Takamasa Onoki

Bioactive titanate nanomesh layer on the Ti-based bulk metallic glass by hydrothermal–electrochemical technique

Titanate nanomesh layers were fabricated on Ti-based bulk metallic glass (BMG) to induce bioactivity in the form of apatite-forming ability. Titanate nanomesh layers were prepared by hydrothermal-electrochemical treatment at 90 degrees C for 2 h, with an aqueous solution of NaOH as an electrolyte. A constant electric current of 0.5 mA cm(-2) was applied between the BMG substrate and a Pt electrode acting as the anode and cathode, respectively. A nanomesh layer, consisting of nanowires (approximately 20 nm in diameter) formed on the BMG. An immersion test in simulated body fluid for 12 days revealed that the titanate nanomesh layer on the BMG promoted the growth of bone-like hydroxyapatite.

Multifunctional porous titanium oxide coating with apatite forming ability and photocatalytic activity on a titanium substrate formed by plasma electrolytic oxidation

Plasma electrolytic oxidation (PEO) was used to make a multifunctional porous titanium oxide (TiO2) coating on a titanium substrate. The key finding of this study is that a highly crystalline TiO2 coating can be made by performing the PEO in an ammonium acetate (CH3COONH4) solution; the PEO coating was formed by alternating between rapid heating by spark discharges and quenching in the solution. The high crystallinity of the TiO2 led to the surface having multiple functions, including apatite forming ability and photocatalytic activity. Hydroxyapatite formed on the PEO coating when it was soaked in simulated body fluid. The good apatite forming ability can be attributed to the high density of hydroxyl groups on the anatase and rutile phases in the coating. The degradation of methylene blue under ultraviolet radiation indicated that the coating had high photocatalytic activity.

Regulation of the protein-loading capacity of hydroxyapatite by mercaptosuccinic acid modification

Loading and releasing protein in a controllable way is extremely important for the protein vehicles used in bone tissue engineering. To obtain a suitable carrier material for basic proteins, such as BMP or bFGF, hydroxyapatite particles containing mercaptosuccinic acid (mercaptosuccinic acid (Mer), (Mer-HAp)) were synthesized. Physicochemical evaluation of Mer-HAp suggested that Mer was contained in HAp particles: it either simply adsorbed onto HAp crystals or was trapped among the HAp crystals. A protein adsorption study using basic and acidic model proteins indicated that the synthesized Mer-HAp had selective loading properties of the basic protein. The loaded protein was gradually released from Mer-HAp in phosphate buffered saline. The protein release rate was different in each Mer-HAp synthesized with a different concentration of Mer. In addition, the protein release from Mer-HAp showed a similar profile with the Ca dissolution in different pH solutions, indicating that the Mer-HAp dissolution was concerned with the protein release from Mer-HAp. Thus, Mer-HAp is a useful candidate for the basic protein carrier because it has properties which enable the loading and releasing of protein in a controllable way.

Evaluation of microstructures and properties of bulk mesoporous silica

Synthesis of mesoporous MCM-type bulks prepared by hydrothermal hot-pressing (HHP) method using MCM-type mesoporous powder was attempted. Scanning electron microscopy (SEM), bulk density measurement, N2 adsorption-desorption isotherms and formaldehyde adsorption test have been employed to characterize the bulky products. As a result, we succeeded in preparing a dense and strong mesoporous bulks with high BET over 1000 m2/g through the hydrothermal hot-pressing method under appropriate conditions.

Joining Hydroxyapatite Ceramics and Titanium Alloys by Hydrothermal Method

Solidificatioin of hydroxyapatite (HA) and its bonding with titanium (Ti) alloys was achieved simultaneously by using a hydrothermal hot-pressing (HH P) method. The reaction temperature used for the HHP treatment was as low as 150 ̊C. Tw o types of Ti alloys; Ti-15Mo-5Zr-3Al and Ti-6Al-2Nb-1Ta were tested to examine the eff ct of NaOH hydrothermal treatment. The NaOH treatment was shown to be useful to enhance the interfac e fracture property in the bonded HA/Ti body for both Ti alloys. The use of Ti-15Mo-5Zr-3Al was more effective in the NaOH treatment and the bonded HA/Ti body provided approximately three im s higher interface toughness compared with that for the non-treated Ti alloy. Introduction Titanium (Ti) and its alloys are widely used as orthopedic and dental implant mater ials b cause of their high mechanical strength, low modulus and good corrosion re sistance [1]. However, when embedded in the body, a fibrous tissue encapsulates the implant, isolat ing it from the surrounding bone. Some bioactive ceramics such as hydroxyapatite (Ca 10(PO4)6(OH)2) (HA), bioglass and glass ceramics can directly bond to living bones when used as a bone replac ement materials [2]. The mechanical properties of HA only allow its applications in the sma ll non-loaded structures. The possibility of HA deposited into the films and its bioactive properti es exploited in the structural prostheses, for instance teeth root, hip, knee and shoulder joint replacement . Therefore, the HA is used as coating materials of those prostheses surface in order to pr pare the bioactive layers on the Ti alloys. The HA surface improves the fixation of the implants due to the penetrative growth of the bone into the coating, forming a mechanical interlock. Plasma spraying techniques traditionally have been used in process f hydroxyapatite coating [3]. However, this high temperature method results in a number of sig ni icant problems, including phase and chemical decomposition of the HA, absence of a chemical int erface/bond between the HA coating and substrate. We have recently reported a new method for bonding HA ceramics and pur e Ti disk by using a hydrothermal hot-pressing (HHP) [4]. The hydrothermal reaction of calcium hydrogen phosphate dihydrate (CaHPO4.2H2O; DCPD) and calcium hydroxide (Ca(OH) 2) occurs in a liquid phase as follows: 6CaHPO4.2H2O + 4Ca(OH) 2 Ca10(PO4)6(OH)2 + 18H2O . (1) The water of crystallization in DCPD is slowly lost below 100 °C is well known phenome a [5]. If the released water can be utilized as a reaction solvent duri ng the HHP treatment, then the synthesis and solidification of HA and joining the HA to metal can be achieved simultaneously under the hydrothermal condition. Recently, it has been reported that if the Ti and its alloys surface is treated with natrium hydroxide (NaOH) solution it obtains the ability of joining HA directly by a bi omimetic method [6]. This paper describes a new bonding technique of HA ceramics and Ti alloys and discusses the effects of the NaOH solution treatment on the interface property of bonded HA/Ti alloy bodies in HHP method. Experimental Sample preparation. Firstly DCPD powder is used as a starting material was prepared by mixing 1.0M calcium nitrate solution (Ca(NO)3.4H2O ; Kanto Chemical Co., Inc., 99.0%, Japan) and 1.0M diammonium hydrogen phosphate solution ((NH 4)2 PO4 ; Kanto Chemical Co., Inc., Key Engineering Materials Online: 2003-05-15 ISSN: 1662-9795, Vols. 240-242, pp 571-574 doi:10.4028/www.scientific.net/KEM.240-242.571

Blood compatibility and tissue responsiveness on simple and durable methylsiloxane coating.

This study was conducted to evaluate the blood compatibility and tissue responsiveness of methylsiloxane (MS)-coated inorganic (glass and metal) substrates both in vitro and in vivo. MS was prepared from methyltriethoxysilane (MTES) through hydrolysis of a sol-gel solution at 80 °C. The adhesive strength of the MS coating was evaluated by using a tear-off test, revealing that the MS strongly adhered to the surface of the inorganic substrates. Blood compatibility was evaluated by assessing platelet adhesion and blood plasma coagulation time. The platelet aggregation ratio of the MS-coated glass tube was reduced to 10%, which was much smaller than that of the coating-free glass tubes (99%) and conventional blood-compatible polystyrene (PS) tubes (18%). Coagulation time was measured by active partial thromboplastin time (APTT) test, which showed that MS coating is as inert as PS in activating blood coagulation factor XII. Tissue responsiveness to the bulk MS sample, evaluated by animal test, showed a desirable compatibility comparable to that of the control titanium sample. This study indicated that MS coating is readily available to convert inorganic materials to useful biomaterials that have suitable mechanical strength and are compatible with blood and tissue.

Sol-Gel Derived Methylsiloxane-Ca-Nb-Ta Coating on Titanium Surface by Double Layered Structure

Titanium (Ti) and its alloy have sufficient mechanical properties to be utilized as artificial hip joints and article teeth. However, they have no bioactivity. In this work, we prepared bioactive coatings on Ti by sol-gel techniques. The coatings had a double layered structure. Underlying layer was methylsiloxane (MS) consisted of methyltriethoxysilane (MTES). Top layer was MS-Ca-Nb-Ta hybrid composed of MTES, calcium nitrate tetrahydrate, pentaethoxy-niobium and pentaethoxy-tantalum. The coating exhibited formation of bone-like apatite in SBF immersion test. Adhesive strength of the coating was found to be 1.8 MPa.

Novel Method for Hydroxyapatite Coating by Hydrothermal Hot-Pressing via Double Layered Capsule

A new hydrothermal method is proposed which enables us to prepare thin hydroxyapatite (HA) ceramic coatings on Ti substrates with a curved surface at low temperatures. The method uses double layered capsules in order to produce a suitable hydrothermal condition; the inner capsule encapsulates the coating materials and a Ti substrate, and the outer capsule is subjected to isostatic pressing under the hydrothermal condition. In this study, it is demonstrated that a pure HA ceramic layer with the thickness of 50 µm could be coated to a Ti cylindrical rod at the low temperature as low as 135°C under the confining pressure of 40 MPa. Pull-out tests were conducted to obtain an estimate for the adhesion properties of the HA coating prepared by the double layered capsule method. The shear strength obtained from the pull-out tests was in the range of 4.0-5.5 MPa. It was also shown that the crack propagation occurred within the HA coating layer, not along the HA/Ti interface in the pull-out tests.

Mechanical Properties of Carbon Nanotubes / Hydroxyapatite Composites Prepared by Spark Plasma Sintering

In this study, Multi‐Walled Carbon Nanotubes (MWCNTs) / Hydroxylapatite (HAp) composites were made to improve mechanical properties by using Spark Plasma Sintering (SPS) method. Slurry 6 mol of CaHPO4⋅2H2O (DCPD), 4 mol calcium hydroxide and MWCNTs were mixed and sintered by using SPS at 5–120 MPa pressure, 1200–1250 °C and in vacuum or N2 atmosphere. The fracture toughness of sintered MWCNTs/HAp composites was increased.

Effects of NaOH Concentration on CO2 Reduction via Hydrothermal Water

The reductions of CO2 under hydrothermal conditions were investigated by using the micro autoclave (45cm3) lined with Hastelloy‐C alloy. Sodium hydrogen carbonate (NaHCO3) was used as a starting material. H2 gas was used as reducing agents. NaHCO3 powder, H2 gas and water put into the autoclave simultaneously. The autoclave was heated upto 300°C by induction heater. In this study, effects of pH value of the NaOH solution in the autoclave are investigated. Reaction products were analyzed with gas chromatographs (GC), liquid chromatographs (LC), X‐ray diffractometor (XRD) and Scanning electron microscopy (SEM). The following things were showed in this research: CO2 was reducted to HCOO− and CH4 at high conversion ratio under hydrothermal conditions. HCOO− was formed at high selectivity using Hastelloy‐C reactor in the alkaline solution with Raney Ni catalyst. Raney Ni was exellent methanation catalyst, and CH4 formation progressed via HCO3−, not via CO. It is cleared that the NaOH solution in the autoclave ...