Key Engineering Materials Vols. 309-311

Abstract: Bioactive glass scaffolds have been developed with interconnected macropore networks, with pore diameters in excess of 500µm and apertures in excess of 100µm, by foaming sol-gel derived bioactive glasses. Bioactive glasses bond to bone by forming a hydroxycarbonate apatite (HCA) layer on their surface on contact with body fluid, which is similar to the composition of the apatite in bone. The aim of this work was to investigate the how changing the atomic structure of the glass affects HCA layer formation. Scaffolds were synthesised at 3 sintering temperatures and were characterised using 29Si and proton MAS-NMR, from which the silica network connectivity and Si-OH groups were quantified. The rate of HCA layer formation decreased as the number of Si-OH groups decreased, confirming the role of Si-OH groups in HCA layer formation.

Abstract: The objective of this work is to evaluate the cytotoxicity, acute and chronic inflammatory response and mutagenicity of a high porosity bioactive glass (BG60S), produced by sol-gel method. The BG60S analyzed by direct contact and elution tests showed cytotoxic levels compatible with international standards (ISO 10,993-5). The BG60S extract reduced by ≈50% the cellular viability of L929, CHO and CPis cells measured by the MTT assay. The diluted extract (1:3) restored the cellular viability. We did not find edema induction in the rat paw test, nor cell migration to peritoneum, as measured by the inflammatory acute response. A BG60S implant did not induce chronic inflammation measured by hemoglobin levels (blood vessels formation), as well as the presence of macrophages and neutrophils (NAG and MPO activities, respectively). The BG60S extract was unable to induce colony reversion of Salmonella thyphimurium (with or without S9), thus precluding its mutagenic activity.

Abstract: Porous composites of magnetite / hydroxyapatite with bimodal pore size distribution were prepared by hydrothermal method. Magnetite particles of about 1 µm in size with polyhedral shape were dispersed into hydroxyapatite porous matrix. The hydroxyapatite particles were rod-shaped crystals and the size of crystals were about 10 µm in length with the aspect ratio of over 25. Rod-shaped hydroxyapatite crystals were locked together to make micro-pores of about 0.8 µm in size. In addition, macro-pores of about 400 µm in size were prepared by our unique method. Hydroxyapatite in this composite was non-stoichiometric hydroxyapatite with calcium deficient composition. This composite must have the advantage of adsorptive activity and osteoconductivity, because the hydroxyapatite has many specific crystal surface and micro-pores. The composites of magnetite / hydroxyapatite must be suitable for the hyperthermia therapy of cancer in bones.

Abstract: Porous HA ceramics has been developed for the scaffold materials because the porous structure has been recognized to be necessary to invasion of body fluid and ingrowth of bone. The synthesized porous HA ceramics with several porosities were electrically polarized, and then the TSDC spectra were measured. The maximum electric current density and the stored polarization charges decreased with increasing the porosity. Therefore it was thought that the decreasing the amount of proton of porous HA ceramics was one of the reasons of decreasing of the maximum electric current densities and the stored charges. The simulated body fluid (SBF) test implied that electrovector effects enhanced the apatite formabilities.

Abstract: The objective of this study was to produce a macroporous hydroxyapatite(HA) scaffold with high strength by controlling the size of HA particles as well as cooling rate from the sintering temperature. Macroporous polyurethane sponge was employed as template to manufacture the macroporous HA scaffolds. Particle sizes of HA powders selected in this study were 4 µm and 7 µm. They were dispersed in distilled water with organic additives and infiltrated into polyurethane sponge. After drying and sintering at 1300oC, cooled down to room temperature slowly to prevent microcracking either 1oC/min or 3oC/min. Density, porosity and compressive strength were measured with different particle size and cooling rate. Both density and compressive strength were increased with decreasing particle size or cooling rate, while porosity was not related to.

Abstract: Abstract. Bioabsorbable and functionally graded apatites (fg-HAp) ceramics were designed using calcined bovine bone (b-HAp) by the partial dissolution-precipitation methods. The fg-HAp ceramics with micro-pores of 10-160 nm had larger specific surface areas (30-40 m2･g-1) than the b-HAp ceramics, although the two HAp ceramics exhibited same macro-pore sizes of 100-600 µm and porosities of 60-80 %. Surface structure of these ceramics was modified by soaking at 309.5 K for 1-90 days in a simulated body fluid (SBF). At 8 days after the soaking, microstructure of the fg-HAp changed from small grains to dense cocoon-like ones by rapid precipitation of HAp microcrystals, while at 14 days, that of the b-HAp was porous urchin-like grains, suggesting that the fg-HAp had higher bone-bonding ability than the b-HAp.

Abstract: Two kinds of tri-calcium phosphate ceramics, β-TCP, which have the same macrostructure and microstructure, but different special surface area and particle size, were used in porous ceramics. A slip was obtained by adding the powders to a solution 1.0 wt% of deflocculant, respectively. The specimen obtained by casting a polyurethane foam with 0.5wt% into a slip, and drying it under vacuum, was heated at 1150
, for 3 hours. The porous ceramics samples about 0.5g were individually soaked into 30 mL of phosphate buffer saline (PBS) at 20
for 1,3,7 and 10 days, respectively. The calcium content of the PBS solution was analyzed by (ICP). The porous bodies were filtered, dried, and characterized using SEM, XPD, and FT-IR.

Abstract: Porous granules of β-tricalcium phosphate (β-Ca3(PO4)2; β-TCP) were prepared from porous hydroxyapatite granules with calcium deficient composition synthesized by hydrothermal method. The β-TCP granules were composed of rod-shaped particles of about 10-20 µm in length. Rod-shaped particles were locked together to make micro-pores, and the size of micro-pores formed by tangling of rod-shaped particles was about 0.1-0.5 µm. The granule size, particle size, and micro-pore size could be controlled by our unique method. The porous granules of β-TCP must be suitable for the bone graft material and for scaffold of cultured bone.

Abstract: Newly developed porous β-tricalcium phosphate composed of rod-shaped particles was grafted into distal end of the left femur of female Japan White rabbit. As a control, hydrixyapatite generated in the same size was grafted. In both implants, 350µm in diameter-sized holes were created vertically and horizontally. Three weeks after grafting, margin of the β-tricalcium phosphate was absorbed by osteoclasts and bone formation was seen near the absorbed region. Twenty-four weeks after grafting, more than 80% of the β-tricalcium phosphate was absorbed and newly formed bone was prominently observed. The hydroxyapatite was not remarkably absorbed even 24 weeks after grafting, and newly formed bone was observed only in the holes created in the implants. These results suggest that porous β-tricalcium phosphate composed of rod-shaped particles has highly biodegradable and osteoconductive nature, and appropriate to bone graft substitute.

Abstract: Porous hydroxyapatite has been prepared using a hydrothermal hot pressing method from calcium carbonate as a starting material. SEM result shows porous hydroxyapatite block is formed of three dimensionally inter-connected pores of 100-400µm in size, similar to human cancellous bone. At the ~ 70% porosity, the compressive strength was about 4MPa, which is similar to that of the commercially available porous hydroxyapatite derived from natural coral.