Functional polymer brushes via surface-initiated atom transfer radical graft polymerization for combating marine biofouling

Dense and uniform polymer brush coatings were developed to combat marine biofouling. Nonionic hydrophilic, nonionic hydrophobic, cationic, anionic and zwitterionic polymer brush coatings were synthesized via surface-initiated atom transfer radical polymerization (SI-ATRP) of 2-hydroxyethyl methacrylate, 2,3,4,5,6-pentafluorostyrene, 2-(methacryloyloxy)ethyl trimethylammonium chloride, 4-styrenesulfonic acid sodium and N,N'-dimethyl-(methylmethacryloyl ethyl) ammonium propanesulfonate, respectively. The functionalized surfaces had different efficacies in preventing adsorption of bovine serum albumin (BSA), adhesion of the Gram-negative bacterium Pseudomonas sp. NCIMB 2021 and the Gram-positive Staphylococcus aureus, and settlement of cyprids of the barnacle Amphibalanus amphitrite (=Balanus amphitrite). The nonionic hydrophilic, anionic and zwitterionic polymer brushes resisted BSA adsorption during a 2?h exposure period. The nonionic hydrophilic, cationic and zwitterionic brushes exhibited resistance to bacterial fouling (24?h exposure) and cyprid settlement (24 and 48?h incubation). The hydrophobic brushes moderately reduced protein adsorption, and bacteria and cyprid settlement. The anionic brushes were least effective in preventing attachment of bacteria and barnacle cyprids. Thus, the best approach to combat biofouling involves a combination of nonionic hydrophilic and zwitterionic polymer brush coatings on material surfaces.     

Functional polymer brushes via surface-initiated atom transfer radical graft polymerization for combating marine biofouling

Dense and uniform polymer brush coatings were developed to combat marine biofouling. Nonionic hydrophilic, nonionic hydrophobic, cationic, anionic and zwitterionic polymer brush coatings were synthesized via surface-initiated atom transfer radical polymerization (SI-ATRP) of 2-hydroxyethyl methacrylate, 2,3,4,5,6-pentafluorostyrene, 2-(methacryloyloxy)ethyl trimethylammonium chloride, 4-styrenesulfonic acid sodium and N,N′-dimethyl-(methylmethacryloyl ethyl) ammonium propanesulfonate, respectively. The functionalized surfaces had different efficacies in preventing adsorption of bovine serum albumin (BSA), adhesion of the Gram-negative bacterium Pseudomonas sp. NCIMB 2021 and the Gram-positive Staphylococcus aureus, and settlement of cyprids of the barnacle Amphibalanus amphitrite (=Balanus amphitrite). The nonionic hydrophilic, anionic and zwitterionic polymer brushes resisted BSA adsorption during a 2 h exposure period. The nonionic hydrophilic, cationic and zwitterionic brushes exhibited resistance to bacterial fouling (24 h exposure) and cyprid settlement (24 and 48 h incubation). The hydrophobic brushes moderately reduced protein adsorption, and bacteria and cyprid settlement. The anionic brushes were least effective in preventing attachment of bacteria and barnacle cyprids. Thus, the best approach to combat biofouling involves a combination of nonionic hydrophilic and zwitterionic polymer brush coatings on material surfaces.     

Effect of polymer brush architecture on antibiofouling properties

Polymer brushes show great promise in next-generation antibiofouling surfaces. Here, we have studied the influence of polymer brush architecture on protein resistance. By carefully optimizing reaction conditions, we were able to polymerize oligoglycerol-based brushes with sterically demanding linear or dendronized side chains on gold surfaces. Protein adsorption from serum and plasma was analyzed by surface plasmon resonance. Our findings reveal a pronounced dependence of biofouling on brush architecture. Bulky yet flexible side chains as in dendronized brushes provide an ideal environment to repel protein-possibly through formation of a hydration layer, which can be further enhanced by presenting free hydroxyl groups on the polymer brushes. A deeper understanding of how brush architecture influences protein resistance will ultimately enable fabrication of surface coatings tailored to specific requirements in biomedical applications.     

Stability and nonfouling properties of poly(poly(ethylene glycol) methacrylate) brushes under cell culture conditions

This paper investigates the stability and nonfouling properties of poly(poly(ethylene glycol) methacrylate) (PPEGMA) brushes prepared by surface-initiated atom transfer radical polymerization from SiO(x) substrates modified with a trimethoxysilane-based ATRP initiator. At high chain densities, PPEGMA brushes were found to detach rapidly from glass or silicon substrates. Detachment of the PPEGMA brushes could be monitored with contact angle measurements, which indicated a decrease in the receding water contact angle upon detachment. Detachment of the PPEGMA brushes also resulted in an increase in nonspecific protein adsorption. The stability, and as a consequence the long-term nonfouling properties, of the PPEGMA brushes could be improved by tailoring the brush density and, to a lesser extent, the molecular weight of the polymer chains. By appropriate decrease of the grafting density, the stability of the brushes in cell culture medium could be improved from less than 1 to more than 7 days, without compromising the nonfouling properties.     

Generation of functional coatings on hydrophobic surfaces through deposition of denatured proteins followed by grafting from polymerization

Hydrophilic coatings were produced on flat hydrophobic substrates featuring n-octadecyltrichlorosilane (ODTS) and synthetic polypropylene (PP) nonwoven surfaces through the adsorption of denatured proteins. Specifically, physisorption from aqueous solutions of α-lactalbumin, lysozyme, fibrinogen, and two soy globulin proteins (glycinin and β-conglycinin) after chemical (urea) and thermal denaturation endowed the hydrophobic surfaces with amino and hydroxyl functionalities, yielding enhanced wettability. Proteins adsorbed strongly onto ODTS and PP through nonspecific interactions. The thickness of adsorbed heat-denatured proteins was adjusted by varying the pH, protein concentration in solution, and adsorption time. In addition, the stability of the immobilized protein layer was improved significantly after interfacial cross-linking with glutaraldehyde in the presence of sodium borohydride. The amino and hydroxyl groups present on the protein-modified surfaces served as reactive sites for the attachment of polymerization initiators from which polymer brushes were grown by surface-initiated atom-transfer radical polymerization of 2-hydroxyethyl methacrylate. Protein denaturation and adsorption as well as the grafting of polymeric brushes were characterized by circular dichroism, ellipsometry, contact angle, and Fourier transform infrared spectroscopy in the attenuated total reflection mode.     

Substrate-independent approach for the generation of functional protein resistant surfaces

A new route for coating various substrates with antifouling polymer layers was developed. It consisted in deposition of an amino-rich adhesion layer by means of RF magnetron sputtering of Nylon 6,6 followed by the well-controlled, surface-initiated atom transfer radical polymerization of antifouling polymer brushes initiated by bromoisobutyrate covalently attached to amino groups present in the adhesion layer. Polymer brushes of hydroxy- and methoxy-capped oligoethyleneglycol methacrylate and carboxybetaine acrylamide were grafted from bromoisobutyrate initiator attached to a 15 nm thick amino-rich adhesion layer deposited on gold, silicon, polypropylene, and titanium-aluminum-vanadium alloy surfaces. Well-controlled polymerization kinetics made it possible to control the thickness of the brushes at a nanometer scale. Zero fouling from single protein solutions and a reduction of more than 90% in the fouling from blood plasma observed on the uncoated surfaces was achieved. The feasibility of functionalization with bioactive compounds was tested by covalent attachment of streptavidin onto poly(oligoethylene glycol methacrylate) brush and subsequent immobilization of model antibodies and oligonucleotides. The procedure is nondestructive and does not require any chemical preactivation or the presence of reactive groups on the substrate surface. Contrary to current antifouling modifications, the developed coating can be built on various classes of substrates and preserves its antifouling properties even in undiluted blood plasma. The new technique might be used for fabrication of biotechnological and biomedical devices with tailor-made functions that will not be impaired by fouling from ambient biological media.     

Analysis of protein interaction and function with a 3-dimensional MALDI-MS protein array

Protein profiling and characterization of protein interactions in biological samples ultimately require indicator-free methods of signal detection, which likewise offer an opportunity to distinguish specific interactions from nonspecific protein binding. Here we describe a new 3-dimensional protein microchip for detecting biomolecular interactions with matrix-assisted laser desorption-ionization mass spectrometry (MALDI-MS); the microchip comprises a high-density array of methacrylate polymer elements containing immobilized proteins as capture molecules and directly interfaces with a commercially available mass spectrometer. We demonstrated the performance of the chip in three types of experiments by detecting antibody-antigen interactions, enzymatic activity, and enzyme-inhibitor interactions. MALDI-MS biochip-based tumor necrosisfactor alpha (TNF-alpha) immunoassays demonstrated the feasibility of detecting antigens in complex biological samples by identifying molecular masses of bound proteins even at high nonspecific protein binding. By detecting model interactions of trypsin with trypsin inhibitors, we showed that the protein binding capacity of methacrylate polymer elements and the sensitivity of MALDI-MS detection of proteins bound to these elements surpassed that of other 2- and 3-dimensional substrates tested Immobilized trypsin retained functional (enzymatic) activity within the protein microchip and the specificity of macromolecular interactions even in complex biological samples. We believe that the underlying technology should therefore be extensible to whole-proteome protein expression profiling and interaction mapping.     

Sensing capabilities of colloidal gold monolayer modified with a phenylboronic acid-carrying polymer brush

A dithiolated random copolymer with pendent phenylboronic acid residues [Cys-poly(3-acrylamidophenylboronic acid-co-N,N-dimethylaminopropyl methacrylamide), Cys-poly(APBA-co-DMAPMA)] that shows the abilities of initiation, transfer, and termination (iniferter) was obtained by using a benzyl N,N-diethyldithiocarbamoyl (BDC) derivative. The obtained disulfide-carrying copolymer was accumulated on a colloidal gold-immobilized glass substrate, and the usefulness of the polymer brush as a sensing element for glycoproteins such as ovalbumin (OVA) was examined by UV-visible spectrophotometry with the help of localized surface plasmon resonance (LSPR). The sensor showed a concentration-dependent binding of OVA with a detection limit of 100 nM, and it had a very high stability at high ionic strength. The sensor chip could be used for a detection of another glycoprotein, avidin, as well. Furthermore, the binding of biotin-modified human serum albumin (biotinylated HSA) to the avidin-phenylboronic acid- (PBA-) carrying polymer brush complex and further specific binding of anti-HSA immunoglobulin G to the biotinylated HSA-avidin-PBA-carrying polymer brush ternary complex could clearly be observed. The polymer-brush-coated device examined here not only was useful as a simple sensor chip, but also is expected to open a new perspective on interfacial phenomena performed by various functional polymer brushes fixed to colloidal gold on glass substrates.     

Correlating transfection barriers and biophysical properties of cationic polymethacrylates

Transfection efficiencies of several polymeric gene carriers were compared and correlated quantitatively to the amounts of cellular accumulation of plasmid DNA and to the expression of mRNA by quantitative real-time polymerase chain reaction (real-time PCR). Three polycations polymers with similar chemical structure were used in this study: poly(dimethylamino)ethyl methacrylate (PDMA) homopolymer, PEO-b-PDMA copolymer, and PEO-b-poly(diethylamino)ethyl methacrylate (PEO-b-PDEA) copolymer. Despite their similar chemical structures, the transfection efficiencies were significantly different. PEO-b-PDEA copolymer was significantly less efficient as gene carrier as compared to both PDMA and PEO-b-PDMA. Correlations between cytotoxicity, cellular uptake of plasmid DNA, expression levels of transgene and protein, and the physical properties of the polymers were observed. With the PEO-b-PDEA studies, cytotoxicity was due primarily to the excess of polymers that did not participate in the DNA binding. In addition, the inability of the polymer/DNA polyplexes to interact with cell effectively was identified as a critical barrier for high efficiency of transfection. This study demonstrated that the use of quantitative real-time PCR in combination with physical characterization techniques could provide useful insights into the transfection barrier at different cellular levels.     

Synthesis, characterization, and evaluation as transfection reagents of ampholytic star copolymers: effect of star architecture

Five star polymers based on the positively ionizable hydrophilic 2-(dimethylamino)ethyl methacrylate (DMAEMA) and the hydrophobic but hydrolyzable tetrahydropyranyl methacrylate (THPMA) were prepared by group-transfer polymerization (GTP) using ethylene glycol dimethacrylate (EGDMA) as the coupling agent. In particular, four isomeric star copolymers (one heteroarm, two star block, and the statistical star), all with a 3:1 DMAEMA:THPMA molar ratio, plus one star homopolymer of DMAEMA, with degrees of polymerization of the arms equal to 15, were synthesized. After star polymer preparation and preliminary characterization, the THPMA units were hydrolyzed to negatively ionizable hydrophilic methacrylic acid (MAA) untis, thus yielding star polyampholytes. All the star polyampholytes as well as the commercially available transfection reagent SuperFect were evaluated for their ability to transfect human cervical HeLa cancer cells with the modified plasmid pRLSV40 bearing the enhanced green fluorescent protein (EGFP) as the reporter gene. The transfection efficiency was affected by star architecture. The DMAEMA15-star-MAA5 polyampholyte presented the highest transfection efficiency of all the star polymers tested but lower than that of SuperFect at its optimum conditions. All four star copolymers showed decreased toxicity compared to the DMAEMA star homopolymer for the same amounts of star polymer tested and also compared to the SuperFect at its optimum conditions.     

Preparation and Friction Force Microscopy Measurements of Immiscible,Opposing Polymer Brushes

Solvated polymer brushes are well known to lubricate high-pressure contacts, because they can sustain a positive normal load while maintaining low friction at the interface. Nevertheless, these systems can be sensitive to wear due to interdigitation of the opposing brushes. In a recent publication, we have shown via molecular dynamics simulations and atomic force microscopy experiments, that using an immiscible polymer brush system terminating the substrate and the slider surfaces, respectively, can eliminate such interdigitation. As a consequence, wear in the contacts is reduced. Moreover, the friction force is two orders of magnitude lower compared to traditional miscible polymer brush systems. This newly proposed system therefore holds great potential for application in industry. Here, the methodology to construct an immiscible polymer brush system of two different brushes each solvated by their own preferred solvent is presented. The procedure how to graft poly(N-isopropylacrylamide) (PNIPAM) from a flat surface and poly(methyl methacrylate) (PMMA) from an atomic force microscopy (AFM) colloidal probe is described. PNIPAM is solvated in water and PMMA in acetophenone. Via friction force AFM measurements, it is shown that the friction for this system is indeed reduced by two orders of magnitude compared to the miscible system of PMMA on PMMA solvated in acetophenone.     

Grafting of antibacterial polymers on stainless steel via surface‐initiated atom transfer radical polymerization for inhibiting biocorrosion by Desulfovibrio desulfuricans

To enhance the biocorrosion resistance of stainless steel (SS) and to impart its surface with bactericidal function for inhibiting bacterial adhesion and biofilm formation, well‐defined functional polymer brushes were grafted via surface‐initiated atom transfer radical polymerization (ATRP) from SS substrates. The trichlorosilane coupling agent, containing the alkyl halide ATRP initiator, was first immobilized on the hydroxylated SS (SS‐OH) substrates for surface‐initiated ATRP of (2‐dimethylamino)ethyl methacrylate (DMAEMA). The tertiary amino groups of covalently immobilized DMAEMA polymer or P(DMAEMA), brushes on the SS substrates were quaternized with benzyl halide to produce the biocidal functionality. Alternatively, covalent coupling of viologen moieties to the tertiary amino groups of P(DMAEMA) brushes on the SS surface resulted in an increase in surface concentration of quaternary ammonium groups, accompanied by substantially enhanced antibacterial and anticorrosion capabilities against Desulfovibrio desulfuricans in anaerobic seawater, as revealed by antibacterial assay and electrochemical studies. With the inherent advantages of high corrosion resistance of SS, and the good antibacterial and anticorrosion capabilities of the viologen‐quaternized P(DMAEMA) brushes, the functionalized SS is potentially useful in harsh seawater environments and for desalination plants. Biotechnol. Bioeng. 2009;103: 268–281. © 2009 Wiley Periodicals, Inc.     

Protein binding to amphoteric polymer brushes grafted onto a porous hollow-fiber membrane

Three kinds of ampholites, i.e., 3-aminopropionic acid (NH2C2H4COOH), (2-aminoethyl)phosphonic acid (NH2C2H4PO3H2), and 2-aminoethane-1-sulfonic acid (NH2C2H4SO3H), were introduced into an epoxy group-containing polymer brush grafted onto a porous hollow-fiber membrane with a porosity of 70% and pore size of 0.36 microm. The amphoteric group density of the hollow-fiber ranged from 0.50 to 0.72 mmol/g. Three kinds of proteins, i.e., lactoferrin (Lf), cytochrome c (Cyt c), and lysozyme (Ly), were captured by the amphoteric polymer brush during the permeation of the protein solution across the ampholite-immobilized porous hollow-fiber membrane. Multilayer binding of the protein to the amphoteric polymer brush, with a degree of multilayer binding of 3.3, 8.6, and 15 for Lf, Cyt c, and Ly, respectively, with the (2-aminoethyl)phosphonic acid-immobilized porous hollow-fiber membrane, was demonstrated with a negligible diffusional mass-transfer resistance of the protein to the ampholite immobilized. The 2-aminoethane-1-sulfonic acid-immobilized porous hollow-fiber membrane exhibited the lowest initial flux of the protein solution, 0.41 m/h at a transmembrane pressure of 0.1 MPa and 298 K, and the highest equilibrium binding capacity of the protein, e.g., 130 mg/g for lysozyme. Extension and shrinkage of the amphoteric polymer brushes were observed during the binding and elution of the proteins.     

Antimicrobial surfaces of viologen-quaternized poly((2-dimethyl amino)ethyl methacrylate)-Si(100) hybrids from surface-initiated atom transfer radical polymerization

To improve the antimicrobial ability of silicon-based bioelectronics and to tailor the silicon surfaces for inhibiting biofilm formation, well-defined functional polymer-Si(100) hybrids, consisting of nearly monodispersed poly((2-dimethylamino)ethyl methacrylate) (P(DMAEMA)) covalently tethered on the silicon surface and functionalized by viologen moieties, were prepared. P(DMAEMA)-Si hybrids were prepared via surface-initiated atom transfer radical polymerization (ATRP) of (2-dimethylamino)ethyl methacrylate (DMAEMA) on the hydrogen-terminated Si(100) surfaces (Si−H surfaces). The tertiary amino groups of the covalently immobilized (Si−C bonded) P(DMAEMA) brushes on the silicon substrates were quaternized by an alkyl halide to produce a high concentration of quaternary ammonium groups with biocidal functionality. Alternatively, covalent coupling of viologen moieties to the tertiary amino groups of P(DMAEMA) brushes produced the quaternized P(DMAEMA)-Si(100) hybrids with substantially enhanced antimicrobial capability, as well as capability to effectively inhibit biofilm formation. Thus, the viologen-quaternized P(DMAEMA)-Si(100) hybrids possess good antibacterial surface properties and are potentially useful to the silicon-based bioelectronics to ensure their efficiency, durability and reliability.     

Covalent immobilization of glucose oxidase on well-defined poly(glycidyl methacrylate)-Si(111) hybrids from surface-initiated atom-transfer radical polymerization

A simple one-step procedure was employed for the covalent immobilization of an atom-transfer radical polymerization (ATRP) initiator, via the robust Si-C bond, on the hydrogen-terminated Si(111) surface (Si-H surface). Well-defined poly(glycidyl methacrylate) [P(GMA)] brushes, tethered directly on the (111)-oriented single-crystal silicon surface, were prepared via surface-initiated ATRP. Kinetics study on the surface-initiated ATRP of glycidyl methacrylate revealed that the chain growth from the silicon surface was consistent with a "controlled" process. A relatively high concentration of glucose oxidase (GOD; above 0.2 mg/cm2) could be coupled directly to the well-defined P(GMA) brushes via the ring-opening reaction of the epoxide groups with the amine moieties of the enzyme. The resultant GOD-functionalized P(GMA) brushes, with the accompanying hydroxyl groups from the ring-opening reaction of the epoxide groups, serves as an effective spacer to provide the GOD with a higher degree of conformational freedom and a more hydrophilic environment. An equivalent enzyme activity above 1.6 units/cm2 [micromoles of beta-D-(+)-glucose oxidized to d-gluconolactone per minute per square centimeter] and a corresponding relative activity of about 60% could be readily achieved. The immobilized GOD also exhibited an improved stability during storage over that of the free enzyme. The GOD-functionalized silicon substrates are potentially useful to the development of silicon-based glucose biosensors.     

Poly(HEMA) brushes emerging as a new platform for direct detection of food pathogen in milk samples

Surface plasmon resonance (SPR) biosensors capable of in real time detection of Cronobacter at concentrations down to 10? cells mL?1 in samples of consumer fresh-whole fat milk, powder whole-fat milk preparation, and powder infant formulation were developed for the first time. Antibodies against Cronobacter were covalently attached onto polymer brushes of poly(2-hydroxyethyl methacrylate) (poly(HEMA)) grafted from the SPR chip surface. The lowest detection limit, 10? cells mL?1, was achieved in phosphate buffered saline (pH 7.4) with sensors prepared by covalent immobilization of the same antibodies onto a self assembled monolayer (SAM) of hexa(ethylene glycol) undecanethiol (EG?). However, when the EG? based sensors were challenged with milk samples the non-specific response due to the deposition of non-targeted compounds from the milk samples was much higher than the specific response to Cronobacter hampering the detection in milk. Similar interfering fouling was observed on antifouling polymer brushes of hydroxy-capped oligoethylene glycol methacrylate and even a 10 times higher fouling was observed on the widely used SAM of mixed hydroxy- and carboxy-terminated alkanethiols. Only poly(HEMA) brushes totally suppressed the fouling from milk samples. The robust well-controlled surface initiated atom transfer radical polymerization of HEMA allowed the preparation of highly dense brushes with a minimal thickness so that the capture of antigens by the antibodies immobilized on the brush layer could take place close to the gold SPR surface to provide a stronger optical response while the fouling was still suppressed. A minimum thickness of 19 nm of poly(HEMA) brush layer was necessary to suppress completely non-specific sensor response to fouling from milk.     

High-capacity purification of His-tagged proteins by affinity membranes containing functionalized polymer brushes

Porous membrane absorbers are attractive for increasing the rate of protein purification, but their binding capacity is low relative to porous beads. Modification of membranes with functionalized polymer brushes, however, can greatly enhance capacity. This work demonstrates that membrane modification with poly(2-hydroxyethyl methacrylate) (PHEMA) brushes derivatized with nitrilotriacetate-Ni2+ (NTA-Ni2+) complexes allows purification of polyhistidine-tagged ubiquitin (HisU) in less than 30 min with a binding capacity of 120 mg of HisU/cm3 of porous alumina membrane. Adsorption isotherms show that saturation of the brushes occurs at HisU concentrations as low as 0.04 mg/mL and that these brushes can bind up to 23 monolayers of HisU. Gel electrophoresis reveals that the purity of eluted HisU is more than 99%, even when the initial feed solution contains 10% bovine serum or a 20-fold excess of BSA. Thus, reusable porous membranes modified by PHEMA-NTA-Ni2+ brushes are attractive candidates for rapid purification of polyhistidine-tagged proteins.     

Control of nanobiointerfaces generated from well-defined biomimetic polymer brushes for protein and cell manipulations

To better understand protein/material and cell/material interactions at the submolecular level, well-defined polymer brushes consisting of poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) on silicon wafers were prepared by atom transfer radical polymerization (ATRP). Silicon wafers were treated with 3-(2-bromoisobutyryl)propyl dimethylchlorosilane (BDCS) to form a monolayer that acts as initiators for ATRP. Silicon-supported BDCS monolayers were soaked in a methanol/water mixture solution containing Cu(I)Br, bipyridine, and a sacrificial initiator. After MPC was added to the solution, ATRP was carried out for 18 h. The molecular weight and thickness of the PMPC brush layer on the silicon surface increased with an increase in the polymerization time. The dense polymer brushes were obtained by the "grafting from" system. By selective decomposition of the BDCS monolayer by UV light-irradiation, the PMPC brush region and the sizes were well controlled, resulting in fabricating micropatterns of the PMPC brushes. When the thickness of the PMPC brush layer was greater than 5.5 +/- 1.0 nm (3 h polymerization), serum protein adsorption and fibroblast adhesion were effectively reduced, i.e., proteins and cells could recognize such thin polymer brushes on the surface. In addition, the density of the adherent cells on the patterned PMPC brush surface could be controlled by changing the size of the pattern.     

Cell fouling resistance of polymer brushes grafted from ti substrates by surface-initiated polymerization: effect of ethylene glycol side chain length

This paper presents a comparative study on the antifouling properties of poly(ethylene glycol) (PEG)-based polymer coatings prepared by surface-initiated polymerization (SIP). Three types of poly(oligo(ethylene glycol) methyl ether methacrylate) (POEGMEMA) polymer thin films of approximate 100 nm thickness were grafted from a catechol initiator that was immobilized on a Ti substrate. OEGMEMA monomers containing side chains of 4, 9, and 23 EG units were used in surface-initiated atom transfer radical polymerization (SI-ATRP) to form POEGMEMA-4, -9, and -23 polymer brushes. The chemical composition, thickness, and wettability of the polymer brushes were characterized by X-ray photoelectron spectroscopy (XPS), ellipsometry, and static water contact angle measurements, respectively. The dependence of antifouling performance on EG side chain length was systemically tested and compared by 3T3 fibroblast cell adhesion assays. Results from 4-h cell culture experiments revealed the complete absence of cell attachment on all the grafted Ti substrates. Excellent cell fouling resistance continued with little dependence on EG side chain length up to three weeks, after which long-term antifouling performance depended on the EG chain length as the grafted samples reached confluent cell coverage in 7, 10, and 11 weeks for POEGMEMA-4, -9, and -23, respectively.     

Electrochemical deposition and surface-initiated RAFT polymerization: protein and cell-resistant PPEGMEMA polymer brushes

This paper introduces a novel and versatile method of grafting protein and cell-resistant poly(poly ethylene glycol methyl ether methacrylate) (PPEGMEMA) brushes on conducting Au surface. The process started with the electrochemical deposition and full characterization of an electro-active chain transfer agent (CTA) on the Au surface. The electrochemical behavior of the CTA was investigated by cyclic voltammetry (CV) while the deposition and stability of the CTA on the surface were confirmed by ellipsometry, contact angle, and X-ray photoelectron spectroscopy (XPS). The capability of the electrodeposited CTA to mediate surface-initiated reversible addition-fragmentation chain transfer (SI-RAFT) polymerization on both the polymethyl methacrylate (PMMA; model polymer) and PPEGMEMA brushes was demonstrated by the increase in thicknesses of the films after polymerization. Contact angles also decreased with the incorporation of the more hydrophilic brushes. Significant changes in the morphologies of the films before and after polymerization were also observed with atomic force microscopy (AFM) analyses. Furthermore, XPS results showed an increase in the O 1s peak intensity relative to C 1s after polymerizations, which confirmed the grafting of polyethyleneglycol (PEG) bearing brushes. The ability of the PPEGMEMA-modified Au surface to resist nonspecific adhesion of proteins and cells was monitored and confirmed by XPS, ellipsometry, contact angle, AFM, and fluorescence imaging. The new method presented has potential application as robust protein and cell-resistant coatings for electrically conducting electrodes and biomedical devices.