Faculty Profiles - NAKANISHI Kazuki

Papers - NAKANISHI Kazuki

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Morphology control of macroporous silica-zirconia gel based on phase separation Reviewed

Takahashi R, Nakanishi K, Soga N

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN Vol. 106 ( 8 ) page： 772 - 777 1998.8

Apatite formation on silica gel in simulated body fluid: effects of structural modification with solvent-exchange Reviewed

SB Cho, F Miyaji, T Kokubo, K Nakanishi, N Soga, T Nakamura

JOURNAL OF MATERIALS SCIENCE-MATERIALS IN MEDICINE Vol. 9 ( 5 ) page： 279 - 284 1998.5

Language：English Publishing type：Research paper (scientific journal) Publisher：KLUWER ACADEMIC PUBL

The prerequisite for glasses and glass-ceramics to bond to living bone is the formation of biologically active bone-like apatite on their surfaces. It has been shown that even a pure silica gel forms the bone-like apatite on its surface in a simulated body fluid. In the present study, pore structure of silica gels prepared by hydrolysis and polycondensation of tetraethoxysilane in an aqueous solution containing polyethylene glycol was modified by 1M HNO3, and 0.1M and 1M NH4OH solution treatments. The three kinds of resultant gels all contained large amounts of silanol groups and trisiloxane rings, but differ greatly in pore structure of nanometre pore size. Irrespective of these differences, all the gels formed the bone-like apatite on their surface in the simulated body fluid. It was speculated that a certain type of structural unit of silanol groups, which is easily formed in the presence of the polyethylene glycol, is effective for the apatite formation. (C) 1998 Chapman & Hall.

DOI： 10.1023/A:1008808828567

Designing double pore structure in alkoxy-derived silica incorporated with nonionic surfactant Reviewed

K Nakanishi, T Nagakane, N Soga

JOURNAL OF POROUS MATERIALS Vol. 5 ( 2 ) page： 103 - 110 1998.5

Language：English Publishing type：Research paper (scientific journal) Publisher：KLUWER ACADEMIC PUBL

The principle of designing double-pore structure in alkoxy-derived silica is described with the experimental system containing polyoxyethylene nonylphenylether. The formation of macropores is consistently explained in terms of the concurrence of a phase separation and a sol-gel transition in the polymerizing silica-surfactant-solvent system. The composition-morphology relationship exhibited a substantial variation depending on the length of oxyethylene units in the surfactant molecule. The mesopore volume obtained after basic solvent exchange and a heat-treatment suggested that the surfactant with shorter oxyethylene chain tends to be incorporated more in the gel phase to give higher mesopore volume. The small-angle X-ray scattering measurement of the gelling and aging system supported this hypothesis indicating micelle formation in the system containing a surfactant with shorter oxyethylene chain.

DOI： 10.1023/A:1009633102016

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Designing monolithic double-pore silica for high-speed liquid chromatography Reviewed

N Ishizuka, H Minakuchi, K Nakanishi, N Soga, N Tanaka

JOURNAL OF CHROMATOGRAPHY A Vol. 797 ( 1-2 ) page： 133 - 137 1998.2

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

A novel type of silica-based chromatographic column without particle-packed structure has been recently developed. A monolithic silica gel having continuous gel skeletons and through-pores together with open mesopores is the key material of this 'rod column'. The principle and procedure of designing the built-in pore structure is explained. (C) 1998 Elsevier Science B.V.

DOI： 10.1016/S0021-9673(97)01202-8

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Effect of domain size on the performance of octadecylsilylated continuous porous silica columns in reversed-phase liquid chromatography Reviewed

Minakuchi H, Nakanishi K, Soga N, Ishizuka N, Tanaka N

JOURNAL OF CHROMATOGRAPHY A Vol. 797 ( 1-2 ) page： 121 - 131 1998.2

SilicaROD (TM) - A new challenge in fast high-performance liquid chromatography separations Reviewed

Cabrera K, Wieland G, Lubda D, Nakanishi K, Soga N, Minakuchi H, Unger KK

TRAC-TRENDS IN ANALYTICAL CHEMISTRY Vol. 17 ( 1 ) page： 50 - 53 1998.1

Monolithic HPLC column via sol-gel route Reviewed

Nakanishi K, Minakuchi H, Ishizuka N, Soga N

SOL-GEL SYNTHESIS AND PROCESSING Vol. 95 page： 139 - 150 1998

Structure design of double-pore silica and its application to HPLC Reviewed

Nakanishi K, Minakuchi H, Soga N, Tanaka N

JOURNAL OF SOL-GEL SCIENCE AND TECHNOLOGY Vol. 13 ( 1-3 ) page： 163 - 169 1998

Pore Structure Control of Silica Gels Based on Phase Separation Reviewed

Nakanishi Kazuki

JOURNAL OF POROUS MATERIALS Vol. 4 ( 2 ) page： 67 - 112 1997.6

Phase separation in silica sol-gel system containing poly(ethylene oxide) .2. Effects of molecular weight and temperature Reviewed

Nakanishi K, Soga N

BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN Vol. 70 ( 3 ) page： 587 - 592 1997.3

Effect of skeleton size on the performance of octadecylsilylated continuous porous silica columns in reversed-phase liquid chromatography Reviewed

Minakuchi H, Nakanishi K, Soga N, Ishizuka N, Tanaka N

JOURNAL OF CHROMATOGRAPHY A Vol. 762 ( 1-2 ) page： 135 - 146 1997.2

Double pore silica gel monolith applied to liquid chromatography Reviewed

K Nakanishi, H Minakuchi, N Soga, N Tanaka

JOURNAL OF SOL-GEL SCIENCE AND TECHNOLOGY Vol. 8 ( 1-3 ) page： 547 - 552 1997

Language：English Publishing type：Research paper (scientific journal) Publisher：KLUWER ACADEMIC PUBL

Silica gels retaining double pore structure in the size ranges of micrometer and nanometer have been applied to the rod-shaped monolithic column for liquid chromatography. The macropore structure was designed by controlling the phase separation process induced by the hydrolysis and polycondensation of alkoxysilane, whereas the mesopore structure was tailored by the solvent exchange treatments on wet gels. The size exclusion chromatograms on polystyrene standards exhibited almost similar features for octadecyl-modified rod and conventional packed beads columns. The dependence of plate height on the velocity of mobile phase determined for amylbenzene was by far weaker in the rod column than in the packed beads column, suggesting that additional geometrical factors should be considered in describing the separation mechanism in the rod column.

DOI： 10.1023/A:1018331101606

Phase separation process of polymer-incorporated silica-zirconia sol-gel system Reviewed

Takahashi R, Nakanishi K, Soga N

JOURNAL OF SOL-GEL SCIENCE AND TECHNOLOGY Vol. 8 ( 1-3 ) page： 71 - 76 1997

Apatite-forming ability of silicate ion dissolved from silica gels Reviewed

SB Cho, F Miyaji, T Kokubo, K Nakanishi, N Soga, T Nakamura

JOURNAL OF BIOMEDICAL MATERIALS RESEARCH Vol. 32 ( 3 ) page： 375 - 381 1996.11

Language：English Publishing type：Research paper (scientific journal) Publisher：JOHN WILEY & SONS INC

It is known that the prerequisite for glasses and glass-ceramics to bond to living bone is the formation of biologically active bonelike apatite on their surfaces, and a certain type of hydrated silica developed on their surfaces plays an important role in nucleating the apatite. In the present study, the apatite-forming ability of silicate ion dissolved from different silica materials into a simulated body fluid was examined as follows. Polyether sulfone substrates pretreated with O-2 plasma were placed in parallel to plates of three kinds of silica gels prepared in different media and silica glass, with a distance of 0.5 mm between them in a simulated body fluid with ion concentrations nearly equal to those of human blood plasma for 4 days, and then soaked in a solution with ion concentrations 1.5 times those of the simulated body fluid for 6 days. After the first soaking, silicon combined with oxygen was detected on the surfaces of the substrates faced to all the silica gels, whereas it was not detected on that faced to the silica glass. After the second soaking, the former formed a bonelike apatite layer on their surfaces, but the latter did not. These results indicate that silicate ion which is dissolved from the silica gels and adsorbed on the substrates has an apatite-forming ability, irrespective of the microstructure of the original silica gels. (C) 1996 John Wiley & Sons, Inc.

DOI： 10.1002/(SICI)1097-4636(199611)32:3<375::AID-JBM10>3.0.CO;2-G

Octadecylsilylated porous silica rods as separation media for reversed-phase liquid chromatography Reviewed

Minakuchi H, Nakanishi K, Soga N, Ishizuka N, Tanaka N

ANALYTICAL CHEMISTRY Vol. 68 ( 19 ) page： 3498 - 3501 1996.10

Apatite formation on various silica gels in a simulated body fluid containing excessive calcium ion Reviewed

SB Cho, F Miyaji, T Kokubo, K Nakanishi, N Soga, T Nakamura

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN Vol. 104 ( 5 ) page： 399 - 404 1996.5

Language：English Publishing type：Research paper (scientific journal) Publisher：CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI

It was previously shown that a silica gel prepared in a solution containing polyethylene glycol (S-PEG) induces the apatite nucleation in SBF, but those prepared in pure water (S-W) and a solution containing polyacrylic acid (S-PAA) do not induce it. This indicates that a limited type of silanol groups is effective for apatite nucleation. In the present study, apatite-forming ability of these silica gels was examined in SBF containing excessive calcium ion. It was found that all these silica gels formed the apatite on their surfaces in this fluid, although the rate of apatite formation decreased in the order S-PEG > S-PAA > S-W. This indicates that any type of silanol groups has potential for inducing apatite nucleation under this condition. Such environment rich in calcium ion is produced around the surfaces of CaO, SiO2-based glasses and glass-ceramics when they are implanted into living body. The present results indicate that the CaO-SiO2 system can be a good basic composition for bioactive glasses and glass-ceramics.

DOI： 10.2109/jcersj.104.399

Apatite formation on silica gel in simulated body fluid: Its dependence on structures of silica gels prepared in different media Reviewed

Sung-Baek Cho, Kazuki Nakanishi, Tadashi Kokubo, Naohiro Soga, Chikara Ohtsuki, Takashi Nakamura

Journal of Biomedical Materials Research Vol. 33 ( 3 ) page： 145 - 151 1996

Language：English Publishing type：Research paper (scientific journal)

It has been shown that the prerequisite for glasses and glass-ceramics to bond to living bone is the formation of a layer of biologically active bonelike apatite on their surfaces. The hydrated silica formed on the surfaces of glasses and glass-ceramics plays an important role in nucleating the apatite. In the present study, the structure of the hydrated silica responsible for the apatite nucleation was investigated in an acellular simulated body fluid with ion concentrations nearly equal to those of human blood plasma. Three kinds of porous silica gels were prepared by hydrolysis and polycondensation of tetraethoxysilane in pure water or in aqueous solution containing polyethylene glycol or polyacrylic acid. The silica gels prepared in aqueous solution containing polyethylene glycol or polyacrylic acid had micron-size interconnected pores, whereas the gel prepared in pure water did not. All the gels contained a large volume of nanometer-size pores, almost the same amounts of silanol groups and D2 defect, and showed a high dissolution rate of the silica. Despite this, only the gel prepared in the solution containing polyethylene glycol formed the apatite on its surface in the simulated body fluid. This indicates that only a certain type of structural unit of the silanol group is responsible for the apatite nucleation.

DOI： 10.1002/(SICI)1097-4636(199623)33:3<145::AID-JBM4>3.0.CO;2-Q

EFFECTS OF AGING AND SOLVENT EXCHANGE ON PORE STRUCTURE OF SILICA-GELS WITH INTERCONNECTED MACROPORES Reviewed

TAKAHASHI R, NAKANISHI K, SOGA N

JOURNAL OF NON-CRYSTALLINE SOLIDS Vol. 189 ( 1-2 ) page： 66 - 76 1995.8

DEPENDENCE OF APATITE FORMATION ON SILICA-GEL ON ITS STRUCTURE - EFFECT OF HEAT-TREATMENT Reviewed

SB CHO, K NAKANISHI, T KOKUBO, N SOGA, C OHTSUKI, T NAKAMURA, T KITSUGI, T YAMAMURO

JOURNAL OF THE AMERICAN CERAMIC SOCIETY Vol. 78 ( 7 ) page： 1769 - 1774 1995.7

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CERAMIC SOC 735 CERAMIC PLACE

The prerequisite for glasses and glass-ceramics to bond to living bone is the formation of biologically active bonelike apatite on their surfaces in the body. Our previous study showed that a silica gel prepared by hydrolysis and polycondensation of tetraethoxysilane in aqueous solution containing poly(ethylene glycol) induces apatite nucleation on its surface in a simulated body fluid. In the present study, the effects of heat treatment of silica gel on its catalytic effects in apatite nucleation was investigated in a simulated body fluid, It was found that apatite forms on the surfaces of silica gels heat-treated below 800 degrees C, but not on those heat-treated above 900 degrees C. The volume of nanometer-range pores in the gel remarkably decreased by heat treatment above 900 degrees C. The concentration of silanol groups in the silica gels gradually decreased with increasing heat treatment temperature. The rate of silica dissolution from the gel into the simulated body fluid decreased remarkably by heat treatment above 900 degrees C. This suggested that a special type of silanol group which is formed by soaking the gel treated below 800 degrees C into the simulated body fluid is responsible for apatite nucleation.

DOI： 10.1111/j.1151-2916.1995.tb08887.x

Formation of porous gel morphology by phase separation in gelling alkoxy-derived silica. Phenomenological study

Kaji H.

Journal of Non-Crystalline Solids Vol. 185 ( 1-2 ) page： 18-30 1995.5

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