Yoshio Ota

Preparation and mechanical properties of polylactic acid composites containing hydroxyapatite fibers

Ceramic-polymer composite biomaterials were prepared by hot-pressing a mixture consisting of poly-L-lactic acid (PLA) and hydroxyapatite fibers (HAF) with dimensions of 40-150 microm length and 2-10 microm diameter, which were converted from beta-Ca(PO3)2 fibers. After PLA dissolved with methylene chloride was mixed with the fibers, the mixture was dried completely and subsequently hot-pressed uniaxially under a pressure of 40 MPa at 180 degrees C, resulting in the fabrication of the PLA/HAF composite. The modulus of elasticity was improved effectively even by introducing a small amount of HAF; almost no degradation in the bending strength was observed and the modulus of elasticity showed high values of 5-10 GPa when the fibers of 20-60 wt% were introduced. With increasing HAF content, the maximum strain decreases and the specimen is apt to show a brittle fracture; this result implies that HAF in the composites can share the applied load efficiently due to the formation of a bond between HAF and PLA.

Electrospun microfiber meshes of silicon-doped vaterite/poly(lactic acid) hybrid for guided bone regeneration

Silicon-releasable microfiber meshes consisting of silicon-doped vaterite (SiV) particles and poly(lactic acid) (PLA) hybrids were prepared by electrospinning. Due to their flexibility and porosity they formed ideal membranes or scaffolds for guided bone regeneration. In addition, a trace amount of silicon species has been reported to stimulate osteogenic cells to mineralize and enhance bone formation. We propose a new method of preparation of silicon-releasing microfiber meshes by electrospinning. Their structure and hydroxyapatite (HA)-forming abilities in simulated body fluid were examined. In addition, we studied their stimulatory effects on osteoblast-like cells in vitro and bone-forming ability in vivo, with a special emphasis on their ability to release silicon. The meshes consisted of a hybrid of carboxy groups in PLA and amino groups in siloxane, derived from aminopropyltriethoxysilane or calcium ions on the SiV surface. This hybrid exhibited an enhanced ability to form HA. The meshes coated with HA released 0.2-0.7 mg l(-1) silicon species into the culture medium over 7 days. Enhanced proliferation of osteoblast-like cells was observed using the meshes and new bone formed on the meshes when implanted into the calvaria of rabbits. These meshes, therefore, provide an excellent substrate for bone regeneration and exhibit enhanced bone-forming ability under both in vitro and in vivo conditions.

Biomimetic apatite formation on poly(lactic acid) composites containing calcium carbonates

Poly(lactic acid) composites containing a mixture of calcium carbonates (vaterite, aragonite, and calcite) were prepared by a carbonation process in methanol. Soaking of the composites for 3 h in simulated body fluid (SBF) at 37 °C resulted in the deposition of bonelike apatite particles on the composite surface. After soaking the composites, vaterite phase in the composites was forward to dissolve rapidly, resulting in increase the supersaturation of the apatite in SBF. 1 3 C cross-polarization magic angle spinning nuclear magnetic resonance ( 1 3 C CP/MAS-NMR) spectra of the composites suggested the formation of a bond between Ca 2 + ion and the COO - group, which induces the apatite nucleation. These results may elucidate the mechanism of means to reduce the induction period for apatite formation.

Surface modification of calcium metaphosphate fibers.

Abstractβ-calcium metaphosphate fibers having high aspect ratios of 10–120 with diameters of 2–10 μm show high strength and good biocompatibility. When the fibers are soaked in simulated body fluid at 37 °C, however, no calcium phosphate phase is newly formed on the fibers. In the present work, by treating the fibers at 70 °C with dilute NaOH aqueous solution, the surface phase was converted successfully into the orthophosphate phase that was in fine sizes and was adhered. After soaking the treated fibers in simulated body fluid at 37 °C for 30 days, a new calcium phosphate phase was precipitated. This was attributed to the surface phase modified using dilute NaOH. The treated fibers are expected to show bone-bonding ability, i.e. bioactivity. ©2000 Kluwer Academic Publishers

Bone formation following implantation of fibrous calcium compounds (β−Ca(PO3)2, CaCO3(aragonite)) into bone marrow

Bone formation around three types of fibrous calcium-containing crystals has been examined histologically using rats. The implanted materials are (i) calcium metaphosphate (β−Ca(PO3)2) fibers having aspect ratios of 15–80 with 2–20 μm in diameter, (ii) β−Ca(PO3)2) fibers surface-modified using dilute NaOH and (iii) calcium carbonate (CaCO3; aragonite phase) whiskers having aspect ratios of 15–40 with 0.5–3 μm in diameter. β−Ca(PO3)2 fibers show a mechanically high strength with a low modulus of elasticity, and the surface-modified fibers have a thin layer consisting of a calcium orthophosphate phase. CaCO3 whiskers were used for comparison reasons. The materials were implanted for 4, 8, and 12 weeks into bone defects created in the bone marrow of rat tibiae. Cancellous bone formation was observed around β−Ca(PO3)2 fibers, the surface-modified fibers and CaCO3 whiskers after implantation for 12, 4 and 4 weeks, respectively. CaCO3 whiskers were scarcely observed after 12 weeks for resorbing. The calcium phosphate fibrous materials show combined advantages of mechanically high strength for toughening a matrix phase and biological activities; thus, these materials may prove to be useful for novel applications in the biomedical field.

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.

Development of Magnesium and Siloxane-Containing Vaterite and Its Composite Materials for Bone Regeneration

Development of novel biomaterials with Mg2+, Ca2+, and silicate ions releasability for bone regeneration is now in progress. Several inorganic ions have been reported to stimulate bone-forming cells. We featured Ca2+, silicate, and especially, Mg2+ ions as growth factors for osteoblasts. Various biomaterials, such as ceramic powders and organic–inorganic composites, that release the ions, have been developed and investigated for their cytocompatibilities in our previous work. Through the investigation, providing the three ions was found to be effective to activate osteogenic cells. Magnesium and siloxane-containing vaterite was prepared by a carbonation process as an inorganic particle that can has the ability to simultaneously release Ca2+, silicate, and Mg2+ ions to biodegradable polymers. Poly (l-lactic acid) (PLLA)- and bioactive PLLA-based composites containing vaterite coatings were discussed regarding their degradability and cytocompatibility using a metallic Mg substrate as Mg2+ ion source. PLLA/SiV composite film, which has a releasability of silicate ions besides Ca2+ ion, was coated on a pure Mg substrate to be compared with the PLLA/V coating. The degradability and releasability of inorganic ions were morphologically and quantitatively monitored in a cell culture medium. The bonding strength between the coatings and Mg substrates was one of the key factors to control Mg2+ ion release from the substrates. The cell culture tests were conducted using mouse osteoblast-like cells (MC3T3-E1 cells); cellular morphology, proliferation, and differentiation on the materials were evaluated. The PLLA/V and PLLA/SiV coatings on Mg substrates were found to enhance the proliferation, especially the PLLA/SiV coating possessed a higher ability to induce the osteogenic differentiation of the cells.

Osteoblast-like cell responses to ion products released from magnesium- and silicate-containing calcium carbonates

BACKGROUND Inorganic ions released from bioceramics and bioactive glasses have been reported to influence osteogenic cell functions. Cell responses depend on types of the ions provided, for example, silicate ion has been found to up-regulate their proliferation, differentiation and mineralization. OBJECTIVE Mouse osteoblast-like cells (MC3T3-E1) were cultured in media containing silicate and calcium ions with/without magnesium ion to evaluate their combined effects on the cells functions. METHODS The cells were cultured in the media containing the extract of silicate-containing vaterite (SiV) and magnesium- and siloxane-containing one (MgSiV) and normal medium and then their adhesion, proliferation, differentiation and mineralization were evaluated. RESULTS The adhesion of the cells was enhanced when they were cultured in the medium containing MgSiV-extract. Their proliferation and differentiation were up-regulated in both media containing MgSiV-extract and SiV-extract. In particular, the MgSiV-extract significantly enhanced their differentiation than the SiV-extract. This was supported by the mineralization tests results, which showed a large amount of mineral deposit was observed in the cells cultured in the MgSiV-extract medium. CONCLUSIONS Providing the three kinds of ions was effective for up-regulating the cells mineralization compared to providing silicate and calcium ions without magnesium ion.

Preparation of Silicon-Containing Poly(lactic acid)-Vaterite Hybrid Membranes

Microfiber meshes releasing a trace amount of silicon species were prepared by electrospinning silicon-doped vaterite (SiV) and poly(lactic acid) (PLA) hybrids for application to membranes for guided bone regeneration (GBR). A trace amount of silicon-species has been reported to enhance the mineralization and bone-forming abilities of osteogenic cells. The microfiber meshes prepared by electrospinning are regarded to be a useful candidate for the GBR membrane, because they have adequate flexibility and porosity for it. In this study, hydroxyapatite (HA)-forming abilities in simulated body fluid, silicon-releasabilities, compatibility with osteoblast-like cells of the prepared microfiber meshes were examined. The meshes were completely coated with HA after soaking in simulated body fluid for 1 day. The meshes coated with HA released 0.2 -0.7 mg/L of silicon species in a cell culture medium for 7 days. The cells elongated on the microfibers of the meshes and some of them entered the mesh after 1 day-culturing. The meshes are expected to provide an excellent substrate for bone regeneration and enhance bone-forming ability of the cells.