Papers by Author: Sami Areva

Abstract: Glass and glazes are easy-to-clean surfaces often used in everyday environments where the surface needs to repel soils and deposits. In general, these surfaces have good chemical durability in everyday environments. However, the durability is rapidly degraded in solutions of high or low pH. This kind of surface corrosion has been found to diminish the cleanability. Surface topography has also a certain influence on the soil attachment and cleanability. Self-cleaning and easy-to-clean coatings have been employed to enhance the cleanability of surfaces. In this report surface properties of three coatings reported to enhance the cleanability of glass and glazed surfaces are summarized. The properties discussed are the surface appearance, roughness, wettability, soil attachment and soil removal. Also the chemical and mechanical durability of the coatings are discussed. The coatings studied were a commercial fluoropolymer film applied at room temperature, an experimental sol-gel derived TiO2 coating calcined at 500°C, and an experimental liquid flame sprayed TiO2-Ag coating applied on the substrates at 500-800°C. The advantages of the fluoropolymer coating are easy application and soil good soil repellence, but the coating has limited chemical and mechanical durability. The manufacture of the sol-gel TiO2 coating requires several processing steps. The coated surface showed excellent cleanability, and good chemical and mechanical durability. The liquid flame sprayed coating has potential to be applied online in the material manufacture. However, the processing parameters should be optimized in order to achieve desired improvements in the cleanability.

Abstract: Series of TiO2-SiO2 films with a silica content of 70 mol% were prepared on glass slides by dip-coating method. The mixed sols were prepared via prehydrolyzing of the titania sol in different acidity. The surface chemistry was analyzed by XPS and the topography by AFM. Dissolution of silica was performed in TRIS buffer and the stability of the coatings was tested in simulated body fluid (SBF). The coatings remained crack-free after the TRIS and SBF tests. The formed nanostructure was practically same in all surfaces. The dissolution of silica was slightly increased with the increased acidity of the titania sol. Furthermore, the binding energies (BEs) of the Si(2p) and Ti(2p3/2) peaks obtained from XPS were both shifted upward with increased acidity of the sol. The sol-gel titania-silica materials made with prehydrolyzed titania formed heterogeneous structure where the TiO2 and SiO2 particles were partly interconnected and covered with soluble silica.

Abstract: 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.

Abstract: Bioactive ceramic coatings have been widely applied to ensure direct chemical implant-bone contact, thus reducing the time required for osseointegration. In this respect the plasma-sprayed CaP coatings are the most widely applied, although the composition, structure and the adhesion to the substrate are difficult to control. Despite the success in preparing a large variety of bioactive ceramics, metal implants are still widely used in load-bearing orthopedic and dental applications. Regardless, that the inert metallic materials do not form a chemical bond with tissues, in both hard and soft tissue environments, but rather a fibrous tissue capsule is formed. In order for a material to chemically attach to bone, spontaneous formation (or ready-made presence) of bone-mineral like calcium phosphate (CaP) on the materials’ surface in physiological environments is needed. In this review both conventional and sol-gel derived ceramics are discussed as well as the recent attempts to ensure implant fixation. Special focus is put on the use of sol-gel derived titania coatings and their applications including the newest findings in soft tissue environment.

Abstract: 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.

Abstract: Different silica and carbonate containing calcium phosphate (CaP) layers were prepared on bioactive glass S53P4 in conventional C-SBF and revised R-SBF. In R-SBF the CaP layer formed faster compared to C-SBF, and the CaP layer formed in R-SBF was amorphous compared to the poorly crystalline bonelike HCA formed in C-SBF. In addition, the influence of chemical composition, dissolution and structure of biomimetically processed CaP layers on osteoclast and osteoblast activity was studied. In general, biomimetic CaP layers on bioactive glass S53P4 did not affect so much on bone cell activity as it was expected compared to the untreated glass. Additionally, it was observed that the mechanism for good osteoclast activity is multifactorial. The optimal surface for osteoclast adhesion and growth was an amorphous CaP having mesoporous nanotopography and proper dissolution rate of calcium and silica. Also osteoblasts grew well on such surface.