Polymeric systems of antimicrobial peptides--strategies and potential applications

Antimicrobial Peptide Screening for Designing Custom Bactericidal Hydrogels

Staphylococcus aureus (S. aureus) is an opportunistic pathogen that lives on surfaces and skin and can cause serious infections inside the body. Antimicrobial peptides (AMPs) are part of the innate immune system and can eliminate pathogens, including bacteria and viruses, and are a promising alternative to antibiotics. Although studies have reported that AMP-functionalized hydrogels can prevent bacterial adhesion and biofilm formation, AMP dosing and the combined effects of multiple AMPs are not well understood. Here, three AMPs with different antibacterial properties were synthesized and the soluble minimum inhibitory concentrations (MICs) of each AMP against methicillin-susceptible S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA) were determined. Hydrogels with immobilized AMPs at their MIC (DD13-RIP 27.5 µM; indolicidin 43.8 µM; P10 120 µM) were effective in preventing MRSA adhesion and biofilm formation. Checkerboard AMP screens identified synergy between indolicidin (3.1 µM) and P10 (12.5 µM) based on soluble fractional inhibitory concentration indices (FICIs) against MRSA, and hydrogels formed with these AMPs at half of their synergistic concentrations (total peptide concentration, 7.8 µM) were highly efficacious in killing MRSA. Mammalian cells cultured atop these hydrogels were highly viable, demonstrating that these AMP hydrogels are biocompatible and selectively eradicate bacteria, based on soluble checkerboard-screening data.

Nanoparticles incorporated hydrogels for delivery of antimicrobial agents: developments and trends

The prevention and treatment of microbial infections is an imminent global public health concern due to the poor antimicrobial performance of the existing antimicrobial regime and rapidly emerging antibiotic resistance in pathogenic microbes. In order to overcome these problems and effectively control bacterial infections, various new treatment modalities have been identified. To attempt this, various micro- and macro-molecular antimicrobial agents that function by microbial membrane disruption have been developed with improved antimicrobial activity and lesser resistance. Antimicrobial nanoparticle-hydrogels systems comprising antimicrobial agents (antibiotics, biological extracts, and antimicrobial peptides) loaded nanoparticles or antimicrobial nanoparticles (metal or metal oxide) constitute an important class of biomaterials for the prevention and treatment of infections. Hydrogels that incorporate nanoparticles can offer an effective strategy for delivering antimicrobial agents (or nanoparticles) in a controlled, sustained, and targeted manner. In this review, we have described an overview of recent advancements in nanoparticle-hydrogel hybrid systems for antimicrobial agent delivery. Firstly, we have provided an overview of the nanoparticle hydrogel system and discussed various advantages of these systems in biomedical and pharmaceutical applications. Thereafter, different hybrid hydrogel systems encapsulating antibacterial metal/metal oxide nanoparticles, polymeric nanoparticles, antibiotics, biological extracts, and antimicrobial peptides for controlling infections have been reviewed in detail. Finally, the challenges and future prospects of nanoparticle-hydrogel systems have been discussed.

Imidazolium Salts for Candida spp. Antibiofilm High-Density Polyethylene-Based Biomaterials

The species of Candida present good capability to form fungal biofilms on polymeric surfaces and are related to several human diseases since many of the employed medical devices are designed using polymers, especially high-density polyethylene (HDPE). Herein, HDPE films containing 0; 0.125; 0.250 or 0.500 wt% of 1-hexadecyl-3-methylimidazolium chloride (C₁₆MImCl) or its analog 1-hexadecyl-3-methylimidazolium methanesulfonate (C₁₆MImMeS) were obtained by melt blending and posteriorly mechanically pressurized into films. This approach resulted in more flexible and less brittle films, which impeded the Candida albicans, C. parapsilosis, and C. tropicalis biofilm formation on their surfaces. The employed imidazolium salt (IS) concentrations did not present any significant cytotoxic effect, and the good cell adhesion/proliferation of human mesenchymal stem cells on the HDPE-IS films indicated good biocompatibility. These outcomes combined with the absence of microscopic lesions in pig skin after contact with HDPE-IS films demonstrated their potential as biomaterials for the development of effective medical device tools that reduce the risk of fungal infections.

Succinyl Chitosan-Colistin Conjugates as Promising Drug Delivery Systems

The growth of microbial multidrug resistance is a problem in modern clinical medicine. Chemical modification of active pharmaceutical ingredients is an attractive strategy to improve their biopharmaceutical properties by increasing bioavailability and reducing drug toxicity. Conjugation of antimicrobial drugs with natural polysaccharides provides high efficiency of these systems due to targeted delivery, controlled drug release and reduced toxicity. This paper reports a two-step synthesis of colistin conjugates (CT) with succinyl chitosan (SucCS); first, we modified chitosan with succinyl anhydride to introduce a carboxyl function into the polymer molecule, which was then used for chemical grafting with amino groups of the peptide antibiotic CT using carbodiimide chemistry. The resulting polymeric delivery systems had a degree of substitution (DS) by CT of 3-8%, with conjugation efficiencies ranging from 54 to 100% and CT contents ranging from 130-318 μg/mg. The size of the obtained particles was 100-200 nm, and the ζ-potential varied from -22 to -28 mV. In vitro release studies at pH 7.4 demonstrated ultra-slow hydrolysis of amide bonds, with a CT release of 0.1-0.5% after 12 h; at pH 5.2, the hydrolysis rate slightly increased; however, it remained extremely low (1.5% of CT was released after 12 h). The antimicrobial activity of the conjugates depended on the DS. At DS 8%, the minimum inhibitory concentration (MIC) of the conjugate was equal to the MIC of native CT (1 µg/mL); at DS of 3 and 5%, the MIC increased 8-fold. In addition, the developed systems reduced CT nephrotoxicity by 20-60%; they also demonstrated the ability to reduce bacterial lipopolysaccharide-induced inflammation in vitro. Thus, these promising CT-SucCS conjugates are prospective for developing safe and effective nanoantibiotics.

Recent advancements and perspective of ciprofloxacin-based antimicrobial polymers

In recent years, microbial pathogens, which are major sources of infections, have become a widespread concern across the world. The number of deaths caused by infectious diseases is continually rising, according to World Health Organization records. Antimicrobial resistance, particularly resistance to several drugs, is steadily growing in percentages of organisms. Ciprofloxacin is a second-generation fluoroquinolone with significant antimicrobial activity and pharmacokinetic characteristics. According to studies, many bacteria are resistant to the antibiotic ciprofloxacin. In this article, we look into polymers as ciprofloxacin macromolecular carriers with a wide range of antibacterial activity. We also discuss the latter form of coupling, in which ciprofloxacin and polymers are covalently bonded. This article also discusses the use of antimicrobial polymers in combination with ciprofloxacin in a various sectors. The current review article provides an overview of publications in the last five years on polymer loaded or modified with ciprofloxacin having applications in numerous sectors.

A hyaluronic acid-based nanogel for the co-delivery of nitric oxide (NO) and a novel antimicrobial peptide (AMP) against bacterial biofilms

Biofilms are a global health concern because they are associated with chronic and recurrent infections as well as resistance to conventional antibiotics. The aim of this study was to prepare a nanogel for the co-delivery of NO and AMPs against bacteria and biofilms. The NO-releasing nanogel was prepared by crosslinking HA solution with divinyl sulfone and extensively characterized. The nanogel was found to be biocompatible, injectable and NO release from the gel was sustained over a period of 24 h. In vitro antibacterial studies showed that the NO-AMP-loaded nanogel exhibited a broad spectrum antibacterial/antibiofilm activity. The NO-releasing nanogel had a greater antibacterial effect when compared to NO alone with MIC values of 1.56, 0.78 and 0.39 μg/ml against Escherichia coli, Methicillin-resistant Staphylococcus aureus and Pseudomonas aeruginosa bacteria respectively. The antibiofilm results showed there was a 12.5 and 24-folds reduction in biofilms of MRSA, and P. aeruginosa respectively for catheters exposed to nanogel loaded with AMP/NO when compared to only NO, while a 7 and 9.4-folds reduction in biofilms of MRSA, and P. aeruginosa respectively was displayed by the nanogel loaded with only NO compared to only NO. The AMP/NO-releasing nanogel showed the potential to combat both biofilms and bacterial infections.

Promising Methods of Antibacterial Finishing of Textile Materials

A review article, containing information on the options, possibilities, and prospects for the development of antibacterial finishing of textile materials, is presented. A wide range of products designed to impart antibacterial, antimicrobial, and antiviral properties to textile materials is considered. The main factors determining the appropriate decision on the technological and functional choice of the protective composition are presented, including the nature of the fiber-forming polymer, the tasks that the resulting material is designed to solve, and its application options. Compositions providing the required effect of destruction of the pathogenic flora and their application technologies are described. Special attention is paid to antimicrobial agents based on silver nanoparticles. Nanoparticles of this metal have a detrimental effect on antibiotic-resistant strains of bacteria; their effectiveness is higher as compared to a number of well-known antibiotics, for example, penicillin and its analogues. Silver nanoparticles are harmless to the human body. Acting as an inhibitor, they limit the activity of the enzyme responsible for oxygen consumption by single-cell bacteria, viruses, and fungi. In this case, silver ions bind to the outer and inner proteins of the bacterial cell membranes, blocking cellular respiration and reproduction. Various options to apply microencapsulation methods for the implementation of antibacterial finishing are considered, including: phase separation, suspension crosslinking, simple and complex coacervation, spray drying, crystallization from the melt, evaporation of the solvent, co-extrusion, layering, fluidized bed spraying, deposition, emulsion and interphase polymerization, layer-by-layer electrostatic self-assembly etc. All presented technologies are at various development stages-from the laboratory stage to production tests, they all have certain advantages and disadvantages. The accelerated development and implementation of the described methods in production of textile materials is relevant and is related to the existing complex epidemiological situation in the world.

The Potential of Modified and Multimeric Antimicrobial Peptide Materials as Superbug Killers

Antimicrobial peptides (AMPs) are found in nearly all living organisms, show broad spectrum antibacterial activity, and can modulate the immune system. Furthermore, they have a very low level of resistance induction in bacteria, which makes them an ideal target for drug development and for targeting multi-drug resistant bacteria 'Superbugs'. Despite this promise, AMP therapeutic use is hampered as typically they are toxic to mammalian cells, less active under physiological conditions and are susceptible to proteolytic degradation. Research has focused on addressing these limitations by modifying natural AMP sequences by including e.g., d-amino acids and N-terminal and amino acid side chain modifications to alter structure, hydrophobicity, amphipathicity, and charge of the AMP to improve antimicrobial activity and specificity and at the same time reduce mammalian cell toxicity. Recently, multimerisation (dimers, oligomer conjugates, dendrimers, polymers and self-assembly) of natural and modified AMPs has further been used to address these limitations and has created compounds that have improved activity and biocompatibility compared to their linear counterparts. This review investigates how modifying and multimerising AMPs impacts their activity against bacteria in planktonic and biofilm states of growth.

Antimicrobial activity of synthetic antimicrobial peptides loaded in poly-Ɛ-caprolactone nanoparticles against mycobacteria and their functional synergy with rifampicin

Tuberculosis (TB) treatment has become a challenge because of the natural presence of multilayered cell wall rich in lipids which restrict antibiotic permeability within the bacteria. The development of mutations conferring resistance has aggravated the situation. Consequently, maximum pharmaceutical efforts are required to improve the treatment, and antimicrobial peptides (AMPs) with antimycobacterial activity can be exploited as a new treatment strategy against TB. The synergistic interaction between conventional antibiotics and AMPs has broadened its application landscape. To overcome peptide instability and bioavailability issues, encapsulation of these bioactive in biocompatible polymers was adopted. In this study, the effect of synthetic AMPs HHC-8 [KIWWWWRKR] and MM-10 [MLLKKLLKKM] encapsulated in poly (ε-caprolactone) nanoparticles (PCL-NPs) was evaluated against mycobacteria using REMA (Resazurin Microtiter Assay Plate) technique. PCL encapsulation allowed us to load the required amount of peptides, i.e. HHC-8 and MM-10, with an efficiency of ∼ 18.9 ± 5.24 and ∼ 21.1 ± 6.19 % respectively, and sphere size was around 376.5 ± 14.9 nm and 289.87 ± 17.98 nm for PCL-HHC-8-NPs and PCL-MM-10-NPs, respectively. Minimal degradation and sustained release of peptides from nanoparticles improved antimicrobial activity, decreasing the MIC₅₀ from 75 µg/ml to 18.75 µg/ml against M. smegmatis and from 75 µg/ml to 9 µg/ml against M. tuberculosis, respectively. The combinatorial MIC assays of encapsulated AMP with rifampicin antibiotics against M. smegmatis showed synergism between AMP-PCL-NPs and antibiotics with fractional inhibitory concentrations (FICs) around ∼ 0.09. The combinations of AMP NPs also demonstrated synergy against the mycobacteria. Our findings suggest that enhanced efficacy is due to protection offered by AMPs encapsulation resulting in augmentation of membrane permeation by AMPs and enhanced accumulation of antibiotics within mycobacteria resulting in synergy. The study findings might assist in the preclinical development of AMP for the fight against TB.

Chitosan-Based Hydrogel for the Dual Delivery of Antimicrobial Agents Against Bacterial Methicillin-Resistant Staphylococcus aureus Biofilm-Infected Wounds

Chronic wound infections caused by antibiotic-resistant bacteria have become a global health concern. This is attributed to the biofilm-forming ability of bacteria on wound surfaces, thus enabling their persistent growth. In most cases, it leads to morbidity and in severe cases mortality. Current conventional approaches used in the treatment of biofilm wounds are proving to be ineffective due to limitations such as the inability to penetrate the biofilm matrix; hence, biofilm-related wounds remain a challenge. Therefore, there is a need for more efficient alternate therapeutic interventions. Hydrogen peroxide (HP) is a known antibacterial/antibiofilm agent; however, prolonged delivery has been challenging due to its short half-life. In this study, we developed a hydrogel for the codelivery of HP and antimicrobial peptides (Ps) against bacteria, biofilms, and wound infection associated with biofilms. The hydrogel was prepared via the Michael addition technique, and the physiochemical properties were characterized. The safety, in vitro, and in vivo antibacterial/antibiofilm activity of the hydrogel was also investigated. Results showed that the hydrogel is biosafe. A greater antibacterial effect was observed with HP-loaded hydrogels (CS-HP; hydrogel loaded with HP and CS-HP-P; hydrogel loaded with HP and peptide) when compared to HP as seen in an approximately twofold and threefold decrease in minimum inhibitory concentration values against methicillin-resistant Staphylococcus aureus (MRSA) bacteria, respectively. Similarly, both the HP-releasing hydrogels showed enhanced antibiofilm activity in the in vivo study in mice models as seen in greater wound closure and enhanced wound healing in histomorphological analysis. Interestingly, the results revealed a synergistic antibacterial/antibiofilm effect between HP and P in both in vitro and in vivo studies. The successfully prepared HP-releasing hydrogels showed the potential to combat bacterial biofilm-related infections and enhance wound healing in mice models. These results suggest that the HP-releasing hydrogels may be a superior platform for eliminating bacterial biofilms without using antibiotics in the treatment of chronic MRSA wound infections, thus improving the quality of human health.

pH and light-responsive polycaprolactone/curcumin@zif-8 composite films with enhanced antibacterial activity

Food packaging materials, especially biodegradable polymer composites incorporated with natural antimicrobial agents with excellent antibacterial activities, are in high demand and attracted immense attention. Herein, a polycaprolactone/curcumin@zeolitic imidazolate framework-8 (PCL/Cur@ZIF-8) composite film with enhanced antibacterial activity was developed. Curcumin, a natural photosensitizer, was loaded in the highly porous nanocrystals ZIF-8 to improve its poor water solubility and stability. The integral structure of Cur@ZIF-8 was maintained well in the PCL matrix even at the highest loading of 35% (w/w), and all composite films had good light transmittance at 420-430 nm. The PCL/Cur@ZIF-8 composite films responded to the acidic growth environment of bacteria by releasing zinc ions and curcumin molecules. Furthermore, upon blue light irradiation (420-430 nm, 2.2 mW/cm² ), curcumin molecules generated singlet oxygen. With the synergistic effects of zinc ions and singlet oxygen, the composite films exhibited a 99.9% reduction of Escherichia coli and Staphylococcus aureus strains when the amount of Cur@ZIF-8 loading was more than 15% (w/w), as well as a strong anti-adhesion effect on bacteria. Moreover, bacterial resuscitation tests indicated that the composite films exhibited 99.9% reduction in the adhered bacteria population through treatment with photodynamic sterilization. This is the first study presenting that the incorporated curcumin ZIF-8 nanoparticles in the matrix of polymer are pH and light responsive for anti-adhesion of bacteria, which is of great potential application as antibacterial packaging material for the food industry. PRACTICAL APPLICATION: A novel, biodegradable, pH, and light-responsive composite film was developed for antibacterial activity. Natural photosensitizer curcumin was encapsulated in ZIF-8 nanocrystals (Cur@ZIF-8) as the antimicrobial agent. With the synergistic effects of Zn²⁺ and singlet oxygen, the composite film exhibited a 99.9% reduction of Escherichia coli and Staphylococcus aureus strains, and a strong anti-adhesion property toward bacteria. This composite film is of great potential application as an antibacterial packaging material that enhances the shelf life of fruits, meat, and so on.

Nanomedicine-based antimicrobial peptide delivery for bacterial infections: recent advances and future prospects

Background

Antimicrobial peptides (AMPs) have gained wide interest as viable alternatives to antibiotics owing to their potent antimicrobial effects and the low propensity of resistance development. However, their physicochemical properties (solubility, charge, hydrophobicity/hydrophilicity), stability issues (proteolytic or enzymatic degradation, aggregation, chemical degradation), and toxicities (interactions with blood components or cellular toxicities) limit their therapeutic applications.

Area covered

Nanomedicine-based therapeutic delivery is an emerging concept. The AMP loaded nanoparticles have been prepared and investigated for their antimicrobial effects. In this review, we will discuss different nanomedicine-based AMP delivery systems including metallic nanoparticles, lipid nanoparticles, polymeric nanoparticles, and their hybrid systems along with their future prospects for potent antimicrobial efficacy.

Expert opinion

Nanomedicine-based AMP delivery is a recent approach to the treatment of bacterial infections. The advantageous properties of nanoparticles including the enhancement of AMP stability, controlled release, and targetability make them suitable for the augmentation of AMP activity. Modifications in the nanomedicine-based approach are required to overcome the problems of nanoparticle instability, shorter residence time, and toxicity. Future rigorous studies for both the AMP loaded nanoparticle preparation and characterization, and detailed evaluations of their in vitro and in vivo antimicrobial effects and toxicities, are essential.

Catechol-Based Antimicrobial Polymers

Catechol is a key constituent in mussel adhesive proteins and is responsible for strong adhesive property and crosslinking formation. Plant-based polyphenols are also capable of chemical interactions similar to those of catechol and are inherently antimicrobial. This review reports a series of catechol-based antimicrobial polymers classified according to their antimicrobial mechanisms. Catechol is utilized as a surface anchoring group for adhering monomers and polymers of known antimicrobial properties onto various types of surfaces. Additionally, catechol's ability to form strong complexes with metal ions and nanoparticles was utilized to sequester these antimicrobial agents into coatings and polymer matrices. During catechol oxidation, reactive oxygen species (ROS) is generated as a byproduct, and the use of the generated ROS for antimicrobial applications was also introduced. Finally, polymers that utilized the innate antimicrobial property of halogenated catechols and polyphenols were reviewed.

Preparation of lysozyme loaded gelatin microcryogels and investigation of their antibacterial properties

Antibacterial micron-sized cryogels, so-called microcryogels, were prepared by cryogelation of gelatin and integration of lysozyme. Gelation yield, specific surface area, macro-porosity and swelling degree of the microcryogels were examined in order to characterize their physical properties. MTT method was utilized to measure cell viability of the gelatin microcryogels with a period of 24, 48, and 72 h and no significant decrease was observed at 72 h. Apoptotic staining assay also showed high viability at 24, 48, 72 h in parallel with the control group. The antibacterial performances of the gelatin microcryogels against Bacillus subtilis, Staphylococcus aureus, and Escherichia coli were examined. The results showed that the incorporation of lysozyme into gelatin microcryogels exhibited the antibacterial activity against S. aureus, B. subtilis, and E. coli, that may provide great potential for various applications in the biomedical industry.

Functionalized Polymeric Materials with Bio-Derived Antimicrobial Peptides for "Active" Packaging

Food packaging is not only a simple protective barrier, but a real “active” component, which is expected to preserve food quality, safety and shelf-life. Therefore, the materials used for packaging production should show peculiar features and properties. Specifically, antimicrobial packaging has recently gained great attention with respect to both social and economic impacts. In this paper, the results obtained by using a polymer material functionalized by a small synthetic peptide as “active” packaging are reported. The surface of Polyethylene Terephthalate (PET), one of the most commonly used plastic materials in food packaging, was plasma-activated and covalently bio-conjugated to a bactenecin-derivative peptide named 1018K6, previously characterized in terms of antimicrobial and antibiofilm activities. The immobilization of the peptide occurred at a high yield and no release was observed under different environmental conditions. Moreover, preliminary data clearly demonstrated that the “active” packaging was able to significantly reduce the total bacterial count together with yeast and mold spoilage in food-dairy products. Finally, the functionalized-PET polymer showed stronger efficiency in inhibiting biofilm growth, using a Listeria monocytogenes strain isolated from food products. The use of these “active” materials would greatly decrease the risk of pathogen development and increase the shelf-life in the food industry, showing a real potential against a panel of microorganisms upon exposure to fresh and stored products, high chemical stability and re-use possibility.

Anti-Cancerous Potential of Polyphenol-Loaded Polymeric Nanotherapeutics

Recent evidence has extensively demonstrated the anticancer potential of nutraceuticals, including plant polyphenols. Polymeric nanocarrier systems have played an important role in improving the physicochemical and pharmacological properties of polyphenols, thus ameliorating their therapeutic effectiveness. This article summarizes the benefits and shortcomings of various polymeric systems developed for the delivery of polyphenols in cancer therapy and reveals some ideas for future work.

Peptide based antimicrobials: Design strategies and therapeutic potential

Therapeutic activity of antibiotics is noteworthy, as they are used in the treatment of microbial infections. Regardless of their utility, there has been a steep decrease in the number of drug candidates due to antibiotic resistance, an inevitable consequence of noncompliance with the full therapeutic regimen. A variety of resistant species like MDR (Multi-Drug Resistant), XDR (Extensively Drug-Resistant) and PDR (Pan Drug-Resistant) species have evolved, but discovery pipeline has already shown signs of getting dried up. Therefore, the need for newer antibiotics is of utmost priority to combat the microbial infections of future times. Peptides have some interesting features like minimal side effect, high tolerability and selectivity towards specific targets, which would help them successfully comply with the stringent safety standards set for clinical trials. In this review, we attempt to present the state of the art in the discovery of peptide-based antimicrobials from a design perspective.

Synthesis, Self-Assembly, and Biomedical Applications of Antimicrobial Peptide-Polymer Conjugates

Antimicrobial peptides (AMPs) have been attracting much attention due to their excellent antimicrobial efficiency and low rate in driving antimicrobial resistance (AMR), which has been increasing globally to alarming levels. Conjugation of AMPs into functional polymers not only preserves excellent antimicrobial activities but reduces the toxicity and offers more functionalities, which brings new insight toward developing multifunctional biomedical materials such as hydrogels, polymer vesicles, polymer micelles, and so forth. These nanomaterials have been exhibiting excellent antimicrobial activity against a broad spectrum of bacteria including multidrug-resistant (MDR) ones, high selectivity, and low cytotoxicity, suggesting promising potentials in wound dressing, implant coating, antibiofilm, tissue engineering, and so forth. This Perspective seeks to highlight the state-of-the-art strategy for the synthesis, self-assembly, and biomedical applications of AMP-polymer conjugates and explore the promising directions for future research ranging from synthetic strategies, multistage and stimuli-responsive antibacterial activities, antifungi applications, and potentials in elimination of inflammation during medical treatment. It also will provide perspectives on how to stem the remaining challenges and unresolved problems in combating bacteria, including MDR ones.

Silane Modified Diopside for Improved Interfacial Adhesion and Bioactivity of Composite Scaffolds

Diopside (DIOP) was introduced into polyetheretherketone/polyglycolicacid (PEEK/PGA) scaffolds fabricated via selective laser sintering to improve bioactivity. The DIOP surface was then modified using a silane coupling agent, 3-glycidoxypropyltrimethoxysilane (KH570), to reinforce interfacial adhesion. The results showed that the tensile properties and thermal stability of the scaffolds were significantly enhanced. It could be explained that, on the one hand, the hydrophilic group of KH570 formed an organic covalent bond with the hydroxy group on DIOP surface. On the other hand, there existed relatively high compatibility between its hydrophobic group and the biopolymer matrix. Thus, the ameliorated interface interaction led to a homogeneous state of DIOP dispersion in the matrix. More importantly, an in vitro bioactivity study demonstrated that the scaffolds with KH570-modified DIOP (KDIOP) exhibited the capability of forming a layer of apatite. In addition, cell culture experiments revealed that they had good biocompatibility compared to the scaffolds without KDIOP. It indicated that the scaffolds with KDIOP possess potential application in tissue engineering.

Polyphenols delivery by polymeric materials: challenges in cancer treatment

Nanotechnology can offer different solutions for enhancing the therapeutic efficiency of polyphenols, a class of natural products widely explored for a potential applicability for the treatment of different diseases including cancer. While possessing interesting anticancer properties, polyphenols suffer from low stability and unfavorable pharmacokinetics, and thus suitable carriers are required when planning a therapeutic protocol. In the present review, an overview of the different strategies based on polymeric materials is presented, with the aim to highlight the strengths and the weaknesses of each approach and offer a platform of ideas for researchers working in the field.

Novel human bioactive peptides identified in Apolipoprotein B: Evaluation of their therapeutic potential

Host defence peptides (HDPs) are short, cationic amphipathic peptides that play a key role in the response to infection and inflammation in all complex life forms. It is increasingly emerging that HDPs generally have a modest direct activity against a broad range of microorganisms, and that their anti-infective properties are mainly due to their ability to modulate the immune response. Here, we report the recombinant production and characterization of two novel HDPs identified in human Apolipoprotein B (residues 887-922) by using a bioinformatics method recently developed by our group. We focused our attention on two variants of the identified HDP, here named r(P)ApoB_L and r(P)ApoB_S, 38- and 26-residue long, respectively. Both HDPs were found to be endowed with a broad-spectrum antimicrobial activity while they show neither toxic nor haemolytic effects towards eukaryotic cells. Interestingly, both HDPs were found to display a significant anti-biofilm activity, and to act in synergy with either commonly used antibiotics or EDTA. The latter was selected for its ability to affect bacterial outer membrane permeability, and to sensitize bacteria to several antibiotics. Circular dichroism analyses showed that SDS, TFE, and LPS significantly alter r(P)ApoB_L conformation, whereas slighter or no significant effects were detected in the case of r(P)ApoB_S peptide. Interestingly, both ApoB derived peptides were found to elicit anti-inflammatory effects, being able to mitigate the production of pro-inflammatory interleukin-6 and nitric oxide in LPS induced murine macrophages. It should also be emphasized that r(P)ApoB_L peptide was found to play a role in human keratinocytes wound closure in vitro. Altogether, these findings open interesting perspectives on the therapeutic use of the herein identified HDPs.

Nanoparticles for radiooncology: Mission, vision, challenges

Cancer is one of the leading non-communicable diseases with highest mortality rates worldwide. About half of all cancer patients receive radiation treatment in the course of their disease. However, treatment outcome and curative potential of radiotherapy is often impeded by genetically and/or environmentally driven mechanisms of tumor radioresistance and normal tissue radiotoxicity. While nanomedicine-based tools for imaging, dosimetry and treatment are potential keys to the improvement of therapeutic efficacy and reducing side effects, radiotherapy is an established technique to eradicate the tumor cells. In order to progress the introduction of nanoparticles in radiooncology, due to the highly interdisciplinary nature, expertise in chemistry, radiobiology and translational research is needed. In this report recent insights and promising policies to design nanotechnology-based therapeutics for tumor radiosensitization will be discussed. An attempt is made to cover the entire field from preclinical development to clinical studies. Hence, this report illustrates (1) the radio- and tumor-biological rationales for combining nanostructures with radiotherapy, (2) tumor-site targeting strategies and mechanisms of cellular uptake, (3) biological response hypotheses for new nanomaterials of interest, and (4) challenges to translate the research findings into clinical trials.

Functionalization of nanostructures for antibiotic improvement: an interdisciplinary approach

The resistance of infectious bacteria to current antibiotics is a worldwide problem caused, partially, by the overuse of antimicrobials. The use of nanotechnology as an innovative tool against bacterial infections provides a range of methodologies to redesign old antibiotics for novel and remarkable new strategies. Thus, functionalized antibiotics present structures with improved bioavailability, low toxicity and specificity to bacterial membrane. In this context, this review will describe the use of nanotechnology as an innovative tool to functionalize antibiotics. In addition, the importance of the interdisciplinary context to understand, develop and apply these systems as an innovative tool for drug development and improvement is discussed.

Antimicrobial Polymers and Surfaces – Natural Mimics or Surpassing Nature?

Fighting pathogenic microbes is one of the great current challenges of mankind. Nature has developed several techniques to counteract microbial attacks. Science has also yielded several technologies, including antimicrobial polymers as biocides and polymers used for microbe killing and repelling surfaces. Recent scientific antimicrobial approaches are mimicking natural concepts. In this chapter, current developments in antimicrobial and antifouling polymers and surfaces are reviewed and discussed regarding the question whether they mimic nature or surpass it.

Bactericidal, quorum quenching and anti-biofilm nanofactories: a new niche for nanotechnologists

Despite several conventional potent antibacterial therapies, bacterial infections pose a significant threat to human health because they are emerging as the leading cause of death worldwide. Due to the development of antibiotic resistance in bacteria, there is a pressing demand to discover novel approaches for developing more effective therapies to treat multidrug-resistant bacterial strains and biofilm-associated infections. Therefore, attention has been especially devoted to a new and emerging branch of science "nanotechnology" to design non-conventional antimicrobial chemotherapies. A range of nanomaterials and nano-sized carriers for conventional antimicrobial agents have fully justified their potential to combat bacterial diseases by reducing cell viability, by attenuating quorum sensing, and by inhibiting/or eradicating biofilms. This communication summarizes emerging nano-antimicrobial therapies in treating bacterial infections, particularly using antibacterial, quorum quenching, and anti-biofilm nanomaterials as new approaches to tackle the current challenges in combating infectious diseases.

Antimicrobial Approaches for Textiles: From Research to Market

The large surface area and ability to retain moisture of textile structures enable microorganisms' growth, which causes a range of undesirable effects, not only on the textile itself, but also on the user. Due to the public health awareness of the pathogenic effects on personal hygiene and associated health risks, over the last few years, intensive research has been promoted in order to minimize microbes' growth on textiles. Therefore, to impart an antimicrobial ability to textiles, different approaches have been studied, being mainly divided into the inclusion of antimicrobial agents in the textile polymeric fibers or their grafting onto the polymer surface. Regarding the antimicrobial agents, different types have been used, such as quaternary ammonium compounds, triclosan, metal salts, polybiguanides or even natural polymers. Any antimicrobial treatment performed on a textile, besides being efficient against microorganisms, must be non-toxic to the consumer and to the environment. This review mainly intends to provide an overview of antimicrobial agents and treatments that can be performed to produce antimicrobial textiles, using chemical or physical approaches, which are under development or already commercially available in the form of isolated agents or textile fibers or fabrics.

Evaluation of Antimicrobial Efficiency of New Polymers Comprised by Covalently Attached and/or Electrostatically Bound Bacteriostatic Species, Based on Quaternary Ammonium Compounds

In the present work a detailed study of new bacteriostatic copolymers with quaternized ammonium groups introduced in the polymer chain through covalent attachment or electrostatic interaction, was performed. Different copolymers have been considered since beside the active species, the hydrophobic/hydrophilic nature of the co-monomer was also evaluated in the case of covalently attached bacteriostatic groups, aiming at achieving permanent antibacterial activity. Homopolymers with quaternized ammonium/phosphonium groups were also tested for comparison reasons. The antimicrobial activity of the synthesized polymers after 3 and 24 h of exposure at 4 and 22 °C was investigated on cultures of Gram-negative (P. aeruginosa, E. coli) and Gram-positive (S. aureus, E. faecalis) bacteria. It was found that the combination of the hydrophilic monomer acrylic acid (AA), at low contents, with the covalently attached bacteriostatic group vinyl benzyl dimethylhexadecylammonium chloride (VBCHAM) in the copolymer P(AA-co-VBCHAM88), resulted in a high bacteriostatic activity against P. aeruginosa and E. faecalis (6 log reduction in certain cases). Moreover, the combination of covalently attached VBCHAM units with electrostatically bound cetyltrimethylammonium 4-styrene sulfonate (SSAmC₁₆) units in the P(SSAmC₁₆-co-VBCHAMx) copolymers led to efficient antimicrobial materials, especially against Gram-positive bacteria, where a log reduction between 4.9 and 6.2 was verified. These materials remain remarkably efficient even when they are incorporated in polysulfone membranes.

Polyvinyl alcohol nanofiber formulation of the designer antimicrobial peptide APO sterilizes Acinetobacter baumannii-infected skin wounds in mice

Native and designer cationic antimicrobial peptides are increasingly acknowledged as host defense molecules rather than true antimicrobials. Due to their ability to activate the innate immune system, these structures are used to treat uninfected and bacterially-infected wounds, including those harboring Acinetobacter baumannii. Previously we documented that when administered intramuscularly or topically in liquid formulations, the proline-rich host defense peptide dimer A3-APO accelerates uninfected wound re-epithelization and eliminates systemic and local A. baumannii, methicillin-resistant Staphylococcus aureus and other pathogen load from infected lesions better than conventional antibiotics. In the current study we sought to produce and characterize a novel delivery system, suitable for immediate and convenient application in non-hospital environments. The APO monomer was incorporated into polyvinyl alcohol nanofibers and the complex was polymerized into a solid patch dressing. Mice were subjected to skin abrasion where the wounds were either left uninfected or were inoculated with a near lethal dose of multidrug resistant A. baumannii strain. Analyzed after 3 days, APO monomer-containing patches improved wound appearance significantly better than polymer patches without antibiotics. When compared to colistin, the APO patches accelerated wound healing, and statistically significantly reduced wound size and wound bacterial load. The in vivo antimicrobial effect was more extensive than after intramuscular administration of the peptide drug, by using only one tenth of the active pharmaceutical ingredient. These data suggest that the APO monomer-impregnated nanofiber dressing can be developed as an economical first-line treatment option to skin injuries in general and battlefield burn and blast injuries in particular.

Chitosan nanoparticles loaded with the antimicrobial peptide temporin B exert a long-term antibacterial activity in vitro against clinical isolates of Staphylococcus epidermidis

Nowadays, the alarming rise in multidrug-resistant microorganisms urgently demands for suitable alternatives to current antibiotics. In this regard, antimicrobial peptides (AMPs) have received growing interest due to their broad spectrum of activities, potent antimicrobial properties, unique mechanisms of action, and low tendency to induce resistance. However, their pharmaceutical development is hampered by potential toxicity, relatively low stability and manufacturing costs. In the present study, we tested the hypothesis that the encapsulation of the frog-skin derived AMP temporin B (TB) into chitosan nanoparticles (CS-NPs) could increase peptide's antibacterial activity, while reducing its toxic potential. TB-loaded CS-NPs with good dimensional features were prepared, based on the ionotropic gelation between CS and sodium tripolyphosphate. The encapsulation efficiency of TB in the formulation was up to 75%. Release kinetic studies highlighted a linear release of the peptide from the nanocarrier, in the adopted experimental conditions. Interestingly, the encapsulation of TB in CS-NPs demonstrated to reduce significantly the peptide's cytotoxicity against mammalian cells. Additionally, the nanocarrier evidenced a sustained antibacterial action against various strains of Staphylococcus epidermidis for at least 4 days, with up to 4-log reduction in the number of viable bacteria compared to plain CS-NPs at the end of the observational period. Of note, the antimicrobial evaluation tests demonstrated that while the intrinsic antimicrobial activity of CS ensured a "burst" effect, the gradual release of TB further reduced the viable bacterial count, preventing the regrowth of the residual cells and ensuring a long-lasting antibacterial effect. The developed nanocarrier is eligible for the administration of several AMPs of therapeutic interest with physical-chemical characteristics analog to those of TB.

Effects of antimicrobial peptides on Staphylococcus aureus growth and biofilm formation in vitro following isolation from implant-associated infections

To prevent biomaterial-associated infections, antibiotic agents are recommended for various medical conditions requiring biomaterial implants, but resistance often appears after the introduction of antibiotics into clinical use. Therefore, new strategies for the prevention or treatment for biomaterial-associated infections are required. The purpose of this study was to evaluate the effects of antimicrobial peptides on growth and biofilm formation of Staphylococcus aureus isolated from implant-associated infections. A total of 20 patients with culture-proven staphylococcal infection associated with stable orthopedic implants were selected as the experimental group. S. aureus were isolated from tissue biopsies for identification, the isolated strains were mixed with Tet213 incubated at 37°C and viable bactrial number of S. aureus was counted. For the biofilm formation, the broad spectrum AMP Tet213 was selected and loaded onto the Ti coating first. At the same time Ti coated with Tet213 were mixed with S. aureus in vitro to form biofilm. After 30 min, 2 h, 4 h, 6 h, 8 h, the population of S. aureus in the biofilm was counted. Tet213 showed significant antibacterial effect on 16 strains (P < 0.05, Table 1). The inhibition rate reached above 80% among 12 strains of the clinically isolated strain. In biofilm experiments, counts of the NO. 1, 2, 3, 4 strains in biofilms decreased significantly after 2 h (P < 0.05), while there was no obvious difference in counts of NO. 5 strain (P > 0.05). The broad spectrum AMP Tet213 could strongly reduce the growth and biofilm formation of S. aureus in vitro, and the use of this might be an important new approach to target implant-associated infections.

Enzymatic polymerization of cyclic monomers in ionic liquids as a prospective synthesis method for polyesters used in drug delivery systems

Biodegradable or bioresorbable polymers are commonly used in various pharmaceutical fields (e.g., as drug delivery systems, therapeutic systems or macromolecular drug conjugates). Polyesters are an important class of polymers widely utilized in pharmacy due to their biodegradability and biocompatibility features. In recent years, there has been increased interest in enzyme-catalyzed ring-opening polymerization (e-ROP) of cyclic esters as an alternative method of preparation of biodegradable or bioresorbable polymers. Ionic liquids (ILs) have been presented as green solvents in enzymatic ring-opening polymerization. The activity, stability, selectivity of enzymes in ILs and the ability to catalyze polyester synthesis under these conditions are discussed. Overall, the review demonstrates that e-ROP of lactones or lactides could be an effective method for the synthesis of useful biomedical polymers.

Novel formulations for antimicrobial peptides

Peptides in general hold much promise as a major ingredient in novel supramolecular assemblies. They may become essential in vaccine design, antimicrobial chemotherapy, cancer immunotherapy, food preservation, organs transplants, design of novel materials for dentistry, formulations against diabetes and other important strategical applications. This review discusses how novel formulations may improve the therapeutic index of antimicrobial peptides by protecting their activity and improving their bioavailability. The diversity of novel formulations using lipids, liposomes, nanoparticles, polymers, micelles, etc., within the limits of nanotechnology may also provide novel applications going beyond antimicrobial chemotherapy.

Optical and dielectric sensors based on antimicrobial peptides for microorganism diagnosis

Antimicrobial peptides (AMPs) are natural compounds isolated from a wide variety of organisms that include microorganisms, insects, amphibians, plants, and humans. These biomolecules are considered as part of the innate immune system and are known as natural antibiotics, presenting a broad spectrum of activities against bacteria, fungi, and/or viruses. Technological innovations have enabled AMPs to be utilized for the development of novel biodetection devices. Advances in nanotechnology, such as the synthesis of nanocomposites, nanoparticles, and nanotubes have permitted the development of nanostructured platforms with biocompatibility and greater surface areas for the immobilization of biocomponents, arising as additional tools for obtaining more efficient biosensors. Diverse AMPs have been used as biological recognition elements for obtaining biosensors with more specificity and lower detection limits, whose analytical response can be evaluated through electrochemical impedance and fluorescence spectroscopies. AMP-based biosensors have shown potential for applications such as supplementary tools for conventional diagnosis methods of microorganisms. In this review, conventional methods for microorganism diagnosis as well new strategies using AMPs for the development of impedimetric and fluorescent biosensors are highlighted. AMP-based biosensors show promise as methods for diagnosing infections and bacterial contaminations as well as applications in quality control for clinical analyses and microbiological laboratories.

Treatment of microbial biofilms in the post-antibiotic era: prophylactic and therapeutic use of antimicrobial peptides and their design by bioinformatics tools

The treatment for biofilm infections is particularly challenging because bacteria in these conditions become refractory to antibiotic drugs. The reduced effectiveness of current therapies spurs research for the identification of novel molecules endowed with antimicrobial activities and new mechanisms of antibiofilm action. Antimicrobial peptides (AMPs) have been receiving increasing attention as potential therapeutic agents, because they represent a novel class of antibiotics with a wide spectrum of activity and a low rate in inducing bacterial resistance. Over the past decades, a large number of naturally occurring AMPs have been identified or predicted from various organisms as effector molecules of the innate immune system playing a crucial role in the first line of defense. Recent studies have shown the ability of some AMPs to act against microbial biofilms, in particular during early phases of biofilm development. Here, we provide a review of the antimicrobial peptides tested on biofilms, highlighting their advantages and disadvantages for prophylactic and therapeutic applications. In addition, we describe the strategies and methods for de novo design of potentially active AMPs and discuss how informatics and computational tools may be exploited to improve antibiofilm effectiveness.