Kazuhide Ozeki

Phase composition of sputtered films from a hydroxyapatite target

Abstract Hydroxyapatite (HA) was coated onto a cellulose filter acting as a substrate from a crystalline HA powder target using radio-frequency magnetron sputtering at Ar pressure of 0.5–5.0 Pa and discharge power of 50–150 W. After coating, the films were heated to 700 °C to remove the substrate and the crystalline phases were identified using XRD. The Ca/P ratio of the films was analyzed using EDS. The films were composed of HA, β-tricalcium phosphate (TCP), β-calcium pyrophosphate (PYR) and CaO. The weight ratio of HA and the Ca/P ratio of the films decreased with increasing Ar pressure and were largest at 100 W of discharge power. After coating, the surface of the HA target was decomposed into α-TCP, β-TCP and CaO.

A functionally graded titanium/hydroxyapatite film obtained by sputtering.

A functionally graded film of titanium/hydroxyapatite (HA) was prepared on a titanium substrate using a radio frequency magnetron sputtering. The ratio of titanium to HA was controlled by moving the target shutter. The film was composed of five layers, with overall film thickness of 1 μm. The HA was concentrated close to the surface, while the titanium concentration increased with proximity to the substrate. The bonding strength between the film and the substrate was 15.2 MPa in a pull-out test and the critical load from a scratch test was 58.85 mN. The corresponding values of a pure HA sputtered film were 8.0 MPa and 38.47 mN, respectively. The bonding strength of a pure HA plasma spray coating was 10.4 MPa in the pull-out test. The graded film and the pure HA film were sputter-coated to a thickness of 1 μm on titanium columns (10 mm in length and 4 mm in diameter). These columns were implanted in diaphyses of the femora of six adult dogs and a push-out test was carried out after 2, 4, and 12 weeks. After 12 weeks, the push-out strengths of the graded film, the pure HA film and the non-coated columns were 3.7, 3.5, and 1.0 MPa.

Development of tissue adhesion method using integrated low-level energies.

We have developed a method that allows biological tissues to be adhered together with minimal invasion by delivering integrated low-level energies from heat, pressure, and vibration. Tensile tests on adhered slices of porcine aorta were performed to determine the relationships between adhesive strength and conditions such as adhesion temperature, time, pressure, and vibration. The maximal adhesive shear tensile strength using the proposed method was 0.2MPa, which is half the strength of the porcine aorta and stronger than surgical tissue adhesive. Adhesion strength increased in proportion to temperature, time, and pressure, and also in the presence of vibration, indicating that vibrational energy contributes to the adhesive mechanism and strength. Adhesive stability, the effect of heat on adhesive strength, and the ability of tissue to adhere to artificial materials were also clarified.

Adsorptive properties of albumin, fibrinogen, and γ-globulin on fluorinated diamond-like carbon films coated on PTFE

Fluorinated diamond-like carbon (F-DLC) films were deposited on polytetrafluoroethylene (PTFE) using radio frequency (RF) plasma-enhanced chemical vapor deposition (CVD) by changing the ratio of tetrafluoromethane (CF4) and methane (CH4). To enhance the adhesion strength of the F-DLC film to the PTFE substrate, the PTFE surface was modified with a N2 plasma pre-treatment. XPS analysis of the films showed that the C–C bond decreased with increases in the CF4 ratio, whereas the C–F bond increased with the CF4 ratio. The F/C ratio of the film also increased with the CF4 ratio. The pull-out test showed that the adhesion strengths of the films (CF4-0–60%) were improved with the plasma pre-treatment. In the film without the plasma pre-treatment, adhesion strength increased with the CF4 ratio. In contrast, in the case with the plasma pre-treatment, the adhesion strength of the F-DLC film decreased with the increased CF4 ratio. Regarding the adsorption of albumin, fibrinogen, and γ-globulin, the amount of adsorbed albumin on the film decreased with an increasing CF4 ratio, and the amount of adsorbed fibrinogen and γ-globulin increased with the CF4 ratio. The CF4-0% DLC film showed the most adsorbed albumin and the least adsorbed fibrinogen and γ-globulin. This indicates that the CF4-0% DLC film has higher anti-thrombogenicity than the F-DLC film.

Biocompatibility of Diamond-Like Carbon Coated NiTi Orthodontic Wire and Acrylic Resin Teeth

A variety of dental devices such as orthodontics, artificial teeth are implanted in oral cavity for long term. The implant coated with protective films, which can reduce corrosion and wear, may prevent the problems described above and extend the lifetime of implants to the benefit of the patients. Diamond-like carbon films have extreme hardness, low friction coefficients, chemical inertness, and high-corrosion resistance. Moreover, these properties make the good candidates as biocompatible coatings for dental devices. In this study, DLC films using the plasma CVD method deposited on acrylic resin and orthodontic archwires have investigated to detect the Ni release from the wires and to estimate cell growth in E-MEM immersed acrylic plates. After 6 months, the concentration of the nickel release from DLC-coated wire and Non-coated wire was 150 [ppb] and 933 [ppb], respectively. Results indicated DLC films inhibit the release of these materials, and prevent degradation of these materials in the solution.

Characterization of a hydroxyapatite sputtered film subject to hydrothermal treatment using FE-SEM and STEM

Hydroxyapatite (HA) was coated onto a titanium substrate using radio frequency magnetron sputtering. The sputtered film was crystallized using a hydrothermal treatment. The films were observed using X-ray diffractometry, field emission scanning electron microscopy (FE-SEM) and scanning transmission electron microscopy (STEM) equipped with energy dispersive X-ray spectroscopy (EDX).It was observed that the surface of the hydrothermally-treated film was covered with globular particles. The FE-SEM observations indicated that these particles were composed of columnar grains with a grain size of 20-50 nm. In the STEM cross-sectional observation of the HA-Ti interface, HA crystalline phase regions were observed, in part, in the non-crystalline phase layer of the as-sputtered film. After the hydrothermal treatment, the HA layer crystallized; the HA crystallization proceeded to a distance of 30 nm above the titanium surface. From an EDX line scan analysis, the titanium oxide layer was not observed at the HA-Ti interface of the as-sputtered film; however, in the hydrothermally-treated film, the titanium oxide layer, with a 15 nm thickness, was observed between the mixing layer and the titanium substrate. The formation of titanium oxide at the HA-Ti interface would contribute to the adhesion improvement of the sputtered film following the hydrothermal treatment.

Thermal denaturation behavior of collagen fibrils in wet and dry environment.

We have developed a new minimally invasive technique--integrated low-level energy adhesion technique (ILEAT)--which uses heat, pressure, and low-frequency vibrations for binding living tissues. Because the adhesion mechanism of the living tissues is not fully understood, we investigated the effect of thermal energy on the collagen structure in living tissues using ILEAT. To study the effect of thermal energy and heating time on the structure of the collagen fibril, samples were divided in two categories-wet and dry. Further, atomic force microscopy was used to analyze the collagen fibril structure before and after heating. Results showed that collagen fibrils in water denatured after 1 minute at temperatures higher than 80 °C, while partial denaturation was observed at temperatures of 80 °C and a heating time of 1 min. Furthermore, complete denaturation was achieved after 90 min, suggesting that the denaturation rate is temperature and time dependent. Moreover, the collagen fibrils in dry condition maintained their native structure even after being heated to 120 °C for 90 min in the absence of water, which specifically suppressed denaturation. However, partial denaturation of collagen fibrils could not be prevented, because this determines the adhesion between the collagen molecules, and stabilizes tissue bonding.

Characterization of Sr-substituted hydroxyapatite thin film by sputtering technique from mixture targets of hydroxyapatite and strontium apatite.

Sr-substituted hydroxyapatite thin films were prepared by sputtering technique from mixture targets of hydroxyapatite (HA) and strontium apatite (SrAp). The HA and SrAp powders were mixed at 0-100% Sr/(Sr+Ca) target ratios. The coated films were recrystallized by a hydrothermal treatment to reduce film dissolution. The films were then characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and inductively coupled plasma atomic emission spectrometry (ICP). The osteocompatiblity of the films was also evaluated by the size of the bone formation area in osteoblast cells.In the XRD patterns, peaks shifted to lower 2θ values with increasing Sr/(Sr+Ca) target ratios, which indicated Sr incorporation into the HA lattice. In the SEM observation of the hydrothermally treated films, the surface was covered with globular particles, and the size of the globular particles increased from Sr0 to Sr40, and then the size decreased from Sr60 to Sr100. The ICP analysis showed that the Sr/(Sr+Ca) film ratios were almost the same as the target ratios. In the cell culture, the bone formation area on the Sr-substituted HA films increased with increasing Sr concentration, and saturated at Sr60.

The adsorptive behavior of albumin and lysozyme proteins on rod-shaped and plate-shaped hydroxyapatite

The adsorption behavior of albumin (BSA) and lysozyme (LSZ) on rod-shaped and plate-shaped hydroxyapatite (HA) was investigated to evaluate the influence of crystal orientation and morphology on the selective protein adsorption of HA. The rod-shaped HA was prepared by hydrothermal treatment from β-tricalcium phosphate (β-TCP) in H3PO4 solution (pH 2.0 and 4.0 for HA-pH 2.0 and HA-pH 4.0). The plate-shaped HA was synthesized by hydrolysis of CaHPO4-2H2O (DCPD) in NaOH solution at 40°C and 80°C (HA-40°C and HA-80°C). The synthesized HA was characterized using scanning electron microscopy (SEM) and X-ray diffractometry (XRD). HA-pH 2.0 and HA-pH 4.0 produced rod-shaped crystals that were highly oriented to the a-face plane, whereas HA-40°C and HA-80°C showed a plate-like shape and a c-face preferred orientation. The peak intensity ratio I(300)/I(002) (a/c intensity ratio) from the XRD patterns increased in the following order: HA-80°C, HA-40°C, HA-pH 2.0 and HA-pH 4.0. It also increased as the Ca/P ratio decreased. The amount of adsorbed BSA increased in the following order: HA-pH 4.0, HA-pH 2.0, HA-40°C and HA-80°C. The amount of adsorbed LSZ on HA increased in the following order--HA-pH 2.0, HA-pH 4.0, HA-40°C and HA-80°C--with a corresponding decrease in the a/c intensity ratio. The BSA/LSA adsorption ratio increased with the a/c intensity ratio in the range of 3.3-8.9, and the BSA and LSZ were selectively adsorbed on HA, depending on the crystal shape.

The wear properties and adhesion strength of the diamond-like carbon film coated on SUS, Ti and Ni-Ti with plasma pre-treatment.

Diamond-like carbon (DLC) films were deposited on stainless steel (SUS), titanium (Ti) and nickel titanium (Ni-Ti) substrates using a radiofrequency plasma chemical vapour deposition method. Prior to DLC coating, the substrates were exposed to O2 and N2 plasma to enhance the adhesion strength of the DLC film to the substrate. After the plasma pre-treatment, the chemical composition and the wettability of the substrate surface was investigated by X-ray photoelectron spectroscopy (XPS) and water contact angle measurement, respectively. A pull-out test and a ball-on-disc test were carried out to evaluate the adhesion strength and the wear properties of the DLC-coated substrates. The XPS results showed that the N2 and O2 plasma pre-treatment produced nitride and oxide on the substrate surfaces, such as TiO2, TiO, Fe2O3, CrN and TiNO. In the pull-out test, the adhesion strengths of the DLC film to the SUS, Ti and Ni-Ti substrates were improved with the plasma pre-treatment. In the ball-on-disc test, the DLC coated SUS, Ti and Ni-Ti substrates without the plasma pre-treatment showed severe film failure following the test. The DLC coated SUS and Ni-Ti substrates with the N2 plasma pre-treatment showed good wear resistance, compared with that with the O2 plasma pre-treatment.