Papers by Author: Masao Tanihara

Abstract: Si-containing tricalcium phosphate (TCP) ceramics are expected to be useful biodegradable bone substitutes that enhance bone regeneration because TCP is a biodegradable ceramic and Si is the trace element that enhances bone formation. We successfully synthesized the Si-containing TCP with different Si contents through a wet process. The Si addition lowered the temperature of phase transition from β-TCP to α-TCP. After the sintering the compacts of Si-containing TCP powders at 1400 oC, the sintered ceramics showed higher density than those of Si-free TCP. The Si addition was effective to promote the sintering of TCP.

Abstract: Electrophoresis can transport ions more rapidly and directionally in a gel. The controlled precipitation of calcium phosphates in an agarose gel was attempted by electrophoresis of calcium and phosphate ions. Wells were prepared on an agarose gel. A CaCl2 solution was placed in wells on the positive side and a Na2HPO4 solution in wells on the negative side. A potential of 100 V was then applied. White precipitates appeared in the gel after 11 min. The white area initially became larger and more intense with increasing time. However, after longer periods, the white area decreased and became weaker, before disappearing after 45 min. Spinous precipitates with a diameter of about 500 nm were obtained when the gels were collected after 20 min. The precipitates were characterized as particles of calcium phosphate.

Abstract: Natural bone has excellent mechanical properties such as high fracture toughness and high flexibility. These properties are achieved by specific microstructure of natural bone that is composed of the organic collagen and inorganic apatite. On the basis of these findings, apatite-polymer hybrids are expected as novel bone substitutes having excellent mehcanical performances and high bone-bonding ability, i.e. bioactivity. In this study, we attempted preparation of apatite-polyglutamic acid hybrids through biomimetic process that mimics the principle of biomineralization. Simple chemical modification of the polyglutamic acid gel with 1 M (= mol/L) calcium chloride solution provided the gel with apatite-forming ability in simulated body fluid (SBF, Kokubo solution). This type of hybrid is also useful for designing bioactive bone substitutes with injectability, since viscosity of the polyglutamic acid gel can be easily controlled according to degree of cross-linking.

Abstract: Our previous study presented that sericin, a kind of silk protein, had high ability of apatite formation under a condition mimicking body environment when the sericin contains high content of β sheet structure. To confirm the effectiveness of β sheet structure on apatite nucleation, we attempted to synthesize of polypeptide containing β sheet structure and investigate apatite formation in 1.5SBF that has 1.5 times the inorganic ion concentrations of human blood plasma. Poly(FEFEFEFG) was synthesized as the polypeptide consisting mainly of β sheet structure. Formation of hydroxyapatite was observed on the film of the poly(FEFEFEFG) after soaking in 1.5SBF within 7 days. We could confirm that β sheet structure was effective even in the synthetic polypeptide.

Abstract: Apatite formation on polyamide films containing either carboxyl or sulfonic groups was compared in 1.5SBF, whose ion concentrations are 1.5 times those of a simulated body fluid (SBF). The sulfonic groups induced the apatite nucleation earlier than the carboxyl groups. In contrast, the rate of crystal growth depended not on the kind of functional group, but on the degree of supersaturation of the surrounding solution. The more ready association of sulfonic groups with calcium ions may lead to earlier apatite nucleation than that of carboxyl groups. Adhesive strength of the apatite layer to polyamide film containing sulfonic groups was significantly lower than that with carboxyl groups depending on the chemical interactions as well as on the mechanical properties of the polyamide film.

Abstract: Tricalcium phosphate (3CaO⋅P2O5, TCP) is known as a biodegradable material and already used clinically as important bone-repairing materials. However, the control of its bone-bonding ability, i.e. bioactivity, and biodegradability is not easy. On the other hand, diopside (CaO⋅MgO⋅2SiO2) ceramic shows a potential of direct contact with bone and high mechanical strength, but low biodegradability. We expected that a glass-ceramic containing TCP and diopside show high bioactivity and high mechanical strength, as well as biodegradability. Glasses with composition x(3CaO⋅P2O5)⋅(100-x) (CaO⋅MgO⋅2SiO2) (x = 0, 38, 50, 60 mass%) were prepared. They were pulverized and the compacts of the resultant powders were heated to obtain the glass-ceramics. Only diopside was precipitated at x = 0 in the glass composition, whitlockite (β-TCP) and diopside were at x = 38, 50 and 60, when the compacts were sintered at 1200 °C. The prepared glass-ceramics formed apatite on their surfaces in a simulated body fluid (SBF). This indicates that these glass-ceramics have a potential to show bioactivity.

Abstract: CaO-SiO2 gels for bioactive organic-inorganic composites were prepared from tetraethoxysilane (TEOS) and calcium nitrate tetrahydrate (Ca(NO3)2⋅4H2O) by a sol-gel method with the addition of polyethylene glycol (PEG) and methacryloxypropyltrimethoxysilane (MPS). The effects of PEG and MPS on morphology and bioactivity of the gel were investigated. The samples with the nominal compositions of Ca(NO3)2:TEOS:MPS = 30:70:0 and 30:63:7 (in molar ratio) were prepared with or without coexistence of PEG at a molar ratio of (TEOS+MPS):PEG = 70:0.16. Spherical powders were obtained regardless of the addition of MPS after removal of PEG by washing, whereas the samples prepared without PEG gave crack-free bulk bodies. Incorporation of MPS was confirmed form the results of Fourier transform infrared spectroscopy (FT-IR). All the samples, regardless of addition of PEG and MPS, formed apatite on their surfaces in simulated body fluid (SBF), when washing time was 3 h during the preparation. These results show that the bioactive spherical powder of CaO-SiO2 gel modified with MPS can be obtained by the present method. It is expected to induce the increase of the chemical bonding with surrounding organic matrix when it was used as fillers for composite materials.

Abstract: Apatite formation behavior of tricalcium phosphate (TCP) ceramics with different phases and porosity was investigated in a simulated body fluid (SBF, Kokubo solution). The pure α-TCP with 80% porosity did not form hydroxyapatite (HAp) on its surface after soaking in SBF for 7 days. On the other hand, the pure α-TCP with 20% porosity formed HAp on its surface after soaking in SBF within 7 days, and the biphasic TCP, which consisted of mixture of α-TCP and β-TCP and had 20% porosity, formed HAp within 1 day. The low porosity and coexistence of α-TCP and β-TCP phases in TCP ceramics were effective for apatite formation in SBF.

Abstract: Hybrids consisting of hydroxyapatite and biodegradable polymers are attractive materials for bone repair. We recently developed hydroxyapatite-alginate hybrids through a soaking process of alginate modified with 3-aminopropyltriethoxysilane (APES), ethylenediamine (EDA) and CaCl2 in a solution mimicking body fluid such as SBF, 1.5SBF proposed by Kokubo et al.. In this study, biological behavior of the apatite-alginate hybrid fabricated through modification with APES and CaCl2 were evaluated after implantation in a rat tibia, in comparison with that of alginate gel without hydroxyapatite. The higher degree of calcification was observed for the hydroxyapatitealginate hybrid than the alginate gel without hydroxyapatite. The hydroxyapatite precipitated on and inside alginate allowed the hybrid to show not only osteoconduction but also suitable biodegradation after implantation in bony defect.

Abstract: Apatite formation in living body is essential condition for artificial materials to exhibit bone-bonding ability, i.e. bioactivity. It has been recently revealed that sulfonic group triggers apatite nucleation in body environment. Organic-inorganic hybrids consisting of organic polymer and the sulfonic group are therefore expected to be useful for novel bone-repairing materials exhibiting flexibility as well as bioactivity. In the present study, organic-inorganic hybrids were prepared from vinylsulfonic acid sodium salt and hydroxyethylmethacrylate (HEMA), a kind of acrylic polymer. Bioactivity of the hybrids was assessed in vitro by examining their acceptance of apatite formation in simulated body fluid (SBF, Kokubo solution). The obtained hybrids showed the apatite deposition after soaking in SBF within 7 d.