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PubMed2006

Flux stabilization of silicon nitride microsieves by backpulsing and surface modification with PEG moieties.

The influence of the surface properties of chemically modified silicon nitride microsieves on the filtration of protein solutions and defatted milk is described in this research. Prior to membrane filtrations, an antifouling polymer based on poly(ethylene glycol), poly(TMSMA-r-PEGMA) was synthesized and applied on silicon-based surfaces like silicon, silicon nitride, and glass. The ability of such coating to repel proteins like bovine serum albumin (BSA) was confirmed by ellipsometry and confocal fluorescence microscopy. In BSA and skimmed milk filtrations no differences could be seen between unmodified and PEG-coated membranes (decreasing permeability in time). On the other hand, reduced fouling was observed with PEG-modified microsieves in combination with backpulsing and air sparging.

Air Pollutants, Occupational↗
PubMed2004

Impact-induced seismic activity on asteroid 433 Eros: a surface modification process.

High-resolution images of the surface of asteroid 433 Eros revealed evidence of downslope movement of a loose regolith layer, as well as the degradation and erasure of small impact craters (less than approximately 100 meters in diameter). One hypothesis to explain these observations is seismic reverberation after impact events. We used a combination of seismic and geomorphic modeling to analyze the response of regolith-covered topography, particularly craters, to impact-induced seismic shaking. Applying these results to a stochastic cratering model for the surface of Eros produced good agreement with the observed size-frequency distribution of craters, including the paucity of small craters.

Journal Article↗
PubMed2000

Surface modification of poly(methyl methacrylate) used in the fabrication of microanalytical devices.

We report here the chemical modification of poly(methyl methacrylate) (PMMA) surfaces by their reaction with the monoanion of alpha,omega-diaminoalkanes (aminolysis reaction) to yield amine-terminated PMMA surfaces. It is found that the amine functionalities are tethered to the PMMA backbone through an alkane bridge to amide bonds formed during the aminolysis of the surface ester functionalities. The distribution of the amine termini is quite uniform as judged by fluorescence micrographs. It is found that the electroosmotic flow in aminated PMMA microchannels is reversed when compared to that in unmodified channels. In addition, it is demonstrated that enzymes can be immobilized onto the amine-terminated PMMA surfaces and are effective in the restriction digestion of dsDNAs. Finally, the availability of the surface amine groups is further demonstrated by their reaction with n-octadecane-1-isocyanate to form PMMA surfaces terminated with well-ordered and highly crystalline octadecane chains.

Amines↗
PubMedDate not supplied

The effect of additives and mechanical agitation in surface modification of acrylic fibres by cutinase and esterase.

The surface of an acrylic fibre containing about 7% of vinyl acetate was modified using Fusarium solani pisi cutinase and a commercial esterase, Texazym PES. The effect of acrylic solvents and stabilising polyols on cutinase operational stability was studied. The half-life time of cutinase increased by 3.5-fold with the addition of 15% N,N-dimethylacetamide (DMA) and by 3-fold with 1M glycerol. The impact of additives and mechanical agitation in the protein adsorption and in the hydrolysis of vinyl acetate from acrylic fabric was investigated. The hydroxyl groups produced on the surface of the fibre were able to react specifically with Remazol Brilliant Blue R (cotton reactive dye) and to increase the colour of the acrylic-treated fabric. The best staining level was obtained with a high level of mechanical agitation and with the addition of 1% DMA. Under these conditions, the raise in the acrylic fabric colour depth was 30% for cutinase and 25% for Texazym. The crystallinity degree, determined by X-ray diffraction, was not significantly changed between control samples and samples treated with cutinase. The results showed that the outcome of the application of these enzymes depends closely on the reaction media conditions.

Acrylic Resins↗
PubMed1994

Surface modifications of hydroxyapatite ceramics in aqueous media.

Hydroxyapatite (HA) surfaces exposed, at room temperature, to various aqueous media of different compositions (distilled water, saline solution, cell culture media, saturated HA solution) have been studied by X-ray photoelectron spectroscopy (XPS) angular analysis and IR reflectance spectroscopy. An important decrease of the Ca/P atomic ratio of the surface layer was seen on all exposed surfaces, reaching 1, the Ca/P ratio of dicalcium phosphate dihydrate (DCPD) for the uppermost surface layer. Furthermore, HPO4(2-) ions were observed by XPS and IR. These chemical changes seem to be related to an equilibration process of the surface independent of the dissolution mechanism. Despite the Ca/P ratio observed, no specific phosphate ion environments, such as that of DCPD, were seen by IR.

Calcium↗
PubMed1998

Surface modification of superparamagnetic nanoparticles (Ferrofluid) studied with particle electrophoresis: application to the specific targeting of cells.

Colloidal aqueous suspension of superparamagnetic nanoparticles (9 nm in diameter) composed of maghemite (gamma Fe2O3) and forming an ionic ferrofluid in aqueous solution are covalently coupled with lectins, enzymes or antibodies, using specific thiol chemistry. The surface charge modifications of nanoparticles, caused by ligand coupling, were monitored by measuring their electrophoretic mobilities using laser-Doppler velocimetry. Particle electrophoretic mobility (PEM) changes are shown to correlate well with the amount of ligand fixed on the particles, as probed by its biological activity. The PEM method provides a useful tool to optimize ligand immobilization at the surface of nanoparticles, and may be advantageous when biological activity measurements are not convenient.

Animals↗
PubMed2003

Surface modification of chitosan films. Effects of hydrophobicity on protein adsorption.

The surface of chitosan films was modified using acid chloride and acid anhydrides. Chemical composition at the film surface was analyzed by attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS). ATR-FTIR data verified that the substitution took place at the amino groups of chitosan, thus forming amide linkages, and the modification proceeded to the depth at least 1 microm. Choices of molecules substituted at the amino groups of the glucosamine units did affect the hydrophobicity of the film surface, as indicated by air-water contact angle analysis. The surface became more hydrophobic than that of non-modified film when a stearoyl group (C(17)H(35)CO-) was attached to the films. The reaction of chitosan films with succinic anhydride or phthalic anhydride, however, produced more hydrophilic films. Selected modified films were subjected to protein adsorption study. The amount of protein adsorbed, determined by bicinchoninic acid (BCA) assay, related to the types of attached molecules. The improved surface hydrophobicity affected by the stearoyl groups promoted protein adsorption. In contrast, selective adsorption behavior was observed in the case of the chitosan films modified with anhydride derivatives. Lysozyme adsorption was enhanced by H-bonding and charge attraction with the hydrophilic surface. While the amount of albumin adsorbed was decreased possibly due to negative charges that gave rise to repulsion between the modified surface and albumin. This study has demonstrated that it is conceivable to fine-tune surface properties which influence its response to bio-macromolecules by heterogeneous chemical modification.

Acids↗
PubMed2006

Surface modification of poly(hydroxybutyrate) films to control cell-matrix adhesion.

Tailoring surface properties of degradable polymer scaffolds is key to progress in various tissue engineering strategies. Poly(3-hydroxybutyrate) and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) thin films were modified by low pressure ammonia plasma, low pressure water vapour plasma, or immersion in a sodium hydroxide solution to elaborate means to control the cell-matrix adhesion of human umbilical cord vein endothelial cells grown on these materials. Fibronectin (FN) heteroexchange and cell adhesion were correlated to the physicochemical characteristics of the modified polymer surfaces which were investigated by X-ray photoelectron spectroscopy (XPS), scanning force microscopy (SFM), electrokinetic measurements, and contact angle measurements. All treatments increased the hydrophilicity of the polymer samples, which could be accounted to newly created amine or carboxyl functionalities for ammonia plasma or water vapour plasma treatments, respectively, and ester hydrolysis for treatments with alkaline aqueous solutions. Main features of cell adhesion and FN reorganisation-evaluated after 1h and after 5 days-could be attributed to the anchorage strength of pre-coated FN layers at the polymer surface, which was, in turn found to be triggered by the type of modification applied. In line with earlier studies referring to different materials cell adhesion and matrix reorganisation were shown to be sensitively controlled through the physicochemical profile of poly(hydroxybutyrate) surfaces.

Cell Adhesion↗
PubMed2001

Surface modification of titanium through amino group implantation.

We modified Ti surfaces by implantation of amino (NH(2+)) groups at 10(16) and 10(17) cm(-2). The implanted surfaces were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning Auger electron spectroscopy (AES), and second ion mass spectroscopy (SIMS). The experimental results showed that the implanted Ti specimens were covered by a dominant hydrocarbon overlayer due to contamination and the surface oxide layer of implanted specimens became thicker. XPS, AES, and SIMS depth profiles showed that implanted elements had a typical ion implantation distribution and that titanium nitride (TiN) was formed.

Amines↗
PubMed2004

Interior surface modification of bacteriophage MS2.

An efficient strategy for the interior surface functionalization of MS2 viral capsids is reported, featuring a new hetero-Diels-Alder bioconjugation reaction. After virus isolation, the RNA genome was removed from the spherical particles by exposure to pH 11.8 conditions for a period of 4 h. Following this, 180 tyrosine residues on the interior surface of each "empty" capsid shell were modified by using a site-selective diazonium-coupling reaction. To attach additional functionality, the azo conjugate was reduced with Na2S2O4 to afford an ortho-amino tyrosine derivative. Oxidation of this moiety with NaIO4 produced an o-iminoquinone on the protein surface, which was found to undergo an efficient hetero-Diels-Alder reaction with N-(4-aminophenyl)acrylamide. This four-step procedure can be carried out in under 4 h, reaches high levels of conversion, and yields the desired conjugates in >60% overall yield.

Bioreactors↗
PubMed1990

Towards an artificial cornea: surface modifications of optically clear, oxygen permeable soft contact lens materials by ammonia plasma modification technique for the enhanced attachment and growth of corneal epithelial cells.

The advent of high water content, oxygen permeable contact lens materials has made the intracorneal implants more feasible. A major obstacle encountered is the regrowth of a stable epithelium over the implant. Therefore, ammonia gaseous plasma modification technique was used to modify the surface chemical properties of soft contact lens material such as poly(2-hydroxyethyl methacrylate and methacrylic acid), PHEMA-MAA copolymer, in an attempt to enhance the cell attachment and growth of rabbit corneal epithelial cells.

Ammonia↗
PubMed2005

Infrared spectroscopic studies of galvanic effect influence on surface modification of sulfide minerals by surfactant adsorption.

The influence of interaction between mineral components in natural mixtures on the adsorption of organic and inorganic species on the mineral surfaces is recognized. However, the surface phenomena have been meagerly investigated. In this study the formation of different surface species of surfactant (amyl xanthate, C5H11OC(S)S-) adsorbed on FeS2, PbS, and CuFeS2 has been spectroscopically investigated in single-mineral and complex systems. The type and amount of adsorbed species were determined directly on each mineral surface by infrared external reflection spectroscopy. Galvanic interaction between grains of different minerals could have tremendous consequence on the adsorption of surfactants on each mineral component and their future reactivity. The detected changes are dramatic, from no adsorption to the formation of several layers of hydrophobic or hydrophilic surface products depending on which minerals are in contact. It has been documented that even very short contact time between different mineral grains by collision is sufficient to produce dramatic modification of the surface composition and structure. The results obtained indicate clearly that the observations and conclusions aboutthe surfactant adsorption made in a single mineral system cannot be simply extrapolated to describe the real situation in natural multicomponent mineral systems. The obtained information on sulfide mineral interaction in complex systems is indispensable to understand processes taking place in nature at mineral-water interfaces (dissolution of heavy metals). An additional benefit is the improved ability to design efficient separation processes of these minerals.

Adsorption↗
PubMed2003

Surface modification of poly(lactic acid) nanoparticles by covalent attachment of thiol groups by means of three methods.

The aim of the present work was to find a suitable method for the introduction of thiol functions on the surface of poly(DL-lactic acid) (PLA) nanoparticles. Three different approaches were investigated. The modification of the surface involves the activation of PLA carboxylic acid groups followed by the attack of a nucleophile such as cysteine (method #1) or cystamine (method #2 and #3) that provide thiol functions via an amide bond. For the conjugation with cystamine, a second reaction step is required to expose the sulfhydryl function of cystamine that is otherwise protected in a disulfide bond. 1,4-Dithio-DL-threitol (DTT) (method #2) or Tris(2-carboxyethyl)-phosphine hydrochloride (method #3) were evaluated for their ability to reduce this linkage. Method #1 allowed a maximum of 8.5+/-2.8 mmol of thiol functions per mol of PLA to be attached on the surface of the nanoparticles. Method #2 allowed the introduction of a greater number of thiol functions (up to 190+/-15 mmol per mol of PLA). However, this latter method has a major drawback: DTT interacts strongly with the nanoparticle matrix during the reduction step. Method #3 has the advantage over method #2 in that it allowed a significant number of thiol functions to be covalently bound to the particles (up to 107.6+/-0.6 mmol per mol of PLA) without the problem of undesired interaction between DTT and the nanoparticle matrix. The introduction of thiol groups onto the surface of PLA nanoparticles is possible with all three suggested methods. The method #3 provides a straight forward approach for the substitution of carboxylic acid groups with a high number of activated sulfhydryl at the surface of PLA nanoparticles.

Lactic Acid↗
PubMed2004

Improved mechanical properties of HIPS/hydroxyapatite composites by surface modification of hydroxyapatite via in-situ polymerization of styrene.

High impact polystyrene (HIPS)/hydroxyapatite (HA) composites are potential biomaterials for bone replacements due to their good biocompatibility and adequate mechanical properties. At the present work, the surface of the micron-sized hydroxyapatite (HA) particles was modified by in situ polymerization of styrene (St), then compounded with HIPS. The effect of the modification of HA surface on morphology and mechanical properties of HIPS/HA composites were investigated. The results showed that the HA particles does not inhibit the polymerization of St. The PS segments coated on the HA surface by in situ polymerization of St enhances the compatibility between HA and HIPS, improves the dispersion of HA particles in HIPS matrix, and enhances the interfacial adhesion between HA and matrix. Thereby, the stiffness, tensile strength and notch impact strength of HIPS/HA composites are improved at the same time. And there is a critical coating thickness of PS on the HA surface for the optimum mechanical properties of HIPS/HA composites.

Biocompatible Materials↗
PubMed2006

Nylon surface modification: 2. Nylon-supported composite films.

We have developed techniques for the introduction of reactive functional groups to nylon surfaces via site-specific reactions targeting at the naturally abundant amide repeating units on the surface. In this report, we describe the fabrication of nylon-supported composite surfaces using the most efficient modification methods we have developed. N-Alkylation with (3-glycidoxypropyl)triethoxysilane (GPTES) in the presence of potassium tert-butoxide (t-BuOK) leads to surfaces with silica-like reactivity. Subsequent chemical vapor deposition using tetrachlorosilane (SiCl4) and water results in composite films with a thin layer of silica, which was made hydrophobic by reaction with a fluorinated silane reagent. Reduction of the amide groups with borane-THF (BH3-THF) complex leads to a 69% conversion of surface amides to the corresponding secondary amine groups. Alginate was chosen as the model polyelectrolyte for the introduction of a hydrated surface layer. Because of the strong electrostatic interaction between alginate and the amine-enriched nylon surfaces, the adsorption is fast and concentration-independent (within the concentration range studied). The polysaccharide coats the surface homogeneously, without the formation of large aggregates. The amine surfaces obtained by reduction with BH3-THF ((BH3-THF)nylon-NH) and by alkylation with 2-bromoethylamine hydrobromide (BEA-HBr, (EBA-HBr)nylon-NH2) were also used to study gold deposition through electroless plating. Immobilization of a negatively charged metal complex (AuCl4(-)) was achieved through electrostatic interaction. Gold particles disperse preferentially in the bulk of (EBA-HBr)nylon-NH2 films, while they remain confined to the outer surface layer of (BH3-THF)nylon-NH films.

Journal Article↗
PubMed2005

Modification of surface properties of biomaterials influences the ability of Candida albicans to form biofilms.

Candida albicans biofilms form on indwelling medical devices (e.g., denture acrylic or intravenous catheters) and are associated with both oral and invasive candidiasis. Here, we determined whether surface modifications of polyetherurethane (Elasthane 80A [E80A]), polycarbonateurethane, and poly(ethyleneterephthalate) (PET) can influence fungal biofilm formation. Polyurethanes were modified by adding 6% polyethylene oxide (6PEO), 6% fluorocarbon, or silicone, while the PET surface was modified to generate hydrophilic, hydrophobic, cationic, or anionic surfaces. Formation of biofilm was quantified by determining metabolic activity and total biomass (dry weight), while its architecture was analyzed by confocal scanning laser microscopy (CSLM). The metabolic activity of biofilm formed by C. albicans on 6PEO-E80A was significantly reduced (by 78%) compared to that of biofilm formed on the nonmodified E80A (optical densities of 0.054 +/- 0.020 and 0.24 +/- 0.10, respectively; P = 0.037). The total biomass of Candida biofilm formed on 6PEO-E80A was 74% lower than that on the nonmodified E80A surface (0.46 +/- 0.15 versus 1.76 +/- 0.32 mg, respectively; P = 0.003). Fungal cells were easily detached from the 6PEO-E80A surface, and we were unable to detect C. albicans biofilm on this surface by CSLM. All other surface modifications allowed formation of C. albicans biofilm, with some differences in thearchitecture. Correlation between contact angle and biofilm formation was observed for polyetherurethane substrates (r = 0.88) but not for PET biomaterials (r = -0.40). This study illustrates that surface modification is a viable approach for identifying surfaces that have antibiofilm characteristics. Investigations into the clinical utility of the identified surfaces are warranted.

Biocompatible Materials↗