagonal crystals on titanium substrate. The aim was to evaluate their phase stability and in vitro performance. We employed a facile hydrothermal method assisted with a chelating agent and monoethanolamine as regulators of the nucleation and crystal growth. After the hydrothermal reaction, the hydroxyapatite coatings were sintered at different temperatures up to 950 °C. We performed in-depth investigations into the coating surface morphology, topography, wettability, and chemical composition using scanning electron microscopy, profilometry, sessile drop technique, x-ray diffraction and Raman spectroscopy. We assessed the bioactivity of hydroxyapatite structure sintered at different temperatures after incubation in the SBF solution. Simultaneously, we conducted a series of in vitro experiments based on MTT assay using MC3T3 mouse preosteoblast cell line to study the cytocompatibility of synthesized specimens. The results show that the thermal processing of hydroxyapatite coatings leads to their thermal decomposition to β-TCP phase already at 700 °C. As the heat treatment progresses, the edges of hexagonal crystals are melting and smoothing. We show that while as-prepared hydroxyapatite coating exhibits remarkable bioactivity after just 3 days, the sintered samples are not bioactive at all. Biological examination with MC3T3 cells indicates good compatibility of all coatings, with cell proliferation being enhanced on samples heated at higher temperatures. In conclusion, the heat treated HAp coatings with different morphologies and different HAp/β-TCP phase ratios influence the in vitro bioactivity and response of preosteoblast cells. Highlights • Fabrication of hydroxyapatite coatings by the facile hydrothermal method assisted with a chelating agent and monoethanolamine • Evaluation of the phase stability of hydroxyapatite coatings consisting of micrometric hexagonal rods • Assessment of the in vitro bioactivity and cytocompatibility of the synthesized specimens [ABSTRACT FROM AUTHOR]

The surface condition of an implant has a significant impact on response occurring at the implant-biosystem border. The knowledge of physical-chemical and biological processes allows for targeted modification of biomaterials to induce a specified response of a tissue. The present research was aimed at development of technology composing of obtaining the nanotube oxide layers on a porous titanium alloy Ti13Nb13Zr, followed by the deposition of phosphate coating. The porous substrate (porosity about 50%) was prepared by a selective laser melting of the Ti13Nb13Zr powder with the SLM Realizer 100 equipment. The nanotubular oxide layers were fabricated by electrochemical oxidation in H3PO4 + 0.3% HF mixture for 30 min. at a constant voltage of 20V. The calcium phosphate coatings were formed by the electrochemically assisted deposition (ECAD). The presence of nanotubular oxide layers with their internal diameters ranging from 30 to 100 nm was observed by SEM (JEOL JSM-7600F). The nanotubes have dimensions that facilitated the deposition of hydroxyapatite. [ABSTRACT FROM AUTHOR]

The stability and degradability of hydroxyapatite coatings on dental implants depends on the dissolution of the individual chemical phases. Hydroxyapatite-coated dental implants exhibit a range of amorphous-phase content. Two tests were conducted to observe the course of coating degradation. The first test showed degradation of both crystalline and amorphous coatings by cracking and dissolution after immersion in Ringer's solution. Concomitant saturation of the implants in the solution modified the coated surface with precipitated crystalline apatite. A second test, intended to replicate the conditions of infection by decreasing pH, illustrated preferred dissolution of the amorphous phase, liberating crystalline segments. It is expected that morphologic changes could influence the rate of bone bonding and therefore could alter or control implant-tissue interactions. [ABSTRACT FROM AUTHOR]

Although the use of hydroxyapatite-coated (HA-coated) endosseous implants in the treatment of dental patients has been established, their clinical predictability remains controversial. This study is an analysis of the clinical predictability and indications for use of HA-coated endosseous implants. This study also discusses the biochemical composition of commercial HA coatings in relation to in vivo predictability, potential concerns, and potential advantages of HA coatings. Clinical studies suggest that HA-coated implants have short-term survival rates (ranging from 6 months to 6 years) that are comparable to short-term survival rates of titanium implants. In addition, clinical data suggest that HA-coated implants may be valuable treatment modalities when placing implants (1) in type IV bone, (2) in fresh extraction sites, (3) in grafted maxillary and/or nasal sinuses, or (4) when using shorter implants (less than or equal to 10 mm). However, long-term controlled studies are required to validate these observations. [ABSTRACT FROM AUTHOR]

Background: Periprosthetic joint infections are severe complications of arthroplasty, difficult to manage due to biofilm formation on the components. Recently, the use of silver nanoparticles (SNs) has emerged as a method of preventing biofilm formation on orthopaedic implants, however little is known about the systematic toxicity of SNs. Aim: This study used a rabbit model to examine the tissue response of bone, liver and kidney to prototype components with SN doped hydroxyapatite (HA) coatings. Materials and methods: Twelve prototype implants (six with HA, six with SN doped HA coatings) were implanted into the femora of twelve New Zealand Rabbits. After 6 weeks, the animals were euthanised, their femora and samples of livers and kidneys harvested to prepare microscopic slides. The slides were examined for the presence inflammatory or toxic reactions to SNs, implants were examined using scanning electron microscopy (SEM) to determine structural changes related to implantation and verify retention of SNs in vivo. Results: SEM demonstrated that SNs formed submicron conglomerates, which were retained after 6 weeks in vivo and did not interfere with osseointegration. Histologic studies of bone fragments demonstrated no signs of acute toxicity and inflammation. No inflammatory reaction was observed in kidneys, although in some samples signs of acute renal failure related to euthanasia were found. No severe toxic reaction was found in liver samples, however fatty degeneration of liver was found in some animals. Conclusions: This study documented good osteointegration of implants with SN doped HA coatings with low systematic toxicity of SNs.

Introduction. Periprosthetic joint infections are severe complications of arthroplasty, difficult to manage due to biofilm formation on the components. Recently, the use of silver nanoparticles (SNs) has emerged as a method of preventing biofilm formation on orthopaedic implants, however little is known about the systematic toxicity of SNs. Aim. This study used a rabbit model to examine the tissue response of bone, liver and kidney to prototype components with SN doped hydroxyapatite (HA) coatings. Material and Methods. Twelve prototype implants (six with HA, six with SN doped HA coatings) were implanted into the femora of twelve New Zealand Rabbits. After 6 weeks, the animals were euthanised, their femora and samples of livers and kidneys harvested to prepare microscopic slides. The slides were examined for the presence inflammatory or toxic reactions to SNs, implants were examined using scanning electron microscopy (SEM) to determine structural changes related to implantation and verify retention of SNs in vivo. Results. SEM demonstrated that SNs formed submicron conglomerates, which were retained after 6 weeks in vivo and did not interfere with osseointegration. Histologic studies of bone fragments demonstrated no signs of acute toxicity and inflammation. No inflammatory reaction was observed in kidneys, although in some samples signs of acute renal failure related to euthanasia were found. No severe toxic reaction was found in liver samples, however fatty degeneration of liver was found in some animals. Conclusions. This study documented good osteointegration of implants with SN doped HA coatings with low systematic toxicity of SNs. [ABSTRACT FROM AUTHOR]

Hydroxyapatite (HA) is one of the most important bioceramic materials used in medical implants. The structure of HA coatings is closely related to their manufacturing process. In the present study, HA coatings were deposited on Ti-6Al-4V substrate by micro-plasma spraying. Results show that three distinct HA coatings could be obtained by changing the spraying power from 0.5 to 1.0 kW and spraying stand-off distance from 60 to 110 mm: (1) high crystallinity (93.3%) coatings with porous structure, (2) high crystallinity coatings (86%) with columnar structure, (3) higher amorphous calcium phosphate (ACP, 50%) coatings with dense structure. The in-flight particles melting state and splat topography was analyzed to better understand the formation mechanism of three distinct HA coatings. Results show that HA coatings sprayed at low spraying power and short stand-off distance exhibit high crystallinity and porosity is attributed to the presence of partially melted particles. High crystallinity HA coatings with (002) crystallographic texture could be deposited due to the complete melting of the in-flight particles and low cooling rate of the disk shape splats under higher spraying power and shorter SOD. However, splashed shape splats with relative high cooling can be provided by increasing SOD, which leads to the formation of ACP. [ABSTRACT FROM AUTHOR]

Hydroxyapatite coatings were deposited on stainless steel substrates. The arc current was varied to study its effect on the coating crystallinity. The crystallinity was calculated according to the XRD patterns via Jade 6.0 software and the full width at half maximum (FWHM) of Raman peak at 962 cm −1 . The FE-SEM images showed that HA coatings had rod-like nanostructures and agglomerated into microspheres. The XRD patterns indicated that the as-sprayed coatings were composed of HA and some decomposition phases. Micro-Raman spectroscopies demonstrated that the main phase in the coatings was HA. The results showed that the crystallinity was increased from 68.68% to 76.84% while the FWHM varied from 9.74 to 6.38 cm −1 , when the arc current increased from 400 A to 600 A. The selected area electron diffraction (SEAD) patterns were used to analyze the crystallinity qualitatively, and the results agreed with the conclusions of XRD and FWHM of Raman peak. [ABSTRACT FROM AUTHOR]

• Preparation of blasting-laser composite pretreatment surface to improve the bonding strength of the coating. • The effect of texture on the bonding strength of the coating is significantly larger than that of blasting. • The bonding form of the coating on the substrate surface contributes more to its bonding strength. • The groove depth and irregularity of the composite texturing interface increase the energy required for crack expansion. Hydroxyapatite (HA) coatings are widely used for surface modification of artificial joints and dental implants, and the bonding property is a key factor in the effectiveness and longevity of the implants. To improve the bonding performance of the coating and investigate the bonding mechanism of the coating at different interfaces, a composite texturing surface pretreatment method of blasting-laser is proposed in this study. HA ceramic coatings were deposited on blasted and composite textured substrates by atmospheric plasma spraying (APS) technology. The tensile and shear strengths of the coatings were evaluated by tensile tests. The bonding properties of coatings on different pretreated surfaces and the mechanism of interface effects on the failure behavior of the coatings were investigated. The results show that the average tensile strength of the coatings on composite texturing surfaces was increased by 29.5% and the average shear strength was enhanced by 26.6% compared with grit blasting (GB). This is because the composite texturing surface increases the surface roughness of the substrate, enlarges the interfacial contact area of the coating, and weakens the stress concentration effect. Meanwhile, the bonding form of the coating on the composite texturing surface is dominated by stronger embedded and occluded bonds. The shear interface exhibits stepped lamellar fracture morphology with directional expansion along the internal crevices of the coating, showing weak surface shear damage characteristics. The shear strength of the coating is related to its deposition quality. The columnar texture interface contributes to the shear resistance of the coating. The tensile force causes microcracks in the coating to expand along internal defects, forming pull-out pits and emission cracks, and the tensile strength is positively correlated with the damage degree of the coating. In particular, the texturing interface with a depth-to-width ratio (d/w) near 0.65 contributes to the tensile properties of the coating. [ABSTRACT FROM AUTHOR]

Nd:YAG (532 nm) pulsed laser deposition (PLD) has been used to produce crystalline hydroxyapatite (HAP) coatings at room temperature onto silicon substrates. The PLD HAP coatings were homogeneous (100.4 nm RMS roughness) and consisted of micrometric particles (> 10 μm) coalesced over a nanometric dense layer. The deposition parameters of 532 nm laser, 30 J/cm 2 fluence, 10 − 4 Pa vacuum environment and room temperature are capable of coating any surface with crystalline HAP without requiring heat treatment. It was confirmed by Synchrotron Radiation Grazing Angle X-ray Diffraction (GAXRD) patterns that the nanocrystalline component present in the coatings was reduced and did not hide peaks of decomposition to other calcium phosphate (CaP) phases when in situ heat treatments of 200 °C and 800 °C were performed. The use of dense and stoichiometric HAP targets that could withstand the high-fluence laser allowed producing 150 nm crystalline HAP coatings in only 5 min of deposition time, although 532 nm laser wavelength is outside the absorption range of the HAP. This contribution opens the perspective to produce controlled PLD HAP coating over thermally sensitive substrates with reduced processing time for large-scale production for biomedical applications. As a demonstration, HAP coating was deposited and characterized on thermal sensitive bioabsorbable polylactide (PLA) surfaces. [ABSTRACT FROM AUTHOR]

Pulsed Laser Deposition (PLD) and Matrix Assisted Pulsed Laser Evaporation (MAPLE) techniques were applied for growing hydroxyapatite (HA) thin films on titanium substrates. All experiments were conducted in a reaction chamber using a KrF* excimer laser source (λ = 248 nm, τ FWHM ≈ 25 ns). Half of the samples were post-deposition thermally treated at 500 °C in a flux of water vapours in order to restore crystallinity and improve adherence. Coating surface morphologies and topographies specific to the deposition method were evidenced by scanning electron, atomic force microscopy investigations and profilometry. They were shown to depend on deposition technique and also on the post-deposition treatment. Crystalline structure of the coatings evaluated by X-ray diffraction was improved after thermal treatment. Biocompatibility of coatings, cellular adhesion, proliferation and differentiation tests were conducted using human mesenchymal stem cells (MSCs). Results showed that annealed MAPLE deposited HA coatings were supporting MSCs proliferation, while annealed PLD obtained films were stimulating osteogenic differentiation. [ABSTRACT FROM AUTHOR]

Coatings of hydroxyapatite (HAp) were prepared by plasma spraying with induction preheating of titanium substrate from 200 to 1000 °C. The combination of conventional plasma spraying and induction preheating ensured high mechanical properties of HAp coatings. The coatings produced in the temperature range 400–600 °C were characterized by homogeneous nanostructure of splats with an average grain size of 12–31 nm. According to the results of nanoindentation HAp coatings with high hardness 0.9–1.2 GPa and elastic modulus 7–16 GPa were formed on the titanium. [ABSTRACT FROM AUTHOR]

To obtain hydroxyapatite (HA) coatings with high crystallinity which have long-term stability in clinical applications, coarse powders were usually injected to less energetic plasma. However, the HA coatings accumulated by partly melted particles usually have high porosity and poor mechanical properties, especially poor bonding strength. In this work, by profiting its quenching and mechanical impact, dry-ice blasting was in-situ employed during plasma spray process to improve the microstructure characterization and bonding strength of HA coatings. In addition, the influence of in-situ dry-ice blasting on the phase composition and crystallinity of plasma-sprayed HA coatings was investigated. The results show that a significant reduction of porosity and an apparent increase in bonding strength are revealed in plasma-sprayed HA coatings due to the cleaning effect of dry-ice blasting on the convex unmelted particles and splashing fragments. HA coatings prepared by the combination process of plasma spraying and dry-ice blasting have a compromise structure with minimum globular pores but with pronounced microcracks. The disappearance of CaO phase and the increase in crystallinity also derive from the application of dry-ice blasting. [ABSTRACT FROM AUTHOR]

Solution precursor plasma spraying (SPPS) is a promising method of obtaining coatings with unique microstructural features. The present study reports about the development of hydroxyapatite (HA) coatings by SPPS using water-based calcium-phosphate solution and about the analyses of their microstructure. X-ray diffraction (XRD) analysis showed that HA was the major crystal phase of the coatings, being present in the range from 95% to 98%. The coatings of greater HA content were obtained while spraying using shorter spray distance. The coating crystallinity ranges from 24% to 69% depending on the temperature at deposition. An increase of the temperature results in greater crystallinity. The obtained coatings' microstructures may be described by dome-like surface and by the columnar-like cross-section when using precursor with low concentration. The use of concentrated solution precursor results in cauliflower-like structures composed of agglomerated fragmented shells and fine spherical particles. The possible phenomena occurring in droplets in contact with the plasma jet and the coating build-up mechanisms were tentatively explained. [ABSTRACT FROM AUTHOR]

The aim of this work was to examine the dependence of the local surface structure (surface structural heterogeneity) on the local thickness (thickness uniformity) and structure properties along the thickness of hydroxyapatite coatings (HACs) deposited by using the high power (52 kW) laminar plasma jet. For the deposition process, a relatively small size of the feedstock hydroxyapatite powder (HAP) (33 μm) was used. The HACs were deposited at different stand-off distances (SODs) (80, 100, and 150 mm) without preheating of substrates. The thickness measurements were performed by using the calibrated micrometer and light microscopy (LM). The surface micro-structure was analyzed by using the micro-Raman spectroscopy (MRS), whereas the micro-structure along the thickness of HACs was studied by using the MRS, X-ray powder diffractometry (XRPD), and LM (combined with chemical etching). The results showed a heterogeneous phase distribution on the surface of each HAC analyzed as well as the non-uniform thickness of HACs. Apparently, a correlation existed between the local surface structure and the local thickness of HACs. However, the MRS, XRPD, and LM analyses of micro-structure along the thickness of HACs indicated that the differences in the local surface structure could be related to the different recrystallization established during the plasma deposition process in the different parts along the thickness of each HAC analyzed. [ABSTRACT FROM AUTHOR]

Titanium alloys are successfully used in medicine as implants due to their high mechanical properties and good biocompatibility. To improve implant osseointegration of titanium alloys, they are covered with hydroxyapatite because of its bioactive properties. Coating the implants with hydroxyapatite by thermal spraying, due to the temperatures developed during the deposition process, the structure can be degraded, leading to formation of secondary phases, such as TCP, TT CP, CaO. The paper presents the experimental results of hydroxyapatite layers deposition by two thermal spraying methods: Atmospheric Plasma Spraying (APS) and High Velocity Oxy-Fuel (HVOF). The microstructure of the deposited layers is characterized by X-ray diffraction analysis and electronic microscopy. The bioactivity of the hydroxyapatite layers was investigated in Simulated Body Fluid (SBF) by immersing the covered samples deposited by the two thermal spraying methods. In both cases the coatings did not present defects as cracks or microcracks. X-ray diffraction performed on hydroxyapatite deposited layers shows that the structure was strongly influenced by plasma jet temperature, the structure consisting mainly of TCP (Ca3PO4)2. The samples deposited by HVO F after immersing in SBF lead to formation of biological hydroxyapatite, certifying the good bioactivity of the coatings.

Suspension plasma spraying is a process that enables the production of finely grained nanometric or submicrometric coatings. The suspensions are formulated with the use of fine powder particles in water or alcohol with some additives. Subsequently, the suspension is injected into plasma jet and the liquid additives evaporate. The remaining fine solids are molten and subsequently agglomerate or remain solid, depending on their trajectory in the plasma jet. The coating’s microstructure results from these two groups of particles arriving on a substrate or previously deposited coating. Previous experimental studies carried out for plasma sprayed titanium oxide and hydroxyapatite coatings enabled us to observe either a finely grained microstructure or, when a different suspension injection mode was used, to distinguish two zones in the microstructure. These two zones correspond to the dense zone formed from well molten particles, and the agglomerated zone formed from fine solid particles that arrive on the substrate in a solid state. The present paper focuses on the experimental and theoretical analysis of the formation process of the agglomerated zone. The experimental section establishes the heat flux supplied to the coating during deposition. In order to achieve this, calorimetric measurements were made by applying experimental conditions simulating the real coatings’ growth. The heat flux was measured to be in the range from 0.08 to 0.5 MW/m2,depending on the experimental conditions. The theoretical section analyzes the sintering during the coating’s growth, which concerns the fine particles arriving on the substrate in the solid state. The models of volume, grain boundary and surface diffusion were analyzed and adapted to the size and chemistry of the grains, temperature and time scales corresponding to the suspension plasma spraying conditions. The model of surface diffusion was found to best describe the sintering during suspension plasma spraying. The formation of necks having the relative size equal to 10% of particle diameter was found to be possible during the thermal cycles occurring at the coatings’ deposition. Transmission electron microscopic observations of the agglomerated zone hydroxyapatite coating confirm the sintering of some of the fine grains.

Hydroxyapatite (HA) crystals exhibit rod-like shape with c -axis orientation and plate-like shape with a ( b )-axis orientation in vertebrate bones and tooth enamel surfaces, respectively. Herein, we report the synthesis of HA coatings with the oriented nanorod arrays (RHACs) and HA coatings with oriented nanoplate arrays (PHACs) by using bioglass coatings as sacrificial templates. After soaking in simulated body fluid (SBF) at 120 °C, the bioglass coatings are hydrothermally converted into the HA coatings via a dissolution-precipitation reaction. If the Ca/P ratios in SBF are 2.50 and 1.25, the HA crystals on the coatings are oriented nanorod arrays and oriented nanoplate arrays, respectively. Moreover, the bioglass coatings are treated with SBF at 37 °C, plate-like HA coatings with a low crystallinity (SHACs) are prepared. As compared with the Ti6Al4V and SHACs, the human bone marrow stromal cells (hBMSCs) on the RHACs and PHACs have better cell adhesion, spreading, proliferation and osteogenic differentiation because of their moderately hydrophilic surfaces and similar chemical composition, morphology and crystal orientation to human hard tissues. Notably, the morphologies of HA crystals have no obvious effects on cytocompatibility and osteogenic differentiation. Hence, the HA coatings with oriented nanoplate arrays or oriented nanorod arrays have a great potential for orthopedic applications. [ABSTRACT FROM AUTHOR]

Preparation of hydroxyapatite coated custom-made metallic bone-implants is very important for the replacement of injured bones of the body. Furthermore, these bone-implants are more stable under the corrosive environment of the body and biocompatible than bone-implants made up of pure metals and metal alloys. Herein, we describe a novel, simple and low-cost technique to prepare biocompatible hydroxyapatite coated titanium metal (TiM) implants through growth of self-formed TiO 2 thin-layer (SFTL) on TiM via a heat treatment process. SFTL acts as a surface binder of HA nanoparticles in order to produce HA coated implants. Colloidal HA nanorods prepared by a novel surfactant-assisted synthesis method, have been coated on SFTL via atomized spray pyrolysis (ASP) technique. The corrosion behavior of the bare and surface-modified TiM (SMTiM) in a simulated body fluid (SBF) medium is also studied. The highest corrosion rate is found to be for the bare TiM plate, but the corrosion rate has been reduced with the heat-treatment of TiM due to the formation of SFTL. The lowest corrosion rate is recorded for the implant prepared by heat treatment of TiM at 700 °C. The HA-coating further assists in the passivation of the TiM in the SBF medium. Both SMTiM and HA coated SMTiM are noncytotoxic against osteoblast-like (HOS) cells and are in high-bioactivity. The overall production process of bone-implant described in this paper is in high economic value. [ABSTRACT FROM AUTHOR]

In this study, surface properties of Ti-6Al-4V alloy coated with hydroxyapatite coatings were investigated. Wear resistance and fatigue behaviour of samples with coating thicknesses of 10 and 50 µm as well as uncoated samples were examined. Wear experiments demonstrated that the friction factor of the uncoated titanium decreased from 0.31 to 0.06, through a fluctuating trend, after 50 cycles of wear tests. However, the friction factor of both the coated samples (10 and 50 µm) gradually decreased from 0.20 to 0.12 after 50 cycles. At the end of the 50th cycle, the penetration depth of the 10 and 50 µm coated samples were 7.69 and 6.06 µm, respectively. Fatigue tests showed that hydroxyapatite coatings could improve fatigue life of a notched Ti-6Al-4V member in both low and high cycle fatigue zones. It was understood, from fractography of the fracture surfaces, that the fatigue zone of the uncoated specimens was generally smaller in comparison with that of the coated specimens. No significant difference was observed between the fatigue life of coated specimens with 10 and 50 µm thicknesses. [ABSTRACT FROM AUTHOR]

Although titanium and its alloys are widely used as implant material for orthopedic and dental applications they show only limited corrosion stability and osseointegration in different cases. The aim of the presented research was to develop and characterize a novel surface modification system from a thin diamond base layer and a hydroxyapatite (HAp) top coating deposited on the alloy Ti6Al4V widely used for implants in contact with bone. This coating system is expected to improve both the long-term corrosion behavior and the biocompatibility and bioactivity of respective surfaces. The diamond base films were obtained by Microwave Plasma Assisted Chemical Vapor Deposition (MW-PACVD); the HAp coatings were formed in aqueous solutions by electrochemically assisted deposition (ECAD) at varying polarization parameters. Scanning electron microscopy (SEM), Raman microscopy, and electrical conductivity measurements were applied to characterize the generated surface states; the calcium phosphate coatings were additionally chemically analyzed for their composition. The biological properties of the coating system were assessed using hMSC cells analyzing for cell adhesion, proliferation, and osteogenic differentiation. Varying MW-PACVD process conditions resulted in composite coatings containing microcrystalline diamond (MCD/Ti-C), nanocrystalline diamond (NCD), and boron-doped nanocrystalline diamond (B-NCD) with the NCD coatings being dense and homogeneous and the B-NCD coatings showing increased electrical conductivity. The ECAD process resulted in calcium phosphate coatings from stoichiometric and non-stoichiometric HAp. The deposition of HAp on the B-NCD films run at lower cathodic potentials and resulted both in the highest coating mass and the most homogenous appearance. Initial cell biological investigations showed an improved cell adhesion in the order B-NCD > HAp/B-NCD > uncoated substrate. Cell proliferation was improved for both investigated coatings whereas ALP expression was highest for the uncoated substrate. [ABSTRACT FROM AUTHOR]

The aim of the present study was to investigate the influence of substrate preheating on the structural properties of hydroxyapatite coatings (HACs) deposited by using the high power (52 kW) laminar plasma jet. The deposition experiments were performed within the 20–200 °C temperature range at different stand-off distances. The structural properties in the thickness direction and at the surface of the HACs were investigated by using the micro-Raman spectroscopy, scanning electron microscopy coupled with energy dispersive spectrometry, and X-ray powder diffractometry. The deposition without the preheating of the substrate produced HACs with crystallinity gradient in the thickness direction. At the stand-off distance of 80 mm, the preheating of the substrate at 200 °C practically eliminated the crystallinity gradient. At distances from the coating/substrate interface shorter than ~100 µm, the increase of crystallinity with the preheating of the substrate was dominantly attributed to the recrystallization of hydroxyl-rich ACP into HA. At longer distances and higher initial substrate temperatures (>100 °C), the crystallinity changes were negligible, whereas the recrystallization of hydroxyl-deficient ACP into oxyapatite (OA) was also possible. The X-ray diffractometry indicated the deposition conditions under which a minimum residual stress was achieved. The results of the present study strongly suggested the relation between the ACP→HA recrystallization process and the bonding strength of the HACs. [ABSTRACT FROM AUTHOR]

Various attempts have been made during recent decades to improve the functionality, biocompatibility and osseointegration of metallic implants. With technological advancement, modifying superficial properties of orthopedic implants has undergone great evolution. Current efforts of scientists and the orthopedic industry have focused on modifying surface properties to achieve a specific biointerface that can reduce patient's healing time and prevent aseptic loosening. This study investigates the contribution of a protective tantalum interlayer deposited on titanium substrates on the growth of hydroxyapatite (HAp) crystals with hydrothermal synthesis method. We investigated the morphology and structure of the produced coatings, as well as in vitro bioactivity in simulated body fluid and biocompatibility in osteoblast-like cell culture. The hydrothermal method allows to synthesize coating with micro-sized HAp crystallites that exhibit rod-like hexagonal shape. The diameter of HAp crystallites may be controlled and driven by nature of the interlayer (tantalum, tantalum oxide or titanium oxide) previously formed on the titanium substrate. Coatings with smaller diameters of HAp crystals (between 0,3 μm and 0,6 μm) synthesized on tantalum-based films were found to be more favorable for cell viability and attachment. High bioactivity and positive effect on the osteoblast-like cells of the HAp biointerface with a tantalum intermediate layer was observed. [Display omitted] • Ta-based interlayers affect morphology and structure of bioactive HAp coatings. • Size of HAp crystallites is moderated by chemical nature of the intermediate layer. • Hydrothermal synthesis favores growth of HAp crystals with rod-like geometry. • Ta-based intermediate layers produce HAp crystals with smaller diameter. • Smaller HAp crystals are more favorable for cell viability and attachment. [ABSTRACT FROM AUTHOR]

The hydroxyapatite coatings were deposited by mechanical alloying on Ti substrates using vibratory and planetary ball mills. The structure and morphology of the deposited coatings were analyzed by X-ray diffraction and scanning electron microscopy. The tribological properties and biocompatibility of the deposited coatings were also studied. A relatively high density and adhesion coating were observed for the coating obtained in a vibratory ball mill for powder mixture ratio of hydroxyapatite to α-Ti as 1:1, respectively. The average value of the hemolysis of the obtained coating was about 6.98%, which was statistically significant. [ABSTRACT FROM AUTHOR]

Hydroxyapatite coatings were successfully produced on modified titanium substrates via hydrothermal synthesis in a Ca(EDTA) 2 − and (NH 4 ) 2 HPO 4 solution. The morphology of modified titanium substrates as well as hydroxyapatite coatings was studied using scanning electron microcopy and phase identification by X-ray diffraction, and Raman and FTIR spectroscopy. The results show that the nucleation and growth of hydroxyapatite needle-like crystals with hexagonal symmetry occurred only on titanium substrates both chemically and thermally treated. No hydroxyapatite phase was detected on only acid etched Ti metal. This finding demonstrates that only a particular titanium surface treatment can effectively induce the apatite nucleation under hydrothermal conditions. [ABSTRACT FROM AUTHOR]