Hydrophilic Polymer Brushes Research Articles

Double water compatible molecularly imprinted polymers applied as solid-phase extraction sorbent for selective preconcentration and determination of triazines in complicated water samples

In the present work, double water compatible molecularly imprinted polymers (DWC-MIPs) with water compatible core and hydrophilic polymer brushes were prepared by reversible addition–fragmentation chain transfer precipitate polymerization (RAFTPP) and applied as solid-phase extraction (SPE) sorbent for selective preconcentration and specific recognition of triazines in water samples. The DWC-MIPs employed as SPE sorbent presented much higher extraction efficiency for four triazines in aqueous media based on the double water compatible property. The validated method was also successfully applied to tap water and river water sample analysis, and satisfactory recoveries were attained, such as 69.2–95.4% with the precision of 1.59–3.94% for four triazines at 100μgL−1. The DWC-MIPs-SPE proves to be a highly effective cleanup and enrichment method for simultaneous separation and sensitive determination of triazines in complicated water samples.

Surface imprinted core‐shell nanorod with ultrathin water‐compatible polymer brushes for specific recognition and adsorption of sulfamethazine in water medium

ABSTRACTA surface imprinted core‐shell nanorod with water‐compatible property was first prepared, using a two‐step “living” polymerization technique, with magnetic attapulgite (MATP) as core, and it was applicable in the enhanced selective removal of sulfamethazine residue from pure water environments. MATP was synthesized by an impregnation and pyrolysis method, and polymerable group was subsequently attached onto the surface. The imprinted polymer nanoshell (13 nm) with the “living” fragments was formed via a reverse atom transfer radical precipitation polymerization, avoiding the tedious graft of initiator and providing the easy‐accessible imprinted sites. Ultrathin hydrophilic polymer brushes (2.0 nm) were surface‐grafted to improve their water‐compatibility. The nanoadsorbent exhibited good thermal stability, magnetism, and hydrophilicity through characterization. The nanoadsorbent showed large adsorption capacity toward sulfamethazine from water, which increased with the increase of contact temperature. Langmuir isotherm fitted the equilibrium data better, and the kinetic data (within 45 min) were well‐analyzed by the pseudo‐second‐order kinetic model. Also, the specific adsorption property of the nanoadsorbent was greatly improved through the surface‐grafting, which exhibited excellent selectivity to sulfamethazine compared with other reference antibiotics. Efficient magnetic separation and good reuse of the nanoadsorbent provided the potential possibility for selective recognition and fast removal of antibiotic pollutions from water environments. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40854.

Well-Defined Hydrophilic Molecularly Imprinted Polymer Microspheres for Efficient Molecular Recognition in Real Biological Samples by Facile RAFT Coupling Chemistry

A facile and highly efficient new approach (namely RAFT coupling chemistry) to obtain well-defined hydrophilic molecularly imprinted polymer (MIP) microspheres with excellent specific recognition ability toward small organic analytes in the real, undiluted biological samples is described. It involves the first synthesis of "living" MIP microspheres with surface-bound vinyl and dithioester groups via RAFT precipitation polymerization (RAFTPP) and their subsequent grafting of hydrophilic polymer brushes by the simple coupling reaction of hydrophilic macro-RAFT agents (i.e., hydrophilic polymers with a dithioester end group) with vinyl groups on the "living" MIP particles in the presence of a free radical initiator. The successful grafting of hydrophilic polymer brushes onto the obtained MIP particles was confirmed by SEM, FT-IR, static contact angle and water dispersion studies, elemental analyses, and template binding experiments. Well-defined MIP particles with densely grafted hydrophilic polymer brushes (∼1.8 chains/nm(2)) of desired chemical structures and molecular weights were readily obtained, which showed significantly improved surface hydrophilicity and could thus function properly in real biological media. The origin of the high grafting densities of the polymer brushes was clarified and the general applicability of the strategy was demonstrated. In particular, the well-defined characteristics of the resulting hydrophilic MIP particles allowed the first systematic study on the effects of various structural parameters of the grafted hydrophilic polymer brushes on their water-compatibility, which is of great importance for rationally designing more advanced real biological sample-compatible MIPs.

Aqueous Lubrication with Poly(Ethylene Glycol) Brushes

Hydrophilic polymer brushes constitute a man-made approach to imitating nature’s lubrication mechanisms. A polymer that has been frequently used to explore such systems is poly(ethylene glycol) (PEG). While PEG may not be the ideal solution for water-lubricated tribosystems for a number of technical reasons, this well-characterized polymer has served as an extremely useful model for the development of other polymer-brush-based lubricant approaches. This review covers the history of PEG brushes used as aqueous lubricants, including the large body of work on electrostatically attached PEG brushes, and ends with a discussion of current and future research directions that build upon the knowledge gained over a decade and a half of PEG-brush research in tribology.

Fabrication of Contrast Agents for Magnetic Resonance Imaging from Polymer-Brush-Afforded Iron Oxide Magnetic Nanoparticles Prepared by Surface-Initiated Living Radical Polymerization

The aim of this study is to fabricate a contrast agent for magnetic resonance imaging (MRI) by using hybrid particles composed of a core of iron oxide magnetite (Fe3O4) nanoparticles and a shell of hydrophilic polymer brush synthesized by surface-initiated (SI) living radical polymerization. To achieve this, Fe3O4 nanoparticles were surface-modified with initiating groups for atom transfer radical polymerization (ATRP) via a ligand-exchange reaction in the presence of a triethoxysilane derivative having an ATRP initiation site. The ATRP-initiator-functionalized Fe3O4 nanoparticles were used for performing the SI-ATRP of methyl methacrylate to demonstrate the ability of the synthesized nanoparticles to produce well-defined polymer brushes on their surfaces. The polymerization proceeded in a living fashion so as to produce graft polymers with targeted molecular weights and narrow molecular weight distribution. The average graft density was estimated to be as high as 0.7 chains/nm(2), which indicates the formation of so-called concentrated polymer brushes on the Fe3O4 nanoparticles. Dynamic light scattering and transmission electron microscope observations of the hybrid nanoparticles revealed their uniformity and dispersibility in solvents to be excellent. A similar polymerization process was conducted using a hydrophilic monomer, poly(ethylene glycol) methyl ether methacrylate (PEGMA), to prepare Fe3O4 nanoparticles grafted with poly(PEGMA) brushes. The resultant hybrid nanoparticles showed excellent dispersibility in aqueous media including physiological conditions without causing any aggregations. The blood clearance and biodistribution of the hybrid particles were investigated by intravenously injecting particles labeled with a radio isotope, (125)I, into mice. It was found that some hybrid particles exhibited an excellently prolonged circulation lifetime in the blood with a half-life of about 24 h. When such hybrid particles were injected intravenously into a tumor-bearing mouse, they preferentially accumulated in the tumor tissues owing to the so-called enhanced permeability and retention effect. The tumor-targeted delivery was visualized by a T2-enhaced MRI measurement.

Surface hydrophilic modification of polyethersulfone membranes by surface-initiated ATRP with enhanced blood compatibility

Surface-initiated atom transfer radical polymerization (SI-ATRP) was used to tailor the functionality of polyethersulfone (PES) membranes. A two-step method including nitration reaction and amination reaction was used to synthesize aminated polyethersulfone (PES-NH2) for the preparation of PES/PES-NH2 membranes. Covalently tethered hydrophilic polymer brushes of poly(N-vinylpyrrolidone) (PVP) were prepared via SI-ATRP at low temperature in an aqueous solvent. Attenuated total reflection–Fourier transform infrared (ATR–FTIR), scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS), and water contact angle were used to characterize the modified membranes surfaces. The PVP-grafted PES membranes showed lower protein adsorption and suppressed platelet adhesion compared with the pristine PES membrane. Moreover, the activated partial thromboplastin time (APTT) for the PVP-grafted PES membranes was increased. These results indicated that the surface hydrophilic modification by grafting PVP brushes provided practical application for the PES membranes with good blood compatibility.

N-hydroxymethyl acrylamide polymer brush and its application in catalyzing coupling reaction

Poly (N-hydroxy methyl acrylamide)-grafted silicon, glass, and quartz surfaces were successfully prepared by surface-initiated atom transfer radical polymerization (SI-ATRP) with methyl alcohol/water mixtures as solvents and CuCl/2,2-dipyridyl as a catalyst. The modified surfaces were characterized by water contact angle, atomic force microscope (AFM), Fluorescence spectrophotometer, Low-angle X-ray diffraction (LAXRD), and X-ray Photoelectron Spectroscopy (XPS). The results showed that the homogeneous and well hydrophilic N-hydroxymethyl acrylamide polymer brushes (NHAM-brushes), which had high hydrophilic properties and the added advantage of providing 3-D coatings with higher binding capacities, were obtained successfully. Cyclopalladated arylimine functionalized polymer brushes were also obtained by reacting HAM-brushes with N,N′-Carbonyldiimidazole (CDI) and cyclopalladated arylimine. The catalyst functionalized PHAM-brushes had good catalytic activity in heterogeneous compared to homogeneous catalyst and exhibited much improved stability and recyclability over time in Suzuki cross-coupling reaction.

Localized surface plasmon-enhanced nanosensor platform using dual-responsive polymer nanocomposites

The fast and accurate identification of unknown liquids is important for the safety and security of human beings. Recently, sensors based on the localized surface plasmon resonance (LSPR) effect demonstrated an outstanding sensitivity in detecting chemical and biological species. In the present study, we suggest that a dual-responsive nanocomposite composed of two polymer brushes and two noble metal nanoparticles provides a significantly improved selectivity (improvement of a factor of 30 in figure-of-merit) for distinguishing diverse liquids compared to a single-responsive LSPR sensor. The dual-responsive LSPR sensor platform was realized by the synergic combinations of two hydrophobic and hydrophilic polymer brushes, which respond differently depending on the degree of interaction between the polymer brushes and the surrounding liquids. Moreover, the mixing ratio of two solvents can also be estimated with high accuracy using the dual-nanocomposite LSPR sensor, suggesting that this approach would be highly practical for in situ process monitoring systems that can instantly detect the change of solvent composition.

Narrowly Dispersed Hydrophilic Molecularly Imprinted Polymer Nanoparticles for Efficient Molecular Recognition in Real Aqueous Samples Including River Water, Milk, and Bovine Serum

In river water, milk, and bovine serum, molecularly imprinted polymer nanoparticles with hydrophilic polymer brushes showed excellent molecular recognition (see picture). Readily prepared by precipitation polymerization with a macromolecular chain-transfer agent, such nanoparticles are promising alternatives to antibodies for many applications owing to their superior dispersion and binding properties in biological matrices.

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.

Facile Preparation of Polymeric Dimers from Amphiphilic Patchy Particles

A straightforward strategy for assembling polymeric dimers from amphiphilic nanoparticles is reported. Amphiphilic polymeric nanoparticles with a mixed-shell of PEO/P2VN blocks and a flexible core of PAA blocks are fabricated by a non-covalent crosslinking method. Uniform polymeric dimers are efficiently and simply obtained via hydrophobic interactions under optimized conditions in selective solvent. The steric hindrance generated by reorganization of hydrophilic polymer brushes during the interparticle association is critical for morphological selectivity in the assembly. General applicability offers the possibility to organize functional NPs into superstructures with well-defined geometry and association numbers.

Effects of dynamics of water molecules at hydrophilic polymer brush surfaces on protein adsorption behavior

Effects of dynamics of water molecules at hydrophilic polymer brush surfaces on protein adsorption behavior

Field‐Induced Nanolithography for Patterning of Non‐Fouling Polymer Brush Surfaces

Electric-field induced nanolithography (FINL) on four hydrophilic polymer brushes is demonstrated. FINL is a nanoscale surface patterning method that depends on an electrochemical reaction at the tip–brush interface. FINL feature size depends on the applied bias, relative humidity, and exposure time. FINL patterning yields electrochemically modified brush surfaces that can be used to attach diagnostically relevant probes.

Improving the Stability in Aqueous Media of Polymer Brushes Grafted from Silicon Oxide Substrates by Surface‐Initiated Atom Transfer Radical Polymerization

AbstractHydrophilic polymer brushes grown via surface‐initiated ATRP from silicon oxide surfaces are susceptible to detachment via hydrolytic cleavage of the anchoring siloxane bond. This paper investigates the influence of the structure of the ATRP initiator on the stability of these brushes and seeks for strategies to further enhance their stability. It is found that increasing the hydrophobicity of the organosilane modified ATRP initiator reduces the susceptibility of the brushes toward cleavage. Robust, hydrophilic polymer brushes are prepared, which are obtained by introducing a short, hydrophobic PMMA or PEHMA block between the silicon oxide substrate and the hydrophilic polymer brush. magnified image

Adsorption of core-shell nanoparticles at liquid–liquid interfaces

The use of nanoparticles as building blocks for the self-assembly of functional materials has been rapidly increasing in recent years. In particular, two-dimensional materials can be effectively self-assembled at liquid interfaces thanks to particle localization and mobility at the interface in combination with tailoring of specific interactions. Many recent advances have been made in the understanding of the adsorption and assembly at liquid interfaces of small hydrophobic nanoparticles stabilized by short-chain rigid dispersants but the corresponding studies on core-shell nanoparticles sterically stabilized by extended hydrophilic polymer brushes are presently missing. Such particles offer significant advantages in terms of fabrication of functional, responsive and bio-compatible materials. We present here a combination of experimental and numerical data together with an intuitive and simple model aimed at elucidating the mechanisms governing the adsorption of iron oxide nanparticles (5–10 nm) stabilized by low molecular weight poly(ethylene glycol) (1.5–10 kDa). We show that the adsorption dynamics and the structure of the final assembly depend on the free energy of the particles at the interface and discuss the thermodynamics of the adsorption in terms of the polymer solubility in each phase.

Adhesion force of proteins against hydrophilic polymer brush surfaces

Protein adsorption occurs on the surface of biomaterials when they are exposed to physiological environments. The protein adsorption layer induces severe biological responses, including cellular reactions. Protein adsorption layers are formed mainly by two distinct processes: monolayer adsorption of proteins on the surface and a subsequent additional adsorption on the first layer to form a multilayer. Therefore, evaluating the first protein adsorption is important to understand the biological responses on the surface of materials. In this study, we applied the atomic force microscopic (AFM) technique to directly measure the adhesion force of proteins against the surface (i.e., the interaction between proteins and surface). We also prepared hydrophilic polymer brush surfaces with well-known high repellency against protein adsorption through surface-initiated atom transfer radical polymerization. Polymer brush layers have a well-defined surface structure; therefore, it could be a good model for clarifying the relationship between the surface structure and protein adsorption behavior. The influence of chemical structure of monomer unit and thickness of polymer brush layers on the adhesion force of proteins was discussed here, while that of graft density was not discussed. The adhesion force of bovine serum albumin (BSA) immobilized on an AFM cantilever against the thin polymer brush surfaces differed from the chemical structures of the monomer unit. The adhesion force of BSA decreased with increasing thickness of the polymer brush layer, and there was little difference in the adhesion force of BSA against the thick polymer brush surfaces regardless of the chemical structure of the monomer unit. The results demonstrate that the thickness of the polymer brush layer would be an important parameter that reduced the interaction between proteins and surfaces compared with the chemical structure of the monomer unit.

Preparation of peptide- and protein-based molecular assemblies and their utilizations as nanocarriers for tumor imaging

Three types of nanocarriers from our group for imaging probes are reviewed here. Novel nanocarriers of “peptosome” and “lactosome” were prepared from amphiphilic polymers uniquely having a helical segment as a hydrophobic block. Apoferritin was chemically modified on the surface, and used for nanocontainer of a novel Gd-chelator. Lactosome was intensively studied and labeled with indocyanine, 18F, and 131I for tumor imaging by NIRF, PET, and SPECT, respectively. Those labeled lactosomes are shown to be effective for tumor imaging on the basis of the EPR effect and the stealth property in vivo. The superiority of lactosome over other commercially available imaging agents is experimentally confirmed, which is explained by the dense and thick hydrophilic polymer brush formed on the surface and the helix bundles at the hydrophobic core. Our final goal is to develop the next-generation lactosome, which is the nanocarrier which is usable for a diagnostic agent and a therapeutic agent showing the same in vivo disposition even upon frequent administration.

Surface-initiated atom-transfer radical polymerization from polyethersulfone membranes and their use in antifouling

AbstractA simple one-step method for the chloromethylation of polyethersulfone (PES) under mild conditions provided surface benzyl chloride groups as the active initiators for the surface-initiated atom-transfer radical polymerization (ATRP) to tailor the functionality of the PES membrane. Functional hydrophilic polymer brushes of poly(ethylene glycol)monomethacrylate (PEGMA) and sodium 4- styrenesulfonate (NaStS), as well as their block copolymer brushes, were prepared via surface initiated ATRP from the chloromethylated PES surfaces. X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) were used to characterize the surface-modified membranes. The PEGMA-grafted PES membranes showed great protein resistance to protein adsorption compared to the pristine PES surface.

Liposomes Tethered to Omega-Functional PEG Brushes and Induced Formation of PEG Brush Supported Planar Lipid Bilayers

Self-assembly of planar supported lipid bilayers on top of hydrophilic polymer brushes is a desirable alternative to solid supported lipid bilayers and covalently tethered lipid bilayers for applications like sensing on transmembrane proteins which require a large aqueous volume between membrane and substrate. We present a simple dip-and-rinse method to produce poly(ethylene glycol) (PEG) brushes with sparse positively charged hydrophobic tethers, using poly(l-lysine)-graft-poly(ethylene glycol)-quaternary ammonium compound copolymers. The interaction of such polymer coatings with liposomes of different compositions and the conditions for formation of planar lipid bilayers of extraordinarily high fluidity on top of the >10 nm thick reservoir by liposome self-assembly and sequentially triggered rupture are investigated.

Barrier Capacity of Hydrophilic Polymer Brushes To Prevent Hydrophobic Interactions: Effect of Graft Density and Hydrophilicity

The performance of biomaterials in contact with biological systems can be greatly affected by hydrophobic interactions at the interface between the biomaterial surface and surrounding biomolecules. Polymer brushes can function as a protective layer, preventing such interfacial hydrophobic interactions. In this paper, a systematic study of the barrier properties of a hydrophilic polymer brush is made by investigating the influence of graft density and its chemical nature (hydrophilicity/hydrophobicity) on hydrophobic interactions with the surface. To achieve this, a series of novel thermoresponsive poly-N-[(2,2-dimethyl-1,3-dioxolane)methyl]acrylamide (PDMDOMA) polymer brushes were grown from silicon wafers via surface-initiated atom transfer radical polymerization. Without changing graft density or degree of polymerization, the hydrophilicity of the PDMDOMA brushes was manipulated by partial or complete hydrolysis of the pendent dioxolane moieties. A lower critical solution temperature (LCST) was observed at 22−24 °C, below which the PDMDOMA brush was found to be in a hydrated state (amphiphilic), while at temperatures above the LCST, the PDMDOMA brush formed a collapsed, more hydrophobic structure. A physical method was developed to analyze the ability of these brushes to act as a barrier against hydrophobic interactions based on AFM force−distance measurements. The adhesive forces between the Si3N4 tip and the silicon wafer surface upon (a) modification with ATRP initiator, (b) grafting of PDMDOMA brushes, and (c) partial and complete hydrolysis of PDMDOMA were investigated. Hydrophobic interactions decreased after each modification, while graft density and the degree of hydrolysis increased the barrier function of the surface layer. In particular, when graft density was above 0.22 chains/nm2, the barrier capacity completely counteracted the hydrophobic interactions, as evidenced from the disappearance of the adhesive force in AFM measurements. Further studies revealed that the barrier property as assessed by AFM correlated well with the wettability of the surfaces.