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Calcium carbonate (CaCO3) can show various properties related to its different crystalline phases and is therefore a useful material for various applications. Wet processes are known to be suitable for preparing metastable CaCO3 polymorphs. Electrolysis has been proposed as a preparation method at ambient conditions. Although several electrolytic approaches have been reported, the effects of the applied current and temperature of the electrolyte on the crystalline phase and morphology of CaCO3 remain unclear. In the present study, we attempted the electrochemical preparation of CaCO3 particles under various electrolysis conditions and discuss the mechanism of CaCO3 particle formation. The crystalline phases and morphologies of the CaCO3 precipitates markedly changed depending on the applied current and method of cooling the electrolyte. We assume that these factors were governed by the degree of change in temperature, supersaturation, and pH of the electrolyte that were induced by differences in the electrolysis current.

Magnetite (Fe3O4) nanoparticles such as thermoseeds for hyperthermia and contrast media in magnetic resonance imaging are attracting increasing attention in biomedicine. The organic modification of nanoparticles is an important technique to improve the biological compatibility and drug delivery functions. Also, the addition of organic molecules and the use of hydrogels as a reaction field in Fe3O4 preparation enable controlling the crystalline phase and particle size. In this chapter, the organic modification of Fe3O4 nanoparticles for biomedical applications is reviewed.

Nanocomposites of magnetite (Fe3O4) and reduced graphene oxide (rGO) generate heat under an alternating magnetic field and therefore have potential applications as thermoseeds for cancer hyperthermia treatment. However, the properties of such nanocomposites as biomaterials have not been sufficiently well characterized. In this study, the osteoconductivity of Fe3O4-rGO nanocomposites of various compositions was evaluated in vitro in terms of their apatite-forming ability in simulated body fluid (SBF). Furthermore, the heat generation of the nanocomposites was measured under an alternating magnetic field. The apatite-forming ability in SBF improved as the Fe3O4 content in the nanocomposite was increased. As the Fe3O4 content was increased, the nanocomposite not only rapidly raised the surrounding temperature to approximately 100 °C, but the specific absorption rate also increased. We assumed that the ionic interaction between the Fe3O4 and rGO was enhanced and that Brown relaxation was suppressed as the proportion of rGO in the nanocomposite was increased. Consequently, a high content of Fe3O4 in the nanocomposite was effective for improving both the osteoconductivity and heat generation characteristics for hyperthermia applications.

Autograft has been carried out for anterior cruciate ligament (ACL) reconstruction surgery. However, it has negative aspect because patients lose their healthy ligaments from other part. We focus on a chitosan-hydroxyapatite (HAp) composite fiber as a scaffold of ligament regeneration. Chitosan- HAp composite fiber was made by using coagulation method. Chitosan-NaH2PO4 solution was coagulated with coagulation bath including calcium ion to get the mono-fiber and then treated with sodium hydroxide solution to form HAp in fiber matrix. The mechanical property of the fiber was improved by the stretching of the wet one because of the orientation of chitosan molecule and the interaction between chitosan and HAp. Maximum stress was improved with increasing of sodium dihydrogen phosphate until 0.03 M. The swelling ratio of the fiber was inhibited by composited with HAp. Additionally, bone-bonding ability was confirmed by SBF soaking tests.

Bioactive titania (TiO2) microparticles can be used as drug-releasing cement fillers for the chemotherapeutic treatment of metastatic bone tumors. Porous anatase-type TiO2 microspheres around 15 μm in diameter were obtained through a sol–gel process involving a water-in-oil emulsion with 30:70 SiO2/H2O weight ratio and subsequent NaOH solution treatment. The water phase consisted of methanol, titanium tetraisopropoxide, diethanolamine, SiO2 nanoparticles, and H2O, while the oil phase consisted of kerosene, Span 80, and Span 60. The resulting microspheres had a high specific surface area of 111.7 m2·g− 1. Apatite with a network-like surface structure formed on the surface of the microspheres within 8 days in simulated body fluid. The good apatite-forming ability of the microspheres is attributed to their porous structure and the negative zeta potential of TiO2. The release of rhodamine B, a model for a hydrophilic drug, was rapid for the first 6 h of soaking, but diffusion-controlled thereafter. The burst release in the first 6 h is problematic for clinical applications; nonetheless, the present results highlight the potential of porous TiO2 microspheres as drug-releasing cement fillers able to form apatite.

Natural bone has features such as high fracture toughness and bone-bonding bioactivity, and is organic–inorganic hybrid composed of collagen and apatite crystals. Therefore, apatite-polymer hybrids designed to mimic the structure of bone represent candidates for high-performance bone substitutes. In this study, we prepared pectin hydrogels through covalent cross-linking using divinylsulfone (DVS) and investigated their apatite-forming abilities of the gels in simulated body fluid (SBF) and mechanical properties by tensile test. The obtained results were interpreted in terms of surface charge of the gels and chemical reaction with SBF. The apple- and citrus-derived gels formed the apatite on their surfaces in SBF within 3 days. These gels showed tensile strength around 30 MPa.

Bioactive ceramics have attractive feature for bone repair such as direct bone-bonding in the body. However their clinical application is limited to low loaded portions due to their inappropriate mechanical performances such as higher brittleness and lower flexibility than natural bone. The essential condition for artificial materials to show bioactivity is formation of bone-like apatite on their surfaces in body environment. This apatite formation is triggered by silanol (Si–OH) group on the material surfaces and release of Ca2+. These findings bring us an idea that novel bioactive materials with high flexibility can be designed by organic modification of calcium silicate. We synthesized organic–inorganic hybrids from organic polymers including 2-hydroxyethylmethacrylate (HEMA), starch and alginate by modification with alkoxysilane and calcium chloride. The hybrids formed apatite on their surfaces in simulated body fluid (SBF, Kokubo solution). Such a modification was also effective for providing conventional polymethylmethacrylate (PMMA)-based bone cement with bioactivity., IX Conference and Exhibition of the European Ceramic Society: June 19-23, 2005, Portorož, Slovenia

Problems with poly(methylmethacrylate) (PMMA) bone cement arise owing to loosening between the bone and the cement after a long implantation period, due to a lack of bone-bonding ability, i.e. bioactivity. Bone-like apatite formation in the body environment is needed for an artificial material to show bioactivity. The silanol (Si–OH) group and calcium ions are effective components for inducing apatite nucleation. Organic–inorganic hybrids prepared by organic modification of these components have attracted much attention as novel bonerepairing materials having both bioactivity and flexibility like natural bone. We attempted to prepare bioactive PMMA cement by chemical modification based on the Organic–inorganic hybrids. Specifically, we added alkoxysilane and water-soluble calcium salts to the cements. The cement formed an apatite layer in simulated body fluid, which reproduces the body environment well, when the type of calcium salt was appropriately selected.

This paper develops a damage model for the evaluation of low cycle fatigue lives under complex cyclic multiaxial loadings. One of the authors has proposed the equivalent strain parameter for the life prediction of the nonproportional low cycle fatigue. This strain parameter can evaluate the dependence of fatigue lives on strain history and material, and correlates the fatigue lives within a small scatter band for 15 kinds of proportional and nonproportional strain paths. However, the parameter was only applicable to the life prediction under a limited nonproportional strain history, so that some modifications were required. In this study, a simple damage model for the life prediction is proposed by combining the equivalent strain parameter with Miner's law in order to apply it to the life prediction under more complex nonproportional loadings. The applicability of the proposed model is examined for the life evaluation of nonproportional low cycle fatigue for different materials; type 304 stainless steels, copper, aluminum alloys, chromium-molybdenum and carbon steels, which were obtained from different research institutes. The model can correlate most of the fatigue data within a factor of two scatter band and has a potential to become a good damage model for nonproportional low cycle fatigue.