Papers by Author: Yoshiyuki Yokogawa

Abstract: Spherical calcium-alginate gel beads containing HAIO, iron oxide (IO) nanoparticles embedded on hydroxapatite (HA), were prepared along with and poly (N-isopropylacrylamide) (PNIPAAM) or chitosan. These spheres, HAIO, HAIO-PNIPAAM and HAIO-chitosan spheres, were used as carriers of 5-fluorouracil (5-FU), one of the drugs for cancer chemical therapy, and the 5-FU release behavior in PBS solution was investigated at ambient and elevated temperatures using U-V spectrometry. The amount of the released 5-FU from the HAIO spheres was somewhat higher than that from HAIO-PNIPAAM and HAIO-chitosan spheres at ambient temperature. At elevated temperature, HAIO spheres showed an increase in quantity of released 5-FU. The amount of released 5-FU from HAIO-PNIPAAM spheres was almost the same, and that from HAIO-chitosan spheres was reduced compared to those at ambient temperature. These spheres, HAIO, HAIO-PNIPAAM and HAIO-chitosan spheres, show the similar swelling properties at elevated temperature. However, the combinations of Ca-alginate - PNIPAAM or Ca-alginate - chitosan may produce the different structures, which are core-shell network for HAIO-PNIPAAM spheres and or a polyelectrolyte complex for HAIO-chitosan spheres, leading to a different release behavior of 5-FU.

Abstract: Bad breath is mainly caused by malodorous materials, volatile sulfur compounds (VSC), hydrogen sulfide (H₂S). 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 compounds are expected to prevent the teeth from decaying and peiodontics disease. The layered double hydroxides, of which composition is A_1-xB_x(OH)₂C_x/n·mH₂O, where A and B are zinc and Fe ions are effective as the absorbents for VSC. The VSC adsorption capabilities of zinc or iron oxide in comparison with that of layered double hydroxides containing zinc or iron ion. The high capacity of sulfide adsorption of layered double hydroxide may be due to the large number of adsorption sites of layered double hydroxide materials. The layered double hydroxides (LDH) have a structure favorable for ion or free molecules exchange, and high affinity with sulfide may be involved in iron or zinc containing LDH materials.

Abstract: Mesoporous silica (MPS) coatings on β-tricalcium phosphate (β-TCP) granules and their protein adsorptive capabilities were studied. β-TCP granules containing 2 wt% of aluminum oxide and 6 wt% of silicon oxide were prepared using a pan-type granulator and heated at 1200 oC. MPS coatings on β-TCP granules was carried out by a dip-coating method, but the β-TCP granules were not covered by the MPS particles. A silica interlayer was formed on the β-TCP granules via magnetron sputtering prior to the coating of the MPS. The β-TCP granules coated with the silica interlayer were fully covered by the MPS particles. A silica interlayer may offer bonding between the β-TCP granules and MPS coating. The adsorption of protein on the MPS-coated β-TCP granules was evaluated by UV-VIS spectroscopy. The adsorption capacity of protein on the β-TCP granules was improved by the MPS coatings on the β-TCP granules, and that of the β-TCP granules coated with the silica interlayer showed a higher protein adsorption capacity.

Abstract: The wettability and durability of Si-O coatings prepared on zirconia substrate using radiofrequency magnetron sputtering (rf-sputtering) was studied. XRD analysis revealed no phase transformation of zirconia before/after rf-sputtering process. XPS spectroscopy showed that as-deposited films with a SiO₂ configuration was formed. EDX analysis indicated that the Si/Zr ratio was high and when magnetron rf-sputtering was performed using a plasma gas Ar+5% O₂, which may be the optimum condition of rf-sputtering to form a sustainable hydrophilic layer on zirconia substrate. The wear testing using pin on disc wear apparatus was performed. The wettability and durability of Si-O coatings fabricated by magnetron radiofrequency magnetron sputtering (rf-sputtering) on zirconia substrate was studied. A plasma gas Ar+5% O₂ may be the optimum condition of rf-sputtering to form a sustainable hydrophilic layer on zirconia substrate

Abstract: The self-hardening calcium phosphate cement (CPC) has widely been used in bone defect repairs. CPC tends to decay or disintegrate upon early contact with blood or body fluids, and the gelation of CPC paste using sodium alginate, chitosan, or collagen may overcome such a wash-out property. The incorporation of chitosan in CPC paste increased the compressive strength and work-of-fracture. However, the viscosity of CPC paste increased with an increase of chitosan content, and acidic liquid is not favorable, as chitosan must be dissolved in an acidic solution. The CPC paste using the liquid prepared from freeze-dried chitosan powder was easily push out from the syringe, but the content of chitosan was reduced. An addition of polyol-phosphate salt to chitosan solution produces a transparent liquid at physiological pH, and the chitosan content was found to be increased. Chitosan content of liquid was increased from 0.09% to 0.54 % by adding polyol to liquid, and the compressive strength of CPC was also increased.

Abstract: Mesoporous silica (MPS) coatings on hydroxyapatite (HAp) granules and their protein adsorptive capabilities were studied. MPS particles were coated on HAp granules using a dip-coating method, but the HAp granules were not totally covered by the MPS particles. A silica interlayer was formed on the HAp granules via magnetron sputtering or the sol-gel method prior to the coating of the MPS. The HAp granules coated with the silica interlayer were fully covered by the MPS particles. An silica interlayer may offer bonding between the HAp granules and MPS coating. The adsorption of protein on the MPS-coated HAp granules was evaluated by UV-VIS spectroscopy. The adsorption capacity of protein on the HAp granules was improved by the MPS coatings on the HAp granules, and that of the HAp granules coated with the silica interlayer showed a higher protein adsorption capacity.

Abstract: The preparation of mesoporous silica compact through spark plasma sintering (SPS) and adsorption / desorption of protein onto SPS mesoporous silica (MPS) compact is reported. MPS powders, prepared using triblock copolymer, PEO₂₀PPO₇₀PEO₂₀, were compacted in carbon die and heated at 400 or 500 °C for 5 min under uniaxial pressure. The products are referred to as MPS-400 and MPS-500, respectively. The MPS sinters keep the mesoporous configuration, but the mode diameter of MPS-400 was smaller than that of MPS powders and MPS-500. The adsorbed amounts of protein on MPS-400 was higher than that on MPS-500, while the pore diameter, BET surface area, pore volume of MPS-400 are less than those of MPS-500. The interstices in MPS-500 are narrower than that in MPS-400, which may restrict the protein to penetrate through the narrow channels to reach the mesopores of MPS. The quantity of adsorbed amount of protein on MPS sinters does not depend on mesopore configuration but on the macropore configuration of the MPS sinters.

Abstract: Mechanical and biological functions of b-tricalcium phosphate (b-TCP) ceramics is of importance with respect to medical application such as bone graft substitute. The degrees of crystallynity and morphology of as-prepared b-TCP powders are concerned with the above functions. Mechanochemical synthesis is a process of producing a fine particle of b-TCP through an intermediate phases (precursor) of calcium phosphate. The b-TCP precursor synthesized by mechanochemical reaction, followed by heat-treatment, was analysed by using transmission electron microscopy, X-ray diffraction and Fourier transformation infrared spectroscopy. The hydrate layer and carbonate ions involved in the precursor were found to affect the degrees of crystallinity and morphology of as-prepared b-TCP particles at a certain temperature, 700 °C. The specific characteristics of crystallinity and morophology of as-prepared b-TCP particle is expected to be favorble to forming and sintering of b-TCP ceramics.

Abstract: Etiology of halitosis is often concerned with gram-negative anaerobic bacteria, which produce the malodorous compounds such as volatile sulfur compounds (VSC), hydrogen sulfide and methyl mercaptan. The absorbents for the malodorous compounds 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 LDH CO₃) and fluorine (F ^- : MgFe LDH F) ions in aqueous medium was studied by GC/FPD. The concentration of H₂S rapidly decreased for first 1 hours of soaking in H₂S water and fell to 0% in 4-5 h when MgFe LDH CO₃ was applied. MgFe LDH F was used, then the H₂S concentration was quickly decreased the same as MgFe LDH CO₃, and 8 mg/l of fluorine was released at a time. The iron ion was not detected in the H₂S water after soaking for 18 hours. The MgFe LDHF are expected to be likely adsorbent for the fast removal of VSC from the mouth and fluorine releasing agent.

Abstract: Hyperthermia is a promising cancer therapy due to its minimally-invasive procedure, and the cancer therapeutic efficacy can be improved by magnetic hyperthermia combined with pharamacotherapy. Iron oxide (IO) nanoparticle is a popular medium for hyperthermia treatment, and hydroxyapatite (HA) has been widely used for bone filling and augmentation. IO nanoparticle embedded on hydroxyapatite (HAIO) was synthesized through co-precipitation method, and chitosan or poly (N-isopropylacrylamide) (PNIPAAM) were coated on the HAIO with calcium alginate to form the spheres (Chitosan coated HAIO and PNIPAAM coated HAIO). HAIO, Chitosan coated HAIO and PNIPAAM coated HAIO were used as carriers of 5-fluorouracil (5-FU), one of the drugs for cancer chemical therapy, and the 5-FU release behavior in PBS solution was investigate at ambient and elevated temperatures. The amount of the released 5-FU from the HAIO, Chitosan coated HAIO and PNIPAAM coated HAIO are almost the same at ambient temperature. But at elevated temperature, that from Chitosan coated HAIO was reduced while that from the PNIPAAM coated HAIO was increased.