Polyetheretherketone Substrate Research Articles

Simultaneous application of diamond-like carbon coating and surface amination on polyether ether ketone: Towards superior mechanical performance and osseointegration

Poor osseointegration ability and the release of worn debris after implantation are the main issues impeding the clinic application of polyether ether ketone (PEEK) as orthopedics. To address these problems, we expect that the initial deposition of diamond-like carbon (DLC) coating on PEEK substrate and the subsequent introduction of amino groups onto sample surface using plasma immersion ion implantation (PIII) have the potential to simultaneously improve the mechanical performance and osseointegration. On one hand, the surface hardness is raised from 0.38 ​GPa to 2.99 ​GPa and the elastic modulus reaches 35 ​GPa after DLC deposition, while no failure is observed in the scratch tests even the loading force is up to 100 ​N. On the other hand, the introduced amino groups facilitate the adhesion, proliferation, and osteogenic differentiation of the osteoblasts in vitro, and further enhanced the peri-implant bone regeneration in vivo. With the merits of low cost, clean approach, and ease of operation, the approach described here holds great potential for biomedical applications.

A bionic PEEK composite structure with negatively charged surface adsorbing molecular brushes possessing improved biotribological properties for artificial joints

To improve the contact mode of artificial joints and their tribological performance, inspired by the ‘soft-on-hard’ structure of ‘cartilage-subchondral bone’ as well as negatively charged characteristic of the cartilage surface with brush-like molecules, a polyetheretherketone (PEEK)-hydrogel composite structure with negatively charged surface adsorbing cationic molecules through electrostatic interaction was designed and fabricated. Characterization results demonstrated that polyacrylic acid (PAA) hydrogel strengthened by polyvinyl alcohol (PVA) microcrystals was successfully fabricated on the PEEK substrate through ultra-violet (UV) radiation. Adsorption of cationic monomers was also confirmed. The PEEK-hydrogel composite structure had significantly reduced friction coefficient, ~80% lower than that of PEEK, owing to the synergistic effect of biphasic and boundary lubrication. This work proposes a novel route to develop the friction surface of artificial joints with advanced performance and contributes to the understanding of lubrication mechanism of artificial joints.

The Surface Characterisation of Polyetheretherketone (PEEK) Modified via the Direct Sputter Deposition of Calcium Phosphate Thin Films

Polyetheretherketone (PEEK) has emerged as the material of choice for spinal fusion devices, replacing conventional materials such as titanium and its alloys due to its ability to easily overcome a lot of the limitations of traditional metallic biomaterials. However, one of the major drawbacks of this material is that it is not osteoinductive, nor osteoconductive, preventing direct bone apposition. One way to overcome this is through the modification of the PEEK with bioactive calcium phosphate (CaP) materials, such as hydroxyapatite (HA–Ca10(PO4)6(OH)2). RF magnetron sputtering has been shown to be a particularly useful technique for the deposition of CaP coatings due to the ability of the technique to provide greater control of the coating’s properties. The work undertaken here involved the deposition of HA directly onto PEEK via RF magnetron at a range of deposition times between 10–600 min to provide more bioactive surfaces. The surfaces produced have been extensively characterised using X-Ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM), stylus profilometry, and Time of Flight Secondary Ion Mass Spectrometry (ToFSIMS). XPS results indicated that both Ca and P had successfully deposited onto the surface, albeit with low Ca/P ratios of around 0.85. ToFSIMS analysis indicated that Ca and P had been homogeneously deposited across all the surfaces. The SEM results showed that the CaP surfaces produced were a porous micro-/nano-structured lattice network and that the deposition rate influenced the pore area, pore diameter and number of pores. Depth profiling, using ToFSIMS, highlighted that Ca and P were embedded into the PEEK matrix up to a depth of around 1.21 µm and that the interface between the CaP surface and PEEK substrate was an intermixed layer. In summary, the results highlighted that RF magnetron sputtering can deliver homogenous CaP lattice-like surfaces onto PEEK in a direct, one-step process, without the need for any interlayers, and provides a basis for enhancing the potential bioactivity of PEEK.

Bio-inspired surface modification of PEEK through the dual cross-linked hydrogel layers

The biocompatible high-performance material PEEK (polyetheretherketone) is an attractive implant material, however, its hydrophobicity and high friction coefficients severely hinder its biomedical applications. Thus, it is inferred from the recent advances in surface modification technology, achieving the biomimetic natural joint lubrication systems on PEEK still remains a challenge. In view of the above, herein we proposed a novel two-step strategy to fabricate a “soft (dual cross-linked hydrogel) layer-hard (PEEK) substrate” texture that mimics the structure and function of soft cartilage on the hard basal bone in joints. At first, a layer of acrylic acid-co-acryl amide (AA-AM) hydrogel is anchored to the PEEK substrate through UV-initiated polymerization. In the second step, hydrogel coated PEEK substrate is immersed in ferric nitrate solution to create the secondary cross-linkage between Fe3+ and –COOH groups in the hydrogel. As a result, the consequential top-coat hydrogel layer not only transforms the surface wettability (hydrophobic to hydrophilic) but also provides scratch resistance to the underlying PEEK substrate. The modified specimens display low friction coefficients in water under different load conditions. In addition, the obtained surface exhibits a certain self-repairing ability due to its unique physically reversible network structure. Therefore, this work provides a promising strategy for broadening the use of PEEK in orthopedic implants.

Fabrication of a novel hydroxyapatite/polyether ether ketone surface nanocomposite via friction stir processing for orthopedic and dental applications.

There is increasing interest in the use of polyether ether ketone (PEEK) for orthopedic and dental implant applications due to its elastic modulus (close to that of bone), biocompatibility and radiolucent properties. However, PEEK is still categorized as bioinert owing to its low integration with surrounding tissues. Methods such as depositing hydroxyapatite (HA) onto the PEEK surface could increase its bioactivity. However, depositing HA without damaging the PEEK substrate is still required further investigation. Friction stir processing is a solid-state processing method that is widely used for composite substrate fabrication. In this study, a pinless tool was used to fabricate a HA/PEEK surface nanocomposite for orthopedic and dental applications. Microscopical images of the modified substrate confirmed homogenous distribution of the HA on the surface of the PEEK. The resultant HA/PEEK surface nanocomposites demonstrated improved surface hydrophilicity coupled with better apatite formation capacity (as shown in the simulated body fluid) in comparison to the pristine PEEK, making the newly developed material more suitable for biomedical application. This surface deposition method that is carried out at low temperature would not damage the PEEK substrate and thus could be a good alternative for existing commercial methods for PEEK surface modification.

A nanosized zirconium phosphate coating for PEEK implants and its effect in vivo

Surface treatments and coatings can be applied to polyether ether ketone (PEEK) implants to improve their ability to osseointegrate. A new coating, consisting of amorphous nanosized zirconium phosphate (ZrP) was applied to PEEK and titanium substrates. The coating was applied by using a microemulsion as a carrier for the nanoparticles. It was found that the coating formed a thin continuous porous layer on top of the substrate, with pore diameters of 10–50 nm. The thickness of the coating was estimated to <100 nm. The resistance to acidic (pH = 4) conditions and exposure to ultrasonication was investigated with XPS, which showed no loss of coating. The adherence of the coating was investigated by insertion of implants in simulated bone material, which showed a minor loss in coating. In vitro (SBF) testing showed that the coating promoted crystallization of calcium phosphates, for uncoated PEEK, no crystallization was detected. The in vivo performance of the ZrP coating was examined by coating screw shaped PEEK implants which were implanted in rabbit tibia for 6 weeks. The anchoring strength of the implants was evaluated with removal torque (RTQ) measurements. The average RTQ for the ZrP coated implants was significantly higher compared to the non-coated implants. The results show that a nanosized ZrP coating on PEEK implants can transform the surface from having a low ability to osseointegrate to a surface which stimulates bone tissue growth. This makes the ZrP coating an interesting alternative for coating PEEK implants, such as spinal fusion cages and tendon fixation screws.

Improved biotribological properties of polyetheretherketone composites for artificial joints with a ‘soft-on-hard’ structure and brushlike molecules

On the purpose of improving the biotribological performance of polyetheretherketone (PEEK) for artificial joints, mimicking the ‘soft-on-hard’ contact mode of ‘cartilage-subchondral bone’ construction as well as the special brushlike structure of natural articular cartilage, a ‘soft-on-hard’ structure with a poly acrylic acid-poly acrylamide (PAA-PAAm) hydrogel layer connected onto a PEEK substrate was fabricated. Meanwhile, methacrylated sodium alginate (SAGMA) was introduced into the hydrogel layer to form molecular brushes. Compared to the friction coefficient of a pristine PEEK (0.22), that of the PEEK-hydrogel-molecular brush structure was significantly lower (0.02) benefiting from the synergistic effect of biphasic lubrication and boundary lubrication. This work develops a useful method to effectively improve the biotribological properties of artificial joints.

Preparation and Characterization for Antibacterial Activities of 3D Printing Polyetheretherketone Disks Coated with Various Ratios of Ampicillin and Vancomycin Salts

In this study, polyetheretherketone (PEEK) materials coated with various ratios of two kinds of antibiotic agents (ampicillin and/or vancomycin salts) were prepared. A modified 3D printer based on fused deposition modeling was employed to prepare PEEK disks. Coating ampicillin and/or vancomycin salts onto the PEEK disks was carried out using the biodegradable poly (lactic-co-glycolic acid) (PLGA) polymer as a binder and a control unit for the drug release in the buffer solution. The effects of various rations of ampicillin and/or vancomycin salts in the PLGA polymer on the PEEK substrates, the release profiles of various drugs, and antibacterial activities of the samples were investigated. Temperature of the heated nozzle in a commerical 3D printer was set at 340 °C. After systemic investigations of the qualities of PEEK disks, a diameter of the heated nozzle of 0.6 mm in the 3D printer was employed for the preparation of PEEK disks. Results of drug release profiles from samples into buffer solution show that the antibacterial activities of samples can continue up to 28 days. In the inhibition zone test of samples, the release amounts of antibiotic agents from the PEEK samples can inhibit S. aureus with activity of over 40% in 30 days tests and most of them can have inhibition activities of higher than 60% during the test. These results showed that a simple and low-cost 3D printing method for the preparation of PEEK/antibiotic agents/PLGA samples can have further applications in biomedical-related technology.

Antibacterial Application on Staphylococcus aureus Using Antibiotic Agent/Zinc Oxide Nanorod Arrays/Polyethylethylketone Composite Samples.

In this study, zinc oxide (ZnO) nanorod arrays as antibiotic agent carriers were grown on polyetheretherketone (PEEK) substrates using a chemical synthesis method. With the concentration of ammonium hydroxide in the precursor solution kept at 4 M, ZnO nanorod arrays with diameters in the range of 100–400 nm and a loading density of 1.7 mg/cm2 were grown onto the PEEK substrates. Their drug release profiles and the antibacterial properties of the antibiotic agent/ZnO/PEEK samples in the buffer solution were investigated. The results showed that the concentrations of antibiotic agents (ampicillin or vancomycin) released from the samples into the buffer solution were higher than the value of minimum inhibitory concentration of 90% for Staphylococcus aureus within the 96 h test. The bioactivities of ampicillin and vancomycin on substrates also showed around 40% and 80% on the Staphylococcus aureus, respectively. In the antibacterial activity test, sample with the suitable loading amount of antibiotic agent had a good inhibitory effect on the growth of Staphylococcus aureus.

Strontium/adiponectin co-decoration modulates the osteogenic activity of nano-morphologic polyetheretherketone implant.

Polyetheretherketone (PEEK)-based implants have become popular in hard tissue orthopedic and dental field. However, its inherent bio-inertness limited its applications for bone repair/substitution of osteoporosis patients, with poor osteogenesis capability. In order to ameliorate their bioactivity, the 3D porous PEEK substrate was created by sulfonate processing, and the substrate was subsequently incorporated with strontium (Sr) through a hydrothermal reaction in Sr(OH)2 solutions. The adiponectin (APN) protein membrane was deposited on the substrate via polydopamine-assisted deposition. Surface characterization results disclosed that the nanostructures had been formed on sPEEK-Sr-APN surafces, and APN coatings on the substrates could adjust Sr release rate and further mediate cell-material interactions. in vitro experiments indicated that the cellular effects (proliferation and differentiation) of MC3T3-E1 were significantly increased with Sr/APN coordinated regulation. This study provides bioactive Sr and APN as promising active components for bio-functional bone regeneration/substitution, and optimizes the osteointegration of PEEK implants in clinic.

Antibacterial effect of Cu/C:F nanocomposites deposited on PEEK substrates

The study focuses on antibacterial Cu/C:F nanocomposites deposited onto polyether-ether-ketone (PEEK) substrates. The nanocomposites were prepared by means of physical vapour deposition; copper nanoparticles (NPs), produced with the use of a gas aggregation source, were coated with RF sputtered polytetrafluorethylene. It was found that nanocomposites, formed with a properly tailored number of Cu NPs and C:F barrier thickness, offer a strong antibacterial effect against E. coli without any harm to MG63 cells.

Hydroxyapatite Coatings on Polymers Using a Custom Low-Energy Plasma Spray System

The use of polymers in modern orthopedics and tissue engineering represents a big opportunity to overcome the current challenges facing metallic implant technologies, such as the release of toxic metallic ions and particles, as well as the lack of isoelastic property. Furthermore, it is widely sought that these kinds of medical devices support bone ingrowth and enhance osseointegration. Therefore, implants can be coated with bioactive materials such as hydroxyapatite (HAp) by means of atmospheric plasma spray (APS), which is the most widely used for coating implants with materials of high capacity for osseointegration. So far, APS has been primarily applied to metallic substrates, and only a few studies are available on polymeric and composite materials. Consequently, the aim of this paper was to apply HAp coatings on polyetheretherketone (PEEK) substrates—a polymer commonly used for orthopedics implants—using a custom designed low-energy plasma spray (LEPS) system equipped with a built in-house dc torch. Due to the lower enthalpy in the LEPS system, it is expected that it will not degrade the shape or surface condition of the polymers during the process, and still achieve enough energy to properly melt the HAp powder particles. Observation of the as-coated surfaces by scanning electron microscopy shows that a successful deposition with very good coverage was achieved on the PEEK substrates.

Micro-porous polyetheretherketone implants decorated with BMP-2 via phosphorylated gelatin coating for enhancing cell adhesion and osteogenic differentiation.

Polyetheretherketone (PEEK) is a high-performance semicrystalline thermoplastic polymer that is widely used in the orthopedics treatment. However, due to its biological inertness, the surface modification of PEEK using different methods to improve the biocompatibility remains a significant challenge. Herein, we attempted to use the covalently coating of phosphorylated gelatin loaded with bone morphogenetic protein 2 (BMP-2) on hydroxylated micro-porous PEEK films for enhancing the biological activity. Environmental scanning electron microscope (ESEM), fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and water contact angle measurements were applied to characterize the surface of modified or untreated PEEK films. The influence on cell adhesion, proliferation and differentiation was evaluated by culturing of mouse pre-osteoblasts (MC3T3-E1) on different modified PEEK substrates in vitro. Surface characterization showed that the modification was successfully performed on PEEK films. The biological results indicated that surface modification of micro-porous PEEK using phosphorylated gelatin significantly promoted cell adhesion and proliferation. And the osteogenic differentiation was effectively improved while loading with different amounts of BMP-2. Findings from this study indicated that this novel biological modification on PEEK films might be helpful for altering its biological inertness and further expand its medical applications as a kind of orthopedic implants.

Characterizing the differentiation of osteoprogenitor cells on surface modified polyether-ether-ketone

The modified surface of polyether-ether-ketone (PEEK) was sequentially sulfonated, treated with silanization, fixed with glutaraldehyde, and grafted with type I collagen (COL I). Surface roughness and water contact angle measurements, scanning electron microscopy, and Fourier transform infrared spectroscopy were conducted. The viability of mouse fibroblast cells (NIH-3T3) on the modified PEEK was determined to study cytotoxicity, and bone-marrow-derived mouse pluripotent mesenchymal stem cells (D1) were cultured to evaluate the mineralization capability through cell adhesion, proliferation, and differentiation on the modified PEEK substrates. Sulfonated PEEK exhibited an evident rough surface, and the substrate was further silanized and grafted using COL I with spectroscopy absorption frequencies of carbonyl, sulfonyl hydroxide, and amide functional groups, which were incorporated to enhance the hydrophilic properties. Results showed that the substrate of PEEK modified by sulfonation, silanization, and further grafting with COL I generated a higher number of amide functional groups than all other functional groups. The D1 cell viability of each testing group increased with incubation time, but the difference was not significant. Conversely, D1 cell viability obviously decreased for a further prolonged culture period exceeding 14 days. The sulfonated PEEK substrate further treated with silanization and grafted with COL I exhibited the most remarkable performance of alkaline phosphatase (ALP) activity on the 10th day of incubation among all samples. In conclusion, we developed a sulfonated PEEK surface that was further treated with silanization, fixed with glutaraldehyde, and grafted with COL I. The modified surfaces can improve the bioinert property of PEEK through the rough and three-dimensional structures with evident hydrophilic properties for orthopedic implants.

Improving surface wettability and lubrication of polyetheretherketone (PEEK) by combining with polyvinyl alcohol (PVA) hydrogel.

Poor surface wettability and relative high friction coefficients of pristine polyetheretherketone (PEEK) have limited its application in orthopedic implants. In this study, inspired by the structure of natural articular cartilage, we presented a novel method to fabricate a "soft-on-hard" structure on the surface of pristine PEEK specimens, which combined a soft polyvinyl alcohol (PVA) hydrogel layer and a three-dimensional porous layer with PEEK substrates. A variety of analytical methods were used to evaluate their properties, our results demonstrated that the hydrogel layer could be seamlessly connected with substrate, and the hydrogel-covered PEEK owned a highly hydrophilic surface, a very low water contact angle of 7° could be obtained. The friction coefficients of untreated and hydrogel-covered PEEK surfaces were measured using a tribometer under water lubrication, due to the presence of the top hydrogel layer and the hard substrate could provide excellent aqueous lubrication and bearing capacity, respectively, the friction coefficient could be reduced from 0.292 to 0.021. In addition, the porous layer under PVA hydrogel layer could work as gel reservoirs, the reserved hydrogel would be released after the surface layer was sheared off, and a regenerable lubrication status was obtained. This work provides a new route for the design of improving the surface wettability and tribological properties of PEEK.

Metallization of polyether ether ketone (PEEK) by copper coating via cold spray

The metallization of polymer-based materials via cold spray has been attractive to improve its thermal and electrical properties, while the direct deposition of thick Cu coating was rarely reported. In this work, relatively low process parameters were used to metallize PEEK substrate via cold spray to enhance the electrical properties of PEEK. The coating microstructure and properties such as microhardness and electrical conductivity were investigated at different propelling gas pressures. A thick and dense Cu coating was produced on PEEK substrate with only three passes of deposition. Based on Raman spectra, the polymer structures of PEEK substrate were well retained after high-velocity impact in cold spray. Meanwhile, the electrical conductivity and microhardness of the cold sprayed coating on PEEK increase at a higher propelling gas pressure. At last, the splat morphology of single Cu particle deposition on PEEK accompanying the finite element analysis were used to discuss the deposition mechanism of metallic particle on polymer surface. More prominent material jet was formed at the substrate at a higher propelling gas pressure as the adiabatic shear instability is more evident at higher particle impact velocity, which facilitates the deposition of metallic coating on PEEK.

Transferability and Adhesion of Sol-Gel-Derived Crystalline TiO2 Thin Films to Different Types of Plastic Substrates.

Anatase thin films were prepared on various plastic substrates by our recently developed sol-gel transfer technique. Polycarbonate (PC), poly(methyl methacrylate) (PMMA), polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polyether ether ketone (PEEK), and polyvinylidene chloride (PVDC) were employed as plastic substrates. A Si(100) substrate was first coated with a polyimide (PI)/polyvinylpyrrolidone (PVP) mixture layer, and an alkoxide-derived titania gel film was deposited on it by spin-coating. The resulting titania gel film was heated to 600 °C, during which the PI/PVP layer decomposed and the gel film was converted into a 60 nm thick anatase film. The anatase film was then transferred from the Si(100) substrate to the plastic substrate. This was achieved by heating the plastic/anatase/Si(100) stack in a near-infrared image furnace to 120-350 °C, depending on the type of plastic substrate, under unidirectional pressure. The anatase film cracked during transfer to PE, PP, PEEK, and PVDC substrates but did not crack during transfer to PC, PMMA, and PET substrates. The fraction of the total film area that was successfully transferred was assessed with the aid of image analysis. This fraction tended to be large for plastics with C═O and C-O groups and small for those without these groups. The film/substrate adhesion assessed by cross-cut tape tests also tended to be high for plastics with C═O and C-O groups and low for those without these groups. The adhesion to plastics without C═O or C-O groups could be enhanced and their transfer area fraction increased by oxidizing the native plastic surface by ultraviolet-ozone treatment prior to transfer.

Evaluation of a variety of a-C:H coatings on PEEK for biomedical implants

Four different hydrogenated amorphous carbon (a-C:H) coatings were deposited on poly-ether-ether-ketone (PEEK). Their properties in terms of surface roughness, wettability, nanoindentation, residual internal stress, adhesion, scratch resistance, friction and wear resistance were assessed.The two polymer-like carbon coatings were obtained without applying any bias voltage to the substrate. They exhibited very low hardness, Young's modulus and residual internal stress compared with what is generally achieved for diamond-like carbon films. Nonetheless, they enabled to significantly reduce wear when rubbed against an alumina ball. They also showed a very good adhesion to the PEEK substrate and a reduction of the coefficient of friction compared with that of the PEEK substrate.When the titanium layer deposited on the PEEK substrate was biased at either −50V or −100V during the deposition of the a-C:H coatings, the a-C:H coatings were harder, stiffer and more internally stressed than the two polymer-like carbon coatings. However, the a-C:H films obtained with bias voltages of −50V and −100V suffered from adhesive fracture in pull-off testing and early delamination in tribological testing. These results were assumed to be due to a titanium oxide layer which was not properly removed prior to the deposition of the hydrogenated amorphous carbon films and to the higher residual internal stress of the a-C:H films obtained with bias voltages of −50V and −100V compared with the two polymer-like films.

Mechanical properties and in vivo study of modified-hydroxyapatite/polyetheretherketone biocomposites

Polyether ether ketone (PEEK) has received much attention for its excellent mechanical properties and biocompatibility. Here, the silane coupling agent KH560 [γ-(2,3-epoxypropoxy)propyltrimethoxysilane] is used for graft modification of bioactive HA (hydroxyapatite) particles and for preparing HA/PEEK composites via a hot-press molding method. The prepared HA/PEEK composites were tested for their mechanical properties with SEM (scanning electron microscopy), infrared spectroscopy, and thermo-analysis. The results show that silane coupling KH-560 modifies HA successfully and that the tensile strengths of HA/PEEK and m-HA/PEEK composites indicate an increasing and then a decreasing tendency with increasing HA contents. The non-modified HA/PEEK composites display the same trend as the modified specimens with lower tensile strength and consist of sharp points. When the HA content is 5wt.%, the tensile strength of m-HA/PEEK composite reaches its maximum, which is 23% higher than that of pure PEEK specimens. The in vivo experiments of m-HA/PEEK used a biomechanical push-out test, SEM, optical microscopy, and an Image-Pro Express C image analysis system. The growth of the bone tissues around the m-HA/PEEK composites with an HA content of 5wt.% is better than that of specimens with different HA contents. This finding shows the nano-scale effect of the bioactive filler HA in PEEK substrates, which obviously contributes to the growth of the surrounding bone issues in vivo. This study could provide theoretical support for the further promotion and application of high-performance engineering plastics such as PEEK in biomedical fields.

Fabrication of hydroxyapatite thin films on polyetheretherketone substrates using a sputtering technique

Hydroxyapatite (HA) thin films were coated on a polyetheretherketone (PEEK) substrate using a sputtering technique. A thin titanium (Ti) intermediate layer was formed between the HA and the PEEK surface to improve adhesion of the HA film to the PEEK substrate. The coated films were recrystallized using a hydrothermal treatment to reduce the dissolution of the HA film. The films were then characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), and a UV-Vis spectrophotometer. A pull-out test was performed to measure the film-to-substrate adhesion strength, and an immersion test was performed in ultra-pure water.In the XRD patterns of the sputtered film with the Ti intermediate layer on the PEEK substrate, small HA peaks and large Ti peaks were observed. After the hydrothermal treatment, the intensity of the HA peaks increased. The transmittance of the HA films with 5 and 10nm Ti intermediate layers was >79% and 68%, respectively, in the visible light wavelength region (400–700nm) after the hydrothermal treatment. The adhesion strength of the hydrothermally treated HA films increased with decreasing thickness of the Ti intermediate layer, and the strength reached 2.7MPa with the 5-nm-thick Ti intermediate layer. In the immersion test, the HA film with a 5-nm-thick Ti intermediate layer without hydrothermal treatment exhibited a released Ti concentration of 42.0±2.4ppb. After hydrothermal treatment, the released Ti concentration decreased to 17.3±1.1ppb.