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PubMed1999

Surface Modification of Conventional Polymers by Depositing Plasma Polymers of Trimethylsilane and of Trimethylsilane + O2.

The dynamic wetting properties of TMS (trimethylsilane) and TMS + O2 plasma-deposited films on ten low energy conventional polymers were investigated using the Wilhelmy balance method. Plasma deposition resulted in wetting properties that were independent of the underlying polymer substrate for the majority of polymers studied. TMS plasma modification resulted in virtually the same degree of hydrophobicity with an average cosine of the dynamic advancing contact angle from the first immersion, cos θD,a,1 = -0.381 (θD,a,1 = 112 +/- 3.6), for eight of the ten polymers. PTFE and UHMWPE were slightly more hydrophobic after TMS plasma treatment with an average cos θD,a,1 = -0.785 (θD,a,1 = 141 +/- 4.2). TMS + O2 plasma modification resulted in high wettability of all polymers with an average cos θD,a,1 = 0.654 (θD,a,1 = 49.2 +/- 11.7). Dynamic hysteresis, mainly a result of the change in meniscus shape during immersion and emersion, and intrinsic hysteresis, due to the extent of surface configuration change, were both found to vary according to the size of the polymer plate. In general, dynamic hysteresis can be quite large for more hydrophobic TMS treated polymers and considerably smaller for highly hydrophilic TMS + O2 treated polymers. The extent of intrinsic hysteresis of only TMS treated polymers was found to be independent of the underlying polymers within the time-scale of wetting. TMS + O2 plasma treatment resulted in wide variations in intrinsic hysteresis probably due to substrate specific etching of oxygen plasma species. The wettability of the untreated and TMS and TMS + O2 treated polymers, indicated by the static "advancing" contact angles from the sessile droplet method and dynamic "advancing" and "receding" contact angles from the Wilhelmy balance method, were found to conform well to the correlation, cos θS = (cos θD,a,1 + cos θD,r,1)/2. Copyright 1999 Academic Press.

Journal Article↗
PubMed2006

Surface modification of amine-functionalised graphite for preparation of cobalt hexacyanoferrate (CoHCF)-modified electrode: an amperometric sensor for determination of butylated hydroxyanisole (BHA).

A cobalt hexacyanoferrate (CoHCF)-modified graphite paraffin wax composite electrode was prepared by a new approach. An amine-functionalised graphite powder was used for the fabrication of the electrode. A functionalised graphite paraffin wax composite electrode was prepared and the surface of the electrode was modified with a thin film of CoHCF. Various parameters that influence the electrochemical behaviour of the modified electrode were studied by varying the background electrolytes, scan rates and pH. The modified electrode showed good electrocatalytic activity towards the oxidation of butylated hydroxyanisole (BHA) under optimal conditions and showed a linear response over the range from 7.9 x 10(-7) to 1.9 x 10(-4) M of BHA with a correlation coefficient of 0.9988. The limit of detection was 1.9 x 10(-7) M. Electrocatalytic oxidation of BHA was effective at the modified electrode at a significantly reduced potential and at a broader pH range. The utility of the modified electrode as an amperometric sensor for the determination of BHA in flow systems was evaluated by carrying out hydrodynamic and chronoamperometric experiments. The modified electrode showed very good stability and a longer shelf life. The modified electrode was applied for the determination of BHA in spiked samples of chewing gum and edible sunflower oil. The advantage of this method is the ease of electrode fabrication, good stability, longer shelf life, low cost and its diverse application for BHA determination.

Journal Article↗
PubMed2003

Surface modification of PLGA microspheres.

Microspheres made of poly(lactic-co-glycolic acid) (PLGA) are biocompatible and biodegradable, rendering them a promising tool in the context of drug delivery. However, nonspecific adsorption of plasma proteins on PLGA micro- and nanospheres is a main limitation of drug targeting. Poly(L-lysine)-g-poly(ethylene glycol) (PLL-g-PEG), physisorbed on flat metal oxide surfaces, has previously been shown to suppress protein adsorption drastically. The goal of our work was to characterize the efficiency of the protein repellent character of PLL-g-PEG on PLGA microspheres and to show the feasibility of introducing functional groups on the PLGA microspheres via functionalized PLL-g-PEG. To quantify the adsorbed amount of protein, a semiquantitative method that uses confocal laser scanning microscopy (CLSM) was applied. The first part of the experiment confirms the feasibility of introducing specific functional groups on PLL-g-PEG-coated PLGA microspheres. In the second part of the experiment, PLL-g-PEG-coated PLGA microspheres show a drastic decrease of adsorbed proteins by two orders of magnitude in comparison to uncoated PLGA microspheres. Low protein-binding, functionalizable microspheres provide a fundamental basis for the design of drug delivery and biosensor systems.

Biosensing Techniques↗
PubMed1993

Polyphosphazenes as biomaterials: surface modification of poly(bis(trifluoroethoxy)phosphazene) with polyethylene glycols.

Investigations were carried out on the metathetical exchange reaction between the -O-CH2CF3 moieties of poly(bis(trifluoroethoxy)phosphazene) (PTFP), in the state of slightly swollen films, and the alkoxide ions derived from methoxypolyethylene glycol (MPEG) of molecular mass ranging from 350 to 5000 g/mol. The substitution of these hydrophilic chains, mostly confined to thin surface layers, was revealed by means of optical microscopy and scanning electron microscopy observations, surface elemental analysis by energy-dispersive X-ray analysis (EDXA), FTIR-ATR analysis and water contact angle measurements. The surface biocompatibility was enhanced in all cases, whilst the mechanical properties of the original PTFP films were substantially retained in the modified samples exhibiting low substitutions. Such samples were obtained especially when the metathetical reaction was carried out with MPEG5000.

Animals↗
PubMed1999

[Surface modification of low temperature isotropic pyrolytic carbon artificial heart valve material].

In this study, nitrogen ion implantation and titanium oxide film synthesized by ion beam enhanced deposition were adopted to treat low temperature isotropic pyrolytic carbon (LTIC). The chemical composition and valence state of the modified layer were determined by X-ray photoelectron spectroscopy (XPS) and Auger eletron spectroscopy (AES). The electric resisitance and the surface energy were measured by the four-probe system and the contact angle method respectively. The blood compatibility of the modified LTIC was evaluated by clotting time measurement and platelet adhesion test. The results showed that carbon-nitride was formed on the LTIC surface after N+ ion implantation, which had some effect on the improvement of blood compatibility, and a significant improvement of blood compatibility of LTIC coated by TiO2-x film was verified.

Animals↗
PubMed2004

Surface modification of UHMWPE for use in total joint replacements.

To create a hydrophilic, lubricious, more wear-resistant UHMWPE bearing, a novel hyaluronan (HA) derivative and novel UHMWPE-hyaluronan composite were developed. HA was silylated to increase its hydrophobicity and compatibility with UHMWPE. The sily1 HA rapidly diffused into the connected pores of UHMWPE preforms in xylenes solution, and fixed within UHMWPE and on its surface after crosslinking. A micro-composite was obtained after hot-pressing the porous preform. The presence of HA film on the composite surface has been demonstrated through X-Ray photoelectron spectroscopy (XPS) analysis and Toluidine Blue O (TBO) dye assay. The aqueous contact angles of micro-composite samples were significantly lower compared with UHMWPE control samples, and the samples processed with hydrolysis prior to final molding were superior to those processed with hydrolysis after molding.

Equipment Failure Analysis↗
PubMed2000

Surface modification of calcium metaphosphate fibers.

beta-calcium metaphosphate fibers having high aspect ratios of 10-120 with diameters of 2-10 microm show high strength and good biocompatibility. When the fibers are soaked in simulated body fluid at 37 degrees C, however, no calcium phosphate phase is newly formed on the fibers. In the present work, by treating the fibers at 70 degrees C with dilute NaOH aqueous solution, the surface phase was converted successfully into the orthophosphate phase that was in fine sizes and was adhered. After soaking the treated fibers in simulated body fluid at 37 degrees C for 30 days, a new calcium phosphate phase was precipitated. This was attributed to the surface phase modified using dilute NaOH. The treated fibers are expected to show bone-bonding ability, i.e. bioactivity.

Journal Article↗
PubMed1991

The keratoprosthesis: improved biocompatibility through design and surface modification.

Due to poor biocompatibility, the success of keratoprostheses has been limited. We compared a newly-designed PMMA intracorneal keratoprosthesis, covalently coated with type-I collagen, with an identical, uncoated keratoprosthesis were retained for 15 months, the uncoated implants had more extensive adjacent corneal melting, greater inflammatory response, and more epithelial downgrowth than their collagen-coated counterparts. Electron microscopy showed that stromal collagen fibers had attached to the surface of the coated implants, but not to that of the uncoated ones. Intracorneal keratoprostheses covalently coated with type-I collagen may offer superior biocompatibility and become significantly incorporated into corneal tissues.

Animals↗
PubMed1996

Plasmodium falciparum: surface modifications of infected erythrocytes from clinical isolates. Evidence of antigenic diversity using Venezuelan human malarial sera.

Infections of human erythrocytes with the mature asexual blood stages of Plasmodium falciparum result in antigenic changes in the host cell membrane that, by virtue of their position, length of exposure, and close association with functional changes critical to pathogenesis, are a potential important target for host effector mechanisms. These parasite-induced antigens expressed on the surface of infected erythrocytes have been shown to exhibit considerable polymorphism. An antibody-mediated agglutination assay using malaria serum samples from different regions of Venezuela has been developed to examine the extent of antigenic diversity of infected red blood cells (IRBC) taken from subjects with naturally acquired P. falciparum infections. An important humoral immune recognition of surface molecules from red blood cells infected with a wide variety of clinical isolates of P. falciparum was observed even when sera from individuals experiencing a single episode of malaria were used. A process of in vivo antigenic variation of surface molecules is postulated, since agglutination of IRBC was observed with acute heterologous but not autologous sera. When sera obtained from Amerindians inhabiting the Venezuelan Amazon were assayed, a strong immune response to different parasite isolates, including those of another geographic region, was observed, suggesting the recognition of highly conserved immunogenic parasitic epitopes in people exposed to multiple malaria infections.

Agglutination Tests↗
PubMedDate not supplied

Surface modification of polycarbonate with synthetic polyelectrolyte-anticoagulant activity.

Natural rubber with C = C bonds had been modified by reaction with chlorosulfonyl isocyanate (CSI) and 70% of the products were obtained, which yielded polyelectrolyte on treatment with NaOH, having sulfamate and carboxylate groups. The polyelectrolyte showed anticoagulant activity. This might be due to the presence of both sulfamate and carboxylate groups arranged in a steric manner in the molecule as that of Heparin. Surface energy parameters, platelet adhesion and plasma recalcification time were investigated. Possible comparison with heparin had been demonstrated.

Anticoagulants↗
PubMed2006

Monolithic silica-based capillary column with strong chiral cation-exchange type surface modification for enantioselective non-aqueous capillary electrochromatography.

A silica-based monolithic stationary phase prepared by the sol-gel process in a 100 microm I.D. fused-silica (FS) capillary has been modified chemically with 3-mercaptopropyl trimethoxysilane followed by immobilization of a strong cation-exchange (SCX) type chiral selector, (S)-N-(4-allyloxy-3,5-dichlorobenzoyl)-2-amino-3,3-dimethylbutane phosphonic acid, by radical addition reaction onto the reactive sulfhydryl surface. After a fine-tuning of the mobile phase composition, the enantioselective capillary column was evaluated for the separation of various chiral basic drugs by enantioselective non-aqueous capillary electrochromatography (CEC), in comparison to capillary column analogs packed with 3.5 microm silica particles having attached the same selector. The performance of the monolithic silica column was further compared to corresponding polymethacrylate-based organic polymer monoliths. The study indicated that strong counter-ions such as 2-aminobutanol or N,N,N',N'-tetramethylethylenediamine are needed, although they reduce the electroosmotic flow velocity and separation factors in comparison to less efficient counter-ions, in order to allow the elution of the oppositely charged solutes in the ion-exchange retention mode within reasonable run time and as sharp zones. In contrast, weak counter-ions such as N,N-diisopropylethylamine (Huenig base) provided stronger electroosmotic flow and much better separation factors, but relatively poor peak efficiencies. Overall, with the chemically functionalized monolithic silica column the high quality separations of packed column analogs could be approximated, with regards to both separation factors and peak performances. On the other hand, the monolithic capillary column certainly outperformed the packed column in terms of system robustness under capillary electrochromatography conditions and showed excellent column longevity. The enantioselective strong cation-exchange-type monolithic silica column performed also well in comparison to the organic polymer monolith.

Cation Exchange Resins↗
PubMed2000

Surface modification of polyethylene balloon catheters for local drug delivery.

Local drug delivery is an attractive approach to the associated problems of percutaneous transluminal coronary angioplasty (PTCA), including arterial injury. The objective of the present research was to deliver a high concentration of a potent anti-thrombin agent, argatroban (ARG), to the vessel wall in order to reduce arterial injury. Local delivery was accomplished by the ionic attachment of drug particles to a modified balloon surface. Surface graft polymerization of ionic monomers to a high-density poly(ethylene) (PE) substrate was performed utilizing ultra-violet (UV) methods. Acrylic acid (AAc) and 2(dimethylamino) ethyl methacrylate (DMAEMA) were successfully grafted onto PE surfaces. Surface grafting was verified by contact angle, X-ray photoelectron spectroscopy, and zeta potential measurements. The amount of ARG adsorbed onto the modified PE surface was highly dependent on the pH of the drug media for both anionic and cationic grafted monomers. The efficacy of local drug delivery to the arterial wall was analyzed using drug-immobilized PE balloon catheters in the rabbit common carotid artery model. High concentrations of ARG (280 nmol/g tissue) were found within the ballooned arterial segment immediately after angioplasty, followed by a decrease after blood flow was restored.

Acrylates↗
PubMed2004

Surface modification of poly(L: -lactic acid) affects initial cell attachment, cell morphology, and cell growth.

The object of this study was to develop a highly porous scaffold to be used in regeneration of blood vessels, nerves, and other hollow tissues with small openings. Using the phase-inversion method and a mixture of water and methanol as a coagulating agent, we prepared highly porous flat membranes from poly(L: -lactic acid) (PLLA) with numerous pores both on the surface and in the interior of the membranes. Chinese hamster ovary (CHO) cells were cultured on the membranes to evaluate initial cell adhesion, cell proliferation, and cell morphology. Adhesion of CHO cells to PLLA was poor: the cells adhered at approximately half the rate observed with a tissue culture polystyrene dish (TCPS). In contrast, adhesion of cells to PLLA treated with a low-temperature oxygen plasma was good; the adhesion rate was the same as that on TCPS. The rate of cell proliferation on the treated membranes was no different from that on the nontreated membranes, but cell morphologies were quite different. The cells on the nontreated membranes were small and round and proliferated separately from one another. In contrast, the cells on the plasma-treated membranes proliferated in close contact with other cells, spreading out extensively in sheet-like formations. Since the plasma treatment not only accelerated cell adhesion but also enabled cells to proliferate in the form of sheets resembling biological tissue, we believe that oxygen-plasma treatment is extremely effective for modifying surfaces of materials used for tissue regeneration.

Animals↗
PubMed2004

Surface modification with phosphoric acid of SiO2/Nb2O5 prepared by the sol-gel method: structural-textural and acid sites studies and an ion exchange model.

In this work, the structural and textural properties of the SiO2/Nb2O5 system prepared by the sol-gel method and then modified by phosphoric acid were studied. The different materials were prepared, with three different mol % Nb2O5 (2.5, 5.0, and 7.5 mol %), and calcined in the temperature range of 423-1273 K. BET specific surface area determinations, scanning electron microscopy connected to a X-ray emission analyzer, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy (XPS) were used for the investigation. For the lowest temperature of calcination (423 K), the mesopores and micropores of the modified material were blocked, resulting in a decrease of the specific surface area compared to the SBET values obtained for the SiNb matrix. Under intermediate temperatures of calcination (423-873 K), the modified material acquired textural stability. By XPS analysis, the presence of the dihydrogenphosphate species was identified, the P/Nb atomic ratios being independent of the thermal treatment. 31P magic angle spinning NMR confirmed the XPS data and also showed that the chemical shift of the (H2PO4)- ions strongly depended on the crystallization degree of the Nb2O5. Structural thermal stability was also shown by the presence of Brønsted acid sites in the modified material calcined at high temperature (1273 K). The thermal stability is directly associated with obtainment of the same value for K+ exchange capacity (0.74 mmol g(-1), average value) for the modified materials calcined at 423 and 1273 K. The chemical analyses of phosphorus for the modified materials were made by using the inductively coupled plasma. The value was 0.36 mmol g(-1), corroborating the presence of (H2PO4)- ions. The ion exchange isotherms presented an S-shaped form characteristic of energetically heterogeneous ion exchangers, permitting application of a model of fixed polydentate centers, in which ion exchange took place.

Journal Article↗
PubMed2005

Human skin cell cultures onto PLA50 (PDLLA) bioresorbable polymers: influence of chemical and morphological surface modifications.

Poly(alpha-hydroxy acid)s derived from lactic and glycolic acid are bioresorbable polymers which can cover a large range of thermal, physical, mechanical, and biological properties. Human keratinocytes have been shown as able to grow on a poly(DL-lactic acid) film. However the keratinocyte growth was delayed with respect to culture on standard tissue culture polystyrene, even though the same plateau level was observed after 2 weeks. In order to improve the performance of poly(DL-lactic acid) films as skin culture support, their surface was modified by creating tiny cavities using a method based on the leaching out of poly(ethylene oxide) from poly(lactic acid)-poly(ethylene oxide) heterogeneous blends. The surface of the films was also chemically modified by alkaline attack with sodium hydroxide and by type-I collagen coating. Murine fibroblast cell line and primary cultures of human fibroblasts and of two types of keratinocytes were allowed to adhere and to grow comparatively on the different films. The presence of cavities affected neither the adhesion of dermal fibroblasts nor that of keratinocytes. Only keratinocyte proliferation was significantly reduced by the presence of cavities. Collagen coating improved skin cell adhesion and proliferation as well, except in the case of murine fibroblasts. In the case of the NaOH treatments, similar trends were observed but their extent depended on the treatment time. In the case of chemical modifications, fluorescence microscopy bore out adhesion and proliferation tendencies deduced from MTT tests.

Biocompatible Materials↗