Durable contact active antimicrobial materials formed by a one-step covalent modification of polyvinyl alcohol, cellulose and glass surfaces

Rechargeable films for protection of dry foods: A sustainable method for covalent grafting of β-cyclodextrin-thymol complex on PET/viscose platform

Rechargeable materials for the effective protection of dry food products were developed. β-cyclodextrin-thymol inclusion complex was covalently grafted on a solid platform of polyethylene terephthalate-viscose using either traditional cross-linker of epichlorohydrin, or natural cross-linker of citric acid. A correlation between the grafting method and physicochemical properties, loading capacity and release capabilities of the resulted materials was studied. The developed materials demonstrated antimicrobial properties preventing mold propagation in wheat grains. The treated grains showed normal germination abilities verifying that the prepared materials can protect dry food products without using harmful chemicals. The suggested approach can be extended to other applications and active agents. A combination of rechargeable films with natural volatiles can serve as an effective platform for sustainable active materials for food protection and in other fields such as agriculture, cosmetics, and medicine.

Antimicrobial-Loaded Polyacrylamide Hydrogels Supported on Titanium as Reservoir for Local Drug Delivery

Arthroplasty is a highly successful treatment to restore the function of a joint. The contamination of the implant via bacterial adhesion is the first step toward the development of device-associated infections. The emerging concern about antimicrobial resistance resulted in a growing interest to develop alternative therapeutic strategies. Thus, the increment in the incidence of bacterial periprosthetic infections, the complexity of treating infections caused by organisms growing in biofilms, together with the rise in antibiotic resistant bacteria, expose the need to design novel surfaces that provide innovative solutions to these rising problems. The aim of this work is to develop a coating on titanium (Ti) suitable for inhibiting bacterial adhesion and proliferation, and hence, biofilm formation on the surface. We have successfully prepared polyacrylamide hydrogels containing the conventional antibiotic ampicillin (AMP), silver nanoparticles (AgNPs), and both, AMP and AgNPs. The release of the antibacterial agents from the gelled to aqueous media resulted in an excellent antibacterial action of the loaded hydrogels against sessile S. aureus. Moreover, a synergic effect was achieved with the incorporation of both AMP and AgNPs in the hydrogel, which highlights the importance of combining antimicrobial agents having different targets. The polyacrylamide hydrogel coating on the Ti surface was successfully achieved, as it was demonstrated by FTIR, contact angle, and AFM measurements. The modified Ti surfaces having the polyacrylamide hydrogel film containing AgNPs and AMP retained the highest antibacterial effect against S. aureus as it was found for the unsupported hydrogels. The modified surfaces exhibit an excellent cytocompatibility, since healthy, flattened MC3T3-E1 cells spread on the surfaces were observed. In addition, similar macrophage RAW 264.7 adhesion was found on all the surfaces, which could be related to a low macrophage activation. Our results indicate that AMP and AgNP-loaded polyacrylamide hydrogel films on Ti are a good alternative for designing efficient antibacterial surfaces having an excellent cytocompatibility without inducing an exacerbated immune response. The approach emerges as a superior alternative to the widely used direct adsorption of therapeutic agents on surfaces, since the antimicrobial-loaded hydrogel coatings open the possibility of modulating the concentration of the antimicrobial agents to enhance bacterial killing, and then, reducing the risk of infections in implantable materials.

Regulating Alkyl Chain Length on Quaternization TiO2 for Boosting Photocatalytic Performance: Synergism of Promoting Photogenerated Charge Separation and Improving Reactant Adsorption

To explore the effect of surface charge properties of a photocatalyst on photocatalytic activity, quaternization TiO₂ particles with different alkyl chain lengths (CT-X/P25) are first synthesized to boost the photocatalytic activity. The effect of a quaternary ammonium group with different alkyl chain lengths on the photocatalytic activity of CT-X/P25 is investigated. Interestingly, the introduction of a quaternary ammonium group on CT-X/P25 not only contributes to improving the photodegradation efficiency of anionic dyes due to enhancing of adsorption capacity through electrostatic attraction, but also it can improve the photodegradation efficiency of cationic dyes. Therefore, there seems to be another factor affecting the photocatalytic activity. The results of photoelectric characterization show that the photogenerated charge separation of CT-X/P25 is greatly enhanced, which is beneficial to improve the photocatalytic activity. Simultaneously, the results show that the difference in the photocatalytic activity of CT-X/P25 is mainly related to the charge intensity of -N⁺(CH₃)₂- in the quaternary amine salt. According to X-ray photoelectron spectroscopy, the charge intensity of -N⁺(CH₃)₂- in CT-X/P25 gradually increases with the increase in alkyl chain lengths, which is conducive to promoting photogenerated charge separation and improving the adsorption for anionic dyes. The photocatalytic activity has been further enhanced due to the enhancement of this synergy. In summary, the quaternary ammonium salt-modified CT-X/P25 shows an excellent synergistic effect on the process of photodegradation of anionic dyes: promoting photogenerated charge separation and adsorption.

Polymeric Membrane Marine Sensors with a Regenerable Antibiofouling Coating Based on Surface Modification of a Dual-Functionalized Magnetic Composite

Environmentally compatible polymeric membrane marine sensors with excellent antiadhesive and antibacterial properties have recently been developed. However, the regeneration abilities of these sensors after fouling have rarely been investigated. Herein, a novel strategy for preparation of a regenerable antibiofouling coating via surface modification of a dual-functionalized magnetic composite is proposed. A zwitterionic polymer (i.e., poly(sulfobetaine methacrylate)) and a quaternary ammonium compound (i.e., 3-trimethoxysilylpropyl octadecyldimethyl ammonium chloride) are coated on the surface of Fe₃O₄ microspheres for antiadhesion and bacterial inactivation, respectively. The antifouling magnetic composite can readily be modified on the sensor's surface via the magnetically assisted self-assembly technology. Using a polymeric membrane calcium ion-selective electrode as a model sensor, the protection layer-coated electrode shows the markedly improved antibiofouling activities as compared to the unmodified sensor. More importantly, by altering the direction of the external magnetic field, the antifouling coating can easily be removed after fouling along with the removal of the adsorbed bacterial cells from the electrode's surface, which is followed by re-modifying a fresh coating for regeneration of the antifouling electrode. The proposed methodology for fabrication of a regenerable antibiofouling coating is promising to improve the durability of a marine sensor.

Cellulose-Based Nanomaterials Advance Biomedicine: A Review

There are various biomaterials, but none fulfills all requirements. Cellulose biopolymers have advanced biomedicine to satisfy high market demand and circumvent many ecological concerns. This review aims to present an overview of cellulose knowledge and technical biomedical applications such as antibacterial agents, antifouling, wound healing, drug delivery, tissue engineering, and bone regeneration. It includes an extensive bibliography of recent research findings from fundamental and applied investigations. Cellulose-based materials are tailorable to obtain suitable chemical, mechanical, and physical properties required for biomedical applications. The chemical structure of cellulose allows modifications and simple conjugation with several materials, including nanoparticles, without tedious efforts. They render the applications cheap, biocompatible, biodegradable, and easy to shape and process.

Past and Current Progress in the Development of Antiviral/Antimicrobial Polymer Coating towards COVID-19 Prevention: A Review

The astonishing outbreak of SARS-CoV-2 coronavirus, known as COVID-19, has attracted numerous research interests, particularly regarding fabricating antimicrobial surface coatings. This initiative is aimed at overcoming and minimizing viral and bacterial transmission to the human. When contaminated droplets from an infected individual land onto common surfaces, SARS-CoV-2 coronavirus is able to survive on various surfaces for up to 9 days. Thus, the possibility of virus transmission increases after touching or being in contact with contaminated surfaces. Herein, we aim to provide overviews of various types of antiviral and antimicrobial coating agents, such as antimicrobial polymer-based coating, metal-based coating, functional nanomaterial, and nanocomposite-based coating. The action mode for each type of antimicrobial agent against pathogens is elaborated. In addition, surface properties of the designed antiviral and antimicrobial polymer coating with their influencing factors are discussed in this review. This paper also exhibits several techniques on surface modification to improve surface properties. Various developed research on the development of antiviral/antimicrobial polymer coating to curb the COVID-19 pandemic are also presented in this review.

Antimicrobial coatings for environmental surfaces in hospitals: a potential new pillar for prevention strategies in hygiene

Recent reports provide evidence that contaminated healthcare environments represent major sources for the acquisition and transmission of pathogens. Antimicrobial coatings (AMC) may permanently and autonomously reduce the contamination of such environmental surfaces complementing standard hygiene procedures. This review provides an overview of the current status of AMC and the demands to enable a rational application of AMC in health care settings. Firstly, a suitable laboratory test norm is required that adequately quantifies the efficacy of AMC. In particular, the frequently used wet testing (e.g. ISO 22196) must be replaced by testing under realistic, dry surface conditions. Secondly, field studies should be mandatory to provide evidence for antimicrobial efficacy under real-life conditions. The antimicrobial efficacy should be correlated to the rate of nosocomial transmission at least. Thirdly, the respective AMC technology should not add additional bacterial resistance development induced by the biocidal agents and co- or cross-resistance with antibiotic substances. Lastly, the biocidal substances used in AMC should be safe for humans and the environment. These measures should help to achieve a broader acceptance for AMC in healthcare settings and beyond. Technologies like the photodynamic approach already fulfil most of these AMC requirements.

A Synthetic Overview of Preparation Protocols of Nonmetallic, Contact-Active Antimicrobial Quaternary Surfaces on Polymer Substrates

Antibacterial surfaces have been researched for more than 30 years and remain highly desirable. In particular, there is an interest in providing antimicrobial properties to commodity plastics, because these, in their native state, are excellent substrates for pathogens to adhere and proliferate on. Therefore, efficient strategies for converting surfaces of commodity plastics into contact-active antimicrobial surfaces are of significant interest. Many systems have been prepared and tested for their efficacy. Here, the synthetic approaches to such active surfaces are reviewed, with the restriction to only include systems with tested antibacterial properties. The review focuses on the synthetic approach to surface functionalization of the most common materials used and tested for biomedical applications, which effectively has limited the study to quaternary materials. For future developments in the field, it is evident that there is a need for development of simple methods that permit scalable production of active surfaces. Furthermore, in terms of efficacy, there is an outstanding concern of a lack of universal antimicrobial action as well as rapid deactivation of the antibacterial effect through surface fouling.

Probing an Interfacial Ionic Pairing-Induced Molecular Dipole Effect in Ionovoltaic System

A surficial molecular dipole effect depending on ion-molecular interactions has been crucial issues regarding to an interfacial potential, which can modulate solid electronic and electrochemical systems. Their properties near the interfacial region can be dictated by specific interactions between surface and adsorbates, but understandings of the corresponding details remain at interesting issues. Here, intuitive observations of an ionic pair formation-induced interfacial potential shifts are presented with an ionovoltaic system, and corresponding output signal variations are analyzed in terms of the surficial dipole changes on self-assembled monolayer. With aiding of photoelectron spectroscopies and density function theory simulation, the ionic pair formation-induced potential shifts are revealed to strongly rely on a paired molecular structure and a binding affinity of the paired ionic moieties. Chemical contributions to the binding event are interrogated in terms of polarizability in each ionic group and consistent with chaotropic/kosmotropic character of the ionic groups. Based on these findings, the ionovoltaic output changes are theoretically correlated with an adsorption isotherm reflecting the molecular dipole effect, thereby demonstrating as an efficient interfacial molecular probing method under electrolyte interfacing conditions.

Air-ozonolysis activation of polyolefins versus use of laden finishing to form contact-active nonwoven materials

Two synthetic approaches were explored for modification of the polyolefins polyethylene/polypropylene (PE/PP) to form contact-active nonwoven materials. In the first approach, polymer surfaces were activated by O2-free air-ozonolysis, and then the active agent (trimethoxysilyl) propyl-octadecyl-dimethyl-ammonium chloride (C18-TSA) was covalently bound. In the second approach, the active agent was directly conjugated to the commercial 'finishing' that was then applied to the polymer. The chemical, physical and microscopic properties of the modified polymers were comprehensively studied, and their active site density was quantified by fluorescein sodium salt-cetyltrimethylammonium chloride reaction. The antimicrobial activity of the prepared nonwovens against Bacillus subtilis (Gram-positive) and Salmonella enterica (Gram-negative), and their stability at various pHs and temperatures were examined. The two approaches conferred antimicrobial properties to the modified polymers and demonstrated stable linkage of C18-TSA. However, the performance of the nonwovens formed by the first approach was superior. The study suggests two feasible and safe pathways for the modification of polyolefins to form contact-active nonwoven materials that can be further applied in various fields, such as hygiene products, medical fabrics, sanitizing wipes, and more.

Chemical Modification of Bacterial Cellulose for the Development of an Antibacterial Wound Dressing

Bacterial cellulose is a bacterially derived polymer with great potential for application in wound healing due to its innate properties such as high biocompatibility and biodegradability. In addition to this, it is naturally biosynthesized by bacteria as a hydrogel, which makes it an optimal substrate for the treatment of dry wounds, where additional moisture is required to facilitate the healing process. However, this polymer lacks antibacterial properties. As bacterial infections are becoming increasingly common and difficult to treat due to antimicrobial resistance, it is of crucial importance to develop strategies for the modification of cellulose to ensure protection against bacterial contamination. In this study, a green-chemistry approach was proposed for the functionalization of cellulose to introduce antibacterial functional groups. Two different active agents, namely glycidyl trimethylammonium chloride and glycidyl hexadecyl ether, were used for the covalent derivatization of the hydroxyl groups of glucose through a heterogeneous reaction in basic aqueous conditions. The modified material was chemically and mechanically characterized by solid-state techniques and rheological measurements. A biological assessment was then carried out both using bacterial cells and human keratinocytes. It was observed that the functionalization performed induced a reduction of approximately half of the bacterial population within 24 h of direct contact with Staphylococcus aureus subsp. aureus Rosenbach 6538PTM and Escherichia coli (Migula) Castellani and Chalmers ATCC® 8739TM (respectively, a reduction of 53% and 43% in the cell number was registered for the two strains). In parallel, cytotoxicity studies performed on keratinocytes (HaCaT cell line) showed cell viability in the range of 90 to 100% for up to 6 days of direct contact with both unmodified and modified samples. The morphology of the cells was also visually evaluated, and no significant difference was noted as compared to the control. Finally, the in vitro scratch assay evidenced good wound closure rates in the presence of the samples, with complete coverage of the scratched area after 5 days for both the modified cellulose and the positive control (i.e., keratinocytes growth medium). Overall, the modified hydrogel showed promising features, confirming its potential as an alternative substrate to develop a sustainable, antibacterial and biocompatible wound dressing.

Role of Bacillus species in biofilm persistence and emerging antibiofilm strategies in the dairy industry

Biofilm-forming Bacillus species are often involved in persistent contamination and spoilage of dairy products. They therefore present a major microbiological challenge in the field of dairy food quality and safety. Due to their substantial physiological versatility, Bacillus species can survive in various parts of dairy manufacturing plants, leading to a high risk of product spoilage and potential dissemination of foodborne diseases. Furthermore, biofilm and heat-resistant spore formation make these bacteria challenging to eliminate. Thus, some strategies have been employed to remove, prevent, or delay the formation of Bacillus biofilms in the dairy industry, but with limited success. Lack of understanding of the Bacillus biofilm structure and behavior in conditions relevant to dairy-associated environments could partially account for this situation. The current paper reviews dairy-associated biofilm formation by Bacillus species, with particular attention to the role of biofilm in Bacillus species adaptation and survival in a dairy processing environment. Relevant model systems are discussed for the development of novel antimicrobial approaches to improve the quality of dairy food. © 2020 Society of Chemical Industry.

A Review on Surface-Functionalized Cellulosic Nanostructures as Biocompatible Antibacterial Materials

As the most abundant biopolymer on the earth, cellulose has recently gained significant attention in the development of antibacterial biomaterials. Biodegradability, renewability, strong mechanical properties, tunable aspect ratio, and low density offer tremendous possibilities for the use of cellulose in various fields. Owing to the high number of reactive groups (i.e., hydroxyl groups) on the cellulose surface, it can be readily functionalized with various functional groups, such as aldehydes, carboxylic acids, and amines, leading to diverse properties. In addition, the ease of surface modification of cellulose expands the range of compounds which can be grafted onto its structure, such as proteins, polymers, metal nanoparticles, and antibiotics. There are many studies in which cellulose nano-/microfibrils and nanocrystals are used as a support for antibacterial agents. However, little is known about the relationship between cellulose chemical surface modification and its antibacterial activity or biocompatibility. In this study, we have summarized various techniques for surface modifications of cellulose nanostructures and its derivatives along with their antibacterial and biocompatibility behavior to develop non-leaching and durable antibacterial materials. Despite the high effectiveness of surface-modified cellulosic antibacterial materials, more studies on their mechanism of action, the relationship between their properties and their effectivity, and more in vivo studies are required.

Synthesis and antibacterial properties of thymol and carvacrol grafted onto lignocellulosic kraft fibers

Bacterial infections and surface contaminations are worrying public health issues. It becomes urgent to find solutions. One of the ways to limit bacterial proliferation is to develop new antimicrobial materials. The phenolic compounds of essential oils like thymol and carvacrol, are attractive antibacterial candidates, which have gained great popularity in the food, cosmetic, and pharmaceutical industries. This work describes the elaboration of bioinspired antibacterial materials. Thymol and carvacrol are linked to kraft pulp fibers, via triazine link. This novel material has been investigated for its antibacterial properties against Escherichia coli and Staphylococcus aureus. The developed materials show very interesting antibacterial activity. The grafting of thymol and carvacrol by covalent bond allows to avoid the problem of their release and, thus, could maintain the antibacterial properties of support.

Atomic Force Microscopy and Angular-Dependent X-ray Photoelectron Spectroscopy Studies of Anchored Quaternary Ammonium Salt Biocides on Quartz Surfaces

A siloxane surface-anchored quaternary ammonium salt (AQAS: BIOSAFE HM4100 in this study) has been chemisorbed onto a quartz substrate. The aim of this study is to elucidate, using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS), the structure of the chemisorbed AQAS layers. The AQAS biocide includes a C₁₈ alkyl chain previously invoked in lysis potency. The AQAS coverage appears in zones on the surface, which include a first layer (2.6 ± 0.1 nm) and multilayering that were explored using AFM. The XPS data exhibited two N 1s signals at about 402 and 399 eV, with only the former exhibiting angular dependence. This signal at 402 eV was assigned to the first anchored layer with perpendicular orientation determined by the AQAS anchoring to the surface. In preliminary AFM studies of bacteria on these AQAS surfaces, perturbations on the Staphylococcus aureus cells and the degradation of Escherichia coli cells suggest lysis potency.

Novel bioactive surface functionalization of bacterial cellulose membrane

Bacterial cellulose (BC) membrane is a promising biopolymer which can be used for tissue implants, wound healing, and drug delivery due to its unique properties, such as high crystallinity, high mechanical strength, ultrafine fiber network structure, good water holding capacity and biocompatibility. However, BC does not intrinsically present antibacterial properties. In the present study, functionalized BC membranes were prepared. FTIR, SEM and XPS were used to characterize the chemical composition and surface morphology. Static water contact angles were measured to investigate surface wettability. Escherichia coli, Staphylococcus aureus, Bacillus subtilis and Candida albicans were used to evaluate the antibacterial properties of membranes. HEK293 cell lines were applied to assess the biocompatibility of membrane surfaces by MTT assay and their morphologies were observed by Confocal Microscopy. Interestingly, the resultant functionalized BC membranes exhibiting excellent antibacterial property and good biocompatibility demonstrated great utility and potential as biomaterial materials.

Water Purification Using Functionalized Cellulosic Fibers with Nonleaching Bacteria Adsorbing Properties

Portable purification systems are easy ways to obtain clean drinking water when there is no large-scale water treatment available. In this study, the potential to purify water using bacteria adsorbing cellulosic fibers, functionalized with polyelectrolytes according to the layer-by-layer method, is investigated. The adsorbed polyelectrolytes create a positive charge on the fiber surface that physically attracts and bonds with bacteria. Three types of cellulosic materials have been modified and tested for the bacterial removal capacity in water. The time, material-water ratio and bacterial concentration dependence, as well as the bacterial removal capacity in water from natural sources, have been evaluated. Freely dispersed bacteria adsorbing cellulosic fibers can remove greater than 99.9% of Escherichia coli from nonturbid water, with the most notable reduction occurring within the first hour. A filtering approach using modified cellulosic fibers is desirable for purification of natural water. An initial filtration test showed that polyelectrolyte multilayer modified cellulosic fibers can remove greater than 99% of bacteria from natural water. The bacteria adsorbing cellulosic fibers do not leach any biocides, and it is an environmentally sustainable and cheap option for disposable water purification devices.

A review of the recent advances in antimicrobial coatings for urinary catheters

More than 75% of hospital-acquired or nosocomial urinary tract infections are initiated by urinary catheters, which are used during the treatment of 15-25% of hospitalized patients. Among other purposes, urinary catheters are primarily used for draining urine after surgeries and for urinary incontinence. During catheter-associated urinary tract infections, bacteria travel up to the bladder and cause infection. A major cause of catheter-associated urinary tract infection is attributed to the use of non-ideal materials in the fabrication of urinary catheters. Such materials allow for the colonization of microorganisms, leading to bacteriuria and infection, depending on the severity of symptoms. The ideal urinary catheter is made out of materials that are biocompatible, antimicrobial, and antifouling. Although an abundance of research has been conducted over the last forty-five years on the subject, the ideal biomaterial, especially for long-term catheterization of more than a month, has yet to be developed. The aim of this review is to highlight the recent advances (over the past 10years) in developing antimicrobial materials for urinary catheters and to outline future requirements and prospects that guide catheter materials selection and design.

STATEMENT OF SIGNIFICANCE

This review article intends to provide an expansive insight into the various antimicrobial agents currently being researched for urinary catheter coatings. According to CDC, approximately 75% of urinary tract infections are caused by urinary catheters and 15-25% of hospitalized patients undergo catheterization. In addition to these alarming statistics, the increasing cost and health related complications associated with catheter associated UTIs make the research for antimicrobial urinary catheter coatings even more pertinent. This review provides a comprehensive summary of the history, the latest progress in development of the coatings and a brief conjecture on what the future entails for each of the antimicrobial agents discussed.

Anti-Bacterial and Anti-Fungal Activity of Xanthones Obtained via Semi-Synthetic Modification of α-Mangostin from Garcinia mangostana

The microbial contamination in food packaging has been a major concern that has paved the way to search for novel, natural anti-microbial agents, such as modified α-mangostin. In the present study, twelve synthetic analogs were obtained through semi-synthetic modification of α-mangostin by Ritter reaction, reduction by palladium-carbon (Pd-C), alkylation, and acetylation. The evaluation of the anti-microbial potential of the synthetic analogs showed higher bactericidal activity than the parent molecule. The anti-microbial studies proved that I E showed high anti-bacterial activity whereas I I showed the highest anti-fungal activity. Due to their microbicidal potential, modified α-mangostin derivatives could be utilized as active anti-microbial agents in materials for the biomedical and food industry.

Combating Antimicrobial Resistance in Foodborne Microorganisms

This review addresses an important public health hazard affecting food safety. Antimicrobial agents are used in foods to reduce or eliminate microorganisms that cause disease. Many traditional organic compounds, novel synthetic organic agents, natural products, peptides, and proteins have been extensively studied for their effectiveness as antimicrobial agents against foodborne Campylobacter spp., Escherichia coli, Listeria spp. and Salmonella. However, antimicrobial resistance can develop in microorganisms, enhancing their ability to withstand the inhibiting or killing action of antimicrobial agents. Knowledge gaps still exist with regard to the actual chemical and microbiological mechanisms that must be identified to facilitate the search for new antimicrobial agents. Technical implementation of antimicrobial active packing films and coatings against target microorganisms must also be improved for extended product shelf life. Recent advances in antimicrobial susceptibility testing can provide researchers with new momentum to pursue their quest for a resistance panacea.

Self-Sterilizing, Self-Cleaning Mixed Polymeric Multifunctional Antimicrobial Surfaces

Mitigation of bacterial adhesion and subsequent biofilm formation is quickly becoming a strategy for the prevention of hospital-acquired infections. We demonstrate a basic strategy for surface modification that combines the ability to control attachment by microbes with the ability to inactivate microbes. The surface consists of two active materials: poly(p-phenylene ethynylene)-based polymers, which can inactivate a wide range of microbes and pathogens, and poly(N-isopropylacrylamide)-based polymers, which can switch between an hydrophobic "capture" state and a hydrophilic "release" state. The combination of these materials creates a surface that can both bind microbes in a switchable way and kill surface-bound microbes efficiently. Considerable earlier work with cationic poly(p-phenylene ethynylene) polyelectrolytes has demonstrated and characterized their antimicrobial properties, including the ability to efficiently destroy or deactivate Gram-negative and Gram-positive bacteria, fungi, and viruses. Similarly, much work has shown (1) that surface-polymerized films of poly(N-isopropylacrylamide) are able to switch their surface thermodynamic properties from a swollen, relatively hydrophilic state at low temperature to a condensed, relatively hydrophobic state at higher temperature, and (2) that this switch can control the binding and/or release of microbes to poly(N-isopropylacrylamide) surfaces. The active surfaces described herein were fabricated by first creating a film of biocidal poly(p-phenylene ethynylene) using layer-by-layer methods, and then conferring switchable adhesion by growing poly(N-isopropylacrylamide) through the poly(p-phenylene ethynylene) layer, using surface-attached polymerization initiators. The resulting multifunctional, complex films were then characterized both physically and functionally. We demonstrate that such films kill and subsequently induce widespread release of Gram-negative and Gram-positive bacteria.

Dual-function antibacterial surfaces for biomedical applications

Bacterial attachment and the subsequent formation of biofilm on surfaces of synthetic materials pose a serious problem in both human healthcare and industrial applications. In recent decades, considerable attention has been paid to developing antibacterial surfaces to reduce the extent of initial bacterial attachment and thereby to prevent subsequent biofilm formation. Briefly, there are three main types of antibacterial surfaces: bactericidal surfaces, bacteria-resistant surfaces, and bacteria-release surfaces. The strategy adopted to develop each type of surface has inherent advantages and disadvantages; many efforts have been focused on the development of novel antibacterial surfaces with dual functionality. In this review, we highlight the recent progress made in the development of dual-function antibacterial surfaces for biomedical applications. These surfaces are based on the combination of two strategies into one system, which can kill attached bacteria as well as resisting or releasing bacteria. Perspectives on future research directions for the design of dual-function antibacterial surfaces are also provided.

Polydiacetylene nanovesicles as carriers of natural phenylpropanoids for creating antimicrobial food-contact surfaces

The ultimate goal of this study was developing antimicrobial food-contact materials based on natural phenolic compounds using nanotechnological approaches. Among the methyl-β-cyclodextrin-encapsulated phenolics tested, curcumin showed by far the highest activity toward Escherichia coli with a minimum inhibitory concentration of 0.4 mM. Curcumin was enclosed in liposome-type polydiacetylene/phosholipid nanovesicles supplemented with N-hydroxysuccinimide and glucose. The fluorescence spectrum of the nanovesicles suggested that curcumin was located in their bilayer region. Free-suspended nanovesicles tended to bind to the bacterial surface and demonstrated bactericidal activity toward Gram-negative (E. coli) and vegetative cells of Gram-positive (Bacillus cereus) bacteria reducing their counts from 5 log CFU mL(-1) to an undetectable level within 8 h. The nanovesicles were covalently bound to silanized glass. Incubation of E. coli and B. cereus with nanovesicle-coated glass resulted in a 2.5 log reduction in their counts. After optimization this approach can be used for controlling microbial growth, cross-contamination, and biofilm formation on food-contacting surfaces.

Antimicrobial and bacteria-releasing multifunctional surfaces: oligo (p-phenylene-ethynylene)/poly (N-isopropylacrylamide) films deposited by RIR-MAPLE

Antimicrobial oligo (p-phenylene-ethynylene) (OPE) films have previously been demonstrated to show effective ultraviolet A (UVA) light-induced biocidal activity; however, a serious problem arises from the accumulation of dead bacteria and debris on the films that limits their effectiveness and application. In this work, we address this challenge by incorporating thermally-responsive poly (N-isopropylacrylamide) (PNIPAAm), which provides on-demand bacteria-releasing functionality. Multifunctional surfaces comprising blended films of OPE and PNIPAAm were deposited on substrates by resonant infrared, matrix-assisted pulsed laser evaporation (RIR-MAPLE) using a sequential co-deposition mode. In this way, RIR-MAPLE enabled the deposition of multifunctional films with surface properties and film functionality that can be tailored, precisely and systematically, by controlling the chemical composition of the deposited film. The surface properties of these films were characterized by UV-visible (UV-vis) absorbance spectroscopy, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and water contact angle measurements. The interactions between bacteria and the deposited films were tested using two model bacteria: Escherichia coli K12 (Gram-negative) and Staphylococcus epidermidis (Gram-positive). The antimicrobial and bacteria-release properties of the blended films were controlled by varying the OPE/PNIPAAm ratio in the RIR-MAPLE emulsion target, providing an easy way to optimize the multifunctional surface. The OPE/PNIPAAm blended films with optimized composition killed a majority of attached E. coli bacteria at 37 °C and under UVA exposure, and the dead bacteria were then removed from the films simply by rinsing with water at 25 °C.

Lanthano phosphomolybdate-decorated silica nanoparticles: novel hybrid materials with photochromic properties

Novel hybrid nanomaterials prepared through the immobilization of phosphomolybdates onto functional silica nanoparticles revealed promising photochromic properties under UV irradiation.