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We have reported that octacalcium phosphate (OCP) enhances bone repair in critical-sized rat calvaria defects, while OCP is gradually crystallized to apatite structure. Our studies showed that:

Combining OCP with natural polymers, such as collagen and gelatin, improves not only their moldabilities but also increases the osteoconductivity and the biodegradability in vivo. The hydrolysis of OCP may be involved in displaying bone regenerative capacity of OCP.

The present study aimed to examine the relationship between the structure and composition of dentin and odontoblasts and the role of melatonin during the calcification process. The expression of MT1 and MT2 melatonin receptor was confirmed in the odontoblasts of the control group. In addition, the expression of MT1 was stronger than that of MT2. A strong expression of MT1 was detected in the odontoblasts in the melatonin-treated groups. MALDI-TOF MS analysis revealed that two peaks of 795 m/z and 818 m/z were found in dentin. These peaks increased commensurately with the amount of melatonin. The number and size of calcospherites in predentin increased in proportion to the concentration of melatonin. The degree of mineralization increased slightly in the melatonin-treated group using CMR analysis. Two peaks could be clearly detected in the melatonin-treated group at nighttime using X-ray diffraction analysis. Melatonin may participate in the dentin composition and the calcification mechanism of dentin.

HAp nanofibers (or whiskers) have been attracted considerable attention for their application as adsorbents and reinforcing fillers owing to their unique morphologies. However, fabrication of HAp nanofibers has been limited to high-temperature and/or long-term methods. Herein, we report that HAp nanofibers with more than 5 μm in length (aspect ratio >100) can be easily obtained by a simple wet precipitation method without additives at relatively low temperature (80 °C) under acidic conditions (initial pH of 6.5 and final pH of 3.9), without pH control during the precipitation.

Casein phosphopeptides derived from tryptic digests of milk caseins spontaneously assemble with calcium and phosphate ions at high pH to form casein phosphopeptide-amorphous calcium phosphate complexes (CPP-ACP). These complexes have been shown to be able to repair lesions in tooth enamel (biohydroxyapatite – HA) both and (specifically white spot lesions in the early stages of tooth decay). In order to better understand the processes involved in enamel remineralisation, the chemical equilibria between the CPP and calcium and phosphate ions as a function of pH were investigated. Furthermore, a thin-enamel slab technique was developed with enhanced sensitivity to monitor the diffusion of radio-opaque ions into individual lesions over a period of days to weeks.

Phosphorylated peptides derived from milk caseins, known as casein phosphopeptides (CPP), self-assemble and encapsulate the calcium and phosphate mineral in the form of amorphous calcium phosphate (ACP), thus forming CPP-ACP nanocomplexes that are nontoxic and biocompatible. The biomedical application is the repair of tooth surfaces (enamel) at early stages of tooth decay. These nanocomplexes release calcium and phosphate ions to rebuild demineralised HA crystals in enamel subsurface lesions. The topical application of CPP-ACP at the tooth surface initiates a series of interactions at the enamel mineral hydroxyapatite surface and at the enamel salivary pellicle that are not well understood. In this study, we have shown that the β-casein (1-25) peptide binds reversibly to Ca, Mg, Mn, La, Ni, and Cd metal ions. In contrast, binding to Sn, Fe, and Fe ions resulted in ion-induced aggregation. The casein peptides as well as the mineral ions dissociate from the CPP-ACP complexes to adsorb to both the uncoated and saliva-coated mineral surface with the mineralisation increasing monotonically with increasing pH. Furthermore, SEM of the CPP-ACP revealed images of spherical particles surrounded by ACP mineral. In conclusion, the enamel remineralisation process involves an array of interactions between the peptide and mineral ions of the CPP-ACP delivery vehicle and the tooth enamel mineral with its salivary pellicle.

The aim of this study was to evaluate the effect of random and oriented electrospun polycaprolactone (PCL) fiber meshes on conductive indium tin oxide (ITO) electrode on the in vitro electrocrystallization (EC) of calcium oxalate (CaOx). For that, random and aligned PCL fibers were prepared through flat and rotating collectors and directly collected on conductive ITO support that was used as organic solid template for controlling the in vitro EC of CaOx. Our findings revealed that electrospun PCL surface topology induced preferentially the nucleation and crystal growth of CaOx along on individual aligned PCL fibers during the EC of CaOx. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), chronoamperometry, and X-ray diffraction (XRD) spectroscopy of CaOx crystals show that the morphological orientation of PCL fiber meshes acted as selective good nucleation site at PCL surface controlling their CaOx crystal morphologies and the crystallographic orientation of crystals inducing the coexistence of dehydrated CaOx (COD) and monohydrated CaOx (COM) crystals as the unique polymorphism.

Biomineralization approaches have gained significant attention as a means to recover rare earth elements from acidic mine drainage and industrial liquid wastes. We isolated an acidophilic fungus, sp. strain T9, that accumulates dysprosium (Dy) from acidic model drainage during growth. To develop the application of biomineralization by the strain T9, we elucidated the localization and the chemical structure of biomineralized Dy and performed to establish the labo-scale bioprocess for selective recovery of Dy. High-magnification scanning electron microscopic analysis showed that the strain T9 formed a mineralized Dy (T9-Dy) layer with 1.0 μm thickness over the cell surface, along with some intracellular nano-micro meter-sized Dy particles. X-ray photoelectron spectrometry and X-ray absorption fine structure analyses showed that the chemical composition of T9-Dy corresponded to DyPO. X-ray diffraction analysis did not yield any spectrum from T9-Dy. Therefore, we concluded that the strain T9 accumulates and mineralizes Dy as an amorphous DyPO. Dysprosium desorption rate from T9-Dy was 100% using 0.3 M hydrochloric acid. Furthermore, after desorption process, the strain T9 grows again in the new medium and retains the Dy accumulation ability. Thus, the strain T9 has a potential as a bioaccumulator for Dy recovery from acidic drainage through biomineralization.

Gold nanoparticles have particular properties distinct from bulk gold crystals. The gold nanoparticles are used in various applications in optics, catalysis, and drug delivery. Although many reports on microbial synthesis of gold nanoparticles have appeared, the molecular mechanism of gold nanoparticle synthesis in microorganisms is unclear. Previously we reported that the amounts of diglycosyl diacylglycerol (DGDG) and triglycosyldiacylglycerol (TGDG) bearing unsaturated fatty acids were much reduced after formation of gold nanoparticles. DGDG purified from induced the synthesis of gold nanoparticles in vitro. These results suggested that glycolipids, such as DGDG, play important roles in reducing Au(III) to Au(0). In this paper, we reported that the concentration change of DGDG induced various shapes of gold nanoparticles in vitro. Our work will lead to the development of novel and efficient methods to synthesize metal nanoparticles using microorganisms.

The effects of the particle size of β-tricalcium phosphate (β-Ca(PO); β-TCP) on octacalcium phosphate (Ca(HPO)(PO)·5HO; OCP) overgrowth on a β-TCP substrate were evaluated under physiological conditions by using two types of substrate; one composed of micrometer-sized particles (micro-TCP substrate) and one composed of nanometer-sized particles (nano-TCP substrate). When the β-TCP substrate was immersed in a simple calcium phosphate solution, it was quickly covered with OCP. The morphology and size of the OCP crystals, as well as the structure, thickness, and crystal density of the overgrown OCP layer, depended on the β-TCP particle size. In case of the micro-TCP substrate, OCP crystals grew directly on the micrometer-sized particles. In case of the nano-TCP substrate, string-like (S) precipitates initially deposited, and then flake-like (F) crystals formed on them. Plate-like (PL) OCP crystals grew on the flake-like crystals; as a result, a three-layer structure (S-layer/F-layer/PL-layer) was formed. Small amounts of tiny OCP crystals and HAp-nanofibers precipitated in the micro-TCP substrate, whereas only HAp-nanofibers precipitated in the nano-TCP substrate. Thus, various types of OCP-overgrown layers were fabricated on β-TCP scaffold. These findings will facilitate the structural design of OCP-coating layers on a β-TCP scaffold.

Global warming causes serious harm to the Earth’s environment. A more sophisticated and accurate climate model can be developed by reconstructing climatic change since the Industrial Revolution and for other past periods of global warming. Coral skeletons are an important archive of past climate changes, and advances in the ability to read sea surface temperature and salinity in the coral record have been made by applying state-of-the-art technology. Coral skeletal climatology has been successfully applied to characterize both the recent global warming trend in the Western Pacific and the mid-Pliocene warming that occurred 3.5 million years ago, and it has also been used to investigate biological and environmental issues such as ocean acidification and coral bleaching, which is caused by unusually high seawater temperatures. Coral skeletal climatology methods have also been used to study boulders cast ashore by historical tsunamis; such studies have high social value from the perspective of regional disaster prevention. Nevertheless, aspects of coral skeletal climatology still need clarification, including the basic mechanism by which seawater temperature is recorded in coral skeletons, and further research on biomineralization will improve predictions of the future responses of marine calcifying organisms to ocean acidification.