Surface-active and stimuli-responsive polymer--Si(100) hybrids from surface-initiated atom transfer radical polymerization for control of cell adhesion

A simple two-step method was developed for the covalent immobilization of atom-transfer radical polymerization (ATRP) initiators on the hydrogen-terminated Si(100) (Si-H) surface. Well-defined functional polymer-Si hybrids, consisting of covalently tethered brushes of poly(ethylene glycol) monomethacrylate (PEGMA) polymer, N-isopropylacrylamide (NIPAAm) polymer, and NIPAAm-PEGMA copolymers and block copolymers on Si-H surfaces, were prepared via surface-initiated ATRP. Kinetics study revealed that the chain growth from the silicon surface was consistent with a "controlled" process. Surface cultures of the cell line 3T3-Swiss albino on the hybrids were evaluated. The PEGMA graft-polymerized silicon [Si-g-P(PEGMA)] surface is very effective in preventing cell attachment and growth. At 37 degrees C [above the lower critical solution temperature (LCST, approximately 32 degrees C) of NIPAAm], the seeded cells adhered, spread, and proliferated on the NIPAAm graft polymerized silicon [Si-g-P(NIPAAm)] surface. Below the LCST, the cells detached from the Si-g-P(NIPAAm) surface spontaneously. Incorporation of PEGMA units into the NIPAAm chains of the Si-g-P(NIPAAm) surface via copolymerization resulted in more rapid cell detachment during the temperature transition. The "active" chain ends on the Si-g-P(PEGMA) and Si-g-P(NIPAAm) hybrids were also used as the macroinitiators for the synthesis of diblock copolymer brushes. Thus, not only are the hybrids potentially useful as stimuli-responsive adhesion modifiers for cells in silicon-based biomedical microdevices but also the active chain ends on the hybrid surfaces offer opportunities for further surface functionalization and molecular design.     

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.     

Spatially well-defined binary brushes of poly(ethylene glycol)s for micropatterning of active proteins on anti-fouling surfaces

We report a novel method for micropatterning of active proteins on anti-fouling surfaces via spatially well-defined and dense binary poly(ethylene glycol)s (PEGs) brushes with controllable protein-docking sites. Binary brushes of poly(poly(ethylene glycol) methacrylate-co-poly(ethylene glycol)methyl ether methacrylate), or P(PEGMA-co-PEGMEMA), and poly(poly(ethylene glycol)methyl ether methacrylate), or P(PEGMEMA), were prepared via consecutive surface-initiated atom transfer radical polymerizations (SI-ATRPs) from a resist-micropatterned Si(100) wafer surface. The terminal hydroxyl groups on the side chains of PEGMA units in the P(PEGMA-co-PEGMEMA) microdomains were activated directly by 1,1'-carbonyldiimidazole (CDI) for the covalent coupling of human immunoglobulin (IgG) (as a model active protein). The resulting IgG-coupled PEG microdomains interact only and specifically with target anti-IgG, while the other PEG microregions effectively prevent specific and non-specific protein fouling. When extended to other active biomolecules, microarrays for specific and non-specific analyte interactions with a high signal-to-noise ratio could be readily tailored.     

Cellular response to magnetic nanoparticles "PEGylated" via surface-initiated atom transfer radical polymerization

A new method to PEGylate magnetic nanoparticles with a dense layer of poly(poly(ethylene glycol) monomethacrylate) (P(PEGMA)) by surface-initiated atom transfer radical polymerization (ATRP) is reported. In this approach, an initiator for ATRP was first immobilized onto the magnetic nanoparticle surface, and then P(PEGMA) was grafted onto the surface of magnetic nanoparticle via copper-mediated ATRP. The modified nanoparticles were subjected to detailed characterization using FTIR, XPS, and TGA. The P(PEGMA)-immobilized nanoparticles dispersed well in aqueous media. The saturation magnetization values of the P(PEGMA)-immobilized nanoparticles were 19 emu/g and 11 emu/g after 2 and 4 h polymerization respectively, compared to 52 emu/g for the pristine magnetic nanoparticles. The response of macrophage cells to pristine and P(PEGMA)-immobilized nanoparticles was compared. The results showed that the macrophage cells are very effective in cleaning up the pristine magnetic nanoparticles. With the P(PEGMA)-immobilized nanoparticles, the amount of nanoparticles internalized into the cells is greatly reduced to <2 pg/cell over a 5 day period. With this amount of nanoparticles uptake, no significant cytotoxicity effects were observed.     

Patterned biofunctional poly(acrylic acid) brushes on silicon surfaces

Protein patterning was carried out using a simple procedure based on photolithography wherein the protein was not subjected to UV irradiation and high temperatures or contacted with denaturing solvents or strongly acidic or basic solutions. Self-assembled monolayers of poly(ethylene glycol) (PEG) on silicon surfaces were exposed to oxygen plasma through a patterned photoresist. The etched regions were back-filled with an initiator for surface-initiated atom transfer radical polymerization (ATRP). ATRP of sodium acrylate was readily achieved at room temperature in an aqueous medium. Protonation of the polymer resulted in patterned poly(acrylic acid) (PAA) brushes. A variety of biomolecules containing amino groups could be covalently tethered to the dense carboxyl groups of the brush, under relatively mild conditions. The PEG regions surrounding the PAA brush greatly reduced nonspecific adsorption. Avidin was covalently attached to PAA brushes, and biotin-tagged proteins could be immobilized through avidin-biotin interaction. Such an immobilization method, which is based on specific interactions, is expected to better retain protein functionality than direct covalent binding. Using biotin-tagged bovine serum albumin (BSA) as a model, a simple strategy was developed for immobilization of small biological molecules using BSA as linkages, while BSA can simultaneously block nonspecific interactions.     

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.     

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.     

PCL film surfaces conjugated with P(DMAEMA)/gelatin complexes for improving cell immobilization and gene transfection

Successful gene transfection on a tissue scaffold is of crucial importance in facilitating tissue repair and regeneration by enabling the localized production of therapeutic drugs. Polycaprolactone (PCL) has been widely adopted as a scaffold biomaterial, but its unfavorable cell-adhesion property needs to be improved. In this work, the PCL film surface was conjugated with poly((2-dimethyl amino)ethyl methacrylate) (P(DMAEMA))/gelatin complexes via surface-initiated atom transfer radical polymerization (ATRP) for improving cell immobilization and subsequent gene transfection. A simple aminolysis-based method was first used for the covalent immobilization of ATRP initiators on the PCL film. Well-defined P(DMAEMA) brushes were subsequently prepared via surface-initiated ATRP from the initiator-functionalized PCL surfaces. The P(DMAEMA) chains with a pK(a) of 7.0-7.3 were used for conjugating gelatin with a pI of 4.7 via electrostatic interaction. The amount of complexed gelatin increased as that of the grafted P(DMAEMA) layer. The cell-adhesion property on the functionalized PCL surface could be controlled by adjusting the ratio of P(DMAEMA)/gelatin. It was found that the gene transfection property on the immobilized cells was dependent on the density of the immobilized cells on the functionalized PCL film. With the good cell-adhesive nature of gelatin and the efficient gene transfection on the dense immobilized cells, the incorporating the suitable of P(DMAEMA)/gelatin complexes onto PCL surfaces could endow the PCL substrates new and interesting properties for potential tissue engineering applications.     

Micropatterning of polymer brushes: grafting from dewetting polymer films for biological applications

In this novel platform, a micropatterned polymer brush was obtained by grafting poly(poly(ethylene glycol) methyl ether methacrylate) (poly(PEGMA)) from a thin macroinitiator film using atom transfer radical polymerization (ATRP). A pattern of holes was formed in the macroinitiator film by taking advantage of its spontaneous dewetting above the glass transition temperature from a bottom polystyrene film, driven by unfavorable intermolecular forces. Patterning by dewetting can be achieved at length-scales from a few hundred nanometers to several tens of micrometers, by simply thermally annealing the bilayer above the glass transition temperature of the polymer. This approach is substrate-independent, as polymer films can be cast onto surfaces of different size, shape, or material. As a demonstration of its potential, proteins, and individual cells were attached on targeted bioadhesive polystyrene areas of the micropatterns within poly(PEGMA) protein-repellent brushes. We anticipate this approach will be suitable for the patterning of brushes, especially for biomedical applications such as in the study of single cells and of cell cocultures.     

Physicochemical and blood compatibility characterization of polypyrrole surface functionalized with heparin

A surface modification technique was developed for the covalent immobilization of heparin onto electrically conductive polypyrrole (PPY) film. The PPY film was first graft copolymerized with poly(ethylene glycol) methacrylate (PEGMA) and then activated with cyanuric chloride (CC). Heparin was then immobilized onto the film through the reaction between the chloride groups of CC and the amine and/or hydroxyl groups of heparin. X-ray photoelectron spectroscopy (XPS) was used to characterize the surface-modified film after each stage. The biocompatibility of the surface-modified PPY was evaluated using plasma recalcification time (PRT) and platelet adhesion. After surface modification, the film had improved wettability while retaining significant electrical conductivity. With immobilized heparin, platelet adhesion and platelet activation on PPY film was significantly suppressed, and the PRT was significantly prolonged. Electrical stimulation also plays a positive role in decreasing platelet adhesion and increasing PRT on pristine and surface-modified PPY films.     

UV-induced graft copolymerization of monoacrylate-poly(ethylene glycol) onto poly(3-hydroxyoctanoate) to reduce protein adsorption and platelet adhesion

Homogeneous solutions of poly(3-hydroxyoctanoate) (PHO) and the monoacrylate-poly(ethylene glycol) (PEGMA) monomer in chloroform were irradiated with UV light to obtain PEGMA-grafted PHO (PEGMA-g-PHO) copolymers. Variables affecting the degree of grafting (DG), such as the time of UV irradiation and the concentrations of the PEGMA monomer and initiator, were investigated. The PEGMA-g-PHO copolymers were characterized by measuring the water contact angle, molecular weight, thermal transition temperatures and mechanical properties, as well as by nuclear magnetic resonance spectroscopy. The results from all of these measurements indicate that PEGMA groups were present on the PHO polymer. The protein adsorption and platelet adhesion on the PEGMA-g-PHO surfaces were examined using poly(L-lactide) (PLLA) surfaces as the control. The proteins and platelets had a significantly lower tendency to adhere to the PEGMA-g-PHO copolymers than to PLLA. The graft copolymer with a high DG of PEGMA was very effective in reducing the protein adsorption and platelet adhesion and did not activate the platelets. The results obtained in this study suggest that PEGMA-g-PHO copolymers have the potential to be used as blood-contacting devices in a broad range of biomedical applications.     

Cell transfer printing from patterned poly(ethylene glycol)-oleyl surfaces to biological hydrogels for rapid and efficient cell micropatterning

Cell transfer printing from patterned poly(ethylene glycol)-oleyl surfaces onto biological hydrogel sheets is investigated herein, as a new cell stamping method for both cell microarray and tissue engineering. By overlaying a hydrogel sheet on the cells immobilized on the poly(ethylene glycol)-oleyl surface and successively peeling it off, the immobilized cells were transferred onto a hydrogel sheet because the adhesive interaction between the cells and the hydrogel was stronger than that between the cells and the poly(ethylene glycol)-oleyl surface. Four types of human cell could be efficiently transferred onto a rigid collagen sheet. The transfer printing ratios, for all cells, were above 80% and achieved within 90 min. A cell microarray was successfully prepared on a collagen gel sheet using the present stamping method. We have also demonstrated that the transferred pattern of endothelial cells is transformed to the patterned tube-like structure on the reconstituted basement membrane matrix. Finally, the patterns of two types of endothelial cell are shown to be easily prepared on the matrix, and the desired tube-like structures, including the orderly pattern of the two different cells, were formed spontaneously. Thus, the present poly(ethylene glycol)-oleyl coated substrates are useful for rapid and efficient cell stamping, in the preparation of multi-cellular pattern on extracellular matrices.     

Ultralow fouling polyacrylamide on gold surfaces via surface-initiated atom transfer radical polymerization

In this work, polyacrylamide is investigated as an ultralow fouling surface coating to highly resist protein adsorption, cell adhesion, and bacterial attachment. Polyacrylamide was grafted on gold surfaces via surface-initiated atom transfer radical polymerization (ATRP). Protein adsorption from a wide range of biological media, including single protein solutions of fibrinogen, bovine serum albumin, and lysozyme, dilute and undiluted human blood serum, and dilute and undiluted human blood plasma, was studied by surface plasmon resonance (SPR). Dependence of the protein resistance on polyacrylamide film thickness was examined. With the optimal film thickness, the adsorption amount of all three single proteins on polyacrylamide-grafted surfaces was <3 pg/mm(2), close to the detection limit of SPR. The average nonspecific adsorptions from 10% plasma, 10% serum, 100% plasma, and 100% serum onto the polyacrylamide-grafted surfaces were 5, 6.5, 17, and 28 pg/mm(2), respectively, comparable (if not better) than the adsorption levels on poly(ethylene glycol) (PEG) and zwitterionic poly(sulfobetaine methacrylate) surfaces, the best antifouling materials known to date. The polyacrylamide-grafted surfaces were also shown strongly resistant to adhesion from bovine aortic endothelial cells and two bacterial species, Gram-positive Staphylococcus epidermidis ( S. epidermidis ) and Gram-negative Pseudomonas aeruginosa ( P. aeruginosa ). Strong hydrogen bond with water is considered the key attribute for the ultralow fouling properties of polyacrylamide. This is the first work to graft gold surfaces with polyacrylamide brushes via ATRP to achieve ultralow fouling surfaces, demonstrating that polyacrylamide is a promising alternative to traditional PEG-based antifouling materials.     

Immobilization of oligonucleotides on poly(ethylene glycol) brush-coated Si surfaces

High-density poly(ethylene glycol) (PEG) molecules are grafted onto Si surfaces in a brush-like configuration. We demonstrate that this surface is an excellent substrate for oligonucleotide immobilization. p-Maleimidophenyl isocyanate is used as a heterobifunctional cross-linker to tether thiol-modified oligonucleotides to terminal OH groups on the PEG brush. This approach gives excellent immobilization specificity and low background. The immobilized oligonucleotides show high sensitivity for the detection of complementary targets.     

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.     

Dual-functional biomimetic materials: nonfouling poly(carboxybetaine) with active functional groups for protein immobilization

We introduce a dual-functional biocompatible material based on zwitterionic poly(carboxybetaine methacrylate) (polyCBMA), which not only highly resists protein adsorption/cell adhesion, but also has abundant functional groups convenient for the immobilization of biological ligands, such as proteins. The dual-functional properties are unique to carboxybetaine moieties and are not found in other nonfouling moieties such as ethylene glycol, phosphobetaine, and sulfobetaine. The unique properties are demonstrated in this work by grafting a polyCBMA polymer onto a surface or by preparing a polyCBMA-based hydrogel. PolyCBMA brushes with a thickness of 10-15 nm were grafted on a gold surface using the surface-initiated atom transfer radical polymerization method. Protein adsorption was analyzed using a surface plasmon resonance sensor. The surface grafted with polyCBMA very largely prevented the nonspecific adsorption of three test proteins, that is, fibrinogen, lysozyme, and human chorionic gonadotropin (hCG). The immobilization of anti-hCG on the surface resulted in the specific binding of hCG while maintaining a high resistance to nonspecific protein adsorption. Transparent polyCBMA-based hydrogel disks were decorated with immobilized fibronectin. Aortic endothelial cells did not bind to the polyCBMA controls, but appeared to adhere well and spread on the fibronectin-modified surface. With their dual functionality and biomimetic nature, polyCBMA-based materials are very promising for their applications in medical diagnostics, biomaterials/tissue engineering, and drug delivery.     

Synthesis and bioactivities of poly(ethylene glycol)–chitosan hybrids

Poly(ethylene glycol)–chitosan hybrids of various molecular weights having different degree of substitution were synthesized, by reductive N-alkylation of chitosan with poly(ethylene glycol) aldehyde, to study their bioactivities. The influence of these chitosan derivatives on the reactive oxygen species generation from canine polymorphonuclear leukocyte cells was investigated in vitro by chemiluminescence response. Reactive oxygen species generation by the influence of poly(ethylene glycol)–chitosan hybrids was decreased with the increase of degree of substitution. The reduction of interaction of poly(ethylene glycol)–chitosan hybrids with polymorphonuclear leukocyte cells might be caused by the decrease of amino group in chitosan main chain and increase of the steric hindrance by poly(ethylene glycol) chain. The influence of the poly(ethylene glycol)–chitosan hybrids on complement component C3 activation was investigated by single radial immunodiffusion method. Influence on complement component C3 activation by poly(ethylene glycol)–chitosan hybrids was almost same as chitosan.     

Blood clearance and biodistribution of polymer brush-afforded silica particles prepared by surface-initiated living radical polymerization

The physiological properties of polymer brush-afforded silica particles prepared by surface-initiated living radical polymerization were investigated in terms of the circulation lifetime in the blood and distribution in tissues. Hydrophilic polymers consisting mainly of poly(poly(ethylene glycol) methyl ether methacrylate) were grafted onto silica particles by surface-initiated atom transfer radical polymerization that was mediated by a copper complex to produce hairy hybrid particles. A series of hybrid particles was synthesized by varying the diameter of the silica core and the chain length of the polymer brush to examine the relationship between their physicochemical and physiological properties. The hybrid particles were injected intravenously into mice to investigate systematically their blood clearance and body distribution. It was revealed that the structural features of the hybrid particles significantly affected their in vivo pharmacokinetics. Some hybrid particles exhibited an excellently prolonged circulation lifetime in the blood with a half life of ～20 h. When such hybrid particles were injected intravenously into a tumor-bearing mouse, they preferentially accumulated in tumor tissue. The tumor-targeted delivery was optically visualized using hybrid particles grafted with fluorescence-labeled polymer brushes.     

Depth profile of free volume in a mixture and copolymers of poly(N-vinyl-pyrrolidone) and poly(ethylene glycol) studied by positron annihilation spectroscopy

Effect of hydrogen bonding on the depth profile of the free-volume in a mixture (weight ratio of 65:35) of poly(N-vinyl-pyrrolidone) (PVP) and poly(ethylene glycol) (PEG) and the copolymers of vinyl pyrrolidone with poly(ethylene glycol) diacrylate (PVP-PEGDA) and monomethacrylate (PVP-PEGMMA) was studied using positron annihilation spectroscopy. Doppler broadening energy spectra of annihilation radiation and positron annihilation lifetime were measured as a function of positron incident energy (0-30 keV). Significant variations of the free-volume depth profile in terms of the S parameter, ortho-positronium lifetime, intensity, and lifetime distribution are observed as a result of the hydrogen-bonding replacement of covalent bonds. The polymer mixture with hydrogen bonding through two sides of PEG short chains has a larger free volume and a wider distribution than the comb-structured PVP-PEGMMA and the network structured PVP-PEGDA. A longer ortho-positronium lifetime is observed near the surface than in the bulk. This is interpreted in terms of surface effect, free volume, and hydrogen bonding for drug delivery applications of polymeric materials.     

Recyclable antibacterial magnetic nanoparticles grafted with quaternized poly(2-(dimethylamino)ethyl methacrylate) brushes

Highly efficient recyclable antibacterial magnetite nanoparticles consisting of a magnetic Fe(3)O(4) core with an antibacterial poly(quaternary ammonium) (PQA) coating were prepared in an efficient four-step process. The synthetic pathway included: (1) preparation of Fe(3)O(4) nanoparticles via coprecipitation of Fe(2+)/Fe(3+) in the presence of an alkaline solution; (2) attachment of an ATRP initiating functionality to the surface of the nanoparticles; (3) surface-initiated atom transfer radical polymerization (ATRP) of 2-(dimethylamino)ethyl methacrylate (DMAEMA); and (4) transformation of PDMAEMA brushes to PQA via quaternization with ethyl bromide. The success of the surface functionalization was confirmed by FT-IR, thermal gravimetric analysis (TGA), elemental analysis, and transmission electron microscopy (TEM). The PQA-modified magnetite nanoparticles were dispersed in water and exhibited a response to an external magnetic field, making the nanoparticles easy to remove from water after antibacterial tests. The PQA-modified magnetite nanoparticles retained 100% biocidal efficiency against E. coli (10(5) to 10(6)E. coli/mg nanoparticles) during eight exposure/collect/recycle procedures without washing with any solvents or water.