Enhanced Nanoassembly-Incorporated Antibacterial Composite Materials

Formation of Nanofibrillar Self-Healing Hydrogels Using Antimicrobial Peptides

The rise of drug-resistant microorganisms has prompted the development of innovative strategies with the aim of addressing this challenge. Among the alternative approaches gaining increased attention are antimicrobial peptides (AMPs), a group of peptides with the ability to combat microbial pathogens. Here, we investigated a small peptide, KLVFF, derived from the Alzheimer's amyloid-β (Aβ) protein. While Aβ has been associated with the development of neurodegenerative diseases, the core part of the Aβ protein, namely the Aβ 16-20 fragment, has also been exploited to obtain highly functional biomaterials. In this study we found that KLVFF is capable of self-assembling into a fibrillar network to form a self-healing hydrogel. Moreover, this small peptide can undergo a transition from a gel to a liquid state following application of shear stress, in a reversible manner. As an AMP, this material exhibited both antibacterial and antifungal properties while remaining highly biocompatible and noncytotoxic toward mammalian cells. The propensity of the KLVFF hydrogel to rapidly assemble into highly ordered macroscopic structures makes it an ideal candidate for biomedical applications necessitating antimicrobial activity, such as wound healing.

Antimicrobial therapy based on self-assembling peptides

The emergence of drug-resistant microorganisms has threatened global health, and microbial infections have severely limited the use of medical materials. For example, the attachment and colonization of pathogenic bacteria to medical implant materials can lead to wound infections, inflammation and complications, as well as implant failure, shortening their lifespan and even resulting in patient death. In the era of antibiotic resistance, antimicrobial drug discovery needs to prioritize unconventional therapies that act on new targets or adopt new mechanisms. In this regard, supramolecular antimicrobial peptides have emerged as attractive therapeutic platforms, both as bactericides for combination antibiotics and as delivery vehicles. By taking advantage of their programmable intermolecular and intramolecular interactions, peptides can be modified to form higher-order structures (including nanofibers and nanoparticles) with unique functionality. This paper begins with an analysis of the relationship between peptide self-assembly and antimicrobial activity, describes in detail the research and development of various self-assembled antimicrobial peptides in recent years, and finally explores different combinatorial strategies for self-assembling antimicrobial peptides.

Selenium-silk microgels as antifungal and antibacterial agents

Antimicrobial resistance is a leading threat to global health. Alternative therapeutics to combat the rise in drug-resistant strains of bacteria and fungi are thus needed, but the development of new classes of small molecule therapeutics has remained challenging. Here, we explore an orthogonal approach and address this issue by synthesising micro-scale, protein colloidal particles that possess potent antimicrobial properties. We describe an approach for forming silk-based microgels that contain selenium nanoparticles embedded within the protein scaffold. We demonstrate that these materials have both antibacterial and antifungal properties while, crucially, also remaining highly biocompatible with mammalian cell lines. By combing the nanoparticles with silk, the protein microgel is able to fulfill two critical functions; it protects the mammalian cells from the cytotoxic effects of the bare nanoparticles, while simultaneously serving as a carrier for microbial eradication. Furthermore, since the antimicrobial activity originates from physical contact, bacteria and fungi are unlikely to develop resistance to our hybrid biomaterials, which remains a critical issue with current antibiotic and antifungal treatments. Therefore, taken together, these results provide the basis for innovative antimicrobial materials that can target drug-resistant microbial infections.

Peptide Stereochemistry Effects from pKa-Shift to Gold Nanoparticle Templating in a Supramolecular Hydrogel

The divergent supramolecular behavior of a series of tripeptide stereoisomers was elucidated through spectroscopic, microscopic, crystallographic, and computational techniques. Only two epimers were able to effectively self-organize into amphipathic structures, leading to supramolecular hydrogels or crystals, respectively. Despite the similarity between the two peptides' turn conformations, stereoconfiguration led to different abilities to engage in intramolecular hydrogen bonding. Self-assembly further shifted the pKa value of the C-terminal side chain. As a result, across the pH range 4-6, only one epimer predominated sufficiently as a zwitterion to reach the critical molar fraction, allowing gelation. By contrast, the differing pKa values and higher dipole moment of the other epimer favored crystallization. The four stereoisomers were further tested for gold nanoparticle (AuNP) formation, with the supramolecular hydrogel being the key to control and stabilize AuNPs, yielding a nanocomposite that catalyzed the photodegradation of a dye. Importantly, the AuNP formation occurred without the use of reductants other than the peptide, and the redox chemistry was investigated by LC-MS, NMR, and infrared scattering-type near field optical microscopy (IR s-SNOM). This study provides important insights for the rational design of simple peptides as minimalistic and green building blocks for functional nanocomposites.

An Ultrastable Self-Assembled Antibacterial Nanospears Made of Protein

Protein-based nanomaterials have broad applications in the biomedical and bionanotechnological sectors owing to their outstanding properties such as high biocompatibility and biodegradability, structural stability, sophisticated functional versatility, and being environmentally benign. They have gained considerable attention in drug delivery, cancer therapeutics, vaccines, immunotherapies, biosensing, and biocatalysis. However, so far, in the battle against the increasing reports of antibiotic resistance and emerging drug-resistant bacteria, unique nanostructures of this kind are lacking, hindering their potential next-generation antibacterial agents. Here, the discovery of a class of supramolecular nanostructures with well-defined shapes, geometries, or architectures (termed "protein nanospears") based on engineered proteins, exhibiting exceptional broad-spectrum antibacterial activities, is reported. The protein nanospears are engineered via spontaneous cleavage-dependent or precisely tunable self-assembly routes using mild metal salt-ions (Mg²⁺ , Ca²⁺ , Na⁺ ) as a molecular trigger. The nanospears' dimensions collectively range from entire nano- to micrometer scale. The protein nanospears display exceptional thermal and chemical stability yet rapidly disassemble upon exposure to high concentrations of chaotropes (>1 mm sodium dodecyl sulfate (SDS)). Using a combination of biological assays and electron microscopy imaging, it is revealed that the nanospears spontaneously induce rapid and irreparable damage to bacterial morphology via a unique action mechanism provided by their nanostructure and enzymatic action, a feat inaccessible to traditional antibiotics. These protein-based nanospears show promise as a potent tool to combat the growing threats of resistant bacteria, inspiring a new way to engineer other antibacterial protein nanomaterials with diverse structural and dimensional architectures and functional properties.

Selenium Silk Nanostructured Films with Antifungal and Antibacterial Activity

The rapid emergence of drug-resistant bacteria and fungi poses a threat for healthcare worldwide. The development of novel effective small molecule therapeutic strategies in this space has remained challenging. Therefore, one orthogonal approach is to explore biomaterials with physical modes of action that have the potential to generate antimicrobial activity and, in some cases, even prevent antimicrobial resistance. Here, to this effect, we describe an approach for forming silk-based films that contain embedded selenium nanoparticles. We show that these materials exhibit both antibacterial and antifungal properties while crucially also remaining highly biocompatible and noncytotoxic toward mammalian cells. By incorporating the nanoparticles into silk films, the protein scaffold acts in a 2-fold manner; it protects the mammalian cells from the cytotoxic effects of the bare nanoparticles, while also providing a template for bacterial and fungal eradication. A range of hybrid inorganic/organic films were produced and an optimum concentration was found, which allowed for both high bacterial and fungal death while also exhibiting low mammalian cell cytotoxicity. Such films can thus pave the way for next-generation antimicrobial materials for applications such as wound healing and as agents against topical infections, with the added benefit that bacteria and fungi are unlikely to develop antimicrobial resistance to these hybrid materials.

Multifunctional epoxy resin-based composites with excellent flexural strength and X-ray imaging capacity using micro/nano structured QF-Bi2SiO5 fillers

Composites have been widely applied in various industries and are beneficial in attaining complicated functionalities. Particularly, for dental fiber posts or orthopedic implants, the composites should have excellent mechanical properties and good imaging effects for visualization in vivo. The traditional method to improve mechanical strength and visibility by adding reinforcing fillers and radiopacifiers is complicated and has poor distributions and long production times. Hence, fabricating an integrated reinforced filler with radiopacity is of considerable economic and social significance. After ball-milling and sintering quartz fiber (QF) and bismuth trioxide (Bi₂O₃), a multifunctional filler (QF-Bi₂SiO₅) is fabricated to impart excellent flexural strengths and high X-ray imaging qualities to the composites. A composite made of epoxy resin (EP) and QF-Bi₂SiO₅ has a high bending strength (126.87 ± 6.78 MPa) and bending modulus (3649.31 ± 343.87 MPa), which are attributed to the tight mechanical interlock between EP and micro/nano structures of QF-Bi₂SiO₅. The QF-Bi₂SiO₅/EP composite shows good X-ray imaging quality owing to the Bi₂SiO₅ crystal. Furthermore, the mechanical and imaging performances of various composites with commercial fillers were compared with that of the QF-Bi₂SiO₅/EP composite. No filler was found that can perform both functions as well as QF-Bi₂SiO₅. Hence, the fabricated composites containing micro/nano structured QF-Bi₂SiO₅ fillers have the potential to be used in a variety of fields requiring mechanical strength and X-ray imaging capability.

Effectiveness of Se/ZnO NPs in Enhancing the Antibacterial Activity of Resin-Based Dental Composites

Biofilm formation in the resin-composite interface is a major challenge for resin-based dental composites. Using doped z nanoparticles (NPs) to enhance the antibacterial properties of resin composites can be an effective approach to prevent this. The present study focused on the effectiveness of Selenium-doped ZnO (Se/ZnO) NPs as an antibacterial nanofiller in resin composites and their impact on their mechanical properties. Pristine and Se/ZnO NPs were synthesized by the mechanochemical method and confirmed through UV-Vis Spectroscopy, FTIR (Fourier Transform Infrared) analysis, X-ray Diffraction (XRD) crystallography, Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), and Zeta analysis. The resin composites were then modified by varying concentrations of pristine and Se/ZnO NPs. A single species (S. mutans and E. faecalis) and a saliva microcosm model were utilized for antibacterial analysis. Hemolytic assay and compressive strength tests were also performed to test the modified composite resin's cytotoxicity and mechanical strength. When incorporated into composite resin, 1% Se/ZnO NPs showed higher antibacterial activity, biocompatibility, and higher mechanical strength when compared to composites with 1% ZnO NPs. The Se/ZnO NPs has been explored for the first time as an efficient antibacterial nanofiller for resin composites and showed effectiveness at lower concentrations, and hence can be an effective candidate in preventing secondary caries by limiting biofilm formation.

Sustainable agronomic response of carbon quantum dots on Allium sativum: Translocation, physiological responses and alternations in chromosomal aberrations

The revolutionary growth in the usage of carbon quantum dots (CQDs) in different areas have ultimately directed their discharge in the environment and further augmented the exposure of agricultural crops to these released particles. Therefore, the aim of current study is to evaluate the uptake, translocation and phytotoxicity of blue emissive CQDs on Allium sativum plant. The genotoxicity and cytotoxicity assessment of CQDs towards Allium sativum roots was estimated as function of three different concentrations. Considering the role of CQDs in promoting seed germination at 50 ppm concentration, a greenhouse experiment was performed to evaluate their effect on plant growth. Systematic investigations have shown the translocation of CQDs and their physiological response in terms of increased shoot length wherein P-CQDs exhibited more accumulation into Allium sativum parts. Our investigations unfold the opportunity to utilize Aegle marmelos fruit derived CQDs as a growth regulator in variety of other food plants.

Self-Assembling Peptide-Based Hydrogels for Wound Tissue Repair

Wound healing is a long-term, multistage biological process that includes hemostasis, inflammation, proliferation, and tissue remodeling and requires intelligent designs to provide comprehensive and convenient treatment. The complexity of wounds has led to a lack of adequate wound treatment materials, which must systematically regulate unique wound microenvironments. Hydrogels have significant advantages in wound treatment due to their ability to provide spatiotemporal control over the wound healing process. Self-assembling peptide-based hydrogels are particularly attractive due to their innate biocompatibility and biodegradability along with additional advantages including ligand-receptor recognition, stimulus-responsive self-assembly, and the ability to mimic the extracellular matrix. The ability of peptide-based materials to self-assemble in response to the physiological environment, resulting in functionalized microscopic structures, makes them conducive to wound treatment. This review introduces several self-assembling peptide-based systems with various advantages and emphasizes recent advances in self-assembling peptide-based hydrogels that allow for precise control during different stages of wound healing. Moreover, the development of multifunctional self-assembling peptide-based hydrogels that can regulate and remodel the wound immune microenvironment in wound therapy with spatiotemporal control has also been summarized. Overall, this review sheds light on the future clinical and practical applications of self-assembling peptide-based hydrogels.

Molecular Co-assembly of Two Building Blocks Harnesses Both Their Attributes into a Functional Supramolecular Hydrogel

Engineering ordered nanostructures through molecular self-assembly of simple building blocks constitutes the essence of modern nanotechnology to develop functional supramolecular biomaterials. However, the lack of adequate chemical and functional diversity often hinders the utilization of unimolecular self-assemblies for practical applications. Co-assembly of two different building blocks could essentially harness both of their attributes and produce nanostructured macro-scale objects with improved physical properties and desired functional complexity. Herein, we report the co-operative co-assembly of a modified amino acid, fluorenylmethoxycarbonyl-pentafluoro-Phenylalanine (Fmoc-F₅ -Phe), and a peptide, Fmoc-Lys(Fmoc)-Arg-Gly-Asp [Fmoc-K(Fmoc)-RGD] into a functional supramolecular hydrogel. A change in the morphology and fluorescence emission, as well as improvement of the mechanical properties in the mixed hydrogels compared to the pristine hydrogels, demonstrate the signature of co-operative co-assembly mechanism. Intriguingly, this approach harnesses the advantages of both components in a synergistic way, resulting in a single homogeneous biomaterial possessing the antimicrobial property of Fmoc-F₅ -Phe and the biocompatibility and cell adhesive characteristics of Fmoc-K(Fmoc)-RGD. This work exemplifies the importance of the co-assembly process in nanotechnology and lays the foundation for future developments in supramolecular chemistry by harnessing the advantages of diverse functional building blocks into a mechanically stable functional biomaterial. This article is protected by copyright. All rights reserved.

Unravelling the antimicrobial activity of peptide hydrogel systems: current and future perspectives

The use of hydrogels has garnered significant interest as biomaterial and drug delivery platforms for anti-infective applications. For decades antimicrobial peptides have been heralded as a much needed new class of antimicrobial drugs. Self-assembling peptide hydrogels with inherent antimicrobial ability have recently come to the fore. However, their fundamental antimicrobial properties, selectivity and mechanism of action are relatively undefined. This review attempts to establish a link between antimicrobial efficacy; the self-assembly process; peptide-membrane interactions and mechanical properties by studying several reported peptide systems: β-hairpin/β-loop peptides; multidomain peptides; amphiphilic surfactant-like peptides and ultrashort/low molecular weight peptides. We also explore their role in the formation of amyloid plaques and the potential for an infection etiology in diseases such as Alzheimer's. We look briefly at innovative methods of gel characterization. These may provide useful tools for future studies within this increasingly important field.

Rapid Production of Multifunctional Self-Assembling Peptides for Incorporation and Visualization within Hydrogel Biomaterials

Peptides are of continued interest for therapeutic applications, from soluble and immobilized ligands that promote desired binding or uptake to self-assembled supramolecular structures that serve as scaffolds in vitro and in vivo. These applications require efficient and scalable synthetic approaches because of the large amounts of material that often are needed for studies of bulk material properties and their translation. In this work, we establish new methods for the synthesis, purification, and visualization of assembling peptides, with a focus on multifunctional collagen mimetic peptides (mfCMPs) relevant for formation and integration within hydrogel-based biomaterials. First, a methodical approach useful for the microwave-assisted synthesis of assembling peptide sequences prone to deletions was established, beginning with the identification of the deleted residues and their locations and followed by targeted use of dual chemistry couplings for those specific residues. Second, purification techniques that integrate the principles of heating and ion displacement with traditional chromatography and dialysis were implemented to improve separation and isolation of the desired multifunctional peptide product, which contained blocks for thermoresponsiveness and ionic interactions. Third, an approach for fluorescent labeling of these mfCMPs, which is orthogonal to their assembly and their covalent incorporation into a bulk hydrogel material, was established, allowing visualization of the resulting hierarchical fibrillar structures in three dimensions within hydrogels using confocal microscopy. The methods presented in this work allow the production of multifunctional peptides in scalable quantities and with minimal deletions, enabling future studies for better understanding of composition-structure-property relationships and for translating these biomaterials into a range of applications. Although mfCMPs are the focus of this work, the methods demonstrated could prove useful for other assembling peptide systems and for the production of peptides more broadly for therapeutic applications.

Modification of a Single Atom Affects the Physical Properties of Double Fluorinated Fmoc-Phe Derivatives

Supramolecular hydrogels formed by the self-assembly of amino-acid based gelators are receiving increasing attention from the fields of biomedicine and material science. Self-assembled systems exhibit well-ordered functional architectures and unique physicochemical properties. However, the control over the kinetics and mechanical properties of the end-products remains puzzling. A minimal alteration of the chemical environment could cause a significant impact. In this context, we report the effects of modifying the position of a single atom on the properties and kinetics of the self-assembly process. A combination of experimental and computational methods, used to investigate double-fluorinated Fmoc-Phe derivatives, Fmoc-3,4F-Phe and Fmoc-3,5F-Phe, reveals the unique effects of modifying the position of a single fluorine on the self-assembly process, and the physical properties of the product. The presence of significant physical and morphological differences between the two derivatives was verified by molecular-dynamics simulations. Analysis of the spontaneous phase-transition of both building blocks, as well as crystal X-ray diffraction to determine the molecular structure of Fmoc-3,4F-Phe, are in good agreement with known changes in the Phe fluorination pattern and highlight the effect of a single atom position on the self-assembly process. These findings prove that fluorination is an effective strategy to influence supramolecular organization on the nanoscale. Moreover, we believe that a deep understanding of the self-assembly process may provide fundamental insights that will facilitate the development of optimal amino-acid-based low-molecular-weight hydrogelators for a wide range of applications.

Single Amino-Acid Based Self-Assembled Biomaterials with Potent Antimicrobial Activity

The design and development of soft biomaterials based on amino acid and short-peptide have gained much attention due to their potent biomedical applications. A slight alteration in the side-chain of single amino acid in a peptide or protein sequence has a huge impact on the structure and function. Phenylalanine is one of the most studied amino acids, which contains an aromatic phenyl group connected through a flexible -CH₂ - unit. In this work, we have examined whether flexibility and aromatic functionality of phenylalanine (Phe) are important in gel formation of model gelator Fmoc-Phe-OH or not. To examine this hypothesis, we synthesized Fmoc-derivatives of three analogues unnatural amino acids including cyclohexylalanine, phenylglycine, and homophenylalanine; which are slightly varied from Phe. Interestingly, all these three new analogues formed hydrogels in phosphate buffer at pH 7.0 having different gelation efficacy and kinetics. This study suggests that the presence of aromatic side-chain and flexibility are not mandatory for the gelation of this model gelator. Newly synthesized unnatural amino acid derivatives have also exhibited promising antimicrobial activity towards gram-positive bacteria by inhibiting cellular oxygen consumption. We further determined the biocompatibility of these amino acid derivatives by using a hemolysis assay on human blood cells. Overall studies described the development of single amino acid-based new injectable biomaterials with improved antimicrobial activity by the slight alteration in the side-chain of amino acid.

Recent Progress in Antimicrobial Strategies for Resin-Based Restoratives

Repairing tooth defects with dental resin composites is currently the most commonly used method due to their tooth-colored esthetics and photocuring properties. However, the higher than desirable failure rate and moderate service life are the biggest challenges the composites currently face. Secondary caries is one of the most common reasons leading to repair failure. Therefore, many attempts have been carried out on the development of a new generation of antimicrobial and therapeutic dental polymer composite materials to inhibit dental caries and prolong the lifespan of restorations. These new antimicrobial materials can inhibit the formation of biofilms, reduce acid production from bacteria and the occurrence of secondary caries. These results are encouraging and open the doors to future clinical studies on the therapeutic value of antimicrobial dental resin-based restoratives. However, antimicrobial resins still face challenges such as biocompatibility, drug resistance and uncontrolled release of antimicrobial agents. In the future, we should focus on the development of more efficient, durable and smart antimicrobial dental resins. This article focuses on the most recent 5 years of research, reviews the current antimicrobial strategies of composite resins, and introduces representative antimicrobial agents and their antimicrobial mechanisms.

Fluorinated peptide biomaterials

Fluorinated compounds, while rarely used by nature, are emerging as fundamental ingredients in biomedical research, with applications in drug discovery, metabolomics, biospectroscopy, and, as the focus of this review, peptide/protein engineering. Leveraging the fluorous effect to direct peptide assembly has evolved an entirely new class of organofluorine building blocks from which unique and bioactive materials can be constructed. Here, we discuss three distinct peptide fluorination strategies used to design and induce peptide assembly into nano-, micro-, and macrosupramolecular states that potentiate high-ordered organization into material scaffolds. These fluorine-tailored peptide assemblies employ the unique fluorous environment to boost biofunctionality for a broad range of applications, from drug delivery to antibacterial coatings. This review provides foundational tactics for peptide fluorination and discusses the utility of these fluorous-directed hierarchical structures as material platforms in diverse biomedical applications.

Self-Assembling, Ultrashort Peptide Gels as Antimicrobial Biomaterials

Supramolecular antimicrobial hydrogels based on peptides are attractive soft materials for the treatment of infections, considering their ease of preparation and benign fate in biological settings and in the environment. In particular, stimuli-responsive systems that can be assembled/disassembled ad hoc could offer the opportunity to switch on/off their bioactivity as needed. Besides, the shorter is the peptide, the lower its cost of production. However, a structure-to-function relationship is yet to be defined and reported activities are generally not yet competitive relative to traditional antibiotics. Inspiration for their design can be found in host defense peptides (HDPs), which can self-assemble to exert their function. This article reviews research developments in this emerging area, and it examines features, differences and similarities between antimicrobial and amyloid peptides to open the avenue towards the next generation of supramolecular antimicrobial peptides as innovative therapeutic materials.

Self-assembly of diphenylalanine peptides on graphene via detailed atomistic simulations

The self-assembly of diphenylalanine peptides (FF) on a graphene layer, in aqueous solution, is investigated, through all atom molecular dynamics simulations. Two interfacial systems are studied, with different concentrations of dipeptides and the results are compared with an aqueous solution of FF at room temperature. Corresponding length and time scales of the formed structures are quantified providing important insight into the adsorption mechanism of FF onto the graphene surface. A hierarchical formation of FF structures is observed involving two sequential processes: first, a stabilized interfacial layer of dipeptides onto the graphene surface is formulated, which next is followed by the development of a structure of self-aggregated dipeptides on top of this layer. The whole procedure is completed in almost 200 ns, whereas self-assembly in the system without graphene is accomplished much faster; in less than 50 ns cylindrical structures, the microscopic signal of the macroscopic fibrillar ones, are formed. Strong π-π* interactions between FF and the graphene lead to a parallel orientation to the graphene layer of the phenyl rings within a characteristic time of 80 ns, similar to the one indicated by the time evolution of the number of adsorbed FF atoms at the surface. Reduction in the number of hydrogen bonds between FF peptides is observed because of the graphene layer, since it disturbs their self-assembly propensity. The self-assembly of dipeptides and their adsorption onto the graphene surface destruct the hydrogen bond network of water, in the vicinity of FF, however, the total number of hydrogen bonds in all systems increases, promoting the formed structures.

Does the Addition of Zinc Oxide Nanoparticles Improve the Antibacterial Properties of Direct Dental Composite Resins? A Systematic Review

A promising approach to improve the poor antibacterial properties of dental composite resins has been the addition of metal oxide nanoparticles into the resin matrix. This systematic review aimed to determine whether the addition of zinc oxide nanoparticles (ZnO-NPs) improves the antibacterial properties of direct dental composite resins. This review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and registered with the PROSPERO database: CRD42019131383. A systematic literature search was conducted using the following databases: Medline (Ovid), the Cochrane Library, SCOPUS, CINAHL, Web of Science, Trove, Google Scholar, World Cat, and OpenGrey. The initial search retrieved 3178 results, which were then screened against inclusion and exclusion criteria, resulting in a total of four studies that were eligible for qualitative synthesis within this review. All the included studies were in vitro non-randomized post-test design experimental studies. A lack of congruity in the results obtained from these studies that used different tests to evaluate antibacterial activity was evident. Although some studies demonstrated a significant improvement of antibacterial properties in composites containing at least 1% ZnO-NPs (wt %), they are unlikely to present any clear clinical advantage due to the short lifetime of observed antibacterial properties.

Surface Modification by Nano-Structures Reduces Viable Bacterial Biofilm in Aerobic and Anaerobic Environments

Bacterial biofilm formation on wet surfaces represents a significant problem in medicine and environmental sciences. One of the strategies to prevent or eliminate surface adhesion of organisms is surface modification and coating. However, the current coating technologies possess several drawbacks, including limited durability, low biocompatibility and high cost. Here, we present a simple antibacterial modification of titanium, mica and glass surfaces using self-assembling nano-structures. We have designed two different nano-structure coatings composed of fluorinated phenylalanine via the drop-cast coating technique. We investigated and characterized the modified surfaces by scanning electron microscopy, X-ray diffraction and wettability analyses. Exploiting the antimicrobial property of the nano-structures, we successfully hindered the viability of Streptococcus mutans and Enterococcus faecalis on the coated surfaces in both aerobic and anaerobic conditions. Notably, we found lower bacteria adherence to the coated surfaces and a reduction of 86–99% in the total metabolic activity of the bacteria. Our results emphasize the interplay between self-assembly and antimicrobial activity of small self-assembling molecules, thus highlighting a new approach of biofilm control for implementation in biomedicine and other fields.

Collagen-Inspired Helical Peptide Coassembly Forms a Rigid Hydrogel with Twisted Polyproline II Architecture

Collagen, the most abundant protein in mammals, possesses notable cohesion and elasticity properties and efficiently induces tissue regeneration. The Gly-Pro-Hyp canonical tripeptide repeating unit of the collagen superhelix has been well-characterized. However, to date, the shortest tripeptide repeat demonstrated to attain a helical conformation contained 3-10 peptide repeats. Here, taking a minimalistic approach, we studied a single repeating unit of collagen in its protected form, Fmoc-Gly-Pro-Hyp. The peptide formed single crystals displaying left-handed polyproline II superhelical packing, as in the native collagen single strand. The crystalline assemblies also display head-to-tail H-bond interactions and an "aromatic zipper" arrangement at the molecular interface. The coassembly of this tripeptide, with Fmoc-Phe-Phe, a well-studied dipeptide hydrogelator, produced twisted helical fibrils with a polyproline II conformation and improved hydrogel mechanical rigidity. The design of these peptides illustrates the possibility to assemble superhelical nanostructures from minimal collagen-inspired peptides with their potential use as functional motifs to introduce a polyproline II conformation into hybrid hydrogel assemblies.

Emerging Contact-Killing Antibacterial Strategies for Developing Anti-Biofilm Dental Polymeric Restorative Materials

Polymeric materials are the first choice for restoring tooth cavities, bonding tooth-colored fillings, sealing root canal systems, and many other dental restorative applications. However, polymeric materials are highly susceptible to bacterial attachment and colonization, leading to dental diseases. Many approaches have been investigated to minimize the formation of biofilms over polymeric restorative materials and at the tooth/material interfaces. Among them, contact-killing compounds have shown promising results to inhibit dental biofilms. Contact-killing compounds can be immobilized within the polymer structure, delivering a long-lasting effect with no leaching or release, thus providing advantages compared to release-based materials. This review discusses cutting-edge research on the development of contact-killing compounds in dental restorative materials to target oral pathogens. Contact-killing compounds in resin composite restorations, dental adhesives, root canal sealers, denture-based materials, and crown cements have all demonstrated promising antibacterial properties. Contact-killing restorative materials have been found to effectively inhibit the growth and activities of several oral pathogens related to dental caries, periodontal diseases, endodontic, and fungal infections. Further laboratory optimization and clinical trials using translational models are needed to confirm the clinical applicability of this new generation of contact-killing dental restorative materials.

Assembling Anthracene-Tailored Amphiphiles: Charge-Transfer Interactions Directed Hierarchical Nanofibers with Ameliorative Antibacterial Activity toward Plant Pathogens

The effective prevention of plant bacterial infections has been complicated and challenged by unceasing bacterial resistance. The application of traditional bactericides has achieved certain effects to alleviate this situation. However, these chemicals also have limitations, such as short half-life in reality, limited bioavailability, and pollutant emission from their formulations. These disadvantages drive the demand for promoting antibacterial therapeutics. Self-assembled nanostructures based on amphiphiles have inherently versatile characteristics, including high durability, good bioavailability, sustained release, and regenerability. As such, they have garnered wide interest because of these advantages that may serve as a feasible platform for the management of pathogenic infections. Flexible tuning of the shapes of these nanostructures by manipulating noncovalent driving forces consequently results in different levels of antibacterial activity. Herein, an antibacterial amphiphile, 1-[11-(9-anthracenylmethoxy)-11-oxoundecyl]pyridinium bromide (AP), was assembled into microfilms in screening medium. Hierarchical nanofibers were constructed by introducing an electron-deficient trinitrofluorenone (TNF) molecule into the assembling system directed by charge-transfer (CT) interactions to further investigate the contribution of aggregate shape to bioactivity. Biological evaluation revealed that antibacterial efficacy improved after CT complex formation. This study provides an innovative platform for developing versatile assembled structures for restraining the propagation of plant pathogens and an improved understanding of the actual interplay between the self-assembly and antibacterial ability of bactericides at the supramolecular level.

Peptide Self-Assembly Is Linked to Antibacterial, but Not Antifungal, Activity of Histatin 5 Derivatives

Antimicrobial peptides are important modulators of host defense against bacterial, fungal, and viral pathogens in humans and other multicellular organisms. Two converging paradigms point to a link between antimicrobial peptides that self-assemble into amyloid-like nanoassemblies and classical amyloidogenic peptides that often have potent broad-spectrum antimicrobial activity, suggesting that antimicrobial and amyloidogenic peptides may represent two sides of the same coin. Here, we asked if the ability of an antifungal peptide to self-assemble affects its antifungal or antibacterial activity. We found that modifications of classical antifungal peptide derivative allowed it to self-assemble and did not alter its antifungal activity, and yet self-assembly substantially increased the antibacterial activity of the peptide. These results support the idea that peptide self-assembly can enhance antibacterial activities and emphasize a distinction between the action of antifungal peptides and that of antibacterial peptides. Accordingly, we suggest that the possible generality of this distinction should be widely tested.

The rise of multidrug-resistant pathogens has awakened interest in new drug candidates such as antimicrobial peptides and their derivatives. Recent work suggests that some antimicrobial peptides have the ability to self-assemble into ordered amyloid-like nanostructures which facilitate their antibacterial activity. Here, we evaluate a histatin-based antimicrobial peptide, and its self-assembling derivative, in the interplay between self-assembly, membrane interactions, and antibacterial and antifungal activities. We demonstrate substantial membrane targeting by both peptides, as well as mechanistic insights into this mode of action, which correlates to their antifungal activity and is not affected by their self-assembling state. The ability to self-assemble does, however, significantly affect peptide antibacterial activity against both Gram-negative and Gram-positive bacteria. These results are surprising and hint at important distinctions between antifungal and antibacterial peptide activities in prokaryotes and eukaryotic microbes.

IMPORTANCE Antimicrobial peptides are important modulators of host defense against bacterial, fungal, and viral pathogens in humans and other multicellular organisms. Two converging paradigms point to a link between antimicrobial peptides that self-assemble into amyloid-like nanoassemblies and classical amyloidogenic peptides that often have potent broad-spectrum antimicrobial activity, suggesting that antimicrobial and amyloidogenic peptides may represent two sides of the same coin. Here, we asked if the ability of an antifungal peptide to self-assemble affects its antifungal or antibacterial activity. We found that modifications of classical antifungal peptide derivative allowed it to self-assemble and did not alter its antifungal activity, and yet self-assembly substantially increased the antibacterial activity of the peptide. These results support the idea that peptide self-assembly can enhance antibacterial activities and emphasize a distinction between the action of antifungal peptides and that of antibacterial peptides. Accordingly, we suggest that the possible generality of this distinction should be widely tested.

Biocompatible Hybrid Organic/Inorganic Microhydrogels Promote Bacterial Adherence and Eradication in Vitro and in Vivo

Self-assembling peptides and proteins have the potential to serve as multifunctional building blocks for the generation of versatile materials for a wide range of biomedical applications. In particular, supramolecular hydrogels comprised of self-assembled protein nanofibrils, have been used in contexts ranging from tissue engineering to drug delivery. Due to the rapid emergence of multidrug resistant bacteria, development of biomaterials with intrinsic antimicrobial properties has been continuously increasing. Here, we describe hybrid organic/inorganic nanofibrillar silk microgels decorated with silver nanoparticles that display potent antimicrobial activity in vitro and in vivo and are able to adhere bacterial cells to their surfaces while subsequently eradicating them, through a two-step mechanism of action. Importantly, in contrast to treatments involving conventional silver, these silk-silver microgels are nonhemolytic and noncytotoxic toward mammalian cell lines. Finally, we show that these hybrid microgels display substantial efficacy as topical antimicrobial agents in a murine model of surgical site infections.

Polymeric and inorganic nanoscopical antimicrobial fillers in dentistry

Failure of dental treatments is mainly due to the biofilm accumulated on the dental materials. Many investigations have been conducted on the advancements of antimicrobial dental materials. Polymeric and inorganic nanoscopical agents are capable of inhibiting microorganism proliferation. Applying them as fillers in dental materials can achieve enhanced microbicidal ability. The present review provides a broad overview on the state-of-the-art research in the field of antimicrobial fillers which have been adopted for incorporation into dental materials over the last 5 years. The antibacterial agents and applications are described, with the aim of providing information for future investigations. STATEMENT OF SIGNIFICANCE: Microbial infection is the primary cause of dental treatment failure. The present review provides an overview on the state-of-art in the field of antimicrobial nanoscopical or polymeric fillers that have been applied in dental materials. Trends in the biotechnological development of these antimicrobial fillers over the last 5 years are reviewed to provide a backdrop for further advancement in this field of research.