Masahiro Ashizuka

Bioactivity and Mechanical Properties of Cellulose/Carbonate Hydroxyapatite Composites Prepared in situ through Mechanochemical Reaction

Organic-inorganic composites, prepared from bone-bonding bioactive ceramics and organic polymers, are useful for novel bone substitutes having mechanical properties analogous to natural bone. We synthesized composites from cellulose and carbonate hydroxyapatite (CHAp) in situ through mechanochemical reaction. They contained B-type CHAp analogous to bone apatite. They showed a bending strengths of 10-13 MPa and Young’s modulus of 1.5-2.2 GPa. We predicted their microstructure by comparing the measured density with the theoretical one. Cellulose was assumed to be distributed in the pore of CHAp at low cellulose content, and in grain boundaries of CHAp at high cellulose content. The composites formed calcium phosphate on their surfaces in simulated body fluid, meaning that they have a potential to be bioactive.

Synthesis of osteoconductive organic inorganic nanohybrids through modification of chitin with alkoxysilane and calcium chloride.

The so-called bioactive ceramics have been attractive because they spontaneously bond to living bone. Organic—inorganic hybrids consisting of organic polymers and the essential constituents of the bioactive ceramics, i.e., silanol (Si—OH) group and calcium ions (Ca2+), are useful as novel bone substitutes, owing to bioactivity and high flexibility. In the present study, organic—inorganic hybrids are synthesized from chitin by modification with glycidoxypropyltrimethoxysilane (GPS) and calcium chloride (CaCl2). Their apatite-forming ability is examined in a simulated body fluid (SBF). The prepared hybrids form apatite on their surfaces in SBF within 7 days.

Bioactive Organic-Inorganic Hybrids Prepared from Poly(Vinyl Alcohol) via Modification with Metal Oxides and Calcium Salt

Organic polymers with ability of apatite formation in body environment are expected as novel bone substitutes having not only bone-bonding ability, i.e. bioactivity, but also mechanical performance analogous to natural bone. Several metal oxides have been found to be effective for the apatite deposition in body environment. In addition, release of calcium ions from the materials significantly enhances it. In this study, we attempted to synthesize bioactive organic-inorganic hybrids from poly(vinyl alcohol) (PVA) by incorporation of titanium oxide or zirconium oxide as well as calcium salt. Ability of apatite formation on the hybrids was examined in vitro using simulated body fluid (SBF, Kokubo solution). Apatite deposition was observed to occur on the surfaces of PVA/titanium oxide hybrids in SBF, when their compositions were appropriately controlled.

Apatite Deposition on Organic-Inorganic Hybrids Synthesized from Poly(Vinyl Alcohol) and Various Metal Oxides

Organic polymers with ability of apatite formation in body environment are expected as novel bone substitutes having not only bone-bonding ability, i.e. bioactivity, but also mechanical performance analogous to natural bone. Several metal oxides have been found to be effective for the apatite deposition in body environment. In addition, release of calcium ions from the materials significantly enhances it. In this study, we attempted to synthesize bioactive organic-inorganic hybrids from Poly(vinyl alcohol) (PVA) by incorporation of various metal oxides and calcium salt. Silica and molybdenum oxides were selected as metal oxides. Ability of apatite formation on the hybrids was examined in vitro using simulated body fluid (SBF, Kokubo solution). Apatite deposition were observed to occur on the surfaces of PVA/silica and PVA/molybdenum oxide hybrids in SBF, when their compositions were appropriately controlled.

Apatite Formation on Organic-Inorganic Hybrid Containing Sulfonic Group

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.

Apatite Deposition on Organic-inorganic Hybrids Prepared from Chitin by Modification with Alkoxysilane and Calcium Salt

So-called bioactive ceramics have been attractive because they spontaneously bond to living bone. However, they are much more brittle and much less flexible than natural bone. P revious studies reported that the essential condition for ceramics to show bioactivity is formation of a biologically active carbonate-containing apatite on their surface s ft r exposure to the body fluid. The same type of apatite formation can be observed even in a simula ted body fluid (Kokubo solution) with inorganic ion concentrations similar to those of human extracellular f id. Organic-inorganic hybrids consisting of organic polymers and the essential constituents of the bioactive ceramics, i.e. silanol (Si-OH) group and calcium ion (Ca ), are useful as novel bone substitutes, owing to bioactivity and high flexibility. In the present study, organic-inorganic hybrids we re synthesized from chitin by modification with glycidoxypropyltrimethoxysilane (GPS) and calci um chloride (CaCl 2). Their apatite-forming ability was examined in Kokubo solution. Homogeneous bulk gel was obtained when mass ratio of chitin to the total of GPS and chitin was 0.25 or more and molar ratio of CaCl 2 to GPS was 0.25 or more. The prepared hybrids formed apatite on their surf aces in Kokubo solution within 7 days. This indicates that modification with alkoxysilane and calcium salt provides to chitin-based biomaterials with bone-bonding ability. Introduction Several kinds of ceramics such as Bioglass , intered hydroxyapatite and glass ceramics A-W, are known to exhibit specific biological affinity. Namely, they have t h potential to bond to living bone when implanted into a bony defect [1]. They are called bioactive cer amics and have been already subjected to clinical applications as bone substitutes in orthopedic surg ery, neurosurgery, dentistry and so on. However, their higher brittleness and lower flexibilit y than natural bone limits their clinical application to low load conditions. Materials exhibiting both h igh bioactivity and high flexibility are required for novel bone substitutes. The prerequisite for artificial materials to show bioactivity is formation of a bone-like apatite layer on their surfaces in the body environment [2]. The same type of apatite formation can be observed even in a simulated body fluid (Kokubo solution) with inorganic ion conce ntrations similar to those of human extracellular fluid [3]. Fundamental studies on the me chanism of apatite formation on bioactive glass and glass-ceramics show that silanol (Si-OH ) group and calcium ion (Ca ) are essential components to induce apatite deposition in the body environment [4] . Design of organic-inorganic hybrids by modification of these components with flex ible organic polymers is expected to solve the problem of the bioactive ceramics. In this study, we synthesized organic-inorganic hybrids from chiti n by modification with alkoxysilane and calcium salt, which provides a Si-OH group and C a, respectively. Chitin is a natural organic polymer known as a constituent of club shell. Its chem i al structure is shown in Fig. 1. Key Engineering Materials Online: 2003-12-15 ISSN: 1662-9795, Vols. 254-256, pp 545-548 doi:10.4028/www.scientific.net/KEM.254-256.545

Preparation of Cellulose-Carbonate Apatite Composites through Mechanochemical Reaction

Organic-inorganic composites composed of organic polymer and carbonate hydroxyapatite (CHAp) would be useful bone substitute materials exhibiting low young’s modulus and bone-bonding bioactivity. In this work, such a composite was synthesized from cellulose (CEL)and CHAp through mechanochemical reaction. Homogeneous bulk CEL-CHAp composites were obtained when poly( ε-caprolactone) (PCL) was added as plasticizer with PCL/(PCL+CEL) weight ratio of 20 wt% or less. The CEL-CHAp composites contained B-type CHAp in inorganic phase. The composites with (CEL+PCL)/(CHAp) weight ratio = 20/80 and 10/90 kept the shape in simulated body fluid (SBF), and showed apatite formation after soaking in SBF. Therefore, the CEL-CHAp composites are expected to be materials with low young’s modulus and bioactivity.

Thermal shock behavior of Y2O3-partially stabilized zirconia

The thermal shock behavior of 3mol% Y2O3-partially stabilized zirconia with average grain size of 0.4μm (Z3Y-I) and 1.0μm (Z3Y-II) has been studied by the water quench method. Twenty three specimens of rectangular cross-section bar (3 by 3 by 45mm) were quenched at 300°, 350° and 400deg;C temperature differentials (ΔT) and their retained strength (σf) were plotted using the Weibull distribution function and doubly exponential distribution function. The retained strength distribution at ΔT=350°C are similar to the original strength distribution. On the other hand, the distribution at ΔT=350° and 400°C showed a shoulder at F=0.458 and 0.875, respectively, They are the initiation points of thermal shock damage, Assumming the surface heat transfer coefficient (h) of 0.19 and 0.4cal/cm2·°C·s, calculated stress intensity factors KIs for crack initiation by water quench were 73-75% and 91-92% of the critical stress intensity factor KIC for Z3 Y-I, and 69-70% and 86-88% for Z3 Y-II, respectively. A σf-δT curve for a certain failure probability level F showed instantaneous decline at a critical temperature differential δTc. High failure probability level F resulted in a high critical temperature diffrential δTc. Estimated δTcs are 310°, 360° and 400°C for F=0.2, 0.5 and 0.9, respectively.

Bioactivity and Mechanical Property of Starch-Based Organic-Inorganic Hybrids

So-called bioactive ceramics bond to living bone through the apatite layer formed on their surfaces in the body. The apatite deposition is triggered by dissolution of calcium ion (Ca2+) and by silanol (Si-OH) group formed on the surfaces of the ceramics. It is expected that organic modification of these components would produce bioactive materials with high flexibility. In this study, we examined bioactivity and mechanical properties of the organic-inorganic hybrids from starch by modification with silanol group and calcium ion. Effect of cross-linking agent was also investigated. The obtained hybrids showed bioactivity and mechanical properties analogous to those of human cancellous bone by appropriate control in their compositions. Addition of cross-linking agent to improve mechanical strength of the hybrids did not decrease their bioactivity.

Influence of Cross-Linking Agents on Apatite-forming Ability of Pectin Gels

Natural bone is a kind of organic-inorganic hybrid composed of collagen and apatite crystals with a structure that provides specific mechanical properties such as high fracture toughness and flexibility. Materials exhibiting both high flexibility and bioactivity similar to natural bone are required for novel bone-repairing materials in medical fields. We expect that we can design such materials by mimicking the bone structure. Biomimetic process has been paid much attention where bone-like apatite is deposited on organic polymers in simulated body fluid (SBF). In this study, we investigated influence of cross-linking agents on apatite-forming ability of pectin gels. Pectin is a polysaccharide abundant in carboxyl group. Pectin gels were prepared by cross-linking of pectin aqueous solutions with calcium ions or divinylsulfone (DVS). Apatite-forming ability of the gels was examined in SBF. The citrus-derived pectin showed tendency to form the largest amount of the apatite independent on a kind of cross-linking agents in SBF.