Isao Hirata

Influence of the Chemical Structure of Functional Monomers on Their Adhesive Performance

Functional monomers in adhesive systems can improve bonding by enhancing wetting and demineralization, and by chemical bonding to calcium. This study tested the hypothesis that small changes in the chemical structure of functional monomers may improve their bonding effectiveness. Three experimental phosphonate monomers (HAEPA, EAEPA, and MAEPA), with slightly different chemical structures, and 10-MDP (control) were evaluated. Adhesive performance was determined in terms of microtensile bond strength of 4 cements that differed only for the functional monomer. Based on the Adhesion-Decalcification concept, the chemical bonding potential was assessed by atomic absorption spectrophotometry of the dissolution rate of the calcium salt of the functional monomers. High bond strength of the adhesive cement corresponded to low dissolution rate of the calcium salt of the respective functional monomer. The latter is according to the Adhesion-Decalcification concept, suggestive of a high chemical bonding capacity. We conclude that the adhesive performance of an adhesive material depends on the chemical structure of the functional monomer.

Study of complement activation on well-defined surfaces using surface plasmon resonance

It has been accepted that covalent immobilization of C3b on artificial materials is the most important step to initiate the complement activation. However, there are few studies that have directly demonstrated covalent immobilization of C3b on artificial surfaces. In this study, model thin layers were prepared by the self-assembled monolayer method to produce a surface covered with hydroxyl or methyl groups using mercaptododecane (CH(3)-SAM) and mercaptoundecanol (OH-SAM). Interactions of the complement system with the model surfaces were studied using a surface plasmon resonance instrument. The OH-SAM immobilized C3b, resulting in activating of the complement system through the alternative pathway in Veronal-buffered saline, but this surface did not activate the classical pathway. However, the OH-SAM could not activate the alternative pathway in Veronal-buffered saline containing 10 mM EGTA and 2 mM MgCl(2) that is believed not to interfere with the activation of the alternative pathway. The hydrophobic CH(3)-SAM surface could not activate the classical pathway, but activated the alternative pathway, although the extent was small.

Photolysis of a fluorinated polymer film by vacuum ultraviolet radiation

We studied the photolysis of a fluoroethylene–fluoropropylene copolymer (FEP) film by vacuum ultraviolet (VUV) radiation from a resonance Xe lamp at a wavelength of 147 nm and air pressures of 0.05 and 2.5 Torr. The chemical changes in the FEP surface layer were investigated by Fourier-transform infrared spectroscopy with attenuated total reflection attachment and X-ray photoelectron spectroscopy. Double bonds were found to be the main product in the case of VUV treatment at 0.05 Torr, while photo-oxidation of FEP occurred predominantly by VUV treatment at 2.5 Torr under formation of the —CF2C(O)F group. This oxygen-containing group was more effectively formed in the FEP surface layer by VUV photo-oxidation than by conventional surface oxidation techniques such as treatments by plasma and corona discharge and ozone. Storage of the VUV-treated polymers in air at 50% relative humidity resulted in hydrolysis of —CF2C(O)F to the —CF2COOH group. Substantial improvement of the film wettability was noticed after VUV photo-oxidation. These findings suggest that VUV irradiation provides a high potential for surface modification of fluorinated polymers which are known to be particularly resistant against functionalization by conventional surface modification techniques such as plasma treatment.

Influence of chlorine dioxide on cell death and cell cycle of human gingival fibroblasts

OBJECTIVES The effects of chlorine dioxide (ClO2), sodium hypochlorite (NaOCl), and hydrogen peroxide (H2O2) on cell death and the cell cycle of human gingival fibroblast (HGF) cells were examined. METHODS The inhibition of HGF cell growth was evaluated using a Cell Counting Kit-8. The cell cycle was assessed with propidium iodide-stained cells (distribution of cells in G0/G1, S, and G2/M phases) using flow cytometry. The patterns of cell death (necrosis and apoptosis) were analyzed using flow cytometry with annexin V-FITC/PI staining. RESULTS The lethal doses for 50% of the cells (LD50) of ClO2, NaOCl, and H2O2 were 0.16, 0.79, and 0.11 mM, respectively. All three dental disinfectants induced G0/G1 cell cycle arrest. H2O2 induced apoptosis at concentrations of 0.05 and 0.1 mM, while NaOCl and ClO2 did not induce significant apoptosis at any concentration examined. CONCLUSIONS These results suggest that ClO2 is sufficient for use as a dental disinfectant compared with H2O2 or NaOCl.

Acceleration of bone formation with BMP2 in frame-reinforced carbonate apatite-collagen sponge scaffolds.

The development is expected of scaffold biomaterials that feature a shape-maintaining property in addition to high porosity and large pores that cells can easily invade. To develop a new biodegradable scaffold biomaterial reinforced with a frame, synthesized carbonate apatite (CO3Ap) was mixed with neutralized collagen gel, and the CO3Ap–collagen mixtures were lyophilized into sponges in a porous hydroxyapatite (HAp) frame ring. X-ray diffraction and Fourier transform infrared spectroscopy (FT-IR) analyses together with chemical analysis indicated that the synthesized CO3Ap had a crystalline nature and a chemical composition similar to that of bone. Scanning electron microscope (SEM) observation showed that the CO3Ap–collagen sponge had a sui pore size for cell invasion. In proliferation and differentiation experiments with osteoblasts, alkaline phosphatase and osteopontin activity were clearly detected. When these sponge–frame complexes with bone morphogenic protein (rh-BMP2) were implanted beneath the periosteum cranii of rats, significant new bone was created at the surface of the periosteum cranii after 4 weeks of implantation. These reinforced CO3Ap–collagen sponges with rh-BMP2 are expected to be used as hard tissue scaffold biomaterials for the therapeutic purpose of the rapid cure of bone defects.

Hydrophilic modification of a polyimide film surface

The surface of a polyimide [poly(biphenyl 3,3′,4,4′-dianhydride-p-phenylene diamine)] film was modified with an O2 glow plasma and subsequent treatment with polyethyleneimine (PEI) and poly(maleic anhydride-co-vinyl methyl ether) (PMAVM). The density of peroxide groups formed on the surface after O2 plasma exposure was determined with 1,1-diphenyl-2-picrylhydrazyl and was found to level off to 1.2 nmol/cm2 within the plasma exposure time of 20-60 s. The peroxide groups formed were utilized to immobilize PEI covalently onto the plasma-treated polymer film. After that, PMAVM was immobilized on the surface through the formation of amide bonds between the amino groups of PEI and the anhydride groups of PMAVM. The water contact angle on the modified films showed that the hydrophilic durability of the PMAVM-PEI-modified polyimide film was superior to that of the polyimide film treated by O2 plasma alone.

Surface Modification of Si3N4-Coated Silicon Plate for Investigation of Living Cells

We report a simple new method to improve the cell adhesion ability on the Si3N4 surface. Light-addressable potentiometric sensors (LAPS) have become a powerful tool for studying the biological action of cells. The Si3N4 surface of a LAPS structure was coated with poly-L-ornithine and laminin to improve its cell adhesion ability. The thickness of the coated layer was very thin, about 4 nm, as determined by atomic force microscopy measurement and thus this treatment surface is suitable for biological sensing applications such as the detection of cell activities.

Bioactive Surface Modification of Hydroxyapatite

The purpose of this study was to establish an acid-etching procedure for altering the Ca/P ratio of the nanostructured surface of hydroxyapatite (HAP) by using surface chemical and morphological analyses (XPS, XRD, SEM, surface roughness, and wettability) and to evaluate the in vitro response of osteoblast-like cells (MC3T3-E1 cells) to the modified surfaces. This study utilized HAP and HAP treated with 10%, 20%, 30%, 40%, 50%, or 60% phosphoric acid solution for 10 minutes at 25°C, followed by rinsing 3 times with ultrapure water. The 30% phosphoric acid etching process that provided a Ca/P ratio of 1.50, without destruction of the grain boundary of HAP, was selected as a surface-modification procedure. Additionally, HAP treated by the 30% phosphoric acid etching process was stored under dry conditions at 25°C for 12 hours, and the Ca/P ratio approximated to 1.00 accidentally. The initial adhesion, proliferation, and differentiation (alkaline phosphatase (ALP) activity and relative mRNA level for ALP) of MC3T3-E1 cells on the modified surfaces were significantly promoted (P < 0.05 and 0.01). These findings show that the 30% phosphoric acid etching process for the nanostructured HAP surface can alter the Ca/P ratio effectively and may accelerate the initial adhesion, proliferation, and differentiation of MC3T3-E1 cells.

Influence of alkyl chain length on calcium phosphate deposition onto titanium surfaces modified with alkylphosphonic acid monolayers.

Much attention has been paid to the modification of a titanium surface with an alkylphosphonic acid (PA)-based self-assembled monolayer (SAM) to accelerate hydroxyapatite (HA) deposition on the surface. In order to further accelerate the rate of HA deposition, we examined here the effect of alkyl chain length of SAMs on the formation of a HA layer. PAs with three different alkyl chain lengths (3, 6, and 16 methylene units) were used for the preparation of a SAM on titanium. The titanium specimens with monolayers were soaked in a simulated body fluid under physiological conditions for 4 weeks. The deposited substances were analyzed by scanning electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. These analyses revealed that the formation of PA SAMs accelerate the deposition of poorly crystallized HA, in an alkyl chain length-dependent manner. Among PAs studied here, PA containing a 16-carbon alkyl chain gave rise to the titanium surface most effective for the deposition of HA.

The synthesis and characterization of a novel potassium chloride-fluoridated hydroxyapatite varnish for treating dentin hypersensitivity

Dentin hypersensitivity is treated using materials that occlude the dentinal tubules or release potassium ions that induce nerve desensitization. In this study we formulated a novel varnish containing potassium chloride and fluoridated hydroxyapatite and evaluated its physical properties and cytotoxicity. Potassium ion release from the varnish was measured. Dentin permeability was evaluated by measuring the hydraulic conductance of etched dentin discs treated with the varnish. The direct contact test and MTT assay were performed to evaluate the varnishs cytotoxicity. We found that the varnish released potassium ions over 6 h, and demonstrated a statistically higher reduction in dentin permeability compared to commercial fluoride varnish or control. Dentin disc scanning electron microscopy images demonstrated occluded dentinal tubules in the novel varnish group after brushing. The cytotoxicity tests indicated the varnish was biocompatible with gingival and pulpal fibroblasts. We propose the novel varnish is a potential material for use in hypersensitivity management.