Masanobu Kamitakahara

Preparation and evaluation of spherical Ca-deficient hydroxyapatite granules with controlled surface microstructure as drug carriers

Spherical Ca-deficient hydroxyapatite (HA) granules are expected to be useful drug carriers in bony sites because of their bone regeneration and adsorption ability. In order to control drug loading and release ability of the granules, a controlled surface microstructure was constructed. Spherical Ca-deficient granules composed of micron-sized rod-shaped particles were prepared by hydrothermal treatment of α-tricalcium phosphate (α-TCP) granules, and then, submicron HA particles were precipitated on the obtained granules by immersion in a supersaturated calcium phosphate (CP) solution. When bovine serum albumin was used as a drug model, precipitation of submicron particles causes the loading capability to increase and the release rate to decrease. The spherical Ca-deficient HA granules with the controlled surface microstructure are expected to be useful drug carriers that can act as scaffolds for bone repair.

Importance of nucleation in transformation of octacalcium phosphate to hydroxyapatite

Octacalcium phosphate (OCP) is regarded as an in vivo precursor of hydroxyapatite (HA). It is important to understand the mechanism of transformation of OCP to HA in order to reveal the mechanism of mineralization and help in the development of artificial bone-repairing materials. Herein, we have examined the behavior of OCP in a simulated body fluid (SBF) and pure water. The OCP particles immersed in the SBF at 37 °C did not transform to HA even after 720 h of immersion, though the particles showed crystal growth. In distilled water at 60 °C, the OCP particles transformed to HA but the unreactive period was observed. Although the immersed solution became supersaturated with HA within 12h of immersion, the OCP was not transformed in the first 36 h of immersion. These results indicate that the nucleation of HA is the rate-determining step in the transformation of OCP to HA.

Promotion of normal healing of bone defects under estrogen deficiency by implantation of beta-tricalcium phosphate composed of rod-shaped particles

We compared the healing of bone defects in ovariectomized rats implanted with beta‐tricalcium phosphate (β‐TCP) composed of rod‐shaped particles, which were prepared using the applied hydrothermal method (HTCP), and that of bone defects implanted with conventional β‐TCP composed of globular‐shaped particles (CTCP), which were prepared by normal sintering. Eight‐week‐old female Wistar rats were ovariectomized, and 2 weeks after the operation, 0.5‐ to 0.6‐mm diameter spherical granules of each ceramic were implanted in a bone defect created in the distal end of the femur. Four, 8, and 12 weeks after implantation, the amount of newly formed bone implanted with HTCP was significantly larger than that implanted with CTCP and was equivalent to that in non‐ovariectomized sham‐operated rats. Without implantation, spontaneous repair of the trabecular bone was barely observed. The physiological structure of the trabecular network was maintained in the region implanted with HTCP, but that in the region implanted with CTCP was severely destroyed. Gene expression microarray analysis revealed that the expression of genes involved in interferon signaling pathways was upregulated in osteoclasts cultured on HTCP compared with that cultured on CTCP. Our results suggest that the microstructure of β‐TCP affected the biological behavior of osteoclasts and regulated local bone metabolism.

Synthesis of layered double hydroxide coatings with an oriented structure and controllable thickness on aluminium substrates

Layered double hydroxides (LDHs) are applied in environmental purification and biomedicine because of their anion intercalation and exchange properties. This study investigates the formation of LDH layers on aluminium substrates, through the reaction of substrates in solution containing magnesium ions at 30–90 °C. The resulting LDH layer was constructed from many plate-shaped crystals. The LDH crystal size increased with increasing reaction temperature. The LDH layer was preferentially oriented perpendicular to the substrate, thus the LDH crystal orientation was out-of-plane. The oriented structure was formed by crystal-growth-controlled geometrical selection. The LDH layer growth rate also increased with increasing reaction temperature. A high reaction temperature (90 °C) resulted in rapid formation of an approximately 10 μm-thick LDH layer. Milder temperatures (30 and 60 °C) resulted in a moderate LDH layer growth rate, which allowed the LDH layer thickness to be precisely controlled. The LDH layer removed toxic fluoride anions from aqueous solution without damaging the layer. These findings promote the development of oriented LDH coatings with precisely controlled microstructures and thickness.

Adhesion behaviors of Escherichia coli on hydroxyapatite

Optimum design of support materials for microorganisms is required for the construction of bioreactors. However, the effects of support materials on microorganisms are still unclear. In this study, we investigated the adhesion behavior of Escherichia coli (E. coli) on hydroxyapatite (HA), polyurethane (PU), poly(vinyl chloride) (PVC), and carbon (Carbon) to obtain basic knowledge for the design of support materials. The total metabolic activity and number of E. coli adhering on the samples followed the order of HA ≈ Carbon>PVC>PU. On the other hand, the water contact angle of the pellet surfaces followed the order of HA<Carbon<PVC<PU. The high hydrophilicity of the HA surface might be one of the suitable characters for the adhesion of E. coli. The results implied that HA has a potential as a support material for microorganisms used in bioreactors.

Effect of silicate incorporation on in vivo responses of α-tricalcium phosphate ceramics

In addition to calcium phosphate-based ceramics, glass-based materials have been utilized as bone substitutes, and silicate in these materials has been suggested to contribute to their ability to stimulate bone repair. In this study, a silicate-containing α-tricalcium phosphate (α-TCP) ceramic was prepared using a wet chemical process. Porous granules composed of silicate-containing α-TCP, for which the starting composition had a molar ratio of 0.05 for Si/(Pxa0+xa0Si), and silicate-free α-TCP were prepared and evaluated in vivo. When implanted into bone defects that were created in rat femurs, α-TCP ceramics either with or without silicate were biodegraded, generating a hybrid tissue composed of residual ceramic granules and newly formed bone, which had a tissue architecture similar to physiological trabecular structures, and aided regeneration of the bone defects. Supplementation with silicate significantly promoted osteogenesis and delayed biodegradation of α-TCP. These results suggest that silicate-containing α-TCP is advantageous for initial skeletal fixation and wound regeneration in bone repair.

Morphological control of layered double hydroxide through a biomimetic approach using carboxylic and sulfonic acids

Abstract Layered double hydroxides (LDHs) have intercalation properties and are used in various applications. The performances of the LDH materials can be improved by controlling crystal morphology. Morphology of inorganic crystals is controlled by organic molecules in biomineralization. Inspired by biomineralization, we investigated the effect of the addition of mono, di and triacids as morphological control agents on crystal morphology of LDH synthesized by the homogeneous precipitation method. Morphology of LDH was changed from hexagonal plate to stacked disc by addition of monoacids, namely acetic acid and methanesulfonic acid, in the reaction solution. Flower-shaped LDH crystals were formed in the presence of diacids and a triacid, namely succinic acid, 1,2-ethanedisulfonic acid and 1,2,3-propanetricarboxylic acid. We found that the morphology of the LDH crystals was controlled by the number of functional group on the morphological control agent rather than the type of functional group. These findings can contribute for the development of novel and functional LDH materials with precisely controlled morphology.

Spherical porous hydroxyapatite granules containing composites of magnetic and hydroxyapatite nanoparticles for the hyperthermia treatment of bone tumor

Spherical porous granules of hydroxyapatite (HA) containing magnetic nanoparticles would be suitable for the hyperthermia treatment of bone tumor, because porous HA granules act as a scaffold for bone regeneration, and magnetic nanoparticles generate sufficient heat to kill tumor cells under an alternating magnetic field. Although magnetic nanoparticles are promising heat generators, their small size makes them difficult to support in porous HA ceramics. We prepared micrometer-sized composites of magnetic and HA nanoparticles, and then supported them in porous HA granules composed of rod-like particles. The spherical porous HA granules containing the composites of magnetic and HA nanoparticle were successfully prepared using a hydrothermal process without changing the crystalline phase and heat generation properties of the magnetic nanoparticles. The obtained granules generated sufficient heat for killing tumor cells under an alternating magnetic field (300 Oe at 100xa0kHz). The obtained granules are expected to be useful for the hyperthermia treatment of bone tumors.

Carbonate-containing hydroxyapatite synthesized by the hydrothermal treatment of different calcium carbonates in a phosphate-containing solution

Abstract Carbonate-containing hydroxyapatite (CHA) particles were synthesized by the hydrothermal treatment of calcium carbonates in a phosphate-containing solution. Three types of calcium carbonates were synthesized: aragonite particles with rough surfaces, calcite particles with rough surfaces by heat treatment of aragonite particles with rough surfaces, and aragonite particles with smooth surfaces. The effects of the calcium carbonate crystal phase and morphology on the synthesized CHA were investigated and morphological changes in the formed CHA particles were observed. The reaction rates varied depending on the calcium carbonate crystal phase and morphology and this difference in reaction rates mainly affected the morphology of the synthesized CHA. On the other hand, the carbonate content and lattice constants of formed CHA were almost independent of the calcium carbonate crystal phase and morphology. This is because the equilibrium mainly governed the composition of the synthesized CHA. The characteristics of the starting material were highly important factors in controlling the morphology of the synthesized CHA.

Behavior of osteoblast-like cells on calcium-deficient hydroxyapatite ceramics composed of particles with different shapes and sizes

In designing the biomaterials, it is important to control their surface morphologies, because they affect the interactions between the materials and cells. We previously reported that porous calcium-deficient hydroxyapatite (HA) ceramics composed of rod-like particles had advantages over sintered porous HA ceramics; however, the effects of the surface morphology of calcium-deficient HA ceramics on cell behavior have remained unclear. Using a hydrothermal process, we successfully prepared porous calcium-deficient HA ceramics with different surface morphologies, composed of plate-like particles of 200–300, 500–800xa0nm, or 2–3xa0μm in width and rod-like particles of 1 or 3–5xa0μm in width, respectively. The effects of these surface morphologies on the behavior of osteoblast-like cells were examined. Although the numbers of cells adhered to the ceramic specimens did not differ significantly among the specimens, the proliferation rates of cells on the ceramics decreased with decreasing particle size. Our results reveal that controlling the surface morphology that is governed by particle shape and size is important for designing porous calcium-deficient HA ceramics.