P. González

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.

Novel selenium‐doped hydroxyapatite coatings for biomedical applications

Nowadays there is a short-term need of investigating in orthopedic implants with a greater functionality, including an improved osseointegration and also antibacterial properties. The coating of metallic implants with hydroxyapatite (HA) remains to be the main proposal, but superior quality HA coatings with compositions closer to natural bone apatites, including carbonates, trace elements are required. Selenium is an essential nutrient in biological tissues and, at the same time, it also presents antibacterial properties. A pioneering study on the fabrication of selenium-doped carbonated hydroxyapatite (iHA:Se) coatings by Pulsed Laser Deposition (PLD) is presented. Different proportions of selenium were incorporated to obtain the iHA:Se coatings. Their physicochemical characterization, performed by SEM/EDS, FTIR, FT-Raman, Interferometric Profilometry and XPS, revealed typical columnar growth of HA in globular aggregates and the efficient incorporation of selenium into the HA coatings by the, most probably, substitution of SeO(3)(2-) groups in the CO(3)(2-) sites. Biological evaluation illustrated the absence of cytotoxicity when an amount of 0.6 at.% of Se was added to the iHA:Se coatings and excellent proliferation of the MC3T3-E1 preosteoblasts. Antibacterial properties were also proved with the inhibition of P. aeruginosa and S. aureus from establishing bacterial biofilms.

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.

Carbon nitride films prepared by excimer laser ablation

The preparation of carbon nitride films by laser ablation of graphite in ammonia atmosphere is reported. Experiments were performed at room temperature under different NH3 total pressures using an ArF excimer laser (193 nm). The films were deposited on silicon and metal substrates from the ablated carbon radicals and the species generated by the ammonia photodissociation under the laser VUV photons. Profilometry and ellipsometry show an evolution of the growth rate and refractive index. Energy dispersive X-ray and Fourier transform infrared spectroscopies reveal a gradual incorporation of nitrogen in the films for increasing ammonia concentration. Furthermore, infrared spectra show the presence of CN and C–N groups and the incorporation of hydrogen bonded to carbon and nitrogen. These observations were corroborated by Raman spectroscopy and hydrogen effusion.

Photo-induced chemical vapour deposition of silicon oxide thin films

A review of the photo-induced chemical vapour deposition (photo-CVD) processes yielding silicon oxide thin films that have emerged in the last decade is presented. Both lasers and UV lamps as photon sources are included. The basic principles, processing conditions, precursors, geometries, advantages and limitations of the various types of photo-CVD processes are described and compared. Their technological applicability and potential for industrial large-scale installation are discussed.

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 .

Cytocompatibility of bio‐inspired silicon carbide ceramics

Due to its good mechanical and biochemical properties and, also, because of its unique interconnected porosity, bio-inspired silicon carbide (bioSiC) can be considered as a promising material for biomedical applications, including controlled drug delivery devices and tissue engineering scaffolds. This innovative material is produced by molten-Si infiltration of carbon templates, obtained by controlled pyrolysis of vegetable precursors. The final SiC ceramic presents a porous-interconnected microstructure that mimics the natural hierarchical structure of bone tissue and allows the internal growth of tissue, as well as favors angiogenesis. In the present work, the in vitro cytocompatibility of the bio-inspired SiC ceramics obtained, in this case, from the tree sapelli (Entandrophragma cylindricum) was evaluated. The attachment, spreading, cytoskeleton organization, proliferation, and mineralization of the preosteoblastic cell line MC3T3-E1 were analyzed for up to 28 days of incubation by scanning electron microscopy, interferometric profilometry, confocal laser scanning microscopy, MTT assay, as well as red alizarin staining and quantification. Cells seeded onto these ceramics were able to attach, spread, and proliferate properly with the maintenance of the typical preosteoblastic morphology throughout the time of culture. A certain level of mineralization on the surface of the sapelli-based SiC ceramics is observed. These results demonstrated the cytocompatibility of this porous and hierarchical material.

Carbon nitride films prepared by guanazole laser ablation in ammonia atmosphere

Abstract Carbon nitride thin films were deposited using an ArF excimer laser to ablate a target of 3,5 diamino 1,2,4 triazole (guanazole) in a reactive atmosphere of ammonia. Films were obtained at room temperature onto crystalline silicon and aluminium substrates. The dependence of the film properties on the ammonia pressure is reported. Films were characterized systematically by profilometry, Fourier Transform infrared and energy dispersive X-ray (EDX) spectroscopies. Infrared spectra are dominated by a broad absorption band from 1300 to 1650 cm −1 , and a peak located at 2165 cm −1 indicating that nitrogen is bonded to carbon in different configurations. The broad band at high wavenumbers (3100–3500 cm −1 ) is attributed to NH x stretching modes revealing the presence of hydrogen in the films. Additional X-ray photoelectron spectroscopy measurements corroborate the presence of carbon bonded to nitrogen. Composition estimated by EDX shows that as the ammonia pressure is increased, higher concentration of nitrogen is incorporated into the films, reaching values up to 53 at% for NH 3 pressures > 1 Torr. Post-deposition thermal treatments up to 500 °C induce structural changes and promote the CN bond formation. Simultaneous analyses of the effused gases from the film during the thermal annealing are also reported.

Gas mixture dependence of the LCVD of SiO2 films using an ArF laser

Abstract Large-area silica films have been deposited on silicon wafers using silane, nitrous oxide and argon gas mixtures and an ArF excimer laser in parallel configuration. An exhaustive study has been carried out on the role of the total and partial pressure of the various components of the gas mixture on the growth and the properties of silica films. Films are characterized by FT-IR spectroscopy and ellipsometry.