Key Engineering Materials Vols. 396-398

Abstract: Hydroxyapatite powder is produced using combustion synthesis method. The powder was produced using a low-temperature processing method involving time as short as 15 minutes. As silver is known to have anti-bacterial properties, silver-doped hydroxyapatite was also produced by the same method. Both the powders were fully crystalline. XRD indicated the presence of an additional phase of CaO in both the samples. FT-IR indicated the presence of hydroxide, phosphate and carbonate groups. Silver addition tends to control the reactions of powder with a test Tris buffer environment and maintain a stable pH for a longer period of 500-hour duration.

Abstract: The aim of this work is to develop membranes of gelatin/hydorxyapatite composite for using as mechanical barrier. Membranes with 4% of gelatin and 0.5-3% of hydroxyapatite were studied. The composite was obtained by heterogeneous co-precipitation method. X-ray diffractometry showed the formation of a pure phase of hydroxyapatite with excellent crystallinity. Using atomic force microscopy, the distribution of crystals of hydroxyapatite in the gelatin matrix was observed, with nanoparticles of about 50-100nm in a homogeneous mixture. After crosslinking process with glutaraldehyde at different concentrations (0.5, 1, 1.5 and 2%), a significant decrease of the swelling behavior was observed due to the increase of the amount of triple helix in the samples, which increases their stability in aqueous solution.

Abstract: Composites based on hydroxyapatite (HA) and collagen are being used for bone engineering applications. Synthetic composites were produced by precipitating hydroxyapatite in a reaction medium containing collagen fibers. The effect of saline treatment during the procedure of fibrils extraction on the composite morphology, phases presented and in vitro stability was evaluated. The FTIR analysis showed collagen bands well preserved. By Rietveld analysis, additional peaks of sodium chloride were identified on sample made from collagen submitted to saline precipitation. Besides that, the mineral formed phase is a carbonated apatite. This step during fibrils extraction results in larger areas of collagen uncoated and higher stability in culture medium. Despite of this, a cross-linking agent will be necessary to maintain the composite in culture for longer times.

Abstract: The aim of this study was to determine the biaxial flexure strength of a commercially available dental pulp capping or cavity liner material, mineral trioxide aggregate (MTA). MTA and a conventional pulp capping material, calcium hydroxide, were used in this study. Each material was prepared into a disk-shaped specimen. Those specimens were stored in 100% humidity atmosphere at 23 or 37°C for 3 or 24 h. Six specimens in each condition were used for the biaxial flexure test using a piston-on-three-ball according to ISO-6872. Surface pH values were determined. The biaxial flexure strengths of MTA after setting in 24h were larger than those of Dycal (p <0.01). pH value of MTA was higher than that of Dycal. These results indicated that MTA was clinically usage material.

Abstract: Apatite nuclei were dispersed in inorganic binder and the apatite nuclei-contained inorganic binder was coated on polyethyleneterephthalate plate. Hydroxyapatite was induced by the apatite nuclei dispersed in the binder and hydroxyapatite layer was formed on the surface of the substrate by soaking in SBF. The hydroxyapatite layer showed high adhesive strength to the substrate.

Abstract: Silks are naturally occurring polymers and fibroin, its filament core protein, has been shown to support stem cell differentiation in vitro, and promote tissue repair in vivo. The aim of this study is to develop a biomaterial based on silk-fibroin fibers that can be associated with mesenchymal progenitor cells from human perichondrium in vitro, in order to promote auricular reconstruction in vivo. Silk-fibroin concentrate was dissolved with formic acid solution and freeze-dried in auricular moulds. Fibroin-based material was characterized by scanning electron microscopy and by cytotoxic assays. Perichondrium mesenchymal progenitor cells were characterized by flow cytometry. They expressed the standard mesenchymal stem cell markers, and were able to differentiate into several mesenchymal lineages in vitro. This fibroin-based material is a three-dimensional fibrillar scaffold, non-woven and biocompatible, which was also well integrated with alginate and mesenchymal cells.

Abstract: Bone is a kind of biomaterial in nature. It behaves favorable strength, stiffness and fracture toughness which are closely related to its fine microstructures. Scanning electron microscope (SEM) observation on a shinbone shows that the bone is a kind of natural bioceramic composite consisting of hydroxyapatite layers and collagen matrix. The hydroxyapatite layers are arranged in a parallel distribution and consist of many hydroxyapatite sheets. The fracture toughness of the bone was analyzed based on the representative model of the microstructure in the bone and the idea of maximum pullout energy. The analytical result shows that the long and thin shape as well as the parallel distribution of the hydroxyapatite sheets increase the maximum pullout energy of the sheets and enhance the fracture toughness of the bone.

Abstract: With good biocompatibility, collagen is often used in cartilage tissue engineering. Collagen/alginate composite was hoped to improve the poor mechanical property of pure collagen but the biocompatibity was decreased. In this study, hydroxyapatite (HA) particles were used to get collagen/alginate/HA (CAHA) composite film to enhance the bioactivity properties. The bioactivity of the composite was investigated by in vitro co-culture with chondrocytes. During the 6-day cell culture in vitro, the composite showed a significant improvement in promoting proliferation and maintaining morphology/phenotype of the chondrocytes over collagen/alginate composite by MTT, SEM, fluorescent and immunohistochemical assays. Cytocompatibility and cytoviablility of CAHA even come up to that of collagen film alone. The results indicated that the composite film may provide an appropriate environment for the proliferation and maintaining the morphology and phenotype of chondrocytes and have a potential clinical application in the cartilage tissue engineering field.

Abstract: Osteoclast differentiation of bone marrow cells on hydroxyapatite/collagen self-organized bone-like nanocomposite (HAp/Col) disk in vitro was evaluated by coculture of mouse bone marrow cells with mouse osteoblasts with or without addition of osteoclastic inducers, 1,25-Dihydroxyvitamin D3 and 1 µM prostaglandin E2. Dentine slice and tissue culture polystyrene were used as controls. Good osteoclastic differentiation at day 7 were observed among the bone marrow cells cultured on the HAp /Col disk and controls with osteoclastic inducers. On the contrary, osteoclastic differentiation was observed only for marrow cells cultured on the HAp/Col disk. Nano- and micro- structures as well as chemical and mechanical properties have a potential to control cell differentiation.

Abstract: Scanning electron microscope (SEM) observation shows that Solid-trough shell is a kind of bioceramic composite consisting of laminated aragonite and organic materials. The aragonite layers are parallel with the surface of the shell and consist of numerous thin and long aragonite fibers. The aragonite fibers in an arbitrary aragonite layers possess different directions and compose a kind of screwy microstructure. The maximum pullout force of the screwy microstructure was investigated and compared with that of parallel microstructure based on their representative models. It shows that the maximum pullout force of the screwy microstructure is markedly larger than that of the parallel microstructure, which was experimentally validated.