Just Antimicrobial is not Enough: Toward Bifunctional Polymer Surfaces with Dual Antimicrobial and Protein-Repellent Functionality

Dynamic Antimicrobial Poly(disulfide) Coatings Exfoliate Biofilms On Demand Via Triggered Depolymerization

Bacterial biofilms are notoriously problematic in applications ranging from biomedical implants to ship hulls. Cationic, amphiphilic antibacterial surface coatings delay the onset of biofilm formation by killing microbes on contact, but they lose effectiveness over time due to non-specific binding of biomass and biofilm formation. Harsh treatment methods are required to forcibly expel the biomass and regenerate a clean surface. Here, a simple, dynamically reversible method of polymer surface coating that enables both chemical killing on contact, and on-demand mechanical delamination of surface-bound biofilms, by triggered depolymerization of the underlying antimicrobial coating layer, is developed. Antimicrobial polymer derivatives based on α-lipoic acid (LA) undergo dynamic and reversible polymerization into polydisulfides functionalized with biocidal quaternary ammonium salt groups. These coatings kill >99.9% of Staphylococcus aureus cells, repeatedly for 15 cycles without loss of activity, for moderate microbial challenges (≈105 colony-forming units (CFU) mL-1, 1 h), but they ultimately foul under intense challenges (≈107 CFU mL-1, 5 days). The attached biofilms are then exfoliated from the polymer surface by UV-triggered degradation in an aqueous solution at neutral pH. This work provides a simple strategy for antimicrobial coatings that can kill bacteria on contact for extended timescales, followed by triggered biofilm removal under mild conditions.

Advancements in release-active antimicrobial biomaterials: A journey from release to relief

Escalating medical expenses due to infectious diseases are causing huge socioeconomic pressure on mankind globally. The emergence of antibiotic resistance has further aggravated this problem. Drug-resistant pathogens are also capable of forming thick biofilms on biotic and abiotic surfaces to thrive in a harsh environment. To address these clinical problems, various strategies including antibacterial agent delivering matrices and bactericidal coatings strategies have been developed. In this review, we have discussed various types of polymeric vehicles such as hydrogels, sponges/cryogels, microgels, nanogels, and meshes, which are commonly used to deliver antibiotics, metal nanoparticles, and biocides. Compositions of these polymeric matrices have been elaborately depicted by elucidating their chemical interactions and potential activity have been discussed. On the other hand, various implant/device-surface coating strategies which exploit the release-active mechanism of bacterial killing are discussed in elaboration. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Cardiovascular Disease Implantable Materials and Surgical Technologies > Nanomaterials and Implants Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease.

Stimulus-Responsive Polyelectrolyte Surfaces: Switching Surface Properties from Polycationic/Antimicrobial to Polyzwitterionic/Protein-Repellent

Surfaces coated with polyzwitterions are most well-known for their ability to resist protein adsorption. In this article, a surface-attached hydrophobically modified poly(carboxybetaine) is presented. When protonated by changes of the pH of the surrounding medium, this protein-repellent polyzwitterion switches to a polycationic state in which it is antimicrobially active and protein-adhesive. The pH range in which these two states exist are recorded by zeta potential measurements. Adsorption studies at different pH values (monitored by surface plasmon resonance spectroscopy) confirm that the adhesion of protein is pH dependent and reversible, that is, protein can be released upon a pH change from pH 3 to pH 7.4. At physiological pH, the poly(carboxyzwitterion) is antimicrobially active, presumably because it becomes protonated by bacterial metabolites during the antimicrobial activity assay. Stability studies confirm that the here presented material is storage-stable, yet hydrolyses after longer incubation in aqueous media.

Advances of peptides for antibacterial applications

In the past few decades, peptide antibacterial products with unique antibacterial mechanisms have attracted widespread interest. They can effectively reduce the probability of drug resistance of bacteria and are biocompatible, so they possess tremendous development prospects. This review provides recent research and analysis on the basic types of antimicrobial peptides (including poly (amino acid)s, short AMPs, and lipopeptides) and factors to optimize antimicrobial effects. It also summarizes the two most important modes of action of antimicrobial peptides and the latest developments in the application of AMPs, including antimicrobial agent, wound healing, preservative, antibacterial coating and others. Finally, we discuss the remaining challenges to improve the antibacterial peptides and propose prospects in the field.

Access to thermally robust and abrasion resistant antimicrobial plastics: synthesis of UV-curable phosphonium small molecule coatings and extrudable additives

The threat of antibiotic-resistant, biofilm-forming bacteria necessitates a preventative approach to combat the proliferation of robust, pathogenic strains on "high touch surfaces" in the food packaging, biomedical, and healthcare industries. The development of both biocide-releasing and tethered, immobilized biocide surface coatings has risen to meet this demand. While these surface coatings have demonstrated excellent antimicrobial efficacy, there are few examples of antimicrobial surfaces with long-term durability and performance. To this end, UV-curable phosphoniums bearing benzophenone anchors with either an alkyl, aryl, or fluoroalkyl group were synthesized and their efficacy as thermally stable antimicrobial additives in extruded plastics or as surface attached coatings probed. The surface topology and characteristics of these materials were studied to gain insight into the mechanism of their antimicrobial activity. Efficacy against both Gram negative and Gram positive bacteria as either a coating or additive showed compete reductions of the initial bacterial load. Crucially, the materials maintained the ability to kill biofilm-forming bacteria even after being subject to several cycles of abrasion.

UV-Curable Surface-Attached Antimicrobial Polymeric Onium Coatings: Designing Effective, Solvent-Resistant Coatings for Plastic Surfaces

Contact-active ammonium and phosphonium antimicrobial polymeric coatings grafted to plastic surfaces by UV treatment are described. Robust, antimicrobial styrenic polymeric scaffolds copolymerized with a low loading of UV-curable benzophenone were prepared by nitroxide-mediated polymerization (NMP). Similar reversible addition-fragmentation chain-transfer (RAFT)-controlled radical polymerizations were attempted for comparison. These random styrenics were further functionalized into partially quaternarized water-soluble cationic polymers. UV-cured polymeric thin film coatings possessing cationic groups with n-alkyl substituents of n ≤ 2 demonstrate antimicrobial properties against both Gram-positive and Gram-negative bacteria, while species containing bulkier or longer substituents were biologically inactive. The UV-cured cationic antimicrobial polymeric onium thin films also demonstrate enhanced abrasion and chemical resistance.

Fungal spore adhesion on glycidoxypropyltrimethoxy silane modified silica nanoparticle surfaces as revealed by single cell force spectroscopy

Thin film coatings prepared from commercially available glycidoxypropyltrimethoxysilane (GPS) modified silica nanoparticles (SiNPs) (Bindzil® CC301 and Bindzil® CC302) have previously shown excellent antifouling performance against a broad range of microbes [Molino et al., "Hydration layer structure of biofouling-resistant nanoparticles," ACS Nano 12, 11610 (2018)]. In this work, single cell force spectroscopy (SCFS) was used to measure the biological interactions between Epicoccum nigrum fungal spores and the same silica nanoparticle-based surfaces used in the aforementioned study, including a: glass coverslip, unmodified SiNP coatings, and both low (Bindzil® CC301) and high density (CC302) GPS functionalized SiNP coatings as a function of NaCl concentration. From the SCFS curves, the spore adhesion to the surface was greatest on the glass coverslip (20-80 nN) followed by the unmodified SiNP (3-5 nN) across all salt concentrations. Upon approach to both surfaces, the spores showed a long-range attraction generally with a profile characteristic of biointeractions and likely those of the outer cell wall structures or biological constituents. The attractive force allowed the spores to initially adhere to the surface and was found to be linearly proportional to the spore adhesion. In comparison, both high and low density GPS-SINP significantly reduced the spore adhesion (0.5-0.9 nN). In addition, the spore adhesion on high density GPS-SiNP occurred in only 14%-27% of SCFS curves (40%-48% for low density GPS-SiNP) compared to 83%-97% for the unmodified SiNP, indicating that in most cases the GPS functionalization completely prevented spore adhesion. The GPS-SiNP surfaces conversely showed a long-range electrostatic repulsion at low 1mM NaCl that was replaced by short-range repulsion at the higher salt concentrations. From the findings, it is proposed that the attractive force is a critical step in initial adhesion processes of the spore. The effective antifouling properties of the GPS are attributed to the ability to negate the attractive forces, either through electrostatic repulsion in low salt conditions and primarily from short-range repulsion correlating to the previously reported combined steric-hydration effect of the GPS functionalization on SiNP coatings.

Stimulus-Responsive Polyzwitterionic Surfaces Made from Itaconic Acid: Self-Triggered Antimicrobial Activity, Protein Repellency, and Cell Compatibility

A functional monomer carrying a carboxylate and a protected primary ammonium group is synthesized from itaconic acid. When copolymerized with dimethyl acrylamide and 4-methacryloyloxybenzophenone, cross-linkable polyzwitterions are obtained. These are converted to surface-attached polyzwitterion networks by simultaneous UV-triggered C,H insertion reactions. The resulting polyzwitterion-coated substrates were studied by surface plasmon resonance spectroscopy measurements, ζ potential and various biological assays. They were (expectedly) protein repellent, yet at the same time (and unexpectedly) cell-adhesive and antimicrobially active. This was attributed to stimulus-responsiveness of the polyzwitterion (confirmed by the ζ potential measurements), which enables charge adjustment at different pH values. When protonated, the polyzwitterions become amphiphilic polycations and, in this state, kill bacteria upon contact like their parent structures (polymer-based synthetic mimics of antimicrobial peptides, SMAMPs).

Poly(oxanorbornene)-Coated CdTe Quantum Dots as Antibacterial Agents

In this study, synthetic mimics of antimicrobial peptides based on poly(oxanorbornene) molecules (or PONs) were used to coat CdTe quantum dots (QDs). These PONs-CdTe QDs were investigated for their activity against Escherichia coli, a bacterium with antibiotic resistant strains. At the same time, the antibacterial activity of the PONs-CdTe QDs was compared to the antibacterial activity of free PONs and free CdTe QDs. The observed antibacterial activity of the PONs-CdTe QDs was additive and concentration dependent. The conjugates had a significantly lower minimum inhibitory concentration (MIC) than the free PONs and QDs, particularly for PONs-CdTe QDs which contained PONs of high amine density. The maximum activity of PONs-CdTe QDs was not realized by conjugating PONs with the highest intrinsic antibacterial activity (i.e., the lowest MIC in solution as free PONs), indicating that the mechanism of action for free PONs and PONs-CdTe QDs is different. Equally important, conjugating PONs to CdTe QDs decreased their hemolytic activity against red blood cells compared to free PONs, lending to higher therapeutic indices against E. coli. This could potentially enable the use of higher, and therefore more effective, PONs-QDs concentrations when addressing bacterial contamination, without concerns of adverse impacts on mammalian cells and organisms.

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.

Bifunctional Bioactive Polymer Surfaces with Micrometer and Submicrometer-sized Structure: The Effects of Structure Spacing and Elastic Modulus on Bioactivity

This study presents a comparison of two types of bifunctional structured surface that were made from the same polymer -- an antimicrobial polycation (a synthetic mimic of an antimicrobial peptide, SMAMP) and a protein-repellent polyzwitterion (poly(sulfobetaines), PSB). The first type of bifunctional surface was fabricated by a colloidal lithography (CL) based process where the two polymers were immobilized sequentially onto pre-structured surfaces with a chemical contrast (gold on silicon). This enabled site-selective covalent attachment. The CL materials had a spacing ranging from 200 nm to 2 µm. The second type of structured surface (spacing: 1 - 8.5 µm) was fabricated using a microcontact printing (µCP) process where SMAMP patches were printed onto a PSB network, so that 3D surface features were obtained. The thus obtained materials were studied by quantitative nanomechanical measurements using atomic force microscopy (QNM-AFM). The different architectures led to different local elastic moduli at the polymer-air interface, where the CL surfaces were much stiffer (Derjaguin-Muller-Toporov (DMT) modulus = 20 ± 0.8 GPa) compared to the structured 3D networks obtained by µCP (DMT modulus = 42 ± 1.1 MPa). The effects of the surface topology and stiffness on the antimicrobial activity against Escherichia coli, the protein repellency (using fibrinogen), and the compatibility with human gingival mucosal keratinocytes were investigated. The softer 3D µCP surfaces had simultaneous antimicrobial activity, protein repellency, and cell compatibility at all spacings. For the stiffer CL surfaces, quantitative simultaneous antimicrobial activity and protein repellency was not obtained. However, the cell compatibility could be maintained at all spacings. The optimum spacing for the CL materials was in the range of 500 nm-1 µm, with significantly reduced antimicrobial activity at 2 µm spacing. Thus, the soft polymer network obtained by µCP could be more easily optimized than the stiff CL surface, and had a broader topology range of optimal or near-optimal bioactivity.

Tailored Functional Surfaces Using Nanoparticle and Protein "Nanobrick" Coatings

Surface properties are an essential feature in a wide range of functional materials. In this article, we summarize strategies developed in our group that employ nanoparticles and proteins as nanobricks to create thin-film coatings on surfaces. These coatings contain tailorable surface functionality based on the properties of the predesigned nanobricks, parlaying both the chemical and structural features of the precursor particles and proteins. This strategy is versatile, providing the rapid generation of both uniform and patterned coatings that provide "plug-and-play" customizable surfaces for materials and biomedical applications.

Switchable Dual-Function and Bioresponsive Materials to Control Bacterial Infections

The colonization of undesired bacteria on the surface of devices used in biomedical and clinical applications has become a persistent problem. Different types of single-function (cell resistance or bactericidal) bioresponsive materials have been developed to cope with this problem. Even though these materials meet the basic requirements of many biomedical and clinical applications, dual-function (cell resistance and biocidal) bioresponsive materials with superior design and function could be better suited for these applications. The past few years have witnessed the emergence of a new class of dual-function materials that can reversibly switch between cell-resistance and biocidal functions in response to external stimuli. These materials are finding increased applications in biomedical devices, tissue engineering, and drug-delivery systems. This review highlights the recent advances in design, structure, and fabrication of dual-function bioresponsive materials and discusses translational challenges and future prospects for research involving these materials.

Surface Modification by Polyzwitterions of the Sulfabetaine-Type, and Their Resistance to Biofouling

Films of zwitterionic polymers are increasingly explored for conferring fouling resistance to materials. Yet, the structural diversity of polyzwitterions is rather limited so far, and clear structure-property relationships are missing. Therefore, we synthesized a series of new polyzwitterions combining ammonium and sulfate groups in their betaine moieties, so-called poly(sulfabetaine)s. Their chemical structures were varied systematically, the monomers carrying methacrylate, methacrylamide, or styrene moieties as polymerizable groups. High molar mass homopolymers were obtained by free radical polymerization. Although their solubilities in most solvents were very low, brine and lower fluorinated alcohols were effective solvents in most cases. A set of sulfabetaine copolymers containing about 1 mol % (based on the repeat units) of reactive benzophenone methacrylate was prepared, spin-coated onto solid substrates, and photo-cured. The resistance of these films against the nonspecific adsorption by two model proteins (bovine serum albumin-BSA, fibrinogen) was explored, and directly compared with a set of references. The various polyzwitterions reduced protein adsorption strongly compared to films of poly(nbutyl methacrylate) that were used as a negative control. The poly(sulfabetaine)s showed generally even somewhat higher anti-fouling activity than their poly(sulfobetaine) analogues, though detailed efficacies depended on the individual polymer-protein pairs. Best samples approach the excellent performance of a poly(oligo(ethylene oxide) methacrylate) reference.

Preparation and antibacterial activity of silver-loaded poly(oligo(ethylene glycol) methacrylate) brush

Herein, we report on a robust approach to fabricate antibacterial nanocomposite coating simply by immersing poly(oligo(ethylene glycol) methacrylate) (POEGMA) brush into a silver perchlorate solution without using any external reducing agents. The POEGMA brush of 48.3 nm in thickness is prepared via surface-initiated atom transfer radical polymerization method. Field-emission scanning electron microscope and Raman measurements indicate that silver nanoparticles of 14 ∼ 25 nm in diameter are successfully embedded into the POEGMA brush. Antibacterial activities of the resultant silver-loaded POEGMA brushes against both Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus are measured by zone of inhibition and colony-counting methods, respectively. The results show that the silver-loaded POEGMA coatings exhibit enhanced antibacterial efficiency compared to bare POEGMA brush. In order to elucidate their antibacterial mechanism, silver release behaviors of these silver-loaded POEGMA brushes are monitored via inductively coupled plasma mass spectrometry.

Three-Dimensional, Bifunctional Microstructured Polymer Hydrogels Made from Polyzwitterions and Antimicrobial Polymers

Biofilm-associated infections of medical devices are a global problem. For the prevention of such infections, biomaterial surfaces are chemically or topographically modified to slow down the initial stages of biofilm formation. In the bifunctional material here presented, chemical and topographical cues are combined, so that protein and bacterial adhesion as well as bacterial proliferation are effectively inhibited. Upon changes in the surface topography parameters and investigation of the effect of these changes on bioactivity, structure-property relationships are obtained. The target material is obtained by microcontact printing (μCP), a soft lithography method. The antimicrobial component, poly(oxanorbornene)-based synthetic mimics of an antimicrobial peptide (SMAMP), was printed onto a protein-repellent polysulfobetaine hydrogel, so that bifunctional 3D structured polymer surfaces with 1, 2, and 8.5 μm spacing are obtained. These surfaces are characterized with fluorescence microscopy, surface plasmon resonance spectroscopy, atomic force microscopy, and contact angle measurements. Biological studies show that the bifunctional surfaces with 1 and 2 μm spacing are 100% antimicrobially active against Escherichia coli and Staphylococcus aureus, 100% fibrinogen-repellent, and nontoxic to human gingival mucosal keratinocytes. At 8.5 μm spacing, the broad-band antimicrobial activity and the protein repellency are compromised, which indicates that this spacing is above the upper limit for effective simultaneous antimicrobial activity and protein repellency of polyzwitterionic-polycationic materials.

Mussel-Inspired Surface Functionalization of PET with Zwitterions and Silver Nanoparticles for the Dual-Enhanced Antifouling and Antibacterial Properties

Herein, we designed and constructed a dual functional surface with antimicrobial and antifouling abilities to prevent protein and bacterial attachment that are significant challenges in biomedical devices. Primary amino-group-capped sulfobetaine of DMMSA was synthesized and then grafted onto polydopamine pretreated PET sheets via click chemistry. The sheets were subsequently immersed into silver ion solution, in which the absorbed silver ions were reduced to silver nanoparticles (AgNPs) in situ by a polydopamine layer. The antifouling assays demonstrated that the resultant PET/DMMSA/AgNPs sheets exhibited great antifouling performances against bovine serum albumin (BSA), bovine fibrinogen (BFG), platelets, and bacteria, the critical proteins/microorganisms leading to implant failure. The antibacterial data suggested that the sheets had dual functions as inhibitors of bacterial growth and bactericide and could efficiently delay the biofilm formation. This repelling and killing approach is green and simple, with potential biomedical applications.

Povidone-iodine-functionalized fluorinated copolymers with dual-functional antibacterial and antifouling activities

Povidone-iodine-functionalized fluorinated polymer coatings with dual-functional antibacterial and antifouling activities should be very promising in practical biomedical applications.

Stable and self-healable LbL coating with antibiofilm efficacy based on alkylated polyethyleneimine micelles

An antibacterial and self-healing coating was fabricated via LbL assembly based on N-decyl PEI (DPEI) micelles.

Surface-Attached Poly(oxanorbornene) Hydrogels with Antimicrobial and Protein-Repellent Moieties: The Quest for Simultaneous Dual Activity

By copolymerizing an amphiphilic oxanorbornene monomer bearing N- tert-butyloxycarbonyl (Boc) protected cationic groups with an oxanorbornene-functionalized poly(ethylene glycol) (PEG) macromonomer, bifunctional comb copolymers were obtained. Varying the comonomer ratios led to copolymers with PEG contents between 5⁻25 mol %. These polymers were simultaneously surface-immobilized on benzophenone-bearing substrates and cross-linked with pentaerythritoltetrakis(3-mercaptopropionate). They were then immersed into HCl to remove the Boc groups. The thus obtained surface-attached polymer hydrogels (called SMAMP*-co-PEG) were simultaneously antimicrobial and protein-repellent. Physical characterization data showed that the substrates used were homogeneously covered with the SMAMP*-co-PEG polymer, and that the PEG moieties tended to segregate to the polymer⁻air interface. Thus, with increasing PEG content, the interface became increasingly hydrophilic and protein-repellent, as demonstrated by a protein adhesion assay. With 25 mol % PEG, near-quantitative protein-adhesion was observed. The antimicrobial activity of the SMAMP*-co-PEG polymers originates from the electrostatic interaction of the cationic groups with the negatively charged cell envelope of the bacteria. However, the SMAMP*-co-PEG surfaces were only fully active against E. coli, while their activity against S. aureus was already compromised by as little as 5 mol % (18.8 mass %) PEG. The long PEG chains seem to prevent the close interaction of bacteria with the surface, and also might reduce the surface charge density.

Simultaneously Antimicrobial, Protein-repellent and Cell-compatible Polyzwitterion Networks: More Insight on Bioactivity and Physical Properties

A poly(oxanorbornene)-based polyzwitterion with primary ammonium and carboxylate groups (PZI) has been reported previously as the first simultaneously antimicrobial and protein-repellent polyzwitterion. Here, additional physical and biological properties of three poly(oxanorbornene)-based polyzwitterions with different functional groups (PZI, the polycarboxybetaine PCB, and the polysulfobetaine PSB) are compared to understand the molecular origins of this unusual bioactivity. Additionally, the three polyzwitterions and the antimicrobial, polycationic SMAMP are exposed to proteins, bacteria suspensions, human plasma and serum. These interactions are investigated by surface plasmon resonance spectroscopy. In protein adhesion studies, neither fibrinogen nor lysozyme adhere irreversibly to PZI, yet reversible interaction with lysozyme is observed at pH 7 and 8. In the presence of bivalent cations, reversible fibrinogen adhesion on PZI and PSB is observed, but not on PCB. This might explain why mammalian cells grow on PZI and PSB, but not on PCB. PZI does not show human plasma adhesion, while PCB and PSB have 0.27 and 0.48 ng mm^-2 adhered plasma, and SMAMP even 6.3 ng mm^-2. Both PZI and SMAMP show strong serum adhesion, while no serum adhered to PCB, and only little to PSB. This could be related to the pH difference between serum and plasma, to which the pH-responsive primary ammonium groups are susceptible, while the permanently charged NR₄ ⁺ groups are unaffected. Both PZI and PCB showed none or only little bacterial adhesion. PCB is also intrinsically antimicrobial against E. coli and S. aureus bacteria and thus is also simultaneously protein-repellent and antimicrobially active. Thus, while the carboxylate groups of PZI and PCB seems to be a prerequisite for the dual antimicrobial activity and protein-repellency, the pH-responsiveness of the primary ammonium group seems to make the PZI molecule vulnerable for protein adhesion in fluids that are slightly out of the physiological range.

Structure-Property Relationships of Amine-rich and Membrane-Disruptive Poly(oxonorbornene)-Coated Gold Nanoparticles

The article describes the interactions between poly (oxonorbornenes) (PONs)-coated gold nanoparticles (AuNPs) with phospholipid vesicles and shows that the strength of these interactions strongly depends on the molecular structure of PONs, specifically their amine/alkyl side chain ratio. PONs, which are a recently introduced class of cationic polyelectrolytes, can be systematically varied to control the amine/alkyl ratio and to explore how the chemical character of cationic polyelectrolytes affects their interactions and the interactions of their nanoparticle conjugates with model membranes. Our study shows that increasing the amine/alkyl ratio by copolymerization of diamine and 1:1 amine/butyl oxonorbornene monomers impacts the availability of PONs amine/ammonium functional groups to interact with phospholipid membranes, the PONs surface coverage on AuNPs, and the membrane disruption activity of free PONs and PONs-AuNPs. The study makes use of transmission electron microscopy, UV-vis spectroscopy, dynamic light scattering, thermogravimetric analysis, fluorescamine assay, ζ-potential measurements, and X-ray photoelectron spectroscopy measurements to characterize the PONs-AuNPs' size, size distribution, aggregation state, surface charge, and PONs surface coverage. The study also makes use of real-time fluorescence measurements of fluorescent liposomes before and during exposure to free PONs and PONs-AuNPs to determine the membrane disruption activity of free PONs and PONs-AuNPs. As commonly observed with cationic polyelectrolytes, both free PONs and PONs-AuNPs display significant membrane disruption activity. Under conditions where the amine/alkyl ratio in PONs maximizes PONs surface coverage, the membrane disruption activity of PONs-AuNPs is about 10-fold higher than the membrane disruption activity of the same free PONs. This is attributed to the increased local concentration of ammonium ions when PONs-AuNPs interact with the liposome membranes. In contrast, the hydrophobicity of amine-rich PONs, which are made for example from diamine oxonorbornene monomers, is significantly reduced. This leads to a significant reduction of PON surface coverage on AuNPs and in turn to a significant decrease in membrane disruption.

Surface-attached poly(phosphoester)-hydrogels with benzophenone groups

Photo-reactive poly(phosphoester)s (PPEs) forming surface-attached PPE-networks and hydrogels are presented.

Fluorescent ROMP Monomers and Copolymers for Biomedical Applications

The synthesis and characterization of a series of green, blue and red-fluorescent exo-oxanorbornene acid and imide monomers carrying nitrobenzofurazan, coumarin, and Rhodamin B, respectively, as fluorophores is presented. These monomers carry oxanorbornene as polymerizable unit, and were readily copolymerized with bioactive functional oxanorbornene monomers by ring-opening metathesis polymerization (ROMP), as demonstrated by gel permeation chromatography and NMR spectroscopy. Due to the ease of synthesis of these monomers, and their cost-effectiveness compared many to other fluorescent probes, they are useful for biomaterials applications.

UV-Curable Contact Active Benzophenone Terminated Quaternary Ammonium Antimicrobials for Applications in Polymer Plastics and Related Devices

A series of UV active benzophenone ([C₆H₅COC₆H₄-O-(CH₂)_n-N⁺Me₂R][X^-]; 4, R = C₁₂H₂₅, n = 3, X^- = Br^-; 5a-c, R = C₁₈H₃₇, n = 3, X^- = Cl^-, Br^-, I^-; 6a-c, R = C₁₈H₃₇, n = 4, X^- = Cl^-, Br^-, I^-; 7a-c, R = C₁₈H₃₇, n = 6, X^- = Cl^-, Br^-, I^-) terminated C₁₂ and C₁₈ quaternary ammonium salts (QACs) were prepared by thermal or microwave-driven Menshutkin protocols of the appropriate benzophenone alkyl halide (1a-c, 2a-c, 3a-c) with the corresponding dodecyl- or octadecyl N,N-dimethylamine. All new compounds were characterized by NMR spectroscopy, HRMS spectrometry, and, in one instance (4), by single-crystal X-ray crystallography. Representative C₁₂ and C₁₈ benzophenone QACs were formulated into 1% (w/v) water or water/ethanol-based aerosol spray coatings and then UV-cured onto plastic substrates (polypropylene, polyethylene, polystyrene, polyvinyl chloride, and polyether ether ketone) with exposure to low to moderate doses of UV (20-30 J cm^-2). Confirmation as to the presence of the coatings was detected by advancing water contact angle measurements, which revealed a more hydrophilic surface after coating. Further confirmation was gained by X-ray photoelectron spectroscopy analysis, time of flight secondary ion mass spectrometry, and bromophenol blue staining, all of which showed the presence of the attached quaternary ammonium molecule. Analysis of surfaces treated with the C₁₈ benzophenone 5b by atomic force microscopy and surface profilometry revealed a coating thickness of ∼350 nm. The treated samples along with controls were then evaluated for their antimicrobial efficacy against Gram-positive (Arthrobacter sp., Listeria monocytogenes) and Gram-negative (Pseudomonas aeruginosa) bacteria at a solid/air interface using the large drop inoculum protocol; this technique gave no evidence for cell adhesion after a 3 h time frame. These antimicrobial materials show promise for their use as coatings on plastic biomedical devices with the aim of preventing biofilm formation and preventing the spread of hospital acquired infections.

Dual-Functional Polyethylene Glycol-b-polyhexanide Surface Coating with in Vitro and in Vivo Antimicrobial and Antifouling Activities

In recent years, microbial colonization on the surface of biomedical implants/devices has become a severe threat to human health. Herein, surface-immobilized guanidine derivative block copolymers create an antimicrobial and antifouling dual-functional coating. We report the preparation of an antimicrobial and antifouling block copolymer by the conjugation of polyhexanide (PHMB) with either allyl glycidyl ether or allyloxy polyethylene glycol (APEG; MW 1200 and 2400). The allyl glycidyl ether modified PHMB (A-PHMB) and allyloxy polyethylene glycol_1200/2400 modified PHMB (APEG_1200/2400-PHMB) copolymers were grafted onto a silicone rubber surface as a bottlebrush-like coating, respectively, using a plasma-UV-assisted surface-initiated polymerization. Both A-PHMB and APEG_1200/2400-PHMB coatings exhibited excellent broad-spectrum antimicrobial properties against Gram-negative/positive bacteria and fungi. The APEG₂₄₀₀-PHMB coating displayed an improved antibiofilm as well as antifouling properties and a long reusable cycle, compared with two other coatings, due to its abundant PEG blocks among those copolymers. Also, the APEG₂₄₀₀-PHMB-coated silicone coupons were biocompatible toward mammalian cells, as revealed by in vitro hemocompatibile and cytotoxic assays. An in vivo study showed a significant decline of Escherichia coli colonies with a 5-log reduction, indicating the APEG₂₄₀₀-PHMB coating surface worked effectively in the rodent subcutaneous infection model. This PHMB-based block copolymer coating is believed to be an effective strategy to prevent biomaterial-associated infections.

Rationally designed dual functional block copolymers for bottlebrush-like coatings: In vitro and in vivo antimicrobial, antibiofilm, and antifouling properties

Numerous antimicrobial coatings have been developed for biomedical devices/implants, but few can simultaneously fulfill the requirements for antimicrobial and antifouling ability and biocompatibility. In this study, to develop an antimicrobial and antibiofilm surface coating, diblock amphiphilic molecules with antimicrobial and antifouling segments in a single chain were rationally designed and synthesized. Cationic antimicrobial polypeptides (AMP) were first synthesized by N-carboxyanhydride ring-opening polymerization (NCA-ROP). Heterofunctionalized poly(ethylene glycol) with different lengths (methacrylate-PEG_n-tosyl, n=10/45/90) was synthesized and site-specifically conjugated with polypeptides to form diblock amphiphiles. Along with increased PEG chain length, hemolytic activity was considerably improved, and broad-spectrum antimicrobial activity is retained. Three MA-PEG_n-b-AMP copolymers were further grafted onto the surface of silicone rubber (a commonly used catheter material) via plasma/UV-induced surface polymerizations to form a bottlebrush-like coating with excellent antimicrobial activity against several pathogenic bacteria (Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus), and effectively prevent biofilm formation. This bottlebrush coating also greatly reduced protein adsorption and platelet adhesion, indicating its excellent antifouling ability. An in vitro cytotoxicity study also demonstrated that this coating is biocompatible with mammalian cells. After subcutaneous implantation of the materials in rats, we demonstrated that the g-PEG₄₅-b-AMP bottlebrush coating exhibits significant anti-infective activity in vivo. Thus, this facilely synthesized PEGylated AMP bottlebrush coating is a feasible method to prevent biomedical devices-associated infections.

STATEMENT OF SIGNIFICANCE

Current antimicrobial coatings are often associated with concerns such as antibiotic resistance, environmental pollution, short-time antimicrobial activity, biofouling, poor blood compatibility and cytotoxicity, etc. To overcome these drawbacks, a robust PEGylated cationic amphiphilic peptides-based bottlebrush-like surface coating is demonstrated here, which fulfil the requirements of antimicrobial and antifouling as well as biocompatibility in the meantime. Briefly, the rational designed g-PEG_n-b-AMP block copolymers (n=10/45/90) were synthesized and grafted on silicone surface. This bottlebrush-like coating efficiently kill the contacted bacteria and prevent the biofilm formation, greatly reduced protein and platelet adhesion. It also exhibits excellent blood compatibility and low cytotoxicity in vitro. In particular, g-PEG₄₅-b-AMP coating exhibits significant anti-infection effect in vivo. This coating offering an effective strategy for combating biomedical devices-associated infections.

Autoclaving-Derived Surface Coating with In Vitro and In Vivo Antimicrobial and Antibiofilm Efficacies

Biomedical device-associated infections which engender severe threat to public health require feasible solutions. In this study, block copolymers consisting of antimicrobial, antifouling, and surface-tethering segments in one molecule are synthesized and grafted on polymeric substrates by a facile plasma/autoclave-assisted method. Hetero-bifunctional polyethylene glycol (PEG) with allyl and tosyl groups (APEG-OTs) is first prepared. PEGs with different molecular weights (1200 and 2400 Da) are employed. Polyhexamethylene guanidine (PHMG) which has excellent broad-spectrum antimicrobial activity and thermal/chemical stability, is conjugated with APEG-OTs to generate the block copolymer (APEG-PHMG). Allyl terminated PHMG (A-PHMG) without PEG segments is also synthesized by reacting PHMG with allyl glycidyl ether. The synthesized copolymers are thermal initiated by autoclaving and grafted on plasma pretreated silicone surface, forming permanently bonded bottlebrush-like coatings. Both A-PHMG and APEG_1200/2400 -PHMG coatings exhibit potent antimicrobial activity against gram-positive/negative bacteria and fungus, whereas APEG_1200/2400 -PHMG coatings show superior antifouling activity and long-term reusability to A-PHMG coating. APEG₂₄₀₀ -PHMG coating demonstrates the most effective in vitro antibiofilm and protein/platelet-resistant properties, as well as excellent hemo/biocompatibility. Furthermore, APEG₂₄₀₀ -PHMG greatly reduces the bacteria number with 5-log reduction in a rodent subcutaneous infection model. This rationally designed dual-functional antimicrobial and antifouling coating has great potential in combating biomedical devices/implant-associated infections.

An Environmentally Benign Antimicrobial Coating Based on a Protein Supramolecular Assembly

The use of antimicrobial materials, for example, silver nanoparticles, has been a cause for concern because they often exert an adverse effect on environmental and safety during their preparation and use. In this study, we report a class of green antimicrobial coating based on a supramolecular assembly of a protein extracted from daily food, without the addition of any other hazardous agents. It is found that a self-assembled nanofilm by mere hen egg white lysozyme has durable in vitro and in vivo broad-spectrum antimicrobial efficacy against Gram-positive/negative and fungi. Such enhanced antimicrobial capability over native lysozyme is attributed to a synergistic combination of positive charge and hydrophobic amino acid residues enriched on polymeric aggregates in the lysozyme nanofilm. Accompanied with high antimicrobial activity, this protein-based PTL material simultaneously exhibits the integration of multiple functions including antifouling, antibiofilm, blood compatibility, and low cytotoxicity due to the existence of surface hydration effect. Moreover, the bioinspired adhesion mediated by the amyloid structure contained in the nanofilm induces robust transfer and self-adhesion of the material onto virtually arbitrary substrates by a simple one-step aqueous coating or solvent-free printing in 1 min, thereby allowing an ultrafast route into practical implications for surface-functionalized commodity and biomedical devices. Our results demonstrate that the application of pure proteinaceous substance may afford a cost-effective green biomaterial that has high antimicrobial activity and low environmental impact.

Methacrylate-ended polypeptides and polypeptoids for antimicrobial and antifouling coatings

Methacrylate-terminated polypept(o)ides were directly synthesized via NCA-ROP, and then surface-grafted to form a polymer brush coating with infection-resistant efficacy.