Kanji Tsuru

Partial oxidation of TiN coating by hydrothermal treatment and ozone treatment to improve its osteoconductivity

Dental implants made of pure titanium suffer from abrasion and scratch during routine oral hygiene procedures. This results in an irreversible surface damage, facilitates bacteria adhesion and increases risk of peri-implantitis. To overcome these problems, titanium nitride (TiN) coating was introduced to increase surface hardness of pure titanium. However, the osteoconductivity of TiN is considered to be similar or superior to that of titanium and its alloys and therefore surface modification is necessary. In this study, TiN coating prepared through gas nitriding was partially oxidized by hydrothermal (HT) treatment and ozone (O3) treatment in pure water to improve its osteoconductivity. The effects of HT treatment and O3 treatment on surface properties of TiN were investigated and the osteoconductivity after undergoing treatment was assessed in vitro using osteoblast evaluation. The results showed that the critical temperature for HT treatment was 100°C since higher temperatures would impair the hardness of TiN coating. By contrast, O3 treatment was more effective in oxidizing TiN surfaces, improving its wettability while preserving its morphology and hardness. Osteoblast attachment, proliferation, alkaline phosphatase (ALP) expression and mineralization were improved on oxidized specimens, especially on O3 treated specimens, compared with untreated ones. These effects seemed to be consequences of partial oxidation, as well as improved hydrophilicity and surface decontamination. Finally, it was concluded that, partially oxidized TiN is a promising coating to be used for dental implant.

Fully-Interconnected Pore Forming Calcium Phosphate Cement

Calcium phosphate cement that foams fully-interconnected porous structure along with its gradual replacement to bone may be ideal for bone defect reconstruction. In the present study, α-tricalcium phosphate (αTCP) microspheres were exposed to acidic calcium phosphate solution. It was found that the αTCP microspheres set in approximately 10 min to form fully-interconnected porous structure. The porosity was approximately 50% and the pore size was 300µm. The surface of the porous body was dicalcium phosphate dihydrate whereas the inside was αTCP.

Immobilization of calcium and phosphate ions improves the osteoconductivity of titanium implants

In this work, to elevate weak osteoconductivity of titanium (Ti) implant, we prepared a Ti implant having both calcium and phosphate ions on its surface. To modify calcium and phosphate ions onto Ti, phosphate ions were first immobilized by treating the Ti with a NaH2PO4 solution, followed by CaCl2 treatment to immobilize calcium ions, which created the calcium and phosphate ions-modified Ti (Ca-P-Ti). X-ray photoelectron spectroscopy and thin-layer X-ray diffraction measurement confirmed that both phosphate and calcium ions were co-immobilized onto the Ti surface on the molecular level. Three-hour after seeding MC3T3-E1 murine pre-osteoblast cells on substrates, cell number on Ca-P-Ti was much larger than that of Ti and phosphate-modified Ti (P-Ti), but was similar to that of calcium-modified Ti (Ca-Ti). Also, MC3T3-E1 cells on Ca-P-Ti expressed larger amount of vinculin, a focal adhesion protein, than those on other substrates, probably resulting in larger cell size as well as greater cell proliferation on Ca-P-Ti than those on other substrates. Alkaline phosphatase activity of cells on Ca-P-Ti was greater than those on Ti and P-Ti, but was almost comparable to that of Ca-Ti. Moreover, the largest amount of bone-like nodule formation was observed on Ca-P-Ti. These results provide evidence that calcium and phosphate ions-co-immobilization onto Ti increased the osteoconductivity of Ti by stimulating the responses of pre-osteoblast cells. This simple modification would be promising technique for bone tissue implant including dental and orthopedic implants.

Fabrication of interconnected pore forming α-tricalcium phosphate foam granules cement.

Interconnected pore forming calcium phosphate cement is useful for the reconstruction of bone defects as well as scaffold fabrication in tissue engineering. In this study, interconnected pore forming calcium phosphate cement was fabricated using α-tricalcium phosphate (α-TCP) foam granules. When α-TCP foam granules were mixed with acidic calcium phosphate solution prepared from monocalcium phosphate monohydrate (MCPM) and phosphoric acid solution, brushite crystals were precipitated. These crystals bridged the α-TCP foam granules immediately upon mixing. As a result of the brushite bridge between the α-TCP foam granules, fully interconnected macroporous α-TCP was obtained. The amount of brushite precipitate and the mechanical strength of the set cement increased with acidic calcium phosphate concentration.

A superhydrophilic titanium implant functionalized by ozone gas modulates bone marrow cell and macrophage responses.

Bone-forming cells and Mϕ play key roles in bone tissue repair. In this study, we prepared a superhydrophilic titanium implant functionalized by ozone gas to modulate osteoconductivity and inhibit inflammatory response towards titanium implants. After 24xa0h of ozone gas treatment, the water contact angle of the titanium surface became zero. XPS analysis revealed that hydroxyl groups were greatly increased, but carbon contaminants were largely decreased 24xa0h after ozone gas functionalization. Also, ozone gas functionalization did not alter titanium surface topography. Superhydrophilic titanium (O3–Ti) largely increased the aspect ratio, size and perimeter of cells when compared with untreated titanium (unTi). In addition, O3–Ti facilitated rat bone marrow derived MSCs differentiation and mineralization evidenced by greater ALP activity and bone-like nodule formation. Interestingly, O3–Ti did not affect RAW264.7xa0Mϕ proliferation. However, naive RAW264.7xa0Mϕ cultured on unTi produced a two-fold larger amount of TNFα than that on O3–Ti. Furthermore, O3–Ti greatly mitigated proinflammatory cytokine production, including TNFα and IL-6 from LSP-stimulated RAW264.7xa0Mϕ. These results demonstrated that a superhydrophilic titanium prepared by simple ozone gas functionalization successfully increased MSCs proliferation and differentiation, and mitigated proinflammatory cytokine production from both naive and LPS-stimulated Mϕ. This superhydrophilic surface would be useful as an endosseous implantable biomaterials and as a biomaterial for implantation into other tissues.

Fabrication of interconnected porous calcite by bridging calcite granules with dicalcium phosphate dihydrate and their histological evaluation

Interconnected porous calcite has attracted attention as an artificial bone replacement material and as a precursor for the fabrication of carbonate apatite, which is also an artificial bone replacement material. In this study, calcite granules were exposed to acidic calcium phosphate solution, and the feasibility of fabricating interconnected porous calcite using this process was evaluated. No setting reaction was observed under the nonloading condition. In contrast, under loading conditions, calcite granules were bridged with dicalcium phosphate dihydrate crystals, and the calcite granules set into interconnected porous calcite foam. When applied 0.4 MPa of loading pressure during sample preparation, compressive strength of the obtained interconnected porous calcite was ∼1.5 MPa. The exposure of the calcite granules to acidic calcium phosphate solution under loading conditions was the key for the setting reaction to occur. This is because calcite granules cannot contact one another under the nonloading condition because of bubble formation on the surfaces of the calcite granules. The interconnected porous calcite revealed excellent tissue response, and new bone was able to penetrate into the porous calcite 2 weeks after implantation.

Fabrication of strongly attached hydroxyapatite coating on titanium by hydrothermal treatment of Ti–Zn–PO4 coated titanium in CaCl2 solution

Hydroxyapatite (HAp) coating was formed on zinc phosphate (Ti–Zn–PO4) coated Ti plates by hydrothermal treatment in CaCl2 solution at 200xa0°C for 12xa0h. Uniform surface coverage of the fabricated HAp coating was obtained by this method. SEM-EDX analysis of the adhesion test area showed that the presence of fractures only occurred in HAp crystals. On the other words cohesive fracture was seen in HAp coating layer formed on the Ti–Zn–PO4. The measured strength was around 42.3xa0±xa017xa0MPa. Rat bone marrow (RBM) mesenchymal stem cells were cultured and differentiation-induced on each sample (Ti plate, Ti–Zn–PO4 coated and HAp coated), and cell calcification properties were examined. Apparent differences in morphology and extension of the RBM cells were obtained, while the Ti–Zn–PO4 coated samples showed the highest cell number among all samples. After differentiation-induction, HAp coated samples showed the highest amount of alkaline phosphatase activity, and the highest level of cell calcification. Therefore, the hard tissue compatibility of Ti is improved by hydrothermally HAp coating of samples.Graphical abstract

Fabrication of bone cement that fully transforms to carbonate apatite

The objective of this study was to fabricate a type of bone cement that could fully transform to carbonate apatite (CO3Ap) in physiological conditions. A combination of calcium carbonate (CaCO3) and dicalcium phosphate anhydrous was chosen as the powder phase and mixed with one of three kinds of sodium phosphate solutions: NaH2PO4, Na2HPO4, or Na3PO4. The cement that fully transformed to CO3Ap was fabricated using vaterite, instead of calcite, as a CaCO3 source. Their stability in aqueous solutions was different, regardless of the type of sodium phosphate solution. Rate of transformation to CO3Ap in descending order was Na3PO4>Na2HPO4>NaH2PO4. Transformation rate could be affected by the pH of solution. Results of this study showed that it was advantageous to use vaterite to fabricate CO3Ap-forming cement.

Effects of the method of apatite seed crystals addition on setting reaction of α-tricalcium phosphate based apatite cement

Appropriate setting time is an important parameter that determines the effectiveness of apatite cement (AC) for clinical application, given the issues of crystalline inflammatory response phenomena if AC fails to set. To this end, the present study analyzes the effects of the method of apatite seed crystals addition on the setting reaction of α-tricalcium phosphate (α-TCP) based AC. Two ACs, both consisting of α-TCP and calcium deficient hydroxyapatite (cdHAp), were analyzed in this study. In one AC, cdHAp was added externally to α-TCP and this AC was abbreviated as AC(EA). In the other AC, α-TCP was partially hydrolyzed to form cdHAp on the surface of α-TCP. This AC was referred to as AC(PH). Results indicate a decrease in the setting time of both ACs with the addition of cdHAp. Among them, for the given amount of added cdHAp, AC(PH) showed relatively shorter setting time than AC(EA). Besides, the mechanical strength of the set AC(PH) was also higher than that of set AC(EA). These properties of AC(PH) were attributed to the predominant crystal growth of cdHAp in the vicinity of the α-TCP particle surface. Accordingly, it can be concluded that the partial hydrolysis of α-TCP may be a better approach to add low crystalline cdHAp onto α-TCP based AC.

Calcium phosphate crystallization on titania in a flowing Kokubo solution

AbstractnDry titania layers on air-oxidized titanium substrates have been found to be active enough to cause apatite to be deposited in Kokubo’s simulated body fluid (SBF) in narrow confined spaces, such as those in narrow grooves and thin gaps. Such in vitro apatite deposition is the basis of the GRAPE® technique. The aim of the present study is to determine why GRAPE conditions favor apatite deposition when laminar SBF flow (at 0.01–0.3xa0ml/min) passes through a shallow channel (0.5xa0mm) between a pair of titanium substrates each with a dry layer of titania. Assessing the factors that control the heterogeneous nucleation process led to the proposal of the working hypothesis that there are nucleation pre-embryos, ion assemblies that can be stabilized to form embryos, on the titania layer but that they are removed by the SBF flow. Specimens were subjected to different combinations of processes. One combination was that titania layers were exposed to still or flowing SBF, and the other was that half of a specimen, the inlet or outlet side, was exposed to still or flowing SBF with the other half being covered. The surface morphologies of the specimens were then compared in detail. The conclusion was that exposure to still SBF for 2xa0days before exposure to flowing SBF was required for apatite to be deposited. Some complicated apatite deposition modes were observed, e.g., apatite was deposited even on areas unexposed to still SBF. All of the results were successfully interpreted using the working hypothesis. The conclusion was that the GRAPE® technique depends on the confined space holding pre-embryo and embryo assemblies.