Integrated antimicrobial and nonfouling zwitterionic polymers

A self-defensive antibacterial coating acting through the bacteria-triggered release of a hydrophobic antibiotic from layer-by-layer films

Drug delivery systems play important roles in the construction of antibacterial coatings on the surfaces of biomaterials. However, excessive release of antibiotics in the environment can lead to the generation of resistant bacteria. A methoxy poly(ethylene glycol)-poly(ε-caprolactone)-chitosan (MPEG-PCL-CS) block polymer was prepared through covalent grafting of CS onto MPEG-PCL. MPEG-PCL-CS micelles were prepared and showed a high load capacity for the hydrophobic antibiotic triclosan (TCA) (∼5 wt%). Multilayer films were constructed through self-assembling TCA/MPEG-PCL-CS cationic micelles with poly(acrylic acid) (PAA). Transmission and scanning electron microscopy analyses confirmed the presence of micelles on the surface (20-40 nm). As barriers for the antibiotic, the (TCA/MPEG-PCL-CS)/PAA multilayer films contained a high load of TCA (255 μg cm-2). Importantly, the multilayer films showed both bacteria-triggered and pH-responsive release properties and can be used as self-defensive antibacterial coatings. Bacterial adhesion caused a local acidic environment and altered the permeability of the multilayer films, promoting drug release. Both in vitro and in vivo antibacterial tests indicated a high bactericidal activity of drug-loaded multilayer films against both E. coli and S. aureus.

Biofunctionalization of surfaces using polyelectrolyte multilayers

Biomaterials play a central role in modern strategies in regenerative medicine and tissue engineering to restore the structure and function of damaged or dysfunctional tissue and to direct cellular behavior. Both biologically derived and synthetic materials have been extensively explored in this context. However, most materials when implanted into living tissue initiate a host response. Modern implant design therefore aims to improve implant integration while avoiding chronic inflammation and foreign body reactions, and thus loss of the intended implant function. Directing these processes requires an in-depth understanding of the immunological processes that take place at the interface between biomaterials and the host tissue. The physicochemical properties of biomaterial surfaces (charge, charge density, hydrophilicity, functional molecular domains, etc.) are decisive, as are their stiffness, roughness and topography. This review outlines specific strategies, using polyelectrolyte multilayers to modulate the interactions between biomaterial surfaces and biological systems. The described coatings have the potential to control the adhesion of proteins, bacteria and mammalian cells. They can be used to decrease the risk of bacterial infections occurring after implantation and to achieve better contact between biological tissue and implants. In summary, these results are important for further development and modification of surfaces from different medical implants.

A stimuli-responsive methionine-based zwitterionic methacryloyl sulfonium sulfonate monomer and the corresponding antifouling polymer with tunable thermosensitivity

This report describes a dual pH- and thermo-responsive methionine-based zwitterionic methacryloyl sulfonium sulfonate monomer and the corresponding zwitterionic antifouling polymer with ion-induced tunable thermosensitivity.

Co-deposition towards mussel-inspired antifouling and antibacterial membranes by using zwitterionic polymers and silver nanoparticles

Bacterial attachment and the subsequent colonization on the surfaces of bio-materials usually result in biofilm formation, and thus lead to implant failure, inflammation and so on.

Importance of zwitterionic incorporation into polymethacrylate-based hydrogels for simultaneously improving optical transparency, oxygen permeability, and antifouling properties

The introduction of zwitterionic SBMA into HEMA hydrogels enables to improve optical transparency, oxygen permeability, and antifouling property for contact lenses-based ophthalmic applications.

Effect of elimination on antifouling and pH-responsive properties of carboxybetaine materials

α- and β-substituted methyl carboxybetaine materials are developed to investigate the occurrence of elimination in the ethylene intercharge arm in a harsh basic solution.

Polymeric Quaternary Ammonium-Containing Coatings with Potential Dual Contact-Based and Release-Based Antimicrobial Activity

In the present work, reactive blending of copolymers with complementary functional groups was applied to control their antimicrobial activity and antifouling action in real conditions. For this purpose, two series of copolymers, poly(4-vinylbenzyl chloride-co-acrylic acid), P(VBC-co-AAx), and poly(sodium 4-styrenesulfonate-co-glycidyl methacrylate), P(SSNa-co-GMAx), were synthesized via free radical copolymerization and further modified by the incorporation of biocidal units either covalently (4-vinyl benzyl dimethylhexadecylammonium chloride, VBCHAM) or electrostatically bound (cetyltrimethylammonium 4-styrenesulfonate, SSAmC₁₆). The cross-linking reaction of the carboxylic group of acrylic acid (AA) with the epoxide group of glycidyl methacrylate (GMA) of these two series of reactive antimicrobial copolymers was explored in blends obtained through solution casting after curing at various temperatures. The combined results from the ATR-FTIR characterization of the membranes, solubility tests, turbidimetry, and TEM suggest that the reaction occurs already at 80 °C, leading mostly to graft samples, while at higher curing temperatures (120 or 150 °C) insoluble cross-linked samples are usually obtained. Controlled release experiments of selected membranes were performed in pure water and aqueous 1 M NaCl solutions for a period of two months. The released material was followed through gravimetry and TOC/TN measurements, while the evolution of the integrity and the morphology of the membranes were followed visually and through SEM, respectively. Antimicrobial tests also revealed that the cross-linked membranes presented strong antimicrobial activity against S. aureus and P. aeruginosa. Finally, a specific blend combination was applied on aquaculture nets and cured at 80 °C. The modified nets, emerged in the sea for 15 and 35 days, exhibited high antifouling action as compared to blank nets.

Construction of a temperature-responsive terpolymer coating with recyclable bactericidal and self-cleaning antimicrobial properties

Once a biomedical implant is implanted into a human body, proteins and bacteria can easily colonize the implant, and subsequently, a biofilm can grow on the surface. A biofilm can protect the inhabiting bacteria against macrophages and neutrophil cell attack from the host immune system. The most important issue for artificial antibacterial surfaces is the accumulation of the bacteria corpse after they are killed by contact, which promotes further adhesion of bacteria and biofilm formation. Therefore, we constructed a novel multifunctional bactericidal and fouling release antibacterial surface through the combination of temperature-responsive N-vinylcaprolactam (VCL), hydrophilic 2-methacryloyloxyethyl phosphorylcholine (MPC) and a bactericidal quaternary ammonium salt (2-(dimethylamino)-ethyl methacrylate (DMAEMA+)). The terpolymer coating was prepared through surface-initiated reversible addition-fragmentation chain-transfer (RAFT) polymerization and characterized using water contact angle measurements, atomic force microscopy and spectroscopic ellipsometry. At a temperature above the lower critical solution temperature (LCST), the P(VCL-co-DMAEMA+-co-MPC) terpolymer coating was in a compressed and hydrophobic state with low moisture content, which displayed bactericidal efficiency against Gram-positive Staphylococcus aureus. The coating could be switched into a relatively hydrophilic surface at a temperature below the LCST, which showed self-cleaning properties against both bacteria and bovine serum albumin. The functionalized surface showed good biocompatibility against human lens epithelial cells as evaluated by morphology studies and activity measurements.

Antifouling Zwitterionic Coating via Electrochemically Mediated Atom Transfer Radical Polymerization on Enzyme-Based Glucose Sensors for Long-Time Stability in 37 °C Serum

In this study, a versatile fabrication method for coating enzyme-based biosensors with ultrathin antifouling zwitterionic polymer films to meet the challenge of the long-time stability of sensors in vivo was developed. Electrochemically mediated atom transfer radical polymerization (eATRP) was applied to polymerize zwitterionic sulfobetaine methacrylate monomers on the rough enzyme-absorbed electrode surfaces; meanwhile, a refined overall bromination was developed to improve the coverage of polymers on the biosensor surfaces and to maintain the enzyme activity simultaneously for the first time. X-ray photoelectron spectroscopy and atomic force microscopy were used to characterize the properties of the polymer layers. The antifouling performance and long-time stability in 37 °C undiluted bovine serum in vitro were evaluated. The results showed that the polymer brush coatings diminished over 99% nonspecific protein adsorption and that the sensitivity of the evaluated sensor was maintained at 94% after 15 days. The overall sensitivity deviation of 7% was nearly 50% lower than that of the polyurethane-coated ones and also much smaller than the current commercially available glucose biosensors. The results suggested that this highly controllable electrodeposition procedure could be a promising method to develop implantable biosensors with long-time stability.

Constructing safe and durable antibacterial textile surfaces using a robust graft-to strategy via covalent bond formation

Recently zwitterionic materials have been widely applied in the biomedical and bioengineering fields due to their excellent biocompatibility. Inspired by these, this study presents a graft-to strategy via covalent bond formation to fabricate safe and durable antibacterial textile surfaces. A novel zwitterionic sulfobetaine containing triazine reactive group was specifically designed and synthesized. MTT assay showed that it had no obvious cytotoxicity to human skin HaCaT cells as verified by ca. 89.9% relative viability at a rather high concentration of 0.8 mg·mL⁻¹. In the evaluation for its skin sensitization, the maximum score for symptoms of erythema and edema in all tests were 0 in all observation periods. The sulfobetaine had a hydrophilic nature and the hydrophilicity of the textiles was enhanced by 43.9% when it was covalently grafted onto the textiles. Moreover, the textiles grafted with the reactive sulfobetaine exhibited durable antibacterial activities, which was verified by the fact that they showed antibacterial rates of 97.4% against gram-positive S. aureus and 93.2% against gram-negative E. coli even after they were laundered for 30 times. Therefore, the titled zwitterionic sulfobetaine is safe to human for healthcare and wound dressing and shows a promising prospect on antibacterial textile application.

Antimicrobial Polymers and Surfaces – Natural Mimics or Surpassing Nature?

Fighting pathogenic microbes is one of the great current challenges of mankind. Nature has developed several techniques to counteract microbial attacks. Science has also yielded several technologies, including antimicrobial polymers as biocides and polymers used for microbe killing and repelling surfaces. Recent scientific antimicrobial approaches are mimicking natural concepts. In this chapter, current developments in antimicrobial and antifouling polymers and surfaces are reviewed and discussed regarding the question whether they mimic nature or surpass it.

Copolymer Brushes with Temperature-Triggered, Reversibly Switchable Bactericidal and Antifouling Properties for Biomaterial Surfaces

The adherence of bacteria and the formation of biofilm on implants is a serious problem that often leads to implant failure. A series of antimicrobial coatings have been constructed to resist bacterial adherence or to kill bacteria through contact with or release of antibacterial agents. The accumulation of dead bacteria facilitates further bacterial contamination and biofilm development. Herein, we have designed and constructed a novel, reversibly switchable bactericidal and antifouling surface through surface-initiated reversible addition-fragmentation chain transfer (RAFT) polymerization to combine thermally responsive N-isopropylacrylamide (NIPAAm) and bactericidal quaternary ammonium salts (2-(dimethylamino)-ethyl methacrylate (DMAEMA⁺)). Measurements of spectroscopic ellipsometry and water contact angle and X-ray photoelectron spectroscopy were used to examine the process of the surface functionalization. The temperature-responsive P(DMAEMA⁺-co-NIPAAm) copolymer coating can switch by phase transition between a hydrophobic capturing surface at high temperatures and a relatively hydrophilic antifouling surface at lower temperatures. The quaternary ammonium salts of PDMAEMA⁺ displayed bactericidal efficiency against both Escherichia coli and Staphylococcus aureus. The functionalized surface could efficiently prevent bovine serum albumin adsorption and had good biocompatibility against human lens epithelial cells.

Efficient and Tunable Three-Dimensional Functionalization of Fully Zwitterionic Antifouling Surface Coatings

To enhance the sensitivity and selectivity of surface-based (bio)sensors, it is of crucial importance to diminish background signals that arise from the nonspecific binding of biomolecules, so-called biofouling. Zwitterionic polymer brushes have been shown to be excellent antifouling materials. However, for sensing purposes, antifouling does not suffice but needs to be combined with the possibility to efficiently modify the brush with recognition units. So far this has been achieved only at the expense of either antifouling properties or binding capacity. Herein we present a conceptually new approach by integrating both characteristics into a single tailor-made monomer: a novel sulfobetaine-based zwitterionic monomer equipped with a clickable azide moiety. Copolymerization of this monomer with a well-established standard sulfobetaine monomer results in highly antifouling surface coatings with a large yet tunable number of clickable groups present throughout the entire brush. Subsequent functionalization of the azido brushes via widely used strain-promoted alkyne azide click reactions yields fully zwitterionic 3D-functionalized coatings with a recognition unit of choice that can be tailored for any specific application. Here we show a proof of principle with biotin-functionalized brushes on Si₃N₄ that combine excellent antifouling properties with specific avidin binding from a protein mixture. The signal-to-noise ratio is significantly improved over that of traditional chain-end modification of sulfobetaine polymer brushes, even if the azide content is lowered to 1%. This therefore offers a viable approach to the development of biosensors with greatly enhanced performance on any surface.

Fully Zwitterionic Nanoparticle Antimicrobial Agents through Tuning of Core Size and Ligand Structure

Zwitterionic nanoparticles are generally considered nontoxic and noninteracting. Here, we report effective and selective antimicrobial activity of zwitterionic gold nanoparticles (AuNP) through modulation NP size and surface charge orientation. Using a set of 2, 4, and 6 nm core AuNPs, increasing particle size increased antimicrobial efficiency through bacterial membrane disruption. Further improvement was observed through control of the ligand structure, generating antimicrobial particles with low hemolytic activity and demonstrating the importance of size and surface structure in dictating the bioactivity properties of nanomaterials.

Host-Guest Self-Assembly Toward Reversible Thermoresponsive Switching for Bacteria Killing and Detachment

A facile method to construct reversible thermoresponsive switching for bacteria killing and detachment was currently developed by host-guest self-assembly of β-cyclodextrin (β-CD) and adamantane (Ad). Ad-terminated poly(N-isopropylacrylamide) (Ad-PNIPAM) and Ad-terminated poly[2-(methacryloyloxy)ethyl]trimethylammonium chloride (Ad-PMT) were synthesized via atom transfer radical polymerization, and then assembled onto the surface of β-CD grafted silicon wafer (SW-CD) by simply immersing SW-CD into a mixed solution of Ad-PNIPAM and Ad-PMT, thus forming a thermoresponsive surface (SW-PNIPAM/PMT). Atomic force microscopy (AFM), X-ray photoelectron spectrometry (XPS), and water contact angle (WCA) analysis were used to characterize the surface of SW-PNIPAM/PMT. The thermoresponsive bacteria killing and detachment switch of the SW-PNIPAM/PMT was investigated against Staphyloccocus aureus. The microbiological experiments confirmed the efficient bacteria killing and detachment switch across the lower critical solution temperature (LCST) of PNIPAM. Above the LCST, the Ad-PNIPAM chains on the SW-PNIPAM/PMT surface were collapsed to expose Ad-PMT chains, and then the exposed Ad-PMT would kill the attached bacteria. While below the LCST, the previously collapsed Ad-PNIPAM chains became more hydrophilic and swelled to cover the Ad-PMT chains, leading to the detachment of bacterial debris. Besides, the proposed method to fabricate stimuli-responsive surfaces with reversible switches for bacteria killing and detachment is facile and efficient, which creates a new route to extend the application of such smart surfaces in the fields requiring long-term antimicrobial treatment.

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

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

Biosilver nanoparticle interface offers improved cell viability

Silver nanoparticles (AgNP) are promising candidates for fighting drug-resistant infections because of their intrinsic antimicrobial effect. The design of high-yield antimicrobial molecules may inadvertently cause variation in host cells' biological responses. While many factors affect AgNPs' efficacy, their surface is exposed to the biological environment and thus plays a critical role in both the preservation of antimicrobial efficacy against pathogens and the modulation of host cells cytotoxicity. This work investigated an engineered biomimetic interface approach to controlling AgNP surface properties to provide them a competitive advantage in a biological environment. Here, a fusion protein featuring a silver-binding peptide (AgBP) domain was engineered to enable self-assembly and track assembly by a green fluorescent protein (GFP) reporter. Following AgNP functionalisation with GFP-AgBP, their antimicrobial and cytotoxic properties were evaluated. GFP-AgBP binding affinity to AgNPs was evaluated using localized surface plasmon resonance sensing. The GFP-AgBP biomimetic interface on AgNPs' surfaces provided sustained antibacterial efficacy at low concentrations based on bacterial growth inhibition assays. Viability and cytotoxicity measurements in fibroblast cells exposed to GFP-AgBP protein-functionalised AgNPs showed significant improvement compared to controls. Biointerface engineering offers promise towards tailoring AgNP antimicrobial efficacy while addressing safety concerns to maintain optimum cellular interactions.

Zwitterionic materials for antifouling membrane surface construction

Membrane separation processes are often perplexed by severe and ubiquitous membrane fouling. Zwitterionic materials, keeping electric neutrality with equivalent positive and negative charged groups, are well known for their superior antifouling properties and have been broadly utilized to construct antifouling surfaces for medical devices, biosensors and marine coatings applications. In recent years, zwitterionic materials have been more and more frequently utilized for constructing antifouling membrane surfaces. In this review, the antifouling mechanisms of zwitterionic materials as well as their biomimetic prototypes in cell membranes will be discussed, followed by the survey of common approaches to incorporate zwitterionic materials onto membrane surfaces including surface grafting, surface segregation, biomimetic adhesion, surface coating and so on. The potential applications of these antifouling membranes are also embedded. Finally, we will present a brief perspective on the future development of zwitterionic materials modified antifouling membranes.

STATEMENT OF SIGNIFICANCE

Membrane fouling is a severe problem hampering the application of membrane separation technology. The properties of membrane surfaces play a critical role in membrane fouling and antifouling behavior/performance. Antifouling membrane surface construction has evolved as a hot research issue for the development of membrane processes. Zwitterionic modification of membrane surfaces has been recognized as an effective strategy to resist membrane fouling. This review summarizes the antifouling mechanisms of zwitterionic materials inspired by cell membranes as well as the popular approaches to incorporate them onto membrane surfaces. It can help form a comprehensive knowledge about the principles and methods of modifying membrane surfaces with zwitterionic materials. Finally, we propose the possible future research directions of zwitterionic materials modified antifouling membranes.

Hydrolysis-controlled protein adsorption and antifouling behaviors of mixed charged self-assembled monolayer: A molecular simulation study

Understanding the mechanism of the antimicrobial and antifouling properties of mixed charged materials is of great significance. The interactions between human gamma fibrinogen (γFg) and mixed carboxylic methyl ether-terminated (COOCH3-) and trimethylamino-terminated (N(CH3)3(+)-) SAMs and the influence of hydrolysis were studied by molecular simulations. After hydrolysis, the mixed SAMs exhibit behaviors from antimicrobial to antifouling, since the COOCH3-thiols were translated into carboxylic acid (COO(-)-) terminated thiols, which carried a net charge of -1 e. Simulation results showed that the main differences between COOCH3-/N(CH3)3(+)-SAM and COO(-)-/N(CH3)3(+)-SAM are the charged property and the hydration layer above the surface. γFg could stably adsorb on the positively-charged COOCH3-/N(CH3)3(+)-SAM. The adsorption behavior is mainly induced by the strong electrostatic attraction. There is a single hydration layer bound to the surface, which is related to the N(CH3)3(+) groups. The van der Waals repulsion between γFg and the single hydration layer are not strong enough to compensate the strong electrostatic attraction. After hydrolysis, the positively-charged SAM was transferred to a neutral mixed charged surface, the electrostatic attraction between γFg and the surface disappears. Meanwhile, the SAM surface is covered by double hydration layers, which is induced by the N(CH3)3(+) and COO(-) groups; water molecules around COO(-) groups are obviously denser than that around N(CH3)3(+) groups. With the combined contribution from double hydration layers and the vanishment of electrostatic attraction, γFg is forced to desorb from the surface. After hydrolysis, the internal structure of mixed SAM appears more ordered due to the electrostatic interactions between charged groups on the top of SAMs.

STATEMENT OF SIGNIFICANCE

The antimicrobial and antifouling materials are of great importance in many biological applications. The strong hydration property of surfaces and the interactions between proteins and surfaces play a key role in resisting protein adsorption. The mixed SAMs, constructed from a 1:1 combination of COOCH3- and N(CH3)3(+)-terminated thiols, can induce protein adsorption mainly through the electrostatic interaction. When the COOCH3-terminated thiols were hydrolyzed to negatively charged COO(-)-terminated thiols, the mixed-charged SAMs switched from antimicrobial to antifouling. Due to the strong hydration property of the mixed charged SAMs, the adsorbed γFg moved away from the surface. Understanding the interactions between protein and mixed-charged SAMs in the atomistic level is important for the practical design and development of new antimicrobial and antifouling materials.

Recent Developments in Antimicrobial Polymers: A Review

Antimicrobial polymers represent a very promising class of therapeutics with unique characteristics for fighting microbial infections. As the classic antibiotics exhibit an increasingly low capacity to effectively act on microorganisms, new solutions must be developed. The importance of this class of materials emerged from the uncontrolled use of antibiotics, which led to the advent of multidrug-resistant microbes, being nowadays one of the most serious public health problems. This review presents a critical discussion of the latest developments involving the use of different classes of antimicrobial polymers. The synthesis pathways used to afford macromolecules with antimicrobial properties, as well as the relationship between the structure and performance of these materials are discussed.

Durable Antibacterial and Nonfouling Cotton Textiles with Enhanced Comfort via Zwitterionic Sulfopropylbetaine Coating

A rapid, environment-friendly, and cost-effective finishing method has been developed for cotton textiles by using zwitterionic NCO-sulfopropylbetaine as the antibacterial finishing agent through covalent bond. The sulfopropylbetaine-finished cotton textile exhibits durable broad-spectrum antibacterial and nonfouling activity, improved mechanical properties, and enhanced comfort.

Physical Cross-Linking Starch-Based Zwitterionic Hydrogel Exhibiting Excellent Biocompatibility, Protein Resistance, and Biodegradability

In this work, a novel starch-based zwitterionic copolymer, starch-graft-poly(sulfobetaine methacrylate) (ST-g-PSBMA), was synthesized via Atom Transfer Radical Polymerization. Starch, which formed the main chain, can be degraded completely in vivo, and the pendent segments of PSBMA endowed the copolymer with excellent protein resistance properties. This ST-g-PSBMA copolymer could self-assemble into a physical hydrogel in normal saline, and studies of the formation mechanism indicated that the generation of the physical hydrogel was driven by electrostatic interactions between PSBMA segments. The obtained hydrogels were subjected to detailed analysis by scanning electron microscopy, swelling ratio, protein resistance, and rheology tests. Toxicity and hemolysis analysis demonstrated that the ST-g-PSBMA hydrogels possess excellent biocompatibility and hemocompatibility. Moreover, the cytokine secretion assays (IL-6, TNF-α, and NO) confirmed that ST-g-PSBMA hydrogels had low potential to trigger the activation of macrophages and were suitable for in vivo biomedical applications. On the basis of these in vitro results, the ST-g-PSBMA hydrogels were implanted in SD rats. The tissue responses to hydrogel implantation and the hydrogel degradation in vivo were determined by histological analysis (Hematoxylin and eosin, Van Gieson, and Masson's Trichrome stains). The results presented in this study demonstrate that the physical cross-linking, starch-based zwitterionic hydrogels possess excellent protein resistance, low macrophage-activation properties, and good biocompatibility, and they are a promising candidate for an in vivo biomedical application platform.

Functionalization of Polydopamine via the Aza-Michael Reaction for Antimicrobial Interfaces

Polydopamine (pDA) coatings afford tremendous versatility due to their capabilities to provide substrate-independent functionalization with a wide range of amine- and thiol-containing molecules. In this work, we developed a new and facile conjugation approach to the formation of β-amino carbonyl linkages between pDA and acrylate/acrylamide molecules via the aza-Michael reaction. Sulfobetaine acrylamide (SBAA), sulfobetaine methacrylate (SBMA), and poly(ethylene glycol) methacrylate (PEGMA) were employed to graft onto pDA films, giving rise to formation of antifouling coatings. Because of the universal adhesive property of pDA, the coating strategy was applied to different substrates, including TiO2, gold, SiO2, Nitinol alloy, polystyrene, and poly(dimethylsiloxane). The variation of surface chemistry and surface wettability upon pDA modification and subsequent conjugation was monitored with X-ray photoelectron spectroscopy (XPS) and water contact angle measurements. Antifouling properties of coatings were challenged by three common Gram-negative and Gram-positive bacteria. Cytocompatibility of the coatings with NIH-3T3 fibroblasts was accessed using MTT assay. The results showed that pDA coatings grafted with SBAA exhibited superhydrophilicity and excellent fouling resistance likely due to the high chemical reactivity of acrylamide, leading to high grafting density. In addition, dual functional coatings containing passive and active antibacterial components were constructed through the in situ deposition of antimicrobial agent, silver nanoparticles, in pDA, followed by the grafting of SBAA for bacterial repellence. The composite coatings allowed reducing adsorption of E. coli by >95%, while killing attached bacteria by up to 98% upon the releasing of Ag(+) ions as measured by inductively coupled plasma mass spectrometry. Consequently, this work paves a new avenue to the grafting strategy to engineer pDA and to the functional bioinspired antifouling interfaces in a substrate-independent fashion.

Spin-Casting Polymer Brush Films for Stimuli-Responsive and Anti-Fouling Surfaces

Surfaces modified with amphiphilic polymers can dynamically alter their physicochemical properties in response to changes of their environmental conditions; meanwhile, amphiphilic polymer coatings with molecular hydrophilic and hydrophobic patches, which can mitigate biofouling effectively, are being actively explored as advanced coatings for antifouling materials. Herein, a series of well-defined amphiphilic asymmetric polymer brushes containing hetero side chains, hydrophobic polystyrene (PS) and hydrophilic poly(ethylene glycol) (PEG), was employed to prepare uniform thin films by spin-casting. The properties of these films were investigated by water contact angle, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and quartz crystal microbalance (QCM). AFM showed smooth surfaces for all films with the roughness less than 2 nm. The changes in water contact angle and C/O ratio (XPS) evidenced the enrichment of PEG or PS chains at film surface after exposed to selective solvents, indicative of stimuli- responsiveness. The adsorption of proteins on PEG functionalized surface was quantified by QCM and the results verified that amphiphilic polymer brush films bearing PEG chains could lower or eliminate protein-material interactions and resist to protein adsorption. Cell adhesion experiments were performed by using HaCaT cells and it was found that polymer brush films possess good antifouling ability.

A Smart Antibacterial Surface for the On-Demand Killing and Releasing of Bacteria

For various human healthcare and industrial applications, endowing surfaces with the capability to not only efficiently kill bacteria but also release dead bacteria in a rapid and repeatable fashion is a promising but challenging effort. In this work, the synergistic effects of combining stimuli-responsive polymers and nanomaterials with unique topographies to achieve smart antibacterial surfaces with on-demand switchable functionalities are explored. Silicon nanowire arrays are modified with a pH-responsive polymer, poly(methacrylic acid), which serves as both a dynamic reservoir for the controllable loading and release of a natural antimicrobial lysozyme and a self-cleaning platform for the release of dead bacteria and the reloading of new lysozyme for repeatable applications. The functionality of the surface can be simply switched via step-wise modification of the environmental pH and can be effectively maintained after several kill-release cycles. These results offer a new methodology for the engineering of surfaces with switchable functionalities for a variety of practical applications in the biomedical and biotechnology fields.

Antifouling and Antibacterial Multifunctional Polyzwitterion/Enzyme Coating on Silicone Catheter Material Prepared by Electrostatic Layer-by-Layer Assembly

The formation of bacterial biofilms on indwelling medical devices generally causes high risks for adverse complications such as catheter-associated urinary tract infections. In this work, a strategy for synthesizing innovative coatings of poly(dimethylsiloxane) (PDMS) catheter material, using layer-by-layer assembly with three novel functional polymeric building blocks, is reported, i.e., an antifouling copolymer with zwitterionic and quaternary ammonium side groups, a contact biocidal derivative of that polymer with octyl groups, and the antibacterial hydrogen peroxide (H2O2) producing enzyme cellobiose dehydrogenase (CDH). CDH oxidizes oligosaccharides by transferring electrons to oxygen, resulting in the production of H2O2. The design and synthesis of random copolymers which combine segments that have antifouling properties by zwitterionic groups and can be used for electrostatically driven layer-by-layer (LbL) assembly at the same time were based on the atom-transfer radical polymerization of dimethylaminoethyl methacrylate and subsequent partial sulfobetainization with 1,3-propane sultone followed by quaternization with methyl iodide only or octyl bromide and thereafter methyl iodide. The alternating multilayer systems were formed by consecutive adsorption of the novel polycations with up to 50% zwitterionic groups and of poly(styrenesulfonate) as the polyanion. Due to its negative charge, enzyme CDH was also firmly embedded as a polyanionic layer in the multilayer system. This LbL coating procedure was first performed on prefunctionalized silicon wafers and studied in detail with ellipsometry as well as contact angle (CA) and zetapotential (ZP) measurements before it was transferred to prefunctionalized PDMS and analyzed by CA and ZP measurements as well as atomic force microscopy. The coatings comprising six layers were stable and yielded a more neutral and hydrophilic surface than did PDMS, the polycation with 50% zwitterionic groups having the largest effect. Enzyme activity was found to be dependent on the depth of embedment in the multilayer coating. Depending on the used polymeric building block, up to a 60% reduction in the amount of adhering bacteria and clear evidence for killed bacteria due to the antimicrobial functionality of the coating could be confirmed. Overall, this work demonstrates the feasibility of an easy to perform and shape-independent method for preparing an antifouling and antimicrobial coating for the significant reduction of biofilm formation and thus reducing the risk of acquiring infections by using urinary catheters.

Zwitterionic-Modified Starch-Based Stealth Micelles for Prolonging Circulation Time and Reducing Macrophage Response

Over the last few decades, nanoparticles have been emerging as useful means to improve the therapeutic efficacy of drug delivery and medical diagnoses. However, the heterogeneity and complexity of blood as a medium is a fundamental problem; large amounts of protein can be adsorbed onto the surface of nanoparticles and cause their rapid clearance before reaching their target sites, resulting in the failure of drug delivery. To overcome this challenge, we present a rationally designed starch derivative (SB-ST-OC) with both a superhydrophilic moiety of zwitterionic sulfobetaine (SB) and a hydrophobic segment of octane (OC) as functional groups, which can self-assemble into "stealth" micelles (SSO micelles). The superhydrophilic SB kept the micelles stable against aggregation in complex media and imbued them with "stealth" properties, eventually extending their circulation time in blood. In stability and hemolysis tests the SSO micelles showed excellent protein resistance properties and hemocompatibility. Moreover, a phagocytosis test and cytokine secretion assay confirmed that the SSO micelles had less potential to trigger the activation of macrophages and were more suitable as a drug delivery candidate in vivo. On the basis of these results, doxorubicin (DOX), a hydrophobic drug, was used to investigate the potential application of this novel starch derivative in vivo. The results of the pharmacokinetic study showed that the values of the plasma area under the concentration curve (AUC) and elimination half-life (T1/2) of the SSO micelles were higher than those of micelles without SB modifications. In conclusion, the combination of excellent protein resistance, lower macrophage activation, and longer circulation time in vivo makes this synthesized novel starch derivative a promising candidate as a hydrophobic drug carrier for long-term circulation in vivo.