A polycationic antimicrobial and biocompatible hydrogel with microbe membrane suctioning ability

Underwater-transparent nanodendritic coatings for directly monitoring cancer cells

Underwater-transparent nanodendritic coatings are easily fabricated by a three-step template process. After modification with anti-EpCAM, the coatings exhibit the capability for efficiently capturing rare number of cancer cells from whole blood. On the other hand, the unique underwater transparency enables the coatings to directly monitor captured cancer cells by optical imaging.

A simple approach to constructing antibacterial and anti-biofouling nanofibrous membranes

In this work, antibacterial and anti-adhesive polymeric thin films were constructed on polyacrylonitrile (PAN) nanofibrous membranes in order to extend their applications. Polyhexamethylene guanidine hydrochloride (PHGH) as an antibacterial agent and heparin (HP) as an anti-adhesive agent have been successfully coated onto the membranes via a layer-by-layer (LBL) assembly technique confirmed by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), energy-dispersive spectroscopy (EDS) and scanning electron microscopy (SEM). The antibacterial properties of LBL-functionalized PAN nanofibrous membranes were evaluated using the Gram-positive bacterium Staphylococcus aureus and the Gram-negative Escherichia coli. Furthermore, the dependence of the antibacterial activity and anti-biofouling performance on the number of layers in the LBL films was investigated quantitatively. It was found that these LBL-modified nanofibrous membranes possessed high antibacterial activities, easy-cleaning properties and stability under physiological conditions, thus qualifying them as candidates for anti-biofouling coatings.

Identification of antimicrobial peptides and immobilization strategy suitable for a covalent surface coating with biocompatible properties

Bacterial accumulation on solid material displays a major source of biomaterial associated infections, cross contamination, and spreading. To overcome these problems, different investigations on surface modifications for the containment of bacterial adhesion have been done. The aim of this research is the development of a rapid and efficient screening procedure to identify and investigate biologically active peptides in an immobilized state in order to produce an antimicrobial surface coating. We figured out that the antimicrobial mode of action is the most important parameter because only peptides with pronounced membrane disruption abilities displayed meaningful activity in an immobilized state. In addition, we highlighted the influence of the coupling reaction chemistry on the activity and amount of the immobilized peptide. Thereupon we developed an optimized antimicrobial surface coating with unrestricted antimicrobial properties by adjusting the immobilization strategy in combination with lowering the necessary peptide amount. Moreover we demonstrated that this antimicrobial surface coating displayed no cytotoxic activity against a eukaryotic cell line and thereby indicates a promising biocompatibility. Furthermore, different antimicrobial peptides obtained either by chemical peptide synthesis or by recombinant DNA technology were used in this study and their activities as well as their potential applications were discussed.

Antimicrobial polymer nanostructures: synthetic route, mechanism of action and perspective

Protection against bacterial infections is an important research field in modern society. Antimicrobial polymers have received considerable attention as next-generation biocides because they represent an ecologically friendly approach that does not promote resistance. In the last decade, many authors have reported the development of nano-sized antimicrobial polymers with enhanced bactericidal performance by increasing the active-area of biocides. This review presents several suitable methods of synthesis of antimicrobial polymer nanomaterials with various shapes, including a nanosphere and fibrous and tubular structures. We also discuss the antimicrobial mechanisms of these polymers. In addition, antimicrobial polymer thin films, which can inhibit bacterial adhesion, are introduced briefly with examples. Our aim is to present synthetic routes and formation mechanisms of various antimicrobial polymer nanostructures.

Supramolecular pyridyl urea gels as soft matter with antibacterial properties against MRSA and/or E. coli

The development of a family of twelve aryl pyridyl ureas, their crystallography and the ability of a number of these to form hydrogen bonding supramolecular gels with antimicrobial properties are described.

Biomaterials surfaces capable of resisting fungal attachment and biofilm formation

Microbial attachment onto biomedical devices and implants leads to biofilm formation and infection; such biofilms can be bacterial, fungal, or mixed. In the past 15 years, there has been an increasing research effort into antimicrobial surfaces but the great majority of these publications present research on bacteria, with some reports also testing resistance to fungi. Very few studies have focused exclusively on antifungal surfaces. However, with increasing recognition of the importance of fungal infections to human health, particularly related to infections at biomaterials, it would seem that the interest in antifungal surfaces is disproportionately low. In studies of both bacteria and fungi, fungi tend to be the minor focus with hypothesized antibacterial mechanisms of action often generalized to also explain the antifungal effect. Yet bacteria and fungi represent two Distinct biological Domains and possess substantially different cellular physiology and structure. Thus it is questionable whether these generalizations are valid. Here we review the scientific literature focusing on surface coatings prepared with antifungal agents covalently attached to the biomaterial surface. We present a critical analysis of generalizations and their evidence. This review should be of interest to researchers of "antimicrobial" surfaces by addressing specific issues that are key to designing and understanding antifungal biomaterials surfaces and their putative mechanisms of action.

Antimicrobial hydrogels for the treatment of infection

The increasing prevalence of microbial infections, especially those associated with impaired wound healing and biomedical implant failure has spurred the development of new materials having antimicrobial activity. Hydrogels are a class of highly hydrated material finding use in diverse medical applications such as drug delivery, tissue engineering, as wound fillers, and as implant coatings, to name a few. The biocompatible nature of many gels make them a convenient starting platform to develop selectively active antimicrobial materials. Hydrogels with antimicrobial properties can be obtained through the encapsulation or covalent immobilization of known antimicrobial agents, or the material itself can be designed to possess inherent antimicrobial activity. In this review we present an overview of antimicrobial hydrogels that have recently been developed and when possible provide a discussion relevant to their mechanism of action.

Self-assembly to function: design, synthesis, and broad spectrum antimicrobial properties of short hybrid E-vinylogous lipopeptides

Nonribosomal E-vinylogous γ-amino acids are widely present in many peptide natural products and have been exploited as inhibitors for serine and cysteine proteases. Here, we are reporting the broad spectrum antimicrobial properties and self-assembled nanostructures of various hybrid lipopeptides composed of 1:1 alternating α- and E-vinylogous residues. Analysis of the results revealed that self-assembled nanostructures also play a significant role in the antimicrobial and hemolytic activities. In contrast to the α-peptide counterparts, vinylogous hybrid peptides displayed excellent antimicrobial properties against various bacterial and fungal strains. Peptides that adopted nanofiber structures displayed less hemolytic activity, while peptides that adopted nanoneedle structures displayed the highest hemolytic activity.

Enzyme-coated mesoporous silica nanoparticles as efficient antibacterial agents in vivo

Despite the fact that pathogenic infections are widely treated by antibiotics in the clinic nowadays, the increasing risk of multidrug-resistance associated with abuse of antibiotics is becoming a major concern in global public health. The increased death toll caused by pathogenic bacterial infection calls for effective antibiotic alternatives. Lysozyme-coated mesoporous silica nanoparticles (MSNs⊂Lys) are reported as antibacterial agents that exhibit efficient antibacterial activity both in vitro and in vivo with low cytotoxicity and negligible hemolytic side effect. The Lys corona provides multivalent interaction between MSNs⊂Lys and bacterial walls and consequently raises the local concentration of Lys on the surface of cell walls, which promotes hydrolysis of peptidoglycans and increases membrane-perturbation abilities. The minimal inhibition concentration (MIC) of MSNs⊂Lys is fivefold lower than that of free Lys in vitro. The antibacterial efficacy of MSNs⊂Lys is evaluated in vivo by using an intestine-infected mouse model. Experimental results indicate that the number of bacteria surviving in the colon is three orders of magnitude lower than in the untreated group. These natural antibacterial enzyme-modified nanoparticles open up a new avenue for design and synthesis of next-generation antibacterial agents as alternatives to antibiotics.

Block copolymer mixtures as antimicrobial hydrogels for biofilm eradication

Current antimicrobial strategies have mostly been developed to manage infections due to planktonic cells. However, microbes in their nature state will tend to exist by attaching to and growing on living and inanimate surfaces that result in the formation of biofilms. Conventional therapies for treating biofilm-related infections are likely to be insufficient due to the lower susceptibility of microbes that are embedded in the biofilm matrix. In this study, we report the development of biodegradable hydrogels from vitamin E-functionalized polycarbonates for antimicrobial applications. These hydrogels were formed by incorporating positively-charged polycarbonates containing propyl and benzyl side chains with vitamin E moiety into physically cross-linked networks of "ABA"-type polycarbonate and poly(ethylene glycol) triblock copolymers. Investigations of the mechanical properties of the hydrogels showed that the G' values ranged from 1400 to 1600 Pa and the presence of cationic polycarbonate did not affect the stiffness of the hydrogels. Shear-thinning behavior was observed as the hydrogels displayed high viscosity at low shear rates that dramatically decreased as the shear rate increased. In vitro antimicrobial studies revealed that the more hydrophobic VE/BnCl(1:30)-loaded hydrogels generally exhibited better antimicrobial/antifungal effects compared to the VE/PrBr(1:30) counterpart as lower minimum biocidal concentrations (MBC) were observed in Staphylococcus aureus (Gram-positive), Escherichia coli (Gram-negative) and Candida albicans (fungus) (156.2, 312.5, 312.5 mg/L for VE/BnCl(1:30) and 312.5, 2500 and 625 mg/L for VE/PrBr(1:30) respectively). Similar trends were observed for the treatment of biofilms where VE/BnCl(1:30)-loaded hydrogels displayed better efficiency with regards to eradication of biomass and reduction of microbe viability of the biofilms. Furthermore, a high degree of synergistic antimicrobial effects was also observed through the co-delivery of antimicrobial polycarbonates with a conventionally-used antifungal agent, fluconazole. These hydrogels also displayed excellent compatibility with human dermal fibroblasts with cell viability >80% after treatment with hydrogels loaded with cationic polymers and/or fluconazole at minimum biocidal concentrations (MBC).

Fluorescence-based in situ assay to probe the viability and growth kinetics of surface-adhering and suspended recombinant bacteria

Bacterial adhesion and biofilm growth can cause severe biomaterial-related infections and failure of medical implants. To assess the antifouling properties of engineered coatings, advanced approaches are needed for in situ monitoring of bacterial viability and growth kinetics as the bacteria colonize a surface. Here, we present an optimized protocol for optical real-time quantification of bacterial viability. To stain living bacteria, we replaced the commonly used fluorescent dye SYTO(®) 9 with endogenously expressed eGFP, as SYTO(®) 9 inhibited bacterial growth. With the addition of nontoxic concentrations of propidium iodide (PI) to the culture medium, the fraction of live and dead bacteria could be continuously monitored by fluorescence microscopy as demonstrated here using GFP expressing Escherichia coli as model organism. The viability of bacteria was thereby monitored on untreated and bioactive dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride (DMOAC)-coated glass substrates over several hours. Pre-adsorption of the antimicrobial surfaces with serum proteins, which mimics typical protein adsorption to biomaterial surfaces upon contact with host body fluids, completely blocked the antimicrobial activity of the DMOAC surfaces as we observed the recovery of bacterial growth. Hence, this optimized eGFP/PI viability assay provides a protocol for unperturbed in situ monitoring of bacterial viability and colonization on engineered biomaterial surfaces with single-bacteria sensitivity under physiologically relevant conditions.

Effects of Cyclic vs. Acyclic Hydrophobic Subunits on the Chemical Structure and Biological Properties of Nylon-3 Co-Polymers

Nylon-3 co-polymers containing both hydrophobic and cationic subunits can mimic the activity profile of host-defense peptides, if subunit identity and proportion are carefully selected. These sequence- and stereo-random co-polymers inhibit bacterial growth at relatively low concentrations, apparently via disruption of bacterial membranes, but they are relatively non-disruptive toward eukaryotic cell membranes (low hemolytic activity). In all previous examples, the hydrophobic subunits have contained cycloalkyl groups that incorporate the backbone Cα-Cβ bond. Here we have explored the effects of using analogous acyclic hydrophobic subunits. The results indicate that the replacing cyclic with acyclic hydrophobic subunits has a modest influence on biological properties. This influence appears to arise from differences in subunit flexibility.

A review of the biomaterials technologies for infection-resistant surfaces

Anti-infective biomaterials need to be tailored according to the specific clinical application. All their properties have to be tuned to achieve the best anti-infective performance together with safe biocompatibility and appropriate tissue interactions. Innovative technologies are developing new biomaterials and surfaces endowed with anti-infective properties, relying either on antifouling, or bactericidal, or antibiofilm activities. This review aims at thoroughly surveying the numerous classes of antibacterial biomaterials and the underlying strategies behind them. Bacteria repelling and antiadhesive surfaces, materials with intrinsic antibacterial properties, antibacterial coatings, nanostructured materials, and molecules interfering with bacterial biofilm are considered. Among the new strategies, the use of phages or of antisense peptide nucleic acids are discussed, as well as the possibility to modulate the local immune response by active cytokines. Overall, there is a wealth of technical solutions to contrast the establishment of an implant infection. Many of them exhibit a great potential in preclinical models. The lack of well-structured prospective multicenter clinical trials hinders the achievement of conclusive data on the efficacy and comparative performance of anti-infective biomaterials.

Antibacterial hydrogel coating by electrophoretic co-deposition of chitosan/alkynyl chitosan

Despite much effort has been paid to develop aseptic implant devices, the infection associated with medical implant still remains a significant problem. Here, we report a potential coating material derived from a natural biopolymer chitosan. Firstly, chitosan functionalized with alkynyl moiety (ACS) was prepared by reaction between chitosan and 3-bromopropyne. The structure of the alkynyl chitosan was characterized by FT-IR, (1)H NMR, XRD, TGA and element analysis. The minimum inhibitory concentration (MIC) of ACS with a degree of substitution (DS) of 0.40 was 0.03% against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). Subsequently, the alkynyl chitosan was co-deposited with chitosan on stainless steel wire to fabricate a composite hydrogel. The composite hydrogel exhibited better antibacterial activities than pure chitosan hydrogel.

Stimuli-responsive self-assembling peptides made from antibacterial peptides

How to use bioactive peptide sequences as fundamental building blocks to make hydrogel materials which are stimuli-responsive? In this article, we provide a novel designed peptide comprising two antibacterial peptide sequences (KIGAKI)3-NH2 and a central tetrapeptide linker. Results show that balancing the forces of the electrostatic repulsion of the charged lysine residues against the hydrophobic collapse of the isoleucine and alanine residues and backbone β-sheet hydrogen bonding allows the structural transition and formation of individually dispersed nanofibers. Circular Dichroism (CD) and rheology analysis demonstrated that the designed peptide can undergo an abrupt structural transition from a random coil to a stable unimolecular β-hairpin conformation and subsequently form an elastic hydrogel when exposed to external stimuli such as pH, ionic strength and heat. The assembly kinetics of the obtained antibacterial sequence comprising peptide (ASCP) was studied by time-lapse Atomic Force Microscopy (AFM) and Thioflavin T (ThT) binding assay. In addition, the inherent antibacterial activity of the peptide hydrogel was confirmed by the antibacterial assay against Escherichia coli. This example described epitomizes the use of bioactive peptide sequences in the design of finite self-assembled structures with potential inherent activity. These hydrogel materials may find applications in drug delivery, tissue engineering and regenerative medicine.

Nano-silica fabricated with silver nanoparticles: antifouling adsorbent for efficient dye removal, effective water disinfection and biofouling control

A nano-silica-AgNPs composite material is proposed as a novel antifouling adsorbent for cost-effective and ecofriendly water purification. Fabrication of well-dispersed AgNPs on the nano-silica surface, designated as NSAgNP, has been achieved through protein mediated reduction of silver ions at ambient temperature for development of sustainable nanotechnology. The coated proteins on AgNPs led to the formation of stable NSAgNP and protected the AgNPs from oxidation and other ions commonly present in water. The NSAgNP exhibited excellent dye adsorption capacity both in single and multicomponent systems, and demonstrated satisfactory tolerance against variations in pH and dye concentration. The adsorption mainly occurred through electrostatic interaction, though π-π interaction and pore diffusion also contributed to the process. Moreover, the NSAgNP showed long-term antibacterial activity against both planktonic cells and biofilms of Gram-negative Escherichia coli and Pseudomonas aeruginosa. The antibacterial activity of AgNPs retarded the initial attachment of bacteria on NSAgNP and thus significantly improved the antifouling properties of the nanomaterial, which further inhibited biofilm formation. Scanning electron and fluorescence microscopic studies revealed that cell death occurred due to irreversible damage of the cell membrane upon electrostatic interaction of positively charged NSAgNP with the negatively charged bacterial cell membrane. The high adsorption capacity, reusability, good tolerance, removal of multicomponent dyes and E. coli from the simulated contaminated water and antifouling properties of NSAgNP will provide new opportunities to develop cost-effective and ecofriendly water purification processes.

Cationic antimicrobial polymers and their assemblies

Cationic compounds are promising candidates for development of antimicrobial agents. Positive charges attached to surfaces, particles, polymers, peptides or bilayers have been used as antimicrobial agents by themselves or in sophisticated formulations. The main positively charged moieties in these natural or synthetic structures are quaternary ammonium groups, resulting in quaternary ammonium compounds (QACs). The advantage of amphiphilic cationic polymers when compared to small amphiphilic molecules is their enhanced microbicidal activity. Besides, many of these polymeric structures also show low toxicity to human cells; a major requirement for biomedical applications. Determination of the specific elements in polymers, which affect their antimicrobial activity, has been previously difficult due to broad molecular weight distributions and random sequences characteristic of radical polymerization. With the advances in polymerization control, selection of well defined polymers and structures are allowing greater insight into their structure-antimicrobial activity relationship. On the other hand, antimicrobial polymers grafted or self-assembled to inert or non inert vehicles can yield hybrid antimicrobial nanostructures or films, which can act as antimicrobials by themselves or deliver bioactive molecules for a variety of applications, such as wound dressing, photodynamic antimicrobial therapy, food packing and preservation and antifouling applications.

Hydrophobic effect of amphiphilic derivatives of chitosan on the antifungal activity against Aspergillus flavus and Aspergillus parasiticus

Low molecular weight amphiphilic derivatives of chitosan were synthesized, characterized and their antifungal activities against Aspergillus flavus and Aspergillus parasiticus were tested. The derivatives were synthesized using as starting material a deacetylated chitosan sample in a two step process: the reaction with propyltrimethyl-ammonium bromide (Pr), followed by reductive amination with dodecyl aldehyde. Aiming to evaluate the effect of the hydrophobic modification of the derivatives on the antifungal activity against the pathogens, the degree of substitution (DS₁) by Pr groups was kept constant and the proportion of dodecyl (Dod) groups was varied from 7 to 29% (DS₂). The derivatives were characterized by ¹H-NMR and FTIR and their antifungal activities against the pathogens were tested by the radial growth of the colony and minimum inhibitory concentration (MIC) methods. The derivatives substituted with only Pr groups exhibited modest inhibition against A. flavus and A. parasiticus, like that obtained with deacetylated chitosan. Results revealed that the amphiphilic derivatives grafted with Dod groups exhibited increasing inhibition indexes, depending on polymer concentration and hydrophobic content. At 0.6 g/L, all amphiphilic derivatives having from 7.0 to 29% of Dod groups completely inhibited fungal growth and the MIC values were found to decrease from 4.0 g/L for deacetylated chitosan to 0.25-0.50 g/L for the derivatives. These new derivatives open up the possibility of new applications and avenues to develop effective biofungicides based on chitosan.

Nylon-3 polymers with selective antifungal activity

Host-defense peptides inhibit bacterial growth but show little toxicity toward mammalian cells. A variety of synthetic polymers have been reported to mimic this antibacterial selectivity; however, achieving comparable selectivity for fungi is more difficult because these pathogens are eukaryotes. Here we report nylon-3 polymers based on a novel subunit that display potent antifungal activity (MIC = 3.1 μg/mL for Candida albicans ) and favorable selectivity (IC10 > 400 μg/mL for 3T3 fibroblast toxicity; HC10 > 400 μg/mL for hemolysis).

Combinatorial discovery of polymers resistant to bacterial attachment

Bacterial attachment and subsequent biofilm formation pose key challenges to the optimal performance of medical devices. In this study, we determined the attachment of selected bacterial species to hundreds of polymeric materials in a high-throughput microarray format. Using this method, we identified a group of structurally related materials comprising ester and cyclic hydrocarbon moieties that substantially reduced the attachment of pathogenic bacteria (Pseudomonas aeruginosa, Staphylococcus aureus and Escherichia coli). Coating silicone with these 'hit' materials achieved up to a 30-fold (96.7%) reduction in the surface area covered by bacteria compared with a commercial silver hydrogel coating in vitro, and the same material coatings were effective at reducing bacterial attachment in vivo in a mouse implant infection model. These polymers represent a class of materials that reduce the attachment of bacteria that could not have been predicted to have this property from the current understanding of bacteria-surface interactions.

Preparation and characterization of chitosan-silver nanocomposite films and their antibacterial activity against Staphylococcus aureus

In this work different variables have been analyzed in order to optimize the bactericidal properties of chitosan films loaded with silver nanoparticles. The goal was to achieve complete elimination of antibiotic resistant and biofilm forming strains of Staphylococcus aureus after short contact times. The films were produced by solution casting using chitosan as both a stabilizing and reducing agent for the in situ synthesis of embedded silver nanoparticles. We have applied an innovative approach: the influence of the chitosan molecular weight and its deacetylation degree (DD) were analyzed together with the influence of the bacterial concentration and contact time. The best results were obtained with high DD chitosan where a fast reduction was favored; leading to smaller nanoparticles (nucleation is promoted), and a sufficiently high polymer viscosity prevented the resulting nanoparticles from undesired agglomeration. In addition, for the first time, potential detachment of the silver nanoparticles from the films was evaluated and neglected, demonstrating that uncontrolled release of silver nanoparticles from the chitosan films is prevented. The influence of the ionic silver released from the films, silver loading, nanoparticle sizes, contact, and initial number of bacteria was also analyzed to elucidate the mechanism responsible for the strong bactericidal action observed.

A nanoparticulate injectable hydrogel as a tissue engineering scaffold for multiple growth factor delivery for bone regeneration

Gellan xanthan gels have been shown to be excellent carriers for growth factors and as matrices for several tissue engineering applications. Gellan xanthan gels along with chitosan nanoparticles of 297 ± 61 nm diameter, basic fibroblast growth factor (bFGF), and bone morphogenetic protein 7 (BMP7) were employed in a dual growth factor delivery system to promote the differentiation of human fetal osteoblasts. An injectable system with ionic and temperature gelation was optimized and characterized. The nanoparticle loaded gels showed significantly improved cell proliferation and differentiation due to the sustained release of growth factors. A differentiation marker study was conducted, analyzed, and compared to understand the effect of single vs dual growth factors and free vs encapsulated growth factors. Dual growth factor loaded gels showed a higher alkaline phosphatase and calcium deposition compared to single growth factor loaded gels. The results suggest that encapsulation and stabilization of growth factors within nanoparticles and gels are promising for bone regeneration. Gellan xanthan gels also showed antibacterial effects against Pseudomonas aeruginosa, Staphylococcus aureus, and Staphylococcus epidermidis, the common pathogens in implant failure.

Antimicrobial and antifouling hydrogels formed in situ from polycarbonate and poly(ethylene glycol) via Michael addition

A novel class of antimicrobial cationic polycarbonate/PEG hydrogels are designed and synthesized by Michael addition chemistry. These hydrogels demonstrate strong broad-spectrum antimicrobial activities against various clinically isolated multidrug-resistant microbes. Moreover, they exhibit nonfouling properties and prevent the substrate from microbial adhesion. These antimicrobial and antifouling gels are promising materials as catheter coatings and wound dressings to prevent infections.

Broad-spectrum antimicrobial and biofilm-disrupting hydrogels: stereocomplex-driven supramolecular assemblies

Fighting the resistance: biodegradable and injectable/moldable hydrogels with hierarchical nanostructures were made with broad-spectrum antimicrobial activities and biofilm-disruption capability. They demonstrate no cytotoxicity in vitro, and show excellent skin biocompatibility in animals. These hydrogels have great potential for clinical use in prevention and treatment of various multidrug-resistant infections.

Short imidazolium chains effectively clear fungal biofilm in keratitis treatment

Fungal keratitis is a leading cause of ocular morbidity throughout the world. However, current therapies against fungal keratitis are often ineffective. Herein, we have developed the amphiphilic main-chain imidazolium polymer (PIM-45) and oligomer (IBN-1) materials that can efficiently inhibit the growth of fungi with low minimal inhibition concentration (MIC) values and clear the fungal biofilm, while displaying minimal hemolysis. In vivo keratitis treatment indicates that topical solutions of these polyimidazolium salts (PIMSs) are safe and as effective as that of amphotericin B, the most commonly used agent for the treatment of Candida albicans (C. albicans) keratitis. Compared to the costly and unstable amphotericin B and fluconazole, PIM-45 and IBN-1 are easy to prepare, inexpensive and stable. They can be stored in phosphate-buffered saline (PBS) solutions with long shelf life for routine topical use.

Antibacterial activity evaluation of quaternary chitin against Escherichia coli and Staphylococcus aureus

Water-soluble quaternary chitin/chitosan derivatives, O-[(2-hydroxy-3-trimethylammonium)propyl chitin (OHT-chitin), N-[(2-hydroxy-3-trimethylammonium)propyl chitosan (NHT-chitosan), and N,N,N-trimethylchitosan (TMC), having identical molecular weight and same anion, were prepared, and their antibacterial activities against Escherichia coli and Staphylococcus aureus were evaluated. Their minimum inhibitory concentration (MIC) values varied from 0.04 mg/mL to 20.48 mg/mL, and the minimum bactericidal concentration (MBC) values varied from 0.16 mg/mL to 40.96 mg/mL against E. coli and S. aureus, respectively. Transmission electron microscopy (TEM) clearly showed that there was serious damage on the bacterial walls, whereas there was some dissimilarity between TMC-treated E. coli and S. aureus.

Arginine-rich self-assembling peptides as potent antibacterial gels

Hydrogel materials that display inherent activity against bacteria can be used to directly treat accessible wounds to prevent or kill existing infection. Hydrogels composed of self-assembling β-hairpin peptides, having a high content of arginine, were found to be extremely effective at killing both gram-positive and gram-negative bacteria, including multi-drug resistant Pseudomonas aeruginosa. No added antibacterial agents are necessary to realize activity. Using self-assembling peptides for material construction allows facile structure-activity relationships to be determined since changes in peptide sequence at the monomer level are directly transposed to the bulk material's antibacterial properties. SAR studies show that arginine content largely influences the hydrogel's antibacterial activity, and influences their bulk rheological properties. These studies culminated in an optimized gel, composed of the peptide PEP6R (VKVRVRVRV(D)PPTRVRVRVKV). PEP6R gels prepared at 1.5 wt % or higher concentration, demonstrate high potency against bacteria, but are cytocompatible toward human erythrocytes as well as mammalian mesenchymal stem cells. Rheological studies indicate that the gel is moderately stiff and displays shear-thin recovery behavior, allowing its delivery via simple syringe.