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PubMed1996

Polymeric surface modifications of tantalum stents.

PURPOSE: To compare two kinds of polymer-coated tantalum stents with bare tantalum stents (control) to determine if the coatings can improve thromboresistance. METHODS: Twenty-seven Fontaine-Dake stents were balloon expanded in three 8-mm x 80-cm polytetrafluoroethylene (PTFE) grafts; 9 stents were bare tantalum (T); 9 were coated with polyetherurethane (PL); and 9 were coated with parylene (PA). There were 9 stents placed in each graft as follows: 3 tantalum, 3 polyetherurethane, and 3 parylene. In swine whose platelets had been radiolabeled with indium 111, the ends of each stented graft were connected to 14F femoral and venous sheaths to create an ex vivo fistula. Each graft was exposed to blood for 30, 60, and 120 minutes. At the end of each test period, the stented grafts were disconnected from the sheaths, flushed with saline until clear, and then flushed with formalin. The stents were removed from the grafts, and a radionuclide well counter recorded radionuclide counts from each stent type at each period of blood contact. These values were converted to platelet density per 1000 microns 2. Stents were then photographed and scanned with electron microscopy (EM) for qualitative analysis. Possible significant differences in platelet adhesion with the three types of stents (both between stent groups and within stent groups) were examined using a two-tailed Student's t-test. RESULTS: There were significantly fewer platelets adsorbed on PA versus T at all time periods (p < 0.005); on PL versus T at 60 and 120 minutes (p < 0.005); and on PA versus PL at 30 and 120 minutes (p < 0.0005). There was no significant difference in platelet density within each stent group (p = 0.1). Mean platelet density (number of platelets per 1000 microns 2 +/- SD) was as follows: at 30 minutes: T = 1891 +/- 965; PL = 373 +/- 193; and PA = 27 +/- 3; at 60 minutes: T = 6226 +/- 1621; PL = 1573 +/- 793; and PA = 1185 +/- 710; at 120 minutes: T = 5307 +/- 591; PL = 3164 +/- 318; and PA = 180 +/- 100. Gross inspection of the 120-minute groups demonstrated focal areas of thrombus on T, less on PL, and none on PA. Scanning EM demonstrated extensive platelet accumulation covering T at all time periods, less on PL, and even less on PA.

Animals↗
PubMed2004

Tendon surface modification by chemically modified HA coating after flexor digitorum profundus tendon repair.

Carbodiimide derivatized HA (cd-HA) is less soluble in water than normal HA, and therefore has an increased tissue residence time. The purpose of this study was to study the effect of cd-HA gel on gliding and repair integrity during simulated repetitive motion of a repaired tendon in vitro. A total of 36 flexor digitorum profundus (FDP) tendons from six adult mongrel dogs were used and divided into three groups of control, simple HA, and cd-HA. The gliding resistance between the FDP and the proximal pulley, FDS, and bone was measured before laceration and after modified Kessler technique repair at 1, 5, 10, 50, 100, 200, 300, 400, and 500 cycles. After gliding testing, failure load, tendon stiffness, and resistance to gap formation were measured. The results showed from the first cycle to the 10th cycle, there were no significant differences in gliding resistance between the three testing groups (p > 0.05). From the 50th cycle onwards, the friction was significantly lower in the cd-HA gel group than in the control group (p < 0.05). Neither breaking strength, nor tendon stiffness, nor resistance to gap formation of the repairs were significantly different between the three groups (p > 0.05).

Coated Materials, Biocompatible↗
PubMed1975

Surface modifications evoked by antidiuretic hormone in isolated epithelial cells: evidence from lectin probes.

Epithelial cells (80-90% "granular" type) were isolated from urinary bladders of Bufo marinus and Rana catesbiana. The inhibitory effect of alpha-methyl-D-mannoside on fluorescein-labeled concanavalin A (Con A) binding to these cells indicates that they possess specific binding sites for Con A. The lectin also mediates adsorption of erythrocytes to these cells. Both Con A binding and Con A-mediated hemadsorption to epithelial cells are depressed at 4 degrees C, as compared with cells maintained at 22 degrees C. Elevation of temperature to 37 degrees C, however, enhances hemadsorption independently of alterations in lectin binding. Treatment of cells with antidiuretic hormone (ADH) at 22 degrees C followed by 15 min of incubation at 22 degrees or 37 degrees C before exposure of cells to Con A promotes increments in Con A-mediated hemadsorption, but not in lectin binding, at 22 degrees or 37 degrees C. These hormonal effects are not significant when hemadsorption is assayed at 4 degrees C. Treatment of cells with another octapeptide, angiotensin, elicits a small, but significant, increment in hemadsorption to epithelial cells which is likewise uninfluenced by quantitative changes in lectin binding. Collectively, these data and other independent observations suggest that treatment with octapeptide hormones acts to enhance the redistribution and aggregation of lectin-binding proteins in the membranes of granular epithelial cells from amphibian urinary bladder. Such changes, in turn, may contribute to the alterations in membrane transport properties which characterize the hormonal response.

Angiotensin II↗
PubMed1997

Nylon-Based Affinity Membranes: Impacts of Surface Modification on Protein Adsorption.

Nylon microfiltration membranes were activated with bisoxirane and formaldehyde at terminal amino groups and amide groups of the nylon polymer, respectively. Dextrans were covalently immobilized on these activated membranes to yield dextran-coated membrane matrices. Both procedures led to a significant reduction of hemoglobin adsorption; however, bisoxirane activation required additional cross-linking of dextran and a second dextran layer to yield comparable quality of dextran-coated membranes than formaldehyde activation. Formaldehyde activation was easiest and cheapest and resulted in membranes with highest dextran density and relatively lowest nonspecific hemoglobin adsorption. Dextrans of &Mmacr;w >/= 40,000 were required for bisoxirane-activated membranes, whereas dextrans of &Mmacr;w = 6000 were sufficient for formaldehyde-activated membranes. Both activation methods resulted in stable coatings at low and high pH; however, formaldehyde-activated membranes were unstable under strongly acidic conditions at pH < 3. Dextran coils were found responsible for the reduction of the hydraulic permeability but also for the high ligand densities obtained after immobilization of Cibacron Blue F3G-A (360 nmol/cm2) and iminodiacetic acid (400 nmol/cm2). The thermodynamics of protein adsorption on dye ligand affinity (DLA) membranes corresponded with chromatographic sorbents and dye ligand conjugates, with the dextran coating demonstrating similar structure than dextrans in solution. Protein adsorption took place in the extended coil structure of dextrans with binding capacities up to 730 µg/cm2 lysozyme on DLA membranes and 470 µg/cm2 concanavalin A on metal chelate affinity membranes. Copyright 1997 Academic Press.

Journal Article↗
PubMed1984

Cell surface modifications in the epithelium of rat ventral prostate during adaptation to in vitro conditions: an ultrastructural study.

Sequential changes in epithelial cells of collagenase-dissociated rat ventral prostate were studied by thin-section and freeze-fracture electron microscopy. Epithelial cells did not attach to the substrate for 48 h. Pelleted cells obtained 1, 24, and 48 h after dissociation were assigned to three categories depending on morphology and cellular associations. (a) Solitary epithelial cells degenerated as determined by extensive vacuolization in the cytoplasm and aggregation of intramembranous particles (IMP). (b) Epithelial clusters consisted of a homogeneous population of well-maintained, closely packed cells. Aggregation of IMP was minimal. Tight junctions that formed between cells at the periphery of the clusters appeared normal and provided an effective permeability barrier demonstrated by the exclusion of ruthenium red tracer. (c) Tissue fragments were comprised of varying combinations of epithelial, endothelial, and smooth muscle cells as well as fibroblasts and erythrocytes. Maintenance of tissue fragments was variable. Plasma membranes often displayed aggregated IMP and proliferated tight junctional strands. An effective permeability barrier was absent. After the 48 h "latent period," epithelial cells in the clusters lost interdependence, disassociated from one another, and attached to the substrate. These isolated cells, which did not display aggregated IMP, retained the ability to form an effective permeability barrier upon reaching confluency. During the first 48 h, epithelial cells did not tolerate solitary existence, yet as participants in clusters they were well maintained. After this interval, they no longer required interactions with neighbors in order to survive. These results indicate that under our experimental conditions, an adaptation period is required by prostatic epithelial cells. The enhanced quality of maintenance associated with epithelial clusters suggests that control over the internal microenvironment, provided by a tight junctional barrier, may be important during the initial period of adaptation in vitro.

Adaptation, Physiological↗
PubMed1995

Stabilization and surface modification of monoclonal antibodies by 'bi-layer encagement'.

A two step simple procedure for antibody stabilization in soluble form was developed. The antibody is first treated with low molecular weight polyaldehyde (polyglutaraldehyde). Following removal of non-bound polyaldehyde the antibody-polyaldehyde conjugate is crosslinked by polyamine (alkyl amine derivative of polyglutaraldehyde). Feasibility studies were successfully conducted employing monoclonal antibody raised against horseradish peroxidase as model system. The stabilized antibody preparation exhibited improved thermal stability, enhanced resistance to proteolytic digestion and higher 'specific binding activity' in ELISA test, without losing its capability to bind large antigen (enzyme) or being recognized by another antibody (goat anti-mouse IgG).

Antibodies, Monoclonal↗
PubMed2005

Enzymatic surface modification of poly(ethylene terephthalate).

This study unambiguously confirms hydrolysis using cutinase of the persistent synthetic polymer poly(ethylene terephthalate), the most important synthetic fiber in the textile industry by direct measurement and identification of the different hydrolysis products. In this aqueous heterogeneous system, dissolved cutinase from Fusarium solani pisi acts on different solid poly(ethylene terephthalate) substrates. The extent of hydrolysis was detected by measuring the amount of (soluble) degradation products in solution using reversed-phase HPLC. Crystallinity greatly affects the capability of the enzyme to hydrolyze the ester bonds, displaying relatively high activity towards an amorphous polyester film and little activity on a highly crystalline substrate. The enzyme is sufficiently stable, hydrolysis rate on the amorphous substrate maintained at sufficient high level over a long period of time of at least five days. From an industrial point of view it is highly recommended to increase the hydrolysis rates.

Carboxylic Ester Hydrolases↗
PubMed2006

Citrate-assisted synthesis of prickly nickel microwires and their surface modification with silver.

A new type of prickly nickel microwires assembled by thornlike nanocrystals was fabricated through a simple chemical reduction route with the assistance of citrate. Thus-prepared nickel wires were subsequently morphology-retained modified with a thin silver shell via transmetallation. Compared with the uncoated sample, the Ni(core)-Ag(shell) wires exhibited much-enhanced oxidation resistance, slightly changed magnetic properties and stark different catalysis for the creation of carbon particles in pyrolyzing acetone.

Letter↗
PubMed2002

Surface modification of an organosilane self-assembled monolayer on silicon substrates using atomic force microscopy: scanning probe electrochemistry toward nanolithography.

Organosilane self-assembled monolayers (SAMs) have been applied to resist materials for nanolithography based on scanning probe microscopy. An organosilane SAM was prepared on Si substrates from a precursor, that is octadecyltrimethoxysilane. Using an atomic force microscope with a conductive probe, current was injected from the probe into the SAM-covered Si substrate so that the SAM was locally degraded at the probe-contacting point. Nanoscale patterns drawn on the SAM was clearly imaged by lateral force microscopy. The patterning could be conducted in air while, in vacuum at the order of 10(-6) Torr, no detectable patterns were fabricated. The presence of adsorbed water at the probe/sample junction was confirmed to be crucial for the patterning of the SAM/Si. Its mechanism was, thus, ascribed to electrochemical reactions of both the SAM and Si with adsorbed water.

Journal Article↗
PubMed2004

Effects of TiO2 surface modifications on photocatalytic oxidation of arsenite: the role of superoxides.

Using TiO2 photocatalyst, arsenite [As(III)] can be rapidly oxidized to arsenate [As(V)], which is less toxic and less mobile in the aquatic environment. Superoxides have been recently proposed as a main photocatalytic oxidant of As(III) whereas OH radicals are dominant oxidants in most TiO2 photocatalytic oxidation (PCO) reactions. This study confirms that superoxides are mainly responsible for the As(III) PCO by investigating PCO kinetics in pure and modified TiO2 systems. The rate of As(III) oxidation drastically increased on Pt-TiO2, which could be ascribed to the enhanced superoxide generation through an efficient interfacial electron transfer from the conduction band (CB) to O2. Since the addition of tert-butyl alcohol (OH radical scavenger) had little effect on the PCO rate in both naked and Pt-TiO2 suspensions, OH radicals do not seem to be involved. The addition of polyoxometalates (POMs) as an electron shuttle between TiO2 CB and 02 highly promoted the PCO rate whereas the POM alone was not effective at all in oxidizing As(III). Fluorinated TiO2 that had a markedly reduced adsorptive capacity for As(III) did not show a reduced PCO rate, which indicates that the direct hole transfer path is not important. The arsenite oxidation proceeded under visible light with a similar rate to the case of Pt-TiO2/UV when dye-sensitized Pt-TiO2 was used. Since only superoxides can be generated as a photooxidant in this visible light system, their role as a main oxidant of As(III) is confirmed. In addition, the PCO rate was significantly reduced in the presence of superoxide dismutase.

Arsenates↗
PubMed2005

Ordered alignment of CdS nanocrystals on MWCNTs without surface modification.

This paper describes a facile hydrothermal procedure capable of aligning CdS nanocrystals on multiwalled carbon nanotubes (MWCNTs) without the use of organic bridging molecules such as cysteamine and carboxylates. The direct placement of CdS on MWCNTs allows good mixing and better interfacing between the two nanophases. The synthesis conditions can in principle be tuned to produce modulations in compositions, phases, and crystal orientations to the need of optoelectronic and photonic applications.

Journal Article↗