Surface grafting polyethylene glycol (PEG) onto poly(ethylene-co-acrylic acid) films

Two reaction schemes were developed to covalently graft poly(ethylene glycol) (PEG) chains on poly(ethylene-co-acrylic acid) (EAA) surfaces. The schemes involved surface grafting of linker molecules L-lysine or polypropyleneamine dendrimer (AM64), with subsequent covalent bonding of PEG chains to the linker molecules. NHS and EDC were used to activate the carboxylic acid groups of the EAA in the outermost region of the film, estimated to be 20 nm by ATR-FTIR spectroscopy. XPS demonstrated that the conversion of this activation step was almost 100% in the detected region. After activation, L-lysine or dendrimer was grafted onto the EAA surface, followed by PEG grafting. Combining the data from ATR-FTIR, XPS, and contact angle goniometry, it was found that the PEG chains were grafted on the surface of the EAA film and larger surface coverage was achieved when the dendrimer was used as the intermediate layer. This surface also had the lowest water contact angle.     

Surface-grafting of phosphates onto a polymer for potential biomimetic functionalization of biomaterials

In the human body, phosphate groups play important roles in signaling and the biological functions of proteins and peptides. Despite the importance of phosphate groups, polymer surfaces have not been directly grafted with phosphate groups by chemical reactions because the usual organic solvents used to graft phosphate groups can dissolve or swell polymers. We focused this study on grafting phosphate groups onto a poly(ethylene-co-acrylic acid) (PEAA) surface in an aqueous solution. O-phospho L-serine and O-phosphoethanolamine were grafted on PEAA surfaces to introduce phosphate groups by activating carboxylic acid groups of PEAA using N-hydroxysuccinimide (NHS) and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) in an aqueous environment. X-ray photoelectron spectroscopy (XPS) was used to elucidate the process by which surface grafting occurs and the process that the phosphate group is cleaved into a phosphate ion and a hydrolyzed molecule at high pH. It was found that under appropriate reaction conditions the phosphate groups could be successfully grafted on the polymer surfaces. The phosphate-grafted polymer surfaces showed lower water contact angles than the initial polymer surfaces likely due to their highly mobile and hydrophilic phosphate side groups. This work demonstrates a technique to successfully graft phosphate groups onto organic polymer surfaces in a biocompatible aqueous environment, which may open new avenues to functionalizing synthetic polymeric and natural macromolecule derived biomaterials.     

Glass bead grafting with poly(carboxylic acid) polymers and maleic anhydride copolymers

Glass beads were etched with acids and bases to increase the surface porosity and the number of silanol groups that could be used for grafting materials to the surfaces. The pretreated glass beads were functionalized using 3‐aminopropyltriethoxysilane (APS) coupling agent and then further chemically modified by reacting the carboxyl groups of carboxylic acid polymers with the amino groups of the pregrafted APS. Several carboxylic acid polymers and poly(maleic anhydride) copolymers, such as poly(acrylic acid) (PAA), poly(methacrylic acid) (PMA), poly(styrene‐alt‐maleic anhydride) (PSMA), and poly(ethylene‐alt‐maleic anhydride) (PEMA) were grafted onto the bead surface. The chemical modifications were investigated and characterized by FT‐IR spectroscopy, particle size analysis, and tensiometry for contact angle and porosity changes. The amount of APS and the different polymer grafted on the surface was determined from thermal gravimetric analysis and elemental analysis data. Spectroscopic studies and elemental analysis data showed that carboxylic acid polymers and maleic anhydride copolymers were chemically attached to the glass bead surface. The improved surface properties of surface modified glass beads were determined by measuring water and hexane penetration rates and contact angle. Contact angles increased and porosity decreased as the molecular weights of the polymer increased. The contact angles increased with the hydrophobicity of the attached polymer. The surface morphology was examined by scanning electron microscopy (SEM) and showed an increase in roughness for etched glass beads. Copyright © 2007 John Wiley & Sons, Ltd.     

Influence of aqueous electrolytes on the wetting behavior of hydrophobic solid polymers-low-rate dynamic liquid/fluid contact angle measurements using axisymmetric drop shape analysis

The interaction of inorganic ions with low-energy hydrophobic surfaces was examined using model systems of solid polymers without ionizable functional surface groups in aqueous electrolyte solutions. Low-rate dynamic contact angle measurements with captive bubbles in conjunction with axisymmetric drop shape analysis (ADSA) were performed to study the influence of electrolyte ions (in the aqueous test solutions) on the wettability of the polymers. When various types of ions were used, no significant change in advancing and receding contact angles was observed. The contact angle hysteresis was small. The zeta potential of the model polymers in aqueous electrolyte solutions was determined from streaming potential measurements. The variation of the zeta potential at different pH levels indicates preferential adsorption of hydroxyl ions at this interface. However, the presence of electrolytes at the interface between water and the different model polymers did not influence the macroscopic contact angle. The results may suggest the absence of any specific interaction between the ions and the solid polymer, as this should result in changes of hydrophobicity. Similar to the air/water interface, the composition and the potential of the polymer/water interface are obviously determined predominantly by the aqueous phase with only slight influence from the solid phase.     

pH响应性表面对蛋白质吸附的调控

通过表面引发原子转移自由基聚合在固定了引发剂的硅表面接枝了聚甲基丙烯酸叔丁酯(PtBMA),而后通过水解得到聚甲基丙烯酸(PMAA)聚合物刷.通过X射线光电子能谱、椭圆偏振仪和水接触角测试证明了接枝改性的成功.研究发现PMAA改性表面的浸润性和对蛋白质的吸附行为都具有一定的pH响应性.在较低pH值时改性表面相对疏水,随...     

Water-Soluble Polyacids with Capability to Remove Metal Ions in Homogenous Phase by Using the Liquid Phase Polymer-Based Retention Technique

Water-soluble polymers containing carboxylic acid and sulfonic acid groups were investigated as polychelatogens under different experimental conditions in view to study their metal ion binding properties, using the liquid-phase polymer-based retention technique. The divalent metal ions investigated were: Co²⁺, Cu²⁺, Zn²⁺, and Cd²⁺. When the pH increased above 3, and especially at pH 5, metal ion retention capability increased as the majority of the functional groups are carboxylate, which can form more stable complexes with the metal ions. The retention capability also depended on the structure of the polyacid and the filtration factor, Z.     

Chemical changes of polymeric surfaces after modification with multi-source cluster deposition

A new process for surface modification of polymers with multi-source cluster deposition apparatus has been reported in our previous work. The apparatus simultaneously supplies reactant of ammonium sulfamate and activator of energetic Ar(+) ion. In this work chemical changes are analyzed on the basis of XPS spectra and the relations of contact angle and platelet adhesion with chemical changes are discussed. Polymer film, setting on a turning holder, was irradiated by Ar(+) ions during bombardment with ammonium sulfamate clusters. The Ar(+) ion source served for activation of polymer surface and a cluster ion source supplied ammonium sulfamate molecules to react with activated surface. After thorough washing with deionized sterile water, the modified surfaces were evaluated in terms of contact angle of water, elemental composition and binding state on XPS and platelet adhesion with platelet rich plasma (PRP). The modification of polysulfone decreased the contact angle of water on surfaces from 82.6 down to 34.5 degrees. The adhesion number of platelets were decreased to one-tenth of the original surface. Ammonium, amine, sulfate and thiophene combinations were formed on the modified surfaces. The primary studies showed successful modification of polysulfone with ammonium sulfamate by assistance of Ar(+) ion irradiation. The polar groups like N-sulfate were formed on surfaces and contribute to the decrease of surface contact angle and adhesion number of platelets. Since the same process can also be applied to other polymeric materials with various substrates, combining with the features of no solvent and no topographic changes, this method might be developed in a promising way for modification of polymers.     

Photochemically patterned poly(methyl methacrylate) surfaces used in the fabrication of microanalytical devices

We report here the photochemical surface modification of poly(methyl methacrylate), PMMA, microfluidic devices by UV light to yield pendant carboxylic acid surface moieties. Patterns of carboxylic acid sites can be formed from the micrometer to millimeter scale by exposure of PMMA through a contact mask, and the chemical patterns allow for further functionalization of PMMA microdevice surfaces to yield arrays or other structured architectures. Demonstrated here is the relationship between UV exposure time and PMMA surface wettability, topography, surface functional group density, and electroosmotic flow (EOF) of aqueous buffer solutions in microchannels made of PMMA. It is found that the water contact angle on PMMA surfaces decreases from 70 degrees to 24 degrees after exposure to UV light as the result of the formation of carboxylic acid sites. However, upon rinsing with 2-propanol, the water contact angle increases to approximately 80 degrees , and this increase is attributed to changes in surface roughness resulting from removal of low molecular weight PMMA formed from scission events. In addition, the surface roughness and surface coverage of carboxylic acid groups exhibit a characteristic trend with UV exposure time. Electroosmotic flow (EOF) in PMMA microchannels increases upon UV modification and is pH dependent. The possible photolysis mechanism for formation of carboxylic acid groups on PMMA surfaces under the conditions outlined in this work is discussed.     

Surface characterization of atomic oxygen beam-exposed polyimide films using contact angle measurements

Polyimide surfaces exposed to simulated low Earth orbit space environment, i.e., under hyperthermal atomic oxygen bombardment, were characterized by using atomic force microscopy, X-ray photoelectron spectroscopy, and contact angle measurements. The surface analytical results showed that the roughness and the O/C ratio at the atomic oxygen-exposed polyimide surface increased with increasing atomic oxygen fluence. The advancing and receding contact angles decreased with increasing O/C ratios at the polyimide surfaces. The Lifshitz-van der Waals component, the acid and base parameters of the surface free energy of polyimide films were calculated from the contact angles. The base parameter increased with increasing O/C ratio, whereas the acid parameter and the Lifshitz-van der Waals component did not show a remarkable change. These analytical results agree with the in situ XPS data showing the formation of surface functional groups due to atomic oxygen exposure. It was demonstrated in this study that the polyimide surface in a low Earth orbit space environment may become hydrophilic due to the bombardment by atomic oxygen. Received: 4 December 1999 Accepted: 31 August 2000     

Covalent biofunctionalization of silicon nitride surfaces

Covalently attached organic monolayers on etched silicon nitride (SixN4; x >/= 3) surfaces were prepared by reaction of SixN4-coated wafers with neat or solutions of 1-alkenes and 1-alkynes in refluxing mesitylene. The surface modification was monitored by measurement of the static water contact angle, XPS, IRRAS, AFM, and ToF-SIMS, and evidence for the formation of Si-C bonds is presented. The etching can be achieved by dilute HF solutions and yields both Si-H and N-H moieties. The resulting etched SixN4 surfaces are functionalized by terminal carboxylic acid groups in either of two ways: (a) via attachment of a 10-undecenoic acid 2,2,2-trifluoroethyl ester (trifluoro ethanol ester) and subsequent thermal acid hydrolysis; (b) through attachment of a photocleavable ester, and subsequent photochemical cleavage, as this would allow photopatterned functionalized SixN4. The carboxylic acids are successfully used for the attachment of oligopeptides (aspartame) and complete proteins using EDC/NHS chemistry. Finally, an amino-terminated organic monolayer can be formed by reaction of HF-treated SixN4 surfaces with a N-(omega-undecylenyl)phthalimide, which yields an amino-terminated surface upon deprotection with hydrazine.     

Liquid phase formation of alkyl- and perfluoro-phosphonic acid derived monolayers on magnesium alloy AZ31 and their chemical properties

Alkyl- and perfluoro-phosphonic acid derived SAMs were successfully formed on Mg alloy by liquid phase method for the first time. The chemical and anticorrosive properties of the prepared SAMs on magnesium alloys were characterized using contact angle measurements, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and electrochemical measurements. Water contact angle measurements revealed that the maximum advancing/receding water contact angles of n-octyl (OP: CH(3)(CH(2))(7)PO(OH)(2)), n-dodecyl (DP: CH(3)(CH(2))(11)PO(OH)(2)), n-octadecyl (ODP: CH(3)(CH(2))(17)PO(OH)(2)) phosphonic acid, and 2-(perfluorohexyl)ethyl (PFEP: CF(3)(CF(2))(5)CH(2)CH(2)PO(OH)(2)) phosphonic acid were 105.1/64.7°, 108.3/69.6°, 111.9/75.2°, and 115.2/67.4° respectively. In the case of alkylphosphonic acid SAMs (OP, DP, and ODP), the advancing and receding water contact angles increased with an increase in the preparation time. The angle-resolved XPS (AR-XPS) data revealed that the film thicknesses of the OP, DP, ODP, PFEP on Mg alloy were estimated to be 0.8, 1.2, 1.7, and 1.1 nm, respectively. The XPS O 1s data support that the phosphonic acid derived SAM is covalently bound to the oxide or hydroxide surface of the Mg alloy in a monodenate or bidenate manner. Chemical stability of the alkyl- and perfluoro-phosphonic acid modified Mg alloy surfaces was investigated using aqueous solutions at pH=4.0, 7.0, and 10.0. The contact angles of OP, DP, and PFEP modified Mg surface decreased rapidly within the first 5 min after immersion in all the aqueous solutions and were less than 20°. On the other hand, the contact angles of the ODP modified Mg alloy after immersion in aqueous solutions at pH 4, 7 and 10 for 5 min were 45.1°, 89.3,° and 85.5°, respectively. The ODP modified Mg alloy had highest chemical stability in four types of the phosphonic acid derived SAMs used in this study, indicating that the molecular density of ODP on Mg alloy would be higher than those of OP, DP, PFEP on Mg alloy. The corrosion resistance of ODP modified Mg alloy was investigated by potentiodynamic polarization curve measurements. The ODP modified Mg alloy exhibits protective properties in a solution containing Cl(-) ions compared to unmodified Mg alloy.     

Surface functionalization of polystyrene to bind with FMRF peptides for novel biocompatibility

<正>A generic method was described to change surface biocompatibihty by introducing reactive functional groups onto surfaces of polymeric substrates and covalently binding them with biomolecules.A block copolymer with protected carboxylic acid functionality,poly(styrene-b-tert-butyl acrylate)(PS-PtBA),was spin coated from solutions in toluene on a bioinert polystyrene(PS) substrate to form a bilayer structure:a surface layer of the poly(tert-butyl acrylate)(PtBA) blocks that order at the air-polymer interface and a bottom layer of the PS blocks that entangle with the PS substrate.The thickness of the PtBA layer and the area density of tert-butyl ester groups of PtBA increased linearly with the concentration of the spin coating solution until a 2 nm saturated monolayer coverage of PtBA was achieved at the concentration of 0.4%W/W.The protected carboxylic acid groups were generated by exposing the tert-butyl ester groups of PtBA to trifluoroacetic acid (TFA) for bioconjugation with FMRF peptides via amide bonds.The yield of the bioconjugation reaction for the saturated surface was calculated to be 37.1%based on X-ray photoelectron spectroscopy(XPS) measurements.The success of each functionalization step was demonstrated and characterized by XPS and contact angle measurements.This polymer functionalization/modification concept can be virtually applied to any polymeric substrate by choosing appropriate functional block copolymers and biomolecules to attain novel biocompatibility.     

Dynamic behavior of polymer surface and the time dependence of contact angle

The increased attention has been focused on the re-searches of soft materials proposed by Pierre-Gilles de Gennes, a Nobel Prize Laureate in Physics. A special issue of “Science” on soft surfaces was published in 2002 to review specific surface properti…     

Surface modification of an ethylene-acrylic acid copolymer film: grafting amine-terminated linear and branched architectures

Polymer films can be tailored for a specific application by modifying their surface properties. In this study, linear and branched architectures were grafted to ethylene-acrylic acid (EAA) copolymer films using the so-called grafting from approach. Dicyclohexylcarbodiimide was used to activate the carboxylic acid functionality on the surface of the EAA copolymer film before reacting it with selected di- and tri-amine compounds. The carboxylic acid functionality was subsequently regenerated by reacting the amine-grafted film with succinic anhydride. These reaction steps were then repeated to create the linear and branched architectures on the EAA film surface. The film surface resulting from each reaction step was analyzed using attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy and contact angle measurements. A systematic analysis of the ATR-FTIR results was performed to estimate the average conversion of the reaction schemes and to explain the observed contact angle results. A significant reduction in water contact angle for the EAA film grafted with a branched architecture was observed. The EAA film grafted with a linear architecture showed a marginal reduction in water contact angle when ethanol was used as a solvent for ethylenediamine. When the solvent for ethylenediamine was changed to water, the contact angle decreased noticeably. However, analysis of control films showed that the reduction in the contact angles was due to the solvent treatment. In the case of branched architectures, such reduction in contact angle due to the solvent treatment was not observed. Several control experiments were performed to ensure that the reduction in the contact angles was in fact due to the grafted species and not due to exposure to various solvents used in the reaction scheme.     

Fluoroalkylation of poly(cyclopentadienyl)siloxane and the surface properties of poly(fluorocyclopentenyl)siloxane films

In this work, poly(fluorocyclopentenyl)siloxane (FPCS) was obtained via a single electron transfer addition reaction of poly(cyclopentadienyl)siloxane (PCS) and perfluoroalkyl iodides, and reduction reaction of the intermediates. PCS was prepared by substitution and hydrolysis reactions using methyltrichlorosilane and sodium cyclopentadienide (NaCp) as raw materials. Fourier transform infrared (FTIR), ¹H NMR, and ¹⁹F NMR indicated the structures of the target polymers. The XPS results showed that the thin films prepared by dip-coating were fluorine enriched at the surface. Atomic force microscopy (AFM) image showed that on the rough surface of films, there were many pinnacles which were generated through the migration of side chain fluoroalkyl groups. The relative static contact angles of water and n-hexadecane on FPCS and PCS indicated that sodium dithionite initiated the reaction of perfluoroalkyl iodides and PCS so that FPCS was successfully synthesized. The measured surface energy of PCS was 2.57 × 10^?2 N/m; while FPCS was 2.14 × 10^?2 N/m, which represented better liquid repellent property compared to PCS.     

Blood compatibility of surface-engineered poly(ethylene terephthalate) via o-carboxymethylchitosan

Poly(ethylene terephthalate) (PET) films were treated by argon plasma following by graft copolymerization with acrylic acid (AAc). The obtained PET-surface grafted PAA (PET-g-PAA) was coupled with chitosan (CS) and o-carboxymethylchitosan (OCMCS) molecules, respectively. Their surface physicochemical properties were characterized by X-ray photoelectron spectroscopy (XPS), water contact angle and streaming potential measurements. The PET-g-PAA surface containing carboxylic acid, CS immobilized PET surface containing amino and OCMCS immobilized PET surface containing both carboxylic acid and amino groups, make the PET surface exhibited a hydrophilic character. The blood compatibility was evaluated by platelet contacting experiments and protein adsorption experiments in vitro. The results demonstrate that the PET surface coupling OCMCS shows much less platelet adhesive and fibrinogen adsorption compared to the other surface modified PET films. The anticoagulation of PET-OCMCS is ascribed to the suitable balance of hydrophobicity/hydrophilicity, surface zeta potential and the low adsorption of protein.     

GRAFTING OF SULFOBETAINE ONTO A POLYURETHANE SURFACE TO IMPROVE BLOOD COMPATIBILITY

On the molecular level, it is believed that polymers containing zwitterionic structures should be compatible withblood. In this work polyurethane films were grafted with sulfobetaine by a three-step procedure. In the first step, the films'surfaces were treated with hexamethylene diisocyanate (HDI) in toluene at 50℃ in the presence of di-n-butyl tin dilaurate(DBTDL) as a catalyst. The extent of the reaction was monitored by ATR-IR spectra; a maximum number of free NCOgroups was obtained after a reaction time of 90 min. In the second step, the hydroxyl groups of N,N-dimethylethylethanolamine (DMEA) were allowed to react in toluene with NCO groups bound on the surface. In the thirdstep, sulfobetaines were formed on the surface through the ring-opening reaction between tertiary amine of DMEA and 1,3-propanesultone (PS). The surfaces of the films were characterized by ATR-IR and XPS showing that the grafted surfaceswere composed of sulfobetaine. The results of the contact angle measurement show that the surface was strongly hydrophilic.The platelet adhesion test demonstrated that the films grafted with sulfobetaine have excellent blood compatibility.     

Surface modification of ultra‐high molecular weight polyethylene fibers by chromic acid

Ultra‐high molecular weight polyethylene (UHMWPE) fibers were modified by chromic acid. The effects of surface modification were evaluated with Fourier transform infrared spectroscopy (FTIR), X‐ray photoelectron spectroscopy (XPS), contact angle measurement, and scanning electron microscope (SEM). The results showed that both the content of O‐containing functional groups and surface roughness of modified fibers increased. The polar groups on the modified fiber surface decreased the contact angles with water and ethylene glycol, as evidenced by contact angle measurement. The tensile test results showed the strength and the elongation at break of UHMWPE fibers decreased but the modulus increased after chromic acid modification. Copyright © 2016 John Wiley & Sons, Ltd.     

Wettability of biodegradable surfaces

The study of the interfacial characteristics of biodegradable polymers/copolymers is of importance from the point of view of both surface science and pharmaceutical/cosmetic applications. Films formed from biodegradable polymers allow systematic wettability studies on surfaces with a wide range of copolymer (chemical) compositions. The possibility of interchanging these drug carrier polymers, if their wetting characteristics are similar, could be beneficial to diverse applications. Low-rate dynamic contact angles on films (solvent cast on polar substrates, i.e. on silicon wafer) of poly(lactic acid), and its copolymers with poly(glycolic acid), (with four different copolymer ratios of 85/15, 75/25, 65/35 and 50/50) were measured by axisymmetric drop shape analysis-profile (ADSA-P) with four liquids: water, formamide, 2,2′-thiodiethanol and 3-pyridylcarbinol. The solid surface tensions, γ_sv, were calculated from the advancing contact angles, θ_A. The surface topography of the polymer films was investigated by atomic force microscopy (AFM). The surface composition of the polymer layers was analyzed by X-ray photoelectron spectroscopy (XPS). The advancing contact angles were found to be independent of the composition of the copolymers, while the receding angles, θ_R, did decrease with increasing ratio of the polar component [poly(glycolic acid)] in the copolymers. The solid surface tensions calculated from the advancing contact angles of the liquids for all homo- and copolymers were the same within the error limit; the mean value being γ_sv=35.6 ± 0.2 mJ/m². The surface roughness, which was obtained from AFM images, increased with increasing poly(glycolic acid) ratio, without affecting the advancing contact angles. The constancy of γ_sv is attributed to the effect of the surface activity of the nonpolar segments of the polymer chains, which oriented to form the outermost layer of the film. This was confirmed by XPS analysis. Received: 06 November 2000 Accepted: 09 May 2001     

Surface characteristics of polysulfoalkyl methacrylates

Coated hydroxyethyl methacrylate-sodium sulfoalkyl methacrylate copolymer films were surface characterized. The contact angle hysteresis increases and the receding angle decreases with increasing alkyl side-chain length, while the advancing angle decreases with hydration time. It was found that the buoyancy slopes of the advancing (r_a) and receding (r_r) process determined by the Wilhelmy plate method were not parallel. The ratio of r_a to r_r was greater than 1, and increases with the alkyl side-chain length and the hydration time, contrary to that of polyhydroxyethyl methacrylate, where r_a/r_r was less than 1. The slope ratio would be suppressed in solution with added salt, revealing that the reorientation and expansion of the polymer chain in water is being suppressed. X-ray photoelectron spectroscopy (XPS) analysis of the surface of these copolymers showed a striking enrichment of the sulfonate groups in the surface. The zeta potential was between −40 and −50 mV as measured by the streaming potential method. During dehydration, along with a decrease in sulfur and sodium concentration in the surface, the carbon 1s peak at the high binding energy decreased and the alkyl carbon main peak increased. The surface tension of aqueous solutions of sulfoalkyl methacrylate monomers and homopolymers decreases with increasing alkyl side-chain length, which may contribute to the decrease in water-polymer film interfacial tension and thus the increase in the slope ratio.