Polymer Brush Coatings Research Articles

Effect of Surface Charges in Polymer Coatings on Antifouling Performance in Marine Environments with Sediment.

The antifouling efficacy of hydrophilic polymer coatings is closely related to their surface charge. Many biological foulants such as mammalian cells and marine microalgae possess a negative surface charge, discouraging the use of positively charged polymer coatings for antifouling purposes. Instead, electrically neutral yet hydrophilic polymers have been widely employed, leveraging hydration layers to create a barrier against fouling. However, challenges arise in marine environments where both living marine organisms and sediments can adhere to solid surfaces, rendering previous findings less directly applicable. This study investigates the impact of a polymer coating surface charge on marine antifouling properties. Polymer brushes with various charges are applied to solid substrates, and the adhesion behavior of marine diatoms is assessed under both marine sediment-free and marine sediment conditions. The results underscore the effectiveness of negatively charged polymer brush coatings in marine antifouling, regardless of sediment presence.

Roughness-Mediated SI-Fe0CRP for Polymer Brush Engineering toward Superior Drag Reduction.

Surface-initiated iron(0)-mediated controlled radical polymerization (SI-Fe0CRP) with low toxicity and excellent biocompatibility is promising for the fabrication of biofunctional polymer coatings. However, the development of Fe(0)-based catalysts remains limited by the lower dissociation activity of the Fe(0) surface in comparison to Cu(0). Here, we found that, by simply polishing the Fe(0) plate surface with sandpaper, the poly(methacryloyloxy)ethyl trimethylammonium chloride brush growth rate has been increased significantly to 3.3 from 0.14 nm min-1 of the pristine Fe(0) plate. The excellent controllability of roughness-mediated SI-Fe0CRP can be demonstrated by customizing multicompartment brushes and triblock brushes. Furthermore, we found that the resulting polymer brush coatings exhibit remarkably low water adhesion (0.097 mN) and an outstanding drag reduction rate of 52% in water. This work provides a promising strategy for regulating the grafting rate of polymer brushes via SI-Fe0CRP for biocompatible marine drag reduction coatings.

Photoactive polymer coatings for antibacterial applications

Because bacteria can readily induce illnesses in the human body, research into new bactericidal approaches remains relevant to the global community. Photoactive materials (e.g., photocatalysts) provide an environmentally-friendly method for killing bacteria with light. By means of light-mediated reactive oxygen generation, photocatalysts are capable of disrupting bacterial membranes. Much research on antibacterial surfaces has focused on planar substrates or physisorbed coatings, which often provide small active surface areas and limited surface-to-volume ratios, and thereby create a need for new design strategies to incorporate photocatalysts onto more scalable supports. To this end, this contribution describes the synthesis of particle-tethered polymer brush coatings, crosslinked with the organic photocatalyst tetrakis(4-carboxyphenyl)porphyrin (TCPP). Successful engineering on SiO2 surfaces was confirmed using X-ray photoelectron spectroscopy, tensiometry, and ellipsometry. Singlet oxygen (1O2) generation was confirmed through dimethyl sulfoxide oxidation experiments under visible (blue) light and bactericidal activity against Escherichia coli was verified through live/dead assays and cell viability tests.

Creating Anti‐Biofouling Surfaces by Degradable Main‐chain Polyphosphoester Polymer Brushes

AbstractThe implementation of polymer brush coatings has proven crucial in biomedical and biotechnological applications for controlling biological interactions. Despite the extensive research and use of synthetic polymer coatings, concerns regarding their long‐term non‐biodegradability have arisen. This issue is significant as non‐degradable polymers can lead to complications such as inflammatory responses and bioaccumulation, highlighting the need for polymers that degrade in a controlled manner. To address this, polyphosphonate brushes are synthesized as anti‐biofouling coatings on silicon surfaces via controlled surface‐initiated organocatalytic ring‐opening polymerization (SI‐ROP) of cyclic phospholanes. 2‐Ethyl‐2‐oxo‐1,3,2‐dioxaphospholane and 2‐hexyl‐2‐oxo‐1,3,2‐dioxaphospholane are chosen as the monomers to prepare hydrophilic and hydrophobic brushes with thicknesses up to 55 nm, with a proven degradability in aqueous media. In addition, protein adsorption, bacterial adhesion, and biofilm formation are investigated as a function of the polyphosphonate side chain. Compared to non‐coated surfaces and polyester brushes, hydrophilic poly(2‐ethyl‐2‐oxo‐1,3,2‐dioxaphospholane) brushes have an enhanced resistance toward fouling of albumin, fibrinogen, and diluted human serum proteins, as well as toward Escherichia coli and Staphylococcus aureus bacteria. The stability and anti‐biofouling performance of hydrophilic polyphosphonate brushes position them as an attractive option as degradable materials for anti‐biofouling matrices on medical devices and/or lubricious coatings for artificial implant technologies.

Durable, Ultrathin, and Antifouling Polymer Brush Coating for Efficient Condensation Heat Transfer.

Heat exchangers are made of metals because of their high heat conductivity and mechanical stability. Metal surfaces are inherently hydrophilic, leading to inefficient filmwise condensation. It is still a challenge to coat these metal surfaces with a durable, robust, and thin hydrophobic layer, which is required for efficient dropwise condensation. Here, we report the nonstructured and ultrathin (∼6 nm) polydimethylsiloxane (PDMS) brushes on copper that sustain high-performing dropwise condensation in high supersaturation. Due to the flexible hydrophobic siloxane polymer chains, the coating has low resistance to drop sliding and excellent chemical stability. The PDMS brushes can sustain dropwise condensation for up to ∼8 h during exposure to 111 °C saturated steam flowing at 3 m·s-1, with a 5-7 times higher heat transfer coefficient compared to filmwise condensation. The surface is self-cleaning and can reduce the level of bacterial attachment by 99%. This low-cost, facile, fluorine-free, and scalable method is suitable for a great variety of heat transfer applications.

Biomaterials coated with zwitterionic polymer brush demonstrated significant resistance to bacterial adhesion and biofilm formation in comparison to brush coatings incorporated with antibiotics

A critical problem with the use of biomaterial implants is associated with bacterial adhesion on the surface of implants and in turn the biofilm formation. Among different strategies that have been reported to resolve this dilemma, surface design combined with both antiadhesive and antimicrobial properties has proven to be highly effective. Physiochemical properties of polymer brush coatings possess non-adhesive capability against bacterial adhesion and create a niche for further functionalization. The current study aims to evaluate the effect of antibiotics incorporated into the polymer brush on bacterial adhesion and biofilm formation. Brushes made of zwitterionic polymers were synthesized, functionalized with vancomycin via both physical and chemical conjugation, and grafted onto the silicon rubber surfaces. Antibacterial and antiadhesive measurements of designed coated biomaterials were mediated through the use of a parallel plate flow chamber against biofilm growth developed by Staphylococcus aureus and Escherichia coli over a period of 24 h. The analysis of biofilm growth on designed coated biomaterials showed that the pristine coated zwitterionic brushes are significantly resistant to bacterial adhesion and biofilm formation but not in the polymer brush coating incorporated with antibiotics.

An Antimicrobial Polymer Brush Coating to Fabricate High-Performance, Durable, Self-Sterilization, and Recyclable Face Masks

An Antimicrobial Polymer Brush Coating to Fabricate High-Performance, Durable, Self-Sterilization, and Recyclable Face Masks

Nature-inspired surface for simultaneously harvesting water and triboelectric energy from ambient humidity using polymer brush coatings

Atmospheric water harvesting provides a promising, sustainable solution for alleviating the ever-growing water and energy crisis. Here, inspired by the Namib desert beetle, a wettability patterned surface was designed to simultaneously harvest water and triboelectric energy from ambient moisture. Indium tin oxide (ITO) conductive glass was coated by environmentally friendly perfluoropolyether (PFPE) polymer brushes to obtain a hydrophobic surface, decorated by hydrophilic patterns. The PFPE brushes enabled the droplet to slide down and served as the tribonegative material. The water and triboelectric energy harvesting performance of the hydrophilic-hydrophobic “patterned water and energy harvesting” (P-WEH) system was then investigated. In this regard, a water collection rate of 703 mg cm-2 h-1 was achieved when the P-WEH was placed within an artificial fog. The influence of pattern size and tilt angle, and their relationship with water droplet volume and speed on the triboelectric output, were measured. The effect of the water harvesting area on the output performance of the P-WEH was investigated. The P-WEH with an area of 100 cm2 and a tilt angle of 60° exhibited a high output current of 8.15 µA and a maximum output power of 3.35 µW. Finally, the P-WEH was integrated into a four-season greenhouse to demonstrate its application in reducing external water-energy consumption. This study presents insights into the design of simultaneous water and energy harvesting systems and may contribute to building a sustainable society.

Oxygen Tolerance during Surface-Initiated Photo-ATRP: Tips and Tricks for Making Brushes under Environmental Conditions.

Achieving tolerance toward oxygen during surface-initiated reversible deactivation radical polymerization (SI-RDRP) holds the potential to translate the fabrication of polymer brush-coatings into upscalable and technologically relevant processes for functionalizing materials. While focusing on surface-initiated photoinduced atom transfer radical polymerization (SI-photoATRP), we demonstrate that a judicious tuning of the composition of reaction mixtures and the adjustment of the polymerization setup enable to maximize the compatibility of this grafting technique toward environmental conditions. Typically, the presence of O2 in the polymerization medium limits the attainable thickness of polymer brushes and causes the occurrence of "edge effects", i.e., areas at the substrates' edges where continuous oxygen diffusion from the surrounding environment inhibits brush growth. However, the concentrations of the Cu-based catalyst and "free" alkyl halide initiator in solution emerge as key parameters to achieve a more efficient consumption of oxygen and yield uniform and thick brushes, even for polymerization mixtures that are more exposed to air. Precise variation of reaction conditions thus allows us to identify those variables that become determinants for making the synthesis of brushes more tolerant toward oxygen, and consequently more practical and upscalable.

Arylazopyrazole-Modified Thiolactone Acrylate Copolymer Brushes for Tuneable and Photoresponsive Wettability of Glass Surfaces.

Photoswitches have long been employed in coatings for surfaces and substrates to harness light as a versatile stimulus to induce responsive behavior. We previously demonstrated the viability of arylazopyrazole (AAP) as a photoswitch in self-assembled monolayers (SAMs) on silicon and glass surfaces for photoresponsive wetting applications. We now aim to transfer the excellent photophysical properties of AAPs to polymer brush coatings. Compared to SAMs, polymer brushes offer enhanced stability and an increase of the thickness and density of the functional organic layer. In this work, we present thiolactone acrylate copolymer brushes which can be post-modified with AAP amines as well as hydrophobic acrylates, making use of the unique chemistry of the thiolactones. This strategy enables photoresponsive wetting with a tuneable range of contact angle change on glass substrates. We show the successful synthesis of thiolactone hydroxyethyl acrylate copolymer brushes by means of surface-initiated atom-transfer radical polymerization with the option to either prepare homogeneous brushes or to prepare micrometer-sized brush patterns by microcontact printing. The polymer brushes were analyzed by atomic force microscopy, time-of-flight secondary ion spectrometry, and X-ray photoelectron spectroscopy. Photoresponsive behavior imparted to the brushes by means of post-modification with AAP is monitored by UV/vis spectroscopy, and wetting behavior of homogeneous brushes is measured by static and dynamic contact angle measurements. The brushes show an average change in static contact angle of around 13° between E and Z isomer of the AAP photoswitch for at least five cycles, while the range of contact angle change can be fine-tuned between 53.5°/66.5° (E/Z) and 81.5°/94.8° (E/Z) by post-modification with hydrophobic acrylates.

Antiviral Polymer Brushes by Visible-Light-Induced, Oxygen-Tolerant Covalent Surface Coating

This work presents a novel route for creating metal-free antiviral coatings based on polymer brushes synthesized by surface-initiated photoinduced electron transfer-reversible addition-fragmentation chain transfer (SI-PET-RAFT) polymerization, applying eosin Y as a photocatalyst, water as a solvent, and visible light as a driving force. The polymer brushes were synthesized using N-[3-(decyldimethyl)-aminopropyl] methacrylamide bromide and carboxybetaine methacrylamide monomers. The chemical composition, thickness, roughness, and wettability of the resulting polymer brush coatings were characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), water contact angle measurements, and ellipsometry. The antiviral properties of coatings were investigated by exposure to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and avian influenza viruses, with further measurement of residual viable viral particles. The best performance was obtained with Cu surfaces, with a ca. 20-fold reduction of SARS-Cov-2 and a 50-fold reduction in avian influenza. On the polymer brush-modified surfaces, the number of viable virus particles decreased by about 5-6 times faster for avian flu and about 2-3 times faster for SARS-CoV-2, all compared to unmodified silicon surfaces. Interestingly, no significant differences were obtained between quaternary ammonium brushes and zwitterionic brushes.

Temperature-Responsive Polymer Brush Coatings for Advanced Biomedical Applications.

Modern biomedical technologies predict the application of materials and devices that not only can comply effectively with specific requirements, but also enable remote control of their functions. One of the most prospective materials for these advanced biomedical applications are materials based on temperature-responsive polymer brush coatings (TRPBCs). In this review, methods for the fabrication and characterization of TRPBCs are summarized, and possibilities for their application, as well as the advantages and disadvantages of the TRPBCs, are presented in detail. Special attention is paid to the mechanisms of thermo-responsibility of the TRPBCs. Applications of TRPBCs for temperature-switchable bacteria killing, temperature-controlled protein adsorption, cell culture, and temperature-controlled adhesion/detachment of cells and tissues are considered. The specific criteria required for the desired biomedical applications of TRPBCs are presented and discussed.

Synthetic strategies to enhance the long-term stability of polymer brush coatings.

High-density, end-anchored macromolecules that form so-called polymer brushes are popular components of bio-inspired surface coatings. In a bio-mimetic approach, they have been utilized to reduce friction, repel contamination and control wetting, in particular in the development of biomedical materials. For reliable application of these coatings, it is critical that the performance of these coatings does not degrade in time. Yet, it is well-known that polymer brushes can deteriorate and degraft when exposed to water(-vapor) and this strongly limits the durability of these coatings. In this article, we provide an overview of the current status of research on the stability of polymer brushes. Moreover, we review different synthetic strategies, some of which are bio-inspired by itself, to enhance the long-term stability of these brushes. Based on this overview, we identify open question and issues to be resolved for brushes to be applied as durable bio-inspired surface coatings.

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.

Cellphone enabled point-of-care assessment of breast tumor cytology and molecular HER2 expression from fine-needle aspirates

Management of breast cancer in limited-resource settings is hindered by a lack of low-cost, logistically sustainable approaches toward molecular and cellular diagnostic pathology services that are needed to guide therapy. To address these limitations, we have developed a multimodal cellphone-based platform—the EpiView-D4—that can evaluate both cellular morphology and molecular expression of clinically relevant biomarkers directly from fine-needle aspiration (FNA) of breast tissue specimens within 1 h. The EpiView-D4 is comprised of two components: (1) an immunodiagnostic chip built upon a “non-fouling” polymer brush-coating (the “D4”) which quantifies expression of protein biomarkers directly from crude cell lysates, and (2) a custom cellphone-based optical microscope (“EpiView”) designed for imaging cytology preparations and D4 assay readout. As a proof-of-concept, we used the EpiView-D4 for assessment of human epidermal growth factor receptor-2 (HER2) expression and validated the performance using cancer cell lines, animal models, and human tissue specimens. We found that FNA cytology specimens (prepared in less than 5 min with rapid staining kits) imaged by the EpiView-D4 were adequate for assessment of lesional cellularity and tumor content. We also found our device could reliably distinguish between HER2 expression levels across multiple different cell lines and animal xenografts. In a pilot study with human tissue (n = 19), we were able to accurately categorize HER2-negative and HER2-positve tumors from FNA specimens. Taken together, the EpiView-D4 offers a promising alternative to invasive—and often unavailable—pathology services and may enable the democratization of effective breast cancer management in limited-resource settings.

Grafting Density-Dependent Phase Transition Mechanism of Thermoresponsive Poly(glycidyl ether) Brushes: A Comprehensive QCM-D Study.

Thermoresponsive coatings that exhibit "switchable" protein- and cell-adhesive properties are frequently used for the fabrication of cell sheets. Among other architectures, polymer brush coatings have shown to be especially viable due to their distinct phase transition behavior, which can be tailored via a manifold of adjustable brush characteristics, such as the (co)monomer composition, polymer chain length, and grafting density. Brush coatings based on poly(glycidyl ether)s (PGEs) have shown to efficiently mediate cell sheet fabrication when tethered to various tissue culture substrates. Herein, we report the phase transition of self-assembled PGE brushes with respect to polymer molecular weight (M: 10 and 22 kDa) and grafting density (0.07-0.5 chains nm-2) on gold model substrates studied by quasi-static QCM-D temperature ramp measurements. The brush grafting density can be tuned via the applied grafting conditions, and all brushes investigated feature broad phase transition regimes (ΔT ∼15°C) with volume phase transition temperatures (VPTTs) close to the cloud point temperatures (CPTs) of the PGEs in solution. We further demonstrate that brush coatings with a low grafting density (0.07-0.12 chains nm-2) exhibit a continuous brush-to-mushroom transition, whereas brushes with medium grafting densities (0.3-0.5 chains nm-2) undergo a brush-to-brush transition comprising vertical phase separation during the phase transition progress. These insights help to understand the transition behavior of thin, thermoresponsive brushes prepared via grafting-to strategies and contribute to their rational design for improved functional surfaces.

Drug Release from Thermo-Responsive Polymer Brush Coatings to Control Bacterial Colonization and Biofilm Growth on Titanium Implants.

Despite decades of biomedical advances, the colonization of implant devices with bacterial biofilms is still a leading cause of implant failure. Clearly, new strategies and materials that suppress both initial and later stage bacterial colonization are required in this context. Ideal would be the implementation of a bactericidal functionality in the implants that is temporally and spatially triggered in an autonomous fashion at the infection site. Herein, the fabrication and validation of functional titanium-based implants with triggered antibiotic release function afforded via an intelligent polymer coating is reported. In particular, thermo-responsive poly(di(ethylene glycol) methyl ether methacrylate) (PDEGMA) brushes on titanium implants synthesized via a surface-initiated atom transfer radical polymerization with activators regenerated through the electron transfer technique (ARGET ATRP) allows for a controlled and thermally triggered release of the antibiotic levofloxacin at the wound site. Antibiotic loaded brushes are investigated as a function of thickness, loading capacity for antibiotics, and temperature. At temperatures of the infection site >37°Cthelower critical solution temperature behavior of the brushes afforded the triggered release. Hence, in addition to the known antifouling effects, the PDEGMA coating ensured enhanced bactericidal effects, as demonstrated in initial in vivo tests with rodents infected with Staphylococcus aureus.

Synthesis of Polymer Brushes Via SI-PET-RAFT for Photodynamic Inactivation of Bacteria.

Biofilms are a persistent issue in healthcare and industry. Once formed, the eradication of biofilms is challenging as the extracellular polymeric matrix provides protection against harsh environmental conditions and physically enhances resistance to antimicrobials. The fabrication of polymer brush coatings provides a versatile approach to modify the surface to resist the formation of biofilms. Herein, the authors report a facile synthetic route for the preparation of surface-tethered polymeric brushes with antifouling and visible light activated bactericidal properties using surface-initiated photoinduced electron transfer-reversible addition-fragmentation chain transfer polymerization (SI-PET-RAFT). Bactericidal property via the generation of singlet oxygen, which can be temporally and spatially controlled, is investigated against both Gram-positive and Gram-negative bacteria. In addition, the antibacterial properties of the surface can be recycled. This work paves the way for the preparation of polymer films that can resist and kill bacterial biofilms.

Temperature-responsive and multi-responsive grafted polymer brushes with transitions based on critical solution temperature: synthesis, properties, and applications

Temperature responsivity of polymer brushes may be driven by different mechanisms, from which the lower critical solution temperature (LCST) is the most famous one. The using of the grafted temperature-responsive polymer brushes based on LCST opens numerous opportunities for fabrication of “smart” or responsive surfaces. In this review, we try to join information on thermoresponsive and multi-responsive grafted polymer brushes with transitions based on LCST. The overwhelming majority of previously reported temperature-responsive grafted polymer brush coatings were based on PNIPAM and POEGMA, despite the fact that a wide range of other thermoresponsive polymers demonstrate similar properties. In this work, we not only give the detailed account for fabrication, mechanisms of action, and applications of well-known PNIPAM- and POEGMA-grafted brush coatings but also point to other types of thermoresponsive grafted brushes.

Polymer Brush Coating and Adhesion Technology at Scale.

Creating strong joints between dissimilar materials for high-performance hybrid products places high demands on modern adhesives. Traditionally, adhesion relies on the compatibility between surfaces, often requiring the use of primers and thick bonding layers to achieve stable joints. The coatings of polymer brushes enable the compatibilization of material surfaces through precise control over surface chemistry, facilitating strong adhesion through a nanometer-thin layer. Here, we give a detailed account of our research on adhesion promoted by polymer brushes along with examples from industrial applications. We discuss two fundamentally different adhesive mechanisms of polymer brushes, namely (1) physical bonding via entanglement and (2) chemical bonding. The former mechanism is demonstrated by e.g., the strong bonding between poly(methyl methacrylate) (PMMA) brush coated stainless steel and bulk PMMA, while the latter is shown by e.g., the improved adhesion between silicone and titanium substrates, functionalized by a hydrosilane-modified poly(hydroxyethyl methacrylate) (PHEMA) brush. This review establishes that the clever design of polymer brushes can facilitate strong bonding between metals and various polymer materials or compatibilize fillers or nanoparticles with otherwise incompatible polymeric matrices. To realize the full potential of polymer brush functionalized materials, we discuss the progress in the synthesis of polymer brushes under ambient and scalable industrial conditions, and present recent developments in atom transfer radical polymerization for the large-scale production of brush-modified materials.