Surface-grafted Polymer Brushes Research Articles

Antifouling hydrogel film based on a sandwich array for salivary glucose monitoring.

A glucose biosensor prepared using interpenetrating polymer network (IPN) hydrogel as a sensing material is the subject of growing interest due to its fast response and high sensitivity. However, the IPN hydrogel circumvents the traditional antifouling strategy, which often requires thick antifouling coating that can result in poor glucose sensitivity owing to its energetic physical barrier (greater than 43 nm); thus a complex, time-consuming and high-cost salivary preprocessing is needed to remove protein contaminants before salivary glucose detection using the IPN hydrogel. This limits its practical application in trace salivary glucose-level monitoring. Herein, a new hydrogel film based on a sandwich array (HFSA) with a weak physical barrier, which exhibits superior antifouling and sensitivity in salivary glucose detection is reported. HFSA relies on the formation of the sandwich structure containing substrate-grafted, surface-grafted zwitterionic polymer brushes (pSBMA) and phenylboronic acid (PBA)-functionalized hydrogel. The synergistic effect originating from pSBMA brushes on the surface of HFSA and inside the HFSA matrix provides a suitable physical barrier (∼28 nm) and a robust hydration layer for HFSA, which can enhance its sensitivity and antifouling. The results show that HFSA reduce the adsorption of nonspecific protein in 10% saliva by nearly 90% and enhanced the glucose sensitivity by 130%, compared to the IPN hydrogel film. These results demonstrate that HFSA exhibits significant potential as an antifouling and sensitive glucose probe for QCM sensors in non-invasive salivary glucose monitoring.

Interfacial Assembly Inspired by Marine Mussels and Antifouling Effects of Polypeptoids: A Neutron Reflection Study.

Polypeptoid-coated surfaces and many surface-grafted hydrophilic polymer brushes have been proven efficient in antifouling-the prevention of nonspecific biomolecular adsorption and cell attachment. Protein adsorption, in particular, is known to mediate subsequent cell-surface interactions. However, the detailed antifouling mechanism of polypeptoid and other polymer brush coatings at the molecular level is not well understood. Moreover, most adsorption studies focus only on measuring a single adsorbed mass value, and few techniques are capable of characterizing the hydrated in situ layer structure of either the antifouling coating or adsorbed proteins. In this study, interfacial assembly of polypeptoid brushes with different chain lengths has been investigated in situ using neutron reflection (NR). Consistent with past simulation results, NR revealed a common two-step structure for grafted polypeptoids consisting of a dense inner region that included a mussel adhesive-inspired oligopeptide for grafting polypeptoid chains and a highly hydrated upper region with very low polymer density (molecular brush). Protein adsorption was studied with human serum albumin (HSA) and fibrinogen (FIB), two common serum proteins of different sizes but similar isoelectric points (IEPs). In contrast to controls, we observed higher resistance by grafted polypeptoid against adsorption of the larger FIB, especially for longer chain lengths. Changing the pH to close to the IEPs of the proteins, which generally promotes adsorption, also did not significantly affect the antifouling effect against FIB, which was corroborated by atomic force microscopy imaging. Moreover, NR enabled characterization of the in situ hydrated layer structures of the polypeptoids together with proteins adsorbed under selected conditions. While adsorption on bare SiO2 controls resulted in surface-induced protein denaturation, this was not observed on polypeptoids. Our current results therefore highlight the detailed in situ view that NR may provide for characterizing protein adsorption on polymer brushes as well as the excellent antifouling behavior of polypeptoids.

Modulation of Living Cell Behavior with Ultra-Low Fouling Polymer Brush Interfaces.

Ultra-low fouling and functionalizable coatings represent emerging surface platforms for various analytical and biomedical applications such as those involving examination of cellular interactions in their native environments. Ultra-low fouling surface platforms as advanced interfaces enabling modulation of behavior of living cells via tuning surface physicochemical properties are presented and studied. The state-of-art ultra-low fouling surface-grafted polymer brushes of zwitterionic poly(carboxybetaine acrylamide), nonionic poly(N-(2-hydroxypropyl)methacrylamide), and random copolymers of carboxybetaine methacrylamide (CBMAA) and HPMAA [p(CBMAA-co-HPMAA)] with tunable molar contents of CBMAA and HPMAA are employed. Using a model Huh7 cell line, a systematic study of surface wettability, swelling, and charge effects on the cell growth, shape, and cytoskeleton distribution is performed. This study reveals that ultra-low fouling interfaces with a high content of zwitterionic moieties (>65 mol%) modulate cell behavior in a distinctly different way compared to coatings with a high content of nonionic HPMAA. These differences are attributed mostly to the surface hydration capabilities. The results demonstrate a high potential of carboxybetaine-rich ultra-low fouling surfaces with high hydration capabilities and minimum background signal interferences to create next-generation bioresponsive interfaces for advanced studies of living objects.

Towards mimicking biological function with responsive surface-grafted polymer brushes

Responsive or smart polymer brushes undergo pronounced changes in their surface properties and conformation in response to changes in their environment, including variation in temperature, solution pH or ionic strength, and presence of light. Because the brush stimulus response resembles the ability of natural systems to react to environmental changes, responsive polymer brushes have been incorporated into a number of soft biomimetic structures. Nonetheless, the ability to design soft matter systems that recreate the complexity of life remains limited. Here, we survey the use of responsive surface-grafted polymer brushes to mimic biological function. We summarize various ways in which surface-grafted brushes respond to stimuli. Next, we highlight examples of biomimetic engineering that mimic specific biological structures, including molecular motors, ion channels, leukocytes, and leaves. Finally, we discuss recent studies that design brushes to generate lifelike behavior and interrogate their response under the non-equilibrium, spatiotemporally heterogeneous conditions in living systems. Specifically, we focus on hysteresis in the brush response, as one example of nonlinear response; slow diffusion, used by biological systems to maintain chemical gradients; self-oscillation, as an example of auto-amplification of stimuli; and patterned responsiveness, as an example of compartmentalization. This focus emphasizes the emerging need to rationally design the response of brushes for use as soft components in dynamic, life-inspired systems.

Controlled hierarchical architecture in poly [oligo (ethylene glycol) methacrylate-b-glycidyl methacrylate] brushes for enhanced label-free biosensing

Surface-grafted polymer brushes have been long reported as a desired matrix for biosensing applications, owing to enhanced immobilization capacity and anti-fouling properties. However, simultaneous optimizing binding signal and minimizing non-specific adsorption using polymer matrix is still a challenge, due to the lack of systematic structural and composition optimization at molecular level. In this research, a series of block copolymer brushes with controlled hierarchical architectures, poly [oligo (ethylene glycol) methacrylate-b-glycidyl methacrylate] (POEMGA-b-PGMA) were prepared by two-stage surface-initiated polymerization. Surface plasmon resonance imaging (SPRi), as a real-time and label-free biosensing technology, was used as means to evaluate their detecting performances of bio-interactions. In contrast to one-layer poly (glycidyl methacrylate) (PGMA), 4.7-fold enhancement of signal-to-background (S/B) was achieved in bi-layer POEGMA-b-PGMA surface, by using rabbit IgG (R-IgG, in 10% serum) and a microarray of goat-anti-rabbit IgG (G-R-IgG) as the system of study. Interestingly, the binding signals and anti-fouling performances of the polymer brushes could be enhanced simultaneously by increasing the length of the monomer in the primary layer. Theoretically, it mainly owed to the formation of a densely packing protective primary layer against non-specific physical adsorption and a spatially optimized secondary layer of minimized steric hindrance that allowed optimum binding of analytes.

Electrochemical triggering and control of atom transfer radical polymerization

Summary Electrochemically mediated atom transfer radical polymerization (eATRP) is an advanced method to produce well-defined polymers. In eATRP, an electric current is used to trigger the polymerization, (re)generate the active catalyst, and strictly control the process. This review describes the fundamentals of eATRP and its applications to prepare homopolymers, block copolymers, star polymers, and surface-grafted polymer brushes.

Photoactive Surface‐Grafted Polymer Brushes with Phthalocyanine Bridging Groups as an Advanced Architecture for Light‐Harvesting

Surface-grafted polymer brushes of novel ladder-like architecture were proposed for inducing ordering of chromophores embedded therein. The brushes with acetylene side groups were obtained by surface-initiated photoiniferter-mediated polymerization. The acetylene moieties reacted then through a "click" process with an axially azide-bifunctionalized silicon phthalocyanine bridging the neighboring chains that inherently adopt extended conformations in dense brushes. FTIR, quartz crystal microbalance, and atomic force microscopy were used to study formation and structure of the photoactive brushes varying in grafting densities. Importantly, photophysical properties of the chromophores were virtually unaffected upon embedding them into the brushes, as evidenced by UV/Vis absorption and emission spectroscopy. Owing to the unique ordering of the chromophores, the proposed method may open new opportunities for the fabrication of light-harvesting systems suitable for photovoltaic or sensing applications.

Bio-Inspired Renewable Surface-Initiated Polymerization from Permanently Embedded Initiators.

Herein, we describe a simple and robust approach to repeatedly modify surfaces with polymer brushes through surface-initiated atomic transfer radical polymerization (SI-ATRP), based on an initiator-embedded polystyrene sheet that does not rely on specific surface chemistries for initiator immobilization. The surface-grafted polymer brushes can be wiped away to expose fresh underlying initiator that re-initiates polymerization. This strategy provides a facile route for modification of molded or embossed surfaces, with possible applications in the preparation of fluidic devices and polymer-embedded circuits.

Total removal of intact blood plasma proteins deposited on surface-grafted polymer brushes

Buffers/solutions suitable for total desorption of adsorbed proteins on low fouling polymer brushes are presented, enabling analysis not only by MS, but also a plethora of other state-of-the-art proteomics methods.

Tribology of surface-grafted polymer brushes

The tribological properties, lubrication mechanism, characterization methods and potential applications of surface-attached polymer-based boundary lubricants are reviewed.

Water Structure Change-Induced Expansion and Collapse of Zwitterionic Polymers Surface-Grafted onto Carbon Black

We demonstrate the expansion and collapse of surface-grafted zwitterionic polymer brushes in water caused by the addition of urea. We hypothesize that at low urea concentrations, this is an effect of an ion–dipole interaction between urea and the polymer, and at high urea concentrations, an effect of a change in water structure causing change in solvation of the brushes and hence a change in the dipole–dipole interaction, and that it is analogous to the effects of urea on protein stability.

Meso‐ and Microscopic Motions in Photoresponsive Liquid Crystalline Polymer Films

Photoresponsive azobenzene-containing systems ranging from molecular to macroscopic material levels have greatly been increasing their significance in materials chemistry. This review focuses on the studies on light induced or triggered motions in azobenzene liquid crystalline (LC) polymer films at mesoscopic and microscopic levels. Due to the cooperative nature of liquid crystalline materials, highly efficient photoalignment and photo-triggered migrating motions are realized in mostly repeated manners. Here, recent advances in surface-grafted LC polymer brushes, LC block copolymer films, and LC polymer films that exhibit mass migrations are overviewed. Such newly emerged photoresponsive systems are expected to provide new possibilities and applications in polymer thin film technologies.

Modifying graphite oxide with grafted methyl acrylate brushes for the attachment of magnetite nanoparticles

Surface-grafted polymer brushes of methyl acrylate of graphite oxide (GO) have been constructed to anchor poly(amidoamine) 2.0G (PAMAM 2.0G) dendrites for the attachment of magnetite nanoparticles. Monomers of methyl acrylate were copolymerized on the GO sheets by atom transfer radical polymerization. Then the PAMAM 2.0G was attached via covalent bond at the end of the grafted chains. Thus the inexpensive Fe(III) of ferric trichloride could coordinate with the remaining amino groups of PAMAM 2.0G and were reduced by the added sodium borohydrite at appropriate pH value to obtain nano magnetite-decorated GO hybrid materials. The hybrids exhibited a powerful catalysis on the degradation of aqueous solutions of hydroquinone.

An experimental-theoretical analysis of protein adsorption on peptidomimetic polymer brushes.

Surface-grafted water-soluble polymer brushes are being intensely investigated for preventing protein adsorption to improve biomedical device function, prevent marine fouling, and enable applications in biosensing and tissue engineering. In this contribution, we present an experimental-theoretical analysis of a peptidomimetic polymer brush system with regard to the critical brush density required for preventing protein adsorption at varying chain lengths. A mussel adhesive-inspired DOPA-Lys (DOPA = 3,4-dihydroxy-phenylalanine; Lys = lysine) pentapeptide surface grafting motif enabled aqueous deposition of our peptidomimetic polypeptoid brushes over a wide range of chain densities. Critical densities of 0.88 nm(-2) for a relatively short polypeptoid 10-mer to 0.42 nm(-2) for a 50-mer were identified from measurements of protein adsorption. The experiments were also compared with the protein adsorption isotherms predicted by a molecular theory. Excellent agreements in terms of both the polymer brush structure and the critical chain density were obtained. Furthermore, atomic force microscopy (AFM) imaging is shown to be useful in verifying the critical brush density for preventing protein adsorption. The present coanalysis of experimental and theoretical results demonstrates the significance of characterizing the critical brush density in evaluating the performance of an antifouling polymer brush system. The high fidelity of the agreement between the experiments and molecular theory also indicate that the theoretical approach presented can aid in the practical design of antifouling polymer brush systems.

Binary Polymer Brushes on Silica@Polymer Hybrid Nanospheres and Hollow Polymer Nanospheres by Combined Alkyne−Azide and Thiol−Ene Surface Click Reactions

Silica@polymer core−shell hybrid nanospheres and air@polymer hollow nanospheres with surface-grafted binary polymer brushes were synthesized by a combination of sol−gel reaction, distillation−precipitation polymerization, and dual “click” reactions (alkyne−azide and thiol−ene “click” chemistry). Initially, 179 nm silica@poly(methacrylic acid-co-propargyl methacrylate-co-divinylbenzene) (SiO2@P(MAA-co-PMA-co-DVB)) core−shell hybrid nanospheres were prepared by distillation−precipitation copolymerization of MAA, PMA, and DVB in acetonitrile, using the 151 nm silica nanospheres from sol−gel reaction as templates. The propargyl groups from PMA and residual C═C double bonds from DVB on the SiO2@P(MAA-co-PMA-co-DVB) core−shell hybrid nanospheres provided dual clickable functionalities for the respective alkyne−azide and thiol−ene reactions with the azido-terminated hydrophobic polystyrene (PS-N3, Mn = 2550 g/mol) and thiol-terminated hydrophilic poly(ethylene glycol) (PEG-SH, Mn = 5000 g/mol). Finally, hairy ho...

Fusion and alloying of (bi)metallic nanocrystals onto TiO2 nanowires in the presence of surface grafted polymer brushes

In present paper, the fusion of metal nanocrystals on TiO2 nanowires is studied and utilized to synthesize bimetallic nanoparticles on nanowires. Cationic polydimethyl aminoethyl methacrylate (PDMAEMA) brushes are grafted onto TiO2 nanowires, and palladium nanocrystals are produced by polymer brush-bound PdCl(4)(2-) and subsequent in situ reduction with NaBH4 in high density and low polydispersity. It is found that Pd nanocrystals of 2-3 nm starts to fuse even at 100 °C, but are apparently obstructed by the polymer brush matrix. Nanocrystal fusion speeds up instantly after polymer decomposition degradation at temperatures above 300 °C. By taking advantage of the polymer brush technique successive, templated uploading of different nanoparticles and fusion, Pd-Au bimetallic nanoparticles or alloys are formed on TiO2 nanowires. The results provide a novel method towards TiO2 nanowire supported (bi)metallic nanoparticles and have hinted at practical uses for elucidating the catalytic behavior of the composites.

Reversibly cross-linked surface-grafted polymer brushes.

Reversibly cross-linked surface-grafted polymer brushes.