Enhancement of Bactericidal Activity via Cyclic Poly(cationic liquid) Brushes.

In addition to extensive studies of conventional linear poly(ionic liquids) (PILs), exploration of the effects of PIL topology, especially cyclic architecture, on bactericidal properties will expand the design possibilities for the development of excellent antibacterial surfaces. Herein, the preparation of antibacterial surfaces based on cyclic PIL brushes is reported for the first time and how the cyclic PIL architecture affects bactericidal activity is investigated. It is shown that the cyclic architecture imparted PIL brushes with enhanced bactericidal activity, achieving only 1.7% of bacterial viable percentage against gram-negative Escherichia coli using Live/Dead staining methods, compared to 6.6% for the corresponding linear PIL brushes. The enhanced bactericidal activity is also validated by the direct observation of scanning electron microscopy and a colony counting assay. Further mechanism studies reveal that the substantially different morphologies of cyclic aggregates and altered surface charge density induced by the cyclic PIL architecture can account for the enhanced bactericidal activity.

Protein-resistant properties of poly(N-vinylpyrrolidone)-modified gold surfaces: The advantage of bottle-brushes over linear brushes.

Poly(N-vinylpyrrolidone) (PVP)-modified surfaces have been shown to possess excellent protein resistance and good biocompatibility. However, PVP-modified surfaces with different molecular architectures have not been prepared, and their protein-resistant properties have not been studied. Herein, gold surfaces modified with linear PVP brush and PVP bottle-brush architectures were prepared by photoinitiated surface grafting polymerization. Ellipsometry, X-ray photoelectron spectroscopy (XPS), water contact angle, Fourier transform infrared (FTIR) spectroscopy and atomic force microscopy (AFM) were utilized to characterize the prepared surfaces. The protein-resistant properties were investigated by a quartz crystal microbalance with dissipation (QCM-D) with bovine serum albumin (BSA), fibrinogen (Fg) and lysozyme (Lyz). Compared with the ungrafted QCM-D chips, the PVP bottle-brush-grafted chips (9.3 nm thickness) showed superior protein resistance over linear PVP brush-grafted chips (9.9 nm thickness). Furthermore, the PVP bottle-brushes reduced the levels of BSA, Fg and Lyz adsorption by 97%, 85% and 69%, respectively. Moreover, to demonstrate potential applications as functional biosensors and in the biomedical field, PVP bottle-brushes containing glycopolymer-grafted gold surfaces were fabricated. Laser scanning confocal microscopy (LSCM) demonstrated that these glycopolymer surfaces showed excellent protein resistance and specific ConA binding ability. Overall, we speculate that the data presented here can provide useful information for the development of excellent antifouling materials and functional biosensors.

Design, Synthesis, and Application of a Difunctional Y-Shaped Surface-Tethered Photoinitiator.

Mixed homopolymer brushes have unique interfacial properties that can be exploited for both fundamental studies and applications in technology. Herein, the synthesis of a new catechol-based biomimetic Y-shaped binary photoinitiator (Y-photoinitiator) and its applications for surface modification with polymer brushes through both "grafting to" and "grafting from" strategies are reported. The "leg" of the Y consists of a catechol group as surface anchoring moiety. The arms are photoinitiator moieties that can be "addressed" independent of each other by radiation of different wavelengths. Using ultraviolet and visible light successively, each arm of the Y-photoinitiator was activated, thereby allowing the synthesis of Y-shaped block copolymer brushes with dissimilar polymer chains. The suitability of the Y-photoinitiator for surface modification was first investigated using N-vinylpyrrolidone and styrene as the model monomers for successive UV-photoiniferter-mediated polymerization and visible-light-induced polymerization, respectively. Switching of the wetting properties of the Y-shaped block copolymer brush poly( N-vinylpyrrolidone)- block-poly(styrene) (PVP- b-PS)-grafted surfaces by contact with different solvents was also investigated. To further exploit this novel Y-photoinitiator for the preparation of functional interfaces, Y-shaped block copolymer brushes poly(1-(2-methacryloyloxyhexyl)-3-methylimidazolium bromide)- block-poly( N-vinylpyrrolidone- co-glycidyl methacrylate) (PIL(Br)- b-P(NVP- co-GMA)) were also prepared and subsequently functionalized with the cell-adhesive arginine-glycine-aspartic acid (RGD) peptides by reaction with the glycidyl groups (PILPNG-RGD). The PILPNG-RGD grafted surfaces showed excellent cell-adhesive, bacteriostatic, and bactericidal properties. Thus, it can be concluded that further exploitation of this novel Y-photoinitiator for graft polymerization should allow the preparation of a wide range of functional interfaces with tailored properties.

A rapid one-step surface functionalization of polyvinyl chloride by combining click sulfur(vi)-fluoride exchange with benzophenone photochemistry.

Polyvinyl chloride (PVC) is an important biomedical material, but there is a lack of convenient functionalization methods. Here, a rapid, effective and simple one-step strategy for PVC surface functionalization by combining the "sulfur(vi)-fluoride exchange" (SuFEx) reaction with benzophenone photochemistry is presented.

"Click-chemical" modification of cellulose acetate nanofibers: a versatile platform for biofunctionalization.

Cellulose acetate nanofibers have attracted considerable interest in the biomedical sciences, but lack convenient biofunctionalization methods. In this work the "sulfur(vi)-fluoride exchange reaction", a new type of click chemistry, is used for the first time to overcome many of the difficulties previously encountered and provide a platform for biofunctionalization generally.

Facile fabrication of a "Catch and Release" cellulose acetate nanofiber interface: a platform for reversible glycoprotein capture and bacterial attachment.

Surfaces engineered to selectively capture and release target biomolecules and cells "on demand" are of considerable interest in a variety of biomedical applications, such as diagnostics and detection. In this work, a strategy is proposed to achieve "catch and release" using boronic acid ligand-functionalized electrospun cellulose acetate (CA) nanofiber mats. To achieve this goal, a simple method based on the one-step visible light-induced grafting copolymerization of 3-(acrylamido)phenylboronic acid (BA) and acrylamide (AM) is established. The copolymer poly(AM-co-BA)-grafted CA nanofiber mats (CA-g-P(AM-co-BA)) showed high capacity for the binding of glycoproteins such as horseradish peroxidase (HRP) and ovalbumin (OVA) under alkaline (pH 9.0) and physiological conditions (pH 7.4). Moreover, the bound glycoproteins can be released from the CA-g-P(AM-co-BA) mats by simple exposure to an acetic acid-sodium acetate (HAc-NaAc) buffer solution (pH 4.0). In addition, this system can be applied to directly extract glycoproteins from egg white samples. Likewise, the CA-g-P(AM-co-BA) mats acted as favorable substrates for Gram-negative E. coli bacterial attachment. The release of the attached bacteria is triggered by competitive sugar binding involving the addition of glucose. It can be envisioned that such boronic acid ligand-functionalized CA nanofiber mats that can "catch and release" biomolecules and bacterial cells hold considerable promise for diverse applications.

Microfluidic channels with renewable and switchable biological functionalities based on host-guest interactions.

Poly(dimethylsiloxane) (PDMS)-based microfluidic systems are gaining increasing attention due to their ease of fabrication, optical transparency and mechanical properties. However, the inherent hydrophobicity and chemical inertness of PDMS hinder its wider application in microfluidic systems. There is thus a strong need for methods for surface modification of PDMS-based microfluidic channels. In this work, oligo(ethylene glycol)methacrylate (OEGMA) and adamantane-containing OEGMA (OEGMA-Ada) were graft copolymerized on PDMS microchannel surfaces using a simple photochemical process to give PDMS-POA. OEGMA was chosen for its resistance to non-specific protein adsorption, and OEGMA-Ada was chosen for its subsequent attachment of mannose with bacteria binding affinity or biotin with avidin binding affinity. ß-CD decorated with biotin (CD-B) and/or mannose (CD-M) was attached to the PDMS-POA microchannels via host-guest interactions between the adamantane and ß-CD moieties. The data obtained suggest that the functions of the PDMS-POA/CD-B and PDMS-POA/CD-M microchannels with respect to biotin binding and bacterial adhesion were renewable. In addition, the biofunction of the PDMS-POA microchannels could be switched by treatment with SDS to release the CD component followed by treatment with a different ß-CD derivative. Different from previous surface modification strategies for PDMS-based microfluidic channels, the combination of visible light-induced grafting and host-guest chemistry provides modified PDMS microchannels with renewable and switchable biofunctions for the detection and measurement of specific proteins and bacteria.

Combining Click Sulfur(VI)-Fluoride Exchange with Photoiniferters: A Facile, Fast, and Efficient Strategy for Postpolymerization Modification.

"Click" type reactions represent the currently most prevalent postpolymerization strategy for the preparation of functional polymeric materials. Herein, a novel photoiniferter agent 4-(fluorosulfonyl)benzyl diethylcarbamodithioate (FSB-DECT) containing both dithiocarbamates and sulfonyl fluoride moieties is developed to act as both photoinitiator and click sulfur(VI)-fluoride exchange (SuFEx) agent. The photopolymerization behavior of FSB-DECT is demonstrated via standard photoiniferter-mediated polymerization for various types of monomer including N-isopropylacrylamide (NIPAAm), glycidyl methacrylate, and vinyl acetate (VAc). Gel permeation chromatography data show that the polymerization is relatively well controlled, with polydispersity indices of the product homopolymers in the range of 1.3-1.6. 1 H and 19 F NMR spectra and "reinitiated" photopolymerization indicate that the sulfonyl fluoride and diethyldithiocarbamyl groups remain at the respective ends of the homopolymer chains. Furthermore, using the sulfonyl fluoride end-functionalized poly(N-isopropylacrylamide) as a model polymer, the utility of the SuFEx reaction for efficient postpolymerization functionalization is demonstrated.

One-Pot Multicomponent Synthesis of Glycopolymers through a Combination of Host-Guest Interaction, Thiol-ene, and Copper-Catalyzed Click Reaction in Water.

There is a common phenomenon that the heterogeneity of natural oligosaccharides contains various sugar units, which can be used to enhance affinity and selectivity toward a specific receptor, so the synthesis of heterogeneous glycopolymers is always an important issue in the glycopolymer field. Herein, this study conducts a one-pot method to prepare polyrotaxane-based heteroglycopolymers anchored with different sugar units and fluorescent moieties via the combination of host-guest interaction, thiol-ene, and copper-catalyzed click chemistry in water. Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, gel permeation chromatography, X-ray diffraction, and Ellman's assay test are used in the paper to characterize the compounds. Quartz crystal microbalance-dissipation (QCD-D) experiments and bacterial adhesion assay are utilized to study the interactions of polyrotaxane-based heteroglycopolymers with Con A and Escherichia coli. The results reveal that polyrotaxanes (PRs) with mannose and glucose present better specificity toward Con A and E. coli than PRs with glucose due to synergistic effects.

Antibacterial surfaces based on poly(cationic liquid) brushes: switchability between killing and releasing via anion counterion switching.

The development of a smart antibacterial surface that can both kill attached live bacteria and release dead bacteria is reported. The surface consists of counterion-responsive poly(cationic liquid) brushes of poly(1-(2-methacryloyloxyhexyl)-3-methylimidazolium bromide) (PIL(Br)), the properties of which can be switched repeatedly between bacterial killing and bacterial release. Upon counter-anion exchange of PIL(Br) chains using lithium bis(trifluoromethanesulfonyl) amide (LiTf2N) to yield PIL(Tf2N), the wettability of the surface changes from hydrophilic (water contact angle ∼52°) to hydrophobic (∼97°). The PIL(Br) chains adopt an extended conformation with bactericidal properties. Counter-anion switching to PIL(Tf2N) gives a collapsed chain conformation allowing the release of killed bacteria. The switchable killing and releasing actions of the surface were maintained over three cycles. Thus it is concluded that PIL(Br) layers provide a viable approach for the fabrication of "smart" antibacterial surfaces.