Hirotaka Maeda

Hydrothermal preparation of diatomaceous earth combined with calcium silicate hydrate gels.

A novel composite for the removal of color in waste water was prepared by subjecting slurries consisting diatomaceous earth and slaked lime to a hydrothermal reaction at 180 °C. Subsequently, calcium silicate hydrate gels covered the surface of diatomaceous earth due to the reaction between the amorphous silica of diatomaceous earth and slaked lime. The formation of calcium silicate hydrate gels led to an increase in the specific surface area. The composites showed higher methylene blue adsorption capacity compared with diatomaceous earth. The improved adsorption capacity of the composites depended on the amount of the calcium silicate hydrate gels and their silicate anion chain-lengths.

Potential utilization of riverbed sediments by hydrothermal solidification and its hardening mechanism.

Hydrothermal solidification of riverbed sediments (silt) has been carried out in a Teflon (PTFE) lined stainless steel hydrothermal apparatus, under saturated steam pressure at 343-473 K for 2-24 h by calcium hydrate introduction. Tobermorite was shown to be the most important strength-producing constituent of the solidified silt. A longer curing time or a higher curing temperature was shown to be favorable to the tobermorite formation, thus promoting strength development; however, overlong curing time (24 h) seemed to affect the strength development negatively. The hardening mechanism consisted of the crystal growth/morphology evolution during the hydrothermal process. The species dissolved from the silt were precipitated first as fine particles, and then some of the particles seemed to build up the rudimental morphology of calcium silicate hydrate (CSH) gel. The CSH gel, with precipitated particles, appeared to cause some reorganization within the matrix, which made the matrix denser and thus gave an initial strength development. Tobermorite, transformed inevitably from the CSH gel, reinforced the matrix with its interlocked structure, and thus further promoted the strength development.

Preparation of Bioactive Polylactic Acid Composites Containing Calcium Carbonates

Polylactic acid composites containing a mixture of calcium ca rbonates (vaterite, aragonite and calcite) were prepared using a carbonation process in methanol. T he composites containing a large amount of vaterite formed bonelike apatite particles on the s urface in simulated body fluid (SBF) at 37 °C for 3 h. After soaking the composites, vaterite phase in th composites was forward to dissolve rapidly, resulting in increase in the supersaturation of the apatite in SBF. C CP/MAS-NMR spectra of the composites suggested the formation of a bond between Ca 2+ ion and COO group, which induces the apatite nucleation. These results may elucidate the m echanism of means to reduce the induction period for the apatite formation.

Preparation of Bonelike Apatite Composite Sponge

A novel sponge, coated with bonelike hydroxycarbonate apatite (HCA) on it s skeleton surface, was derived via a particle-leaching technique combined with a b omimetic processing. In the present work, a compact consisting of calcium carbonate / poly(lacti c acid) composite (CCPC) and sucrose formed by hot-pressing, was soaked in the simulated body fluid at 37 °C. Within initial 1 h, the sucrose was completely dissolved out, resulting in the formation of large-sized pores in the compact, and subsequently, after 3 d of soaking, bonelike HCA formed on the skeleton consisting of CCPC. The formed sponge has numerous, large pores of 450 to 580 μm in diamet er, which are connected with channels having a diameter in the range of 70 to 120 μm, as well a high porosity of 89 %.

Preparation of Poly(Lactic Acid) Composite Hollow Spheres with an Open Channel

Novel hollow spheres for bone fillers incorporating cells were prepared using composites consisting of poly(lactic acid) and calcium carbonates. An open channel of ~800 µm in diameter was easily formed using a chemical etching method to provide a pathway to the interior of the sphere. Cells could migrate through the open channel into the interior of the sphere. Bonelike apatite coating on the surface of the sphere was prepared by soaking in calcium chloride solution to supply excess Ca2+ ions on the surface and subsequently by soaking in simulated body fluid. The hollow spheres with an open channel may be one of the great potential candidates as novel bone fillers combined with a cell-delivery system.

Preparation of Poly(Lactic Acid) Composites Containing Vaterite for Bone Repair

Calcium carbonate (vaterite)-containing poly(lactic acid) (PLA) composites (CCPCs) were prepared for novel biomaterials that are expected to exhibit high bioresorbability and osteoconductivity. CCPC containing 30% vaterite showed bending strengths of 40~50 MPa. 13C CP/MAS-NMR spectrum of CCPC suggested the formation of a bond between Ca2+ ion and COOgroup. The bond may play an important role in the improvement of the mechanical properties. On the surface of CCPC containing 30 % vaterite, ~10-μm-thick hydroxycarbonate apatite (HCA) formed after 1 day of soaking in SBF at 37oC. After 1-week incubation of human osteoblasts (HOBs) on the HCA-coated CCPC, numerous HOBs attached. The adhesion of cells on the composite was greater than that on PLA. After 3-week culture of HOBs on HA-coated CCPC, numerous bone nodules could be seen on the surface. CCPC is believed to be one of the most promising materials for bone repair. A novel CCPC containing polysiloxane was also prepared using aminopropyltriethoxysilane (APTES). Polysiloxane partially assembled in the membrane and a molecular chain of PLA was bonded at the end of an organic chain in APTES through the amide bond formed between carboxy groups in PLA and amino groups in APTES. The composite formed HA on its surface after 3 days of soaking in SBF. The HA layer included Si with Ca and P. The composite coated with silicon-containing HCA had higher cell-proliferation ability than that without HA. The existence of silicon-containing HCA may be apt to stimulate the proliferation.

Preparation of vaterite/poly(lactic acid) composites with excellent apatite-forming ability

A new type of ceramic-polymer biomaterial having excellent apatite-forming ability in simulated body fluid (SBF) was prepared by hot-pressing a mixture consisting of poly(-L-lactic acid)(PLA) and calcium carbonate (vaterite). The composite containing 30% vaterite showed no brittle fracture behavior and comparably high bending strength of ~50 MPa. Apatite layer of several micrometers in thickness formed on its surface after soaking in SBF at 37°C only for 1 day. Osteoclast culture tests showed that the composite coated with apatite has excellent bioresorbability. After incubation of human osteoblasts, mineralized bone nodule formation was seen on the surface.

Preparation of Calcium Carbonate / Poly(lactic acid) Composite (CCPC) Hollow Spheres

Novel hollow spheres were prepared using calcium carbonate / poly(la ctic acid) composite (CCPC). The CCPC slurry was drop-wise added to 1 % poly(ethylene g lycol) (PEG) aqueous solution with stirring for 1 d. Numerous CO 2 gas generated from calcium carbonates in CCPC during the process which contributes to the formation of the hollow sphere. The size of the sphere is around 0.8 ~ 1.5 mm in diameter. The spheres have thicknesses of the shells in the range of 50 to 300 μm.

Preparation of Poly(L-lactic Acid) Hybrid Membrane with Silicon-Ion-Releasing Ability

A novel poly(lactic acid) (PLA)/calcium carbonates hybrid membrane containing siloxane was prepared using aminopropyltriethoxysilane (APTES) for biodegradable bone guided regeneration. The PLLA in the membrane was an amorphous phase. By heating the membrane at 100 °C for 1 h, the PLLA in the membrane crystallized. Numerous pores of 0.5-1 ,m in diameter were newly formed at the surface. After soaking the membranes before and after heat-treatment in simulated body fluid, the amount of silicon species in SBF released from the membrane after heat-treatment was higher than that before heat-treatment. A test of osteoblast-like cellular proliferation on the membrane showed the membrane after heat-treatment has much higher cell-proliferation ability than that before heat-treatment.

Preparation of Silica-Doped Poly(Lactic Acid) Composite Hollow Spheres Containing Calcium Carbonates

Silica-doped poly(lactic acid) (PLA) composite hollow spheres containing calcium carbonates (Si-CCPC spheres) were prepared using aminopropyltriethoxysilane (APTES) for injectable bone fillers combined with a cell-delivery system. Si-CCPC spheres have a hollow spherical shape of ~1 mm in the external diameter and an open channel in the shell, which is selfformed. The channel size is about 500 *m in diameter. X-ray energy dispersive spectroscopy (EDS) analysis showed incorporation of silicon in Si-CCPC spheres. After soaking Si-CCPC spheres in simulated body fluid (SBF), hydroxycarbonate apatite formed on the Si-CCPC spheres. Inductively coupled plasma atomic emission spectroscopy (ICP-AES) showed that the Si4+ ion is released from Si-CCPC spheres in SBF.