Published papers

© 2018, Springer Science+Business Media, LLC, part of Springer Nature. The adhesion behavior of microorganisms on different materials was examined to obtain basic knowledge for designing support materials for microorganisms. The microorganisms were isolated from soil, and their adhesion behavior on hydroxyapatite (HA), carbon-coated HA (Carbon), poly (vinyl chloride) (PVC), and polyurethane (PU) pellets was investigated. The total metabolic activity on and adherence of microorganisms to the tested materials were in the following order: HA > Carbon > PVC > PU. This order was consistent with the extent of hydrophilicity of the materials. Morphological examination and polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE) analysis of microorganisms adhered to the materials revealed that the activities and states of microorganisms were affected by the composition of the pellets. PCR-DGGE analysis revealed various species of microorganisms adhered to the HA pellet. HA ceramics are expected to be one of the most suitable materials for supporting microorganisms.

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/(P + Si), 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.

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.

© 2018 The Ceramic Society of Japan. All rights reserved. Suitable support materials for microorganisms are useful for bioreactors to achieve high efficiencies. Spherical porous hydroxyapatite (HA) granules about 5 mm in diameter composed of rod-like particles were prepared through hydrothermal treatment. The granules with and without pores tens of micrometers in size were prepared. These granules were immersed in a suspension containing microorganisms obtained from the soil, and the adhesion of microorganisms on the granules was examined. The adhesion of microorganisms on the surfaces of the HA granules was observed. The total metabolic activity of the microorganisms adhering onto the granule with pores tens of micrometers in size was higher than that adhering onto the granule without such pores. These results suggested that the HA granules had an affinity for microorganisms, and that granules with pores tens of micrometers in size are expected to be support materials for microorganisms.

© 2018 American Chemical Society. Biomimetic mineralization is useful in obtaining organic-inorganic composite and inorganic materials with controlled sizes and morphologies. The formation of hydroxyapatite (HA) granules with porous structures can be achieved by using electrophoresis processes inside an agarose gel in which the compulsory migration of calcium and phosphate ions are driven by an electric field, causing precipitation of the granules. In the present study, we examined the formation process of HA granules through electrophoresis and the subsequent aging process. Spherical particles of amorphous calcium phosphate (ACP) precipitated, increasing their size with increased running time during electrophoresis; then the ACP granules gradually transformed to the HA granules during the aging process in ultrapure water. When the ACP granules were large, one HA granule was formed from one ACP granule. One HA granule was formed from multiple ACP granules for small-sized ACP granules. The size of ACP granules depends on the gel concentration and pH in the electrophoresis. The dominant transformation process from ACP to HA was the dissolution-precipitation process.