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[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]

• Hydroxyapatite nanoparticles were synthesized utilizing the microemulsion method. • In this synthesis utilized two surfactants with different concentrations of CTAB and a constant amount of DMSO. • Hydroxyapatite coatings in the presence of CTAB were well prepared with smaller particle sizes. • In the presence of surfactants, crack-free and uniform films coated on Ti-6Al-4V with high corrosion resistance. • The coatings prepared with CTAB generated a uniform and ordered array of HAP-NPs with a well-regular spherical shape. Hydroxyapatite nanoparticles (HAP-NPs) were synthesized using a microemulsion (cetyltrimethylammonium bromide (CTAB) and dimethyl sulfoxide (DMSO) as surfactants) method. The influence of the optimum ratios of CTAB concentrations as surfactants in the microemulsion on HAP morphology was investigated. After dispersing the HAP powders, a high-speed spin coating process at 2500 RPM was employed to produce HAP coatings on the Ti-6Al-4V alloy. The HAP-NP properties were characterized using techniques such as XRD, FTIR, FESEM, and AFM. Studies utilizing electrochemical impedance spectroscopy (EIS) in a simulated body fluid (SBF) solution. The corrosion resistance of coated samples compared to bare substrate increased from 67 to 853.34 kΩ cm2. [ABSTRACT FROM AUTHOR]

• A method for hydroxyapatite immobilization on PEKK surfaces was suggested. • Up to 29 ± 3 % of PEKK surface was coated with hydroxyapatite. • Maximum Ca and P content of 5.3 ± 0.1 and 0.5 ± 0.1 at. % was achieved. • Hydroxyapatite immobilization improved cell adhesion to PEKK surface. A novel approach for the immobilization of hydroxyapatite (HAp) on polyetherketoneketone (PEKK) surface was suggested. HAp immobilization was performed in two steps. On the first step, PEKK surface was swelled in 1,1,1,3,3,3-hexafluoropropan-2-ol (HFIP) vapor. Then, the treated sample was placed in HAp water suspension. Up to 29 ± 3 % of the PEKK surface was coated with HAp. The maximum calcium and phosphorus content on the surface of the modified samples was found at 5.3 ± 0.1 and 0.5 ± 0.1 at. %, respectively. Despite the confirmed HAp immobilization, the hydrophobic character of the PEKK surfaces was preserved. HAp immobilization resulted in the enhanced adhesion of multipotent stem cells to the PEKK surfaces: the number of the adhered cells and cell-covered sample area increased nearly 10-fold and 25-fold, respectively. Thus, the suggested approach of HAp immobilization allows improving cell adhesion to PEKK-based surfaces. [ABSTRACT FROM AUTHOR]

[Display omitted] • Strontium-HAp was coated on anodized titanium surfaces via the EPD technique. • Anodization was done at different times to attain varying thicknesses. • The anodized layer greatly influences the adhesion strength of the coating. • As the anodized layer thickness increased, the surface roughness of the coating increased. • Substitution of strontium in HAp enhances the adhesion strength of the coating. The anodization of the titanium surface is believed to assist in good adhesion strength for electrophoretic deposition (EPD) of hydroxyapatite (HAp) coatings. Different time durations are employed to attain the varying thicknesses of anodized TiO 2 nanotube (ATNT) arrays. Strontium was substituted in HAp (SrHAp) to elevate the bioactivity and mechanical properties of the HAp. The surface roughness (Ra) of the coatings was increased with the increase of ATNT thickness. The HAp and SrHAp coatings exhibited average Ra values of 2.861 ± 0.418 μm and 2.668 ± 0.458 μm respectively, at 3 h anodization. Conversely, the adhesion strength of the EPD coatings decreased at 3 h of ATNT. Hence, the tailored ATNT thickness and optimized EPD parameters provide bioactive and mechanically stable coatings for efficient osseointegration. [ABSTRACT FROM AUTHOR]

• Electrophoretic deposition on Vitex negundo -HAP coating on CP-Ti for implant applications. • GCMS results indicate the formation of structure and compound. • It will enhance the corrosion resistance after coating. • SEM morphology shows the porous flaky with flower-like structure was revealed after coating. • The VH-Hap coating enhance the 80% cell viability percentage. In the present work, we aim to synthesize hydroxyapatite with Vitex-negundo plant extract, for coating Cp-titanium for biomedical applications. Titanium has good biocompatibility and excellent corrosion resistance. This study reports the synthesis of Vitex-negundo hydroxyapatite with enhanced osteoblast activity. Vitex-negundo has good anti-oxidant and anti-inflammation activity, etc. Synthesized plant extract was confirmed by the GCMS to find out the structure. The surface morphological studies of EPD coating on Ti surfaces exhibited porous flakes with flower-like morphology. The occurrence of functional groups and the crystalline structure validated VH-HAp with and without coating on Ti. Potentiodynamic polarization studies evaluated in Hank's solution exhibited the lowest i corr value of 3.2 µA. In-vitro studies of MG63 cell culture showed 80% cell viability after 48 h of incubation in DMEM solution. Thereby, the biosynthesis of VH-hydroxyapatite coatings is a potential candidate for biomedical implant applications. [ABSTRACT FROM AUTHOR]

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

• A novel Ta/hydroxyapatite (HA) composite coating was fabricated. • Ta and HA are evenly distributed in the composite powders and composite coatings. • Ta and HA did not appear to undergo oxidation, decomposition and phase transformation. • The as-prepared Ta/HA composite coating has high bioactivity. To avoid the decomposition of hydroxyapatite (HA) and thus further increase its bioactivity, a novel bioactive Ta/HA composite coating (∼23 μm) is firstly fabricated by cold spraying mechanical milling Ta/HA composite powders. The results indicate that HA without decomposition and phase transformation is well contained and evenly distributed in the composite powders and coating. The simulated body fluid (SBF) test shows that bone-like apatite layer is mineralized on the surface of composite coating after 1–3 days. It demonstrates that the as-prepared Ta/HA composite coating has high bioactivity. [ABSTRACT FROM AUTHOR]

• It is possible to electrodeposited Sr-HA and Sr/Mg-HA coatings onto Ti-40Nb alloys. • Sr-HA coating exhibits a homogenous cauliflower-like nanostructure. • Mg as co-dopant inhibits HA crystallization and produces nanosphere-like crystals. • The co-doping process increases Ca-deficiency. Ti-40Nb alloy is an excellent choice for long-term implant applications due to its biocompatibility, high corrosion resistance and low Young's modulus. To improve osteointegration and biological performance, hydroxyapatite (HA) coatings with ionic substitutions such as Sr or/and Mg have been proposed. Thus, the aim of this work was to obtain Sr substituted HA and Sr/Mg-co-substituted hydroxyapatite coatings using electrochemical deposition onto Ti-40Nb alloys. This technique has a high versatility and ability to coat irregular surfaces. The results showed it is possible to obtain a Sr-HA or Sr/Mg-HA coatings onto Ti-40Nb alloys using this method. The incorporation of 0.5% of Sr into HA produces a homogenous layer with a cauliflower-like microstructure of calcium deficient hydroxyapatite nanocrystals; while the addition of Mg as co-dopant (Sr + Mg = 1%) inhibits the hydroxyapatite crystallization, modified the microstructure to nanosphere-like crystals and increases Ca-deficiency. [ABSTRACT FROM AUTHOR]

Highlights • Various nanocrystal shapes of HA were prepared by hydrothermal process. • The synthesized HA's crystals were used for EPD to produce nanostructured coatings. • The rMSC viability on SHA coatings was higher that MHA and LHA coatings. • MHA coatings showed higher cell adhesion compare to SHA and LHA (MHA > SHA > LHA). • MHA coatings showed higher spreading compare to SHA and LHA at 12 and 24 h. Abstract Bioactive nanostructured coating has been a key strategy to improve the cell adhesion and osseointegration of metallic implants. This study presents the electrophoretic coatings of hydroxyapatite with tunable nanocrystal morphologies. The hydroxyapatite nanocrystals were prepared with three different elongated dimensions by the hydrothermal method (∼80 nm; SHA, ∼300 nm; MHA, and ∼900 nm; LHA), which were used in combination with a fugitive biopolymer chitosan for the electrophoretic deposition on titanium. All the HA coatings were densely and homogeneously deposited and had different and unique nanotopologies and corresponding surface areas. The coating parameter significantly altered the cell behaviors including anchorage, spreading and proliferation; the cell adhesion was better on the small- and middle-sized nanocrystals (SHA, MHA > LHA), which was interestingly opposite in cell spreading (LHA > SHA, MHA), and then the cell proliferation was again up-regulated on SHA and MHA. Although more studies are needed to elucidate the biological phenomenon, the sets of results imply the importance of tailored nanocrystal morphology in the initial (adhesion and growth) cellular events. [ABSTRACT FROM AUTHOR]

In this study, the natural hydroxyapatite (HA) has been obtained from Corbicula moltkiana shell (CS), which are available as waste from local food processing. The shell can be used as an inexpensive source of natural HA providing at the same time to give added value to food processing by-products as well as reducing the undesirable environmental impact. The synthesized natural HA have been characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), X-ray Fluorescence (XRF) spectrometer and transmission electron microscopy (TEM) studies. The XRD peaks were in agreement with the standard JCPDS file (ICSD-157481). The material obtained at 900 and 1000 °C (HA 900 and HA 1000) have a low crystallinity of hydroxyapatite. At 1000 °C, a tetracalcium phosphate (TTCP) peak was observed. In addition, the crystal size of HA calculated from XRD pattern was found to be a nanosized crystal of 28.90 nm and 6.31 nm for HA 1000 and HA 900 respectively. [ABSTRACT FROM AUTHOR]

Hydroxyapatite nanocrystals were synthesized by wet chemical precipitation using bio-waste shells of mollusk (clam and mussel) and egg as feedstock materials. The powdered shells were calcined, dissolved in water, and the resulting product was reacted with phosphoric acid. X-ray diffraction analysis identified pure phase of hydroxyapatite for the three different raw materials. Transmission electron microscopy observations of hydroxyapatite indicated that rod-like crystals were produced in nanometric scale, which showed pH-dependent surface charges using zeta potential analysis. Overall, this study proved that calcium-rich bio-wastes are valuable materials to be used as feedstock for production of high purity and economically feasible hydroxyapatite nanocrystals for biomedical and technological applications. [ABSTRACT FROM AUTHOR]

Carbon nanotubes and SiC nanoparticles reinforced Na and F co-doped hydroxyapatite coating (CS-NFH) was fabricated by electrochemical deposition method. The morphology, microstructure, shear strength, wettability and in-vitro bioactivity of CS-NFH coating were analyzed. Homogeneous and crackfree CS-NFH coatings composed of spherical particles were achieved. The shear strength for CS-NFH was 9.04 MPa, which was more than twice the value of that for pure hydroxyapatite coating. Wettability test showed CS-NFH coating had super-hydrophilicity surface with water contact angle of 0°. The in-vitro bioactivity test showed that the coating could induce the formation of new apatite in simulated body fluid. CS-NFH may have potential application as coating materials in orthopaedic applications. [ABSTRACT FROM AUTHOR]

In this paper, the titanium (Ti) surfaces with different structure, composition, crystal form and grain size are prepared by micro arc oxidation and thermal treatment, and then their hydrophilicity and surface roughness are investigated. The experimental results show that there is no necessary relationship between hydrophilicity and surface roughness. For hydroxyapatite (HA) coatings with different surface structures, the structure with more HA amount has better hydrophilicity. And, with the same porous structure, HA surface endows better hydrophilicity than TiO 2 . Anatase surface with small grain size has better hydrophilicity and rutile has better hydrophilicity than anatase. Combined with their biological properties which have been well reported, the dependent relationship of hydrophilicity and biological properties can be concluded, namely the good biological properties can be obtained by improving the hydrophilicity. This research work sheds light on the methods for optimization of biological properties of the implant materials. [ABSTRACT FROM AUTHOR]

Polydopamine (PDA)/casein phosphopeptide (CPP) bilayers were prepared on titanium (Ti) substrates through a simple two-step immersion process at room temperature. The adhering PDA interlayers linked the natural biomolecule, CPP, to the Ti surface via covalent bonds. The outer layer of CPP served as a template to bind Ca 2+ and thus promoted nucleation and growth of hydroxyapatite (HA). Our results indicate that: (i) PDA and CPP can be successfully grafted onto Ti substrates; (ii) an HA coating can be formed within 1 day through the biomimetic HA coating method on the Ti substrate modified with PDA/CPP bilayer; and (iii) no cracking is observed in the HA coating, indicating stable binding between HA and the modified substrate. [ABSTRACT FROM AUTHOR]

Hydroxyapatite (HAP) scaffolds with a hierarchical porous architecture were prepared by a new dual-template (corn starch and cetyltrimethylammonium bromide (CTAB) surfactant) used to cast HAP nanoparticles and development scaffolds with size hierarchical porous distribution. The powder X-ray diffraction (XRD) results showed that only the HAP crystalline phase is present in the samples after calcination; the Scanning Electron Microscopy (SEM) combined with Small Angle (SAXS) and Ultra-Small Angle X-ray Scattering (USAXS) techniques showed that the porous arrangement is promoted by needle-like HAP nanoparticles, and that the pore size distributions depend on the drip-order of the calcium and the phosphate solutions during the template preparation stage. [ABSTRACT FROM AUTHOR]

In this study, for the first time we have developed the composite coatings using sol-gel derived hydroxyapatite [HAP: (Ca) 10 (PO 4 ) 6 (OH) 2 ] and magnetite (Fe 3 O 4 ) on alkali treated Ti-6Al-4V alloy using various concentrations of Fe 3 O 4 nanoparticles such as 1, 3 and 5 wt% respectively. The fabricated composite coatings were characterized by XRD, SEM-EDAX and contact angle measurements. In vitro bioactivity study confirmed that the composite coated Ti-6Al-4V was highly bioactive and induces bone like apatite formation in the presence of Fe 3 O 4 NPs which involves the nucleus formation by developing Fe-OH groups on the surface of coatings. The corrosion resistance study proved that 1 wt% of Fe 3 O 4 with HAP composite coatings exhibit good anticorrosion behaviour than the 3, 5 wt% of composites due to lower Fe-OH groups and uniform with adherent layer which restricts the leaching of ions. Hence, this finding suggested that HAP/Fe 3 O 4 composites coated implants can be used for biomedical applications. [ABSTRACT FROM AUTHOR]

This study focuses on optimizing nanocomposite coatings of nanophase hydroxyapatite (nHA) and poly(lactic- co -glycolic acid) (PLGA) on magnesium (Mg) substrates using one-step electrophoretic deposition (EPD). The nHA, PLGA and Mg are all biodegradable in the human body, which makes them favorable for temporary implant applications. Mg and its alloys possess the elastic modulus and strength comparable to cortical bone, and thus reduce the detrimental effects of stress-shielding while providing necessary strength for load-bearing applications. The nHA is an attractive coating material for bone healing due to its osteoconductivity. PLGA promotes coating adhesion, and may neutralize the alkaline degradation products of Mg substrates. The nHA_PLGA composite coatings were deposited on Mg substrates using EPD with acetone as the electrolyte solvent. The parameters for EPD process, such as deposition voltage, time and electrolyte concentration, were studied to determine the optimal condition for creating the nHA_PLGA coating on Mg. The nHA_PLGA coating showed a desirable thickness of 65.85±11.95 µm with a complete homogenous coverage on Mg substrates when the deposition voltage of 75 V was applied for 6 min using an electrolyte containing 1 mg/mL nHA and 0.2 mg/mL PLGA in acetone. The characterization of the coating confirmed the presence of both nHA and PLGA. [ABSTRACT FROM AUTHOR]

Degradation properties of bone scaffolds are strongly related to cell growth, host response and tissue regeneration. However, bone formation is a very slow process and, in the first few weeks after implantation, the mechanical stability of the scaffold plays a key role for the success of the regeneration progression. In the present study, in vitro properties of highly porous hydroxyapatite (HA) scaffolds were analysed in terms of bioactivity and biodegradation by observing their microstructure, measuring the weight loss and evaluating their mechanical stability. HA scaffolds fabricated by sponge replica method have been incubated for different periods of time in Simulated Body Fluid and in tris-HCL buffer. The morphological and mechanical characterizations performed on the scaffolds before and after immersion demonstrated the scaffolds being bioactive and almost not biodegradable in four weeks in terms of weight loss and mechanical resistance. [ABSTRACT FROM AUTHOR]

Hydroxyapatite (HAp) scaffolds with uniform pore size and interconnected pore network were constructed based on the inverted colloidal crystal (ICC) geometry and a simple sol-gel formulation. Monodisperse polystyrene microspheres were self-assembled and annealed into a hexagonal close packed structure. HAp sol-gel was infiltrated in this template followed by thermal treatment for simultaneous HAp matrix sintering and polymeric colloidal crystal calcination. The resultant ICC scaffolds exhibit an ordered architecture that was able to offer a favorable environment for human osteoblasts adhesion and proliferation, an essential feature for bone ingrowth in tissue engineering applications. [ABSTRACT FROM AUTHOR]

This study fabricated porous spherical hydroxyapatite (HA) bioceramic granules via a novel method by combining the ionotropic gelation of sodium alginate with H 2 O 2 gas-foaming. Firstly, HA powder was dispersed in sodium alginate solution; then, the bubbly slurry prepared by H 2 O 2 gas-foaming was dripped into CaCl 2 solution to form hydrogel spheres; finally, these hydrogel spheres were washed, dried and sintered to obtain the HA bioceramic granules. SEM images revealed that the obtained HA granules exhibited spherical shape and interconnected porous structure. XRD, FT-IR and ICP-OES tests confirmed the phase composition and the purity of the HA spherical granules. Compared with commercialized HA irregular granules (BAM ® P2040), the HA spherical granules had smaller grain size, more micropores, larger specific surface area and stronger protein adsorption ability. Therefore, the porous spherical HA bioceramic granules shows potential to be a good candidate for bone defect filling materials. [ABSTRACT FROM AUTHOR]

The present work demonstrates a low cost route to produce hydroxyapatite (HA) from fish bones (natural source) by a simple heat treatment process. The produced HA was characterized by X-ray diffraction (XRD), scanning electron microscopy and transmission electron microscopy (TEM). Elemental composition obtained from energy dispersive X-ray analysis confirmed the presence of Ca, P, O and Mg. XRD analysis has clearly shown that the produced phase as HA. The powders were heated from 600 to 1000 °C and from the TEM observations, large fused crystals (≈200 nm) were noticed. XRD analysis of the heat treated powders have also not shown new phases and which is an indication of the purity level of HA. [ABSTRACT FROM AUTHOR]

Micro-plasma spraying was used to fabricate HA coatings on Ti-6Al-4V substrate. The coating phase distribution significantly changed throughout the coating depth. Crystalline HA, ACP and ß-TCP were observed near the coating-substrate interface. However, HA content increased with increasing distance from interface, and it was ~90% at top surface of the coating (>40 μm) according to micro-Raman analysis. Columnar structure was found in such region, which was related to a strong (002) crystallographic texture. In addition, dissolution behavior of the coating was evaluated by immersing the material in balanced salt solution for 14 days. The study revealed that HA coating exhibited superior chemical stability, and the columnar structure emerged on the surface of the coating during immersion experiment. [ABSTRACT FROM AUTHOR]

• The PDA@Ag coating on α-TCP cement was prepared conveniently and efficiently. • The effect of the coating on mineralization properties of cement was investigated. • The antibacterial assay of the cement was performed and the mechanism was analyzed. The ideal orthopedic material demands excellent antimicrobial properties and bioactivity after initial implantation in vivo. In this paper, a polydopamine (PDA) film was prepared by dopamine self-polymerization on α-tricalcium phosphate (α-TCP) cement, and then silver (Ag) particles were immobilized in-situ on the surface of PDA via a dipping method. The presence of PDA and Ag in the composition of modified cement was confirmed by XPS. The results showed that after the modification of PDA coating and Ag particles, the roughness and contact angle of the cement increased from 36.4 nm to 120 nm and 18.8° to 58.8°, respectively. Moreover, the mineralization capacity of modified cement was considerably enhanced, generating dense hydroxyapatite (HA) layer with a thickness of 3.04 μm. Furthermore, the modified cement was revealed to provide antibacterial rate over 99 %. It is suggested that good bioactivity and antimicrobial properties of the cement can be achieved using the promising method. [ABSTRACT FROM AUTHOR]

Cuttlefish bone is a calcium carbonate composite with a homogeneous, interconnected porous structure. The aim of this study was to investigate the potentiality of surface modified unprocessed cuttlefish bone as a bone substitute. For this purpose, the surface of unprocessed cuttlefish bone (CB) was modified with hydroxyapatite (HA) and collagen (COL). The internal lamellar matrix of cuttlefish bone was cut into small uniform blocks and kept submerged into simulated body fluid (SBF) to form a hydroxyapatite layer on the surface (CB-HA scaffold). Then it was coated with collagen using the freeze drying method (CB-HA-COL scaffold). Scaffolds were characterized morphologically. Biocompatibility of the scaffolds was tested using rat bone marrow mesenchymal stem cells (RBMSCs). CB-HA-COL scaffold exhibited higher cell proliferation rate and alkaline phosphatase activity of RBMSCs in vitro conditions. These findings suggest that surface modified unprocessed cuttlefish bone can be beneficial for bone tissue engineering. [ABSTRACT FROM AUTHOR]

Crystalline hydroxyapatite (HAP) was successfully coated on titanium substrate via a combined biomimetic-hydrothermal method, throughout all synthesis processes were simply chemical-treated under a moderate condition while the highest temperature would not exceed 180 °C. Biomimetic mineralization was applied to provide the seeded layer, which was prerequisite and facilitated the subsequent hydrothermal growth, while hydrothermal process promoted the nucleation and crystal growth, finally the phase-pure and high crystalline nano prism-like HAP was achieved well-arrayed onto titanium surface with a multi-level structure. Furthermore, this way combined biomimetic-hydrothermal method could be easily extended as a universal technique for surface modification and coating fabrication of versatile materials. [ABSTRACT FROM AUTHOR]

This paper describes evaluation process of bending strengths of plasma-sprayed hydroxyapatite (HAp) coatings. Plasma-sprayed HAp coatings are widely used in the fields of medical implant in order to improve the biocompatibility of substrate alloys in vivo. Their strength is normally evaluated by indentation-fracture method (IF method) or shearing tests. However, these results are considerably varied because of the pores on the surfaces of coatings and to accurately discuss the quality of coatings, the effects of pore size distributions on their strengths must be considered. The maximum pore size was then predicted using extreme statistics and modified Saltycov's method. In order to calculate fracture toughness of the specimen, indentation fracture method (IF) was applied. Fracture probability model were then used to determine the strength of the coating layers. [ABSTRACT FROM AUTHOR]

To better construct the interface between implant and natural bone, novel gradient nano-hydroxyapatite/polyamide (nHA/PA) composite coating with hierarchically porous structures was prepared using phase-inversion technique and particle-leaching processing. Scanning electron microscopy observation shows that the size of macropores on the surface ranges from 300 to 500 µm. There are abundant micron/submicron-scale pores distributed on the walls of the macropores. Energy-dispersive X-ray spectroscopy analysis indicates that nHA component increases gradually at the interface from the porous transition region to nHA-rich coating layer and then keeps stable towards the coating surface. The osteoblast-like cells (MG63) were cultured on the samples. The results confirm that the samples with nHA-rich coatings and hierarchical structures are favorable to the attachment and proliferation of MG63 cells, and they are potentially attractive candidates for bone repair applications. [ABSTRACT FROM AUTHOR]

Abstract: Calcium phosphate (CaP) ceramics are used in orthopedics and dentistry due to their excellent biocompatibility and osseointegration. Plasma spraying has been the most common process for application of hydroxyapatite (HAp) coatings. Although electrodeposition (ED) has many potential advantages, very little has been published on ED of HAp at near-physiological conditions. Here we report the ED of uniform HAp–OCP (octacalcium phosphate) coatings on Ti–6Al–4V substrate at 37°C, pH=7.4, following surface pretreatment. Thermodynamic calculations were first used to predict which CaP phases may precipitate from solution under different experimental conditions. Microscopic observation revealed that the coating formed in this study is similar to that formed by chemical deposition, and better mimics the biological apatites in terms of structure and phase content than coatings currently used in orthopedics. [Copyright &y& Elsevier]

Abstract: Hydroxyapatite coatings were thermally sprayed on the Ti6Al4V alloy substrate. Antimicrobial properties were obtained by immersion of the coatings in changing concentrations of silver nitrate followed by thermal treatment. To assess antibacterial and antifungal efficacy, the materials were challenged against hospital isolates using a modified Kirby–Bauer method. Cytotoxicity to human osteoblasts was studied by observing changes in the cells morphology, viability and proliferation as a function of the AgNO3 concentration. Physicochemical evaluation showed that silver was successfully deposited on the surface of bioceramic material and biological assessment indicated that good antibacterial and antifungal properties were combined with lack of cytotoxic effect on the human osteoblasts for the materials obtained from the solutions containing ≤1mmol/L of AgNO3. [Copyright &y& Elsevier]

Abstract: This study presents a new bio-ceramic processing technique, which can be used to deposit thick porous hydroxyapatite(HA) coatings on strong three-dimensional (3D) zirconia substrates with a strong coating-substrate interface bonded by bio-glass infiltration during the sintering process. A thin bio-glass coating was first painted on the micro-porous zirconia substrates, pre-sintered at 900°C, then followed by thick HAslip coating with gelatin and ceramic and polymer additives. Freeze-drying was used to create porous scaffold structures within the thick HA coating. The green tri-layer ceramic composites were then co-sintered at 1300°C, resulting in thick scaffold-like HA-coating bonded strongly on load-bearing zirconia substrate or implant core. Such bio-ceramic composites with suitable strength and bio-active and bio-resorbable surface coating can provide useful implant options, bridging the gap between weak and fragile HA scaffolds and strong titanium implants. [Copyright &y& Elsevier]

Abstract: A well-developed three-dimensional (3-D) biphasic calcium phosphate (BCP) scaffold with interconnectivity and high porosity was fabricated for bone tissue engineering. After being coated with hydroxyapatite/poly-l-lactide (HA/PLLA) nanocomposites, the scaffold maintained the framework structure, and the porous network structure of scaffolds remained unchanged. MTT assay showed significantly increased proliferation of human bone mesenchymal stem cells (hBMSCs) on coated BCP scaffolds compared with uncoated scaffolds 5 days after seeding (p<0.05). Under scanning electron microscopy, hBMSCs on the coated BCP scaffolds showed more spreading on the first day after seeding. Furthermore, flocculent mineral accretions were formed on the surface of HA/PLLA coating. Cell adherence and proliferation ability of hBMSCs on scaffolds were improved by coating with HA/PLLA nanocomposites. [Copyright &y& Elsevier]

Abstract: Magnesium alloys have been gaining much importance as metallic biodegradable materials for clinical applications. The present study explores the possibility of developing MgO/hydroxyapatite (HA) composite coating on AZ31 magnesium alloy in order to control its biodegradability. The coating was developed by using a hybrid process combining plasma electrolytic oxidation (PEO) and electrophoretic deposition (EPD) and characterized to substantiate the presence of hydroxyapatite incorporated in the oxide phase. Biodegradability of HA coating was evaluated by conducting potentiodynamic polarization tests at a pH of 4.5, simulating the condition of osteoclast resorption in-vitro and also in simulated body fluid (SBF) environment at a pH of 7.4. The results showed that the MgO/HA composite coating significantly improved the corrosion resistance of AZ31 magnesium alloy in both the conditions. [Copyright &y& Elsevier]

Abstract: Chitosan was widely used as an antibacterial component. While most antibacterial materials also possess cytotoxicities, we hypothesize that selectively destruction of bacterial cells can be achieved by controlling the material parameters of chitosan, due to its intrinsic antibacterial mechanism. In this study, porous hydroxyapatite coatings prepared by the liquid precursor plasma spraying process were used for loading the chitosan with different concentrations: 10, 20, 50, and 100g/L, respectively. The antibacterial properties and osteoblastic cell response of the hydroxyapatite/chitosan complex coatings were studied as a function of chitosan concentration. The results indicated that the antimicrobial activity was directly proportional to the chitosan concentration, while loading of chitosan with lower concentrations (10 and 20g/L) was even beneficial to the proliferation of osteoblastic cells. Overall, our study demonstrated that combined antibacterial activity and superior osteoblast cell response can be achieved by using hydroxyapatite/chitosan complex coatings, which have great potential in bone replacement and regeneration applications. [Copyright &y& Elsevier]

Abstract: The development of the new technologies of bone tissue engineering requires the production of bioactive and biodegradable macroporous scaffolds. Hydroxyapatite (HA) ceramics are useful bone substitutes, but they degrade minimally. Tricalcium phosphates also show poor ability of Ca–P formation both in-vitro and in-vivo, although they are degradable. The present study introduces a biodegradable, bioactive, and macroporous scaffold with suitable mechanical properties. The prepared hydroxyapatite scaffold was coated with a nanocrystalline bioactive glass layer to be subsequently sintered at different temperatures. The bioactivity and degradability of the coated scaffolds were investigated by standard procedures. The ability to induce Ca–P formation in SBF (simulated body fluid) was also investigated semi-quantitatively. BS1 scaffolds (scaffolds sintered at 800°C with a holding time of 2h) showed remarkable bioactivity and degradability simultaneously. Formation of a nanocrystalline phase (Si2PO7) during the sintering considerably decreased the capability of BS1 scaffolds for Ca–P formation and the rate of degradation but enhanced their mechanical properties. The BS1 scaffolds showed not only significant bioactivity but also good degradability and suitable mechanical property. [Copyright &y& Elsevier]

Abstract: The influence of surface-coated nano-crystalline hydroxyapatite (nano-HA) on the mechanical properties of self setting nano-HA/polymer network composites was studied. Nano-HA was coated with the surface modifiers ethylene glycol methacrylate phosphate (EGMP) and bis[2-(methacryloyloxy)ethyl] phosphate (BIS-EGMP) prior to composite formation. The prepared composites were characterized by compression testing and scanning electron microscopy. The results revealed that the compressive strengths and Young''s moduli were changed by coating nano-HA with different amounts of the surface modifiers. The toughness of the composites was considerably increased by coating nano-HA with EGMP resulting in a large plastic deformation of the composite before failure. In contrast, by addition of BIS-EGMP the ductile behaviour disappeared and the composites showed brittle behaviour. An explanation for these changes of the mechanical properties is given. [Copyright &y& Elsevier]

Abstract: Highly porous Ti scaffolds with a bioactive microporous hydroxyapatite (HA)/TiO2 hybrid coating layer were fabricated using the sponge replication process and micro-arc oxidation (MAO) treatment to produce the porous Ti scaffold and hybrid coating layer, respectively. In particular, the morphology and chemical composition of the hybrid coating layer were controlled by carrying out the MAO treatment in electrolyte solutions containing various concentrations of HA, ranging from 0 to 30 wt.%. The fabricated sample showed high porosity of approximately 70 vol.% with interconnected pores and reasonably high compressive strength of 18±0.3 MPa. Furthermore, the surfaces could be coated successfully with a bioactive microporous HA/TiO2 hybrid layer. The amount of HA particles in the hybrid coating layer increased with increasing HA content in the electrolyte solution, while preserving the microporous morphology. This hybrid coating improved the osteoblastic activity of the porous Ti scaffolds significantly. [Copyright &y& Elsevier]

• Composite coating of HA-Cu was fabricated on titanium dioxide nanotubes (TNT) substrates. • TNT-HA-Cu exhibits strong antibacterial property against E. coli and S. aureus. • TNT-HA-Cu was biocompatible and could induce osteogenesis. The aim of this study was to enhance the antibacterial property and osteogenic ability of copper ions-substituted hydroxyapatite (HA-Cu)-based titanium dioxide nanotubes (TNT) implants. The morphology and crystal structure of HA-Cu nanoparticles were characterized by transmission electron microscope (TEM) and X-ray diffraction (XRD). Morphologies and hydrophilic property of Ti, TNT, TNT-HA, and TNT-HA-Cu were evaluated by scanning electron microscope (SEM) and water contact angle (WCA) measurement. Antibacterial assays confirmed that the TNT-HA-Cu presented strong antibacterial abilities against E. coli (82.3%) and S. aureus (87.0%) compared with native Ti substrates. Cellular experiments indicated that TNT-HA-Cu was biocompatible and could induce osteogenesis by stimulating osteoblasts adhesion, proliferation, differentiation, and up-regulating the expression of osteogenic-related genes. The HA-Cu modified TNT substrates were an effective approach of designing both antibacterial and osteogenic Ti-based implants in the orthopedic field. [ABSTRACT FROM AUTHOR]

[Display omitted] • Converting marine shells into Hydroxyapatite (HA) microspheres by hydrothermal method. • HA microspheres showed regular spherical structures and good crystalline. • HA microspheres have excellent adsorption capacity for Congo red (CR) • The adsorption process of CR by HA microspheres is spontaneous and exothermic. In recent years, numerous dyes have been discharged into rivers and oceans, which causes serious environmental pollution. Hydroxyapatite (HA) may have a wide range of applications as a candidate adsorbent in the adsorption of dyes. In this study, marine shell waste was converted into HA microspheres using a hydrothermal self-assembly method. Phosphoric acid was used as a source of phosphorus while poly-L-aspartic acid (PASP) and sodium citrate (SC) acted as co-chelating agents for self-assembly. Prepared HA microspheres have high specific surface area and negative surface potential. HA microspheres were used to adsorb Congo red (CR) in solution. The effects of solution pH, initial CR concentration and temperature were investigated. The maximum adsorption capacity of abalone HA microspheres for CR could reach 495.5626 mg/g when the initial CR concentration reaches 800 mg/L. The adsorption process of CR by HA microspheres is spontaneous and exothermic. This study may provide a novel method for the preparation of HA microspheres and an excellent adsorbent for the removal of CR. [ABSTRACT FROM AUTHOR]

Abstract: Magnesium and its alloys are potential biodegradable implant materials due to their attractive biological property. But their poor corrosion resistance may result in the sudden failure of the implants. The bioactive hydroxyapatite (HA) coating was electrodeposited on AZ91D magnesium alloy surface to improve its biodegradation performance. The biodegradable behavior of HA coating was investigated by electrochemical tests and immersion tests. The experimental results indicated that the as-deposited coating consisting of dicalcium phosphate dehydrate ((DCPD, CaHPO4 ·2H2O) and β-tricalcium phosphate (β-TCP, Ca3 (PO4)2) was transformed into uniform hydroxyapatite (HA, Ca10 (PO4)6(OH)2) coating after immersion in 1 M NaOH solution for 2 h. The HA coating can obviously slow down the biodegradation rate of AZ91D magnesium alloy in stimulated body fluid (SBF). [Copyright &y& Elsevier]

Abstract: Titania nanotubes have been thought to be a novel material for improving bioactivity of titanium. In this work, the effect of precalcification (Pre-Ca) on the bioactivity of the TiO2 nanotubes was investigated, which was applied by soaking the TiO2 nanotubes in Na2HPO4 solution overnight and then in saturated Ca(OH)2 solution for 5 h. It was observed that, only after 7 days immersion in a supersaturated calcium phosphate solution (SCP), hydroxyapatite (HA) was formed apparently on the surface of the precalcified TiO2 nanotube specimens. But no obvious HA was observed on the non-precalcified specimens even up to 14 days immersion in the SCP. The bioactivity of titania nanotubes was enhanced by the precalcification procedure. Therefore, it is much easier and faster for the Ca–P coating fabrication on titanium implants with cooperation of the anodic oxidation and precalcification procedure than that with only an anodic oxidation. [Copyright &y& Elsevier]

Abstract: A new composite biocoating of hydroxyapatite/Al2O3 on titanium, in which hydroxyapatite served as the outer layer and porous Al2O3 as the intermediate layer, was fabricated by a multi-step process consisting of physical vapor deposition (PVD), anodization, electrodeposition, and hydrothermal treatment. The obtained composite biocoatings were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray analysis (EDX). Characterization results indicated that micrometric plate-like Ca-deficient hydroxyapatite (CDHA) crystals formed the outer layer of the composite biocoating during electrodeposition and then were converted into nanosized needle-like Ca-rich hydroxyapatite (CRHA) ones by hydrothermal treatment in alkaline ammonia medium. The CRHA outer layer in the hydrothermally-formed composite biocoating showed good ability for the induction of apatite in simulated body fluid (SBF). A possible mechanism was proposed for the formation of CRHA. [Copyright &y& Elsevier]

Abstract: The aim of this study was to design and produce a novel surface composite coating on metallic substrate in order to improve the biocompatibility of metallic dental implant and the bone osteointegration simultaneously. Stainless steel 316L (SS) was used as a metallic substrate and a novel double-layer hydroxyapatite/tantalum (HA/Ta) coating was prepared on it. Tantalum coating was made using physical vapor deposition process and HA coating was produced using plasma-spraying technique on it. X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques were utilized to investigate the coating characterization. Electrochemical polarization tests were performed in two types of physiological solutions at 37±1 °C in order to determine the corrosion behavior of the coated and uncoated specimens as indication of biocompatibility. The results indicated that the decrease in corrosion current density was significant for HA/Ta coated specimens and was much lower than the value obtained for uncoated 316L SS. The novel double-layer HA/Ta composite coating could improve the corrosion resistance and thus the biocompatibility of 316L SS dental implant. [Copyright &y& Elsevier]

Abstract: A low-temperature route consisting of four simple steps was employed in preparing a titania–hydroxyapatite coating on NiTi. NiTi was first treated with hydrogen peroxide to form a thick titania gel, which was then partially transformed to a titanate hydrogel by alkali hydrothermal treatment. The hydrogel was subsequently soaked in a solution containing calcium and dihydrogen phosphate ions to form a dicalcium phosphate dihydrate (DCPD, CaHPO4·2H2O) coating containing some β-tricalcium phosphate (β-TCP, β-Ca3(PO4)2). Finally, the DCPD and β-TCP were partly or totally transformed to hydroxyapatite (HA, Ca10(PO4)6(OH)2) by NaOH treatment. EDS analysis showed an overall Ca/P ratio of 1.55 for the final calcium phosphate coating, while XRD analysis revealed that the calcium phosphate coating was biphasic, being composed of HA (Ca/P=1.67) together with some untransformed DCPD (Ca/P=1.0). [Copyright &y& Elsevier]

Abstract: A simple sol–gel method was successfully developed for a hydroxyapatite (HA)/TiO2 double layer deposition on a pure titanium substrate. Phase formation, surface morphology, and interfacial microstructure were investigated by differential scanning calorimetry analysis (DSC), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The TiO2 layer was coated by a spin coating method at a speed of 1500 rpm for 15 s, followed by a heat treatment at 560 °C for 20 min. The HA film was subsequently spin coated on the outer surface at the same speed and then heat-treated at difference temperatures. Results indicated that the HA phase began to crystallize after a heat treatment at 580 °C; and the crystallinity increased obviously at a temperature of 780 °C. The HA film showed a porous structure and a thickness of 5–7 μm after the heat treatment at 780 °C. SEM observations revealed no delamination and crack at the interfaces of HA/TiO2 and TiO2/Ti. The HA film with a porous structure is expected to be more susceptible to the natural remodeling processes when it is implanted in a living body. [Copyright &y& Elsevier]

Abstract: Composites of hydroxyapatite (HA) and nanosize-alpha-(α)-Al2O3 with 5 wt.% CaF2 were coated on Ti-6Al-4V rods by cold pressing and sintered in air or argon atmosphere at 1100 °C to improve the bonding between the metal and the ceramic. 25 and 40 wt.% α-Al2O3-5 wt.% CaF2-HA composites gave the best results of strong bonding. 25 wt.% α-Al2O3-5 wt.% CaF2-HA and Ti-6Al-4V showed the same thermal expansion coefficients. The thermal expansion coefficient of the 40 wt.% α-Al2O3-5 wt.% CaF2-HA composite was slightly smaller than that of Ti-6Al-4V, which created a compressive stress on the coating, resulting in improved bonding between the metal and the ceramic. [Copyright &y& Elsevier]

With the increase in the life expectancy of humans, the maintenance of bone in our bodies has become crucial. Allografts extracted from different human and bovine sources bring the problem of potential disease transmittal, particularly the transmittal of disease that are difficult to detect. Autogen grafts bring another problem in surgery because the bone harvesting procedure creates cause for an additional surgery. In this study, the hydroxyapatite (HA) material was produced from bovine bones with the calcination method prohibits the transmission of various disease like mad cow disease (bovine spongiform encephalopathy (BSE)). In this study, the calcinated powder was used as plasma feeding powder for the plasma spraying process in biomedical applications. In industrial applications, the use of bond-coating prevents thermal coefficient mismatching and usually results in a stronger material. However, it was seen than bovine hydroxyapatite (BHA) was so strong that it does not need any bond-coating application. Nonetheless, bond-coating can be used to prevent the formation of micro-cracks. BHA material produced with the calcination method can be a very economic biomaterial for plasma spraying purposes when compared to other commercially available biomaterials. [Copyright &y& Elsevier]

[Display omitted] • Antibacterial-functionalized Ag-loaded HAp coatings were fabricated by EPD process. • Ag ions were adsorbed around surface of HAp particles and deposited with them. • Coatings have strong adhesion, not only for HAp particles but also for loaded Ag. Antibacterial-functionalized Ag-loaded hydroxyapatite (HAp) coatings were successfully fabricated by the EPD process, with adding various concentrations of Ag ions. Loaded Ag ions were adsorbed around the surface of HAp particles in the suspension, which made the particles become positively charged, and then were deposited together with the HAp particles onto the surface of titanium substrate. The thickness of deposited Ag-loaded HAp coating was dependent on the Ag addition amount and the coatings have strong adhesion, not only for the deposited HAp particles but also for the loaded Ag ions, due to the use of Mg2+ as inorganic binder. The Ag-loaded HAp coatings show potential application in implant surgery, owing to the surface antibacterial function for preventing bacterial infection in surgery, for improving surgical success. [ABSTRACT FROM AUTHOR]

A thin film of hydroxyapatite (HA) was coated on a magnesium–calcium (Mg–Ca) alloy using radio frequency (RF) magnetron sputtering. The thickness of the HA coating was in the range of 550–750 nm. In vitro degradation behaviour of the HA coated alloy was evaluated in simulated body fluid (SBF) using electrochemical methods. The ultrathin film coating has significantly improved the degradation resistant of the alloy. The polarisation resistance ( R p ) of the coated alloy was more than two-order of magnitude higher and the corrosion current density ( i corr ) reduced by ~98% as compared to the base alloy. [ABSTRACT FROM AUTHOR]

Abstract: To control the degradation of Magnesium alloys, uniform nano-hydroxyapatite (n-HAP) coating was applied on AZ31 Magnesium alloy using both direct and pulse voltage electrodeposition methods. The in vivo corrosion of AZ31 with n-HAP coating was investigated by electrochemical tests. The results showed that by the pulse electrodeposition method brushite (DCPD or CaHPO4·2H2O) was not formed. Also, the results indicated that the degradation of AZ31 Magnesium alloy substrate and the amount of hydrogen evolution was significantly decreased after surface was modified by n-HAP coating, so that the rate of hydrogen evolution decreased from 0.1 to 0.01mlcm−2 h−1. [Copyright &y& Elsevier]