Key Engineering Materials Vols. 361-363

Abstract: Chitosan pyruvic acid derivatives was successfully prepared from chitosan and pyruvic acid under reducing conditions, via aldimine formation. The chemical structure of the derivatives was proved by 13C NMR and IR. It was found ratio between glucose residues and pyruvic acid, reaction time, pH, and molecular weight of original chitosan had great influence on the degree of substitution (DS). N-(1-carboxyethyl) chitosan (N-CE-CTS) showed similar moisture absorption-retention curve and ability with HA, and much better ability than the original chitosan. Hydroxyl radical scavenging ratio of 4g/L chitosan and N-CE-CTS was 35.0% and 41.7%, respectively.

Abstract: A variety of types of organic polymers have been employed in the synthesis of hybrids with silica. In this work the sol-gel method was used for preparation of macroporous 3D hybrid scaffolds based on silica and chitosan in various compositions (10, 20 and 30% wt). The hybrids were analyzed by Scanning Electron Microscopy (SEM), X-ray Diffraction (DRX) and Infra-red Spectroscopy (FTIR) and the effect of addition of the polymer was evaluated. The foams obtained by sol-gel process were appropriate to produce hybrids based on chitosan-silica and showed large pore size distribution and porosity, except for hybrids with higher polymer content. The FTIR spectroscopy showed a band relative to Si-O-C bond that was also found to increase with the increasing the amounts of chitosan in the hybrid. This fact can suggest an interaction between the organic-inorganic phases in the material and provide new insights on the advantages of chitosansilica hybrid materials produced via sol-gel methodology.

Abstract: In many in-vivo and in vitro studies, the behavior of calcium phosphate ceramics like β - tricalcium phosphate in biological environments has been reported to be predictive and positive. In terms of bone tissue growth, this ceramic can be more attractive presenting a porous microstructure. To obtain biomaterial quality ceramics, in this investigation β- TCP porous ceramics were prepared by a special consolidation method with albumin as a foam generating agent. This technique enables preparation a variety of formats with complex geometries. To obtain porous samples using albumin, heat had to be introduced into the system during the consolidation stage. After consolidation, the samples were sintered at 1250oC for 30 minutes and characterized using X-ray diffractometry, scanning electron microscopy and mercury porosimetry. The foams that were obtained by this method exhibited spherical and interconnected pores, characteristics desirable in biomedical implants.

Abstract: We have previously reported that the carbonate apatite (CAP) foam that has similarities in both inorganic chemical composition and morphology to cancellous bone could be prepared from α-tricalcium phosphate (α-TCP) foam by the hydrothermal treatment with Na2CO3 at 200°C for 24 hrs. However, the crystallinity of the CAP foam was much higher than that of bone. In order to prepare CAP foam similar to cancellous bone in crystallinity as well as its inorganic composition and morphology, this study attempted to prepare CAP foam at lower temperature. Hydrothermal treatment at 100°C allowed low-crystalline CAP foam whereas longer period was imposed for complete conversion of α-TCP foam into CAP foam.

Abstract: Long-term studies in the non-human primate Papio ursinus were set to investigate the induction of bone formation in biphasic hydroxyapatite tricalcium phosphate (HA/TCP) biomimetic matrices, 20/80 and 40/60, respectively. Biomimetic matrices were implanted in the rectus abdominis and in calvarial defects of 4 adult Papio ursinus. Morphological analyses on day 90 and 365 showed significant induction of bone formation within concavities of the biomimetic matrices implanted in both heterotopic and orthotopic sites with resorption of the implanted biomimetic matrices. The smart biomimetic matrices induced de novo bone formation even in the absence of exogenously applied osteogenic proteins of the transforming growth factor-β superfamily.

Abstract: Dense and porous HA and Si-HA discs and granules with varying percentages of silicon substitution have been produced and physically and chemically characterised using scanning electron microscopy, surface area analysis, porosimetry, density measurement, image analysis, Xray diffraction, X-ray fluorescence, FT-infrared spectroscopy and in-vitro and in-vivo testing. Results have shown that cell adhesion in-vitro and bone apposition in-vivo are enhanced by the presence of silicon substitution in the hydroxyapatite structure. The biological response to the materials appears to indicate an optimum outcome for levels of silicon substitution of 0.8wt%.

Abstract: Porous materials of β-tricalcium phosphate (β-Ca3(PO4)2; β-TCP) were prepared from porous hydroxyapatite (Ca10(PO4)6(OH)2; HA) with calcium deficient composition of Ca/P molar ratio of 1.50 synthesized by hydrothermal method. The porous β-TCP was 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 particle size and micro-pore size could be controlled by our unique method. It must be suitable for the bone graft material and as the scaffold of cultured bone.

Abstract: The present study was designed to investigate the mechanism of in vivo conversion from synthetic octacalcium phosphate (OCP) into hydroxyapatite (HA) at ultrastructural level, where the implanted OCP is enhancing bone regeneration in mouse calvarial bone defect. OCP granules were implanted into the subperiosteal area of the calvaria of 7-week-old BALB/c mice for 3 weeks. Transmission electron microscopy of undecalcified frontal sections, obtained from the acrylic resin-embedded skull specimens showed that the bone crystals in newly formed bone directly bonded to the OCP particles implanted. The morphological characteristic of original plate-like OCP particles was remained unchanged even after the implantation, whereas a number of de novo nano-particles were also directly formed onto the plate-like OCP particles. Some of OCP particles were linked with other OCP particles through these nano-particles. The results suggest that the OCP-apatite conversion, involving the enhanced bone regeneration, advances via topotaxial conversion without changing the original OCP morphology, accompanied by solution-mediated de novo nano-apatite formation, in the vicinity of the implanted OCP particles.

Abstract: Since 2001, we have clinically utilized human bone marrow-derived mesenchymal stem cells (MSCs) for bone regeneration. The osteogenic ability of MSCs has been assessed by measurement of alkaline phosphatase activity and calcium deposition. As for the detection of in vitro calcium deposition, we have established the method using calcein, which is a calcium-binding fluorescence material. Using this fluorescence material, we could observe the calcium deposition and then estimate the value of calcium deposition. In this report, we cultured rat MSCs on culture plate as well as transparent β-TCP, and calcium deposition was visualized and quantitated using an image analyzer. After 2 weeks differentiation of rat MSCs to osteoblasts, calcium deposition on β-TCP was observed as a signal of calcium-binding fluorescence. This fluorescence signal was also quantitated with an image analyzer.

Abstract: We recently developed a new biomimetic calcium phosphate bone cement enriched with gelatin (GEL-CP) which exhibits improved mechanical properties with respect to the control cement (C-CP) and a good response to osteoblast-like cells. In this work, we have extended the investigation to primary culture of osteoblasts derived from normal (N-OB) and osteopenic (O-OB) sheep bones cultured on samples of GEL-CP, and their behavior was compared to that of cells cultured on C-CP as control. Cell morphology, proliferation, and differentiation were evaluated at 3 and 7 days. Preliminary in vivo tests were carried out onto critical size defects in the radius diaphysis of rats.