Hydroxyapatite coating on titanium by thermal substrate method in aqueous solution.

A new hydrocoating method (the thermal substrate method) is proposed for coating calcium phosphates such as hydroxyapatite (HA), on titanium substrates in an aqueous solution. Several factors (e.g., the type of ion source, the heating time and temperature, and the surface roughness of the substrate) affected the characteristics of the precipitate formed by this method. The solution used included 3 mmol dm(-3) Ca(H(2)PO(4))(2) and 7 mmol dm(-3) CaCl(2), and its pH was adjusted to 6.5. The experimental studies were conducted under the following conditions: temperature 45-160 degrees C, heating time 10-20 min, and surface roughness of substrate #120-#2000 grid ground using energy paper. A high quality of precipitate, whose predominant component was HA, was obtained on titanium substrates by the thermal substrate method in an aqueous solution. No significant difference in the precipitates was found with the type of ion source. The amount of HA precipitate increased with increasing temperature and with increasing heating time. The features of the precipitate were different, depending on the surface roughtness of the substrate: HA regularly nucleated along the grooves of the rough surface (#120 and #400 grid), and in the case of the fine surface (#1200-#2000 grid), a uniform precipitation occurred.     

Hydroxyapatite and fluor-hydroxyapatite layered film on titanium processed by a sol-gel route for hard-tissue implants

A double-layered coating, consisting of a hydroxyapatite (HA) outer film and a fluor-hydroxyapatite (FHA) inner film, was produced on a Ti substrate by a sol-gel route to improve the biocompatibility and functionality of the system. Dissolution behavior of and in vitro cellular responses to the layered film were investigated. Calcium nitrate and triethyl phosphite were used for calcium and phosphate precursors, respectively, and ammonium fluoride was added as a fluorine-ion source for FHA. The FHA layer was deposited on Ti by spin coating and subsequent heat treatment at 550 degrees C for 30 min in air, and then the HA layer was laid down over the FHA-coated Ti under the same conditions. After heat treatment, characteristic apatite structures and phases were developed on both FHA and HA films. The cross-section view of the HA/FHA film clearly showed a double-layered structure on Ti with each layer approximately 0.6-0.8-microm thickness. The coating layer was highly uniform and dense, and adhered to Ti substrate strongly with an adhesion strength of about 40 MPa. The in vitro solubility of the HA/FHA layered film in a physiological solution was between that of HA and FHA pure film, and the dissolution profile was quite biphasic, that is, an initial rapid period and a slowdown with increasing time, reflecting the gradient solubility of the fast HA outer structure/slow FHA inner structure. The human osteoblast-like HOS TE85 cells cultured on the HA/FHA layered film attached, spread, and grew favorably. The proliferation rate of the cells on the layered film was significantly higher (considered at p < 0.05 for n = 6) than that on Ti substrate and was similar to that on pure HA film. The alkaline phosphatase (ALP) activity and osteocalcin (OC) produced by the cells on the layered film were significantly higher (considered at p < 0.05 for n = 6) than those on Ti substrate. Moreover, the ALP and OC levels of cells on the layered film showed the trends of HA outer/FHA inner structure with respect to culture period, that is, HA initially and FHA later. These observations suggest that the HA/FHA layered film on Ti obtained by a sol-gel route possesses gradient functionality in terms of solubility and cellular responses, and find that those parameters can be tailored for specific use in hard-tissue implants.     

Fluor-hydroxyapatite sol-gel coating on titanium substrate for hard tissue implants

Hydroxyapatite (HA) and fluor-hydroxyapatite (FHA) films were deposited on a titanium substrate using a sol-gel technique. Different concentrations of F- were incorporated into the apatite structure during the sol preparation. Typical apatite structures were obtained for all coatings after dipping and subsequent heat treatment at 500 degrees C. The films obtained were uniform and dense, with a thickness of approximately 5 microm. The dissolution rate of the coating layer decreased with increasing F- incorporation within the apatite structure, which demonstrates the possibility of tailoring the solubility by a functional gradient coating of HA and FHA. The cell proliferation rate on the coating layer decreased slightly with increasing F- incorporation. The alkaline phosphatase (ALP) activity of the cells on all the HA and FHA coated samples showed much higher expression levels compared to pure Ti. This confirmed the improved activity of cell functions on the substrates with the sol-gel coating treatment.     

Plasma-sprayed hydroxyapatite+titania composite bond coat for hydroxyapatite coating on titanium substrate

A two-layer hydroxyapatite (HA)/HA+TiO(2) bond coat composite coating (HTH coating) on titanium was fabricated by plasma spraying. The HA+TiO(2) bond coat (HTBC) consists of 50 vol% HA and 50 vol% TiO(2) (HT). The microstructural characterization of the HTH coatings before and after heat treatment was conducted by using scanning electron microscopy (SEM), electron probe microanalyser (EPMA), X-ray diffractometer (XRD) and transmission electron microscopy (TEM), in comparison with that of HT coating and pure HA coating. The results revealed that HA and TiO(2) phases layered in an alternating pattern within the HTBC, and the HTBC bonded well to HA top coating (HAT coating) and Ti substrate. The as-sprayed HT coating consists mainly of crystalline HA, rutile TiO(2) and amorphous Ca-P phase. The post-spray heat treatment at 650 degrees C for 120 min effectively restores the structural integrity of HA by transforming non-HA phases into HA. It was found that there exists interdiffusion of the elements within the HTBC, but no chemical product between HA and TiO(2), such as CaTiO(3) was formed. The cross-sectional morphologies confirmed that there is a shift towards a relatively tighter bonding from the HAT coating/HTBC interface in the as-sprayed HTH coating to the HTBC/Ti substrate interface in the heat-treated HTH coating. On quenching the coatings into water, the surface cracking indicates more apparently the positive effect of the HTBC on the decrease of residual stress in HAT coating. The in situ surface cracking also suggests that the stress on the surface of the HTH coating is stable under subjection to a repetitious heat treatment. The toughening and strengthening of HTBC is thought to be mainly due to TiO(2) as obstacles embarrassing cracking, the reduction of the near-tip stresses resulting from stress-induced microcracking and the decrease of CTE mismatch. In the HTH composite coating, the HAT coating is toughened by the decreased CTE mismatch with Ti through the addition of HTBC, which bonds well to the Ti substrate via its TiO(2) hobnobbing with the Ti oxides formed on Ti substrate.     

Hydroxyapatite/titania sol-gel coatings on titanium-zirconium alloy for biomedical applications

A simple sol-gel method was developed for hydroxyapatite/titania (HA/TiO(2)) coatings on non-toxic titanium-zirconium (TiZr) alloy for biomedical applications. The HA/TiO(2)-coated TiZr alloy displayed excellent bioactivity when soaked in a simulated body fluid (SBF) for an appropriate period. Differential scanning calorimetry, thermogravimetric analysis, X-ray diffraction and scanning electron microscopy-energy dispersive spectrometry were used to characterize the phase transformations and the surface structures and to assess the in vitro tests. The HA/TiO(2) layers were spin-coated on the surface of TiZr alloy at a speed of 3000rpm for 15s, followed by a heat treatment at 600 degrees C for 20min in an argon atmosphere sequentially. The TiO(2) layer exhibited a cracked surface and an anatase structure and the HA layer displayed a uniform dense structure. Both the TiO(2) and HA layers were 25microm thick, and the total thickness of the HA/TiO(2) coatings was 50microm. The TiZr alloy after the above HA/TiO(2) coatings displayed excellent bone-like apatite-forming ability when soaked in SBF and can be anticipated to be a promising load-bearing implant material.     

Hydroxyapatite and titania sol-gel composite coatings on titanium for hard tissue implants; mechanical and in vitro biological performance

Hydroxyapatite (HA) composites with titania (TiO2) up to 30 mol % were coated on a titanium (Ti) substrate by a sol-gel route, and the mechanical and biological properties of the coating systems were evaluated. Using polymeric precursors, highly stable HA and TiO2 sols were prepared prior to making composite sols and coatings. Coatings were produced under a controlled spinning and heat treatment process. Pure phases of HA and TiO2 were well developed on the composites after heat treatment above 450 degrees C. The HA-TiO2 composite coating layers were homogeneous and highly dense with a thickness of about 800-900 nm. The adhesion strength of the coating layers with respect to Ti substrate increased with increasing the TiO2 addition. The highest strength obtained was as high as 56 MPa, with an improvement of about 50% when compared to pure HA (37 MPa). The osteoblast-like cells grew and spread actively on all the composite coatings. The proliferation and alkaline phosphatase (ALP) activity of the cells grown on the composite coatings were much higher than those on bare Ti, and even comparable to those on pure HA coating. Notably, the HA-20% TiO2 composite coating showed a significantly higher proliferation and ALP expression compared to bare Ti (p < 0.05). These findings suggest that the sol-gel-derived HA-TiO2 composite coatings possess excellent properties for hard tissue applications from the mechanical and biological perspective.     

Biomimetic coating of compound titania and hydroxyapatite on titanium

The modification on the titanium implant surface is an effective method to improve the biocompatibility of titanium. This article describes efforts to improve implant biocompatibility by applying titania and hydroxyapatite to form a three-layer coating on the titanium surface. This three-layer coating is made up of HA as the top layer (formed by hydrothermal treatment), porous TiO2 as the middle layer (formed by micro-arc oxidation) and a dense TiO2 film as the inner layer (formed by preanodic oxidation). The physicochemical characteristics, cell behavior and in vivo studies were assessed. The physicochemical characteristics were investigated using scanning electron micoscopy observation, fibronectin and laminin adsorption, corrosion test and X-ray diffraction analysis. Cell behavior included morphology observation with scanning electron microscopy (SEM), number count with methylthiazol tetrazolium (MTT) assay and Alkaline phosphatase (ALP, a representative enzyme of osteoblastic differentiation) activity of osteoblast-like MC3T3-E1 cells. In study in vivo the specimens were embedded in skull wound for repair. By the analysis of experiments, the titanium coated with this three-layer coating has been proved to have excellent corrosion resistance and good biocompatibility, which can promote cell proliferation and bone formation. So this modified titanium is an improved alternative to untreated titanium for bone repair applications.     

Bioactive macroporous titanium surface layer on titanium substrate

A macroporous titanium surface layer is often formed on titanium and titanium alloy implants for morphological fixation of the implants to bone via bony ingrowth into the porous structure. The surface of titanium metal was recently shown to become highly bioactive by being subjected to 5.0 M-NaOH treatment at 60 degrees C for 24 h and subsequent heat treatment at 600 degrees C for 1 h. In the present study, the NaOH and heat treatments were applied to a macroporous titanium surface layer formed on titanium substrate by a plasma spraying method. The NaOH and heat treatments produced an uniform amorphous sodium titanate layer on the surface of the porous titanium. The sodium titanate induced a bonelike apatite formation in simulated body fluid at an early soaking period, whereby the apatite layer grew uniformly along the surface and cross-sectional macrotextures of the porous titanium. This indicates that the NaOH and heat treatments lead to a bioactive macroporous titanium surface layer on titanium substrate. Such a bioactive macroporous layer on an implant is expected not only to enhance bony ingrowth into the porous structure, but also to provide a chemical integration with bone via apatite formation on its surface in the body.     

Synthesis and properties of hydroxyapatite-containing porous titania coating on ultrafine-grained titanium by micro-arc oxidation

Equal channel angular pressing results in ultrafine-grained (～200–500 nm) Ti with superior mechanical properties without harmful alloying elements, which benefits medical implants. To further improve the bioactivity of Ti surfaces, Ca/P-containing porous titania coatings were prepared on ultrafine-grained and coarse-grained Ti by micro-arc oxidation (MAO). The phase identification, composition, morphology and microstructure of the coatings and the thermal stability of ultrafine-grained Ti during MAO were investigated subsequently. The amounts of Ca, P and the Ca/P ratio of the coatings formed on ultrafine-grained Ti were greater than those on coarse-grained Ti. Nanocrystalline hydroxyapatite and α-Ca₃(PO₄)₂ phases appeared in the MAO coating formed on ultrafine-grained Ti for 20 min (E20). Incubated in a simulated body fluid, bone-like apatite was completely formed on the surface of E20 after 2 days, thus evidencing preferable bioactivity. Compared with initial ultrafine-grained Ti, the microhardness of the E20 substrate was reduced by 8% to 2.9 GPa, which is considerably more than that of coarse-grained Ti (～1.5 GPa).     

Initial responses of human osteoblasts to sol-gel modified titanium with hydroxyapatite and titania composition

Sol-gel thin films of hydroxyapatite (HA) and titania (TiO(2)) have received a great deal of attention in the area of bioactive surface modification of titanium (Ti) implants. Sol-gel coatings were developed on Ti substrates of pure HA and TiO(2) and two composite forms, HA+10% TiO(2) and HA+20% TiO(2), and the biological properties of the coatings were evaluated. All the coating layers exhibited thin and homogeneous structures and phase-pure compositions (either HA or TiO(2)). Primary human osteoblast cells showed good attachment, spreading and proliferation on all the sol-gel coated surfaces, with enhanced cell numbers on all the coated surfaces relative to uncoated Ti control at day 1, as observed by MTT assay and scanning electron microscopy. Cell attachment rates were also enhanced on the pure HA coating relative to control Ti. The pure HA and HA+10% TiO(2) composite coating furthermore enhanced proliferation of osteoblasts at 4 days. Moreover, the gene expression level of several osteogenic markers including bone sialoprotein and osteopontin, as measured by RT-PCR at 24h, was shown to vary according to coating composition. These findings suggest that human primary bone cells show marked and rapid early functional changes in response to HA and TiO(2) sol-gel coatings on Ti.     

Adherent apatite coating on titanium substrate using chemical deposition

Plasma-sprayed "HA" coatings on commercial orthopedic and dental implants consist of mixtures of calcium phosphate phases, predominantly a crystalline calcium phosphate phase, hydroxyapatite (HA) and an amorphous calcium phosphate (ACP) with varying HA/ACP ratios. Alternatives to the plasma-spray method are being explored because of some of its disadvantages. The purpose of this study was to deposit an adherent apatite coating on titanium substrate using a two-step method. First, titanium substrates were immersed in acidic solution of calcium phosphate resulting in the deposition of a monetite (CaHPO4) coating. Second, the monetite crystals were transformed to apatite by hydrolysis in NaOH solution. Composition and morphology of the initial and final coatings were identified using X-ray diffraction (XRD), Scanning Electron Microscopy, and Energy Dispersive Spectroscopy (EDS). The final coating was porous and the apatite crystals were agglomerated and followed the outline of the large monetite crystals. EDS revealed the presence of calcium and phosphorous elements on the titanium substrate after removing the coating using tensile or scratching tests. The average tensile bond of the coating was 5.2 MPa and cohesion failures were observed more frequently than adhesion failures. The coating adhesion measured using scratch test with a 200-microm-radius stylus was 13.1N. Images from the scratch tracks demonstrated that the coating materials were squashed without fracturing inside and/or at the border of the tracks until the failure point of the coating. In conclusion, this study showed the potential of a chemical deposition method for depositing a coating consisting of either monetite or apatite. This method has the advantage of producing a coating with homogenous composition on even implants of complex geometry or porosity. This method involves low temperatures and, therefore, can allow the incorporation of growth factors or biogenic molecules.     

Electrolytic deposition of calcium etidronate drug coating on titanium substrate

Wear debris-induced osteolysis is the major cause of aseptic loosening and failure of hip implants. One of the promising therapeutic interventions to improve the longevity of hip implants is to administrate bisphosphonate drug to inhibit osteoclastic bone resorption. This study aimed at developing new techniques of directly combining bisphosphonate with implants to achieve local delivery and controlled release of the drug. Instead of using soluble sodium salt, we proposed to apply sparingly soluble calcium salt of bisphosphonate as a potential long-term antiosteolysis coating on hip implants. Calcium salt of etidronate, a member of the bisphosphonate family of potent osteoclast inhibitors, was used in this pilot study. By adopting the electrolytic deposition (ELD) technique, which was developed for ceramic coatings including calcium phosphates, we demonstrated that a thin layer of calcium bisphosphonate could be deposited onto titanium surface. The drug coating is amorphous as characterized with X-ray diffraction, and has globular morphology under the scanning electron microscope. Electrospray-ionization mass-spectrometry (ESI-MS) and Fourier-transformed infrared spectroscopy confirmed that the molecular structure of the etidronate (m/z 205, H3L-, the single dissociated form of parent etidronic acid, denoted as H4L) was preserved after the ELD process. In vitro release into a "physiological" buffer solution confirmed that the etidronate concentration was limited by its low solubility. The etidronate concentration was 8 x 10(-5) M at day 1 and kept relatively stable at approximately 6 x 10(-5) M from day 2 to day 8. The deposition mechanisms of the drug coating and its potential efficacy as an antiosteolytic release source were discussed.     

Hydroxyapatite formation on alkali-treated titanium with different content of Na+ in the surface layer

Titanium can form a bone-like apatite layer on its surface in SBF when it is treated in NaOH. When pre-treated titanium is exposed to SBF, the alkali ions are released from the surface into the surrounding fluid. The Na+ ions increase the degree of supersaturation of the soaking solution with respect to apatite by increasing pH. On the other hand, the released Na+ cause an increase in external alkalinity that triggers an inflammatory response and leads to cell death. Therefore, it would be beneficial to decrease the release of Na+ into the surrounding tissue. The purpose of this study was to evaluate the hydroxyapatite formation on alkali-treated titanium with different content of Na+ in the surface layer. Using SEM, gravimetric analysis and measurement of calcium and phosphate concentration, it was found that the rate of apatite formation was not significantly influenced by a lower amount of Na+ in the surface layer. Titanium with the lowest content of Na+ could be more suitable for implantation in the human body. The amount of alkali ions released in the surrounding tissue is lower and the rate of apatite formation is identical to titanium with the highest content of Na+ in the surface layer.     

Silver/hydroxyapatite composite coatings on porous titanium surfaces by sol-gel method

Hydroxyapatite (HA) coatings loaded with nanosilver particles is an attractive method to impart the HA coating with antibacterial properties. Producing Ag/HA coatings on porous Ti substrates have been an arduous job since commonly used line-of-sight techniques are not able to deposit uniform coatings on the inner pore surfaces of the porous Ti. In this study, porous Ti scaffolds with high porosity and interconnected structures were prepared by polymer impregnating method. A sol-gel process was used to produce uniform Ag/HA composite coatings on the surfaces of porous Ti substrates. Ca(NO(3) )(2) ·4H(2) O and P(2) O(5) in an ethyl alcohol based system was selected to prepare the sol, which ensured the homogeneous distribution of Ag in the sol. The characterization revealed that silver particles uniformly distributed in the coatings without agglomeration. High antibacterial ratio (>95%), against E. coli and S. albus was expressed by the silver-containing coatings (Ag/HA 0.8 and 1.6 wt %). The biocompatibility of the Ag/HA 0.8 surfaces was as good as that of pure HA surface, as revealed by culturing osteoblasts on them. The results indicated that Ag/HA 0.8 had the good balance between the biocompatibility and antibacterial properties of the coatings.     

A novel ordered nano hydroxyapatite coating electrochemically deposited on titanium substrate

A novel porous nano hydroxyapatite (HA) coating has been prepared on commercially pure titanium substrate by a modified electrochemical deposition method. The physico-chemical and biological properties of the coating were characterized by SEM, XRD, FTIR, Raman, and in vitro cell culture test respectively. The SEM patterns show a uniform microporous morphology consisting of wirelike crystals at nanometer scale. It is suggested that under controlled deposition conditions, the primary HA nanowires grow and self-assemble to construct an ordered microporous nest-like morphology, thus to form a nano-micro two-level structure. The XRD results demonstrate that the HA nanowires are orderly arranged with their c-axis preferentially perpendicular to the substrate surface. The Raman and IR spectra affirm that the main component of the coating is well crystallized HA. An interdigitation phenomenon of the MG63 human osteosarcoma cells with the HA nanowires is observed in the in vitro test, indicating excellent biocompatibility and bioactivity for the prepared coating.     

Hydroxyapatite deposition by electrophoresis on titanium sheets with different surface finishing

Hydroxyapatite coatings are commonly applied to metallic biomedical implants to accelerate osseointegration. These coatings, usually produced by plasma spray techniques, can be obtained by alternative processes, like biomimetic process, electrolytic deposition, or electrophoretic process as well. Electrophoretic deposition of hydroxyapatite exhibits several advantages like simplicity and low cost. In this article, titanium sheets with three different surface finishing were coated with hydroxyapatite by using electrophoresis. Surface treatments include: (1) abrading with SiC paper; (2) abrading with SiC paper plus electrolytic etch with H3PO4 solution; and (3) blasting with alumina powder followed by etch with a solution containing H2O2 and HF. Stoichiometric hydroxyapatite was used to coat titanium sheets. Blasted samples were also coated using a calcium-deficient hydroxyapatite. SEM, XRD, and FTIR were employed to characterize titanium substrates and coatings produced. Results show that electrophoretic process can produce a uniform thin layer, satisfactorily adhered, of hydroxyapatite on treated titanium samples. Furthermore, sintering at 800 degrees C do not promote the decomposition of calcium-deficient hydroxyapatite.     

Enhanced osteoblast adhesion on hydrothermally treated hydroxyapatite/titania/poly(lactide-co-glycolide) sol-gel titanium coatings

Sol-gel processing was used to coat titanium substrates with hydroxyapatite (HA), TiO2, and poly(DL-lactic-glycolic acid). Coating surface characteristics were analyzed with XRD, EDS, AFM, SEM, and water contact angle measurements which indicated that the coatings had a high degree of crystallinity and good resistance to cracking. Coatings were also evaluated by cytocompatibility testing with osteoblast-like cells (or bone-forming cells). The cytocompatibility of the HA composite coatings prepared in the present in vitro study was compared to that of a traditional plasma-sprayed HA coating. Results showed that osteoblast-like cell adhesion was promoted on the novel HA sol-gel coating compared to the traditional plasma-sprayed HA coating. In addition, hydrothermal treatment of the sol-gel coating improved osteoblast-like cell adhesion. Since osteoblast adhesion is a necessary prerequisite for subsequent formation of bone, these results provided evidence that hydrothermally sol-gel processed HA may improve bonding of titanium implants to juxtaposed bone and, thus, warrants further investigation.     

Prevention of Staphylococcus epidermidis biofilm formation using a low-temperature processed silver-doped phenyltriethoxysilane sol-gel coating

Sol-gel coatings which elute bioactive silver ions are presented as a potential solution to the problem of biofilm formation on indwelling surfaces. There is evidence that high-temperature processing of such materials can lead to diffusion of silver away from the coating surface, reducing the amount of available silver. In this study, we report the biofilm inhibition of a Staphylococcus epidermidis biofilm using a low-temperature processed silver-doped phenyltriethoxysilane sol-gel coating. The incorporation of a silver salt into a sol-gel matrix resulted in an initial high release of silver in de-ionised water and physiological buffered saline (PBS), followed by a lower sustained release for at least 6 days-as determined by graphite furnace-atomic absorption spectroscopy (GF-AAS). The release of silver ions from the sol-gel coating reduced the adhesion and prevented formation of a S. epidermidis biofilm over a 10-day period. The presence of surface silver before and after 24 h immersion in PBS was confirmed by X-ray photoelectron spectroscopy (XPS). These silver-doped coatings also exhibited significant antibacterial activity against planktonic S. epidermidis. A simple test to visualise the antibacterial effect of silver release coatings on neighbouring bacterial cultures is also reported.     

Antibacterial nano-structured titania coating incorporated with silver nanoparticles

Titanium (Ti) implants are widely used clinically but post-operation infection remains one of the most common and serious complications. A surface boasting long-term antibacterial ability is highly desirable in order to prevent implant associated infection. In this study, titania nanotubes (TiO(2)-NTs) incorporated with silver (Ag) nanoparticles are fabricated on Ti implants to achieve this purpose. The Ag nanoparticles adhere tightly to the wall of the TiO(2)-NTs prepared by immersion in a silver nitrate solution followed by ultraviolet light radiation. The amount of Ag introduced to the NTs can be varied by changing processing parameters such as the AgNO(3) concentration and immersion time. The TiO(2)-NTs loaded with Ag nanoparticles (NT-Ag) can kill all the planktonic bacteria in the suspension during the first several days, and the ability of the NT-Ag to prevent bacterial adhesion is maintained without obvious decline for 30 days, which are normally long enough to prevent post-operation infection in the early and intermediate stages and perhaps even late infection around the implant. Although the NT-Ag structure shows some cytotoxicity, it can be reduced by controlling the Ag release rate. The NT-Ag materials are also expected to possess satisfactory osteoconductivity in addition to the good biological performance expected of TiO(2)-NTs. This controllable NT-Ag structure which provides relatively long-term antibacterial ability and good tissue integration has promising applications in orthopedics, dentistry, and other biomedical devices.     

Ion-beam-assisted deposition (IBAD) of hydroxyapatite coating layer on Ti-based metal substrate

A hydroxyapatite layer was formed on the surface of a Ti-based alloy by ion-beam-assisted deposition. The deposition methodology comprised of an electron beam vaporizing a pure hydroxyapatite target, while an Ar ion beam was focused on the metal substrate to assist deposition. All deposited layers were amorphous, regardless of the current level of the ion beam. The bond strength between the layer and the substrate increased steadily with increasing current, while the dissolution rate in a physiological saline solution decreased remarkably. These improvements were attributed to an increase in the Ca/P ratio of the layer. Without ion beam assistance, the Ca/P ratio was much lower than the stoichiometric HAp (Ca/P = 1.67). With ion-beam assistance, the Ca/P ratio of the layer increased presumably due to the high sputtering rate of P compared to that of Ca from the layer being coated.