Key Engineering Materials Vols. 396-398

Abstract: Porous scaffolds, consisted of hydroxyapatite (HAp), chondroitinsulfate (ChS) and collagen, were prepared by freeze-drying technique. HAp/ChS composite particles were incorporated into a collagen matrix. Scanning electron microscope (SEM) observations showed that the porous scaffolds involved interconnected pores whose size was 80~200 µm in diameter. The HAp/ChS particles were homogeneously distributed in the collagen matrix. Surface area of the scaffolds was increased by the incorporation of the particles. Compression tests in phosphate buffer saline indicated that the porous scaffolds had elastic property and had larger compressive modulus than the pure collagen scaffold. The porous scaffolds obtained in this study could be useful for a cartilage tissue engineering.

Abstract: The synthetic nanostructured HA powder was prepared by the reaction of calcium hydroxide Ca(OH)2 aqueous solution and phosphoric acid H3PO4. The powders were foamed using hydrogen peroxide and heat treated at temperatures ranging from 120 to 700°C. Bovine deproteinized bone BioOss was used as a reference material. Elemental analysis, X-ray diffraction, chemical analysis, differential thermal analysis, scanning electron microscopy, gas adsorption and mercury porosimetry were used to characterize the precipitates. In vitro cytotoxicity test and the preclinical evaluation of this material were performed. In vivo tests were carried out in the tibiae of beagle dogs. All animals were euthanized 3 and 6 months after implantation. The material degradation and new bone formation was observed. The process of precipitation and coagulation can be applied to obtain pure synthetic HA powder. Foaming with H2O2 represents a method suitable to produce HA material with higher surface area and porosity. The physico-chemical properties of HA granules and in vivo tests determined that synthetic scaffold is comparable with bovine bone material. No significant differences between synthetic HA150 scaffolds and bovine bone BioOss were observed in vivo. The heat treatment of HA results in slower resorption and remodeling.

Abstract: The extracellular matrix in skeletal tissue besides being responsible for its structure and function also provides key regulatory signals for cell proliferation and differentiation by interacting directly with cell receptors, controlling the diffusion of soluble growth factors. Immature bone marrow cells can migrate through capillaries to systemic circulation as well as return to bone marrow. This phenomenon is the biological basis for bone marrow transplant. The mechanisms that control the migration and the return of these immature bone marrow cells are still to be described in a generally accepted model. Thirty days-old Wistar rats were employed as recipients for the implantation of ceramic blocks or demineralized femur diaphysis. The material was implanted subcutaneously at the dorsum. The rats were euthanized with CO2 at 15, 40 and 68 days after implantation. The whole area of implantation was harvested from skin deep up to the muscle. Liver, spleen, lungs, femurs and the vertebral spine, ribs and sternum were also harvested. The harvested material was fixed in Millonig formalin and decalcified with EDTA, if applicable. The material was then progressively dehydrated in alcohol, immersed in xylol, impregnated and embedded in paraffin. The paraffin blocks were then sliced in 5µm sections with a microtome, stained in Haematoxilin – Eosin, Lennert's Giemsa and Gomori's reticulin for histological analysis under brightfield optical microscopy. All implants produced an intense fibroblastic reaction, angiogenesis and subsequent modulation into a loose stroma. However, hematopoesis was not observed. Implantation of endogenous haematopoetic cells in an inductive stroma, which might propitiate hematopoesis is a model scarcely studied. Experiments such as the one described here might be good models for understanding the sequence of events leading to formation of the stroma and implantation and differentiation of haematopoetic precursors.

Abstract: Neutron brachytherapy show better results than conventional photon therapy for radioresistant tumors with hypoxic regions. Herein a comparative radiodosimetric analysis is presented considering 125I photon emitter seeds, often applied to brachytherapy, and a proposed Sol-Gel glass, synthesized with incorporated 252Cf neutron emitter, on a brain tumor implant. The proposition is to verify the viability of applying this bioceramic material. The methodology is based on the investigation of the specific energy deposition (dose) from 252Cf-Glass in deep brain interstitial implants through a stochastic computer code (MCNP5) and comparison with 125I seed’s energy deposition. 252Cf-Glass show dose per transition values higher than 125I seed’s set. RBE-isodose curves show a faster decrease of dose with the source distance increasing which can improve healthy tissue sparing.

Abstract: Series of TiO2-SiO2 films with a silica content of 70 mol% were prepared on glass slides by dip-coating method. The mixed sols were prepared via prehydrolyzing of the titania sol in different acidity. The surface chemistry was analyzed by XPS and the topography by AFM. Dissolution of silica was performed in TRIS buffer and the stability of the coatings was tested in simulated body fluid (SBF). The coatings remained crack-free after the TRIS and SBF tests. The formed nanostructure was practically same in all surfaces. The dissolution of silica was slightly increased with the increased acidity of the titania sol. Furthermore, the binding energies (BEs) of the Si(2p) and Ti(2p3/2) peaks obtained from XPS were both shifted upward with increased acidity of the sol. The sol-gel titania-silica materials made with prehydrolyzed titania formed heterogeneous structure where the TiO2 and SiO2 particles were partly interconnected and covered with soluble silica.

Abstract: The effect of substitution of zinc into the hydroxyapatite lattice(ZnHA) was evaluated using experimental precipitation studies and with ab initio modelling data. When attempting to introduce zinc into the hydroxyapatite (HA) lattice not all of the zinc is substituted and ICP confirms its presence in the supernatant. Modelling suggests that this is likely to be because of the high formation energy introducing zinc into the pure hydroxyapatite lattice, 4.6 - 4.9eV. In the experimental study it was found that a maximum of 0.61wt% zinc could be substituted into the HA lattice at 10oC with less being substituted at room temperature »22oC. Experimental measurements revealed that the presence of zinc in the lattice decreased the a-lattice parameter and increased the c-lattice parameter. Modelling showed that this was likely to be caused by the movement of the hydroxyl ions away from the c-axis, towards the zinc atoms which were substituted in calcium type II positions. The type II position was shown to be the most stable substitution site.