Copolymer Brushes Research Articles

Thermoresponsive bio-affinity interfaces for temperature-modulated selective capture and release of targeted exosomes.

The existing methods for exosome isolation, such as ultracentrifugation, size exclusion, and affinity separation, suffer from some limitations. Herein, we aimed to develop temperature-modulated exosome-capturing materials using thermoresponsive polymers and peptides with affinity for exosomes. Poly(2-hydroxyethyl methacrylate-co-propargyl acrylate)-b-poly(N-isopropylacrylamide) (P(HEMA-co-PgA)-b-PNIPAAm) was grafted on silica beads via a two-step process of activator regenerated by electron transfer atom transfer radical polymerization. Peptides with affinity for exosomes were conjugated to the propargyl group of the bottom P(HEMA-co-PgA) segment of the copolymer via a click reaction. The prepared copolymer-grafted beads were characterized by elemental analysis, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, gel permeation chromatography, and the turbidity of the polymer solution. Results indicated that the copolymer and peptide were successfully modified on the silica beads. Exosomes from SK-BR-3​cells, a human breast cancer cell line, were selectively captured on the prepared beads at 37​°C, as the upper PNIPAAm segment shrank and the affinity between the peptide and exosome was enhanced. Upon lowering the temperature to 4​°C, the captured exosomes were released from the copolymer brush because of the extension of the PNIPAAm segment that reduced the affinity between peptides and exosomes. These findings demonstrated that the prepared copolymer brush-grafted silica beads can capture and release targeted exosomes via temperature modulation. Taken together, the developed copolymer brush-grafted silica beads would be useful for the separation of exosomes using simple procedures such as temperature modulation.

Preparation and chromatographic evaluation of a mixed polymer brush-silica stationary phase with temperature-sensitive property.

In this study, a developed chromatographic stationary phase combines the high selectivity of mixed-mode retention with a temperature-responsive property to boost separation efficiency. Copolymer brushes were grafted onto silica gels through surface initiated-atom transfer radical polymerization by polymerizing two types of monomer, temperature-responsive vinylcaprolactam (VCl) and quinine (Qun) containing benzopyridine, a tertiary ammonium positive center, and hydroxyl groups. The obtained silica@poly(Qun-co-VCl) stationary phases were packed as a chromatographic column, and the retention behavior of hydrophobic polycyclic aromatics, highly polar nucleosides, charged organic acids and β-agonists was studied for this column under different separation modes. The ability to separate different types of analyte shows that the silica@poly(Qun-co-VCl) column provides multiple hydrophobic, hydrophilic and electrostatic interactions toward analytes, achieving the separation of various compounds in one column. In addition, temperature-dependent resolution of polycyclic aromatics, nucleosides, organic acids and β-agonists was investigated using modulation of the column temperature, and the column exhibited adjustable separation selectivity by simply changing the column temperature. These results demonstrate that the grafting of copolymer brushes on a silica surface, consisting of temperature-responsive poly-VCl and multifunctional groups of poly-Qun, is useful as a mixed-mode chromatographic stationary phase for thermally-modulated multiple interactions. Additionally, this column was also used for the quantitative detection of uridine and inosine from cordyceps.

Dual functionalized brush copolymers as versatile antifouling coatings.

Polymer coatings containing both fouling-resistant and fouling-release components have been reported to show synergistic antifouling properties. However, it remains unclear how the polymer composition influences the antifouling performance, particularly regarding foulants of different sizes and biological natures. Herein, we prepare dual functionalized brush copolymers containing fouling-resistant poly(ethylene glycol) (PEG) and fouling-release polydimethylsiloxane (PDMS) and examine their antifouling performances against different biofoulants. We utilize poly(pentafluorophenyl acrylate) (PPFPA) as a reactive precursor polymer and graft amine-functionalized PEG and PDMS side chains to create PPFPA-g-PEG-g-PDMS brush copolymers of systematically varying compositions. The copolymer films spin-coated on silicon wafers exhibit surface heterogeneity that can be correlated well with the bulk composition of the copolymer. When the copolymer-coated surfaces are examined against protein (human serum albumin and bovine serum albumin) adsorption and cell (lung cancer cells and microalgae) adhesion, they are found to perform better than the homopolymers. The enhanced antifouling properties are attributed to the copolymers having a PEG-rich top layer and a PEG/PDMS mixed bottom layer that work synergistically to resist biofoulant attachment. Furthermore, the composition of the best-performing copolymer is different for different foulants, with PPFPA-g-PEG39-g-PDMS46 exhibiting the best antifouling properties against proteins and PPFPA-g-PEG54-g-PDMS30 exhibiting the best antifouling properties against cells. We explain this difference by considering the changes in the length scale of the surface heterogeneity in relation to the foulant sizes.

Synthesis of superhydrophilic Gradient-Like Copolymers: Kinetics of the RAFT copolymerization of methacryloyloxyethyl phosphorylcholine with PEO methacrylate

Brush copolymers containing PEO side chains and zwitterionic units of 2-methacryloyloxyethyl phosphorylcholine (MPC) were synthesized by RAFT copolymerization with an especial attention to compositional microstructure of the copolymers. Two complementary methods – size exclusion chromatography (SEC) and 1H NMR spectroscopy – were used to study the kinetics of the RAFT copolymerization of MPC (M1) and the macromonomer poly(ethylene oxide) methyl ether methacrylate with medium-length PEO chain (PEOMEMA, M2) in methanol–water mixed solutions. Analysis of the reaction mixtures by the two methods allowed concluding that in mixed solutions of methanol and water, every molecule of MPC carries about 15 molecules of water as an integral part of the monomer. Monomer reactivity ratios calculated by the method of Meyer and Lowry were r1 = 2.48 and r2 = 0.40. The dependences of the copolymer composition on monomer conversion determined experimentally and calculated by the terminal model of free-radical copolymerization differed significantly, demonstrating the specific impact of the mechanism of RAFT on the distribution of copolymer compositions. The copolymers p(MPC-co-PEOMEMA) possessed strongly expressed gradient microstructure, and were characterized by moderately low dispersity (Ð < 1.3). The copolymers showed evident superhydrophilicity with a water contact angle of about 7° and, like pMPC, exhibited cononsolvency in water–ethanol mixed solutions.

Shape Matters: Highly Selective Antimicrobial Bottle Brush Copolymers via a One-Pot RAFT Polymerization Approach.

The one-pot synthesis of antimicrobial bottle brush copolymers is presented. Reversible addition-fragmentation chain-transfer (RAFT) polymerization is used for the production of the polymeric backbone, as well as for the grafts, which were installed using a grafting-from approach. A combination of N-isopropyl acrylamide and a Boc-protected primary amine-containing acrylamide was used in different compositions. After deprotection, polymers featuring different charge densities were obtained in both linear and bottle brush topologies. Antimicrobial activity was tested against three clinically relevant bacterial strains, and growth inhibition was significantly increased for bottle brush copolymers. Blood compatibility investigations revealed strong hemagglutination for linear copolymers and pronounced hemolysis for bottle brush copolymers. However, one bottle brush copolymer with a 50% charge density revealed strong antibacterial activity and negligible in vitro blood toxicity (regarding hemolysis and hemagglutination tests) resulting in selectivity values as high as 320. Membrane models were used to probe the mechanism of shown polymers that was found to be based on membrane disruption. The trends from bioassays are accurately reflected in model systems indicating that differences in lipid composition might be responsible for selectivity. However, bottle brush copolymers were found to possess increased cytotoxicity against human embryonic kidney (HEK) cells compared with linear analogues. The introduced synthetic platform enables screening of further, previously inaccessible parameters associated with the bottle brush topology, paving the way to further improve their activity profiles.

Smart Nano-switch with Flexible Modulation of Ion Transport Using Multiple Environmental Stimuli.

In this work, we demonstrate a unique nano-switch with triple environmental stimuli based on the action of functional copolymer brushes in a single conical nanochannel. This nanodevice flexibly and efficiently modulates ion transport properties under the influence of three environmental stimuli: light, pH and temperature. The triple factors can not only play a regulatory role independently, but their synergistic cooperation could fully activate the ionic gate and reversibly control the gating direction. In addition, the nano-switch can switch transport properties on demand in the face of complex combinations of different factors. This work promotes the development of intelligent bionic ion channels, which holds promise for biosensing, energy conversion and biomedical research.

A thermoresponsive cationic block copolymer brush-grafted silica bead interface for temperature-modulated separation of adipose-derived stem cells

Adipose-derived mesenchymal stem cells (ADSCs) have beneficial effects in cell transplantation therapy; these cells are collected from adipose tissue using low-invasive methods. However, to prepare ADSCs for cell therapy, a cell separation method that neither involves modification of the cell surface nor causes loss of cell activity is needed. Here, we aimed to develop ADSC separation columns using thermoresponsive cationic block copolymer brush-grafted beads as packing materials. The block copolymer brush was formed by a bottom cationic segment, poly(N,N-dimethylaminopropylacrylamide) (PDMAPAAm), and an upper thermoresponsive segment, poly(N-isopropylacrylamide) (PNIPAAm), and was grafted in two atom transfer radical polymerization reactions. The copolymer brush-grafted silica beads were packed into a column. An ADSC suspension was introduced into the columns at 37 °C and adsorbed on the copolymer brush-modified beads through electrostatic and hydrophobic interactions with the PDMAPAAm and PNIPAAm segments, respectively. The adsorbed ADSCs eluted from the column by lowering the temperature to 4 °C. In contrast, most Jurkat and vascular endothelial cells eluted at 37 °C, because of the relatively weaker electrostatic interactions with the block copolymer brush compared to ADSCs. Using the prepared column, a mixture of ADSCs and Jurkat cells was separated by changing the column temperature. The recovered ADSCs exhibited cell activity. The developed cell separation column may be useful for isolating ADSCs without cell surface modification, while maintaining cell activity.

Bioactive PCL-Peptide and PLA-Peptide Brush Copolymers for Bone Tissue Engineering.

We report the modular synthesis of bioactive brush-type polycaprolactone-peptide and polylactide-peptide copolymers for applications in bone tissue engineering. The brush copolymers containing pendant side chains of polycaprolactone (PCL) or polylactide (PLA) and PEGylated peptides, including linear Arg-Gly-Asp and collagen-like peptide (Gly-Pro-Hyp)3, were synthesized by ring-opening metathesis polymerization with high conversions and low dispersities (<1.5). These PCL-peptide and PLA-peptide copolymers exhibited good thermal stability for material processing using melt-extrusion-based methods. The copolymers were blended with commercial PCL or PLA, extruded into filaments, and 3D printed using fused filament fabrication methods. These bioactive PCL and PLA materials promoted osteogenic differentiation in vitro and showed good biocompatibility in in vivo murine model study. The promising results presented herein will serve as a useful guide for the design and functionalization of PCL or PLA materials for use in bone tissue engineering.

Functionalized poly(oligo(lactic acid) methacrylate)-block-poly(oligo(ethylene glycol) methacrylate) block copolymers: A synthetically tunable analogue to PLA-PEG for fabricating drug-loaded nanoparticles

PL(G)A-PEG block polymers have been widely used in a variety of drug delivery applications but are inherently limited in terms of their capacity for functionalization and thus customization to specific delivery tasks. Herein, we report synthetically tunable and functionalizable brush co-polymer analogues of conventional PL(G)A-PEG polymers fabricated via atom transfer radical polymerization (ATRP) of methacrylate-based co-monomers with oligo(lactic acid) side chains in the hydrophobic block and oligo(ethylene glycol) side chains in the hydrophilic block. Block co-polymers prepared by varying the molecular weights of each block, the functionality of either block (via functional monomer copolymerization), as well as the number of lactic acid repeat units in the hydrophobic block were subsequently used to fabricate nanoparticles with sizes of 100–500 nm and tunable degradation rates via flash nanoprecipitation. The resulting nanoparticles exhibited high colloidal stability (consistent with the dense brush-like POEGMA interface), favorable in vitro cytocompatibility, and the capacity for effective drug loading (>96% encapsulation efficiency for paclitaxel and 41% even for the hydrophilic therapeutic doxorubicin hydrochloride). Furthermore, functionalization of the hydrophobic POLAMA block with methacrylic acid residues enabled controlled dissolution of the nanoparticle over time, offering potential to tune drug release via an alternative mechanism not readily accessible with conventional PLA-PEG-based block copolymers. Combining these properties with the flexible chemical compositions and the generally recognized as safe degradation properties of the brush polymer analogues, POLAMA-b-POEGMA polymers represent a highly versatile platform for nanoparticle-based drug delivery applications.

Topologically Induced Heterogeneity in Gradient Copolymer Brush Particle Materials

Topologically Induced Heterogeneity in Gradient Copolymer Brush Particle Materials

Quaternized Sodium Alginate-g-Ethyl-Oxazoline Copolymer Brushes and Their Supramolecular Networks via Hydrogen Bonding.

Novel copolymer brushes of quaternized sodium alginate-g-(2-ethyl-2-oxazoline)n are achieved by the grafting reaction of 2-ethyl-2-oxazoline (EOX) from benzyl bromide groups in quaternized sodium alginate (QSA). The average number of (EOX)n structural units is mediated from 1 to 5 by changing the molar ratio of the EOX monomer to benzyl bromide side groups. There exists obvious microphase separation between the QSA backbone and (EOX)n segments in the copolymer brushes due to their thermodynamic incompatibility. The strong hydrogen-bonding interaction between -OH groups in the backbone and N─C═O groups in (EOX)n segments is helpful for the construction of reversible supramolecular networks. The copolymer brushes show low cytotoxicity for HeLa cells and good antibacterial properties for Escherichia coli and Staphylococcus aureus for the contribution of hydrophilic (EOX)n segments and antibacterial activity of the quaternary ammonium. The antiprotein behavior of polymer surfaces is improved after rearrangement of (EOX)n segments by tetrahydrofuran (THF) vapor induction. These copolymer brushes have good prospects for biomedical applications.

Fabrication of copolymer brushes grafted superporous agarose gels: Towards the ultimate ideal particles for efficient affinity chromatography

A composite immobilized-metal affinity agarose particle was designed for the selective separation and purification of histidine-tagged proteins from complicated biological samples. The composite particle was constructed using superporous agarose particles as supporting matrix, flexible copolymer brushes as scaffolds to render higher ligand densities, and Ni2+-chelated iminodiacetic acids as recognition elements. Superporous agarose composite particles endow high permeability and interfering substance tolerance. The copolymer brush was prepared by surface-initiated atom transfer radical polymerization of N-isopropylacrylamide and glycidyl methacrylate, followed by iminodiacetic acids and Ni2+ ions. The physical and chemical properities of the composite particle were thoroughly investigated. The composite particles were shown to be able to selectively separate histidine-tagged recombinant proteins in the presence of high quantities of interfering chemicals in a model protein-binding experiment. By altering the temperature, the protein binding of the composite particles can be modulated. The superporous agarose particles supported polymer brush enables fast and efficient separation and purification of target proteins with high permeability, low backpressure, and high interfering matrix tolerance, which pave the path for bioseparation through designing and fabrication of novel agarose particles-based functional materials.

Enabling Reversible Addition-Fragmentation Chain-Transfer Polymerization for Brush Copolymers with a Poly(2-oxazoline) Backbone

The combination of different monomer classes has been sought after to access a wider range of brush copolymers owing to their unique properties derived from their dense macromolecular structures. Herein, we report the synthesis of a 2-oxazoline monomer (RAFTOx) containing a chain transfer agent at the 2-position and its subsequent utilization in reversible addition-fragmentation chain-transfer (RAFT) polymerization. With the aim of tuning the brush density in these polymers, homopolymers, block copolymers, and gradient copolymers of various ratios with 2-ethyl-2-oxazoline and RAFTOx have been prepared. Selected brush macroCTAs were then used for the RAFT polymerization of N,N-dimethylacrylamide and 2-ethyhexyl acrylate to prepare brush copolymers of different architectures.

Optimizing Chain Topology of Bottle Brush Copolymer for Promoting the Disorder-to-Order Transition

The order-disorder transitions (ODT) of core-shell bottle brush copolymer and its structural isomers were investigated by dissipative particle dynamics simulations and theoretically by random phase approximation. Introducing a chain topology parameter which parametrizes linking points between M diblock chains each with N monomers, the degree of incompatibility at ODT (; being the Flory–Huggins interaction parameter between constituent monomers) was predicted as a function of chain topology parameter () and the number of linked diblock chains per bottle brush copolymer (M). It was found that there exists an optimal chain topology about at which gets a minimum while the domain spacing remains nearly unchanged. The prediction provides a theoretical guideline for designing an optimal copolymer architecture capable of forming sub-10 nm periodic structures even with non-high components.

A Facile Fabrication of CdSe/ZnS QDs-Block Copolymer Brushes-Modified Graphene Oxide Nanohybrid with Temperature-Responsive Behavior.

In this paper, we described a straightforward one-step chemical method for the synthesis of semiconductor quantum dots(QDs)—block copolymer brushes functionalized graphene oxide(GO) fluorescence nanohybrids. The azobenzene-terminated block copolymer poly(N-isopropylacrylamid)-b-poly(styrene-co-5-(2-methacryoylethyloxymethyl)-8-quinolinol)(PNIPAM-b-P(St-co-MQ)) was modified on the surface of GO sheets via host–guest interactions between β-cyclodextrin-modified GO and azobenzene moieties, and simultaneously CdSe/ZnS QDs were integrated on the block copolymer brushes through the coordination between 8-hydroxyquinoline units in the polymer brushes and CdSe/ZnS QDs. The resulting fluorescence nanohybrid exhibited dual photoluminescence at 620 nm and 526 nm, respectively, upon excitation at 380 nm and LCST-type thermo-responsive behavior which originated from the change in the PNIPAM conformation in the block copolymer brushes of GO sheets.

Aziridine-Capped Poly(ethylene glycol) Brush Copolymers with Tunable Architecture as Versatile Cross-Linkers for Adhesives

Aziridine-Capped Poly(ethylene glycol) Brush Copolymers with Tunable Architecture as Versatile Cross-Linkers for Adhesives

Thermoresponsive, Pyrrolidone‐Based Antifouling Polymer Brushes

AbstractCommonly, modification of surfaces with thermoresponsive polymers is performed using poly(N‐isopropylacrylamide) (poly(NIPAM)). However, integration of poly(NIPAM) with a second polymer to obtain more complex copolymer structures has proven challenging due to inherently poorly controllable polymerization characteristics of acrylamides. In this study, (N‐(2‐methacryloyloxyethyl)pyrrolidone (NMEP) is synthesized and polymerized under controlled conditions from silicon oxide substrates via surface‐initiated atom transfer radical polymerization (SI‐ATRP) to produce thermoresponsive poly(NMEP) brushes. The livingness of the brushes is demonstrated by reinitiation of poly(NMEP) brushes using oligo(ethylene glycol) methyl ether methacrylate to obtain diblock copolymer brushes. Following extensive characterization, the reversible thermoresponsive behavior of these poly(NMEP) brushes is demonstrated using phase‐controlled AFM topography measurements in an aqueous liquid environment. These measurements indicate that at 27 °C the poly(NMEP) brushes are solvated and extend away from the surface, whereas at 60 °C the polymers are insoluble and reside in a collapsed conformation. Finally, to investigate the potential applicability of poly(NMEP) brushes in biomedical devices, the antifouling properties of the coating are tested in aqueous media containing BSA, fibrinogen, or 10% diluted human serum using quartz crystal microbalance with dissipation monitoring (QCM‐D). These measurements reveal very good antifouling properties, even when exposed to 10% diluted human serum.

Cell Adhesion and Migration on Thickness Gradient Bilayer Polymer Brush Surfaces: Effects of Properties of Polymeric Materials of the Underlayer.

In the field of tissue engineering and biomaterials, controlling the surface properties and mechanical properties of scaffold materials is crucial and has attracted much attention. Here, two types of bilayer polymer brushes composed of a hydrophilic underlying layer and a cationic surface layer [made of poly(2-aminoethyl methacrylate)] with a thickness gradient were prepared by surface-initiated atom-transfer radical polymerization. To investigate the influence of the stiffness as a mechanical property of the polymer brush on cell behavior, the underlayer was prepared from either 2-methacryloyloxyethyl phosphorylcholine or oligo(ethylene glycol) methyl ether methacrylate, with the bilayers designated as gradient poly(2-methacryloyloxyethyl phosphorylcholine)-block-poly(2-aminoethyl methacrylate) [grad-pMbA] and gradient poly(oligo[ethylene glycol] methyl ether methacrylate)-block-poly(2-aminoethyl methacrylate) [grad-pEGbA], respectively. Characterization of these surfaces was performed by spectroscopic ellipsometry, X-ray reflectivity, and determination of the zeta potential, static contact angle, and force curve. These diblock copolymer brushes with a thickness gradient helped to distinguish the effects of the mechanical and surface properties of the brushes on cell behavior. The attachment and motility of L929 fibroblasts and epithelial MCF 10A cells on the fabricated brushes were then assessed. L929 cells had a round shape on the thin surface layer of grad-pMbA and spread well on thicker areas. In contrast, MCF 10A cells spread well in areas of any thickness of either grad-pMbA or grad-pEGbA. Single MCF 10A cells migrated randomly on grad-pMbA, whereas grouped cells started to climb up along the thickness gradient of grad-pMbA. In contrast, both single and grouped MCF 10A cells migrated randomly on grad-pEGbA. These thickness gradient diblock copolymer brushes are simple, reproducible, and reasonable platforms that can facilitate practical applications of biomaterials, for example, in tissue engineering and biomaterials.

Synthesis, Hydrophilicity and Micellization of Coil-Brush Polystyrene-b-(polyglycidol-g-polyglycidol) Copolymer-Comparison with Linear Polystyrene-b-polyglycidol.

In this paper, an original method of synthesis of Coil-Brush amphiphilic polystyrene-b-(polyglycidol-g-polyglycidol) (PS-b-(PGL-g-PGL)) block copolymers was developed. The hypothesis that their hydrophilicity and micellization can be controlled by polyglycidol blocks architecture was verified. The research enabled comparison of behavior in water of PS-b-PGL copolymers and block–brush copolymers PS-b-(PGL-g-PGL) with similar composition. The Coil-Brush copolymers were composed of PS-b-PGL linear core with average DPn of polystyrene 29 and 13 of polyglycidol blocks. The DPn of polyglycidol side blocks of coil–b–brush copolymers were 2, 7, and 11, respectively. The copolymers were characterized by 1H and 13C NMR, GPC, and FTIR methods. The hydrophilicity of films from the linear and Coil-Brush copolymers was determined by water contact angle measurements in static conditions. The behavior of Coil-Brush copolymers in water and their critical micellization concentration (CMC) were determined by UV-VIS using 1,6-diphenylhexa-1,3,5-trien (DPH) as marker and by DLS. The CMC values for brush copolymers were much higher than for linear species with similar PGL content. The results of the copolymer film wettability and the copolymer self-assembly studies were related to fraction of hydrophilic polyglycidol. The CMC for both types of polymers increased exponentially with increasing content of polyglycidol.

Enhanced vapor sorption in block and random copolymer brushes.

Polymer brushes in gaseous environments absorb and adsorb vapors of favorable solvents, which makes them potentially relevant for sensing applications and separation technologies. Though significant amounts of vapor are sorbed in homopolymer brushes at high vapor pressures, at low vapor pressures sorption remains limited. In this work, we vary the structure of two-component polymer brushes and investigate the enhancement in vapor sorption at different relative vapor pressures compared to homopolymer brushes. We perform molecular dynamics simulations on two-component block and random copolymer brushes and investigate the influence of monomer miscibility and formation of high-energy interfaces between immiscible monomers on vapor sorption. Additionally, we present absorption isotherms of pure homopolymer, mixed binary brush and 2-block, 4-block, and random copolymer brushes. Based on these isotherms, we finally show that random copolymer brushes absorb more vapor than any other architecture investigated thus far. Random brushes display enhanced sorption at both high and low vapor pressures, with the largest enhancement in sorption at low vapor pressures.