Nature-inspired antimicrobial polymers--assessment of their potential for biomedical applications

Bioinspired Polymers: Transformative Applications in Biomedicine and Regenerative Medicine

Bioinspired polymers have emerged as a promising field in biomaterials research, offering innovative solutions for various applications in biomedical engineering. This manuscript provides an overview of the advancements and potential of bioinspired polymers in tissue engineering, regenerative medicine, and biomedicine. The manuscript discusses their role in enhancing mechanical properties, mimicking the extracellular matrix, incorporating hydrophobic particles for self-healing abilities, and improving stability. Additionally, it explores their applications in antibacterial properties, optical and sensing applications, cancer therapy, and wound healing. The manuscript emphasizes the significance of bioinspired polymers in expanding biomedical applications, addressing healthcare challenges, and improving outcomes. By highlighting these achievements, this manuscript highlights the transformative impact of bioinspired polymers in biomedical engineering and sets the stage for further research and development in the field.

Evaluation of the Efficiency of Random and Diblock Methacrylate-Based Amphiphilic Cationic Polymers against Major Bacterial Pathogens Associated with Cystic Fibrosis

Cystic fibrosis (CF) is associated with repeated lung bacterial infection, mainly by Pseudomonas aeruginosa, Staphylococcus aureus, and Mycobacterium abscessus, all known to be or becoming resistant to several antibiotics, often leading to therapeutic failure and death. In this context, antimicrobial peptides and antimicrobial polymers active against resistant strains and less prompt to cause resistance, appear as a good alternative to conventional antibiotics. In the present study, methacrylate-based copolymers obtained by radical chemistry were evaluated against CF-associated bacterial strains. Results showed that the type (Random versus Diblock) and the size of the copolymers affected their antibacterial activity and toxicity. Among the different copolymers tested, four (i.e., Random₁₀₂₀₀, Random₁₅₀₀₀, Random₂₃₉₀₀, and Diblock₉₅₀₀) were identified as the most active and the safest molecules and were further investigated. Data showed that they inserted into bacterial lipids, leading to a rapid membranolytic effect and killing of the bacterial. In relation with their fast bactericidal action and conversely to conventional antibiotics, those copolymers did not induce a resistance and remained active against antibiotic-resistant strains. Finally, the selected copolymers possessed a preventive effect on biofilm formation, although not exhibiting disruptive activity. Overall, the present study demonstrates that methacrylate-based copolymers are an interesting alternative to conventional antibiotics in the treatment of CF-associated bacterial infection.

Open-Bandgap Graphene-Based Field-Effect Transistor Using Oligo(phenylene-ethynylene) Interfacial Chemistry

Organic interfacial compounds (OICs) are required as linkers for the highly stable and efficient immobilization of bioprobes in nanobiosensors using 2D nanomaterials such as graphene. Herein, we first demonstrated the fabrication of a field-effect transistor (FET) via a microelectromechanical system process after covalent functionalization on large-scale graphene by introducing oligo(phenylene-ethynylene)amine (OPE). OPE was compared to various OICs by density functional theory simulations and was confirmed to have a higher binding energy with graphene and a lower band gap than other OICs. OPE can improve the immobilization efficiency of a bioprobe by forming a self-assembly monolayer via anion-based reaction. Using this technology, Magainin I-conjugated OGMFET (MOGMFET) showed a high sensitivity, high selectivity, with a limit of detection of 10⁰  cfu mL^-1 . These results indicate that the OPE OIC can be applied for stable and comfortable interfacing technology for biosensor fabrication.

pH- and concentration-dependent supramolecular assembly of a fungal defensin plectasin variant into helical non-amyloid fibrils

Self-assembly and fibril formation play important roles in protein behaviour. Amyloid fibril formation is well-studied due to its role in neurodegenerative diseases and characterized by refolding of the protein into predominantly β-sheet form. However, much less is known about the assembly of proteins into other types of supramolecular structures. Using cryo-electron microscopy at a resolution of 1.97 Å, we show that a triple-mutant of the anti-microbial peptide plectasin, PPI42, assembles into helical non-amyloid fibrils. The in vitro anti-microbial activity was determined and shown to be enhanced compared to the wildtype. Plectasin contains a cysteine-stabilised α-helix-β-sheet structure, which remains intact upon fibril formation. Two protofilaments form a right-handed protein fibril. The fibril formation is reversible and follows sigmoidal kinetics with a pH- and concentration dependent equilibrium between soluble monomer and protein fibril. This high-resolution structure reveals that α/β proteins can natively assemble into fibrils.

Here the authors report the cryo-EM structure of a triple-mutant of the anti-microbial peptide plectasin, PPI42, assembling in a pH- and concentration dependent manner into helical non-amyloid fibrils. The fibrils formation is reversible, and follows a sigmoidal kinetics. The fibrils adopt a right-handed helical superstructure composed by two protofilaments, stabilized by an outer hydrophobic ring and an inner hydrophobic centre. These findings reveal that α/β proteins can natively assemble into fibrils.

Molecular Research on Oral Diseases and Related Biomaterials: A Journey from Oral Cell Models to Advanced Regenerative Perspectives

Oral diseases such as gingivitis, periodontitis, and oral cancer affect millions of people worldwide. Much research has been conducted to understand the pathogenetic mechanisms of these diseases and translate this knowledge into therapeutics. This review aims to take the reader on a journey from the initial molecular discoveries to complex regenerative issues in oral medicine. For this, a semi-systematic literature search was carried out in Medline and Web of Science databases to retrieve the primary literature describing oral cell models and biomaterial applications in oral regenerative medicine. First, an in vitro cell model of gingival keratinocytes is discussed, which illustrates patho- and physiologic principles in the context of oral epithelial homeostasis and carcinogenesis and represents a cellular tool to understand biomaterial-based approaches for periodontal tissue regeneration. Consequently, a layered gradient nonwoven (LGN) is described, which demonstrates that the key features of biomaterials serve as candidates for oral tissue regeneration. LGN supports proper tissue formation and obeys the important principles for molecular mechanotransduction. Furthermore, current biomaterial-based tissue regeneration trends, including polymer modifications, cell-based treatments, antimicrobial peptides and optogenetics, are introduced to represent the full spectrum of current approaches to oral disease mitigation and prevention. Altogether, this review is a foray through established and new concepts in oral regenerative medicine and illustrates the process of knowledge translation from basic molecular and cell biological research to future clinical applications.

Optimal Balance of Hydrophobic Content and Degree of Polymerization Results in a Potent Membrane-Targeting Antibacterial Polymer

Globally, excessive use of antibiotics has drastically raised the resistance frequency of disease-causing microorganisms among humans, leading to a scarcity of efficient and biocompatible drugs. Antimicrobial polymers have emerged as a promising candidate to combat drug-resistance pathogens. Along with the amphiphilic balance, structural conformation and molecular weight (M _n) play an indispensable role in the antimicrobial potency and cytotoxic activity of polymers. Here, we synthesize cationic and amphiphilic methacrylamide random copolymers using free-radical copolymerization. The mole fraction of the hydrophobic groups is kept constant at approximately 20%, while the molecular weight (average number of linked polymeric units) is varied and the antibacterial and cytotoxic activities are studied. The chemical composition of the copolymers is characterized by ¹H NMR spectroscopy. We observe that the average number of linked units in a polymer chain (i.e., molecular weight) significantly affects the polymer activity and selectivity. The antibacterial efficacy against both of the examined bacteria, Escherichia coli and Staphylococcus aureus, increases with increasing molecular weight. The bactericidal activity of polymers is confirmed by live/dead cell viability assay. Polymers with high molecular weight display high antibacterial activity, yet are highly cytotoxic even at 1 × MIC. However, low-molecular-weight polymers are biocompatible while retaining antibacterial potency. Furthermore, no resistance acquisition is observed against the polymers in E. coli and S. aureus. A comprehensive analysis using confocal and scanning electron microscopy (SEM) techniques shows that the polymers target bacterial membranes, resulting in membrane permeabilization that leads to cell death.

Host Defense Peptide-Mimicking Polymers and Polymeric-Brush-Tethered Host Defense Peptides: Recent Developments, Limitations, and Potential Success

Amphiphilic antimicrobial polymers have attracted considerable interest as structural mimics of host defense peptides (HDPs) that provide a broad spectrum of activity and do not induce bacterial-drug resistance. Likewise, surface engineered polymeric-brush-tethered HDP is considered a promising coating strategy that prevents infections and endows implantable materials and medical devices with antifouling and antibacterial properties. While each strategy takes a different approach, both aim to circumvent limitations of HDPs, enhance physicochemical properties, therapeutic performance, and enable solutions to unmet therapeutic needs. In this review, we discuss the recent advances in each approach, spotlight the fundamental principles, describe current developments with examples, discuss benefits and limitations, and highlight potential success. The review intends to summarize our knowledge in this research area and stimulate further work on antimicrobial polymers and functionalized polymeric biomaterials as strategies to fight infectious diseases.

Approaches for the inhibition and elimination of microbial biofilms using macromolecular agents

Biofilms are complex three-dimensional structures formed at interfaces by the vast majority of bacteria and fungi. These robust communities have an important detrimental impact on a wide range of industries and other facets of our daily lives, yet their removal is challenging owing to the high tolerance of biofilms towards conventional antimicrobial agents. This key issue has driven an urgent search for new innovative antibiofilm materials. Amongst these emerging approaches are highly promising materials that employ aqueous-soluble macromolecules, including peptides, proteins, synthetic polymers, and nanomaterials thereof, which exhibit a range of functionalities that can inhibit biofilm formation or detach and destroy organisms residing within established biofilms. In this Review, we outline the progress made in inhibiting and removing biofilms using macromolecular approaches, including a spotlight on cutting-edge materials that respond to environmental stimuli for "on-demand" antibiofilm activity, as well as synergistic multi-action antibiofilm materials. We also highlight materials that imitate and harness naturally derived species to achieve new and improved biomimetic and biohybrid antibiofilm materials. Finally, we share some speculative insights into possible future directions for this exciting and highly significant field of research.

Synthesis and evaluation of an amphiphilic deferoxamine:gallium-conjugated cationic random copolymer against a murine wound healing infection model of Pseudomonas aeruginosa

Multidrug resistant (MDR) Gram-negative bacteria are an urgent global health threat. We report on the design and evaluation of a xenosiderophore-conjugated cationic random copolymer (pGQ-DG) which exhibits selective antibacterial activity against Pseudomonas aeruginosa (P. aeruginosa) by targeting select outer membrane (OM) receptors for scavenging xenosiderophores such as deferoxamine (DFO), while possessing favorable cytocompatibility and exhibiting low hemolysis, to enhance and safely damage the bacterial OM. pGQ-DG demonstrated synergistic properties in combination with vancomycin (VAN) when evaluated in vitro against P. aeruginosa. In addition, pGQ-DG plus VAN cleared the P. aeruginosa infection and efficiently accelerated healing in a murine wound healing model as effectively as colistin, suggesting that this strategy could serve as an alternative to colistin against MDR bacteria. STATEMENT OF SIGNIFICANCE: P. aeruginosa exhibits intrinsic antibiotic resistance due to limited permeability of its outer membrane (OM). A triple combination antipseudomonal approach was investigated by 1) selectively targeting P. aeruginosa through the complex DFO:gallium, 2) disrupting the OM through a cationic random copolymer, and 3) enhancing bacteria sensitivity to VAN as a result of the OM disruption. Synthesis and characterization of the lead polymer pGQ-DG, mechanism of action, antimicrobial activity, and biocompatibility were investigated in vitro and in vivo. Overall pGQ-DG plus VAN cleared the P. aeruginosa infection and accelerated wound healing in mice as effectively as colistin, suggesting that this strategy could serve as an alternative to colistin against multidrug resistant P. aeruginosa.

Biobased polymers derived from itaconic acid bearing clickable groups with potent antibacterial activity and negligible hemolytic activity

We report the synthesis of new biobased polymers derived from itaconic acid with excellent antibacterial activity against Gram-positive bacteria and very low hemotoxicity.

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.

Quantified Membrane Permeabilization Indicates the Lipid Selectivity of Membrane-Active Antimicrobials

Most antimicrobial peptides (AMPs) and their synthetic mimics (SMAMPs) are thought to act by permeabilizing cell membranes. For antimicrobial therapy, selectivity for pathogens over mammalian cells is a key requirement. Understanding membrane selectivity is thus essential for designing AMPs and SMAMPs to complement classical antibiotics in the future. This study focuses on membrane permeabilization induced by SMAMPs and their selectivity for membranes with different lipid compositions. We measure release and fluorescence lifetime of a self-quenching dye in lipid vesicles. Apart from the dose-response, we quantify the strength of individual leakage events, and, employing cumulative kinetics, categorize permeabilization behavior. We propose that differing selectivities in a series of SMAMPs arise from a combination of the effect of the antimicrobial agent and the susceptibility of the membrane (with a given lipid composition) for certain types of leakage behavior. The unselective and hemolytic SMAMP is found to act mainly by the asymmetry stress mechanism, mediated by hydrophobic insertion of SMAMPs into lipid layers. The more selective SMAMPs induced leakage events occurring stochastically over several hours. Lipid intrinsic properties might additionally amplify the efficiency of leakage events. Leakage behavior changes with both the design of the SMAMP and the lipid composition of the membrane. Understanding how leakage behavior contributes to the selectivity and activity of antimicrobial agents will aid the design and screening of antimicrobials. An understanding of the underlying processes facilitates the comparison of membrane permeabilization across in vitro and in vivo assays.

Self-Regenerating Antimicrobial Polymer Surfaces via Multilayer-Design - Sequential and Triggered Layer Shedding under Physiological Conditions

Regeneration of materials properties through surface regeneration could extend the lifetime of devices and is still an emerging field of research. (Self-)regenerating antimicrobial polymer surfaces could help to fight biofilm formation and related bacterial infections. In this paper, four different polymer multilayer designs for the regeneration of antimicrobial surfaces by layer shedding are presented. The multilayer architectures consist of 100-200 nm thick, discrete polymer layers. They are made from poly(guanidinium oxanorbornene) networks as the antimicrobial component, and different interlayers made from degradable poly(adipic anhydrides), depolymerizable poly(ethyl glyoxylate), or water-soluble poly(acrylamide). Layer shedding is designed to occur after hydrolysis, dissolution or depolymerization under simulated physiological conditions. The multilayer fabrication and disassembly is monitored by fluorescence microscopy, ellipsometry FT-IR spectroscopy and atomic force microscopy. By testing the antimicrobial activity of the restored surfaces, their functional integrity after layer shedding is confirmed.

Surface Structuring Combined with Chemical Surface Functionalization: An Effective Tool to Manipulate Cell Adhesion

In this study, we investigate how a surface structure underneath a surface-attached polymer coating affects the bioactivity of the resulting material. To that end, structured surfaces were fabricated using colloidal lithography (lateral dimensions: 200 nm to 1 µm, height ~15 to 50 nm). The surface structures were further functionalized either with antimicrobial, cell-adhesive polycations or with protein-repellent polyzwitterions. The materials thus obtained were compared to non-functionalized structured surfaces and unstructured polymer monolayers. Their physical properties were studied by contact-angle measurements and atomic force microscopy (AFM). Protein adhesion was studied by surface plasmon resonance spectroscopy, and the antimicrobial activity against Escherichia coli bacteria was tested. The growth of human mucosal gingiva keratinocytes on the materials was analyzed using the Alamar blue assay, optical microscopy, and live-dead staining. The data shows that the underlying surface structure itself reduced protein adhesion and also bacterial adhesion, as evidenced by increased antimicrobial activity. It also enhanced cell adhesion to the surfaces. Particularly in combination with the adhesive polycations, the surfaces increased the cell growth compared to the unstructured reference materials. Thus, functionalizing structured surfaces with adhesive polymer could be a valuable tool for improved tissue integration.

A Degradable and Antimicrobial Surface-attached Polymer Hydrogela

Surface-attached, degradable polymer hydrogels with potential antimicrobial activity are reported. They were obtained by ring-opening metathesis copolymerization (ROMP) of a monomer with potential bioactivity and a monomer that carries a benzophenone cross-linker and a hydrolyzable group. The hydrolyzable group was either an ester or an anhydride group. The copolymers thus obtained were spin-coated onto silicon wafers and UV-irradiated to induce C,H cross-linking of the benzophenone groups and obtain the target polymer networks. Immersion of these networks into aqueous media triggered network degradation. The degradation speed depended on the nature of the intended break points (ester or anhydride groups), the number of cross-links per polymer chain, and the surrounding medium. By releasing bioactive polymer fragments to the medium ("leaching") and by regenerating the hydrogel surface during the degradation process, the hydrogels potentially have two ways to prevent biofilm formation on their surface.

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.

Activity of preparations from Spilanthes oleracea, propolis, Nigella sativa, and black garlic on different microorganisms involved in oral diseases and on total human salivary bacteria: A pilot study

Due to continuous rise in antibiotic resistance, there is a need for alternative treatment options to reduce the levels of oral pathogens for the maintenance of oral as well as overall health. The aim of this study was to evaluate the in vitro antibacterial potential of tinctures of Spilanthes oleracea and propolis, Nigella seed oil, and an ethanolic extract of black garlic on microorganisms involved in oral diseases. Both the minimum inhibitory concentration assay and the minimum bactericidal/fungicidal concentration assay were used in this study. Inhibition effects against total human salivary bacteria were also determined. Our results show that all of the preparations tested had potent antimicrobial activities. When measured 10 min after exposure, even low concentrations of the propolis tincture were found to have killed more than 99% of salivary bacteria, whereas Spilanthes tincture and black garlic extract killed more than 90% and Nigella seed oil more than 60% of the pathogens. This suggests that all preparations are promising candidates for the use in oral health care products and that all have the potential to control biofilm associated infections.

Synthesis and Bioactivity of Polymer-Based Synthetic Mimics of Antimicrobial Peptides (SMAMPs) Made from Asymmetrically Disubstituted Itaconates

A series of asymmetrically disubstituted diitaconate monomers is presented. Starting from itaconic anhydride, functional groups could be placed selectively at the two nonequivalent carbonyl groups. By using 2D NMR spectroscopy, it was shown that the first functionalization step occurred at the carbonyl group in the β position to the double bond. These monomers were copolymerized with N,N-dimethylacrylamide (DMAA) to yield polymer-based synthetic mimics of antimicrobial peptides (SMAMPs). They were obtained by free radical polymerization, a metal-free process, and still maintained facial amphiphilicity at the repeat unit level. This eliminates the need for laborious metal removal and is advantageous from a regulatory and product safety perspective. The poly(diitaconate-co-DMAA) copolymers obtained were statistical to alternating, and the monomer feed ratio roughly matched that of the repeat unit content of the copolymers. Investigations of varied R group hydrophobicity, repeat unit ratio, and molecular mass on antimicrobial activity against Escherichia coli and on compatibility with human keratinocytes showed that the polymers with the longest R groups and lowest DMAA content were the most antimicrobial and hemolytic. This is in agreement with the biological activity of previously reported SMAMPs. Thus, the design concept of facial amphiphilicity has successfully been transferred, but the selectivity of these polymers for bacteria over mammalian cells still needs to be optimized.

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.

Sub-micrometer Sized, 3D-Surface-attached Polymer Networks by Microcontact Printing: Using UV-Crosslinking Efficiency to Tune Structure Height

The lateral dimensions of micro- and nanostructures obtained by microcontact printing (μCP) can be easily varied by selecting stamps with the desired spacing and pattern. However, the height of these structures cannot be tuned as easily, and in most cases only 2D structures are obtained. Here, we show how the chemical cross-linking properties of polymer inks designed for μCP can be used to obtain 3D structures with heights ranging from 3 to 750 nm using the same μCP stamps. This is technologically relevant because the ink concentration affects the quality and resolution of the printed image, and therefore can only be varied in a certain range. By exploiting the cross-linking efficiency to tune the height, an additional parameter is available to reach the desired structure height without compromising the image quality. The inks were made from copolymers containing a low percentage of different UV cross-linkable repeat units: nitrobenzoxadiazole (NBD), coumarin (COU), and/or benzophenone (BP). The base polymer of the here presented model system was an antimicrobially active poly(oxanorbornene) (SMAMP), however the concept should be transferable to many other polymer backbones. We describe the fabrication and characterization of the printed micro- and nanostructures made from pure SMAMP, NBD-SMAMP, coumarin-SMAMP, BP-SMAMP, BP-NBD-SMAMP and BP-coumarin-SMAMP polymer inks. The photo-dimerization of COU during UV irradiation at λ = 254 nm was confirmed by UV-Vis spectroscopy. Since NBD and COU are fluorescent, the polymer could be visualized by fluorescence microscopy. Additionally, their height profiles were measured by atomic force microscopy (AFM). The heights of the 3D surface-attached polymer networks obtained from the here presented polymer inks correlated with the gel-content of the corresponding unstructured polymer layers, and thus with the cross-linking efficiency of the NBD, COU and BP cross-linkers. Due to being covalently cross-linked, these 3D-surface attached polymer structures were solvent-stable and stable in aqueous surroundings.

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.

Label-free technology and patient cells: from early drug development to precision medicine

Drug development requires physiologically more appropriate model systems and assays to increase understanding of drug action and pathological processes in individual humans. Specifically, patient-derived cells offer great opportunities as representative cellular model systems. Moreover, with novel label-free cellular assays, it is often possible to investigate complex biological processes in their native environment. Combining these two offers distinct opportunities for increasing physiological relevance. Here, we review impedance-based label-free technologies in the context of patient samples, focusing on commonly used cell types, including fibroblasts, blood components, and stem cells. Applications extend as far as tissue-on-a-chip models. Thus, applying label-free technologies to patient samples can produce highly biorelevant data and, with them, unique opportunities for drug development and precision medicine.

Surface Structuring Meets Orthogonal Chemical Modifications: Toward a Technology Platform for Site-Selectively Functionalized Polymer Surfaces and BioMEMS

A manufacturing process for the site-selective modification of structured (bio)material surfaces with two different polymers/biomolecules is presented. In the first step, a chemical surface contrast is created (e.g., a gold-on-silicon contrast obtained by colloidal lithography), and is combined with two orthogonal surface reactions for polymer/biomolecule immobilization. To demonstrate this, an antimicrobial SMAMP polymer and a protein-repellent polyzwitterion were site-selectively surface-immobilized on the gold-silicon structures. By varying the structure spacing and the surface architecture, structure-property relationships for the interaction of these bifunctional polymer surfaces with bacteria and proteins were obtained (studied by fluorescence microscopy, atomic force microscopy, surface plasmon resonance spectroscopy, and antimicrobial assays). At 1 μm spacing, a fully antimicrobially active bifunctional material was obtained, which also near-quantitatively reduced protein adhesion. As the process is generally applicable to polymers/biomolecules with aliphatic CH-groups, it is an interesting platform technology for site-selectively functionalized bifunctional (Bio)MEMS.

Modulating Antimicrobial Activity and Mammalian Cell Biocompatibility with Glucosamine-Functionalized Star Polymers

The development of novel reagents and antibiotics for combating multidrug resistance bacteria has received significant attention in recent years. In this study, new antimicrobial star polymers (14-26 nm in diameter) that consist of mixtures of polylysine and glycopolymer arms were developed and were shown to possess antimicrobial efficacy toward Gram positive bacteria including methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus (VRE) (with MIC values as low as 16 μg mL(-1)) while being non-hemolytic (HC50 > 10,000 μg mL(-1)) and exhibit excellent mammalian cell biocompatibility. Structure function analysis indicated that the antimicrobial activity and mammalian cell biocompatibility of the star nanoparticles could be optimized by modifying the molar ratio of polylysine to glycopolymers arms. The technology described herein thus represents an innovative approach that could be used to fight deadly infectious diseases.

Towards Self-regenerating Antimicrobial Polymer Surfaces

Regeneration of functional polymer surfaces after damage or contamination is an unresolved scientific challenge, and also of practical importance. In this proof-of-concept study, we present a method to regenerate a functional surface property using a polymer multi-layer architecture. This is exemplified using antimicrobially active surfaces. The idea is to shed the top layer of the polymer layer stack, like a reptile shedding its skin. The proof-of-concept stack consists of two antimicrobial layers and a degradable interlayer. Shedding of the top layer is enabled by degrading that interlayer. The shedding process was analyzed by quantitative fluorescence microscopy, ellipsometry, and FTIR spectroscopy. Antimicrobial assays revealed that the functionality of the emerging antimicrobial layer was fully retained after shedding.

Pilot investigation of the molecular discrimination of human osteoblasts from different bone entities

In oral and maxillofacial surgery, autologous grafts from the iliac crest remain the 'gold standard' for alveolar ridge reconstruction, whereas intraoral bone grafts are considered in smaller defects. To date, a comparison of the osteogenic potential of osteoblasts with regard to their tissue origin is missing. Primary osteoblasts have proven useful for the investigation of the tissue-specific osteogenic properties. The present study compares primary human alveolar (aHOBs) and iliac osteoblasts (iHOBs) derived from three female patients undergoing routine intraoral bone grafting. Proliferation potential of the osteoblasts was evaluated using real-time impedance monitoring. Relative gene expression of bone specific biomarkers was analyzed and quantified using quantitative polymerase chain reactions (qPCR). Immunohistochemistry and phase contrast microscopy were performed, as well as alkaline phosphatase assay and alizarin red staining to visualize morphology and mineralization capacity. A twofold faster proliferation rate of aHOBs compared with iHOBs (130 h vs. 80 h) was observed. Alkaline phosphatase activity and alizarin red staining in both HOBs indicated similar mineralization capacity. Gene expression of seven genes (BMP1, CSF-1, TGFBR1, ICAM1, VCAM1, SPP1 and DLX5) was significantly higher in iHOB than in aHOB samples. These data suggest a higher osteogenic potential of osteoblasts derived from the iliac crest compared with primary osteoblasts from the alveolar bone and may lead to a better understanding of the molecular impact of bone cells from different bone entities on bone regeneration in alveolar ridge reconstructions.

Antimicrobial and cell-compatible surface-attached polymer networks - how the correlation of chemical structure to physical and biological data leads to a modified mechanism of action

We present a synthetic platform based on photo-induced thiol-ene chemistry, by which surface-attached networks from antimicrobial poly(oxonorbornene) (so-called polymeric synthetic mimics of antimicrobial peptides, SMAMPs) could be easily obtained. By systematically varying hydrophobicity and charge density, surface-attached polymer networks with high antimicrobial activity and excellent cell compatibility were obtained. For the homopolymer networks with constant charge density, antimicrobial activity increased systematically with increasing hydrophobicity (i.e. decreasing swellability and apparent surface energy). Irrespective of charge density, the antimicrobial activity of all networks correlated with the acid constant pK and the isoelectric point (IEP) - the lower pK and IEP, the higher the antimicrobial activity. The cell compatibility of the networks increased with increasing swellability and apparent surface energy, and decreased with increasing charge density. The data corroborates that the mechanism of action of antimicrobial polymer surfaces depends on at least two mechanistic steps, one of which is hydrophobicity-driven and the other charge related. Therefore, we suggest a modified mechanistic model with a charge-driven and a hydrophobicity-driven step. For antimicrobial networks that only varied in hydrophobicity, the antimicrobial activities on surfaces and in solution also correlated - the higher the activity in solution, the higher the activity on surfaces. Thus, the hydrophobicity-driven step for activity on surfaces may be similar to the one in solution. Cell compatibility of SMAMPs in solution and on surfaces also showed a systematic positive correlation for all polymers, therefore this property also depends on the net hydrophobic balance of the polymer.

The SMART model: Soft Membranes Adapt and Respond, also Transiently, in the presence of antimicrobial peptides

Biophysical and structural studies of peptide-lipid interactions, peptide topology and dynamics have changed our view on how antimicrobial peptides insert and interact with membranes. Clearly, both the peptides and the lipids are highly dynamic, change and mutually adapt their conformation, membrane penetration and detailed morphology on a local and a global level. As a consequence, the peptides and lipids can form a wide variety of supramolecular assemblies in which the more hydrophobic sequences preferentially, but not exclusively, adopt transmembrane alignments and have the potential to form oligomeric structures similar to those suggested by the transmembrane helical bundle model. In contrast, charged amphipathic sequences tend to stay intercalated at the membrane interface where they cause pronounced disruptions of the phospholipid fatty acyl packing. At increasing local or global concentrations, the peptides result in transient membrane openings, rupture and ultimately lysis. Depending on peptide-to-lipid ratio, lipid composition and environmental factors (temperature, buffer composition, ionic strength, etc.), the same peptide sequence can result in a variety of those responses. Therefore, the SMART model has been introduced to cover the full range of possibilities. With such a view in mind, novel antimicrobial compounds have been designed from amphipathic polymers, peptide mimetics, combinations of ultra-short polypeptides with hydrophobic anchors or small designer molecules.

Development of a standardized and safe airborne antibacterial assay, and its evaluation on antibacterial biomimetic model surfaces

Bacterial infection of biomaterials is a major concern in medicine, and different kinds of antimicrobial biomaterial have been developed to deal with this problem. To test the antimicrobial performance of these biomaterials, the airborne bacterial assay is used, which involves the formation of biohazardous bacterial aerosols. We here describe a new experimental set-up which allows safe handling of such pathogenic aerosols, and standardizes critical parameters of this otherwise intractable and strongly user-dependent assay. With this new method, reproducible, thorough antimicrobial data (number of colony forming units and live-dead-stain) was obtained. Poly(oxonorbornene)-based Synthetic Mimics of Antimicrobial Peptides (SMAMPs) were used as antimicrobial test samples. The assay was able to differentiate even between subtle sample differences, such as different sample thicknesses. With this new set-up, the airborne bacterial assay was thus established as a useful, reliable, and realistic experimental method to simulate the contamination of biomaterials with bacteria, for example in an intraoperative setting.

Cationic methacrylate polymers as topical antimicrobial agents against Staphylococcus aureus nasal colonization

The in vitro and in vivo antimicrobial activity of primary ammonium ethyl methacrylate homopolymers (AEMPs) was investigated. AEMPs with different degrees of polymerization (DP = 7.7–12) were prepared by reversible addition–fragmentation chain-transfer (RAFT) polymerization. The AEMPs showed higher inhibitory effects against Gram-positive bacteria, including methicillin-resistant Staphylococcus aureus (MRSA), than Gram-negative bacteria. The AEMPs also showed potent anti-S. aureus activity in the presence of fetal bovine serum, whereas the activity of the antibiotic mupirocin was reduced under the same conditions. The AEMPs showed very little or no hemolytic activity. The cytotoxicity of AEMPs against mammalian cells HEp-2 and COS-7 was concentration-dependent, and the cell viability significantly decreased at higher polymer concentrations. The AEMPs significantly reduced the number of viable S. aureus cells in the nasal environment of cotton rats when compared to that of the control. This study demonstrates that AEMPs have potential for use in treating topical S. aureus infections.

On the design of supramolecular assemblies made of peptides and lipid bilayers

Peptides confer interesting properties to materials, supramolecular assemblies and to lipid membranes and are used in analytical devices or within delivery vehicles. Their relative ease of production combined with a high degree of versatility make them attractive candidates to design new such products. Here, we review and demonstrate how CD- and solid-state NMR spectroscopic approaches can be used to follow the reconstitution of peptides into membranes and to describe some of their fundamental characteristics. Whereas CD spectroscopy is used to monitor secondary structure in different solvent systems and thereby aggregation properties of the highly hydrophobic domain of p24, a protein involved in vesicle trafficking, solid-state NMR spectroscopy was used to deduce structural information and the membrane topology of a variety of peptide sequences found in nature or designed. (15)N chemical shift solid-state NMR spectroscopy indicates that the hydrophobic domain of p24 as well as a designed sequence of 19 hydrophobic amino acid residues adopt transmembrane alignments in phosphatidylcholine membranes. In contrast, the amphipathic antimicrobial peptide magainin 2 and the designed sequence LK15 align parallel to the bilayer surface. Additional angular information is obtained from deuterium solid-state NMR spectra of peptide sites labelled with (2)H3-alanine, whereas (31)P and (2)H solid-state NMR spectra of the lipids furnish valuable information on the macroscopic order and phase properties of the lipid matrix. Using these approaches, peptides and reconstitution protocols can be elaborated in a rational manner, and the analysis of a great number of peptide sequences is reviewed. Finally, a number of polypeptides with membrane topologies that are sensitive to a variety of environmental conditions such as pH, lipid composition and peptide-to-lipid ratio will be presented.

Antibacterial polymeric nanostructures for biomedical applications

A topical review on recent advances in the research and applications of antimicrobial polymeric nanostructures, such as silver-decorated polymeric nanostructures, and polymeric micelles and vesicles based on antimicrobial polymers and antimicrobial peptides.