Papers by Author: Yoshiyuki Yokogawa

Abstract: The preparation of mesoporous silica coated rf-sputterd apatite / titanium substrate and protein adsorptive property is reported. Hydroxyapatite coated titanium implant has been used, and the adsorption of proteins onto implant is very important for bond formation between bone and implant. Mesoporous silica (MPS) materials have been extensively studied as carriers of bio-molecules due to their potential practical applications in medical materials. Pore diameters of 1.5 – 30 nm of the periodic mesoporous materials are close to the diameters of target molecules and high adsorbed amount of proteins onto MPS has been reported, and also enclosure of the protein in a well-defined space may help to prevent denaturation. Previously, we reported the MPS coating on the porous hydroxyapatite (HAp) ceramics obtained by dip-coating method, and by the vapor phase synthesis. Protein adsorption on the porous HAp with the MPS coatings was evaluated using UV-VIS spectrometry, and the quantity of adsorbed amount of protein was remarkably improved. In this study, the HAp deposition on Ti substrate (HAp/Ti) was carried out by rf magnetron sputtering and hydrothermal treatment, and MPS coating on HAp/Ti using LB deposition apparatus to improve the protein adsorptive property of HAp/Ti. The quantity of adsorbed protein onto the HAp /Ti was around 12 times high, and that onto the MPS/HAp/Ti was 18 times high compared to that on Ti substrate.

Abstract: Most etiology of bad breath is often concerned with gram-negative anaerobic bacteri, and pharmacotherpy using pharmaceutical drugs should be effective but limited, because bacteria at deep periodontal pocket may be sterilized but cannot be washed out and the malodorous compounds remain. The absorbents for the malodorous compound such as volatile sulfur compounds (VSC), hydrogen sulfide (H₂S), are expected to prevent the teeth from decaying and peiodontics disease. The VSC adsorption capabilities of layered double hydroxides, of which composition is A_1-xB_x(OH)₂C_x/n·mH₂O, where A and B are Mg and Fe ions, and C are carbonate (CO₃^2- : MgFe HTCO₃) and chlorine (Cl ^- : MgFe HTCl) ions in aqueous medium was studied by GC/FPD. The concentration of H₂S rapidly decrease to less than 15% for first 1 hours of soaking in H2S water and fell to 0% in 4-5 h when the MgFe HTCO₃ and MgFe HTCl were used. The iron ion was not detected in the H₂S water after soaking for 18 hours.The MgFe HTCO₃ and MgFe HTCl are expected to be likely adsorbent for the fast removal of VSC from the mouth.

Abstract: Many people worldwide assess themselves as having halitosis, often caused by bio-film and microbial putrefaction of the debris in the mouth, leading to the production of mal-odorous compounds, volatile sulfur compounds (VSC) such as hydrogen sulfide (H₂S), methyl mercaptan and dimethyl sulfide. Some desulfurizing agents such as CaO and Na₂CO₃ in the industry are widely used, but there are few dental desulfurizing agents or adsorbents for removal of VSC. Ag ion exchanged zeolite material showed a high adsorptive property of H₂S in aqueous solution (H₂S water), however Ag sulfides were formed in aqueous solution. The VSC adsorption capabilities of layered double hydroxides, of which composition is A_1-xAl_x(OH)₂B_x/n·mH₂O, where A is Mg and/or Zn and B is CO₃^2-, in aqueous medium was studied by FPD/GC. The concentration of H₂S fell to 0% in 2 h when the Zn hydrotalcite was used, while that decreased to 20% in 18 h when the Mg hydrotalcite heated at 500 °C was used. The zinc ion was not detected in the H₂S water after soaking for 18 hours.The Zn hydtotalcite is expected to be likely adsorbent for the fast removal of VSC from the mouth.

Abstract: Many people worldwide assess themselves as having halitosis, often caused by bio-film and microbial putrefaction of the debris in the mouth, leading to the production of mal-odorous compounds, volatile sulfur compounds (VSC) such as hydrogen sulfide (H₂S), methyl mercaptan and dimethyl sulfide. Some desulfurizing agents such as CaO and Na₂CO₃ in the industry are widely used, but there are few dental desulfurizing agents or adsorbents for removal of VSC. Ag ion exchanged zeolite material showed a high adsorptive property of H₂S in aqueous solution (H₂S water), however Ag sulfides were formed in aqueous solution. The VSC adsorption capabilities of layered double hydroxides, of which composition is A_1-xAl_x(OH)₂B_x/n·mH₂O, where A is Mg and/or Zn and B is CO₃^2-, in aqueous medium was studied by FPD/GC. The concentration of H₂S fell to 0% in 2 h when the Zn hydrotalcite was used, while that decreased to 20% in 18 h when the Mg hydrotalcite heated at 500 °C was used. The zinc ion was not detected in the H₂S water after soaking for 18 hours.The Zn hydtotalcite is expected to be likely adsorbent for the fast removal of VSC from the mouth.

Abstract: The preparation of mesoporous silica coated hydroxyapatite (HAp) ceramics is reported. The adsorption of proteins onto hydroxyapatite (HAp) is important in a variety of oral or osseous biological events. HAp has been used as bone filler, and the protein adsorption onto HAp materials is of importance for the bond formation. HAp has been also used as the material for column packing of liquid chromatography to separate and refine proteins due to the adsorptive capabilities with respect to the HAp. Mesoporous silica (MPS) materials have been extensively studied as carriers of bio-molecules due to their potential practical applications in medical materials. Pore diameters of 1.5 30 nm of the periodic mesoporous materials are close to the diameters of target molecules and enclosure of the protein in a well-defined space may help to prevent denaturation. Previously, we reported the MPS coating on the porous hydroxyapatite (HAp) ceramics obtained by dip-coating method. Protein adsorption on the porous HAp with the MPS coatings was evaluated using UV-VIS spectrometry, and the quantity of BSA adsorbed onto the HAp ceramics with the MPS coatings is around 1.5 times high compared to that on porous HAp ceramics. In this study, the vapor-phase synthesis of MPS film on HAP ceramics was carried out to improve the protein adsorptive property of HAp ceramics. The quantity of adsorbed protein onto the HAp ceramic disc with MPS coatings is around 5 times high compared to that on HAp ceramic disc.

Abstract: Volatile sulfur compounds (VSCs) such as hydrogen sulfide (H₂S), methyl mercaptan and dimethyl sulfide produced in mouth. Some oral (Gram-negative) bacteria produce VSCs, which induces permeability of mucous membrane, cause the oral malordor, dental caries, color change of the dental fillings. Thus, material which adsorbs VSCs should be useful to keep health in mouth. Previously, we reported the H₂S adsorptive properties of zeolite and hydrotalcite materials having micro pores. The amount of H₂S adsorbed on the zeolite or hydrotalcite at room temperature was found to be around 300-400 ppm, and and 3 % of H₂S was desorbed when heated at 400 °C. The hydrotalcite, whose compositon is Mg_1-xAl_x(OH)₂A_x/n·mH₂O, where A is CO₃^2-, and x is 0.25, was heat-treated at 500 °C, and put into aqueous solution containing H₂S. In this study, the relation between heat-treatment tempearture and the sulfide adsorption on hydrotalcite in aqueous solution was investigated. The hydrotalcite materials were hydrothermally synthesized and identified by powder X-ray diffraction method. The change in concentrations of H₂S in aqueous solution was measured using FPD gas chromatography (GC). The concentrations of H₂S was decreased with time for the hydrotalcite heated at 500 °C or 600 °C, and fell to 20 % for 12 hours. But, the concentration was decreased by 40% for 12 hours for the hydrotalcite materials heated at higher temperatue. XRD and FT-IR analysis revealed that the sulfides were into or out of the hydrotalcite structure through topochemical reactions.

Abstract: The Time – Dependent Adsorptive Behavior of Biomolecules on/in Mesoporous Silica Materials (MPS) Have Been Studied by Using Transmission Electron Microscopy (TEM). Highly Ordered Hexagonal Mesoporous Silica Materials (SBA-15) Synthesized Were Immersed in Phosphate Buffer Saline (PBS) Solution Containing Cytochrome C for 2, 48, and 120 Hours at 4 °C. after that, MPS Materials Were Rinsed with PBS Solution, and then Immersed in PBS Solution without Cytochrome C. the Amount of Protein Adsorbed on/in MPS Materials Soaked for 2, 48, and 120 Hours Was 75 Mg/g, 135 Mg/g and 178 Mg/g, Respectively. the Time Profiles for Adsorption of Proteins Can Be Well Described by Intraparticle Diffusion Model. the Holes of MPS Materials Were Observed to Be Overlapped with Stained Proteins for First 2 Hours Immersion. the Stained Proteins Were Observed between Primary Particles and Partly inside the Mesoporous Channels in the MPS Material Immersed for 48 Hours. for MPS Immersed for 120 Hours, Stained Proteins Were Observed in Almost All Meso-Scale Channels of MPS. the Ratio of Desorbed Proteins from those Embedded on/in MPS Materials Was 13 % in Case of the MPS Materials Immersed in PBS Containing Cytochrome C for 2 Hours, while 8 % in Case of the MPS Materials Immersed for 48 and 120 Hours. Cytochrome C May Be Strongly Embedded on/in MPS Materials due to the Electrostatic Effect.

Abstract: The encapsulation and immobilization of biomolecules on/in mesoporous silica materials (MPS) have been studied by using transmission electron microscopy (TEM). The mixture of tetraethyl orthosilicate (TEOS) and the triblock copolymer as a template was stirred, hydrothermally treated to form the mesoporous SBA-15 structure, and heat-treated at 550 °C. SEM observation indicated that long and narrow particles were linked together in the long axis direction to form secondary particles of SBA-15. UV-spectrometry was performed to determine the amount of bovine serum albumin (BSA), cytochrome C, myoglobin or -lactoglobulin encapsulated on/in SBA-15. The time profiles for adsorption of proteins can be well described by intraparticle diffusion model. The TEM observations of proteins on/in mesoporous SBA-15 revealed that proteins were embedded on/in mesoporous SBA-15 and the protein behaviors given by TEM observations may correspond to the intraparticle diffusion model.

Abstract: There is a clinical need for synthetic scaffolds that will promote bone regeneration. Important factors include obtaining an optimal porosity and size of interconnecting macropores whilst maintaining scaffold mechanical strength, enabling complete penetration of cells and nutrients throughout the scaffold, preventing the formation of necrotic tissue in the centre of the scaffold. To address this we investigated flexural strength of bimodal porous apatite ceramics prepared using apatite slurry and its slurry synthesis was studied. Slips with different contents of HAp (K-HAp and T-HAp) and deflocculant were prepared by milling in a pot mill. The viscosity of slurries made of commercial T-HAp powder showed a drop after 3 hours’ milling, but the viscosity of slurry with high solid content of k-HAp and 2.0 wt% deflocculant increased with an increase of milling time after 2 hours’ milling. The porosity and flexural strength of the porous HAp prepared by heating the foam dipped in K-HAp slip with 2.0 wt% of deflocculant and 0.5wt% of foaming regent heated at 1200°C were 62.4 % and 14.7 MPa, and those in T-HAp were 59.7 % and 15.2 MPa with 1.5 wt% of deflocculant and 0.5wt% of foaming regent heated at 1200°C.

Abstract: Biphasic calcium phosphate (BCP) ceramics, a mixture of hydroxyapatite (HAp) and betatricalcium phosphate (β-TCP), of varying HAp/β-TCP ratios was prepared. One kinds of HAp and one kind of β-TCP powders were used to produce porous BCP bioceramics with HAp/β-TCP weight rations of 20/80, 40/60, and 80/20. A slip was obtained by adding a mixed powders of HAp and β-TCP to a solution 1.5% of deflocculant and 0.5 wt% of foaming agent. The optimum value for the minimum viscosity in these present slips with respect to its solid loading and the optimum amount of the deflocculant were investigated. The specimen obtained by casting a polyurethane foam with 1.5 wt% of deflocculant into a slip, and drying it under vacuum, was heated at 1150°C for 3 hours. The resultant porous BCP sintered body had large spherical pores of 300 /m with interconnecting rectangular voids. Many small pores in the size range of 2-3 /m or below were observed in the specimen obtained by heating at 1150°C for 3 hours. The dissolution test was done as follows. The obtained porous ceramics samples about 0.5g individually soaked into 30 mL of simulated body fluid (SBF) solution at 36.5°C. The calcium and phosphorous content of the SBF solution was analyzed by ICP. The porous body was dried, and characterized using SEM, XRD, and FT-IR.