UV-induced Graft Polymerization Research Articles

Highly hydrophilic and low-protein-fouling polypropylene membrane prepared by surface modification with sulfobetaine-based zwitterionic polymer through a combined surface polymerization method

Poly(sulfobetaine methacrylate) [poly(SBMA)], a zwitterionic polymer, was successfully tethered in high density onto polypropylene (PP) membrane surface through a combined method consisting of UV-induced surface graft polymerization followed by surface-initiated atom transfer radical polymerization (ATRP). 2-Hydroxyethyl methacrylate (HEMA) was first immobilized onto PP membrane surface by UV-induced graft polymerization, and then each of the grafted poly(HEMA) chains, after coupled with 2-bromopropionyl groups, provided multiple initiation sites for subsequent ATRP of SBMA. Images from scanning electron microscope (SEM) showed that the membrane surface was fully covered with small dot-like surface structures of poly(SBMA) after 6 h of ATRP. Both attenuated total reflectance Fourier transform infrared spectroscopy (FTIR/ATR) and X-ray photoelectron spectroscopy (XPS) confirmed the grafted poly(HEMA) and poly(SBMA) on the membrane surface. Water contact angle measurements showed that the surface hydrophilicity of the PP membrane was improved significantly with the increase of the grafted poly(SBMA) content, and a water contact angle of as low as 17.4° was obtained in this study. Experimental results for protein solution filtration demonstrated that the extent of fouling was significantly reduced and most of the fouling on the modified PP membrane surface was reversible, suggesting good anti-protein-fouling performance.

On‐chip cell culture on a microarray of extracellular matrix with surface modification of poly(dimethylsiloxane)

Microfluidic cell culture chips allow to perform assays of small-volume samples rapidly and reproducibly. Most of these chips are made of poly(dimethylsiloxane) (PDMS), which is a flexible, durable, transparent and inexpensive polymer that can be easily applied to fabrication of microstructures by photolithography and replica molding. However, not many cells are able to grow on unmodified PDMS because the cells need appropriate scaffolds on the surface. Here we report surface modification of a PDMS substrate with a microarray of extracellular matrix (ECM) for on-chip cell culture. The ECM proteins collagen and fibronectin were covalently immobilized on an 8 x 8 microarray format by micropatterned UV-induced graft polymerization through a photomask and dehydration-condensation reaction through a microfabricated stencil. Identical spots of ECMs were successfully formed and the geometry of the spots accurately corresponded to the micropattern of the photomask and stencil. We demonstrate the culture of CHO-K1 cells on the ECM microarray chip. Cells proliferated on the fibronectin spots during the 2-day culture.

Achieving Highly Effective Non-biofouling Performance for Polypropylene Membranes Modified by UV-Induced Surface Graft Polymerization of Two Oppositely Charged Monomers

A major problem in membrane technology for applications such as wastewater treatment or desalination is often the loss of membrane permeability due to biofouling initiated from protein adsorption and biofilm formation on the membrane surface. In this study, we developed a relatively simple and yet versatile approach to prepare polypropylene (PP) membrane with highly effective non-biofouling performance. Copolymer brushes were grafted to the surface of PP membrane through UV-induced polymerization of two oppositely charged monomers, i.e., [2-(methacryloyloxy)ethyl]trimethylammonium chloride (TM) and 3-sulfopropyl methacrylate potassium salt (SA), with varying TM:SA molar ratios. Surface analysis with scanning electron microscope (SEM) clearly showed the grafted copolymer brushes on the membrane surfaces and that with X-ray photoelectron spectroscope (XPS) revealed a similar TM:SA ratio of the grafted copolymer brushes to that of the monomer solution used for the polymerization. Water contact angle measurements indicated that the hydrophilicity of the membrane surfaces was remarkably improved by the grafting of the TM/SA copolymer brushes, with the lowest water contact angle of 27 degrees being achieved at the TM:SA ratio of around 1:1. Experiments for antiprotein adsorption with bovine serum album (BSA) and lysozyme (LYZ) and antibiofilm formation with Escherichia coli (E. coli) demonstrated a great dependence of the membrane performance on the TM:SA ratios of the grafted copolymer brushes. It was found that the characteristics of the surface charges of the membrane surfaces played a very important role in the non-biofouling performance, and the membrane surface with balanced positive and negative charges showed the best non-biofouling performance for the proteins and bacteria tested in this study.

Surface Modification of Alumina Nano-Particles by UV-Induced Grafting Polymerization of 2-Hydroxyethyl Methacrylate

Alumina nano-particles was grafted with poly(2-hydroxyethyl methacrylate) (PHEMA) utilizing the sequential method; that is, the alumina surface was first rendered with initiator, benzophenone, by UV-irradiation followed by the grafting polymerization of HEMA on the surface which was initiated thermally and propagated via the free-radical polymerization. FT-IR spectroscopy confirmed the successful grafting of PHEMA onto the alumina surface. Determined by thermalgravimetry (TG), the amount of benzophenone on the alumina surface was found to increase with the UV-irradiation time; however upon grafting of PHEMA, the amount of grafted-PHEMA was the same irrespective of the reaction time. The glass transition temperature (Tg) of grafted-PHEMA on alumina particles was approximately 93 °C that is higher than that of PHEMA which has Tg around 85 °C. This indicates the more restricted movement of grafted-PHEMA compared with the ungrafted-PHEMA.

USE QCM TO MEASURE SELF-ASSEMBLING MONOLAYER, PLASMA MODIFICATION, AND SURFACE GRAFT POLYMERIZATION

The aim of this study was to investigate the frequency shift of the gold film electrode of a quartz crystal microbalances (QCM) made by steps of applying self-assembling monolayer (SAM), plasma treatment, and UV-induced graft polymerization on the surface. Thiol group containing 11-mercaptoundecanoic acid (MUA) was employed for depositing SAM onto gold surfaces. Oxygen plasma treatment was then applied to the SAM to generate sufficient amounts of peroxides and hydroperoxides, which could further initiate UV-induced graft polymerization. Measurements of contact angle and oscillation frequency on the prepared QCM indicate that the SAM-modified gold film surface provides an effective method of making the surface hydrophilic and altering the frequency of QCM through the plasma treatment and graft copolymerization with an appropriate monomer.

UV-induced graft polymerization of acrylamide on cellulose by using immobilized benzophenone as a photo-initiator

Photo-active moiety, benzophenone, was incorporated onto cotton fabrics by using butyl tetracarboxylic acids (BTCA). Then, grafting of polyacrylamide on the cotton fabrics was performed by exposing the fabrics to longer UV wavelength irradiation. The chemical structure and thermal properties of the polyacrylamide grafted cotton fabrics were investigated by SEM, FTIR, XRD, and TGA, and the results verified the successful grafting of polyacrylamide on cotton fabrics. Also, it was observed that active chlorine contents were created on the polyacrylamide grafted cotton fabrics through simple chlorination process, and the chlorine treated cotton fabrics showed excellent antibacterial abilities like the powerful cyclic amide halamines.

INTERACTION BETWEEN THE SURFACE GLYCOSYLATED POLYPROPYLENE MAMBRANE AND LECTIN

A glycopolymer bearing glucose residues was tethered onto the surface of polypropylene microporous membrane by UV-induced graft polymerization of α-allyl glucoside. Concanavalin A (Con A), a glucose recognizing lectin, could be specifically adsorbed to the membrane surface. On the other hand, the membrane surface showed no recognition ability to another lectin peanut agglutinin. Moreover, the recognition complex between the glycosylated membrane surface and Con A could be inhibited by glucose and mannose solution. This surface glycosylated membrane could be used as affinity membrane for protein separation and purification.

Construction of a Comb-like Glycosylated Membrane Surface by a Combination of UV-Induced Graft Polymerization and Surface-Initiated ATRP

Carbohydrate residues are found on the extracellular side of the cell membrane. They form a protective coating on the outer surface of the cell and are involved in intercellular recognition. Synthetic carbohydrate-based polymers, so-called glycopolymers, are emerging as important well-defined tools for investigating carbohydrate-based biological processes and for simulating various functions of carbohydrates. In this work, the surface of a polypropylene microporous membrane (PPMM) was modified with comb-like glycopolymer brushes by a combination of UV-induced graft polymerization and surface-initiated atom-transfer radical polymerization (ATRP). 2-Hydroxyethyl methacrylate (HEMA) was first grafted to the PPMM surface under UV irradiation in the presence of benzophenone and ferric chloride. ATRP initiator was then coupled to the hydroxyl groups of poly(HEMA) brushes. Surface-initiated ATRP of a glycomonomer, D-gluconamidoethyl methacrylate, was followed at ambient temperature in aqueous solvent. Water had a significant acceleration effect on the ATRP process; however, loss of control over the polymerization process was also observed. The addition of CuBr2 to the ATRP system largely increased the controllability at the cost of the polymerization rate. The grafting of HEMA, the coupling of ATRP initiator to the hydroxyl groups, and the surface-initiated ATRP were confirmed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy.

Immobilized Heparin onto TiNi Shape Memory Alloy Modified with Acrylamide by UV-Induced Grafting

SiC:H organic-like thin films are deposited on Ti50Ni50 shape memory alloy by DC-pulsed plasma enhanced chemical vapor deposition (PECVD) in the gas mixture of Hexamethyldisilazane (HMDSN) and Ar at room temperature. The organic-like thin films containing peroxides or free radicals can be successfully grafted with hydrophilic polymer acrylamide (AAm) by UV-induced grafting polymerization. After grafting, a new dense organic and slippery surface with low friction coefficient is obtained. Heparin is finally immobilized onto grafted-AAm thin films to take TiNi SMA into the anti-thrombin biomaterials. [doi:10.2320/matertrans.48.348]

Characterization of UV-Induced Graft Polymerization of Poly(acrylic acid) Using Optical Waveguide Spectroscopy

UV-induced graft polymerization is a simple and effective method for the surface modification and functionalization of polymeric materials. The structure of poly(acrylic acid) (PAAc) grafted onto a polymeric surface by UV-induced graft polymerization of acrylic acid was investigated using optical waveguide spectroscopy (OWS). The PAAc graft layer exhibited a large increase in thickness in water compared to that in the dry state due to the swellability of the PAAc chains. Its thickness further increased with increasing the pH of the aqueous solution. This could be attributed to the increased electrostatic repulsion of the carboxylate anions on the PAAc chains, as the ionization degree of the carboxylic groups increases with pH. The thickness of the PAAc graft layer is dependent on the graft condition employed, including the UV intensity and irradiation time, and the AAc monomer concentration. On the basis of these data, we propose a model for the structure of the PAAc graft layer and a PAAc layer modified by galactose ligands.

Fabrication of Glycosylated Surface on Polymer Membrane by UV-Induced Graft Polymerization for Lectin Recognition

Increasingly, carbohydrate-protein interactions are viewed as important mechanisms for many biological processes such as blood coagulation, immune response, viral infection, inflammation, embryogenesis, and cellular signal transfer. However, the weak affinity of the interactions and the structural complexity of carbohydrates have hindered efforts to develop a comprehensive understanding of carbohydrate functions. Fortunately, synthetic polyvalent glycoligands give us a chance to reveal the nature of these biological processes. In this work a sugar-containing monomer (alpha-D-allyl glucoside (AG)) was grafted onto polypropylene microporous membrane (PPMM) by UV-induced graft polymerization to generate a glycosylated porous surface for the first time. Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy were employed to confirm the glycosylation. Water contact angle measurement was used to evaluate the hydrophilicity change of the surfaces before and after the graft polymerization of AG. It was found that the grafting density increased reasonably with the increase of AG monomer concentration, and then this increase slowed when the AG concentration exceeded 80 g/L. At the same time a 20-25 min UV irradiation was enough for the grafting polymerization. The photoinitiator concentration also influenced the grafting density obviously, and there was an optimal concentration of the photoinitiator for the grafting process. The water contact angle of the polyAG-tethered membrane surface decreased from 149 degrees to 80 degrees with the increase of grafting density from 0 to 187.76 microg/cm2, which indicated a hydrophilic variation of the membrane surface by the grafting of AG. Results also indicated that the surface-grafted polyAG chains showed weak interaction with Con A when the grafting density was low. However, when the sugar density exceeded 90 microg/cm2, the binding affinity increased dramatically which was the due to the "glycoside cluster effect".

Enhancing the hydrophilicity of polypropylene microporous membranes by the grafting of 2-hydroxyethyl methacrylate via a synergistic effect of photoinitiators

Membrane surfaces modified with polymers based on 2-hydroxyethyl methacrylate (HEMA) is promising for hydrophilicity, biocompatibility, and functionality. In this work, the UV-induced graft polymerization of HEMA onto polypropylene microporous membrane (PPMM) was studied using ferric chloride (FeCl 3) and benzophenone (BP) as co-photoinitiators with different methods for the first time. It was found that the conventional photoinitiator, BP, could not initiate the grafting polymerization of HEMA on the PPMM. Incorporation of FeCl 3 into the reaction system remarkably enhanced the grafting of HEMA onto PPMM, which could be ascribed to the “synergistic effect” between Fe 3+ and BP. Results indicated that the maximum grafting degree for the soak method, which added monomer, photoinitiators and membranes in acetone/water mixture together was 2.5-fold greater than that for the adsorption method. Therefore, the grafting degree of HEMA on the membrane surface could be modulated in a wide range through the variation of UV irradiation time, monomer concentration, and BP/FeCl 3 ratio. The poly(HEMA)-modified membrane surfaces were characterized by attenuated total reflectance Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy. Static water contact angle of the membrane surface indicated a decrease from 145° to 42° with the grafting degree increasing from 0 to 35.67 wt.%. Water drop lied on the modified surface with 35.67 wt.% of grafting degree permeated completely into the membrane pores in 3 s. Furthermore, these poly(HEMA)-tethered membranes showed well protein resistance and potential hemocompatibility due to the enhancement of surface hydrophilicity.

Urease immobilization on an ion-exchange textile for urea hydrolysis

Ion-exchange textiles are used as organic supports for urease immobilization with the aim of developing reactive fibrous materials able to promote urea removal. A non-woven, polypropylene-based cation-exchange textile was prepared using UV-induced graft polymerization. Urease was covalently immobilized onto the cation-exchange textile using three different coupling agents: N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (EDC), N-cyclohexyl-N′-(b-[N-methylmorpholino]ethyl)carbodiimide p-toluenesulfonate (CMC), and glutaraldehyde (GA). The immobilized biocatalyst was characterized by means of FT-IR spectrometry, SEM micrographs, dependence of the enzyme activity on pH and temperature, and according to the kinetic constants of the free and immobilized ureases. The biotextile prepared with EDC in the presence of N-hydroxysuccinimide performs best. The optimum pH was 7.2 for the free urease and 7.6 for the immobilized ureases. The reactivity was maximal at 45 °C for free urease, 50 °C for biotextiles prepared using EDC or CMC, and 55 °C for biotextiles prepared with GA. The activation energy for the immobilized ureases was 4.73–5.67 kcal mol−1, which is somewhat higher than 4.3 kcal mol−1 for free urease. The urea conversion for a continuous-flow immobilized urease reactor is nearly as good as a continuously stirred tank reactor having a much longer residence time, suggesting that the packed bed reactor had sufficient diffusive mixing and residence time to reach nearly optimal results. Urease immobilized on a biotextile using EDC has good storage and operational stability. Copyright © 2006 Society of Chemical Industry

Surface modification of silica nanoparticles by UV-induced graft polymerization of methyl methacrylate

In this study we modified the surface of silica nanoparticles with methyl methacrylate by UV-induced graft polymerization. It is a surface-initiated polymerization reaction induced by ultraviolet irradiation. The resulting organic–inorganic nanocomposites were near-monodisperse and fabricated without homopolymerization of the monomer. Substantial increase in mean particle size was observed by SEM image analysis after UV-induced grafting of methyl methacrylate onto pure silica particles. FT-Raman spectroscopy and X-ray photoelectron spectroscopy studies of these materials revealed the successful grafting of methyl methacrylate onto the silica surface. The formation of a covalent bond between the grafted PMMA chains and silica surface was indicated by FT-Raman spectra. Thermogravimetric analysis of the PMMA-grafted silica particles indicated the polymer contents in good agreement with SEM photographs.

Novel Sequence for Generating Glycopolymer Tethered on a Membrane Surface

Cell surface carbohydrates, usually binding with other biomacromolecules (such as lipids and proteins), are involved in numerous biological functions, including cellular recognition, adhesion, cell growth regulation, and inflammation. Synthetic carbohydrate-based polymers, so-called glycopolymers, are emerging as important well-defined tools for investigating carbohydrate-based biological processes and for simulating various functions of carbohydrates. In this study, a novel two-step sequence for the generation of a glycopolymer layer tethered on a polypropylene microporous membrane is described. First, a UV-induced graft polymerization of 2-aminoethyl methacrylate hydrochloride (AEMA) was carried out on the membrane to generate an amino-functionalized surface, and the effects of polymerization factors (monomer/initiator concentration and UV irradiation time) on the grafting density were studied. Second, sugar moieties were bound with the grafted functional layer to form glycopolymer by the reaction between the amino groups on the membrane surface and carbohydrate lactones. Chemical analysis by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy combined with surface morphology observation by scanning electron microscopy confirmed the graft polymerization of AEMA and the formation of glycopolymer. The decreases of water contact angle and protein adsorption on the membrane revealed the enhancement of hydrophilicity and protein resistance due to the typical characteristics of the glycopolymer tethered on the surface. These results indicated that the novel sequence reported in this work is a facile process to form glycopolymer-modified surfaces.

Surface organic modification of inorganic substrates by plasma deposition of tin oxide organic-like thin films and grafting polymerization

The plasma deposition and surface grafting polymerization have been used to modify the surface structure and properties of inorganic substrates such as organic nature, structural constitution, hydrophilicity, functional groups, and conductivity. In this study, tin oxide (SnO x ) organic-like thin films were deposited by plasma enhanced chemical vapor deposition (PECVD) of tetramethyltin (TMT) and O 2 gas mixtures at low temperature. Higher proportion of TMT in the TMT/O 2 mixtures tends to increase organic nature of the deposited films and makes the surface hydrophobic. The organic-like thin films containing peroxides or free radicals can be subsequently grafted hydrophilic polymer acrylamide (AAm) by UV-induced grafting polymerization.

Water-Soluble Poly(acrylic acid) Grafted Luminescent Silicon Nanoparticles and Their Use as Fluorescent Biological Staining Labels

UV-induced graft polymerization of acrylic acid (AAc) on the surface of silicon nanoparticles was used to prepare a stable aqueous luminescent silicon nanoparticle solution. By grafting a water-soluble polymer on the particle surface, the dispersions in water of the silicon nanoparticles became very stable and clear aqueous solutions could be obtained. XPS and NMR spectroscopy confirmed that PAAc was covalently grafted to the silicon nanoparticles. The grafted PAAc on silicon particles increased not only the dispersibility but also improved the photoluminescence stability of the silicon nanoparticles against degradation by water. The surface-modified nanoparticles were used as biological labels for cell imaging. The Si quantum dot labels exihibited bright fluorescence images and provided higher resistance to photobleaching than the commonly used organic dyes.

UV-induced graft polymerization of polypropylene-g-glycidyl methacrylate membrane in the vapor phase

UV-induced graft polymerization of glycidyl methacrylate (GMA) to a polypropylene (PP) membrane was carried out in the vapor phase with benzophenone (BP) as a photoinitiator. Attenuated total reflection Fourier transform infrared spectroscopy, atomic force microscopy (AFM), and scanning electron microscopy (SEM) were utilized to characterize the copolymer. The degree of grafting increased with increasing reaction time, increased UV irradiation source intensity, and increased immersion concentration of the BP solution. The optimum synthetic condition for the PP-g-GMA membrane was obtained with a reaction time of 2 hrs, a UV irradiation source intensity of 450W, and an immersion concentration of the BP solution of 0.5 mol/L. The pure water flux decreased upon increasing the degree of grafting and increasing the amount of diethylamino functional group introduced. The analysis of AFM and SEM images shows that the graft chains and diethylamino groups of PP-g-GMA grew on the PP membrane surface, resulting in a change in surface morphology.

Viologen-Functionalized Conductive Surfaces: Physicochemical and Electrochemical Characteristics, and Stability

The surface functionalization of electrically conductive substrates (indium−tin oxide (ITO), gold, free-standing polypyrrole film (PPY)) with a vinyl group containing viologen (vinyl benzyl viologen, VBV) has been carried out. The ITO was first silanized, while for the gold substrate, self-assembled alkanethiol monolayers were first prepared. Both substrates were then subjected to argon plasma pretreatment prior to UV-induced VBV graft polymerization. No pretreatment of the PPY film was necessary before UV-induced VBV graft polymerization. The surface composition and microstructure of the as-functionalized substrates were characterized by X-ray photoelectron spectroscopy (XPS), UV−visible absorption spectroscopy, and atomic force microscopy (AFM). The effects of plasma pretreatment time of the silane-modified ITO substrates and monomer concentration on the VBV graft polymer concentration were investigated. The cyclic voltammetric (CV) response of the as-functionalized ITO substrates was studied in aqueous sodium chloride solution. The CV results support the viologen redox mechanism in which VBV is first reduced to the radical cation during the cathodic scan and subsequently oxidized to the dication during the anodic scan. Good stability of the VBV was observed after repeated CV scans, as well as after being maintained at 100 °C for an extended period of time. This approach of surface functionalization of electrically conductive surfaces with viologen shows great promise for designing electrodes for use in electrochromic and sensing devices.

Covalent attachment of polymer thin layers to self-assembled monolayers on gold surface by graft polymerization

Graft polymerization of functional monomers onto self-assembled monolayers (SAMs) on gold via argon plasma treatment and then UV irradiation has been carried out. Two alkanethiols, viz., 3-mercaptopropionic acid and 3-mercaptopropionic acid-2-ethylhexyl ester, were employed for the deposition of SAMs from ethanol solutions onto gold surfaces. The monomers used for graft polymerization were water-soluble acrylic acid (AAc) and hydrophobic allylpentafluorobenzene. Angle-resolved X-ray photoelectron spectroscopy (XPS) and contact angle measurements were used to investigate the surface chemical composition, surface coverage, film thickness, and wettablity. XPS results suggest that mild and brief plasma treatments can be employed to generate sufficient peroxides and hydroperoxides on the SAMs for the subsequent UV-induced graft polymerization while maintaining the SAMs intact. For all the cases investigated, XPS results reveal that the graft polymer forms a thin layer of 6–7 nm in thickness on the SAM surfaces. Contact angle measurements indicate that the SAM-modified Au surfaces could be selectively made hydrophilic or hydrophobic through the graft copolymerization with an appropriate monomer. It was also demonstrated that the AAc graft polymerized SAMs selectively adsorbed Fe 3+ ions via coordination complexation.