Novel silica membrane material for molecular sieve applications

Development of new silica membranes properties, e.g., molecular sieving properties, has been increasingly gaining importance in the last few years. A novel unsupported silica membrane, referred to as hydrophobic metal-doped silica, was developed by cobalt-doping within the organic templated silica matrix. The novel material was prepared by the acid-catalyzed hydrolysis and condensation process of tetraethylorthosilicate (TEOS) and methyltriethoxysilane (MTES), which is the precursor for methyl ligand covalently bounded to the silica matrix. The synthesis and surface properties of the novel unsupported silica membrane as well as the unsupported blank silica and modified silica membranes were revealed by surface and microstructural techniques, such as water contact angle measurement, FTIR, X-ray, Solid-state 29Si MAS NMR, TGA and N2 and CO2 adsorption measurements. The results showed that the thermal stability of the organic templated silica matrix was enhanced by cobalt-doping process. A hydrophobic microporous silica membrane material with high thermal stability up to ∼560 °C in oxidizing atmosphere and a narrow pore size distribution centered at 1.1 nm was obtained. Therefore, a novel precursor material for molecular sieve silica membranes applications has been achieved and developed.

Instrumentation for measuring pavement-vehicle interaction. Volume I: system description, operation, calibration and maintenance manual. Final report.

Federal Highway Administration, Structures and Applied Mechanics Division, Washington, D.C.

Instrumentation for measuring pavement-vehicle interaction. Volume II: Digalog Systems operation and maintenance manual, data acquisition system, model DLI 203. Final report.

Federal Highway Administration, Structures and Applied Mechanics Division, Washington, D.C.

Instrumentation for measuring pavement-vehicle interaction. Volume III: Kennedy Co. operation and maintenance manual, formatter and digital tape transport. Final report.

Federal Highway Administration, Structures and Applied Mechanics Division, Washington, D.C.

Detectable warnings: testing and performance evaluation at transit stations. Final report.

Federal Transit Administration, Washington, D.C.

A bibliography of paper testing.

Each part brought up to date by supplements.

Zr-Laponite pillared clay-based nickel catalysts for methane reforming with carbon dioxide

Zr-Laponite pillared clays were prepared and used as supports of nickel catalysts for the methane reforming reaction with carbon dioxide to synthesis gas. The structural and textural characteristics of supports and catalysts were systematically examined by N-2 adsorption/desorption and X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron spectroscopy (TEM) techniques. The catalytic performance and carbon deposition were investigated. It is found that Zr-Laponite pillared clays are promising catalyst supports for carbon dioxide reforming of methane. The pore structure and surface properties of such supports greatly affect the catalytic behaviors of catalysts derived. Carbon deposition on catalysts was also affected by the property and structure of supports. The sintering of nickel metal and zirconia was another factor responsible for catalyst deactivation. This new-type nickel supported catalyst Ni/Zr-Laponite(8), with well-developed porosity, gave a higher initial conversion and a relatively long-term stability, and is therefore a promising catalyst for potential application to carbon dioxide reforming of methane to synthesis gas. (C) 2002 Elsevier Science B.V All rights reserved.

Poly(beta-hydroxybutyrate-co-beta-hydroxyvalerate) supports in vitro osteogenesis

Studies have demonstrated that polymeric biomaterials have the potential to support osteoblast growth and development for bone tissue repair. Poly( beta- hydroxybutyrate- co- beta- hydroxyvalerate) ( PHBV), a bioabsorbable, biocompatible polyhydroxy acid polymer, is an excellent candidate that, as yet, has not been extensively investigated for this purpose. As such, we examined the attachment characteristics, self- renewal capacity, and osteogenic potential of osteoblast- like cells ( MC3T3- E1 S14) when cultured on PHBV films compared with tissue culture polystyrene ( TCP). Cells were assayed over 2 weeks and examined for changes in morphology, attachment, number and proliferation status, alkaline phosphatase ( ALP) activity, calcium accumulation, nodule formation, and the expression of osteogenic genes. We found that these spindle- shaped MC3T3- E1 S14 cells made cell - cell and cell - substrate contact. Time- dependent cell attachment was shown to be accelerated on PHBV compared with collagen and laminin, but delayed compared with TCP and fibronectin. Cell number and the expression of ALP, osteopontin, and pro- collagen alpha 1( I) mRNA were comparable for cells grown on PHBV and TCP, with all these markers increasing over time. This demonstrates the ability of PHBV to support osteoblast cell function. However, a lag was observed for cells on PHBV in comparison with those on TCP for proliferation, ALP activity, and cbfa- 1 mRNA expression. In addition, we observed a reduction in total calcium accumulation, nodule formation, and osteocalcin mRNA expression. It is possible that this cellular response is a consequence of the contrasting surface properties of PHBV and TCP. The PHBV substrate used was rougher and more hydrophobic than TCP. Although further substrate analysis is required, we conclude that this polymer is a suitable candidate for the continued development as a biomaterial for bone tissue engineering.

Adsorption of pure fluids in activated carbon with a modified lattice gas model

In this article we study the effects of adsorbed phase compression, lattice structure, and pore size distribution on the analysis of adsorption in microporous activated carbon. The lattice gas approach of Ono-Kondo is modified to account for the above effects. Data of nitrogen adsorption at 77 K onto a number of activated carbon samples are analyzed to investigate the pore filling pressure versus pore width, the packing effect, and the compression of the adsorbed phase. It is found that the PSDs obtained from this analysis are comparable to those obtained by the DFT method. The discrete nature of the PSDs derived from the modified lattice gas theory is due to the inherent assumption of discrete layers of molecules. Nevertheless, it does provide interesting information on the evolution of micropores during the activation process.

Evolutionary origin of Venturia canescens virus-like particles

Insect host-parasitoid interactions provide fascinating examples of evolutionary adaptations in which the parasitoid employs a variety of measures and countermeasures to overcome the immune responses of its host. Maternal factors introduced by the female wasps during egg deposition play an important role in interfering with cellular and humoral components of the host's immune defence. Some of these components actively suppress host immune components and some are believed to confer protection for the developing endoparasitoid by rather passive means. The Venturio conescens/Ephestia kuehniella parrositoid-host system is unique among other systems in that the cellular defence capacity of the host remains virtually intact after parasitization. This system raises some important questions that are discussed in this mini-review: If immune protection of the egg and the emerging larva is achieved by surface properties comprising glycoproteins and virus-like particles (VLPs) produced by the female wasp, why is the prophenoloxidose activating cascade blocked in parasitized caterpillars? Another question is the evolutionary origin of these particles, given that the functional role and structural features of V. canescens VLP proteins are more related to cellular proteins than to viruses.

A blank slate? Layer-by-layer deposition of hyaluronic acid and chitosan onto various surfaces

Although poly(alpha-hydroxy esters), especially the PLGA family of lactic acid/glycolic acid copolymers, have many properties which make them promising materials for tissue engineering, the inherent chemistry of surfaces made from these particular polymers is problematic. In vivo, they promote a strong foreign-body response as a result of nonspecific adsorption and denaturation of serum proteins, which generally results in the formation of a nonfunctional fibrous capsule. Surface modification post-production of the scaffolds is an often-utilized approach to solving this problem, conceptually allowing the formation of a scaffold with mechanical properties defined by the bulk material and molecular-level interactions defined by the modified surface properties. A promising concept is the so-called blank slate: essentially a surface that is rendered resistant to nonspecific protein adsorption but can be readily activated to covalently bind bio-functional molecules such as extracellular matrix proteins, growth factors or polysaccharides. This study focuses on the use of the quartz crystal microbalance (QCM) to follow the layer-by-layer (LbL) electrostatic deposition of high molecular weight hyaluronic acid and chitosan onto PLGA surfaces rendered positively charged by aminolysis, to form a robust, protein-resistant coating. We further show that this surface may be further functionalized via the covalent attachment of collagen IV, which may then be used as a template for the self-assembly of basement membrane components from dilute Matrigel. The response of NIH-3T3 fibroblasts to these surfaces was also followed and shown to closely parallel the results observed in the QCM.

Ocular biotribology and contact lens lubrication mechanisms

The work described in this thesis is concerned with mechanisms of contact lens lubrication. There are three major driving forces in contact lens design and development; cost, convenience, and comfort. Lubrication, as reflected in the coefficient of friction, is becoming recognised as one of the major factors affecting the comfort of the current generation of contact lenses, which have benefited from several decades of design and production improvements. This work started with the study of the in-eye release of soluble macromolecules from a contact lens matrix. The vehicle for the study was the family of CIBA Vision Focus® DAILIES® daily disposable contact lenses which is based on polyvinyl alcohol (PVA). The effective release of linear soluble PVA from DAILIES on the surface of the lens was shown to be beneficial in terms of patient comfort. There was a need to develop a novel characterisation technique in order to study these effects at surfaces; this led to the study of a novel tribological technique, which allowed the friction coefficients of different types of contact lenses to be measured reproducibly at genuinely low values. The tribometer needed the ability to accommodate the following features: (a) an approximation to eye lid load, (b) both new and ex-vivo lenses, (c) variations in substrate, (d) different ocular lubricants (including tears). The tribometer and measuring technique developed in this way was used to examine the surface friction and lubrication mechanisms of two different types of contact lenses: daily disposables and silicone hydrogels. The results from the tribometer in terms of both mean friction coefficient and the friction profiles obtained allowed various mechanisms used for surface enhancement now seen in the daily disposable contact lens sector to be evaluated. The three major methods used are: release of soluble macromolecules (such as PVA) from the lens matrix, irreversible surface binding of a macromolecule (such as polyvinyl pyrrolidone) by charge transfer and the simple polymer adsorption (e.g. Pluoronic) at the lens surface. The tribological technique was also used to examine the trends in the development of silicone hydrogel contact lenses. The focus of the principles in the design of silicone hydrogels has now shifted from oxygen permeability, to the improvement of surface properties. Presently, tribological studies reflect the most effective in vitro method of surface evaluation in relation to the in-eye comfort.

Cellular interactions with hydrogels

An efficient means of evaluating potential biomaterials is to use the in vitro fibroblast cell culture model. However, the chemistry which influences cell adhesion on polymer substrates is poorly understood. The work in this thesis aims to rationalise several theories of current opinion and introduce new chemical techniques that may predict cellular behaviour. The keratoprosthesis is a typical example of the need to be able to manipulate cell adhesion of materials since both adhesive and non adhesive sections are needed for proper integration and optical function. Calcein AM/ethidium homodimer-1 and DAPI assays were carried out using 3T3 and EKl.BR cells. Poly(HEMA) was found to be the most cell adhesive hydrogel tested. The reactivity of monomers and the resulting sequence distribution were found to affect surface properties and this may explain the poor levels of cell adhesion seen on NVP/MMA copolymers. Surface free energy is shown to be dependent on the polar and non polar groups present along the backbone chain of the polymers. Dehydrated and hydrated contact angle measurements show the effect of rotation of surface groups around the backbone chain. This effect is most apparent on hydrogels containing methacrylic acid. Dynamic contact angle measurements confirm sequence distribution irregularities and demonstrate the mobility of surface groups. Incorporation of NVI or DEAEMA into the hydrogels does not affect the mobility of the surface groups despite their bulkiness. Foetal calf serum was used for the first time as a test solution in an attempt to mimic a biological environment during surface experiments. A Vroman effect may be present, and may involve different surface proteins for each material tested. This interdisciplinary study combines surface characterisation and biological testing to further the knowledge of the biomaterial/host interface. Surface chemistry techniques appear to be insufficiently sensitive to predict cellular behaviour. The degree of ionisation of hydrogels containing ionic groups depends on the nature of the functional groups as well as the concentration and this is an important parameter to consider when comparing charged materials.

Novel cationic polymers for use at biological interfaces

One of the main problems with the use of synthetic polymers as biomaterials is the invasion of micro-organisms causing infection. A study of the properties of polymeric antibacterial agents, in particular polyhexamethylene biguanide, has revealed that the essential components for the design of a novel polymeric antibacterial are a balance between hydrophilicity and hydrophobicity coupled with sites of cationicity. The effect of cation incorporation on the physical properties of hydrogels has been investigated. Hydrogel systems copolymerised with either N-vinyl imidazole or dimethylaminoethyl methacrylate have been characterised in terms of their water binding, mechanical and surface properties. It has been concluded that the incorporation of these monomers does not adversely affect the properties of such hydrogels and that these materials are potential candidates for further development for use in biomedical applications. It has been reported that hydro gels with ionic character may increase the deposition of biological material onto the hydrogel surface when it is in contact with body fluids. An investigation into the deposition characteristics of hydrogels containing the potentially cationic monomers has been carried out, using specific protein adsorption and in vitro spoilation techniques. The results suggest that at low levels of cationicity, the deposition of positively charged proteins is reduced without adversely affecting the uptake of the other proteins. The gross deposition characteristics were found to be comparable to some commercially available contact lens materials. A preliminary investigation into the development of novel antibacterial polymers has been completed and some novel methods of bacterial inhibition discussed. These methods include development of an hydrogel whose potential application is as a catheter coating.

Novel hydrogel polymers

Hydrogels are a unique class of polymers which swell, but do not dissolve in water. A range of 2-hydroxyethyl methacrylate based copolymer hydrogels have been synthesised and are described in this thesis. Initially, hydrogels were synthesised containing acryloylmorpholine, N,N-dimethyl acrylamide and N-vinyl pyrrolidone. Variations in structure and composition have been correlated with the sequence distribution, equilibrium water content (EWC) , mechanical and surface properties of the hydrogels. The sequence distribution was found to be dependant on the structure and reactivity of the monomers. The EWC was found to be dependant on the water structuring groups present in the hydrogel, although the water binding abilities were modified by steric effects. The mechanical properties were also investigated and were found to be dependant on the monomer structure, sequence distribution and the amount and nature of water in the hydrogel. The macroscopic surface properties of the hydrogels were probed using surface energy determinations and were found to be a function of the water content and the hydrogel composition. At a molecular level, surface properties were investigated using an in vitro ocular spoilation model and single protein adhesion studies. The results indicate that the sequence distribution and the polarity of the surface affect the adhesion of biological species. Finally, a range of 2-hydroxyethyl methacrylate based copolymer hydrogels containing both charged monomer groups and linear polyethers have been synthesised and described. Although variations in the EWC are observed with the structure of the monomers, it was observed that the EWC increased due to the polar character of the charged monomers and the chain length and hydrophilicity of the polyethers. Investigation of these hydrogel surfaces revealed subtle changes. The molecular surface properties indicate the significance of the effect of charge and molecular mobility of the groups expressed at the hydrogel surface.