Sami Areva

Cell viability in a wet silica gel

A modified two-step sol-gel route using silicon ethoxide (TEOS) has been used to synthesize amorphous sol-gel-derived silica, which has been successfully used as a cell encapsulation matrix for 3T3 mouse fibroblasts and CRL-2595 epithelial cells due to its non-toxicity. The sol-gel procedure comprised a first, low pH hydrolysis step, followed by a neutral condensation-gelation step. A high water-to-TEOS ratio and the addition of d-glucose as a porogen and source of nutrients were chosen to minimize silica dissolution and improve the biocompatibility of the process. Indeed, the cell integrity in the encapsulation process was preserved by alcohol removal from the starting solution. Cells were then added in a buffered medium, causing rapid gelation and entrapment of the cells within a randomly structured siloxane matrix in the shape of a monolith, which was maintained in the wet state. MTT and alamarBlue assays were used to check the cytotoxicity of the silica gels and the viability of entrapped cells at initial times in contact with silica. To improve cell attachment, cell clumping experiments - where groups of cells were formed - were designed, rendering improved viability. The obtained materials are therefore excellent candidates for designing tissue-culture scaffolds and implantable bioreactors for biomedical applications.

H2S modified atomic layer deposition process for photocatalytic TiO2 thin films

H2S modified TiO2 films were grown by atomic layer deposition (ALD) using TiCl4, H2S and water as precursors. The films were characterized by XRD, XPS, TOF-SIMS, SEM and UV-VIS spectrometry. Photocatalytic activities of the films under UV and visible light were determined by the degradation of a thin layer of stearic acid. Light induced superhydrophilicity of the films was also studied. Although the sulfur content of the films was very low, substantial modification of the film properties occurred. All the films prepared at 400 and 500 °C with H2S were photocatalytically active under visible light. Photocatalytic activity under UV irradiation of the H2S modified films was also drastically improved when proper deposition parameters were applied.

The effect of heat- or ultra violet ozone-treatment of titanium on complement deposition from human blood plasma

Titanium (Ti) is a well known metallic biomaterial extensively used in dental, orthopaedic-, and occasionally also in blood contacting applications. It integrates well to bone and soft tissues, and is shown upon blood plasma contact to activate the intrinsic pathway of coagulation and bind complement factor 3b. The material properties depend largely on those of the nm-thick dense layer of TiO(2) that becomes rapidly formed upon contact with air and water. The spontaneously formed amorphous Ti-oxide has a pzc approximately 5-6 and its water solubility is at the order of 1-2 micromolar. It is often subjected to chemical- and heat treatments in order to increase the anatase- and rutile crystallinity, to modify the surface topography and to decrease the water solubility. In this work, we prepared sol-gel derived titanium and smooth PVD titanium surfaces, and analysed their oxide and protein deposition properties in human blood plasma before and after annealing at 100-500 degrees C or upon UVO-treatment for up to 96 hours. The blood plasma results show that complement deposition vanished irreversibly after heat treatment at 250-300 degrees C for 30 minutes or after UVO exposure for 24 hours or longer. XPS and infrared spectroscopy indicated change of surface water/hydroxyl binding upon the heat- and UVO treatments, and increased Ti oxidation. XRD analysis confirmed an increased crystallinity and both control (untreated) and annealed smooth titanium displayed low XRD-signals indicating some nanocrystallinity, with predominantly anatase phase. The current results show that the behaviour of titanium dioxide in blood contact can be controlled through relatively simple means, such as mild heating and illumination in UV-light, which both likely irreversibly change the stoichiometry and structure of the outmost layers of titanium dioxide and its OH/H(2)O binding characteristics.

Biocompatibility of sol–gel-derived titania–silica coated intramedullary NiTi nails

We investigated bone response to sol-gel-derived titania-silica coated functional intramedullary NiTi nails that applied a continuous bending force. Nails 26 mm in length, either straight or with a radius of curvature of 28 or 15 mm, were implanted in the cooled martensite form from a proximal to distal direction into the medullary cavity of the right femur in 40 Sprague-Dawley rats. Body temperature restored the austenite form, causing the curved implants to generate a bending force on the bone. The femurs were examined after 24 weeks. Bone length measurements did not reveal any bowing or shortening of the bone in the experimental groups. The results from histomorphometry demonstrated that the stronger bending force, together with sol-gel surface treatment, resulted in more bone deposition around the implant and the formation of significantly less fibrous tissue. Straight intramedullary nails, even those with a titania-silica coating, were poorly attached when compared to the implants with a curved austenite structure.

Physical properties and in vitro bioactivity of hierarchical porous silica–HAP composites

In two recent papers (J. Andersson, S. Areva, B. Spliethoff and M. Linden, Biomaterials, 2005, 26, 6827–6835 and J. Andersson, E. Johannessen, S. Areva, M. Jarn and M. Linden, J. Nanosci. Nanotechnol., 2006, 6, 2438–2444) we have presented new means of synthesizing silica–calcium phosphate (hydroxyapatite or tricalcium phosphate) composite materials, where the calcium phosphate is covered by a mesoporous layer of silica. These materials are bifunctional biomaterials, as they can be used both as drug carrier matrices and osteoconductive materials. Some of these materials, especially if synthesized according to a one-pot method, exhibit a very high in vitro bioactivity, and nucleate and grow calcium phosphate on their surfaces in less than 24 h if exposed to a simulated body fluid. In the present study, we have carried out a thorough characterization of the one-pot sol–gel derived composite materials by the means of solid state 29Si magic angle spinning (MAS) NMR, 31P MAS NMR, 23Na MAS NMR, and transfer of population in double resonance (TRAPDOR) NMR spectroscopy, scanning electron microscopy, and transmission electron microscopy. The aim of the study is to relate the material properties to the in vitro bioactivity. The reason for high bioactivity of the composites cannot be ascribed to the silica content, but primarily to the presence of a highly soluble second calcium phosphate phase, NaCaPO4, co-existing with the hydroxyapatite in the hybrid material. Furthermore, the hydroxyapatite becomes increasingly calcium deficient with increasing silica content, which adds to increase the bioactivity. Also the overall crystallinity of the apatitic calcium phosphate phase could contribute to the bioactivity of the composites in vitro.

Sol-gel derived titania coating with immobilized bisphosphonate enhances screw fixation in rat tibia.

A variety of surface modifications have been tested for the enhancement of screw fixation in bone, and locally delivered anti-osteoporosis drugs such as bisphosphonates (BP) are then of interest. In this in vivo study, the impact of surface immobilized BP was compared with systemic BP delivery and screws with no BP. After due in vitro characterization, differently treated stainless steel (SS) screws were divided into four groups with 10 rats each. Three of the groups received screws coated with sol-gel derived TiO(2) and calcium phosphate (SS+TiO(2)+CaP). One of these had no further treatment, one had alendronate (BP) adsorbed to calcium phosphate mineral, and one received systemic BP treatment. The fourth group received uncoated SS screws and no BP (control). The screw pullout force was measured after 4 weeks of implantation in rat tibiae. The immobilized amount and release rate of alendronate could be controlled by different immersion times. The SS+TiO(2)+CaP coating did not increase the pullout force compared to SS alone. Surface delivered alendronate enhanced the pullout force by 93% [p = 0.000; 95% Confidence Interval (CI): 67-118%] compared to SS, and by 39% (p = 0.044; 95% CI: 7-71%) compared to systemic alendronate delivery. Both surface immobilized and systemically delivered alendronate improved implant fixation. Also, locally delivered, that is, surface immobilized alendronate showed a better fixation than systemically delivered. Using sol-gel derived TiO(2) as a platform, it is possible to administer controllable amounts of a variety of BPs.

Excited state absorption processes in Sm3+ doped GdOCl☆

Abstract The FT-Raman spectrum of the polycrystalline GdOCl doped with 1 mol% Sm 3+ was measured at room temperature using a cw Nd:YAG laser with the excitation wavelength of 1064 nm (9400 cm −1 ). Besides the very weak Stokes and anti-Stokes Raman lines the additional strong lines were concluded to result from luminescence processes. The UV–Vis–NIR absorption spectra of GdOCl:Sm 3+ ( x Sm =0.06) and the energy level simulation of Sm 3+ in SmOCl yielded the energy level scheme of Sm 3+ . The additional lines could be assigned to the IR and visible Stokes and anti-Stokes luminescence of Sm 3+ . Absorption of the 9400 cm −1 photons leads first to transition to the 6 F 9/2 and then to the 4 F 3/2 energy level of Sm 3+ . The lines corresponding to luminescence at 13 596 and 12 310 cm −1 could then be assigned to the anti-Stokes transitions from the 4 F 3/2 energy level to the 6 H 13/2 and 6 H 15/2 levels, respectively. Also lines in the Stokes emission originate from the luminescence processes of Sm 3+ . However, all the extra lines in the Raman spectrum have not yet been explained by the luminescence processes.

Rationale of Using Conventional Sol-Gel Derived SiO2 for Delivery of Biologically Active Agents

Progress in the research of mesoporous materials, hierarchical pore structures, chemical modification of surfaces, nanoparticle processing and hybrid materials is important and it provides new and interesting functional properties for silica structures. However, this has also left the conventional, alkoxy-based sol-gel derived silica in the shadow, although it has a lot of non-utilized potential, especially in the delivery and/or encapsulation of sensitive biologically active agents like viral vectors, proteins, nucleic acids and cells. The potential lies in the versatile possibilities to adjust the structure by using alkoxides as precursors and in the proper use of water in different steps of the processing. The conventional, alkoxy-based sol-gel silica structure can be processed so that it results in largely variable biodegradation rates, biodegradation-controlled release of encapsulated agents and beneficial environment even for highly sensitive agents. These kinds of silica structures contain more or less water and hence, they are more or less labile from the traditional viewpoint of materials science. In extreme case they could be called “unfinished silica”. The aim of this paper is to discuss how the biodegradation rate of these kinds of silica materials can be adjusted on a large scale and how this is related to a rather narrow scale adjustment of in vitro dissolution rate of silica, how the unfinished silica structures can be controlled and their properties adjusted, how they can be utilized in the delivery of biologically active agents, and what the potential problems to be solved are.

Corrosion of Glazes Coated with Functional Films in Detergent Solutions

The goal of this work was to establish the compatibility of mat glazes with functional films known to render the surfaces with self-cleaning or easy-to-clean properties. Glazes with wollastonite, pseudowollastonite, diopside and zircon as the main crystalline phases in the surfaces were coated with fluoropolymer as well as ceramic, sol-gel derived titania and zirconia films. The glazes were soaked in typical detergent solutions used in everyday life up to four days. The surface roughness was measured with confocal optical microscope and the surface was imaged and analyzed with SEM/EDXA. When applied on wollastonite and pseudowollastonite containing glazes the functional films readily reacted in water solutions by pitting of the surface in the vicinity of the crystals. The ceramic titania and zirconia films showed better chemical resistance on wollastonite –free glazes, while the fluoropolymer film corroded in the most alkaline environments. The results indicate that functional films could be used also on rough surfaces without markedly affecting the surface topography. However, the films should be applied only on glazes with an excellent chemical resistance.

About Interactions Between Sol-Gel Derived Silica, Titania and Living Organisms

Sol-gel derived silica and titania have a specific interaction with many biological molecules, microbes, algae, cells and living tissue. The specific interactions mean that they differ from common reactions between non-viable materials and biomolecules or living tissues and the interactions are mostly beneficial from the viewpoint of biotechnical applications. Pepetides and proteins may preserve their activity and bacteria, algae and cells may preserve their viability and viruses their infectivity as encapsulated in sol-gel derived silica. Silica and titania are known to form a direct bond with living tissue which can be utilized in the biomaterial applications. Other application areas of silica and titania are in biosensing, tissue engineering, gene therapy, controlled delivery of therapeutic agents and environmental protection.