A Kinetic Approach to Synergize Bactericidal Efficacy and Biocompatibility in Silver-Based Sol-Gel Coatings.

Silver ions are antimicrobial agents with powerful action against bacteria. Applications in surface treatments, as Ag+-functionalized sol-gel coatings, are expected in the biomedical field to prevent contaminations and infections. The potential cytotoxicity of Ag+ cations toward human cells is well known though. However, few studies consider both the bactericidal activity and the biocompatibility of the Ag+-functionalized sol-gels. Here, we demonstrate that the cytotoxicity of Ag+ cations is circumvented, thanks to the ability of Ag+ cations to kill Escherichia coli (E. coli) much faster than normal human dermal fibroblasts (NHDFs). This phenomenon was investigated in the case of two silver nitrate-loaded sol-gel coatings: one with 0.5 w/w% Ag+ cations and the second with 2.5 w/w%. The maximal amount of released Ag+ ions over time (0.25 mg/L) was ten times lower than the minimal inhibition (MIC) and minimal bactericidal (MBC) concentrations (respectively, 2.5 and 16 mg/L) for E. coli and twice lower to the minimal cytotoxic concentration (0.5 mg/L) observed in NHDFs. E. coli were killed 8-18 times, respectively, faster than NHDFs by silver-loaded sol-gel coatings. This original approach, based on the kinetic control of the biological activity of Ag+ cations instead of a concentration effect, ensures the bactericidal protection while maintaining the biocompatibility of the Ag+ cation-functionalized sol-gels. This opens promising applications of silver-loaded sol-gel coatings for biomedical tools in short-term or indirect contacts with the skin.

Electropolymerization of Pyrrole-Tailed Imidazolium Ionic Liquid for the Elaboration of Antibacterial Surfaces.

A strategy was developed to prepare antibacterial surfaces by electropolymerization of a pyrrole-functionalized imidazolium ionic liquid bearing an halometallate anion. The objective was to combine the antibacterial efficiency of polypyrrole (PPy) with those of the ionic liquid's components (cation and anion). For this, N-(1-methyl-3-octylimidazolium)pyrrole bromide monomer [PyC8MIm]Br was synthesized and coordinated to ZnCl2 affording [PyC8MIm]Br-ZnCl2. The antibacterial properties of [PyC8MIm]Br-ZnCl2 monomer were evaluated against Escherichia coli and Staphylococcus aureus by measurement of the minimum inhibitory concentration (MIC) values. This monomer presents higher activity against S. aureus (MIC = 0.098 µmol·mL-1) than against E. coli (MIC = 2.10 µmol·mL-1). Mixtures of pyrrole and the pyrrole-functionalized ionic liquid [PyC8MIm]Br-ZnCl2 were then used for the electrodeposition of PPy films on Fluorine-doped tin oxide (FTO) substrates. The concentration of pyrrole was fixed to 50 mM, while the concentration of [PyC8MIm]Br-ZnCl2 was varied from 5 to 100 mM. The efficient incorporation of the imidazolium cation and zinc halometallate anion into the films was confirmed by X-ray photoelectron spectroscopy (XPS) measurements. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) measurements confirmed the homogeneity of the different films with structures that depend on the [PyC8MIm]Br-ZnCl2 concentration. The films' thickness determined by profilometry varies only slightly with the [PyC8MIm]Br-ZnCl2 concentration from 7.4 µm at 5 mM to 8.9 µM at 100 mM. The films become more hydrophilic with an increase of [PyC8MIm]Br-ZnCl2 concentration with water contact angles varying from 47° at the lowest concentration to 32° at the highest concentration. The antibacterial activities of the different PPy films were determined both by the halo inhibition method and by the colony forming units (CFUs) counting method over time against Gram-positive S. aureus and Gram-negative E. coli bacteria. Films obtained by incorporation of [PyC8MIm]Br-ZnCl2 showed excellent antibacterial properties, at least two times higher than those of neat PPy, validating our strategy. Furthermore, a comparison of the antibacterial properties of the films obtained using the same [PyC8MIm]Br-ZnCl2 concentration (50 mM) evidenced much better activity against Gram-positive (no bacterial survival within 5 min) than against Gram-negative bacteria (no bacterial survival within 3 h). Finally, the antibacterial performances over time could be tuned by the concentration of the employed pyrrole-functionalized ionic liquid monomer. Against E. coli, using 100 mM of [PyC8MIm]Br-ZnCl2, the bacteria were totally killed within a few minutes, using 50 mM, they were killed after 2 h while using 10 mM, about 20% of bacteria survived even after 6 h.

Silver-based coordination polymers assembled by dithioether ligands: potential antibacterial materials despite received ideas.

We report on the first examples on the antibacterial activity towards Gram-negative and Gram-positive bacteria of 2D silver-based coordination polymers obtained by self-assembly with acetylenic dithioether ligands. Their structure imparts a good stability that allows a sustainable release of Ag+ in the media.

Cyto- and bio-compatibility assessment of plasma-treated polyvinylidene fluoride scaffolds for cardiac tissue engineering.

As part of applications dealing with cardiovascular tissue engineering, drop-cast polyvinylidene fluoride (PVDF) scaffolds have been treated by cold plasma to enhance their adherence to cardiac cells. The scaffolds were treated in a dielectric barrier device where cold plasma was generated in a gaseous environment combining a carrier gas (helium or argon) with/without a reactive gas (molecular nitrogen). We show that an Ar-N2 plasma treatment of 10 min results in significant hydrophilization of the scaffolds, with contact angles as low as 52.4° instead of 132.2° for native PVDF scaffolds. Correlation between optical emission spectroscopy and X-ray photoelectron spectroscopy shows that OH radicals from the plasma phase can functionalize the surface scaffolds, resulting in improved wettability. For all plasma-treated PVDF scaffolds, the adhesion and maturation of primary cardiomyocytes is increased, showing a well-organized sarcomeric structure (α-actinin immunostaining). The efficacy of plasma treatment was also supported by real-time PCR analysis to demonstrate an increased expression of the genes related to adhesion and cardiomyocyte function. Finally, the biocompatibility of the PVDF scaffolds was studied in a cardiac environment, after implantation of acellular scaffolds on the surface of the heart of healthy mice. Seven and 28 days after implantation, no exuberant fibrosis and no multinucleated giant cells were visible in the grafted area, hence demonstrating the absence of foreign body reaction and the biocompatibility of these scaffolds.

Correction to "Thiol-Poly(Sodium Styrenesulfonate) (PolyNaSS-SH) Gold Complexes: From a Chemical Design to a One-Step Synthesis of Hybrid Gold Nanoparticles and Their Interaction with Human Proteins".

[This corrects the article DOI: 10.1021/acsomega.0c00376.].

Atomic force microscopy characterization of polyethylene terephthalate grafting with poly(styrene sulfonate).

Polyethylene terephthalate (PET) is widely used to elaborate biomaterials and medical devices in particular for long-term implant applications but tuning their surface properties remains challenging. We investigate surface functionalization by grafting poly(sodium 4-styrene sulfonate, PNaSS) with the aim of enhancing protein adhesion and cellular activity. Elucidating the topography and molecular level organization of the modified surfaces is important for understanding and predicting biological activity. In this work, we explore several grafting methods including thermal grafting, thermal grafting in the presence of Mohr's salt, and UV activation. We characterize the different surfaces obtained using atomic force microscopy (AFM), contact angle (CA), and x-ray photoelectron spectroscopy (XPS). We observe an increase in the percentage of sulfur atoms (XPS) that correlates with changes in (CA), and we identify by AFM characteristic features, which we interpret as patches of polymers on the PET surfaces. This work demonstrates tuning of biomaterials surface by functionalization and illustrates the capability of AFM to provide insights into the spatial organization of the grafted polymer.

Gold, Silver, and Iron Oxide Nanoparticle Incorporation into Silk Hydrogels for Biomedical Applications: Elaboration, Structure, and Properties.

Silk fibroin (SF) is a versatile material with biodegradable and biocompatible properties, which make it fit for broad biomedical applications. In this context, the incorporation of nanosized objects into SF allows the development of a variety of bionanocomposites with tailored properties and functions. Herein, we report a thorough investigation on the design, characterization, and biological evaluation of SF hydrogels incorporating gold, silver, or iron oxide nanoparticles. The latter are synthesized in aqueous media using a biocompatible ligand allowing their utilization in various biomedical applications. This ligand seems to play a pivotal role in nanoparticle dispersion within the hydrogel. Results show that the incorporation of nanoparticles does not greatly influence the mechanism of SF gelation and has a minor impact on the mechanical properties of the so-obtained bionanocomposites. By contrast, significant changes are observed in the swelling behavior of these materials, depending on the nanoparticle used. Interestingly, the main characteristics of these bionanocomposites, related to their potential use for biomedical purposes, show the successful input of nanoparticles, including antibacterial properties for gold and silver nanoparticles and magnetic properties for iron oxide ones.

Strategies for Antimicrobial Peptides Immobilization on Surfaces to Prevent Biofilm Growth on Biomedical Devices.

Nosocomial and medical device-induced biofilm infections affect millions of lives and urgently require innovative preventive approaches. These pathologies have led to the development of numerous antimicrobial strategies, an emergent topic involving both natural and synthetic routes, among which some are currently under testing for clinical approval and use. Antimicrobial peptides (AMPs) are ideal candidates for this fight. Therefore, the strategies involving surface functionalization with AMPs to prevent bacterial attachment/biofilms formation have experienced a tremendous development over the last decade. In this review, we describe the different mechanisms of action by which AMPs prevent bacterial adhesion and/or biofilm formation to better address their potential as anti-infective agents. We additionally analyze AMP immobilization techniques on a variety of materials, with a focus on biomedical applications. Furthermore, we summarize the advances made to date regarding the immobilization strategies of AMPs on various surfaces and their ability to prevent the adhesion of various microorganisms. Progress toward the clinical approval of AMPs in antibiotherapy is also reviewed.

Covalent Grafting of Polyoxometalate Hybrids onto Flat Silicon/Silicon Oxide: Insights from POMs Layers on Oxides.

Immobilization of polyoxometalates (POMs) onto oxides is relevant to many applications in the fields of catalysis, energy conversion/storage, or molecular electronics. Optimization and understanding the molecule/oxide interface is crucial to rationally improve the performance of the final molecular materials. We herein describe the synthesis and covalent grafting of POM hybrids with remote carboxylic acid functions onto flat Si/SiO2 substrates. Special attention has been paid to the characterization of the molecular layer and to the description of the POM anchoring mode at the oxide interface through the use of various characterization techniques, including ellipsometry, AFM, XPS, and FTIR. Finally, electron transport properties were probed in a vertical junction configuration and energy level diagrams have been drawn and discussed in relation with the POM molecular electronic features inferred from cyclic-voltammetry, UV-visible absorption spectra, and theoretical calculations. The electronic properties of these POM-based molecular junctions are driven by the POM LUMO (d-orbitals) whatever the nature of the tether or the anchoring group.

Functional Characterization of Temporin-SHe, a New Broad-Spectrum Antibacterial and Leishmanicidal Temporin-SH Paralog from the Sahara Frog (Pelophylax saharicus).

Amphibian skin is a promising natural resource for antimicrobial peptides (AMPs), key effectors of innate immunity with attractive therapeutic potential to fight antibiotic-resistant pathogens. Our previous studies showed that the skin of the Sahara Frog (Pelophylax saharicus) contains broad-spectrum AMPs of the temporin family, named temporins-SH. Here, we focused our study on temporin-SHe, a temporin-SHd paralog that we have previously identified in this frog but was never structurally and functionally characterized. We synthesized and determined the structure of temporin-SHe. This non-amphipathic α-helical peptide was demonstrated to strongly destabilize the lipid chain packing of anionic multilamellar vesicles mimicking bacterial membranes. Investigation of the antimicrobial activity revealed that temporin-SHe targets Gram-negative and Gram-positive bacteria, including clinical isolates of multi-resistant Staphylococcus aureus strains. Temporin-SHe exhibited also antiparasitic activity toward different Leishmania species responsible for visceral leishmaniasis, as well as cutaneous and mucocutaneous forms. Functional assays revealed that temporin-SHe exerts bactericidal effects with membrane depolarization and permeabilization, via a membranolytic mechanism observed by scanning electron microscopy. Temporin-SHe represents a new member of the very limited group of antiparasitic temporins/AMPs. Despite its cytotoxicity, it is nevertheless an interesting tool to study the AMP antiparasitic mechanism and design new antibacterial/antiparasitic agents.

A New Antibacterial N-Halamine Coating Based on Polydopamine.

To prevent the formation of biofilms on material surfaces, the latter must have antibacterial properties. The aim of this study is to investigate the synthesis and the antibacterial effect of a new N-halamine coating based on polydopamine (PDA). The benefits of this coating are multiple, notably the green process used to prepare it and the wide variety of organic or inorganic materials that can be functionalized. First, the formation of the PDA coating by oxidative polymerization of dopamine in weak alkaline aqueous solution was studied and characterized. Then, these PDA films were exposed to a NaOCl solution in order to form chloramine functions into the coating, i.e., to immobilize oxidative chlorine on and into the coating. The PDA film chlorination was notably followed in situ by a quartz crystal microbalance (QCM). The influence of the NaOCl solution pH and concentration on chlorination kinetics and on PDA film degradation was evidenced. Finally, the antibacterial properties of the modified PDA coatings were highlighted by testing their antiadhesion and bactericidal properties toward the Escherichia coli bacterial strain.

EcDBS1R6: A novel cationic antimicrobial peptide derived from a signal peptide sequence.

BACKGROUND: Bacterial infections represent a major worldwide health problem the antimicrobial peptides (AMPs) have been considered as potential alternative agents for treating these infections. Here we demonstrated the antimicrobial activity of EcDBS1R6, a peptide derived from a signal peptide sequence of Escherichia coli that we previously turned into an AMP by making changes through the Joker algorithm. METHODS: Antimicrobial activity was measured by broth microdilution method. Membrane integrity was measured using fluorescent probes and through scanning electron microscopy imaging. A sliding window of truncated peptides was used to determine the EcDBS1R6 active core. Molecular dynamics in TFE/water environment was used to assess the EcDBS1R6 structure. RESULTS: Signal peptides are known to naturally interact with membranes; however, the modifications introduced by Joker transformed this peptide into a membrane-active agent capable of killing bacteria. The C-terminus was unable to fold into an α-helix whereas its fragments showed poor or no antimicrobial activity, suggesting that the EcDBS1R6 antibacterial core was located at the helical N-terminus, corresponding to the signal peptide portion of the parent peptide. CONCLUSION: The strategy of transforming signal peptides into AMPs appears to be promising and could be used to produce novel antimicrobial agents. GENERAL SIGNIFICANCE: The process of transforming an inactive signal peptide into an antimicrobial peptide could open a new venue for creating new AMPs derived from signal peptides.

Thiol-Poly(Sodium Styrene Sulfonate) (PolyNaSS-SH) Gold Complexes: From a Chemical Design to a One-Step Synthesis of Hybrid Gold Nanoparticles and Their Interaction with Human Proteins.

This study highlights recent advances in the synthesis of nanoconjugates based on gold (Au(III)) complex with a bioactive polymer bearing sulfonate groups called thiol-poly(sodium styrene sulfonate) (PolyNaSS-SH) with various molecular weights (5, 10, and 35 kDa). The three nanomaterials differ substantially in shape and structure. In particular, for PolyNaSS-SH of 35 kDa, we obtained a characteristic core-shell flower shape after chelation of the Au(III) ions and successively reduction with sodium borohydride (NaBH4). The mechanism of formation of the hybrid nanoparticles (PolyNaSS-SH@AuNPs (35 kDa) and their interactions between plasmatic proteins (human serum albumin (HSA), collagen I (Col 1), and fibronectin (Fn)) were deeply studied from a chemical and physical point of view by using several analytical techniques such as Raman spectroscopy, UV-visible, transmission electron microscopy (TEM), 1H NMR, and X-ray photoelectron spectroscopy (XPS).

Electrospun Poly(ε-caprolactone) Fiber Scaffolds Functionalized by the Covalent Grafting of a Bioactive Polymer: Surface Characterization and Influence on in Vitro Biological Response.

The purpose of this study is to present the poly(caprolactone) (PCL) functionalization by the covalent grafting of poly(sodium styrene sulfonate) on electrospun scaffolds using the "grafting from" technique and evaluate the effect of the coating and surface wettability on the biological response. The "grafting from" technique required energy (thermal or UV) to induce the decomposition of the PCL (hydro)peroxides and generate radicals able to initiate the polymerization of NaSS. In addition, UV irradiation was used to initiate the radical polymerization of NaSS directly from the surface (UV direct "grafting from"). The interest of these two techniques is their easiness, the reduction of the number of process steps, and its applicability to the industry. The selected parameters allow controlling the grafting rate (i.e., degree of functionalization). The aim of the study was to compare two covalent grafting in terms of surface functionalization and hydrophilicity and their effect on the in vitro biological responses of fibroblasts. The achieved results showed the influence of the sulfonate functional groups on the cell response. In addition, outcomes highlighted that the UV direct "grafting from" method allows to moderate the amount of sulfonate groups and the surface hydrophilicity presents a considerable interest for covalently immobilizing bioactive polymers onto electrospun scaffolds designed for tissue engineering applications using efficient post-electrospinning chemical modification.

Permanently hydrophilic, piezoelectric PVDF nanofibrous scaffolds promoting unaided electromechanical stimulation on osteoblasts.

Biomimetic functional scaffolds for tissue engineering should fulfil specific requirements concerning structural, bio-chemical and electro-mechanical characteristics, depending on the tissue that they are designed to resemble. In bone tissue engineering, piezoelectric materials based on poly(vinylidene fluoride) (PVDF) are on the forefront, due to their inherent ability to generate surface charges under minor mechanical deformations. Nevertheless, PVDF's high hydrophobicity hinders sufficient cell attachment and expansion, which are essential in building biomimetic scaffolds. In this study, PVDF nanofibrous scaffolds were fabricated by electrospinning to achieve high piezoelectricity, which was compared with drop-cast membranes, as it was confirmed by XRD and FTIR measurements. Oxygen plasma treatment of the PVDF surface rendered it hydrophilic, and surface characterization revealed a long-term stability. XPS analysis and contact angle measurements confirmed an unparalleled two-year stability of hydrophilicity. Osteoblast cell culture on the permanently hydrophilic PVDF scaffolds demonstrated better cell spreading over the non-treated ones, as well as integration into the scaffold as indicated by SEM cross-sections. Intracellular calcium imaging confirmed a higher cell activation on the piezoelectric electrospun nanofibrous scaffolds. Combining these findings, and taking advantage of the self-stimulation of the cells due to their attachment on the piezoelectric PVDF nanofibers, a 3D tissue-like functional self-sustainable scaffold for bone tissue engineering was fabricated.

Engineering of Antimicrobial Surfaces by Using Temporin Analogs to Tune the Biocidal/antiadhesive Effect.

Proliferation of resistant bacteria on biomaterials is a major problem leading to nosocomial infections. Due to their broad-spectrum activity and their ability to disrupt bacterial membranes through a rapid membranolytic mechanism, antimicrobial peptides (AMPs) are less susceptible to the development of bacterial resistance and therefore represent good candidates for surface coating strategies to prevent biofilm formation. In this study, we report on the covalent immobilization of temporin-SHa, a small hydrophobic and low cationic antimicrobial peptide exhibiting broad-spectrum activity, and (SHa) analogs on modified gold surfaces. Several analogs derived from SHa with either a carboxamidated ([K³]SHa, d-[K³]SHa) or a carboxylated C-terminus ([K³]SHa-COOH) were used to achieve peptide grafting on gold surfaces modified by a thiolated self-assembled monolayer (SAM). Surface functionalization was characterized by polarization modulation infrared reflection absorption spectroscopy (PM-RAIRS) and X-ray photoemission spectroscopy (XPS). The antibacterial properties of the temporin-functionalized surfaces were tested against the Gram-positive Listeria ivanovii. Direct visualization of the peptide effects on the bacterial membrane was investigated by scanning electron microscopy equipped with a field emission gun (SEM-FEG). All active temporin analogs were successfully grafted and display significant antibacterial activity (from 80 to 90% killing efficiency) in addition to a 2-fold decrease of bacterial adhesion when all d-SHa analogs were used.

Redox-Triggered Control of Cell Adhesion and Deadhesion on Poly(lysine)-g-poly(ethylene oxide) Adlayers.

Spontaneous adsorption of poly(lysine)-g-poly(ethylene glycol) comb-like copolymers (PLL-g-PEG) is a versatile mean to coat substrates with polymer layers that resist cell adhesion. We prepared redox cleavable PLL-g-PEG to switch adhesion on demand. Redox sensitivity was obtained by introducing disulfide linkers between the PLL backbone and PEG strands. This modification was done alone or in combination with an azide end on the PEG strands that enabled in situ conjugations of adhesion peptides or fluorescent labels (by a simple application of commercially available molecules for copper-free click chemistry compatible with cell survival). To balance the functional (adhesion-promoting) vs cell-repellent copolymers, mixed layers of adjusted compositions were obtained by coadsorption from mixed solutions of the cleavable copolymer with noncleavable and repellant PLL-g-PEG. The deposition of copolymers and quantitative cleavage as triggered by reductive conditions (application of solutions of tris(carboxyethyl)phosphine, dithiothreitol, or glutathione) were characterized by QCM-D, XPS, and fluorescence microscopy. In cell culture conditions, redox-triggered cleavage was obtained by a nontoxic application of TCEP for a few minutes, enabling either to release cell attachment points (i.e., cleavage of RGD-presenting areas) or to "open" nonspecific adherent areas (i.e., transition from PEG-presenting areas to adherent PLL-like coatings).

Fast and potent bactericidal membrane lytic activity of PaDBS1R1, a novel cationic antimicrobial peptide.

Antimicrobial peptides (AMPs) are promising candidates for the development of future antibiotics. In an attempt to increase the efficacy of therapeutic AMPs, computer-based design methods appear as a reliable strategy. In this study, we evaluated the antimicrobial efficiency and mechanism of action of a novel designed AMP named PaDBS1R1, previously designed by means of the Joker algorithm, using a fragment of the ribosomal protein L39E from the archaeon Pyrobaculum aerophilum as a template. PaDBS1R1 displayed low micromolar broad-spectrum antimicrobial activity against Gram-negative (MIC of 1.5 µM) and Gram-positive (MIC of 3 µM) bacteria, including carbapenem-resistant Klebsiella pneumoniae (MIC of 6.25 µM) and methicillin-resistant Staphylococcus aureus (MIC of 12.5 µM), without cytotoxicity towards HEK-293 cells. In addition, membrane permeabilization and depolarization assays, combined with time-kill studies and FEG-SEM imaging, indicated a fast membrane permeation and further leakage of intracellular content. Biophysical studies with lipid vesicles show a preference of PaDBS1R1 for Gram-negative bacteria-like membranes. We investigated the three-dimensional structure of PaDBS1R1 by CD and NMR analyses. Our results suggest that PaDBS1R1 adopts an amphipathic α-helix upon interacting with hydrophobic environments, after an initial electrostatic interaction with negative charges, suggesting a membrane lytic effect. This study reveals that PaDBS1R1 has potential application in antibiotic therapy.

Probing the in-air growth of large area of 3D functional structures into a 2D supramolecular nanoporous network.

Surface-confined host-guest chemistry at the air/solid interface is used for trapping a functionalized 3D Zn-phthalocyanine complex into a 2D porous supramolecular template allowing the large area functionalization of an sp2-hybridized carbon-based substrate as evidenced by STM, resonance Raman spectroscopy, and water contact angle measurements.

In silico optimization of a guava antimicrobial peptide enables combinatorial exploration for peptide design.

Plants are extensively used in traditional medicine, and several plant antimicrobial peptides have been described as potential alternatives to conventional antibiotics. However, after more than four decades of research no plant antimicrobial peptide is currently used for treating bacterial infections, due to their length, post-translational modifications or  high dose requirement for a therapeutic effect . Here we report the design of antimicrobial peptides derived from a guava glycine-rich peptide using a genetic algorithm. This approach yields guavanin peptides, arginine-rich α-helical peptides that possess an unusual hydrophobic counterpart mainly composed of tyrosine residues. Guavanin 2 is characterized as a prototype peptide in terms of structure and activity. Nuclear magnetic resonance analysis indicates that the peptide adopts an α-helical structure in hydrophobic environments. Guavanin 2 is bactericidal at low concentrations, causing membrane disruption and triggering hyperpolarization. This computational approach for the exploration of natural products could be used to design effective peptide antibiotics.