Contact Killing Research Articles

Antibacterial silver (Ag) containing titanium oxynitride (TiOxNy) coatings for inhibiting surgical site infections (SSI)

AbstractThe Center of Disease Control and Prevention states that about one in every thirty‐one patients gets infected with ‘hospital‐acquired infections'. Bacterial colonization on surgical instruments remains one of the most significant factors for causing them. Such infections not only hinder a patient's recovery but can evolve into life‐threatening scenarios. Further, the moderate surface hardness of instruments might degrade their performance. Considering these issues, the central goal of this paper is to develop antibacterial coatings with favourable hardness. The main objective was to take advantage of the hardness property of titanium oxynitride (TiOxNy) while combining silver's (Ag) antibacterial properties. As surgical instruments are mainly fabricated using Ti6Al4V, we chose this material as our substrate. Radiofrequency magnetron sputtering was employed to develop several multi‐phasic coatings. Phase compositions, morphology and hardness values were analysed by X‐ray diffraction, scanning electron microscopy and nanoindentation, respectively. The antibacterial efficacy was evaluated against Escherichia coli using zone of inhibition, plate counting assay and Live/Dead assay. The effect of repetitive sterilization of coated samples was also examined. Results indicated the successful formation of antibacterial coatings with favourable hardness. Ag‐containing coatings exhibited pronounced antibacterial effect by ‘contact killing' method with no functionality change even after five sterilizing cycles.

Contact Killing of Gram-Positive and Gram-Negative Bacteria on PDMS Provided with Immobilized Hyperbranched Antibacterial Coatings

Here we describe in detail the preparation and application of antibacterial coatings on PDMS (poly(dimethylsiloxane)) and the contact-killing properties with 10 bacterial strains. Our aim was to develop a generally applicable coating to prevent biomaterial acquired infections, which is the major mode of failure of biomedical implants. In the first step, the surface was provided with a hydrophobic hyperbranched coating resin that was covalently attached to PDMS, mediated by an appropriate coupling agent. The coupling agent contained a siloxane group that reacts covalently with the silanol groups of air-plasma-treated PDMS and a blocked isocyanate enabling covalent coupling with the amino groups of the hyperbranched coating resins. The coating resins were functionalized with a polyethylenimine and subsequently quaternized with bromohexane and iodomethane. The coatings were highly effective against Gram-positive bacteria (five strains) and sufficiently active against Gram-negative bacteria (five stains). The killing effect on the latter group was strongly enhanced by adding a permeabilizer (EDTA). The biocidal efficacy was not influenced by the presence of (saliva) proteins.

The application of natural antibacterial coating for the surface modification of dental implants and abutments

Background Nowadays, peri-implantitis, a destructive inflammatory process around implants contributing to bone loss, has become the main reason for implant failure. Bacterial colonization and subsequent plaque formation on the implant surface is one of the main factors causing peri-implantitis. Totarol is a kind of natural biocompatible antibacterial agent, with bactericidal effect towards a wide range of gram-positive, even antibiotic-resistant bacteria, including the methicillin-resistant S. aureus. Aim/Hypothesis This in vitro study aims at applying totarol coatings on experimental dental implant and abutment surfaces and investigating the antibacterial capability of totarol coatings in a simulated oral environment. Material and Methods After ultrasonic cleaning with 70% ethanol, highly polished Ti disks (D = 10 mm) are coated with totarol by spin coating. Column chromatography-purified totarol dissolved in ethyl acetate solutions (20 mg/ml) is coated on Ti disks. Ti disks (n = 6 group) with and without totarol coating are incubated in an S. gordonii-suspension in Schaedler medium or in a mixed oral bacteria suspension in Schaedler medium (start OD λ=620 nm = 0.54) in a stirring system (each cycle including pause for 60 min and stirring for 15 min in, 37°C incubator) simulating the eating and resting period in human oral environment. The incubated Ti disks were harvested after 4 h, 8 h, 24 h, 48 h of incubation, respectively, then went through Live Dead staining for testing the vitality and through crystal violet staining for quantifying the amount of surface-bound bacteria. One-way ANOVA was used to analyze differences of the quantity of surface-bound bacteria between totarol coatings and control group. Results Approximately all S. gordonii and all mixed oral bacteria bound onto the totarol surface are red stained compared with the green stained live bacteria in the Ti control group after 4 h, 8 h, 24 h incubation (Fig. 1). This implied a contact killing effect towards S. gordonii and the mixed oral bacteria at a different stage of biofilm formation. Furthermore, crystal violet staining shows a significantly lower density of bacteria (P < 0.05) on totarol compared with the control, indicating an inhibition effect of totarol coatings towards the S. gordonii and multi-species oral biofilm growth (Fig. 2). Conclusion and Clinical Implications The natural antibacterial totarol coating showed promising bactericidal effects towards the early oral colonizer S. gordonii and the multispecies oral bacterial culture, and simultaneously significantly inhibits their biofilm growth. This might favor the undisturbed formation of a tight epithelial seal and prevent bacterial infiltration. Therefore, totarol coatings on dental implant and abutment surfaces showed great potential for the reduction or prevention of bacterial caused peri-implantitis.

Formulation of a promising antimicrobial and anticorrosive bi-functional boronated hyperbranched oleo-polyurethane composite coating through the exploitation of functionalized reduced graphene oxide as chain extender

Herein, a facile route was employed for the construction of novel dual-functional boronated (hybrid) hyperbranched polyurethane composite (HPUC) coatings using covalently functionalized reduced graphene oxide (FRGO) as chain extender and reinforcing agent. The FRGO exhibited excellent compatibility with the boronated HPU matrix that resulted in the chemical, structural and surface transformation of FRGO-HPUC coatings. The electrochemical corrosion studies were employed to confirm the protective performance of these composite coatings. The presence of electron deficient centres (tri-coordinated B) and electron rich FRGO restricted the diffusion of electrons through the coating network, which altered the mechanism of corrosion protection. In addition, the antimicrobial surface activity of these composites were investigated to ascertain their permanent contact killing properties.

Multifunctional antimicrobial chlorhexidine polymers by remote plasma assisted vacuum deposition

Novel antibacterial materials for implants and medical instruments are essential to develop practical strategies to stop the spread of healthcare associated infections. This study presents the synthesis of multifunctional antibacterial nanocoatings on polydimethylsiloxane (PDMS) by remote plasma assisted deposition of sublimated chlorhexidine powders at low pressure and room temperature. The obtained materials present effective antibacterial activity against Escherichia coli K12, either by contact killing and antibacterial adhesion or by biocide agents release depending on the synthetic parameters. In addition, these multifunctional coatings allow the endure hydrophilization of the hydrophobic PDMS surface, thereby improving their biocompatibility. Importantly, cell-viability tests conducted on these materials also prove their non-cytotoxicity, opening a way for the integration of this type of functional plasma films in biomedical devices.

Rechargeable Antibacterial N-Halamine Films with Antifouling Function for Food Packaging Applications.

Pathogenic microbial contamination from microbial adhesion and subsequent formation of the biofilm on surfaces of plastic food packaging materials, especially with robust resistance to antimicrobial agents, is a major reason for the outbreak of foodborne infections. Conventional strategies in controlling the contaminations are significantly limited either by biofouling or by the irreversible consumption of antimicrobial agents. Herein, we report a robust methodology to create rechargeable biocidal poly(vinyl alcohol- co-ethylene) films (SBMA@HAF films) with antifouling function via chemically incorporating both N-halamine (HAF) and zwitterionic moieties [[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide (SBMA)]. The promise of the design exhibits three features to defeat bacterial contaminations: (i) zwitterionic moieties can effectively reduce bacterial attachment onto the films, (ii) N-halamine with robust rechargeable biocidal activity can rapidly kill any attached bacteria, and (iii) any inactivated bacterial debris can be easily released to avoid biofilm formation due to the superhydrophilicity of the zwitterions. The resulting SBMA@HAF films exhibit integrated properties of high transparency, robust mechanical property, great hydrophilicity, ease of chlorine recharging (>250 ppm), long-term stability, high biocidal efficacy (>99.9999% via contact killing), and promising antifouling functions, which enable the SBMA@HAF films to serve as a biocidal material in food packaging applications.

A surface-engineered polyetheretherketone biomaterial implant with direct and immunoregulatory antibacterial activity against methicillin-resistant Staphylococcus aureus

Metal ions or nanoparticles are believed to be promising additives in developing antibacterial biomaterials, owing to possessing favorable bactericidal effects against antibiotic-resistant bacteria. However, the immunomodulatory antibacterial activity of metal ions has seldom been reported. Herein, a porous microstructure designed to trap methicillin-resistant Staphylococcus aureus (MRSA) is fabricated on polyetheretherketone biomaterial surface through sulfonation (SPEEK), following which copper (Cu) nanoparticles, which can kill the trapped MRSA, are immobilized on SPEEK surface using a customized magnetron sputtering technique. In vitro antibacterial and immunological experiments indicate that the Cu-incorporated SPEEK can exert a desirable bactericidal effect against MRSA through the combination of “trap killing” and “contact killing” actions; meanwhile, macrophages cultured on the Cu-incorporated SPEEK can be activated and polarized to a pro-inflammatory phenotype along with improved phagocytic ability on the MRSA. Further in vivo implant-associated infection models evidence the superior antibacterial activity of the Cu-incorporated SPEEK. These results demonstrate multimodal antibacterial actions of the Cu-incorporated SPEEK, which is capable of imposing direct antibacterial and indirect immunomodulatory antibacterial effects simultaneously, in order to prevent and cure MRSA infection. It is believed that this study may shed light on developing novel biomaterial implants that combine antibacterial and immunomodulatory functions.

Grafting antibacterial polymer brushes from titanium surface via polydopamine chemistry and activators regenerated by electron transfer ATRP

An environmentally benign and convenient approach to impart titanium (Ti) surfaces with antibacterial functionalities was described in this work. Polydopamine (PDA) was first deposited onto an alkali activated Ti substrates. Then 2-bromoisobutyryl bromide (BIBB) was immobilized on the surface of PDA coated Ti. Finally, the BIBB functionalized Ti initiated the polymerization of N, N-diethylaminoethyl methacrylate (DEAEMA) and N, N-dimethylaminoethyl methacrylate (DMAEMA) to obtain Ti@PDA-g-polymer brushes by activators regenerated by electron transfer atom transfer radical polymerization (ARGET-ATRP). The prepared PDEAEMA and PDMAEMA brushes on Ti surfaces would be subsequently quaternized by using 1-bromooctane, which would impart the obtained products with quaternary ammonium groups. The surface compositions of the functionalized Ti were characterized by X-ray photoelectron spectroscopy (XPS). The hydrophilic/hydrophobic properties of the functionalized Ti surfaces were determined by static water contact angle measurements, and morphologies were characterized by scanning electron microscope (SEM). Antibacterial abilities of quaternized PDEAEMA and PDMAEMA coated Ti were evaluated by the contact killing test, in which live/dead cell staining method was employed. The results showed that the quaternized polymer decorated Ti exhibited good bactericidal effects against Escherichi coli (E. coli), and its inhibition rate of E. coli were observed to be nearly 90%.

Antibacterial durability and biocompatibility of antibacterial-passivated 316L stainless steel in simulated physiological environment

Stainless steel (SS) has been widely applied as one of the most efficient implant metal materials, although corrosion and infection in body environment are still challenging. Herein, an antibacterial passivation method was employed to enhance the antibacterial performance and corrosion resistance of the medical 316L SS. The result proved that the antibacterial-passivated 316L SS exhibited stable antibacterial activity and effectively inhibited the formation of bacterial biofilm. Electrochemical measurements combined with X-ray photoelectron spectroscopy technique were used to study the corrosion resistance and semiconductor behavior of passivated 316L SS immersed in simulated physiological environment. The results indicated that the 316L SS after antibacterial passivation treatment for 1 h, soaking in the medium for 10 days, showed satisfactory corrosion resistance attributing to proper Cu deposition in the passive film. The anodic stripping voltammetry measurement further confirmed that the Cu-bearing passive film could continuously release Cu ions into medium. The zebrafish test demonstrated an excellent in vivo biocompatibility for the 316L SS with antibacterial passivation for 0.5 and 1 h, respectively. In addition, changes of surface roughness, contact angle and chemical composition after antibacterial passivation played an important role in explaining the antibacterial mechanism, which could be clearly divided into contact killing and ionic release killing. Hence, the antibacterial passivation treatment was preliminarily proved as a potential way for enhancing the persistent antibacterial activity and corrosion resistance of 316L SS.

Mixed polymer brushes with integrated antibacterial and antifouling properties

Development of novel materials with dual antibacterial and antifouling functions is important for many bio-applications. In this work, we design and synthesize a series of mixed polymer brushes grafted from silica surface as a new type of antibiofouling and antimicrobial coating, which combine poly(N-hydroxyethyl acrylamide) (polyHEAA) synthesized by atom transfer radical polymerization (SI-ATRP) and cationic poly(trimethylamino) ethyl methacrylate chloride, polyMETAC) synthesized by photoiniferter-mediated polymerization (SI-PIMP). The surface composition, charge and morphology of the resultant mixed polymer brushes are carefully characterized and optimized by tuning ATRP and PIMP initiator ratios. The mixed polymer brushes possess strong bacterial killing ability from polyMETAC chains and high antifouling property from polyHEAA chains. At the optimal conditions, the mixed polyHEAA/polyMETAC brushes exhibit excellent anti-bacterial adhesion property by retaining ultralow cell adhesion of ˜3.0 × 105 cells/cm2 and high contact killing efficiency by killing more than 90% attached bacteria of Escherichia coli and Staphylococcus. Long-term antibacterial performance indicated the cell adhesion was retained at ultralow level of 5 × 105 cells/cm2 even after 72 h exposure to bacteria solution. The results indicate that surface grafting with polyHEAA and polyMETAC can be potentially useful for long-term biomedical and biomaterial applications.

Short-Time Antibacterial Effects of Dimethylaminododecyl Methacrylate on Oral Multispecies Biofilm In Vitro.

Quaternary ammonium compounds constitute a large group of antibacterial chemicals with a potential for inhibiting dental plaque. The aims of this study were to evaluate short-time antibacterial and regulating effects of dimethylaminododecyl methacrylate (DMADDM) on multispecies biofilm viability, reformation, and bacterial composition in vitro. DMADDM, chlorhexidine (CHX), and sodium fluoride (NaF) were chosen in the present study. Streptococcus mutans, Streptococcus sanguinis, and Streptococcus gordonii were used to form multispecies biofilm. Cytotoxicity assay was used to determine the optimal tested concentration. 3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and resazurin test of biofilm were conducted to study the biomass changes and metabolic changes of controlled multispecies biofilm. Scanning electron microscopy (SEM) was used to observe biofilm images. TaqMan real-time polymerase chain reaction was performed to evaluate the proportion change in multispecies biofilm of different groups. Cytotoxicity assay showed that there existed a certain concentration application range for DMADDM, CHX, and NaF. MTT assay and resazurin test results showed that DMADDM and CHX groups decreased multispecies biofilm growth and metabolic activity (p < 0.05), no matter after 1 min or 5 min direct contact killing or after 24 h regrowth. The proportion of S. mutans decreased steadily in DMADDM and CHX groups after 1 min and 5 min direct contact killing and 24 h regrowth, compared to control groups. A novel DMADDM-containing solution was developed, achieving effective short-time antibacterial effects and regulation ability of biofilm formation.

Gel-like ionic complexes for antimicrobial, hemostatic and adhesive properties.

Ion-specific effects offer a great opportunity to construct intelligent macromolecular systems with diverse architectures, on-demand controlled release behaviors and interfacial responsiveness. Herein, we developed gel-like polyelectrolyte/counterion complexes by ionotropic gelation of poly((trimethylamino)ethyl methacrylate chloride-co-sulfobetaine methacrylate) (poly(TMAEMA-co-SBMA)) and kosmotropic polyphosphate (PP). The strong water-mediated ionic crosslinking between the cationic poly(TMAEMA) and multivalent anionic PP leads to ionic association and formation of stable dispersive colloids and gel-like complexes. Zwitterionic SBMA possesses charge balance and strong hydration as well as insusceptibility to the presence of PP. The unique features of SBMA were applied to finely adjust the physical and biological properties of gel-like complexes. Accordingly, the molar composition of poly(TMAEMA-co-SBMA) was varied to evaluate its effects on the formation of the ionic complexes, water content, gel volume, ion-exchange capability, and viscoelastic recovery upon intermittent shear stress. The state diagrams of the poly(TMAEMA-co-SBMA) solutions as a function of the PP concentration were scrutinized in order to discover the relation between the ionic association and complex formation. The stability of the polymeric ionic complex structures was determined by the cationic molecular composition in the polymers and ionic strength. In terms of applications, the poly(TMAEMA-co-SBMA)/PP gel-like complexes served as an antimicrobial agent to inactivate pathogenic bacteria via leaching and contact killing approaches. The hemostasis of the complex gels in a tail-bleeding assay using Wistar rats was verified to ensure the potential in medical applications. Moreover, the gel-like complex was applied onto various substrates as an adhesive in comparison with commercial superglue gel, revealing the robust, substrate-independent, water-based, repeatable and removable adhesive property of the ionic complex glue. Consequently, this study was carried out in an attempt to explore the structure-property relation of ionically crosslinked polymer networks for a wide spectrum of applications.

Development of multiactive antibacterial multilayers of hyaluronic acid and chitosan onto poly(ethylene terephthalate)

Antibacterial coatings have been widely explored to inhibit biofilm formation in order to prevent post-implantation infections of biomedical devices. However, due to the complex mechanism of bacterial adhesion and proliferation, only the combination of different strategies can lead to higher antibacterial efficiency, especially in the initial stages. For this, layer by layer (LbL) assembly of hyaluronic acid (HA) and chitosan (CHI) was successfully developed onto activated surface of polyethylene terephthalate in order to obtain polyelectrolyte multilayers (PEMs) that combine adhesion resistance, contact killing properties and modulated releasing of antibacterial agents. PEMs showed high efficiency for loading of triclosan (TRI) and rifampicin (RIF). The release of these bactericides could be modulated by their sequential incorporation along the polysaccharide layers. HA/CHI multilayers inhibited E. coli adhesion onto developed surfaces and when TRI and RIF were loaded in the coatings, better antibacterial activity was demonstrated. The possibility of acting as antibacterial reservoir added to the antibacterial properties of the polysaccharide layer make these multilayers promising materials as implants substrates.

Rational Design of Silver Gradient for Studying Size Effect of Silver Nanoparticles on Contact Killing.

The cellular mechanism underlying bacteria responses to silver nanoparticles (AgNPs) has not been fully elucidated. Especially, it is difficult to distinguish the contact killing from release killing as Ag+ releases from AgNPs. In this paper, AgNPs gradient was designed for evaluating the size effect of AgNPs on contact killing. A size gradient of AgNPs (5-45 nm) was achieved on TiO2 nanotubes (TNTs) by rational design of bipolar electrochemical reaction, including applied voltage, electrolyte concentration, and sample size. High-throughput investigation of cellular responses showed that the smallest AgNPs were the most efficient in suppressing bacteria whereas the largest AgNPs were more favorable for MC3T3-E1 cell adhesion and proliferation. As Ag+ concentration was the same for the entire gradient, the difference in cellular responses was dominated by the contact effect (rather than difference in released Ag+) which was tuned by AgNPs size. This method offers new prospect for efficient evaluation of the contact effect of nanoparticles, such as Ag, Au, and Cu.

More thorough washing protocols reveal a new mechanism for antimicrobial materials

Antifungal polyene drugs covalently bound to biomedical materials act through a desorption and physisorption mechanism rather than their oft-cited contact killing method.

PMMA particles coated with chitosan-silver nanoparticles as a dual antibacterial modifier for natural rubber latex films

The antibacterial activity in sulphur prevulcanized natural rubber (SPNR) latex film was effectively improved by deposition of poly(methyl methacrylate) (PMMA) particles encircled with chitosan-coated silver nanoparticles (AgNPs-CS). With the focus on a green process, CS was selected as a safe reducing and stabilizing agent for the one-step synthesis of AgNPs-CS (38 nm, +40.4 mV) in an autoclave. The adsorption of small-sized AgNPs-CS directly onto rubber film did not provide an inhibitory effect on S. aureus. It also had a low antibacterial effect on E. coli. This is because of the particles becoming completely/partially submerged into the soft rubber matrix upon drying. Hence, the AgNPs-CS were fabricated as a shell surrounding a rigid PMMA core (496 nm, -30.9 mV). This was done using a heterocoagulation technique prior to coating on SPNR film. The presence of PMMA/AgNPs-CS on the surface of SPNR film effectively increased the surface roughness from ca. 44 to 150 nm. This substantially promoted the antibacterial activity against E. coli and S. aureus by way of contact killing and repelling mechanisms. The cytotoxicity on L-929 fibroblasts was also suppressed. This study would be, therefore, applicable to the development of antibacterial SPNR film with high surface roughness, low cytotoxicity. It could also be applied for other soft substrates.

Antibacterial multilayer of chitosan and (2-carboxyethyl)- β-cyclodextrin onto polylactic acid (PLLA)

There is a wide demand for new biodegradable materials with innovations to improve the basic functions of traditional food packaging and prolong the shelf life of food, enhancing its security and sensorial properties. Poly(L-lactic acid) (PLLA) is a biodegradable biopolymer used in traditional packaging of food because of its non-toxicity, biodegradability, biocompatibility and transparency. The aim of this work is to modify PLLA films in order to prepare an improved material for food active packaging. For this, PLLA was internally blended with zinc oxide (ZnO) nanoparticles and, it was also superficially modified by the deposition of chitosan (CHI) and β-cyclodextrins (β-CD) by layer-by-layer (LbL). These prepared multilayers were characterized by confocal fluorescence microscopy, contact angle measurements, transmission electron microscopy and UV-Vis spectroscopy. On one hand, the proposed multiple modification inhibits polymer-bacterial interactions and improves the biological properties of the PLLA due to the bactericide effect of ZnO nanoparticles and the contact killing capacity of chitosan. On the other hand, the release of the carvacrol incorporated in β-CDs improves the antibacterial and antioxidant properties of prepared films (more than 95 wt% of totally released carvacrol was released within 14 days). This investigation demonstrates that here specifically modified PLLA films could be promising materials in the new trends of biodegradable and active food packaging.

Novel N-chloramine precursors for antimicrobial application: synthesis and facile covalent immobilization on polyurethane surface based on perfluorophenyl azide (PFPA) chemistry

To control the pathogen cross contaminations on medical material surface, there is a pressing need to develop antimicrobial materials with highly efficacious surface biocidal activity. In this work, N-chloramine precursors containing a quaternary ammonium unit and perfluorophenyl azide unit were synthesized and covalently immobilized on inert polyurethane (PU) film upon UV light irradiation. The surface modification was confirmed by contact angle, Fourier transform infrared (ATR FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) analyses. After bleaching treatment, satisfactory biocidal activity was achieved for the surface-modified PU films. It was found that the introduced surface QA center contributed an even faster surface contact killing behavior and that precursors with a longer structural linker caused higher surface chlorine content and higher antimicrobial efficacy. This approach provides a novel and facile method that enables the covalent immobilization of N-chloramine precursors on inert polymeric surface to produce durable antimicrobial materials.

Functionalization of ultrafiltration membrane with polyampholyte hydrogel and graphene oxide to achieve dual antifouling and antibacterial properties

Membrane modification using zwitterion polymers is an excellent strategy to reduce organic fouling and initial bacterial deposition, and functionalization of the membrane surface with antibacterial material can reduce biofilm formation. In this study, we combined these two approaches to develop an ultrafiltration polyethersulfone (PES) membrane with dual antifouling and antibacterial properties. At the beginning, a zwitterion polyampholyte hydrogel was UV grafted onto PES membrane surface (p-PES membrane). Then, the hydrogel was loaded with graphene oxide (GO) nanosheets using vacuum filtration strategy (GO-p-PES membrane). Raman spectroscopy and scanning electron microscopy (SEM) confirmed the successful incorporation of the GO nanosheets into the zwitterion hydrogel, and contact angle measurements indicated that the membrane hydrophilicity was enhanced. Static adsorption and dynamic filtration experiments demonstrated that the p-PES and GO-p-PES membranes exhibited similar organic fouling propensity. Moreover, the loading of GO induced antibacterial property for the membrane as evidenced by contact killing and antibiofouling filtration experiments. Leaching of GO was very low, with over 98% of the GO remaining on the membrane surface after 7 days. Our findings highlight the potential of this GO-functionalized polyampholyte hydrogel for long-term wastewater treatment.

Peptide-Loaded Microgels as Antimicrobial and Anti-Inflammatory Surface Coatings.

Here we report on covalently immobilized poly(ethyl acrylate- co-methacrylic acid) microgels loaded with the host defense peptide KYE28 (KYEITTIHNLFRKLTHRLFRRNFGYTLR), which is derived from human heparin cofactor II, as well as its poly(ethylene glycol)-conjugated (PEGylated) version, KYE28PEG. Peptide loading and release, as well as the consequences of these processes on the microgel and peptide properties, were studied by in situ ellipsometry, confocal microscopy, zeta potential measurements, and circular dichroism spectroscopy. The results show that the microgel-peptide interactions are electrostatically dominated, thus promoted at higher microgel charge density, while PEGylation suppresses peptide binding. PEGylation also enhances the α-helix induction observed for KYE28 upon microgel incorporation. Additionally, peptide release is facilitated at physiological salt concentration, particularly so for KYE28PEG, which illustrates the importance of electrostatic interactions. In vitro studies on Escherichia coli show that the microgel-modified surfaces display potent antifouling properties in both the absence and presence of the incorporated peptide. While contact killing dominates at low ionic strength for the peptide-loaded microgels, released peptides also provide antimicrobial activity in bulk at a high ionic strength. Additionally, KYE28- and KYE28PEG-loaded microgels display anti-inflammatory effects on human monocytes. Taken together, these results not only show that surface-bound microgels offer an interesting approach for local drug delivery of host defense peptides but also illustrate the need to achieve high surface loads of peptides for efficient biological effects.