S. Liste

Influence of the non-bridging oxygen groups on the bioactivity of silicate glasses

The effect of the composition and bonding configuration of the bioactive silica-based glasses on the initial stage in vitro bioactivity is presented. Information of the IR active Si–O groups of glass in the system SiO2–P2O5–CaO–Na2O–K2O–MgO–B2O3 was obtained by fourier transform Infrared (FTIR) spectroscopy. Two different bands associated to non-bridging oxygen stretching vibrations (Si–O–1NBO and Si–O–2NBO) and a gradual shifting of the bridging oxygen stretching vibration (Si–O) have been observed and evaluated. Both effects are attributed to a decrease of the local symmetry originating from the incorporation of alkali ions into the vitreous silica network. The Si–O–NBO(s)/Si–O(s) absorbance intensity ratio increases with a gradual incorporation of the alkali ions (diminution of SiO2 content) following a linear dependence up to values close to 50 wt % of SiO2. In vitro test analysis by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDXA) showed a correlation between the amount and type of the non-bridging oxygen functional groups and the growth of the silica-rich and CaP layers. It was found that a minimum concentration of Si–O–NBO bonds in the glass network is required in order to have an efficient ion exchange and dissolution of the silica network. Finally, the bioactivity of the glass is favored by the presence of the Si–O–2NBO groups in the glassy network. The role of these functional groups in the dissolution of the silica network through the formation of silanol groups and the adsorption of water is discussed.

Raman spectroscopic study of bioactive silica based glasses

Abstract A study of the structure and bonding configuration of the bioactive glasses in the system Na2O–CaO–P2O5–SiO2 by Fourier transform Raman spectroscopy is presented. The assignment of the Raman lines, the changes in the Si–O–Si bond environment and the identification of the non-bridging silicon–oxygen groups (Si–O–NBO) for a wide range of silicate glasses are discussed. The frequency shifting and intensity variations of the Raman lines as a function of the bioactive glass composition are attributed to a decrease of the local symmetry originated by the addition of alkali and alkali earth oxides to the vitreous silica network. Correlation plots for the quantification of the Si–O–NBO groups as a function of the glass composition are also presented. These Raman analyses contribute to a better knowledge of the structural role of the network modifiers in the bioactive glasses and, as a consequence, improve the understanding of the bioactive process and the chemical routes of the CaP layer formation when exposed body fluids.

Extensive studies on biomorphic SiC ceramics properties for medical applications

Biomorphic silicon carbide ceramics are light, tough and high-strengt h materials with interesting biomedical applications. The fabrication method of the biomor phic SiC is based in the infiltration of molten-Si in carbon preforms with open porosity. The fina l product is a biostructure formed by a tangle of SiC fibers. This innovative process allows the fabrication of complex shapes and the tailoring of SiC ceramics with optimised properties and cont rollable microstructures that will match the biomechanical requirements of the natural host tiss ue. An interdisciplinary approach of the biomorphic SiC fabricated from beech, sapelly and eucalyptus is presented. Their mechanical properties, microstructure and chemical composition were evaluated. The biocompatible behaviour of these materials has been tested in vitro .

Influence of the Network Modifier Content on the Bioactivity of Silicate Glasses

The influence of the substitution of calcium oxide for sodium oxide in the composition of silica-based glasses on the in vitro bioactivity is presented. Valuable information on the active Si-O groups present in the glasses is obtained by Fourier Transform Ra man and Infrared spectroscopies. In vitro test analysis by Scanning Electron Microscopy and Energy Dis persive X-ray Analysis show a correlation between the network disruption induced by the modifier type and the bioactive process. It is demonstrated that glasses with high SiO 2 content can be bioactive depending on the alkali/alkali-earth modifiers ratio included into the vitreous silica network. Introduction Bioactive glasses are interesting materials for medical pur poses due to their ability to bond chemically to living bone and soft tissues when soaked in physiologica l fluids [1, 2]. The clinical applications of bioactive glasses are numerous, especially in maxi llofacial reconstruction, otorhinolaryngology, oral surgery and periodontal repair [1]. The bioactive silica-based glass network is basically the same of vitreous silica, where the structural units consist of slightly distorted SiO 4 tetrahedra. This structure enables the accommodation of alkali and alkali-earth cations which create non-bridging oxygen s it s (Si-O-NBO) throughout the glass network [3]. When the bioactive glasses are soaked in human plasma or an analogous solution, it is known that a partial dissolution of the glass surface oc urs leading to the formation of a silica-rich gel layer and, subsequently, the precipitation of a c alcium phosphate film on the bioactive material takes place. The formation rate of this lay er is a critical parameter, which is directly related to the type and content of the network modifiers [1]. Several spectroscopic techniques, such as Infrared and Raman spectrosc opies, are sensitive to changes in the composition and the bonding configuration of the glasses, and they provide valuable information on the local structure of the silicate glasses. Thus, the aim of this work is to evaluate, through spectroscopic tec hniques and in vitro tests, the role of content and type of network modifiers on the bioactivity of silica-based gla sses. Materials and methods Glasses of different compositions in the quaternary system Na 2O-C O-P2O5-SiO2, with a systematic substitution of CaO and Na 2O concentrations, have been investigated (Table 1). Glasses were obtained by melting the appropriate quantities of analytical grade CaCO3, Na2CO3, CaHPO4·2H2O and commercial Belgian quartz sand in a Pt-crucible at 1360 oC for 3 h. The glasses were cast, annealed, crushed, and remelted to improve homogeneity. In the final casting, a graphite mould of 20 mm diameter and 100 mm long was used. The test pieces were obtai ned by sawing discs of 2 mm thick. The discs were washed and stored in ethanol. The structure of the glasses was studied by X-ray Diffract ion (XRD). Information on the active SiO groups present in the glasses was obtained by Fourier Transfor m Infrared (FTIR) and Raman spectroscopies. Key Engineering Materials Online: 2003-12-15 ISSN: 1662-9795, Vols. 254-256, pp 23-26 doi:10.4028/www.scientific.net/KEM.254-256.23

Biomorphic Silicon Carbide Ceramics Coated with Bioactive Glass for Medical Applications

There is a need to develop new tough bioactive materials capable to withstand high loads when implanted in the body and with improved fixation, which led to the production of bioactive coatings on metallic substrates. A new approach, which consists of biomorphic silicon carbide (SiC) coated with bioactive glass, was recently presented. This new material joins the high mechanical strength, lightness and porosity of biomorphic SiC, and the bioactive properties of PLD glass films. In this work, a multiple evaluation in terms of biocompatibility of this new material was carried out starting from the biomorphic SiC morphology and porosity, following with the bioactivity of the coatings in simulated body fluid, and ending with a deep biocompatibility study with MG-63 cells. Different ranges of porosity and pore size were offered by the biomorphic SiC depending on the starting wood. The PLD glassy coatings had a high bioactivity in vitro and both the biomorphic SiC coated and uncoated presented high levels of biocompatibility.

Evaluation of the Glass Bioactivity Grade by IR Analysis and the Stevels Parameter

The structure of silica-based glasses consists on a disrupted network of SiO4 tetrahedra where network modifiers generate non-bridging oxygen groups (NBO), that play an important role at the initial steps of the bioactive process. Infrared spectroscopy is a sensitive technique to the presence of NBO groups and glass local structure modifications. The infrared study has been complemented with a theoretical approach using the Y Stevels parameter. Moreover, the in vitro bioactivity of the glasses as a function of Y Stevels paremeter has been studied, which can be a finding of a predictive tool for bioactivity of glasses.

In Vitro Bioactivity Study of PLD-Coatings and Bulk Bioactive Glasses

Bioactive glass coatings have been obtained by Pulsed Laser Deposition (PLD) from bulk glasses of different compositions in the system SiO 2-Na2O-K2O-CaO-MgO-P2O5-B2O3. A comparative study of the in vitro bioactive behaviour of the PLD-coatings and bulk glasses was carried out. Fourier Transform Infrared and X-ray Induced Photoele ctron Spectroscopies show that the bonding configuration of the bulk glasses is not congruently trans fe red to the coatings during the ablation process. These results are in agreement with the in vitro tests that show a similar bioactive process but a different bioactivity grade between the bulk glasses and the corresponding PLD coatings. The composition and bonding configuration of the bioactive coa tings grown by PLD should be carefully tuned in order to obtain an adequate biological response.

In Vitro Cytotoxicity Testing of Wood-Based Biomorphic SiC Ceramics

The aim of this study was to test the in vitro cytotoxicity of wood-based biomorphic Silicon Carbide (SiC) ceramics, using MG-63 human osteoblast-like cells. This innovative material has been recently developed and it exhibits unique mechanical properties towards their application in biomedical technology. In the solvent extraction test the SiC ceramic extracts had almost no effect on cellular activity even at 100% concentration. A similar behaviour was found for Ti6Al4V and bioactive glass, used as reference materials. The results of the cell morphology and the cellular attachment response have also demonstrated that the in vitro performance of these biomorphic SiC ceramics is qualitatively comparable to that produced by titanium alloy and bioactive glass, which seems very promising.