Jacinto P. Borrajo

A new generation of bio-derived ceramic materials for medical applications

A new generation of bio-derived ceramics can be developed as a base material for medical implants. Specific plant species are used as templates on which innovative transformation processes can modify the chemical composition maintaining the original biostructure. Building on the outstanding mechanical properties of the starting lignocellulosic templates, it is possible to develop lightweight and high-strength scaffolds for bone substitution. In vitro and in vivo experiments demonstrate the excellent biocompatibility of this new silicon carbide material (bioSiC) and how it gets colonized by the hosting bone tissue because of its unique interconnected hierarchic porosity, which opens the door to new biomedical applications.

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

Marine Precursors-Based Biomorphic SiC Ceramics

Biomorphic silicon carbide ceramics is very promising as a natural base material for biomedical applications due to their excellent mechanical-biochemical properties and biocompatible behaviour. This innovative material is produced by molten-Si infiltration of carbon templates obtained by controlled pyrolysis of biological precursors. The final product is a light, tough and high-strength material with predictable microstructure. In this study the possibility to produce biomorphic silicon carbide ceramics using marine precursors is demonstrated. Due to the great biodiversity offered by the marine medium, a previous selection of algae (Laminaria ochroleuca Bachelot de la Pylaie, Undaria pinnatifida (Harvey) Suringar, Saccorhiza polyschides (Lightfoot) Batters and Cystoseira baccata (Gmelin) Silva) and marine plants (Zostera marina L. and Juncus maritimus L.) was carried out, taking into account its microstructure, porosity and interconnectivity of each species. The bioceramization process was evaluated in three phases: original material analysis, pyrolysis process and reactive melt Si-infiltration. For each marine precursor, a detailed study by Scanning Electron Microscopy (SEM) of the natural material, the carbon preform and the final SiC biomorphic product is described. The viability to obtain biomorphic SiC ceramic material for all the selected marine precursors is discussed.

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.

Bioceramic Coatings on Biomorphic SiC by Electrophoretic Deposition

In this research, bioactive glass powders were electrophoretically deposited on biomorphic SiC ceramic substrates. A post-deposition thermal treatment was carried out to improve the properties of the coatings. Particle size, surface morphology, composition and thickness of the coatings have been studied by Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and interferometric profilometry respectively. The analysis demonstrated that the electrophoresis parameters, such as the voltage, the distance between the electrodes and the deposition time, play an important role on the thickness of the coatings. The post-deposition thermal treatment produces glass particles cohesion and leads to obtaining a homogeneous microstructure. The excellent coverage of the porous SiC surface morphology is also demonstrated. Finally, in order to assess the bioactive character of the glass coatings, in vitro test by immersion in simulated body fluid (SBF) was carried out.

Influence of Substrate Temperature in Plasma Assisted Pulsed Laser Deposition of Hydroxyapatite Thin Films

The bioactive properties of hydroxyapatite (HA) are well known in the implant industry and coatings of HA have been used to enhance the adhesion of living tissue to metal prostheses. Pulsed laser deposition (PLD) in a water vapour atmosphere is an appropriate method for the production of crystalline HA coatings. In this work the effect of RF plasma on thin films of HA grown by PLD at different substrate temperatures has been studied. The physicochemical properties of the films were studied by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS), showing that the incorporation of RF discharge in the deposition chamber can lead to changes in the crystallinity and deposition rate of the films but substrate temperature still plays the most important role.

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.