Surface-initiated Polymerization of Azidopropyl Methacrylate and its Film Elaboration via Click Chemistry

Clicked into Place: Biomimetic Copolymer Adhesive for Covalent Conjugation of Functionalities

Polydopamines (PDA) are a popular class of materials and promising candidates as adhesives for new fastening techniques. PDA layers can be formed on a wide range of substrates in various environments. Here, we present a novel method for functionalizing PDA-based copolymer films by using click chemistry. These copolymers adhere strongly to various surfaces and simultaneously have active groups that allow the attachment of functional groups. We discuss the coupling of two types of chitosan and a rhodamine B dye molecule to the alkyne groups of the copolymers by employing click reactions. Azidopropyl methacrylate (AzMA), methyl methacrylate (MMA), and dopamine methacrylamide (DOMA) are copolymerized and codeposited with (3-aminopropyl)triethoxysilane on silicon wafers, polyethylene (PE), and polytetrafluoroethylene (PTFE). AzMA provides the surfaces with azides for use in click reactions, MMA functions to control the polymer as a nonfunctional diluent, whereas DOMA provides adhesion, as well as cross-linking groups. After codeposition, the dyes are grafted to the copolymer to illustrate the ability of the films to link functional groups covalently. Fourier transform infrared spectroscopy confirms the successful click reaction in solution, and atomic force microscopy shows the surface morphologies following grafting. Fluorescence microscopy provides evidence of successful grafting. As an example of a possible application, layers exhibiting antifouling properties are prepared. Chitosan grafted to PE is tested for antifouling performance. These functionalized layers show nonspecific inhibition of protein adsorption. We find that chitosan can lower the adsorption of fluorescein-labeled bovine serum albumin (BSA) protein by more than 90% for the best performing fluorescein-labeled BSA protein and by more than 90% for the best-performing layer. These results demonstrate the viability of our PDA-based copolymers for surface functionalization through click chemistry grafting at challenging adhesion to surfaces.

Preparation of Protein A Membranes Using Propargyl Methacrylate-Based Copolymers and Copper-Catalyzed Alkyne-Azide Click Chemistry

The development of convective technologies for antibody purification is of interest to the bioprocessing industries. This study developed a Protein A membrane using a combination of graft polymerization and copper(I)-catalyzed alkyne-azide click chemistry. Regenerated cellulose supports were functionalized via surface-initiated copolymerization of propargyl methacrylate (PgMA) and poly(ethylene glycol) methyl ether methacrylate (PEGMEMA300), followed by a reaction with azide-functionalized Protein A ligand. The polymer-modified membranes were characterized using attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR), gravimetric analysis, and permeability measurements. Copolymer composition was determined using the Mayo-Lewis equation. Membranes clicked with azide-conjugated Protein A were evaluated by measuring static and dynamic binding (DBC10) capacities for human immunoglobulin G (hIgG). Copolymer composition and degree of grafting were found to affect maximum static binding capacities, with values ranging from 5 to 16 mg/mL. DBC10 values did not vary with flow rate, as expected of membrane adsorbers.

Photoinduced micropatterning on biodegradable aliphatic polyester surfaces for anchoring dual brushes and its application in bacteria and cell patterning

In view of intrinsic challenges encountered in surface patterning on actual biomaterials such as the ones based on biodegradable polymers, we have demonstrated an innovative strategy to create micro-patterns on the surface of tartaric acid based aliphatic polyester P (poly(hexamethylene 2,3-O-isoprpylidentartarate)) without significant loss of its molecular weight. Around 10 wt% PAG (photoacid generator, 2-(4-methoxystyryl)-4,6-bis(trichloromethyl)-1,3,5-triazine) was purposefully encapsulated in a polyester matrix comprising of P and PLA (polylactide) at a ratio of 5 : 95. With the help of a photomask, selective areas of the matrix were exposed to UV radiation at 395 nm for 25 min to trigger the acid release from PAG entrapped unmasked areas for generating hydroxyl functionality that was later converted to an ATRP (atom transfer radical polymerization) initiating moiety on the irradiated domain of P. In subsequent steps, spatio-selective surface modification by surface initiated ATRP was carried out to generate an alternate pattern of polyPEGMA (poly(ethylene glycol)methyl ether methacrylate) and polyDMAPS (poly(3-dimethyl-(methacryloyloxyethyl)ammonium propane sulfonate)) brushes on the matrix. The patterned surface modified with dual brushes was found to be antifouling in nature (rejection of >97% of proteins). Strikingly, an alternate pattern of live bacterial cells (E. coli and S. aureus) was evident and a relatively high population of bacteria was found on the polyPEGMA brush modified domain. However, a complete reverse pattern was visible in the case of L929 mouse fibroblast cells, i.e., cells were found to predominantly adhere to and proliferate on the zwitterionic brush modified surface. An attempt was made to discuss a plausible mechanism of selective cell adhesion on the zwitterionic brush domain. This novel strategy employed on the biodegradable polymer surface provides an easy and straightforward way to micro-pattern various cells, bacteria, etc. on biodegradable substrates which hold great potential to function as biochips, diagnostics, bacteria/cell microarrays, etc.

Advances in design of polymer brush functionalized inorganic nanomaterials and their applications in biomedical arena

Grafting of polymer brush (assembly of polymer chains tethered to the substrate by one end) is emerging as one of the most viable approach to alter the surface of inorganic nanomaterials. Inorganic nanomaterials despite their intrinsic functional superiority, their applications remain restricted due to their incompatibility with organic or biological moieties vis-à-vis agglomeration issues. To overcome such a shortcoming, polymer brush modified surfaces of inorganic nanomaterials have lately proved to be of immense potential. For example, polymer brush-modified inorganic nanomaterials can act as efficient substrates/platforms in biomedical applications, ranging from drug-delivery to protein-array due to their integrated advantages such as amphiphilicity, stimuli responsiveness, enhanced biocompatibility, and so on. In this review, the current state of the art related to polymer brush-modified inorganic nanomaterials focusing, not only, on their synthetic strategies and applications in biomedical field but also the architectural influence of polymer brushes on the responsiveness properties of modified nanomaterials have comprehensively been discussed and its associated future perspective is also presented. This article is categorized under: Diagnostic Tools > In Vivo Nanodiagnostics and Imaging Therapeutic Approaches and Drug Discovery > Emerging Technologies Nanotechnology Approaches to Biology > Nanoscale Systems in Biology.

“Clickable” Polymer Brush Interfaces: Tailoring Monovalent to Multivalent Ligand Display for Protein Immobilization and Sensing

Facile and effective functionalization of the interface of polymer-coated surfaces allows one to dictate the interaction of the underlying material with the chemical and biological analytes in its environment. Herein, we outline a modular approach that would enable installing a variety of “clickable” handles onto the surface of polymer brushes, enabling facile conjugation of various ligands to obtain functional interfaces. To this end, hydrophilic anti-biofouling poly(ethylene glycol)-based polymer brushes are fabricated on glass-like silicon oxide surfaces using reversible addition–fragmentation chain transfer (RAFT) polymerization. The dithioester group at the chain-end of the polymer brushes enabled the installation of azide, maleimide, and terminal alkene functional groups, using a post-polymerization radical exchange reaction with appropriately functionalized azo-containing molecules. Thus, modified polymer brushes underwent facile conjugation of alkyne or thiol-containing dyes and ligands using alkyne–azide cycloaddition, Michael addition, and radical thiol–ene conjugation, respectively. Moreover, we demonstrate that the radical exchange approach also enables the installation of multivalent motifs using dendritic azo-containing molecules. Terminal alkene groups containing dendrons amenable to functionalization with thiol-containing molecules using the radical thiol–ene reaction were installed at the interface and subsequently functionalized with mannose ligands to enable sensing of the Concanavalin A lectin.

Cytocompatible, soft and thick brush-modified scaffolds with prolonged antibacterial effect to mitigate wound infections

Biomedical device or implant-associated infections caused by pathogenic bacteria are a major clinical issue, and their prevention and/or treatment remains a challenging task. Infection-resistant antimicrobial coatings with impressive cytocompatibility offer a step towards addressing this problem. Herein, we report a new strategy for constructing highly antibacterial as well as cytocompatible mixed polymer brushes onto the surface of 3D printed scaffold made of biodegradable tartaric acid-based aliphatic polyester blends. The mixed brushes were nothing but a combination of poly(3-dimethyl-(methacryloyloxyethyl) ammonium propane sulfonate) (polyDMAPS) and poly((oligo ethylene glycol) methyl ether methacrylate) (polyPEGMA) with varying chain length (n) of the ethylene glycol unit (n = 1, 6, 11, and 21). Both homo and copolymeric brushes of polyDMAPS with polyPEGMA exhibited antibacterial efficacy against both Gram positive and Gram negative pathogens such as E. coli (Escherichia coli) and S. aureus (Staphylococcus aureus) because of the combined action of bacteriostatic effects originating from strongly hydrated layers present in zwitterionic (polyDMAPS) and hydrophilic (polyPEGMA) copolymer brushes. Interestingly, a mixed polymer brush comprising polyDMAPS and polyPEGMA (ethylene glycol chain unit of 21) at 50/50 ratio provided zero bacterial growth and almost 100% cytocompatibility (tested using L929 mouse fibroblast cells), making the brush-modified biodegradable substrate an excellent choice for an infection-resistant and cytocompatible surface. An attempt was made to understand their extraordinary performance with the help of contact angle, surface charge analysis and nanoindentation study, which revealed the formation of a hydrophilic, almost neutral, very soft surface (99.99% reduction in hardness and modulus) after modification with the mixed brushes. This may completely suppress bacterial adhesion. Animal studies demonstrated that these brush-modified scaffolds are biocompatible and can mitigate wound infections. Overall, this study shows that the fascinating combination of an infection-resistant and cytocompatible surface can be generated on biodegradable polymeric surfaces by modulating the surface hardness, flexibility and hydrophilicity by selecting appropriate functionality of the copolymeric brushes grafted onto them, making them ideal non-leaching, anti-infective, hemocompatible and cytocompatible coatings for biodegradable implants.

Compositionally Anisotropic Colloidal Surfactant Decorated with Dual Metallic Nanoparticles as a Pickering Emulsion Stabilizer and Their Application in Catalysis

We aim to introduce compositionally anisotropic Janus particles, hemispheres of which was modified by hydrophilic poly(2-dimethyl amino ethyl methacrylate) [poly(DMAEMA)] brushes to display amphiphilic surfactant-type characteristics. Acquired by the electrohydrodynamic co-jetting technique, these colloidal surfactants were employed to stabilize octanol/water-based Pickering emulsion, which shows prolonged stability for more than 4 months. To explore their potential as the interfacial catalyst, iron(0) nanoparticles were incorporated in one hemisphere during electrojetting, whereas gold nanoparticles (GNPs) were patched onto the surface of the other hemisphere, which was previously modified by the poly(DMAEMA) brush. Ultimately, simultaneous rapid reduction (100% conversion in 1 min) of p-nitrophenol or methyl orange (MO) by GNPs in the aqueous phase and dechlorination of trichloroethylene (a hazardous chlorinated solvent waste) present in the octanol phase were accomplished at the organic-water interface stabilized by the Janus particles decorated by dual metallic nanoparticles. In addition, facile recovery and recyclability of the catalyst were also achieved. The novel colloidal surfactant demonstrated in this study may open up a new avenue to accomplish catalysis of several organic reactions occurring at the water-oil interface.

Protein Patterning on Microtextured Polymeric Nano-brush Templates Obtained By Nanosecond Fibre Laser

Micropatterned polymer brushes have attracted attention in several biomedical areas, i.e., tissue engineering, protein microarray, biosensors etc., for precise arrangement of biomolecules. Herein, we report a facile and scalable approach to create microtextured polymer brushes with the ability to generate different type of protein patterns. Nanosecond fibre laser was exploited to generate micropatterns on polyPEGMA (poly(ethylene glycol) methacrylate) brush modified Ti alloy substrate. Surface initiated atom transfer radical polymerisation was employed to grow PolyPEGMA brush (11-87 nm thick) on Ti alloy surface immobilized with initiator having an initiator density (σ*) of 1.5 initiators/nm² . Polymer brushes were then selectively laser ablated and their presence on non-textured area was confirmed by atomic force microscopy, fluorescence microscopy and X-ray photoelectron spectroscopy. Spatial orientation of biomolecules was first achieved by non-specific protein adsorption on areas ablated by the laser, via physisorption. Further, patterned brushes of polyPEGMA were modified to activated ester that gave rise to protein conjugation specifically on non-laser ablated brush areas. Moreover, the laser ablated brush modified patterned template was also successfully utilized for generating alternate patterns of bacteria. This promising technique can be further extended to create interesting patterns of several biomolecules which are of great interest to biomedical research community. This article is protected by copyright. All rights reserved.

Molecular Dynamics of Functional Azide-Containing Acrylic Films

A report on the syntheses, thermal, mechanical and dielectric characterizations of two novel polymeric acrylic materials with azide groups in their pendant structures is presented. Having the same general structure, these polymers differ in length of oxyethylene units in the pendant chain [-CONH-CH₂CH₂-(O-CH₂CH₂)nN₃], where n is 1 (poly(N-(2-(2-azidoethoxy)ethyl)methacrylamide), PAzMa1) or 2 (poly(N-2-(2-(2-azidoethoxy)ethoxy)ethyl)methacrylamide), PAzMa2), leading with changes in their dynamics. As the thermal decomposition of the azide group is observed above 100 °C, dielectric analysis was carried out in the temperature range of -120 °C to 100 °C. Dielectric spectra of both polymers exhibit in the glassy state two relaxations labelled in increasing order of temperature as γ- and β-processes, respectively. At high temperatures and low frequencies, the spectra are dominated by ohmic conductivity and interfacial polarization effects. Both, dipolar and conductive processes were characterized by using different models. Comparison of the dielectric activity obtained for PAzMa1 and PAzMa2 with those reported for crosslinked poly(2-ethoxyethylmethacrylate) (CEOEMA) was performed. The analysis of the length of oxyethylene pendant chain and the effect of the methacrylate or methacrylamide nature on the dynamic mobility was analysed.

Diels-Alder "Clickable" Polymer Brushes: A Versatile Catalyst-Free Conjugation Platform

Polymeric brushes provide an attractive functional interface for a variety of applications in materials and biomedical sciences. Facile access to functionalized brushes can be realized through effective postpolymerization functionalization of reactive brushes. Over the past decade, efficient chemical transformations based on various "click" reactions have been employed for functionalization of polymeric brushes. This paper reports the first example of utilization of the Diels-Alder cycloaddition reaction based functionalization strategy that allows efficient conjugation of maleimide-containing molecules onto furan-containing polymer brushes under mild and reagent-free conditions. Polymers incorporating furan groups as side chains are "grafted from" silicon oxide surfaces and investigated toward their functionalization. Brushes are fabricated using atom transfer radical polymerization with varying amounts of furfuryl methacrylate to enable control over extent of functionalization, along with a poly(ethylene glycol) chain containing methacrylate as a comonomer to impart hydrophilic and antibiofouling characteristics. Functionalization of these reactive brushes were investigated through the immobilization of a model compound N-ethylmaleimide, a fluorescent dye BODIPY-maleimide, and a maleimide-containing biotin based ligand to direct the immobilization of streptavidin-coated quantum dots.

Surface-Initiated Controlled Radical Polymerization: State-of-the-Art, Opportunities, and Challenges in Surface and Interface Engineering with Polymer Brushes

The generation of polymer brushes by surface-initiated controlled radical polymerization (SI-CRP) techniques has become a powerful approach to tailor the chemical and physical properties of interfaces and has given rise to great advances in surface and interface engineering. Polymer brushes are defined as thin polymer films in which the individual polymer chains are tethered by one chain end to a solid interface. Significant advances have been made over the past years in the field of polymer brushes. This includes novel developments in SI-CRP, as well as the emergence of novel applications such as catalysis, electronics, nanomaterial synthesis and biosensing. Additionally, polymer brushes prepared via SI-CRP have been utilized to modify the surface of novel substrates such as natural fibers, polymer nanofibers, mesoporous materials, graphene, viruses and protein nanoparticles. The last years have also seen exciting advances in the chemical and physical characterization of polymer brushes, as well as an ever increasing set of computational and simulation tools that allow understanding and predictions of these surface-grafted polymer architectures. The aim of this contribution is to provide a comprehensive review that critically assesses recent advances in the field and highlights the opportunities and challenges for future work.

Clickable Polymeric Coating for Glycan Microarrays

The interaction of carbohydrates with a variety of biological targets, including antibodies, proteins, viruses, and cells are of utmost importance in many aspects of biology. Glycan microarrays are increasingly used to determine the binding specificity of glycan-binding proteins. In this study, a novel microarray support is reported for the fabrication of glycan arrays that combines the higher sensitivity of a layered Si-SiO₂ surface with a novel polymeric coating easily modifiable by subsequent click reaction. The alkyne-containing copolymer, adsorbed from an aqueous solution, produces a coating by a single step procedure and serves as a soft, tridimensional support for the oriented immobilization of carbohydrates via azide/alkyne Cu (I) catalyzed "click" reaction. The advantages of a functional 3D polymer coating making use of a click chemistry immobilization are combined with the high fluorescence sensitivity and superior signal-to-noise ratio of a Si-SiO₂ substrate. The proposed approach enables the attachment of complex sugars on a silicon oxide surface by a method that does not require skilled personnel and chemistry laboratories.

Well-controlled ATRP of 2-(2-(2-Azidoethyoxy)ethoxy)ethyl Methacrylate for High-density Click Functionalization of Polymers and Metallic Substrates

The combination of atom transfer radical polymerization (ATRP) and click chemistry has created unprecedented opportunities for controlled syntheses of functional polymers. ATRP of azido-bearing methacrylate monomers (e.g. 2-(2-(2-azidoethyoxy)ethoxy)ethyl methacrylate, AzTEGMA), however, proceeded with poor control at commonly adopted temperature of 50 °C, resulting in significant side reactions. By lowering reaction temperature and monomer concentrations, well-defined pAzTEGMA with significantly reduced polydispersity were prepared within a reasonable timeframe. Upon subsequent functionalization of the side chains of pAzTEGMA via Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) click chemistry, functional polymers with number-average molecular weights (Mn) up to 22 kDa with narrow polydispersity (PDI < 1.30) were obtained. Applying the optimized polymerization condition, we also grafted pAzTEGMA brushes from Ti6Al4 substrates by surface-initiated ATRP (SI-ATRP), and effectively functionalized the azide-terminated side chains with hydrophobic and hydrophilic alkynes by CuAAC. The well-controlled ATRP of azido-bearing methacrylates and subsequent facile high-density functionalization of the side chains of the polymethacrylates via CuAAC offers a useful tool for engineering functional polymers or surfaces for diverse applications.