Titanium and titanium alloys are key biomedical materials because of their good biocompatibility and mechanical properties. Nevertheless, infection on and around titanium implants still remains a problem which is usually difficult to treat and may lead to eventual implant removal. As a result, preventive measures are necessary to mitigate implant-frelated infection. One important strategy is to render the implant surface antibacterial by impeding the formation of a biofilm. A number of approaches have been proposed for this purpose and they are reviewed in this article. ' 2009 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 91B: 470-480, 2009

Antibacterial coatings on titanium implants.

The modification of surfaces by the deposition of a robust overlayer provides an excellent handle with which to tune the properties of a bulk substrate to those of interest. Such control over the surface properties becomes increasingly important with the continuing efforts at down-sizing the active components in optoelectronic devices, and the corresponding increase in the surface area/volume ratio. Relevant properties to tune include the degree to which a surface is wetted by water or oil. Analogously, for biosensing applications there is an increasing interest in so-called “romantic surfaces”: surfaces that repel all biological entities, apart from one, to which it binds strongly. Such systems require both long lasting and highly specific tuning of the surface properties. This Review presents one approach to obtain robust surface modifications of the surface of oxides, namely the covalent attachment of monolayers.

Covalent surface modification of oxide surfaces.

Spherical cerium oxide nanoparticles and microsized rod-shaped and spindle-like CeO2 structures have been synthesized using a polyol method. When the duration of reaction and the concentration of cerium precursor are controlled, CeO2 products of different morphologies can be selectively produced. Results from XRD, XPS, SEM, and FT-IR measurements suggest that the CeO2 nanospheres are formed from the decomposition of the cerium precursor. Further reactions between the as-prepared CeO2 and ethylene glycol yield the rods/spindle-like cerium formate particles. These morphologies are preserved even after calcination. The order of band gap energy of these samples was found to be rod-shaped > spherical > spindle-like samples, as determined by the UV−Vis spectroscopic method. Compared to a nonoriented polycrystalline CeO2, these samples show an increase in band gap energy due to the quantum size effect. The higher catalytic activity on CO conversion in a spindle-like sample can be explained from the extent of Ce(...

Morphology-Controllable Synthesis of Mesoporous CeO2 Nano- and Microstructures

The three main strategies for dispersing carbon nanotubes (NTs) into a polymer matrix to get conductive nanocomposites are described, and illustrated with some appealing examples. The direct mixing of the NTs and the polymer is the ‘simplest' concept to achieve this goal. Other approaches concern the modification of either the polymer matrix or the NT walls in order to improve the wetting of the filler with the matrix material, and thus promote the incorporation of the NTs into the polymer matrix. Most promising results seem to be obtained upon the addition of a third component. The basic concept is the generation of a stable colloidal system containing both a suspension of NTs stabilized by surfactant molecules in water, and polymer latex. After removal of the water, the resulting powder can be processed into the desired shape. This versatile and environmentally benign concept offers low percolation thresholds and relatively high conductivity levels.

Toolbox for Dispersing Carbon Nanotubes into Polymers To Get Conductive Nanocomposites

A simple and economical route based on ethylene glycol mediated process was developed to synthesize three-dimensional (3D) flowerlike ceria micro/nanocomposite structure using cerium chloride as a reactant. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were adopted to investigate the evolution process of ceria precursor, and a two-stage growth process was identified during the morphology evolution. Ceria with the same flowerlike micro/nanocomposite structure was readily obtained by calcination of the ceria precursor. This novel micro/nanocomposite structure held the advantages of both microstructure and nanostructure. Therefore, the as-obtained ceria can be used as not only an effective sorbent for the removal of pollutants in water treatment but also as an excellent support for gold nanoparticles to remove CO by catalytic oxidation, demonstrating a promising potential in environmental remediation.

3D Flowerlike Ceria Micro/Nanocomposite Structure and Its Application for Water Treatment and CO Removal

Surface chemistry and microstructural analysis of CexZr1−xO2−y model catalyst surfaces

Chitosan, a biopolymer found in the exoskeletons of shellfish, has been shown to be antibacterial, biodegradable, osteoconductive, and has the ability to promote organized bone formation. These properties make chitosan an ideal material for use as a bioactive coating on medical implant materials. In this study, coatings made from 86.4% de-acetylated chitosan were bound to implant-quality titanium. The chitosan films were bound through a three-step process that involved the deposition of 3-aminopropyltriethoxysilane (APTES) in toluene, followed by a reaction between the amine end of APTES with gluteraldehyde, and finally, a reaction between the aldehyde end of gluteraldehyde and chitosan. Two different metal treatments were examined to determine if major differences in the ability to bind chitosan could be seen. X-ray photoelectron spectroscopy (XPS) was used to examine the surface of the titanium metal and to study the individual reaction steps. The changes to the titanium surface were consistent with the anticipated reaction steps, with significant changes in the amounts of nitrogen, silicon, and titanium that were present. It was demonstrated that more APTES was bound to the piranha-treated titanium surface as compared to the passivated titanium surface, based on the amounts of titanium, carbon, nitrogen, and silicon that were present. The metal treatments did not affect the chemistry of the chitosan films. Using toluene to bond APTES on titanium surfaces, rather than aqueous solutions, prevented the formation of unwanted polysiloxanes and increased the amount of silane on the surface for forming bonds to the chitosan films. Qualitatively, the films were more strongly attached to the titanium surfaces after using toluene, which could withstand the ultrahigh vacuum environment of XPS, as compared to the aqueous solutions, which were removed from the titanium surface when exposed to the ultrahigh vacuum environment of XPS.

XPS study on the use of 3-aminopropyltriethoxysilane to bond chitosan to a titanium surface.

The electrical conductivity of polymeric materials can be increased by the addition of carbon fillers. The resulting composites can be used in applications such as electrostatic dissipation and interference shielding. Electrical conductivity models are often proposed to predict the conductivity behavior of these materials. The electrical conductivity of carbon-filled polymers was studied here by the addition of three single fillers to nylon 6,6 and polycarbonate in increasing concentrations. The fillers used in this project were carbon black, synthetic-graphite particles, and milled pitch-based carbon fibers. Materials were extruded and injection-molded into test specimens, and then the electrical conductivity was measured. Additional material characterization tests included optical microscopy for determining the filler aspect ratio and orientation. The filler and matrix surface energies were also determined. An updated model developed by Mamunya and others and a new additive model (including the constituent conductivities, filler volume fraction, percolation threshold, constituent surface energies, filler aspect ratio, and filler orientation) fit the electrical conductivity results well. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2280–2299, 2003

Development of an additive equation for predicting the electrical conductivity of carbon‐filled composites

The electrical conductivity of polymeric materials can be increased by the addition of carbon fillers, such as carbon fibers, carbon black, and synthetic graphite. The resulting composites could be used in applications such as electromagnetic and radio frequency interference shielding and electrostatic dissipation. A significant amount of work has been conducted varying the amount of single conductive fillers in a composite material. In contrast, very limited work has been conducted concerning the effect of combinations of various types of conductive fillers. In this study, three different carbon fillers were used: carbon black, synthetic graphite particles, and pitch based carbon fiber. Two different polymers were used: nylon 6,6 and polycarbonate. The goal of this project was to determine the effect of each filler and combinations of different fillers on the electrical conductivity of conductive resins. A 2 3 factorial design was analyzed to determine the effects of the three different carbon fillers in nylon 6,6 and polycarbonate. The results showed that carbon black caused the largest increase in composite electrical conductivity. The factorial design analysis also showed that combinations of different carbon fillers do have a positive synergistic effect, thereby increasing the composite electrical conductivity.

Kirk H. Schulz

Papers

Surface chemistry and microstructural analysis of CexZr1−xO2−y model catalyst surfaces

XPS study on the use of 3-aminopropyltriethoxysilane to bond chitosan to a titanium surface.

Development of an additive equation for predicting the electrical conductivity of carbon‐filled composites

Synergistic effect of carbon fillers in electrically conductive nylon 6,6 and polycarbonate based resins

A XPS investigation of SO2 adsorption on ceria–zirconia mixed-metal oxides