Zwitterionic Peptides: From Mechanism, Design Strategies to Applications

Zwitterionic peptides, as a type of peptide composed of charged residues, are electrically neutral, which combine the advantages of zwitterionic materials and biological peptides, exhibiting hydrophilicity and programmable properties. As attractive candidates for resisting nonspecific adsorption of biomacromolecules and microorganisms, zwitterionic peptides have been applied in materials science, biomedicine, and biochemistry over the past decade. In this review, the development of zwitterionic peptides has been systematically outlined and analyzed, including their mechanisms, structure-function relationships, and design strategies. Furthermore, this review emphasizes and discusses their recent applications for developing functional coatings, biosensors, drug delivery systems, and engineering proteins. Finally, future research perspectives and challenges of zwitterionic peptides are also prospected and discussed. This review is intended to provide clarity and insight into the design and applications of zwitterionic peptides.

Ampholytic Peptides Consisting of an Alternating Lysine/Glutamic Acid Sequence for the Simultaneous Formation of Polyion Complex Vesicles

Nanoarchitectures such as micelles and vesicles that self-assemble via electrostatic interactions between their charged polymeric components have been widely used as material delivery platforms. In this work, ampholytic peptides with a sequence of alternating lysine and glutamic acid residues were designed and synthesized via chemoenzymatic polymerization. This alternating sequence was achieved by trypsin-catalyzed polymerization of a dipeptide monomer. Due to the electrostatic interaction between the anionic and cationic residues, the prepared ampholytic peptides spontaneously formed nanosized assemblies with a size of 100-200 nm in water. Modification with tetra(ethylene glycol) (TEG) at the N-terminus of these ampholytic alternating peptides resulted in the formation of stable nanosized assemblies, while peptides consisting of random sequences of lysine and glutamic acid formed large aggregates with deteriorated stability even with TEG modification. Morphological observations using a field-emission scanning electron microscope and an atomic force microscope revealed that the obtained assemblies were spherical and hollow, indicating the spontaneous formation of vesicles from the TEG-modified ampholytic alternating peptides. These vesicles were able to encapsulate a model fluorescent protein within their hollow structures without structural collapse causing loss of fluorescence, demonstrating the potential of these nanocarriers for use in material delivery systems.

Extracellular Matrix-Mimetic Intrinsic Versatile Coating Derived from Marine Adhesive Protein Promotes Diabetic Wound Healing through Regulating the Microenvironment

The management of diabetic wound healing remains a severe clinical challenge due to the complicated wound microenvironments, including abnormal immune regulation, excessive reactive oxygen species (ROS), and repeated bacterial infections. Herein, we report an extracellular matrix (ECM)-mimetic coating derived from scallop byssal protein (Sbp9Δ), which can be assembled in situ within 30 min under the trigger of Ca2+ driven by strong coordination interaction. The biocompatible Sbp9Δ coating and genetically programmable LL37-fused coating exhibit outstanding antioxidant, antibacterial, and immune regulatory properties in vitro. Proof-of-concept applications demonstrate that the coating can reliably promote wound healing in animal models, including diabetic mice and rabbits, ex vivo human skins, and Staphylococcus aureus-infected diabetic mice. In-depth mechanism investigation indicates that improved wound microenvironments accelerated wound repair, including alleviated bacterial infection, lessened inflammation, appearance of abundant M2-type macrophages, removal of ROS, promoted angiogenesis, and re-epithelialization. Collectively, our investigation provides an in situ, convenient, and effective approach for diabetic wound repair.

A Cysteine-Maleimide-Based Design for Hemostatic, Antibacterial, and Biodegradable Wound Dressing

The field of clinical surgery frequently encounters challenges related to atypical wound tissue healing, resulting in the development of persistent chronic wounds or aesthetically displeasing scar tissue. The use of wound dressings crafted from mussel adhesive proteins and hyaluronic acid has demonstrated the potential in mitigating these undesirable outcomes. However, the synergistic effects of these two biomaterials remain underexplored. In this study, we have engineered a versatile, degradable, and biocompatible dressing that comprises recombinant 3,4-dihydroxyphenylalanine (DOPA)-modified mussel adhesive proteins and maleimide-functionalized hyaluronic acid. We have successfully fabricated this biocompatible dressing and conducted comprehensive experimental assessments to confirm its hemostatic, antibacterial, and biocompatible characteristics. Importantly, this dressing exclusively incorporates biologically derived materials characterized by low toxicity and minimal immunogenicity, thus holding immense promise for clinical applications in the field of wound healing.

Protein-based bioactive coatings: from nanoarchitectonics to applications

Protein-based bioactive coatings have emerged as a versatile and promising strategy for enhancing the performance and biocompatibility of diverse biomedical materials and devices. Through surface modification, these coatings confer novel biofunctional attributes, rendering the material highly bioactive. Their widespread adoption across various domains in recent years underscores their importance. This review systematically elucidates the behavior of protein-based bioactive coatings in organisms and expounds on their underlying mechanisms. Furthermore, it highlights notable advancements in artificial synthesis methodologies and their functional applications in vitro. A focal point is the delineation of assembly strategies employed in crafting protein-based bioactive coatings, which provides a guide for their expansion and sustained implementation. Finally, the current trends, challenges, and future directions of protein-based bioactive coatings are discussed.

Simplified α2-macroglobulin as a TNF-α inhibitor for inflammation alleviation in osteoarthritis and myocardial infarction therapy

Tumor necrosis factor α (TNF-α) is a leading proinflammatory cytokine as the master regulator of inflammation in chronic inflammation diseases. Although TNF-α antagonists such as small molecules and peptides are in development, comparable effectiveness in TNF-α neutralization is hardly achieved only with TNF-α capture. In this study, simplified α2-macroglobulin (SM) as a novel TNF-α inhibitor was fabricated to relieve inflammation response by TNF-α capture and internalization with lysosomal degradation. SM was prepared by conjugating a TNF-α-targeting peptide with a receptor binding domain (RBD) derived from α2-macroglobulin through a synthetic biology strategy. SM exhibited effective capture and bioactivity inhibition of TNF-α. Improved endocytosis of TNF-α into lysosomes was observed with SM in macrophages. Even challenged with LPS/IFNγ, the macrophages showed relieved inflammation response with SM treatment. When administrated in chronic inflammation injury in vivo, SM achieved comparable therapeutic efficacy with Infliximab, showing ameliorated cartilage degeneration with relieved inflammation in osteoarthritis (OA) and preserved cardiac function with mitigated myocardium injury in myocardial infarction (MI). These results suggest that SM functioning in TNF-α capture-internalization mechanism might be promising therapeutic alternatives of TNF-α antibodies.

Mussel-inspired proteins functionalize catheter with antifouling and antibacterial properties

Bacterial adhesion and subsequent biofilm formation on catheter can cause inevitably infection. The development of multifunctional antibacterial coating is a promising strategy to resist the bacteria adhesion and biofilm formation. Herein, a mussel-inspired chimeric protein MZAgP is prepared and employed to modify a variety of polymeric catheters. The MZAgP is composed of mussel-adhesive peptide, zwitterionic peptide, and silver-binding peptide, which can endow catheters with antifouling, bactericidal and biocompatibility performances. Expectedly, negligible biofilm is observed on the MZAgP coated catheters after incubating with bacteria for 120 h. And ignorable hemolysis and cytotoxicity are obtained on coated catheters. In addition, the modified catheters also display persistent antifouling and bacteriostatic properties throughout 168 h under hydrodynamic conditions. Moreover, the coated catheters still remain excellent antifouling and antibacterial properties even after 2 months of storage. This multifunctional coating may be promising as antibacterial and antibiofilm material, and the coated catheters are potential in clinical application.

Construction and hydrophilic modification of dual-network structured nonwoven/UHMWPE composite membranes for water processing

Water pollution caused by the continuous development of industrialization has always been a common concern of mankind. Herein, a novel strategy to fabricate a high-performance composite membrane based on dual-network structured nonwoven net/UHMWPE nanopores via a thermal phase separation and composite technique is reported. By thermal phase separation of ultra-high-molecular weight polyethylene (UHMWPE)/liquid paraffin (LP), this approach enables 3D nanopores to tightly bond with a nonwoven net to form a dual-network structure. The dual-network composite membrane possesses the integrated features of pore structure and high porosity (89.9%). After modification with hyperbranched polymers (HBPs), the composite membrane with the desirable surface chemistry achieves high-efficiency filtration (water flux = 1054 L m^-2 h^-1, rejection rate = 50 nm PS nanospheres almost close to 100%, and antibacterial properties). The fabrication of such composites may provide new insights into the design and development of high-performance filtration and separation materials for various applications.

Integrating a zwitterionic peptide with a two-photoelectrode system for an advanced photoelectrochemical immunosensing platform

An ingenious strategy with the integration of a zwitterionic peptide into a two-photoelectrode system was reported to construct an advanced photoelectrochemical immunosensing platform. The strategy has endowed the platform with both excellent photoelectric properties and an antifouling ability, and was capable of accurate and sensitive detection of target biomarkers in biological specimens.

Zwitterionic Biomaterials

The term "zwitterionic polymers" refers to polymers that bear a pair of oppositely charged groups in their repeating units. When these oppositely charged groups are equally distributed at the molecular level, the molecules exhibit an overall neutral charge with a strong hydration effect via ionic solvation. The strong hydration effect constitutes the foundation of a series of exceptional properties of zwitterionic materials, including resistance to protein adsorption, lubrication at interfaces, promotion of protein stabilities, antifreezing in solutions, etc. As a result, zwitterionic materials have drawn great attention in biomedical and engineering applications in recent years. In this review, we give a comprehensive and panoramic overview of zwitterionic materials, covering the fundamentals of hydration and nonfouling behaviors, different types of zwitterionic surfaces and polymers, and their biomedical applications.

Sticktight-inspired PEGylation for low-fouling coatings

Polyethylene glycol (PEG) has been widely used for modifying surfaces to reduce non-specific interactions with biomolecules, microorganisms, and cells. Herein, we report a sticktight-inspired PEGylation strategy to fabricate low-fouling coatings. The influence of PEG molecular architectures on the PEG density and biological adhesion were studied. Notably, an increase in the number of arms resulted in improved surface PEGylation and an improved antifouling ability against the adhesion of proteins, mammalian cells and bacteria. The molecular architecture-dependent PEGylation strategy is an attractive approach for developing advanced low-fouling coatings.

Mussel-inspired polymeric coatings with the antifouling efficacy controlled by topologies

Block copolymers with different topologies (linear, loop, 3-armed and 4-armed polymers) containing poly(N-vinylpyrrrolidone) (PVP) antifouling blocks and terminal poly(dopamine-acrylamide) (PDAA) anchoring blocks were synthesized. These polymers can form a robust antifouling nanolayer on various surfaces. The morphologies of the polymer-modified surfaces are strongly dependent on the topologies of the polymers: with the increase of arm numbers, the morphology evolves from the smooth surface to the nanoscale coarse surface. As a result, the hydrophilicity of the coatings increases with the increase of degree of nanoscale roughness, and the 4-armed block copolymer forms a superhydrophilic surface with a water contact angle (WCA) as low as 8.7°. Accordingly, the linear diblock copolymer exhibits the worst antifouling efficiency, while the 4-armed polymer exhibits the best antifouling efficiency. This is the first example systematically showing that the antifouling efficacy could be adjusted simply by the topology of the coatings. Cell viability studies revealed that all of the copolymers exhibit excellent cytocompatibility. These biocompatible polymers with narrowly distributed molecular weight might find niches for antifouling applications in various areas such as anti-protein absorption, anti-bacterial and anti-marine fouling.

Hydrophobic Biodegradable Hyperbranched Copolymers with Excellent Marine Diatom Resistance

As the utilization of degradable polymer coatings increased, the accompanying trade-off between good degradability and high-efficiency antidiatom adhesion due to their hydrophobic nature remains unresolved. The study presents a new hydrophobic surface-fragmenting coating consisting of degradable hyperbranched polymers (hereafter denoted as h-LLA_x) synthesized by reversible complexation-mediated copolymerization with isobornyl acrylate (IBOA) and divinyl-functional oligomeric poly(l-lactide) (OLLA-V₂), both derived from biomass, that exhibited superior resistance (∼0 cell mm^-2) to marine diatom Navicula incerta (N. incerta) attachment with higher OLLA content. The combined impact of the microscale hollow semisphere micelles that self-assembled degradable hyperbranched copolymers and hydrolysis-driven self-renewable surfaces following immersion in seawater may account for the remarkable resistance of h-LLA_x coatings against N. incerta. Detailed investigations were conducted across multiple perspectives, from hydrolytic degradation to broad-spectrum antibacterial attachment to ecotoxicity assessment. The excellent features of high resistance to marine diatoms and bacterial attachment, degradability, and environmental friendliness make the as-prepared h-LLA_x coatings widely sought after for antifouling coating applications.

Intrinsically Disordered Protein Condensate-Modified Surface for Mitigation of Biofouling and Foreign Body Response

Mitigation of biofouling and the host's foreign body response (FBR) is a critical challenge with biomedical implants. The surface coating with various anti-fouling materials provides a solution to overcome it, but limited options in clinic and their potential immunogenicity drive the development of more alternative coating materials. Herein, inspired by liquid-liquid phase separation of intrinsically disordered proteins (IDPs) to form separated condensates in physiological conditions, we develop a new type of low-fouling biomaterial based on flexible IDP of FUS protein containing rich hydrophilic residues. A chemical structure-defined FUS IDP sequence tagged with a tetra-cysteine motif (IDP_FUS) was engineered and applied for covalent immobilization on various surfaces to form a uniform layer of protein tangles, which boosted strong hydration on surfaces, as revealed by molecular dynamics simulation. The IDP_FUS-coated surfaces displayed excellent performance in resisting adsorption of various proteins and adhesion of different cells, platelets, and bacteria. Moreover, the IDP_FUS-coated implants largely mitigated the host's FBR compared with bare implants and particularly outperformed PEG-coated implants in reducing collagen encapsulation. Thus, this novel low-fouling and anti-FBR strategy provides a potential surface coating material for biomedical implants, which will also shed light on exploring similar applications of other IDP proteins.

Zwitterionic peptide-functionalized highly dispersed carbon nanotubes for efficient wastewater treatment

Multi-walled carbon nanotubes (MWCNTs) have displayed great potential as catalyst carriers due to their nanoscale structure and large specific surface area. However, their hydrophobicity and poor dispersibility in water restrict their applications in aqueous environments. Herein, the dispersibility of MWCNTs was significantly enhanced with a chimeric protein MPKE which consisted of a zwitterionic peptide unit and a mussel adhesive protein unit. The MPKE could be easily attached to MWCNTs (MPKE-MWCNTs) by a simple stirring process due to the versatile adhesion ability of mussel adhesive unit. As expected, the MPKE-MWCNTs displayed outstanding dispersibility in water (>7 months), as well as in alkaline solutions (pH = 12) and organic solvents (DMSO and ethanol) due to the hydrophilicity of the zwitterionic peptide unit. Moreover, the MPKE-MWCNTs were used as silver nanoparticle carriers for the reduction of 4-nitrophenol in wastewater, with the normalized rate constant k_nor up to 32.9 s^-1 mmol^-1. Meanwhile, they also exhibited excellent biocompatibility and antibacterial activity, which were favorable for wastewater treatment. This work provides a facile strategy for MWCNT modification, functionalization and applications in aqueous environments.

Comparative analysis of mussel foot protein 3B co-expressed with tyrosinases provides a potential adhesive biomaterial

Mussel foot proteins (Mfps), which help mussels attach to various surfaces, are considered to be promising biomaterials due to their outstanding adhesive properties. However, limited production and lack of post-translational modifications of tyrosine residues into 3,4-dihydroxyphenylalanine (Dopa) in bacterial expression systems have hampered their applications. In the present study, for the first time we established the expression of recombinant Mytilus galloprovincialis foot protein type 3 variant B (fp-3B) in Escherichia coli; and achieved its viable production (~51 mg/L). Additionally, the Dopa content and adhesive properties of fp-3B co-expressed using various types of tyrosinases were compared. Consequently, the co-expression of fp-3B construct together with tyrosinase from Verrucomicrobium spinosum (TyrVs) yielded up to 87 mg/L of modified fp-3B; hydroxylation of tyrosine residues accounted for 57.18% by acid-borate difference spectroscopy. The modified fp-3B also showed significant coating and adhesive ability, and its bulk-scale adhesive strength was 2.9-fold higher than that of unmodified fp-3B. Compared with other type 3 mussel foot proteins, the high-yield expression and extensive hydroxylation level of the recombinant protein indicate that fp-3B co-expressed with TyrVs (3B-Vs) has the potential to be widely used as bioglues.

Enhancing resin-dentin bond durability using a novel mussel-inspired monomer

Numerous approaches have been developed to improve the resin-dentin bond performance, among which the bio-application of mussel-derived compounds have drawn great attention recently. To assess the performance of N-(3,4-dihydroxyphenethyl)methacrylamide (DMA), a mussel-derived compound, as a functional monomer in dental adhesive, its potential property to cross-link with dentin collagen and polymerize with adhesive will first be evaluated by transmission electron microscopy (TEM), attenuated total reflectance technique of Fourier transform infrared (ATR-FTIR), and atomic force microscopy (AFM) via Peakforce QNM mode. After validating the influence of DMA on collagen and adhesive separately, the overall performance of DMA/ethanol solution as a primer in dentin bonding was examined using micro-tensile bond strength (μTBS) testing, fracture pattern observation, and nanoleakage evaluation both immediately and after 10,000 times thermocycling aging. The inhibitory effect of DMA on endogenous metalloproteinases (MMPs) was evaluated by in situ zymography using confocal laser scanning microscopy (CLSM) and the cytotoxicity of DMA was evaluated using cell counting kit-8. Results demonstrated that DMA successfully cross-linked with dentin collagen via non-covalent bonds and had no influence on the polymerization and mechanical properties of the adhesive. Furthermore, even after 10,000 times thermocycling aging, the μTBS and nanoleakage expression of the DMA-treated groups showed no significant change compared with their immediate values. In situ zymography revealed reduced endogenous proteolytic activities after the application of DMA, and no cytotoxicity effect was observed for DMA concentration up to 25 ​μmol/L. Thus, DMA could be used as a novel, biocompatible functional monomer in dentin bonding.

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DMA acts as a functional monomer in dentin bonding system with high biocompatibility.

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DMA connects the adhesive and collagen network to resist various external attacks.

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DMA/ethanol inhibits the activity of MMPs and improve resin-dentin bond durability.

Beetle and mussel-inspired chimeric protein for fabricating anti-icing coating

Ice accretion on surfaces can cause serious damages and economic losses in industries and civilian facilities. Antifreeze proteins (AFPs) as evolutionary adaptation products of organisms to cold climates, provide solutions for alleviating icing problems. In this work, a chimeric protein Mfp-AFP was rationally designed combining mussel-inspired adhesive domain with Tenebrio molitor-derived antifreeze protein domain. Expectedly, the multifunctional Mfp-AFP can lower the freezing point of water and inhibit ice recrystallization. The chimeric protein could also readily modify diverse solid surfaces due to the adhesive domain containing Dopa, and resist frosting and delay ice formation due to the beetle-derived antifreeze fragment. Moreover, Mfp-AFP coatings display excellent biocompatibility proved by cytocompatibility and hemolysis assays. Here, the designed multifunctional protein coatings provide an alternative strategy for fabricating anti-icing surfaces.

Mussel Adhesive Mimetic Silk Sericin Prepared by Enzymatic Oxidation for the Construction of Antibacterial Coatings

With the rapid development and advancement in orthodontic and orthopedic technologies, the demand for biomedical-grade titanium (Ti) alloys is growing. The Ti-based implants are susceptible to bacterial infections, leading to poor healing and osteointegration, resulting in implant failure or repeated surgical intervention. Silk sericin (SS) is hydrophilic, biocompatible, and biodegradable and could induce a low immunological response in vivo. As a result, it would be intriguing to investigate the use of hydrophilic SS in surface modification. In this work, the tyrosine moiety in SS was oxidized by tyrosinase (or polyphenol oxidase) to the 3,4-dihydroxyphenylalanine (DOPA) form, generating the catechol moiety-containing SS (SSC). Inspired by the adhesion of mussel foot proteins, the SSC coatings could be directly deposited onto multiple surfaces in SS and tyrosinase mixed stock solutions to create active surfaces with catechol groups. Further, the SSC-coated Ti surfaces were hybridized with silver nanoparticles (Ag NPs) via in situ silver ion (Ag⁺) reduction. The antibacterial properties of the Ag NPs/SS-coated Ti surfaces are demonstrated, and they can prevent bacterial cell adhesion as well as early-stage biofilm formation. In addition, the developed Ag NPs/SSC-coated Ti surfaces exhibited a negligible level of cytotoxicity in L929 mouse fibroblast cells.

Biodegradable Anti-Biofilm Fiber-Membrane Ureteral Stent Constructed with a Robust Biomimetic Superhydrophilic Polycationic Hydration Surface Exhibiting Synergetic Antibacterial and Antiprotein Properties

The biofouling of ureteral stents and subsequent urinary tract infections mainly come from the adsorption and adhesion of proteins and microorganisms and their ensuing proliferation. Although general polycationic surfaces in implants have good antibacterial activities, they suffer from limited durability due to severe protein and bacterial adsorption. Here, a biodegradable and anti-biofilm fiber-membrane structured ureteral stent (FMBUS) with synergetic contact-killing antibacterial activity and antiprotein adsorption is described. The stent is prepared by generating hyperbranched poly(amide-amine)-grafted polydopamine microparticles (≈300 nm) on the surface of fibers by in situ polymerization and Schiff base reactions. The biomimetic surface endows the FMBUS with a positive charge (+21.36 mV) and superhydrophilicity (water contact angle: 0°). As a result, the stents fulfilled the following functions: i) reduced attachment of host protein due to superhydrophilicity (Lysozyme: 92.1%; human serum albumin: 39.4%); ii) high bactericidal activities against contact pathogenic bacteria (contact-killing rate: 99.9999% for both E. coli and S. aureus; antiadhesion rate: 99.2% for E. coli and 99.9999% for S. aureus); iii) biocompatibility in vitro (relative growth rate of L929: >90% on day 3) and in vivo; and iv) gradient biodegradability to avoid a second surgery of stent extraction 1-2 weeks after implantation.

Antifouling biosensors for reliable protein quantification in serum based on designed all-in-one branched peptides

Antifouling electrochemical biosensors based on designed all-in-one branched peptides that combine anchoring, doping, antifouling and recognizing functions were constructed to support sensitive and reliable protein quantification in complex serum samples.

MOF-Based Antibiofouling Hemoadsorbent for Highly Efficient Removal of Protein-Bound Bilirubin

A metal-organic framework (MOF)-based antibiofouling hemoadsorbent (PCB-MIL101) was developed through a facile encapsulation of MIL-101(Cr) in zwitterionic poly carboxybetaine (PCB) hydrogel. PCB-MIL101 possessed strong mechanical strength and superior hemocompatibility, ensuring its safety in hemoperfusion applications. In addition, it showed efficient and effective adsorption toward bilirubin (BR), and its maximum adsorption capacity was ∼583 mg g^-1. Moreover, due to the protection of antibiofouling PCB hydrogel, PCB-MIL101 showed ability to resist protein adsorption, thus working effectively to remove BR molecules from their binding albumin in biological solutions. The finding in this study provides a novel insight into developing MOF-based hemoadsorbents for the improvement of hemoperfusion therapies.

Stable Fabrication of Zwitterionic Coating Based on Copper-Phenolic Networks on Contact Lens with Improved Surface Wettability and Broad-Spectrum Antimicrobial Activity

Ocular dryness and contact lens(CL)-related microbial keratitis (MK) are two major risks of wearing CLs. The development of multifunctional surface coating for CLs with excellent hydrating and antimicrobial properties is a practical strategy to improve the comfort of CL wearers and to prevent corneal infection. Here, we develop zwitterionic and antimicrobial metal-phenolic networks (MPNs) based on the coordination of copper ions (Cu^II) and the poly(carboxylbetaine-co-dopamine methacrylamide) copolymer (PCBDA), which can be easily one-step prepared onto CLs due to the near-universal adherent properties of catechol groups. The zwitterionic and antifouling carboxybetaine (CB) groups of the Cu^II-PCBDA coating can significantly increase the wettability of CLs and reduce their protein adsorptions, resulting in a lens surface that is more water retentive and with lower protein binding to prevent tear film evaporation and eye dryness. In addition, since the immobilized copper ions in the MPNs impart them with ion-mediated antimicrobial activity, the Cu^II-PCBDA coating exhibits a strong and broad-spectrum antimicrobial activity against MK related pathogenic microbes, including bacteria, such as Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus, and fungi, such as Candida albicans. Compared with a pristine CL, the Cu^II-PCBDA-coated CL effectively inhibited biofilm formation even after daily exposure to the above microbial environment for 14 days. Notably, the Cu^II-PCBDA coating developed in this study is not only biocompatible with 100% cell viability following direct contact with human corneal epithelial cells (HCECs) for 48 h but also maintains the optical clarity of the native CLs. Thus, the Cu^II-PCBDA coating has a great application potential for the development of a multifunctional surface coating for CLs for increased CL comfort and prevention of MK.

The design and development of short peptide-based novel smart materials to prevent fouling by the formation of non-toxic and biocompatible coatings

Biofouling refers to the undesirable process that leads to the accumulation of microorganisms such as bacteria or fungi on substrates. This is one of the major concerns associated with several components of our regular life such as food, health, water and energy. In the healthcare sector, biofouling on medical devices is known to cause infections, which are often resistant to conventional antibiotics and lead to increase in the number of hospital and surgery-related deaths. One of the better ways to tackle the problem of biofouling is the development of smart antifouling materials that can produce a biocompatible, non-toxic, eco-friendly and functional coating and maintain a biological environment without any adverse effect. To this end, in the present study, we have reported the design and synthesis of two simple chemically modified peptides, namely, PA1 (PFB-VVD) and PA2 (PFB-LLE). The design as well as the amino acid sequence of the peptides contains three basic components that enable their ability to (i) self-assemble into functional coatings, (ii) bind with the desired surface via the bi-dentate coordination of dicarboxylate groups and (iii) exhibit antifouling activity and generate a non-toxic biocompatible supramolecular coating on the desired surface. PA1 having aspartic acid as the anchoring moiety exhibits better antifouling activity compared to PA2 that has glutamic acid as the anchoring moiety. This is probably due to the greater adhesive force or binding affinity of aspartic acid to the examined surface compared to that of glutamic acid, as confirmed by force measurement studies using AFM. Most importantly, the simple drop-coating method promises great advantages due to its ease of operation, which leads to a reduction in the production cost and increase in the scope of commercialization. To the best of our knowledge, this is the first attempt to develop an ultra-short peptide-based smart antifouling material with a dicarboxylate group as the surface binding moiety. Furthermore, these findings promise to provide further insights into antifouling mechanisms in the future by the development of a smart material using a dicarboxylate group as an anchoring moiety.

Fabrication of Mixed-Charge Polypeptide Coating for Enhanced Hemocompatibility and Anti-Infective Effect

Medical catheters are prone to fouling by protein adsorption and platelet adhesion/activation due to their hydrophobic surface, resulting in bacterial adhesion/biofilm formation, associated infection, and thrombosis. Hence, an ultralow-fouling and exceptional infection-resistant coating on devices is urgently needed. Herein, we synthesized mussel-inspired cationic polypeptide (cPep) and mixed-charge polypeptide (mPep) via an N-carboxyanhydride ring opening polymerization method. In the view of the chemical structure, in addition to the catechol group of levodopa, the cationic group of l-lysine (K), and the hydrophobic group of l-phenylalanine (F), the mPep, comparing with cPep, contains the anionic group of l-glutamic acid (E) since the negatively charge amino acid sequence is newly introduced, so as to guarantee its bactericidal ability, low toxicity, and surface self-deposition. Both cPep and mPep coatings are conveniently obtained by a dopamine-assisted codeposition technique. Compared with the cPep coating, the mPep coating has a similar antibacterial activity level (>99%) against methicillin-resistant Staphylococcus aureus and Pseudomonas aeruginosa. Meanwhile, it is demonstrated that the mPep coating has most effective antibiofilm activity (>3 days) and protein/platelet-resistant ability in vitro, as well as improving hemocompatibility. Furthermore, the mPep-coated silicone catheter induces no inflammatory response and significantly lowers the bacterial cell number with 6 log reduction in a mouse model of infection. Consequently, the rationally designed mPep with a simple coating technique has great potential in combating against medical catheter-related clinical infections.

Bioinspired Multifunctional Protein Coating for Antifogging, Self-Cleaning, and Antimicrobial Properties

A multifunctional coating with antifogging, self-cleaning, and antimicrobial properties has been prepared based on a mussel-inspired chimeric protein MP-KE, which is the first example that these proteins were successfully applied to fabricate antifogging surfaces. The coating exhibits super hydrophilic properties, as indicated by contact angles less than 5° and high light transmittance similar to bare glass substrates about 90%. The zwitterionic peptides of MP-KE empower water molecules to expand into thin hydrated films rapidly, providing the protein coating with diverse surface functions. Moreover, the coatings have excellent stability and a convenient preparation process because of the mussel adhesive motif of MP-KE which makes the coating anchor onto the surface strongly. As a protein material, this multifunctional coating possesses remarkable biocompatibility and has a potential application prospects in the biomedical and pharmaceutical fields.

Novel Mussel-Inspired Universal Surface Functionalization Strategy: Protein-Based Coating with Residue-Specific Post-Translational Modification in Vivo

Surface functionalization can effectively endow materials with desirable properties, promoting the performance between the material and environment, with extensive applications. However, a universal and straightforward surface functionalization method with biocompatibility is scarce. In this study, with synthetic biology strategy, recombinant mussel plaque protein with a zwitterionic peptide inspired by molecular chaperone was engineered through post-translational modification, in which 3,4-dihydroxyphenylalanine was residue-specifically obtained efficiently from tyrosine with tyrosinase coexpressed in vivo. The rational designed chimeric protein coating in this work could successfully anchor to various substrates and exhibit excellent antifouling performance in resisting protein adsorption, cell attachment, and bacterial adhesion with eminent biocompatibility.