Surface-initiated Atom Transfer Radical Polymerization Research Articles

Combination of AFM and Electrochemical QCM-D for Probing Zwitterionic Polymer Brushes in Water: Visualization of Ionic Strength and Surface Potential Effects.

The surface modification of soft zwitterionic polymer brushes with antifouling properties represents a facile approach to enhancing the performance of bioelectronics. Ionic strength and applied potentials play a crucial role in controlling polymer brushes' conformation and hydration states. In this study, we quantitatively investigated and compared poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) and poly(sulfobetaine methacrylate) (PSBMA) brushes at different salt concentrations and applied surface potentials. Initiator-containing poly(3,4-ethylenedioxythiophene) films (poly(EDOT-Br)) were prepared by electropolymerization. After the conducting polymer was deposited, polymer brushes grew from the electrode surface through surface-initiated atom-transfer radical polymerization (SI-ATRP). Polymer brushes were carefully characterized for their surface morphologies using an atomic force microscope (AFM). The force volume method measured using AFM enabled the analysis of the Young's modulus of the two polymer brushes. Hydration states and protein binding behaviors of polymer brushes were examined using quartz crystal microbalance with dissipation (QCM-D). We further integrated a potentiostat with the QCM-D to conduct an electrochemical QCM-D study. The energy dissipation and frequency changes corresponded to the ion adsorption on the film surface under different ionic strengths. The results of both hydration states and nonspecific protein binding behavior indicate that PMPC brushes have greater ionic strength independency, implying the conformation of the unchanged PMPC brushes. Moreover, we illustrated how the surface potential influences nonspecific and specific binding behavior on PMPC brushes on PEDOT films compared with electrified poly(EDOT-PC) electrodes. We concluded that PMPC brushes exhibit unique behaviors that are barely affected by ion concentration, and that the brushes' modification results in less influence by surface potential due to the finite Debye length influencing the electrode surface to outer environment in an NaCl aqueous solution.

Peptide-Modified Surfaces for Binding Carbamylated Proteins from Plasma.

Carbamylation of blood proteins is a common post-translational modification that occurs upon kidney dysfunction that is strongly associated with deleterious outcomes for patients treated using hemodialysis. In this study, we focused on the removal of two representative carbamylated plasma proteins, carbamylated albumin (cHSA) and fibrinogen (cFgn), through adsorption onto a surface functionalized with a specific peptide (cH2p1). Surfaces modified with poly(hydroxyethyl methacrylate) (p(HEMA)) were prepared using surface-initiated atom transfer radical polymerization (SI-ATRP) techniques and functionalized with cH2p1. cH2p1-functionalized surfaces showed selective binding toward cHSA and cFgn, compared to their native protein form, with NH-cH2p1 of superior selectivity than CO-cH2p1. The adsorption capacity of carbamylated protein on NH-cH2p1 was maintained in diluted plasma, and ultralow adsorption of native Fgn was observed. Similar to unmodified p(HEMA) surfaces, NH-cH2p1 showed a low platelet adhesion and activation, suggesting that the designed surface does not adversely affect platelets.

Mesoporous Silica Nanoprodrug Encapsulated with Near-Infrared Absorption Dye for Photothermal Therapy Combined with Chemotherapy.

Based on the tumor microenvironment with weak acidic characteristics, a nano-drug delivery system that achieves controlled release of drugs through the pH response has been a popular strategy to improve the effectiveness of tumor therapy and reduce toxic side effects, and combining photothermal therapy (PTT) on this basis can help improve the antitumor effect. In this study, mesoporous silica nanoparticles (MSNs) were surface-modified with polymer poly(PEGMA-co-HEMA) via surface-initiated atom transfer radical polymerization, and a multifunctional nanoplatform MSN@poly(PEGMA-co-HEMA-g-doxorubicin (DOX)/indocyanine green (ICG) was designed for effective photothermal/chemotherapy combination therapy. The anticancer drug DOX was anchored to the polymer on the surface of MSN by reversible covalent bond cis-aconitic anhydride with a drug loading of 10%. Meanwhile, the small-molecule dye was loaded into the pores of MSN, and PTT mediated by near-infrared (NIR) radiation could further kill cancer cells. Under low-pH stimulation, the cis-aconitic anhydride bond breaks and DOX is released, with a 65% increase in cumulative drug release over 50 h compared to that at pH 7.4 (normal physiological environment). The high temperature induced by photothermal conversion accelerated the reversible covalent bond breakage, and the cumulative drug release at pH 5.0 for 3 h at elevated temperature up to 50 °C increased by 24.3% compared with that under normal physiological conditions (T = 37 °C), demonstrating that increasing the temperature can reduce the time required to reach blood drug concentration. In vitro cytotoxicity results revealed that the prodrug delivery system showed stronger cytotoxicity under NIR light irradiation compared with free DOX, with more than 90% of tumor cells killed after 48 h. Therefore, MSN@poly(PEGMA-co-HEMA-g-DOX)/ICG enhanced the synergistic effect of chemotherapy through photothermal action and accelerated reversible chemical bond cleavage, which has great potential in the combined therapy of cancer.

Ionic Interaction-Driven Switchable Bactericidal Surfaces

The external bacteria will inevitably invade the wound, attach, and subsequently colonize on the wound surface during surgery and biomedical operations, which slows down the process of wound healing and tissue repair, remaining a significant threat to human health. Therefore, developing a smart antibacterial surface has become the focus of antimicrobial research field, which has important social and economic significance. Herein, we present a simple route towards producing ionic interaction-driven switchable multifunctional antibacterial surfaces that decrease bacteria attachment and inactivate attached microorganisms. Briefly, the graded surface was constructed by surface-initiated atom transfer radical polymerization on silicon substrate consisting of antifouling component poly (3-sulfopropyl methacrylate potassium salt) (PSPMA) brushes, an antibacterial positive-charged components lysozyme (LYZ) and hexadecyl trimethyl ammonium bromide (CTAB) were loaded on negative-charged sulfonate groups via electrostatic interaction. The resultant brushes grafted surfaces exhibited more than ~95.5% bactericidal efficacy, and ~92.8% releasing rate after introducing contra-ions (Na+ & Cl-) against both Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus. More importantly, the ionic interaction-driven method used in this work is straightforward to produce renewable antibacterial surfaces. To further extend the applications, we construct smart cotton fabric to develop Fabric-PSPMA/LYZ and Fabric-PSPMA/Chitosan brushes which can promote wound healing and tissue repair. This work will assist in the wider utilization of the switchable antibacterial functionalization of biomedical materials.

Light-promoted synthesis of surface-grafted polymers bearing pyridine groups by metal-free ATRP in microliter volumes

Polymers with pendant pyridine groups (PPPGs) are pH responsive weak polyelectrolytes potentially attractive for many applications such as sensors, antibacterial coatings, and ion gating systems. Synthesis of PPPGs by classical atom transfer radical polymerization (ATRP) is very challenging due to highly probable formation of monomer/metal complexes. In response to that, we report here a facile synthetic strategy to obtain surface-grafted PPPGs that utilizes light-mediated ATRP. Metal-free surface-initiated ATRP catalyzed by 10-phenylphenothiazine is used to polymerize three isomeric monomers with methacrylate groups attached at various positions of a pyridine ring. The reactivity of the isomers is compared for selection of optimal monomer structure leading to thick brushes. The polymerizations are conducted under visible light, at ambient conditions, and using only microliter volumes of the reaction mixture that is important for reducing the complexity and costs of the process as well as limiting chemical waste. The observed linear dependency of the brush thickness vs polymerization time for poly(pyridin-3-yl methacrylate) (PP3M) grafted from indium tin oxide or silicon wafers indicated the controlled characteristics of the developed method. The obtained PP3M brush demonstrated pH responsive behavior associated with protonation of pyridine groups in acidic solution and adoption of highly stretched conformation below pKa.

Sprayable, durable, and superhydrophobic coating of silica particle brushes based on octadecyl bonding and polymer grafting via surface-initiated ATRP for efficient oil/water separation

A facile approach to prepare sprayable, durable, and superhydrophobic coating was designed for highly efficient oil/water separation and oil absorption based on silica particle brushes via surface-initiated (SI-ATRP). Octadecyl group bonded and poly(styrene-co-acrylonitrile) (PSAN) grafted silica nanoparticles (NPs) (C18-SiO2-g-PSAN) were prepared by sequential initiator tethering and SI-ATRP processes, which were directly applied as surface superhydrophobic coating for various porous substrates. The results confirmed that octadecyl group and PSAN were successfully bonded on silica NPs. After facile spraying of C18-SiO2-g-PSAN, the coated porous substrates displayed superhydrophobicity with an advancing water contact angle (WCA) exceeding 150° due to the synergistic effects of low surface energy compositions contributed by the tethered octadecyl group and the rough structure induced by silica NPs and porous substrates. Superhydrophobic porous substrates exhibited high oil/water separation efficiency achieving 98.8% by using cotton fabric as substrate and remarkable oil absorption capacity of 39.2 g/g for isooctane using polyurethane sponge as substrate. The recyclability and strong durability against mechanical abrasion enable them to be promising candidates for industrial oil-contaminated water treatments and marine spilt oil cleanup in harsh environments.

High Adsorption of α-Glucosidase on Polymer Brush-Modified Anisotropic Particles Acquired by Electrospraying-A Combined Experimental and Simulation Study.

In this particular contribution, we aim to immobilize a model enzyme such as α-glucosidase onto poly(DMAEMA) [poly(2-dimethyl amino ethyl methacrylate)] brush-modified anisotropic (cup- and disc-shaped) biocompatible polymeric particles. The anisotropic particles comprising a blend of PLA [poly(lactide)] and poly(MMA-co-BEMA) [poly((methyl methacrylate)-co-(2-(2-bromopropionyloxy) ethyl methacrylate)] were acquired by electrospraying, a scalable and convenient technique. We have also demonstrated the role of a swollen polymer brush grafted on the surface of cup-/disc-shaped particles via surface-initiated atom transfer radical polymerization in immobilizing an unprecedentedly high loading of enzyme [441 mg/g (cup)-589 mg/g (disc) of particles, 15-20 times higher than that of the literature-reported system] as compared to non-brush-modified particles. Circular dichroism spectroscopy was used to predict the structural changes of the enzyme upon immobilization onto the carrier particles. An enormously high amount of enzymes with preserved activity (∼85 ± 13% for cups and ∼78 ± 15% for discs) was found to adhere onto brush-modified particles at pH 7 via electrostatic adsorption. These findings were further explored at the atomistic level using a coarse-grained dissipative particle dynamics simulation approach, which exhibited excellent correlation with experimental results. In addition, accelerated particle separation was also achieved via magnetic force-induced aggregation within 20 min (without a centrifuge) by incorporating magnetic nanoparticles into disc-shaped particles while electrojetting. This further strengthens the technical feasibility of the process, which holds immense potential to be applied for various enzymes intended for several applications.

A general and robust strategy for in-situ templated synthesis of patterned inorganic nanoparticle assemblies

Precisely controlling the spatial organization of inorganic nanoparticles is essential for many applications, such as sensing, catalytic, and optical/electronic systems. Here, we describe a general and robust strategy to fabricate arbitrary quasi-two-dimensional (quasi-2D) nanoparticle assembly structures with tunable size and thickness on a substrate by using block copolymer brushes as the templates. To achieve this, patterned amphiphilic block copolymer brushes were first grown via light-mediated surface-initiated atom transfer radical polymerization. The hydrophilic polymer blocks could interact and enrich the inorganic precursors, and thus accelerate the in-situ growth of nanoparticles within the patterned hydrophilic polymer domains. In our method, the block copolymer template could strictly limit the vertical growth of quasi-2D nanoparticle assemblies to achieve thickness control in the nanometer scale. By changing the design of the photomask and experimental conditions for the light-mediated polymerization, quasi-2D inorganic nanoparticle assemblies with controllable shape and dimension can be feasibly obtained. Moreover, this method is also generally applicable to prepare various patterned inorganic nanoparticle assemblies with different compositions.

Fibronectin adsorption on polystyrene sulfonate-grafted polyester using atomic force microscope.

Cell adhesion and growth over prostheses are strongly influenced by the adsorption and conformation of adhesive proteins from blood and extracellular matrix, such as fibronectin. This key behavior can be possibly exploited to develop a prosthetic ligament based on the surface bioactivation of biodegradable materials. In this work, surface functionalization was performed by grafting poly(sodium 4-styrene sulfonate) on polyethylene terephthalate and polycaprolactone using a thermal surface-initiated atom transfer radical polymerization grafting technique. The morphology and mechanical properties of the adsorbed fibronectin in the presence of albumin were studied by atomic force microscopy. The morphology of fibronectin on two kinds of polyester surfaces was similar. However, the study results showed a remarkable conformation change of fibronectin when adsorbed onto the nongrafted or grafted surface, leading to an increase in cell adhesion and organization in the second case. This research provided evidence of the relationship between the morphology change of fibronectin to the enhancement of the cell adhesion and spreading on the grafted surface of polyester.

Synthesis of Poly(ionic Liquid)s-block-poly(methyl Methacrylate) Copolymer-Grafted Silica Particle Brushes with Enhanced CO2 Permeability and Mechanical Performance.

Poly(ionic liquid) (PIL)-based block copolymers are of particular interest as they combine the specific properties of PILs with the self-assembling behaviors of block copolymers, broadening the range of potential applications for PIL-based materials. In this work, three particle brushes: SiO2-g-poly(methyl methacrylate) (PMMA), SiO2-g-PIL, and SiO2-g-PMMA-b-PIL were prepared through surface-initiated atom transfer radical polymerization. Unlike the homogeneous homopolymer particle brushes, the block copolymer particle brush SiO2-g-PMMA-b-PIL exhibited a bimodal chain architecture and unique phase-separated morphology, which were confirmed by size-exclusion chromatography and transmission electron microscopy. In addition, the influence of the introduction of the PMMA segment on the gas separation and mechanical performance of the PIL-containing block copolymer particle brushes were investigated. A significant improvement of Young's modulus was observed in the SiO2-g-PMMA-b-PIL compared to the SiO2-g-PIL bulk films; meanwhile, their gas separation performances (CO2 permeability and CO2/N2 selectivity) were the same, which demonstrates the possibility of improving the mechanical properties of PIL-based particle brushes without compromising their gas separation performance.

Polymer grafted gibbsite nanoplatelets via direct initiator tethering and surface-initiated atom transfer radical polymerization

An efficient method for the preparation of polymer grafted gibbsite nanoplatelets (NPs) was proposed by direct preparation of initiator-tethered gibbsite (gibbsite-Br) NPs followed by surface-initiated atom transfer radical polymerization (SI-ATRP) to obtain gibbsite particle brushes. By adding portion of water-soluble solvent (e.g., alcohol), individual ATRP initiator-tethered gibbsite NPs were fabricated using 2-bromo-2-methylpropionic acid as a tetherable initiator avoiding the aggregation of gibbsite NPs which are ready for polymer grafting process. To verify the efficiency of the tethered initiator, various polymers grafted gibbsite NPs were fabricated by SI-ATRP. The results indicated that initiator anchored gibbsite NPs and various gibbsite-g-polymers (e.g., gibbsite-g-poly2-(dimethylamino) ethyl methacrylate, gibbsite-g-polyacrylonitrile, gibbsite-g-polymethyl methacrylate) were synthesized successfully. The thermal stabilities of gibbsite-g-polymer hybrid materials have been enhanced significantly. Compared with PMMA matrix, the fire-retardant behavior of gibbsite-g-polymethyl methacrylate was strengthened due to the incorporation of gibbsite NPs. This work proposed a versatile and convenient method for producing initiator-immobilized solid NPs and polymer grafts, which thereby enables promised properties of polymer hybrid materials depending on the orientation and interactions of particle brushes.

Fabrication of Three-Dimensional Polymer-Brush Gradients within Elastomeric Supports by Cu0-Mediated Surface-Initiated ATRP.

Cu0-mediated surface-initiated ATRP (Cu0 SI-ATRP) emerges as a versatile, oxygen-tolerant process to functionalize three-dimensional (3D), microporous supports forming single and multiple polymer-brush gradients with a fully tunable composition. When polymerization mixtures are dispensed on a Cu0-coated plate, this acts as oxygen scavenger and source of active catalyst. In the presence of an ATRP initiator-bearing microporous elastomer placed in contact with the metallic plate, the reaction solution infiltrates by capillarity through the support, simultaneously triggering the controlled growth of polymer brushes. The polymer grafting process proceeds with kinetics that are determined by the progressive infiltration of the reaction solution within the microporous support and by the continuous diffusion of catalyst regenerated at the Cu0 surface. The combination of these effects enables the accessible generation of 3D polymer-brush gradients extending across the microporous scaffolds used as supports, finally providing materials with a continuous variation of interfacial composition and properties.

Enhanced Conductivity and Antibacterial Behavior of Cotton via the Electroless Deposition of Silver.

In this study, the surface-initiated atom transfer radical polymerization (SI-ATRP) technique and electroless deposition of silver (Ag) were used to prepare a novel multi-functional cotton (Cotton-Ag), possessing both conductive and antibacterial behaviors. It was found that the optimal electroless deposition time was 20 min for a weight gain of 40.4%. The physical and chemical properties of Cotton-Ag were investigated. It was found that Cotton-Ag was conductive and showed much lower electrical resistance, compared to the pristine cotton. The antibacterial properties of Cotton-Ag were also explored, and high antibacterial activity against both Escherichia coli and Staphylococcus aureus was observed.

Grafting polymers from cellulose nanocrystals via surface‐initiated atom transfer radical polymerization

AbstractCellulose nanocrystals (CNC) are rod‐like nanoparticles extracted from cellulose. Due to their fascinating properties—renewable, biocompatible, non‐toxic, biodegradable, excellent mechanical performances, high specific surface area, water dispersible, can be assemble in chiral nematic phases—CNC have shown promise in various fields, including oil recovery, polymer composites reinforcing, hydrogels, aerogels, supercapacitors, energy saving buildings, cosmetics, papermaking, coatings, liquid crystals, and waste water treatment. However, the hydrophilic surface of CNC hinders their broader applications. In this context, surface modification of CNC via polymer grafting can be used to finely tune their surficial properties and endow CNC with a variety of functionalities, such as conductivity, pH or temperature responsiveness, reactivity…In particular, surface‐initiated atom transfer radical polymerization (SI‐ATRP) is a powerful tool to graft various polymers with a high grafting density and controlled chain length. In this review, the precise control of grafted polymers from CNC via SI‐ATRP is first discussed, including issues related to the polymer grafting density, chain length and possibility to perform an asymmetric grafting. Then, the properties and applications of CNC grafted with a variety of polymers are presented. Finally, some challenges and outlook related to the SI‐ATRP method applied to the field of CNC is discussed.

Surface modification of nanofiltration membranes with zwitterions to enhance antifouling properties during brackish water treatment: A new concept of a “buffer layer”

Nanofiltration (NF)-based brackish water desalination has been labeled an emerging avenue for alleviating water scarcity, however, membrane fouling still restricts its broad application. Herein, zwitterion-modified membranes were prepared with polydopamine (PDA) and sulfobetaine methacrylate (SBMA) monomers via surface-initiated atom-transfer radical-polymerization (SI-ATRP) and named TFC-PDA-PSBMA. Compared with the control membrane, the TFC-PDA-PSBMA possessed enhanced hydrophilicity, lower negative charge and smaller pore size. Superior salt retention of Na2SO4 and NaCl of up to 99.1% and 80.7% was obtained for TFC-PDA-PSBMA with only a 10% decrease in permeance. Furthermore, TFC-PDA-PSBMA exhibited an outstanding flux recovery of 92.1% during humic acid (HA) filtration. The mechanism driving the improved antifouling properties was analyzed from the aspects of the modified layer, free interfacial energy and hydration layer. TFC-PDA-PSBMA also exhibited superior antibiofouling with reducing 86.1% of E. coli colonies adhered on membrane surface. The SBMA layer and hydration layer acted together as a buffer layer with robust repulsion of foulants. In addition, the TFC-PDA-PSBMA membrane was applied in authentic brackish water desalination and exhibited superior selectivity, desalination and antifouling performance, which matched the simulated solution results well. A new concept of a “buffer layer” was proposed in this work, which may provide insight into antifouling membrane design during brackish water treatment.

A nonionic polymer-brush-grafted PVDF membrane to analyse fouling during the filtration of oil/water emulsions

Hydrophilic polymer brushes on membrane surfaces can alleviate fouling during the separation of oil/water emulsions; the charged moieties on the polymer brushes presumably interact with charged surfactants and weaken the membrane fouling behaviour. However, the oil-repellence mechanism of nonionic polymer brushes has not been thoroughly examined. In this study, a nonionic poly(N-acryloyl morpholine)-brush-grafted-poly(vinylidene fluoride) membrane (PVDF-g-PACMO) was fabricated via surface-initiated atom transfer radical polymerisation (ATRP) to separate various surfactant-stabilised emulsions. PVDF-g-PACMO membranes with high hydrophilicity and high permeation were successfully fabricated by controlling the duration of ATRP. Furthermore, fouling models of oil/water emulsions stabilised by anionic, nonionic, and cationic surfactants were examined. Multicycle filtration experiments revealed that the anionic surfactant-stabilised emulsions severely fouled the similarly charged PVDF-g-PACMO membranes owing to electrostatic repulsion, whereas the nonionic and cationic surfactant-stabilised emulsions exhibited reduced irreversible fouling. In particular, an unusual relief in irreversible membrane fouling was observed with respect to the cationic surfactant-stabilised emulsions, presumably because of strong demulsification and steric effects (surfactant barrier), which repelled the penetration of oil droplets into the internal pores and averted pore blockage. These observations suggest that oppositely charged surface potentials of the PVDF-g-PACMO membranes compared to that of the oil/water emulsions assist in mitigating irreversible fouling. The mechanisms examined herein described the relationship between the surface properties of the oil/water emulsions and the tendency for irreversible fouling, thereby providing valuable guidance for sustainable separation of oil/water emulsions.

Evaluation of 2-Bromoisobutyryl Catechol Derivatives for Atom Transfer Radical Polymerization-Functionalized Polydopamine Coatings.

The use of α-bromoisobutyryl-functionalized polydopamine (PDA), derived from an in situ mixture with dopamine (DA) and α-bromoisobutyryl bromide, enables surface-initiated atom transfer radical polymerization (SI-ATRP) of a broad range of methacrylate monomers for surface functionalization. Although the putative intermediate 2-bromo-N-(3,4-dihydroxyphenethyl)-2-methylpropanamide 1 has been proposed to account for the SI-ATRP activity of α-bromoisobutyryl-functionalized PDA, there has not been a systematic investigation on the efficacy of other catechol-derived 2-bromoisobutyryl derivatives for SI-ATRP. In this work, a number of catechol-derived ATRP initiators containing the 2-bromoisobutyryl moiety were designed and synthesized, in an effort to investigate the effect of changes in structure on initiator immobilization, and subsequent ATRP performance. The change in the length of the linker unit bearing the 2-bromoisobutyryl moiety, the introduction of a free amine group, or the replacement of the amide with an ester were found to have profound effects on the ability of the molecule to deposit ATRP-initiator-modified PDA coatings, as well as the subsequent SI-ATRP performance. Among the ATRP initiators synthesized, 5-(2-aminoethyl)-2,3-dihydroxyphenethyl 2-bromo-2-methylpropanoate hydrobromide 4·HBr was most efficiently incorporated into ATRP-initiator-modified PDA coatings and also the best at effecting SI-ATRP with 2-hydroxyethyl methacrylate; the high performance of this initiator is likely due to the presence of a free amine and an appropriately long methylene linker unit to the 2-bromoisobutyryl moiety. This methodology was found to be suitable for the functionalization of a range of organic and inorganic surfaces, for the fabrication of high-value surface-grafted polymer brush coatings for various applications.

Surface Modification of Polyurethane Membrane with Various Hydrophilic Monomers and N-Halamine: Surface Characterization and Antimicrobial Properties Evaluation.

Reducing microbial infections associated with biomedical devices or articles/furniture noted in a hospital or outpatient clinic remains a great challenge to researchers. Due to its stability and low toxicity, the N-halamine compound has been proposed as a potential antimicrobial agent. It can be incorporated into or blended with the FDA-approved biomaterials. Surface grafting or coating of N-halamine was also reported. Nevertheless, the hydrophobic nature associated with its chemical configuration may affect the microbial interactions with the chlorinated N-halamine-containing substrate. In this study, a polymerizable N-halamine compound was synthesized and grafted onto a polyurethane surface via a surface-initiated atom transfer radical polymerization (SI-ATRP) scheme. Further, using the sequential SI-ATRP reaction method, different hydrophilic monomers, namely poly (ethylene glycol) methacrylate (PEGMA), hydroxyethyl methacrylate (HEMA), and [2-(methacryloyloxy) ethyl] dimethyl-(3-sulfopropyl) ammonium hydroxide (SBMA), were also grafted onto the polyurethane (PU) substrate before the N-halamine grafting reaction to change the surface properties of the N-halamine-modified substrate. It was noted that the chains containing the hydrophilic monomer and the polymerizable N-halamine compound were successfully grafted onto the PU substrate. The degree of chlorination was improved with the introduction of a hydrophilic monomer, except the HEMA. All of these hydrophilic monomer-containing N-halamine-modified PU substrates demonstrated a more than 2 log CFU reduction after microbial incubation. In contrast, the surface modified with N-halamine only exhibited significantly less antimicrobial efficacy instead. This is likely due to the synergistic effects caused by the reduced chlorine content, as well as the reduced surface interactions with the microbes.

Effect of Reaction Media on Grafting Hydrophobic Polymers from Cellulose Nanocrystals via Surface-Initiated Atom-Transfer Radical Polymerization.

Hydrophobic polymer-grafted cellulose nanocrystals (CNCs) were produced via surface-initiated atom-transfer radical polymerization (SI-ATRP) in two different solvents to examine the role of reaction media on the extent of surface modification. Poly(butyl acrylate)-grafted CNCs were synthesized in either dimethylformamide (DMF) (D-PBA-g-CNCs) or toluene (T-PBA-g-CNCs) alongside a free polymer from a sacrificial initiator. The colloidal stability of unmodified CNCs, initiator-modified CNCs, and PBA-g-CNCs in water, DMF, and toluene was evaluated by optical transmittance. The enhanced colloidal stability of initiator-modified CNCs in DMF led to improved accessibility to initiator groups during polymer grafting; D-PBA-g-CNCs had 30 times more grafted chains than T-PBA-g-CNCs, determined by thermogravimetric and elemental analysis. D-PBA-g-CNCs dispersed well in toluene and were hydrophobic with a water contact angle of 124° (for polymer grafts > 13 kDa) compared to 25° for T-PBA-g-CNCs. The cellulose crystal structure was preserved, and individual nanoparticles were retained when grafting was carried out in either solvent. This work highlights that optimizing CNC colloidal stability prior to grafting is more crucial than solvent-polymer compatibility to obtain high graft densities and highly hydrophobic CNCs via SI-ATRP.

Tailoring the Architecture of Cationic Polymer Brush-Modified Carbon Nanotubes for Efficient siRNA Delivery in Cancer Immunotherapy.

The facile and controlled fabrication of homogeneously grafted cationic polymers on carbon nanotubes (CNTs) remains poorly investigated, which further hinders the understanding of interactions between functionalized CNTs with different nucleic acids and the rational design of appropriate gene delivery vehicles. Herein, we describe the controlled grafting of cationic poly(2-dimethylaminoethylmethacrylate) brushes on CNTs via surface-initiated atom transfer radical polymerization integrated with mussel-inspired polydopamine chemistry. The binding of nucleic acids with different brush-CNT hybrids discloses the highly architectural-dependent behavior with dense short brush-coated CNTs displaying the highest binding among all the other hybrids, namely, dense long, sparse long, and sparse short brush-coated CNTs. Additionally, different chemistries of the brush coatings were shown to influence the biocompatibility, cellular uptake, and silencing efficiency in vitro. This platform provides great flexibility for the design of polymer brush-CNT hybrids with precise control over their structure-activity relationship for the rational design of nucleic acid delivery systems.