Highly Stable, Protein-Resistant Surfaces via the Layer-by-Layer Assembly of Poly(sulfobetaine methacrylate) and Tannic Acid

Unravelling Surface Modification Strategies for Preventing Medical Device-Induced Thrombosis

The use of biomaterials in implanted medical devices remains hampered by platelet adhesion and blood coagulation. Thrombus formation is a prevalent cause of failure of these blood-contacting devices. Although systemic anticoagulant can be used to support materials and devices with poor blood compatibility, its negative effects such as an increased chance of bleeding, make materials with superior hemocompatibility extremely attractive, especially for long-term applications. This review examines blood-surface interactions, the pathogenesis of clotting on blood-contacting medical devices, popular surface modification techniques, mechanisms of action of anticoagulant coatings, and discusses future directions in biomaterial research for preventing thrombosis. In addition, this paper comprehensively reviews several novel methods that either entirely prevent interaction between material surfaces and blood components or regulate the reaction of the coagulation cascade, thrombocytes, and leukocytes.

Chemically revised conducting polymers with inflammation resistance for intimate bioelectronic electrocoupling

Conducting polymers offer attractive mixed ionic-electronic conductivity, tunable interfacial barrier with metal, tissue matchable softness, and versatile chemical functionalization, making them robust to bridge the gap between brain tissue and electronic circuits. This review focuses on chemically revised conducting polymers, combined with their superior and controllable electrochemical performance, to fabricate long-term bioelectronic implants, addressing chronic immune responses, weak neuron attraction, and long-term electrocommunication instability challenges. Moreover, the promising progress of zwitterionic conducting polymers in bioelectronic implants (≥4 weeks stable implantation) is highlighted, followed by a comment on their current evolution toward selective neural coupling and reimplantable function. Finally, a critical forward look at the future of zwitterionic conducting polymers for in vivo bioelectronic devices is provided.

Robust Neural Interfaces with Photopatternable, Bioadhesive, and Highly Conductive Hydrogels for Stable Chronic Neuromodulation

A robust neural interface with intimate electrical coupling between neural electrodes and neural tissues is critical for stable chronic neuromodulation. The development of bioadhesive hydrogel neural electrodes is a potential approach for tightly fixing the neural electrodes on the epineurium surface to construct a robust neural interface. Herein, we construct a photopatternable, antifouling, conductive (∼6 S cm-1), bioadhesive (interfacial toughness ∼100 J m-2), soft, and elastic (∼290% strain, Young's modulus of 7.25 kPa) hydrogel to establish a robust neural interface for bioelectronics. The UV-sensitive zwitterionic monomer can facilitate the formation of an electrostatic-assembled conductive polymer PEDOT:PSS network, and it can be further photo-cross-linked into elastic polymer network. Such a semi-interpenetrating network endows the hydrogel electrodes with good conductivity. Especially, the photopatternable feature enables the facile microfabrication processes of multifunctional hydrogel (MH) interface with a characteristic size of 50 μm. The MH neural electrodes, which show improved performance of impedance, charge storage capacity, and charge injection capability, can produce effective electrical stimulation with high current density (1 mA cm-2) at ultralow voltages (±25 mV). The MH interface could realize high-efficient electrical communication at the chronic neural interface for stable recording and stimulation of a sciatic nerve in the rat model.

Engineering metal‐phenolic networks for enhancing cancer therapy by tumor microenvironment modulation

The complicated tumor microenvironment (TME) is featured by low pH values, high redox status, and hypoxia, which greatly supports the genesis, development, and metastasis of tumors, leading to drug resistance and clinical failure. Moreover, a lot of immunosuppressive cells infiltrate in such TME, resulting in depressing immunotherapy. Therefore, the development of TME-responsive nanoplatforms has shown great significance in enhancing cancer therapeutics. Metal-phenolic networks (MPNs)-based nanosystems, which self-assemble via coordination of phenolic materials and metal ions, have emerged as excellent TME theranostic nanoplatforms. MPNs have unique properties including fast preparation, tunable morphologies, pH response, and biocompatibility. Besides, functionalization and surface modification can endow MPNs with specific functions for application requirements. Here, the representative engineering strategies of various polyphenols are first introduced, followed by the introduction of the engineering mechanisms of polyphenolic nanosystems, fabrication, and distinct properties of MPNs. Then, their advances in TME modulation are highlighted, such as antiangiogenesis, hypoxia relief, combination therapy sensitization, and immunosuppressive TME reversion. Finally, we will discuss the challenges and future perspectives of MPNs-based nanosystems for enhancing cancer therapy. This article is categorized under: Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

Impact of Membrane Modification and Surface Immobilization Techniques on the Hemocompatibility of Hemodialysis Membranes: A Critical Review

Despite significant research efforts, hemodialysis patients have poor survival rates and low quality of life. Ultrafiltration (UF) membranes are the core of hemodialysis treatment, acting as a barrier for metabolic waste removal and supplying vital nutrients. So, developing a durable and suitable membrane that may be employed for therapeutic purposes is crucial. Surface modificationis a useful solution to boostmembrane characteristics like roughness, charge neutrality, wettability, hemocompatibility, and functionality, which are important in dialysis efficiency. The modification techniques can be classified as follows: (i) physical modification techniques (thermal treatment, polishing and grinding, blending, and coating), (ii) chemical modification (chemical methods, ozone treatment, ultraviolet-induced grafting, plasma treatment, high energy radiation, and enzymatic treatment); and (iii) combination methods (physicochemical). Despite the fact that each strategy has its own set of benefits and drawbacks, all of these methods yielded noteworthy outcomes, even if quantifying the enhanced performance is difficult. A hemodialysis membrane with outstanding hydrophilicity and hemocompatibility can be achieved by employing the right surface modification and immobilization technique. Modified membranes pave the way for more advancement in hemodialysis membrane hemocompatibility. Therefore, this critical review focused on the impact of the modification method used on the hemocompatibility of dialysis membranes while covering some possible modifications and basic research beyond clinical applications.

Tannic acid: a versatile polyphenol for design of biomedical hydrogels

Tannic acid (TA), a natural polyphenol, is a hydrolysable amphiphilic tannin derivative of gallic acid with several galloyl groups in its structure. Tannic acid interacts with various organic, inorganic, hydrophilic, and hydrophobic materials such as proteins and polysaccharides via hydrogen bonding, electrostatic, coordinative bonding, and hydrophobic interactions. Tannic acid has been studied for various biomedical applications as a natural crosslinker with anti-inflammatory, antibacterial, and anticancer activities. In this review, we focus on TA-based hydrogels for biomaterials engineering to help biomaterials scientists and engineers better realize TA's potential in the design and fabrication of novel hydrogel biomaterials. The interactions of TA with various natural or synthetic compounds are deliberated, discussing parameters that affect TA-material interactions thus providing a fundamental set of criteria for utilizing TA in hydrogels for tissue healing and regeneration. The review also discusses the merits and demerits of using TA in developing hydrogels either through direct incorporation in the hydrogel formulation or indirectly via immersing the final product in a TA solution. In general, TA is a natural bioactive molecule with diverse potential for engineering biomedical hydrogels.

Modifying superparamagnetic iron oxide and silica nanoparticles surfaces for efficient (MA)LDI-MS analyses of peptides and proteins

RATIONALE

Surface functionalization is considered to be the foundation for developing nanomaterial applications in matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) analyses. However, the surface properties of nanostructures can influence their interaction with the analyte and consequently the mass data. In the present study, functionalized nanoparticles (NPs) were used for MALDI-MS and laser desorption/ionization mass spectrometry (LDI-MS) experiments in order to evaluate the effect of the surface properties of NPs on tailoring the intensity of mass signals.

METHODS

Regarding the LDI-MS analyses, the surface of superparamagnetic iron oxide nanoparticles (SPIONs) was coated with nitrosonium tetrafluoroborate, citric acid, nitrodopamine, and gallic acid. Additionally, the SPIONs were applied as a matrix to analyze three small peptides. In the MALDI-MS analyses, silica NPs were selected as co-matrix and functionalized with cysteine, sulfobetaine, and amine alkoxysilanes. Then, the silica NPs were utilized as additives in the MALDI-MS samples of four proteins in a mass range between ~2000 and 60,000 Da.

RESULTS

The results of LDI-MS analyses demonstrated more than one order enhancement in the signal intensity of analytes based on the amount of electrostatic interaction and laser energy absorption by the surface ligands. However, those of MALDI-MS experiments indicated a significant signal improvement when achieving the colloidal stability of silica NPs in the matrix solution.

CONCLUSIONS

Based on the results, the surface properties of NPs affected the (MA)LDI-MS analyses indispensably. Finally, the functionalization of SPIONs represented a new model for the future development of NPs with both affinity and enhanced ionization abilities in mass spectrometry.

Recent progress in Tannic Acid-driven antimicrobial/antifouling surface coating strategies

Medical devices and surgical implants are a necessary part of tissue engineering and regenerative medicines. However, the biofouling and microbial colonization on the implant surface continues to be a major...

Facile Polyphenol-Europium Assembly Enabled Functional Poly(l-Lactic Acid) Nanofiber Mats with Enhanced Antioxidation and Angiogenesis for Accelerated Wound Healing

Burns, trauma, surgery and chronic diabetic ulcers are the most common reasons causing skin wounds in clinic. Thus, developing a functional wound dressing has been an imperative issue. Herein, functional wound dressing (poly(l-lactic acid) PLLA-((tanic acid (TA)/europium (Eu))_n ) is fabricated through a facile polyphenol-europium ion assembly to ameliorate wound microenvironment via scavenging excessive reactive oxygen species (ROS) and promoting angiogenesis. The physicochemical characterization indicates that the multicycle assembled TA/Eu is uniformly deposited on PLLA-(TA/Eu)_n nanofiber mats surface. In vitro 2,2-diphenyl-1-picrylhydrazyl (DPPH) antioxidant tests display good antioxidant ability by scavenging more than 75% ROS, and significantly increasing the antioxidant enzyme levels in vivo. Cytocompatibility experiments illustrate that PLLA-(TA/Eu)_n nanofiber mats can promote the adhesion and proliferation of human umbilical vein endothelial cells (HUVECs) and L929 cells. Meanwhile, real-time quantitative polymerase chain reaction (PCR) (RT-qPCR) and western blot assays illustrate that it can stimulate proangiogenesis by elevating the expression of angiogenesis-related genes and proteins. In vivo Sprague-Dawley (SD) rats experiments indicate that PLLA-(TA/Eu)_n nanofiber mats can significantly promote wound healing by improving both angiogenesis and antioxidant activity. Taken together, the functional PLLA-(TA/Eu)_n nanofiber mats can offer significant promise as wound dressing for accelerated wound healing.

Hemocompatibility of polyzwitterion-modified titanium dioxide nanotubes

Titanium dioxide nanotubes (TNTs) have attracted increasing interest as implantable materials due to their many desirable properties. However, their blood compatibility remains an issue. In this paper, TNTs of different diameters were modified with two types of zwitterionic polymers, poly(sulfobetaine methacrylate) (pSBMA) and poly(carboxybetaine methacrylate) (pCBMA), which were grafted onto the TNTs using ARGET-ATRP (activators regenerated by electron transfer atom transfer radical polymerization) method. Both pSBMA and pCBMA brushes coatings were found to greatly reduce adsorption of bovine serum albumin (BSA) and fibrinogen (Fib) onto the TNTs, showing excellent protein resistance. Moreover, the effects of the surface topography on the amount of protein adsorption were largely suppressed by the polyzwitterion coatings. The conformation of the protein adsorbed to the substrates was analyzed at the molecular level by Fourier-transform infrared reflection spectroscopy (FT-IR), which revealed that the BSA adsorbed on the polyzwitterion-modified TNTs adopted significantly different secondary structures from that on the virgin TNTs, whereas the conformation of the adsorbed Fib remained basically the same. The polyzwitterion-modified TNTs were found to be non-hemolytic, and platelet adhesion and activation was significantly reduced, showing excellent blood compatibility.

Functional ferrocene polymer multilayer coatings for implantable medical devices: Biocompatible, antifouling, and ROS-sensitive controlled release of therapeutic drugs

Bacterial infections and the formation of biofilms on the surface of implantable medical devices are critical issues that cause device failure. Implantable medical devices, such as drug delivery technologies, offer promising benefits for targeted and prolonged drug release, but a number of common disadvantages arise that include inadequate release and side effects. Organic film coatings for antifouling and drug delivery are expected to overcome these challenges. Ferrocene polymer-based multifunctional multilayer films were prepared to control the reactive oxygen species (ROS)-responsive release of therapeutic agents while maintaining an antifouling effect and improving biocompatibility. Polymers based on ferrocene and polyethylene glycol were prepared by controlling the molar ratio of carboxylate and amine groups. Layer-by-layer deposition was optimized to achieve the linear growth and self-assembly of dense and stable films. Outstanding anti-biofilm activity (~91% decrease) could be achieved and the films were found to be blood compatible. Importantly, the films effectively incorporated hydrophobic drugs and exhibited dual-responsive drug release at low pH and under ROS conditions at physiological pH. Drug delivery to MCF-7 breast cancer cells was achieved using a Paclitaxel loaded film, which exhibited an anticancer efficacy of 62%. STATEMENT OF SIGNIFICANCE: Healthcare associated infection is caused by the formation of a biofilm by bacteria on the surface of a medical device. In order to solve this, extensive research has been conducted on many coating technologies. Also, a method of chemical treatment by releasing the drug when it enters the body by loading the drug into the coating film is being studied. However, there is still a lack of technology that can achieve both functions of preventing biofilm production and drug delivery. Therefore, in this study, a multilayer thin film that supports drug and inhibits biofilm formation was prepared through Layer-by-Layer coating of a polymer containing PEG to prevent adsorption. As such, it helps the design of multifunctional coatings for implantable medical devices.

Phenolic-enabled nanotechnology: versatile particle engineering for biomedicine

Phenolics are ubiquitous in nature and have gained immense research attention because of their unique physiochemical properties and widespread industrial use. In recent decades, their accessibility, versatile reactivity, and relative biocompatibility have catalysed research in phenolic-enabled nanotechnology (PEN) particularly for biomedical applications which have been a major benefactor of this emergence, as largely demonstrated by polydopamine and polyphenols. Therefore, it is imperative to overveiw the fundamental mechanisms and synthetic strategies of PEN for state-of-the-art biomedical applications and provide a timely and comprehensive summary. In this review, we will focus on the principles and strategies involved in PEN and summarize the use of the PEN synthetic toolkit for particle engineering and the bottom-up synthesis of nanohybrid materials. Specifically, we will discuss the attractive forces between phenolics and complementary structural motifs in confined particle systems to synthesize high-quality products with controllable size, shape, composition, as well as surface chemistry and function. Additionally, phenolic's numerous applications in biosensing, bioimaging, and disease treatment will be highlighted. This review aims to provide guidelines for new scientists in the field and serve as an up-to-date compilation of what has been achieved in this area, while offering expert perspectives on PEN's use in translational research.

Sulfobetaine Methacrylate Polymers of Unconventional Polyzwitterion Architecture and Their Antifouling Properties

Combining high hydrophilicity with charge neutrality, polyzwitterions are intensely explored for their high biocompatibility and low-fouling properties. Recent reports indicated that in addition to charge neutrality, the zwitterion's segmental dipole orientation is an important factor for interacting with the environment. Accordingly, a series of polysulfobetaines with a novel architecture was designed, in which the cationic and anionic groups of the zwitterionic moiety are placed at equal distances from the backbone. They were investigated by in vitro biofouling assays, covering proteins of different charges and model marine organisms. All polyzwitterion coatings reduced the fouling effectively compared to model polymer surfaces of poly(butyl methacrylate), with a nearly equally good performance as the reference polybetaine poly(3-(N-(2-(methacryloyloxy)ethyl)-N,N-dimethylammonio)propanesulfonate). The specific fouling resistance depended on the detailed chemical structure of the polyzwitterions. Still, while clearly affecting the performance, the precise dipole orientation of the sulfobetaine group in the polyzwitterions seems overall to be only of secondary importance for their antifouling behavior.

Hierarchical Surface Inspired by Geminized Cationic Amphiphilic Polymer Brushes for Super-Antibacterial and Self-Cleaning Properties

Pathogenic bacteria adhesion and formation of biofilm on the implant are the most common reasons for healthcare-associated device failure. Cationic amphiphilic polymer brushes containing covalently linked quaternary ammonium salts (QASs) are considered to be the most promising bactericidal materials, but these surfaces still suffer from incomplete bactericidal ability and serious microorganism accumulation. With this in mind, a novel kind of hierarchical surface integrating both geminized cationic amphiphilic antibacterial upper layer and zwitterionic antifouling sublayer has been developed in this study. Measurements of X-ray photoelectron spectroscopy, spectroscopic ellipsometry, atomic force microscopy, water contact angle, and surface ζ-potential were performed to investigate the surface functionalization process. The thicknesses and grafting densities of the pAGC₈ upper blocks have been optimized to avert the mutual interference among different components. The optimal hierarchical surface exhibits an ultrahigh antibacterial activity and a potent self-cleaning functionality against both Staphylococcus aureus and Escherichia coli bacteria, as well as a certain protein repellence ability. Such a novel hierarchical architecture provides innovative guidance for the construction of super-antibacterial and self-cleaning brushes in many biomedical applications.

Polyphenol-Mediated Assembly for Particle Engineering

Polyphenols are naturally occurring compounds that are ubiquitous in plants and display a spectrum of physical, chemical, and biological properties. For example, they are antioxidants, have therapeutic properties, absorb UV radiation, and complex with metal ions. Additionally, polyphenols display high adherence, which has been exploited for assembling nanostructured materials. We previously reviewed the assembly of different phenolic materials and their applications (Angew. Chem. Int. Ed. 2019, 58, 1904-1927); however, there is a need for a summary of the fundamental interactions that govern the assembly, stability, and function of polyphenol-based materials. A detailed understanding of interactions between polyphenols and various other building blocks will facilitate the rational design and assembly of advanced polyphenol particles for specific applications. This Account discusses how different interactions and bonding (i.e., hydrogen, π, hydrophobic, metal coordination, covalent, and electrostatic) can be leveraged to assemble and stabilize polyphenol-based particles for diverse applications. In polyphenol-mediated assembly strategies, the polyphenols typically exert more than one type of stabilizing attractive force. However, one interaction often dominates the assembly process and dictates the physicochemical behavior of the particles, which in turn influences potential applications. This Account is thus divided into sections that each focus on a key interaction with relevant examples of applications to highlight structure-function relationships. For example, metal coordination generally becomes weaker at lower pH, which makes it possible to engineer metal-phenolic materials with a pH-responsive disassembly profile suitable for drug delivery. Engineered particles, such as hollow capsules, mesoporous and core-shell particles, and self-assembled nanoparticles are some of the systems that are covered to highlight how polyphenols interact with other building blocks and therefore make up the major focus of this Account. Some of the applications of these materials exemplified in this Account include drug delivery, catalysis, environmental remediation, and forensics. Finally, a perspective is provided on the current challenges and trends in polyphenol-mediated particle assembly, and viable near-term strategies for further elucidating the interplay of various competing interactions in particle formation are discussed. This Account is also expected to serve as a reference to guide fundamental research and facilitate the rational design of polyphenol-based materials for diverse emerging applications.

Effects of crosslink density in zwitterionic hydrogel coatings on their antifouling performance and susceptibility to silt uptake

Hydrogel coatings effectively reduce the attachment of proteins and organisms in laboratory assays, in particular when made from zwitterionic monomers. In field experiments with multiple species and non-living material, such coatings suffer from adsorption of particulate matter. In this study, the zwitterionic monomer 3-[N-(2-methacryloyloxyethyl)-N,N-dimethylammonio] propanesulfonate (SPE) was copolymerized with increasing amounts of the photo-crosslinker benzophenon-4-yloxyethyl methacrylate (BPEMA) to systematically alter the density of crosslinks between the polymer chains. The effect of increasing crosslink density on the antifouling (AF) performance of the coatings was investigated in laboratory assays and fields tests. In both cases, the AF performance was improved by increasing the crosslinker content. The coatings reduced protein, diatom, and barnacle accumulation, and showed better resistance to biomass accumulation. The findings underline that the marine AF performance of hydrogel coatings does not only depend on the specific chemical structure of the polymers, but also on their physico-chemical properties such as rigidity and swelling.

Effect of the Buffer on the Buildup and Stability of Tannic Acid/Collagen Multilayer Films Applied as Antibacterial Coatings

The deposition of polyelectrolyte multilayers, obtained by the layer-by-layer (LbL) method, is a well-established technology to design biocompatible and antibacterial coatings aimed at preventing implant-associated infections. Several types of LbL films have been reported to exhibit antiadhesive and/or antibacterial (contact-killing or release-killing) properties governed not only by the incorporated compounds but also by their buildup conditions or their postbuildup treatments. Tannic acid (TA), a natural polyphenol, is known to inhibit the growth of several bacterial strains. In this work, we developed TA/collagen (TA/COL) LbL films built in acetate or citrate buffers at pH 4. Surprisingly, the used buffer impacts not only the physicochemical but also the antibacterial properties of the films. When incubated in physiological conditions, both types of TA/COL films released almost the same amount of TA depending on the last layer and showed an antibacterial effect against Staphylococcus aureus only for citrate-built films. Because of their granular topography, TA/COL citrate films exhibited an efficient release-killing effect with no cytotoxicity toward human gingival fibroblasts. Emphasis is put on a comprehensive evaluation of the physicochemical parameters driving the buildup and the antibacterial property of citrate films. Specifically, complexation strengths between TA and COL are different in the presence of the two buffers affecting the LbL deposition. This work constitutes an important step toward the use of polyphenols as an antibacterial agent when incorporated in LbL films.

Zwitterionic Peptide Enhances Protein-Resistant Performance of Hyaluronic Acid-Modified Surfaces

A convenient and efficient approach for the surface modification of antifouling materials is highly desirable in numerous applications like affinity-based biosensors. Herein, we fabricated a hybrid antifouling coating on Au surfaces, with thiolated hyaluronic acid (HA) being chemically adsorbed to Au surfaces by the "graft to" approach, followed by a self-assembly of a smaller zwitterionic peptide named p-EK to obtain HA/p-EK-modified surfaces. The real-time sensorgrams of surface plasmon resonance biosensor manifested the successful modification of HA and p-EK on Au surfaces, indicating that there were some bare Au substrates on the HA-modified surfaces for peptide binding. The obtained HA/p-EK surfaces exhibited high hydrophilicity with a water contact angle of 9°. Quartz crystal microbalance and surface plasmon resonance experiments verified that further grafting the zwitterionic p-EK peptide on HA-modified surfaces could enhance the antifouling performance by one time. The improved protein resistance could be mainly contributed by the modification of the zwitterionic peptide that shields the exposed Au substrates from interacting with protein foulings. This strategy by grafting a smaller zwitterionic peptide might provide a novel way to achieve an enhanced protein-resistant performance of the macromolecular coating obtained by the "graft to" surface modification approach.

Protein adsorption measurements on low fouling and ultralow fouling surfaces: A critical comparison of surface characterization techniques

Ultralow protein fouling behavior is a common target for new high-performance materials. Ultralow fouling is often defined based on the amount of irreversibly adsorbed protein (< 5 ng cm^-2) measured by a surface ensemble averaging method. However, protein adsorption at solid interfaces is a dynamic process involving multiple steps, which may include adsorption, desorption, and irreversible protein denaturation. In order to better optimize the performance of antifouling surfaces, it is imperative to fully understand how proteins interact with surfaces, including kinetics of adsorption and desorption, conformation, stability, and amount of adsorbed proteins. Defining ultralow fouling surfaces based on a measurement at or near the limit of detection of a surface-averaged measurement may not capture all of this behavior. Single-molecule microscopy techniques can resolve individual protein-surface interactions with high temporal and spatial resolution. This information can be used to tune the properties of surfaces to better resist protein adsorption. In this work, we demonstrate how combining surface plasmon resonance, X-ray photoelectron spectroscopy, atomic force microscopy, and single-molecule localization microscopy provides a more complete picture of protein adsorption on low fouling and ultralow fouling polyelectrolyte multilayer and polymer brush surfaces, over different regimes of protein concentration. In this case, comparing the surfaces using surface plasmon resonance alone is insufficient to rank their resistance to protein adsorption. Our results suggest a revision of the accepted definition of ultralow fouling surfaces is timely: with the advent of time-resolved studies of protein adsorption kinetics at the single-molecule level, it is neither necessary nor sufficient to rely on a surface averaging techniques to qualify ultralow fouling surfaces. Since protein adsorption is a dynamic process, understanding how surface properties affect the kinetics of protein adsorption will enable the design of future generations of advanced antifouling materials. STATEMENT OF SIGNIFICANCE: The design of ultralow fouling surfaces is often optimized based on a single surface-averaging technique measuring the amount of irreversibly adsorbed protein. This work provides a critical comparison of alternative techniques for evaluating protein adsorption on low fouling and ultralow fouling surfaces, and demonstrates how additional information about the dynamics of protein-surface interactions at the interface can be obtained by application of single-molecule microscopy. This approach could be used to better elucidate mechanisms of protein resistance and design principles for advanced ultralow fouling materials.

Protein-resistant surface based on zwitterion-functionalized nanoparticles for marine antifouling applications

A functional nanocomposite (PSBMA@VTMO@silica/TA-PEG) coating was successfully developed through a facile deposition method, and was able to effectively block the adhesion of proteins and subsequent biofouling deposition.

Construction of Antifouling Membrane Surfaces through Layer-by-Layer Self-Assembly of Lignosulfonate and Polyethyleneimine

Lignin is the second most abundant and low-cost natural polymer, but its high value-added utilization is still lack of effective and economic ways. In this paper, waste lignosulfonate (LS) was introduced to fabricate antifouling membrane surfaces via layer-by-layer self-assembly with polyethyleneimine (PEI). The LS/PEI multilayers were successfully deposited on the polysulfone (PSf) membrane, as demonstrated by ATR-FTIR, XPS, Zeta potential measurements, AFM, and SEM. Meanwhile, the effect of the number of bilayers was investigated in detail on the composition, morphologies, hydrophilicity, and antifouling performance of the membrane surface. As a result, with the bilayer numbers increase to 5, the PSf membrane shows smooth surface with small roughness, and its water contact angle reduces to 44.1°, indicating the improved hydrophilicity. Accordingly, the modified PSf membrane with 5 LS/PEI bilayers repels the adsorption of protein, resulting in good antifouling performance. This work provides a green, facile, and low-cost strategy to construct antifouling membrane surfaces.

Supramolecular design and applications of polyphenol-based architecture: A review

Polyphenol-based materials are of wide-spread interest because of the unique properties of the polyphenol itself. Tannic acid, contains high level of galloyl groups, could be coordinated to a range of metal ions to generate robust mental ion-TA films on substrate or even forming hollow capsules. These films or capsules can be used in the field of sensing, separation and catalysis, most importantly in drug/nutraceutical delivery, allowing for the high loading efficiency, high mechanical and thermal stability, pH-responsive disassembly and fluorescence behavior. Additionally, such coating could also provide protection of the sensitive molecules and cells. With the numerous carbonyl and phenolic functional groups, TA has also been demonstrated to form strong hydrogen bonded multilayers with various non-ionic polymers. The properties of the hydrogen-bonded system were highly influenced by the chemical structure of the polymers, which will change the behavior of pH-, temperature- or ionic strength-responsive release of the loading molecules. Additionally, the ionization of galloyl phenol group was attributed to the interaction between TA and other ionic polymers by electrostatic interaction. The electrostatic interaction/hydrogen bonding derived TA/polyme$$%r complexes could deposit on glass slides, microcores or even forming hollow capsules, promising in their applicability to nutraceutical encapsulation, delivery and depot. Notably, polyphenols self-polymerizing could also deposit coatings on different substrates without any exogenous additives, while the comprehensive undertanding about the self-polymerizing mechenism remains unclear. This review provides a promising prospect for utilizing polyphenol-based materials to design versatile architecture in different system, used in the field of chemistry and materials science.

Controllable Interfacial Polymerization for Nanofiltration Membrane Performance Improvement by the Polyphenol Interlayer

It is a huge challenge to have a controllable interfacial polymerization in the fabrication process of nanofiltration (NF) membranes. In this work, a polyphenol interlayer consisting of polyethyleneimine (PEI)/tannic acid (TA) was simply assembled on the polysulfone (PSf) substrate to fine-tune the interfacial polymerization process, without additional changes to the typical NF membrane fabrication procedures. In addition, three decisive factors in the interfacial polymerization process were examined, including the diffusion kinetics of fluorescence-labeled piperazine (FITC-PIP), the spreading behavior of the hexane solution containing acyl chloride, and the polyamide layer formation on the porous substrate by in situ Fourier transform infrared (FT-IR) spectroscopy. The experimental results demonstrate that the diffusion kinetics of FITC-PIP is greatly reduced, and the spreading behavior of the hexane solution is also impeded to some extent. Furthermore, in situ FT-IR spectroscopy demonstrates that by the mitigation of this PEI/TA interlayer, the interfacial polymerization process is greatly controlled. Moreover, the as-prepared NF membrane exhibits an increased water permeation flux of 65 L m^-2 h^-1 (at the operation pressure of 0.6 MPa), high Na₂SO₄ rejection of >99%, and excellent long-term structural stability.

Material-Independent Surface Chemistry beyond Polydopamine Coating

Various methods have been developed in surface chemistry to control interface properties of a solid material. A selection rule among surface chemistries is compatibility between a surface functionalization tool and a target material. For example, alkanethiol deposition on noble metal surfaces, widely known as the formation of a self-assembled monolayer (SAM), cannot be performed on oxide material surfaces. One must choose organosilane molecules to functionalize oxide surfaces. Thus, the surface chemistry strictly depends on the properties of the surface. Polydopamine coating is now generally accepted as the first toolbox for functionalization of virtually any material surface. Layer-by-layer (LbL) assembly is a widely used method to modify properties of versatile surfaces, including organic materials, metal oxides, and noble metals, along with polydopamine coating. On flat solid substrates, the two chemistries of polydopamine coating and LbL assembly provide similar levels of surface modifications. However, there are additional distinct features in polydopamine. First, polydopamine coating is effective for two- or three-dimensional porous materials such as metal-organic frameworks (MOFs), synthetic polyolefin membranes, and others because small-sized dopamine (MW = 153.18 u) and its oxidized oligomers are readily attached onto narrow-spaced surfaces without exhibiting steric hindrance. In contrast, polymers used in LbL assembly are slow in diffusion because of steric hindrance due to their high molecular weight. Second, it is applicable to structurally nonflat surfaces showing special wettability such as superhydrophobicity or superoleophobicity. Third, a nonconducting, insulating polydopamine layer can be converted to be a conducting layer by pyrolysis. The product after pyrolysis is a N-doped graphene-like material that is useful for graphene or carbon nanotube-containing composites. Fourth, it is a suitable method for engineering the surface properties of various composite materials. The surface properties of participating components in composite materials can be unified by polydopamine coating with a simple one-step process. Fifth, a polydopamine layer exhibits intrinsic chemical reactivity by the presence of catecholquinone moieties and catechol radical species on surfaces. Nucleophiles such as amine and thiolate spontaneously react with the functionalized layer. Applications of polydopamine coating are exponentially growing and include cell culture/patterning, microfluidics, antimicrobial surfaces, tissue engineering, drug delivery systems, photothermal therapy, immobilization of photocatalysts, Li-ion battery membranes, Li-sulfur battery cathode materials, oil/water separation, water detoxification, organocatalysts, membrane separation technologies, carbonization, and others. In this Account, we describe various polydopamine coating methods and then introduce a number of chemical derivatives of dopamine that will open further development of material-independent surface chemistry.

Protein Adsorption and Coordination-Based End-Tethering of Functional Polymers on Metal-Phenolic Network Films

Metal-phenolic network (MPN) coatings have generated increasing interest owing to their biologically inspired nature, facile fabrication, and near-universal adherence, especially for biomedical applications. However, a key issue in biomedicine is protein fouling, and the adsorption of proteins on tannic acid-based MPNs remains to be comprehensively studied. Herein, we investigate the interaction of specific biomedically relevant proteins in solution (e.g., bovine serum albumin (BSA), immunoglobulin G (IgG), fibrinogen) and complex biological media (serum) using layer-by-layer-assembled tannic acid/Fe^III MPN films. When Fe^III was the outermost layer, galloyl-modified poly(2-ethyl-2-oxazoline) (P(EtOx)-Gal) could be grafted to the films through coordination bonds. Protein fouling and bacterial adhesion were greatly suppressed after functionalization with P(EtOx)-Gal and the mass of adsorbed protein was reduced by 79%. Interestingly, larger proteins adsorbed more on both the MPNs and P(EtOx)-functionalized MPNs. This study provides fundamental information on the interactions of MPNs with single proteins, mixtures of proteins as encountered in serum, and the noncovalent, coordination-based, functionalization of MPN films.

Molecular Design of Zwitterionic Polymer Interfaces: Searching for the Difference

The widespread occurrence of zwitterionic compounds in nature has incited their frequent use in designing biomimetic materials. Therefore, zwitterionic polymers are a thriving field. A particular interest for this particular polymer class has currently focused on their use in establishing neutral, low-fouling surfaces. After highlighting strategies to prepare model zwitterionic surfaces as well as those that are more suitable for practical purposes relying strongly on radical polymerization methods, we present recent efforts to diversify the structure of the hitherto quite limited variety of zwitterionic monomers and of the derived polymers. We identify key structural variables, consider their influence on essential properties such as overall hydrophilicity and long-term stability, and discuss promising targets for the synthesis of new variants.

Low-Fouling Thin Hydrogel Coatings Made of Photo-Cross-Linked Polyzwitterions

Although zwitterionic chemistries are among the most promising materials for producing nonfouling surfaces, their structural diversity has been low until now. Here, we compare the in vitro fouling behavior of a set of four systematically varied sulfa-/sulfobetaine-containing zwitterionic hydrogel coatings against a series of proteins and nonmotile as well as motile marine organisms as model foulers. The coatings are prepared by simultaneous photoinduced cross-linking and surface anchoring to elucidate the effect of the molecular structure of the zwitterionic moieties on their antifouling activity. Analogously prepared coatings of poly(butyl methacrylate) and poly(oligoethylene glycol methacrylate) serve as references. Photoreactive polymers are synthesized by the statistical copolymerization of sulfobetaine or sulfabetaine methacrylates and methacrylamides with a benzophenone derivative of 2-hydroxyethyl methacrylate and are applied as a thin film coating. While keeping the density of the zwitterionic and cross-linker groups constant, the molecular structure of the zwitterionic side chains is varied systematically, as is the arrangement of the ion pairs in the side chain by changing the classical linear geometry to a novel Y-shaped geometry. All of the polyzwitterions strongly reduce fouling compared to poly(butyl methacrylate). Overall, the sulfabetaine polyzwitterion coatings studied matches the high antifouling effectiveness of oligo(ethylene glycol)-based ones used as a control. Nevertheless, performances varied individually for a given pair of polymer and fouler. The case of the polysulfobetaines exemplifies that minor chemical changes in the polymer structure affect the antifouling performance markedly. Accordingly, the antifouling performance of such polymers cannot be correlated simply to the type of zwitterion used (which could be generally ranked as better performing or poorer performing) but is a result of the polymer's precise chemical structure. Our findings underline the need to enlarge the existing structural diversity of polyzwitterions for antifouling purposes to optimize the potential of their chemical structure.

Biologically Functional Ultrathin Films Made of Zwitterionic Block Copolymer Micelles

We report the preparation of ultrathin coatings of zwitterionic block copolymer micelles and a comparison of their protein adsorption, adhesiveness, and antibacterial properties. Zwitterionic block copolymer micelles were obtained through pH-induced self-assembly of poly[3-dimethyl(methacryloyloxyethyl)ammonium propanesulfonate- b-2-(diisopropylamino)ethyl methacrylate] (βPDMA- b-PDPA) at pH 7.5. βPDMA- b-PDPA micelles with zwitterionic βPDMA-corona and pH-responsive PDPA-core were then used as building blocks to prepare layer-by-layer (LbL) assembled multilayer films together with hyaluronic acid (HA), tannic acid (TA), or poly(sodium 4-styrenesulfonate) (PSS). Protein adsorption tests showed that 3-layer βPDMA- b-PDPA micelles/HA films were the most effective to reduce the adhesion of BSA, lysozyme, ferritin, and casein. In contrast, βPDMA- b-PDPA micelles/TA films were the most attractive surfaces for protein adsorption. Bacterial antiadhesive tests against a model Gram-negative bacterium, Escherichia coli, and a model Gram-positive bacterium, Staphylococcus aureus, were in good agreement with the protein adsorption properties of the films. The differences in the antiadhesive properties between these three different film systems are discussed within the context of chemical nature and the functional chemical groups of the polyanions, layer number, and surface morphology of the films. Multilayers were found to lose their antiadhesiveness in the long term. However, by taking advantage of the pH-responsive hydrophobic micellar cores, we show that an antibacterial agent could be loaded into the micelles and multilayers could exhibit antibacterial activity in the long term especially at moderately acidic conditions. In contrast to antiadhesive properties, no significant differences were recorded in the antibacterial properties between the different film types.

Cell-Membrane-Inspired Silicone Interfaces that Mitigate Proinflammatory Macrophage Activation and Bacterial Adhesion

Biofouling on silicone implants causes serious complications such as fibrotic encapsulation, bacterial infection, and implant failure. Here we report the development of antifouling, antibacterial silicones through covalent grafting with a cell-membrane-inspired zwitterionic gel layer composed of 2-methacryolyl phosphorylcholine (MPC). To investigate how substrate properties influence cell adhesion, we cultured human-blood-derived macrophages and Escherichia coli on poly(dimethylsiloxane) (PDMS) and MPC gel surfaces with a range of 0.5-50 kPa in stiffness. Cells attach to glass, tissue culture polystyrene, and PDMS surfaces, but they fail to form stable adhesions on MPC gel surfaces due to their superhydrophilicity and resistance to biofouling. Cytokine secretion assays confirm that MPC gels have a much lower potential to trigger proinflammatory macrophage activation than PDMS. Finally, modification of the PDMS surface with a long-term stable hydrogel layer was achieved by the surface-initiated atom-transfer radical polymerization (SI-ATRP) of MPC and confirmed by the decrease in contact angle from 110 to 20° and the >70% decrease in the attachment of macrophages and bacteria. This study provides new insights into the design of antifouling and antibacterial interfaces to improve the long-term biocompatibility of medical implants.

Molecular self-assembly of copolymer from renewable phenols: new class of antimicrobial ointment base

Ointments are highly viscous forms intended for external applications either medicated or non-medicated means. Formulation of ointment depends upon the base ingredients to measure the viscosity difference. Several limitations of ointment bases has been encountered timely as agglomeration, oil phase ingredients can form lumps, poor dispersion, poor drug delivery efficiency, make stained, immiscible, and difficult to wash off. Therefore, it is necessary to make a new type of ointment bases that can overcome those limitations. This review summarizes a new type of ointment base preparation from the copolymer of renewable phenolic derivatives. The nanohydrogel preparation from these copolymers are especially effortless and highly efficient in drug delivery, exhibited versatile biological activities such as antioxidant, anti-inflammatory and wound healing in addition to antimicrobial property. Molecular self-assembly mechanisms have been addressed for nanogel formulation. The strategy makes a significant value in health-care application and be supposed to come marketed soon.

Multilayer Assembly of Tannic Acid and an Amphiphilic Copolymer Poloxamer 188 on Planar Substrates toward Multifunctional Surfaces with Discrete Microdome-Shaped Features

Tannic acid (TA) is a natural polyphenol compound with a broad spectrum of biological activities, the most notable of which being antioxidation. Poloxamer 188 (P188), a synthetic triblock copolymer of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide), is amphiphilic in nature and best known for its ability to seal structurally damaged cellular membranes. The integration of both substances onto planar substrates could bring a new option for multifunctional coatings that are advantageous for implantable biomedical devices. Here, we demonstrate the feasibility of multilayer assembly of TA/P188 toward such a coating based on hydrogen bonding between phenolic hydroxyls of TA and ether groups of P188, and the unique surface feature it generates. The interactions between these two compounds were studied both in solution and in substrate-supported layer-by-layer assembly. The multilayer assembly process exhibits an exponential growth pattern as characterized by UV-vis spectrophotometry and quartz crystal microbalance with dissipation. Morphologically unique, microdome-shaped surface features emerge and evolve with the number of layers assembled. Such features bring a reservoir function to this coating, as demonstrated by the loading of hydrophobic nile red dye. Furthermore, the presence of TA in the multilayers was revealed by silver nitrate staining, and its antioxidation activity was demonstrated through a 2,2-diphenyl-1-picryl-hydrazyl free-radical scavenging assay.

Polyphenols at interfaces

Polyphenols are important molecules in living organisms, particularly in plants, where they serve as protectants against predators. They are also of fundamental importance in pharmacology for their antioxidant and antibacterial activities. Since a few years polyphenols are also used in surface functionalization mimicking the tannin deposition observed when tea or red wine are in contact with the surface of cups or glasses respectively. The interaction of polyphenols with proteins to yield colloids and of polyphenol with surfaces will be reviewed in this article to provide an overview of such particles and surface functionalization methods in modern surface science. Particular emphasis will be given to biological applications of polyphenols at interfaces.

Dopamine-assisted co-deposition: An emerging and promising strategy for surface modification

Mussel-inspired chemistry based on polydopamine (PDA) deposition has been developed as a facile and universal method for the surface modification of various materials. However, the inherent shortcomings of PDA coatings still impede their practical applications in the development of functional materials. In this review, we introduce the recent progress in the emerging dopamine-assisted co-deposition as a one-step strategy for functionalizing PDA-based coatings, and improving them in the aspects of deposition rate, morphology uniformity, surface wettability and chemical stability. The co-deposition mechanisms are categorized and discussed according to the interactions of dopamine or PDA with the introduced co-component. We also emphasize the influence of these interactions on the properties of the resultant PDA-based coatings. Meanwhile, we conclude the representative potential applications of those dopamine-assisted co-deposited coatings in material science, especially including separation membranes and biomaterials. Finally, some important issues and perspectives for theoretical study and applications are briefly discussed.

Strategies to prevent the occurrence of resistance against antibiotics by using advanced materials

Drug resistance occurrence is a global healthcare concern responsible for the increased morbidity and mortality in hospitals, time of hospitalisation and huge financial loss. The failure of the most antibiotics to kill "superbugs" poses the urgent need to develop innovative strategies aimed at not only controlling bacterial infection but also the spread of resistance. The prevention of pathogen host invasion by inhibiting bacterial virulence and biofilm formation, and the utilisation of bactericidal agents with different mode of action than classic antibiotics are the two most promising new alternative strategies to overcome antibiotic resistance. Based on these novel approaches, researchers are developing different advanced materials (nanoparticles, hydrogels and surface coatings) with novel antimicrobial properties. In this review, we summarise the recent advances in terms of engineered materials to prevent bacteria-resistant infections according to the antimicrobial strategies underlying their design.

Introduction of Nature's Complexity in Engineered Blood-compatible Biomaterials

Biomaterials with excellent blood-compatibility are needed for applications in vascular replacement therapies, such as vascular grafts, heart valves and stents, and in extracorporeal devices such as hemodialysis machines and blood-storage bags. The modification of materials that are being used for blood-contacting devices has advanced from passive surface modifications to the design of more complex, smart biomaterials that respond to relevant stimuli from blood to counteract coagulation. Logically, the main source of inspiration for the design of new biomaterials has been the endogenous endothelium. Endothelial regulation of hemostasis is complex and involves a delicate interplay of structural components and feedback mechanisms. Thus, challenges to develop new strategies for blood-compatible biomaterials now lie in incorporating true feedback controlled mechanisms that can regulate blood compatibility in a dynamic way. Here, supramolecular material systems are highlighted as they provide a promising platform to introduce dynamic reciprocity, due to their inherent dynamic nature.

Covalent Grafting of Antifouling Phosphorylcholine-Based Copolymers with Antimicrobial Nitric Oxide Releasing Polymers to Enhance Infection-Resistant Properties of Medical Device Coatings

Medical device coatings that resist protein adhesion and bacterial contamination are highly desirable in the healthcare industry. In this work, an antifouling zwitterionic terpolymer, 2-methacryloyloxyethyl phosphorylcholine-co-butyl methacrylate-co-benzophenone (BPMPC), is covalently grafted to a nitric oxide (NO) releasing antimicrobial biomedical grade copolymer of silicone-polycarbonate-urethane, CarboSil, to significantly enhance the biocompatibility, nonspecific protein repulsion and infection-resistant properties. The NO donor embedded into CarboSil is S-nitroso-N-acetylpenicillamine (SNAP) and covalent grafting of the BPMPC is achieved through rapid UV-cross-linking, providing a stable, hydrophilic coating that has excellent durability over a period of several weeks under physiological conditions. The protein adsorption test results indicate a significant reduction (∼84-93%) of protein adhesion on the test samples compared to the control samples. Bacteria tests were also performed using the common nosocomial pathogen, Staphylococcus aureus. Test samples containing both NO donor and BPMPC show a 99.91 ± 0.06% reduction of viable bacteria when compared to control samples. This work demonstrates a synergistic combination of both antimicrobial and antifouling properties in medical devices using NO donors and zwitterionic copolymers that can be covalently grafted to any polymer surface.

Facile Oriented Immobilization of Histidine-Tagged Proteins on Nonfouling Cobalt Polyphenolic Self-Assembly Surfaces

In this study, a completely green and facile protocol to oriented immobilization of histidine-tagged (His-tagged) proteins based on plant polyphenolic tannic acid (TA) is described. This is the first time that TA has been applied as ionic chelators to immobilize His-tagged proteins. To reduce the nonspecific interactions between the TA and immobilized proteins, we assembled nonfouling zwitterionic poly(sulfobetaine methacrylate) (PSBMA) on the TA surface. The use of PSBMA could maintain the high activity of the His-tagged proteins and inhibit the adsorption of untagged protein to the TA surface. Subsequently, the obtained TA/PSBMA film was further chelated with Co^II for specific binding to a His-tagged protein. As Co^III is more stable and inert than Co^II, the chelated Co^II was oxidized to Co^III. Using this approach, His-tagged Chitinase was anchored to TA/PSBMA/Co^III film as a catalyst for the hydrolysis of chitin. The loading capacity of the film for the His-tagged Chitinase can reach ∼4.0 μg/cm². Moreover, the oriented immobilized Chitinase had high catalytic activity and excellent thermal and storage stability as well as being more resistant to proteolytic digestion by papain. This low-cost and green protein-oriented immobilization strategy may serve as a versatile platform for a range of applications, such as biomaterials, biocatalysis, sensors, drug delivery, and so on.

Self-Healable and Cold-Resistant Supercapacitor Based on a Multifunctional Hydrogel Electrolyte

Excellent self-healability and cold resistance are attractive properties for a portable/wearable energy-storage device. However, achieving the features is fundamentally dependent on an intrinsically self-healable electrolyte with high ionic conduction at low temperature. Here we report such a hydrogel electrolyte comprising sodium alginate cross-linked by dynamic catechol-borate ester bonding. Since its dynamically cross-linked alginate network can tolerate high-content inorganic salts, the electrolyte possesses excellent healing efficiency/cyclability but also high ionic conduction at both room temperature and low temperature. A supercapacitor with the multifunctional hydrogel electrolyte completely restores its capacitive properties even after breaking/healing for 10 cycles without external stimulus. At a low temperature of -10 °C, the capacitor is even able to maintain at least 80% of its room-temperature capacitance. Our investigations offer a strategy to assemble self-healable and cold-resistant energy storage devices by using a multifunctional hydrogel electrolyte with rationally designed polymeric networks, which has potential application in portable/wearable electronics, intelligent apparel or flexible robot, and so on.

CuSO4/H2O2-Triggered Polydopamine/Poly(sulfobetaine methacrylate) Coatings for Antifouling Membrane Surfaces

Mussel-inspired polydopamine (PDA) coatings have been broadly exploited for constructing functional membrane surfaces. One-step codeposition of PDA with antifouling polymers, especially zwitterionic polymers, has been regarded as a promising strategy for fabricating antifouling membrane surfaces. However, one challenge is that the codeposition is usually a slow process over 10 h or even several days. Herein, we report that CuSO₄/H₂O₂ is able to notably accelerate the codeposition process of PDA with poly(sulfobetaine methacrylate) (PSBMA). In our case, PSBMA is facilely anchored to the polypropylene microporous membrane (PPMM) surfaces within 1 h with the assistance of PDA because of its strong interfacial adhesion. The PDA/PSBMA-coated PPMMs show excellent surface hydrophilicity, high water permeation flux (7506 ± 528 L/m²·h at 0.1 MPa), and an outstanding antifouling property. Moreover, the antifouling property is maintained after the membranes are treated with acid and alkali solutions as well as organic solvents. To recap, it provides a facile, universal, and time-saving strategy for exploiting high-efficiency and durable antifouling membrane surfaces.

Design and mechanisms of antifouling materials for surface plasmon resonance sensors

Surface plasmon resonance (SPR) biosensors have many possible applications, but are limited by sensor chip surface fouling, which blocks immobilization and specific binding by the recognizer elements. Therefore, there is a pressing need for the development of antifouling surfaces. In this paper, the mechanisms of antifouling materials were firstly discussed, including both theories (hydration and steric hindrance) and factors influencing antifouling effects (molecular structures and self-assembled monolayer (SAM) architectures, surface charges, molecular hydrophilicity, and grafting thickness and density). Then, the most recent advances in antifouling materials applied on SPR biosensors were systematically reviewed, together with the grafting strategies, antifouling capacity, as well as their merits and demerits. These materials included, but not limited to, zwitterionic compounds, polyethylene glycol-based, and polysaccharide-based materials. Finally, the prospective research directions in the development of SPR antifouling materials were discussed.

STATEMENT OF SIGNIFICANCE

Surface plasmon resonance (SPR) is a powerful tool in monitoring biomolecular interactions. The principle of SPR biosensors is the conversion of refractive index change caused by molecular binding into resonant spectral shifts. However, the fouling on the surface of SPR gold chips is ubiquitous and troublesome. It limits the application of SPR biosensors by blocking recognition element immobilization and specific binding. Hence, we write this paper to review the antifouling mechanisms and the recent advances of the design of antifouling materials that can improve the accuracy and sensitivity of SPR biosensors. To our knowledge, this is the first review focusing on the antifouling materials that were applied or had potential to be applied on SPR biosensors.