Papers by Author: Marivalda Pereira

Abstract: Bioactive glass/polymer hybrids are promising materials for biomedical applications because they combine the bioactivity of these bioceramics with the flexibility of polymers. In previous work hybrid foams with 50% bioactive glass and 50% polyvinyl alcohol (PVA) were prepared by the sol-gel process for application as scaffold for bone tissue engineering. In this work the hybrid samples were tested in osteoblast culture to evaluate adhesion and proliferation. Samples were also implanted subcutaneously in the dorsal region of adult rats. The hybrid 50% PVA/bioactive glass foam was chosen as the best scaffold in the composition range studied and it is a promising material for bone repair, providing a good environment for the adhesion and proliferation of osteoblasts in vitro. Concerning the in vivo studies we can assure that the “foreing body” reaction was moderate and that the presence of osteoid indicated bone matrix formation.

Abstract: The cementum, a mineralized tissue lining the tooth root surface, is required for development of a functional periodontal ligament. The presence of healthy cementum is considered to be an important criterion for predictable restoration of periodontal tissues lost as a consequence of disease. Despite the importance of cementum to general oral health, very little is known about the cells responsible for the formation of cementum, cementoblasts. The aim of this study was to examine the effect of the ionic products from the dissolution of bioactive glass with 60% of silica ( BG60S ) on the behavior of cementoblasts, osteoblasts and fibroblasts. The cell viability was tested by MTT assay based on mitochondria activity of the cell and Trypan Blue assay based on membrane cell viability. The membrane cell viability measured by Trypan Blue assay showed the beneficial effect on all the cell types tested. It was observed a higher proliferation in the presence of ionic products from dissolution of BG60S when compared to control. In the MTT assay we also observed increased cell viability on all the cell types, but proliferation of cementoblasts was higher (107%) than observed for the other cells (104%) compared to control. The results from this study suggest that Cementoblasts, osteoblasts and fibroblasts are important cells on events that control the development of mineralizing and not mineralizing tissues and the investigation of the comparative behavior of these cells can be a useful experimental model. The observed effect of the bioactive glass particles on cementoblasts shows that this material is an interesting alternative to be used in composite membranes for cementum tissue engineering.

Abstract: Bioactive glasses are materials that have been used for the repair and reconstruction of diseased bone tissues, as they exhibit direct bonding with human bone tissues. However, bioactive glasses have low mechanical properties compared to cortical and cancellous bone. On the other hand, composite materials of biodegradable polymers with inorganic bioactive glasses are of particular interest to engineered scaffolds because they often show an excellent balance between strength and toughness and usually improved characteristics compared to their individual components. Composite bioactive glass-polyvinyl alcohol foams for use as scaffolds in tissue engineering were previously developed using the sol-gel route. The goal of this work was the synthesis of composite foams modified with higher amounts of PVA. Samples were characterized by morphological and chemical analysis. The mechanical behavior of the obtained materials was also investigated. The degree of hydrolysis of PVA, concentration of PVA solution and different PVA-bioactive glass composition ratios affect the synthesis procedure. Foams with up to 80 wt% polymer content were obtained. The hybrid scaffolds obtained exhibited macroporous structure with pore size varying from 50 to 600 µm and improved mechanical properties.

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: Bioactive glass/polymer hybrids are promising materials for biomedical applications because they combine the bioactivity of these bioceramics with the flexibility of polymers. In previous work hybrid foams with 80% bioactive glass and 20% polyvinyl alcohol (PVA) were prepared by the sol-gel process for application as scaffold for bone tissue engineering. In this work it was evaluated the effect of increasing the PVA content of the hybrids on structural characteristics and mechanical properties of hybrid foams produced by this method. The hybrids were prepared with inorganic phase composition of 70%SiO2-30%CaO and PVA fractions of 20 to 60% by the sol-gel method. The structural and mechanical characterization of the obtained foams was done by FTIR, SEM, Helium Picnometry, and compression tests. To reduce the acidic character of the hybrids due to the catalysts added, different neutralization solutions were tested. The immersion of hybrids in a calcium acetate solution was the most adequate neutralization method, avoiding calcium loss while maintaining pH nearly 7,0 and low PVA loss. The foams presented porosity of 60-85% and pore diameters of 100-500μm with interconnected structure. The pore structure varied with the polymer content in the hybrid. The compression tests showed that an increase of PVA fraction in the hybrids improved their mechanical properties.

Abstract: Porous scaffolds have been developed in many forms and materials, but few have reached the combination of adequate physical, biological and mechanical properties. In previous works hybrid foams bioactive glass polyvinyl alcohol (PVA) were prepared by the sol-gel process for application as scaffold for bone tissue engineering. We observed that synthesis parameters such as PVA hydrolysis grade, PVA solution concentration, and PVA content in the hybrids affected both synthesis results and structural characteristics of the obtained foams. A marked change in foaming behavior occurs for PVA contents around 60%. In this work we analyze the effect of different compositions and synthesis parameters on the mechanical behavior of PVA-bioative glass foams. The compression tests showed that an increase of PVA fraction changes the mechanical behavior due to different mechanisms leading to cell collapse. For hybrids with lower PVA contents (20 to 30%) the cell collapse is due to brittle crushing. For intermediate polymer content (40-60%) the contribution of plastic yielding in the plateau region increases and it becomes the predominant mechanism of cell collapse for samples with higher polymer content (70-80%).

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: The possibility of enhancing mechanical properties by incorporation of polymeric components to sol-gel derived materials is extremely attractive to prepare macroporous scaffolds, leading to materials with potential applications in both hard and soft tissue regeneration. In this work bioactive glass-polyvinyl alcohol hybrids were developed and their mechanical behavior was evaluated. Hybrids were synthesized by adding polyvinyl alcohol to a sol-gel precursor solution, which was then foamed with the addition of a surfactant and vigorous agitation. The foams were cast, aged and dried at 40°C. A cleaning step to decrease the acidic character of the obtained hybrids was undertaken by immersion in a NH4OH solution. The mechanical behavior of the hybrids was evaluated in compression using both stress and strain control tests. Hybrid foams had a high porosity varying from 60-90% and the macropore diameter ranged from 10 to 600 µm. The modal macropore diameter varied with the inorganic phase composition and with the polymer content in the hybrid. The strain at fracture of the as prepared hybrid foams was substantially greater than pure gel-glass foams. The cleaned hybrids presented a slightly higher strength and lower deformation than the as prepared foams.

Abstract: Hybrid bioactive glass-polyvinyl alcohol foams for use as scaffolds in tissue engineering were developed through the sol-gel route. Hybrids produced by this route present a high acidic character due to the catalysts added during processing and may also contain residual organics after the drying step. Therefore, an additional cleaning step is necessary to produce biocompatible materials. In this study hybrid PVA/bioactive glass foams were cleaned using various procedures and cytotoxicity evaluation was conducted. All the cleaning methods used increased the cell viability levels compared to samples not subjected to a cleaning procedure. The most effective cleaning procedure used was the immersion in NH4OH solution. The cleaning procedure changed the composition and pore structure of the final material.

Abstract: Osteoblasts constitutively release glutamate and this release appears to be regulated by calcium entry. In this work we investigated if the bioactive glass with 60% of silicon (BG60S) could alter glutamate release by osteoblasts. We demonstrated that osteoblasts incubated with medium containing ionic products from the dissolution of BG60S showed lower release of glutamate when compared to control. Since intracellular calcium (Cai 2+) increase is required for glutamate release we investigated the subcellular distribution of the calcium channel inositol triphosphate receptors (InsP3Rs) in the presence of BG60S compared to control. We found that the type-III InsP3R was not expressed in osteoblast, while the type-II InsP3R was expressed mainly in the cytosol. We also found that the expression of type-II InsP3R decreased in BG60S treated osteoblasts compared to control. On the other hand, we found that the type-I InsP3R was expressed mainly in the nucleus and its expression increased in the presence of the biomaterial.