Surface Sulfonation Research Articles

Albumin adsorption on unmodified and sulfonated polystyrene surfaces, in relation to cell–substratum adhesion

Albumin is commonly applied for blocking the adsorption of other proteins and to prevent the nonspecific adhesion of cells to diverse artificial substrata. Here we address the question of how effective these albumin properties are--by investigating unmodified and sulfonated polystyrene substrata with distinctly different wettabilities. As clearly shown with (125)I-radioisotopic assays, above a concentration of 10-20 μg/mL, the efficiency of bovine serum albumin (BSA) adsorption became markedly higher on the sulfonated surface than on the unmodified one. This study was assisted with the atomic force microscopy. On the unmodified surface, BSA, adsorbed from sufficiently concentrated solutions, formed a monolayer, with occasional intrusions of multilayered patches. Conversely, the arrangement of BSA on the sulfonated surface was chaotic; the height of individual molecules was lower than on the unmodified polystyrene. Importantly, the adhesion study of LNCaP and DU145 cells indicated that both surfaces, subjected to the prior BSA adsorption, did not completely loose their cell-adhesive properties. However, the level of adhesion and the pattern of F-actin organization in adhering cells have shown that cells interacted with unmodified and sulfonated surfaces differently, depending on the arrangement of adsorbed albumin. These results suggest the presence of some bare substratum area accessible for cells after the albumin adsorption to both types of investigated surfaces.

Highly Charged Inorganic−Organic Colloidal Core−Shell Particles

Highly defined, hybrid inorganic-organic colloidal core-shell particles consisting of a silica core and a shell of fluorinated acrylate are prepared in a two-step route. The core-shell structure of the particles is investigated by means of small-angle X-ray scattering (SAXS). Because of highly acidic sulfonic acid surface groups resulting from the radical initiator sodium peroxodisulfate at the organic shell, long-range electrostatic interactions lead to the formation of liquidlike mesostructures. Increasing the effective interaction by reducing the next-neighbor distances induces a freezing of the liquidlike structures, i.e., a transition to crystalline and glassy structures. Because of the high electron density in the core and the fluorinated polymer shell, these particles are strong X-ray scatterers. In combination with the large number of effective charges and the outstanding monodispersity, these core-shell particles are a promising model system for the investigation of the glass transition by photon correlation spectroscopy employing coherent X-rays.

Simple surface sulfonation retards plasticiser migration and impacts upon blood/material contact activation processes

The use of Di-2-ethylhexyl phthalate (DEHP) plasticised polyvinyl chloride (DEHPPPVC) in medical devices persists despite evidence suggesting that DEHP migration can be harmful. Researchers have shown that a simple surface sulfonation process can retard the migration of DEHP, which may reduce the associated inflammatory response. The present study is designed to investigate the effects of surface sulfonation on DEHP migration and blood contact activation using in vitro and rodent models. The study was carried out in two phases: phase 1, in which the migration rate of DEHP from DEHPPPVC and sulfonated DEHP plasticised PVC (SDEHPPPVC) was measured; phase 2 of the study, in which the materials were incorporated into a rat recirculation biomaterial test model and blood samples taken to assess CD11b expression on neutrophils, IL-6 and Factor XIIa. The initial DEHP concentration washed from the surface after storage was 37.19 +/- 1.17 mg/l in the PPVC group and 5.89 +/- 0.81 mg/l in the SPPVC group (p<0.0001). The post-wash migration rate was 3.07 +/- 0.32 mg/l/hour in the PPVC group compared to 0.46 +/- 0.038 mg/l/hour in the SPPVC group (p<0.0001). In phase 2 of the study, CD11b expression increased by 228.9% +/- 37% over the test period in the PPVC group compared to 118.3% +/- 46% in the SPPVC group (p<0.01). IL-6 levels rose from 3.1 +/- 1.4 pg/ml to 263 +/- 26 pg/ml in the PPVC group and 2.2 +/- 1.6 pg/ml to 161 +/- 29 pg/ml in the SPPVC group (p<0.01). Factor XIIa levels rose from 0.22 +/- 0.13 g/ml to 3.7 +/- 0.32 microg/ml and 0.28 +/- 0.09 to 2.71 +/- 0.21 microg/ml in the PPVC and SPPVC groups, respectively (p<0.05 at 90 minutes). The simple sulfonation process significantly retards the migration of DEHP and is associated with the moderation of contact activation processes.

Bone tissue response to titanium implant surfaces modified with carboxylate and sulfonate groups

The present study assessed in vivo new bone formation around titanium alloy implants chemically grafted with macromolecules bearing ionic sulfonate and/or carboxylate groups. Unmodified and grafted Ti-6Al-4V exhibiting either 100% carboxylate, or 100% sulfonate, or both carboxylate and sulfonate groups in the percent of 50/50 and 80/20 were bilaterally implanted into rabbit femoral condyle. Neither toxicity nor inflammation were observed for all implants tested. After 4 weeks, peri-implant new bone formation varied as a function of the chemical composition of the titanium surfaces. The percent bone-implant contact (BIC) was the lowest (13.4 +/- 6.3%) for the implants modified with grafted carboxylate only. The value of BIC on the implants with 20% sulfonate (24.6 +/- 5.2%) was significantly (P < 0.05) lower than that observed on 100% sulfonate (38.2 +/- 13.2%) surfaces. After both 4 and 12 weeks post-implantation, the BIC value for implants with more than 50% sulfonate was similar to that obtained with the unmodified Ti-6Al-4V. The grafted titanium alloy exhibiting either 100% sulfonate or carboxylate and sulfonate (50% each) groups promoted bone formation. Such materials are of clinical interest because, they do not promote bacteria adhesion but, they support new bone formation, a condition which can lead to osseointegration of bone implants while preventing peri-implant infections.

Molecular Self‐Aggregation of Tetradecylbenzene Sodium Sulfonate Isomers

AbstractThis paper deals with the effect of the surfactant isomeric structure on self‐aggregation in aqueous solution. The relationship between the molecular structure of a series of tetradecylbenzene sulfonate isomers (with the benzene ring located at different positions along the alkyl chain) and surface tension was made clear. It is found that the critical micelle concentration increases and the surface tension at critical micellar concentration decreases as the benzene group moves toward the center of the alkyl chain. The structure of micelles was studied by 1H‐NMR relaxation, which indicates that the density of methylene protons in the surface layer of the micellar core decreases as the branching of the hydrophobic group increases. The spontaneous vesicle formation in aqueous solution was investigated by transmission electron microscopy. The results reveal that, as the benzene group moves toward the center of alkyl chain, the assembly structure changes from micelle to vesicle, then to lamellar bilayers, while the critical packing parameter increases.

Synthesis of novel water-soluble sulfonated cellulose

Water-soluble sulfonated cellulose (SC) samples were synthesized by oxidizing hardwood kraft pulp with sodium periodate followed by the sulfonation reaction with sodium bisulfite. Six levels of oxidation/sulfonation were obtained by using different mmols (0.93–4.67) of periodate per gram of pulp. The aldehyde and sulfonic acid contents, surface morphology, and water solubility property of these treated fibers were characterized. It was found that carbonyl group content increased with the periodate charge and so did the sulfonic acid content in subsequent sulfonation step. Scanning electron microscopy images showed a significant change in surface morphology of the sulfonated samples. Solubility of sulfonated cellulose in water was determined from 1H NMR spectra and a solubility of 28.57g/L was found when cellulose was oxidized with 4.67mmol periodate per gram cellulose followed by the sulfonation reaction.▪

Synthesis and Characterization of Surface Sulfonated Polypropylene Films

The basic reseach on the surface sulfonation of polypropylene (PP) is very important for design of surfaces for higher functionalization. For this purpose, liquid-phase sulfonation of polypropylene surfaces at various temperatures and different time periods was performed using concentrated sulphuric acid. The physical and chemical changes produced by the sulfonation on the polypropylene surfaces were determined by contact angle measurements, mechanical analysis, UV-Vis spectroscopy, differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). Both surface polarity and wettability of PP films were improved by sulfonation at low temperatures for short time periods; however, sulfonation at longer times, or higher temperatures, caused degradation of PP films. All sulfonated film samples had lower yield stress and stress at break.

Surface characterization and in vitro platelet compatibility study of surface sulfonated chitosan membrane with amino group protection–deprotection strategy

Glycosaminoglycans (GAGs) are the main components of the extracellular matrix (ECM). Studies have indicated that scaffolds modified by GAGs could improve cell proliferation and differentiation. Chitosan, the second-most abundant nature polysaccharide, has a structure similar to that of GAGs. Due to its relatively lower cost as compared to GAGs, many researchers have tried to incorporate sulfonate or carboxyl groups into the chitosan structure with the aim to form a GAG-like structure. However, these modifications were carried out on the reactive amino groups that were thought as the major character, resulting in special biological properties associated with chitosan. Such a decrease of amino-functional group density would very likely alter the specific biological properties of chitosan. Therefore, an amino group protection–deprotection strategy was explored in this study for surface sulfonation of chitosan membrane with the aim to imitate GAG structures. Various surface chemical characterization results, as well as surface zeta potential measurements have indicated that both sulfonate/sulfonic and amino functionalities were coexistent on the deprotected sulfonated chitosan specimen. In vitro platelet adhesion testing has shown that such a deprotected sulfonated chitosan membrane can increase the amount of platelet adhesion while keep those adhered remained unactivated. At the same time the presence of deprotected sulfonated chitosan film extended the plasma recalcification time value. With this protection–deprotection strategy, a further chemical grafting of bioactive molecules, such as RGD peptide, using the recovered amino functionalities, can be pursued on these sulfonated chitosan specimens.

Synthesis and characterization of sulfonated single-walled carbon nanotubes and their performance as solid acid catalyst

Single-walled carbon nanotubes (SWCNTs) were treated with sulfuric acid at 300 °C to synthesize sulfonated SWCNTs (s-SWCNTs), which were characterized by electron microscopy, infrared, Raman and X-ray photoelectron spectroscopy, and thermo analysis. Compared with activated carbon, more sulfonic acid groups can be introduced onto the surfaces of SWCNTs. The high degree (∼20 wt%) of surface sulfonation led to hydrophilic sidewalls that allows the SWCNTs to be uniformly dispersed in water and organic solvents. The high surface acidity of s-SWCNTs was demonstrated by NH 3 temperature-programmed desorption technique and tested by an acetic acid esterification reaction catalyzed by s-SWCNTs. The results show that the water-dispersive s-SWCNTs are an excellent solid acid catalyst and demonstrate the potential of SWCNTs in catalysis applications.

Mineral surface reactivity and mass transfer in environmental mineralogy

New concepts and analytical techniques pertinent to environmental mineralogy are reviewed. Environmental mineralogy is defined as: “the application of mineral sciences to understanding low temperature earth surface processes, especially processes which directly or indirectly involve the biosphere”. Because most low-temperature reactions involving minerals are surface-controlled, a key focus in Environmental mineralogy must be mineral surface chemistry and structure. Case studies are used in each to illustrate recent progress in three areas of interest: 1) mineral surface structure; 2) organic surface complexation reactions; and 3) microbiological biofilm growth at mineral surfaces. All three interfacial processes play a critical role in controlling mass transfer processes. In the first section glancing incidence X-ray methods and fractal models of mineral surface evolution are discussed. Dissolving silicate surfaces may best be categorized as falling into the directed percolation depinning (DPD) class based on the fact that in the equation which relates surface roughness (σ) to time ( t ): σ = t β , the exponent β has been constrained in several scattering experiments to be equal to approximately 0.2. Glancing incidence X-ray diffraction patterns for uranium precipitates on feldspar are also presented which show that the micro-precipitates are most likely becquerelite (Ca(UO 2 ) 6 O 4 (OH) 6 .8H 2 O) and thus have incorporated calcium from the mineral surface. Infrared and X-ray spectroscopy as applied to organic surface complexation are presented next. Multiple-internal reflection FTIR spectroscopy is used to show that an organic acid, phthalate, deprotonates and complexes with the fluorite surface. X-ray absorption spectroscopy (XAS) is then used to constrain how polyvinylsulfonate scale inhibitors function on the barite surface: direct binding between the sulfonate group and surface barium is demonstrated. The use of XAS to determine soil sulfur speciation is also presented. Finally, Environmental SEM (ESEM) and other techniques are applied to conditioning film and biofilm growth. Upcoming challenges to Environmental mineralogy and several other promising new techniques are also discussed.

Functionalization of different polymers with sulfonic groups as a way to coat them with a biomimetic apatite layer

Covalent coupling of sulfonic group (-SO 3H) was attempted on different polymers to evaluate efficacy of this functional group in inducing nucleation of apatite in body environment, and thereupon to design a simple biomimetic process for preparing bonelike apatite-polymer composites. Substrates of polyethylene terephthalate (PET), polycaprolactam (Nylon 6), high molecular weight polyethylene (HMWPE) and ethylene-vinyl alcohol co-polymer (EVOH) were subjected to sulfonation by being soaked in sulfuric acid (H2SO4) or chlorosulfonic acid (ClSO 3H) with different concentrations. In order to incorporate calcium ions, the sulfonated substrates were soaked in saturated solution of calcium hydroxide (Ca(OH)2). The treated substrates were soaked in a simulated body fluid (SBF). Fourier transformed infrared spectroscopy, thin-film X-ray diffraction, and scanning electron microscopy showed that the sulfonation and subsequent Ca(OH)2 treatments allowed formation of -SO3H groups binding Ca2+ ions on the surface of HMWPE and EVOH, but not on PET and Nylon 6. The HMWPE and EVOH could thus form bonelike apatite layer on their surfaces in SBF within 7 d. These results indicate that the -SO3H groups are effective for inducing apatite nucleation, and thereby that surface sulfonation of polymers are effective pre-treatment method for preparing biomimetic apatite on their surfaces.

Pore Size Effect on Improvement of Surface Proton Conductivity for Three-Dimensionally Ordered Macroporous Silica Membrane

A proton conducting porous silica matrix for composite membranes was prepared by introducing of sulfonic acid groups onto the silica surface. The proton conductivity of the silica membrane itself was increased in more than two orders of magnitude after the surface sulfonation. In the cases of the composite membranes between proton conductive polymer and silica matrix, the conductivity was also enhanced. Especially, considerably high enhancement on proton conductivity was observed in the composite membrane. Such an improvement on the proton conductivity was more enhanced by using the sulfonated silica matrix with smaller pore size.

Chemo-, regio- and stereo-selective aerial oxidation of limonene to the endo-1,2-epoxide over Mn(Salen)-sulfonated SBA-15

Mn(Salen) complexes immobilized on sulfonic acid-functionalized SBA-15 molecular sieves (SBA-15- pr-SO 3-Mn(Salen)) catalyze the Mukaiyama-type oxidation of R-(+)-limonene selectively to the 1,2-epoxide with molecular oxygen at 298 K (Salen = N, N-ethylenebis(salicylidenaminato)). The endo-diastereomer is formed with a diasteromeric excess of 39.8%. This catalyst exhibited higher catalytic activity than “neat” Mn(Salen) complexes directly supported on SBA-15 or zeolite-Y. A change in the oxidation state of Mn from +3 in the “neat” complex to +2 when immobilized on the sulfonated surface is a probable cause for the observed enhancement of catalytic activity. A part of the Mn complexes was leached out of the solid phase during the reaction.

Enhancement on Proton Conductivity of Three-Dimensionally Ordered Macroporous Silica Membrane by Surface Sulfonation

A new proton-conducting membrane was prepared consisting of uniformly macroporous silica matrix and a proton-conducting gel polymer, 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS). Three-dimensionally ordered macroporous silica membrane was fabricated by use of a colloidal template method with mono-dispersed polystyrene beads. Surface sulfonation of the pores in the silica matrix was performed by using 1,3-propanesultone. The sulfonated silica matrix exhibited about 400 times higher proton conductivity than unmodified one. The proton conductivity of the composite membrane was also successfully enhanced by using the sulfonated silica matrix.

Titania Deposition on PMR-15

The formation, degree of crystallinity, and adherence of dense titania (TiO2) thin film coatings on a high-temperature polyimide resin (PMR-15) can be influenced by the chemical composition of the polymer surface. Furthermore, solution deposition conditions can be adjusted to provide additional control over the morphology and crystallinity of the titania films. Recipes for solution-based titania deposition that used a slowly hydrolyzing titanium fluoride salt in the presence of boric acid as a fluoride scavenger allowed growth of films up to 750 nm thick in 22 h. By adjusting solution pH and temperature, either amorphous titania or oriented crystalline anatase films could be formed. Surface sulfonate groups enhance the adhesion of solution-deposited oxide thin film coatings. While most sulfonation procedures severely damaged the PMR-15 surface, the use of chlorosulfonic acid followed by hydrolysis of the installed chlorosulfonyl groups provided effective surface sulfonation without significant surface damage. In some cases, the oxide deposition solution caused partial hydrolysis of the polymer surface, which itself was sufficient to allow adhesion of the titania film through chelation of titanium ions by exposed benzoic acid groups on the polymer surface.

Direct correlation between adsorption‐induced changes in protein structure and platelet adhesion

It is widely recognized that adsorbed proteins on biomaterial surfaces tend to initiate thrombus formation, although the specific mechanisms involved are still not well understood. In attempts to decrease the conformational change of adsorbed proteins, surface treatments that reduce surface hydrophobicity have been considered, such as the sulfonation of low-density polyethylene and isotactic polypropylene. The objectives of this present research were to study how changes in surface chemistry influence the degree of conformational change of adsorbing proteins and to investigate the correlation between the change in adsorbed protein structure and platelet response. Adsorbed porcine serum albumin and porcine fibrinogen were used as the model proteins for determining the effects of sulfonation on protein conformational change. Circular dichroism spectroscopy studies showed that the proteins were less altered structurally on the sulfonated surfaces. Platelet adhesion studies were used to correlate the number of adhered platelets with the amount of conformational change in adsorbed proteins on the polymer surface. The results of these studies show a linear correlation between platelet adhesion and the degree of adsorption-induced protein conformational change. These findings suggest that the degree of protein conformational change after adsorption is a dominant mechanism governing platelet interactions with biomaterial surfaces.

Fibronectin adsorption and arrangement on copolymer surfaces and their significance in cell adhesion

The adsorption of fibronectin (FN) to (styrene/methyl methacrylate) copolymer surfaces, both sulfonated (hydrophilic) and nonsulfonated (hydrophobic), was studied by means of the radioisotope (125I-FN) and ELISA assays; the latter employed monoclonal antibodies. It was found that the radioiodination-derived isotherms did not follow the Langmuir-type adsorption law within the FN concentration range studied; rather, a quasi-linear FN surface density versus bulk concentration dependence was observed. These isotherms, and our recent ELISA measurements with polyclonal antibodies, allowed us to estimate saturative FN surface densities, which were, within the experimental error, similar on both types of surfaces. This suggested the amount of adsorbed FN to be not responsible for observed differences in leukaemia L1210 cell adhesion (FN-coated sulfonated surfaces are far more pro-adhesive than their nonsulfonated analogues). The presumption that these differences are induced by changes in the FN arrangement was confirmed by the use of monoclonal antibodies directed against distinct FN domains, and by the blocking of alpha5beta1 integrin receptor with the synthetic Gly-Arg-Gly-Asp-Ser-Pro (GRGDSP) peptide. The RGD sequence located within the FN cell-binding domain seems to be masked in the structure adopted on nonsulfonated surfaces, which hinders the integrin-ligand interaction.

Acid-base properties and zeta potentials of self-assembled monolayers obtained via in situ transformations.

Siloxane-anchored, self-assembled monolayers (SAMs) on single crystal Si were prepared with a variety of surface functional groups using a single commercially available surfactant (1-bromo-11-(trichlorosilyl)undecane) followed by in situ transformations. Polar (thioacetate and thiol), nonpolar (methyl), acidic (sulfonic and carboxylic), basic (various amines), and ionic (alkylammonium) surface functionalities were prepared. For primary amine and sulfonate surfaces, the degree of surface charge as a function of pH was determined ex situ using X-ray photoelectron spectroscopy (XPS). Sulfonate SAMs exhibited much higher effective pKa (approximately 2) than dilute sulfonic acid (-5 to -6), and amine SAMs exhibited much lower pKa (approximately 3) than dilute organic amines (approximately 10). This is attributed to the stabilization of nonionized groups by adjacent ionized groups in the SAM. Zeta potentials of these SAMs as a function of pH were consistent with the XPS results and indicated that ionizable SAM surfaces can generate surface potentials much higher than those of nonionic SAMs (thioacetate, methyl) and typical oxide surfaces.

Surface Sulfonation of Polyvinyl Chloride by Plasma for Antithrombogenicity

To enhance the blood compatibility of Polyvinyl Chloride (PVC) film, the film was modified by SO2/O2 gas plasma treatment. The effect of surface sulfonation of PVC treated by various SO2/O2 gas plasma depended on the volume ratio O2/(SO2 + O2). When the volume ratio was 0.5, the effect of sulfonation was the best. Sulfonic acid groups were specifically and efficiently introduced onto the PVC surface, which was proved by x-ray photoelectron spectroscopy (XPS) and Attenuated Total Reflectance Fourier Transfer Infrared (ATR-FTIR) spectroscopy. The surface microstructure of modified PVC film was studied with scanning electron microscopy (SEM). The antithrombogenicity of the samples was determined by the activated partial thromboplastin time (APTT), prothrombin time (PT), thrombin time (TT) and plasma recalcification time (PRT) tests and platelet adhesion experiment. The results indicated that the antithrombogenicity of modified PVC was improved remarkably.

Studies of sulfonated polyethylene for biliary stent application

AbstractPalliative treatment for obstructive jaundice by endoscopic biliary stent insertion is a recent commonly used method. Unfortunately, stent reobstruction may occur within 3 to 6 months as a result of bacterial adhesion and formation of biofilm. Bacterial adhesion was postulated as the initial step of stent clogging and the bacterial enzyme activity of β‐glucuronidase led to the deposition of calcium bilirubinate. In this study, surface sulfonation of the polyethylene lumen was postulated to improve the patency of the biliary stent. Surface modification with sulfonated group formation was carried out with fuming sulfuric acid containing 20 wt % sulfuric trioxide (SO3). The reaction time varied from 1 to 3 h at room temperature. ATR‐FTIR and ESCA techniques showed that the surface amount of sulfonated functionalities increased with sulfonation time. The contact angle of the sulfonated PE, determined by the sessile drop technique, decreased compared to that of unmodified PE, but cannot be detected by the captive bubble method because of the high surface hydrophilicity. SEM micrographs indicated that the sulfonated PE inner lumen remained relatively smooth after extended sulfonation reaction. Adhesion of Escherichia coli to the sulfonated PE stents after 48‐h bile perfusion was about 10‐ to 20‐fold less than that to the unmodified PE, as observed by SEM and surface spreading method. These results indicated that the surface sulfonated groups could effectively decrease the adhesion of E. coli in human bile, probably attributable to the hydrophilic repellence between the bacterial cell membrane and sulfonated groups. This finding suggested that the sulfonated PE tubing could prolong the patency period of plastic stents and may be of great potential as a biliary stent in a real clinical setting. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2450–2457, 2004