Advances in antimicrobial peptides: From mechanistic insights to chemical modifications

This review provides a comprehensive analysis of antimicrobial peptides (AMPs), exploring their diverse sources, secondary structures, and unique characteristics. The review explores into the mechanisms underlying the antibacterial, immunomodulatory effects, antiviral, antiparasitic and antitumour of AMPs. Furthermore, it discusses the three principal synthesis pathways for AMPs and assesses their current clinical applications and preclinical research status. The paper also addresses the limitations of AMPs, including issues related to stability, resistance, and toxicity, while offering insights into strategies for their enhancement. Recent advancements in AMP research, such as chemical modifications (including amino acid sequence optimisation, terminal and side-chain modifications, PEGylation, conjugation with small molecules, conjugation with photosensitisers, metal ligands, polymerisation, cyclisation and specifically targeted antimicrobial peptides) are highlighted. The goal is to provide a foundation for the future design and optimisation of AMPs.

Therapeutic peptides: chemical strategies fortify peptides for enhanced disease treatment efficacy

Therapeutic peptides, as a unique form of medication composed of orderly arranged sequences of amino acids, are valued for their high affinity, specificity, low immunogenicity, and economical production costs. Currently, more than 100 peptides have already secured market approval. Over 150 are actively undergoing clinical trials, while an additional 400-600 are in the preclinical research stage. Despite this, their clinical application is limited by factors such as salt sensitivity, brief residence in the bloodstream, inadequate cellular uptake, and high structural flexibility. By employing suitable chemical methods to modify peptides, it is possible to regulate important physicochemical factors such as charge, hydrophobicity, conformation, amphiphilicity, and sequence that affect the physicochemical properties and biological activity of peptides. This can overcome the inherent deficiencies of peptides, enhance their pharmacokinetic properties and biological activity, and promote continuous progress in the field of research. A diverse array of modified peptides is currently being developed and investigated across numerous therapeutic fields. Drawing on the latest research, this review encapsulates the essential physicochemical factors and significant chemical modification strategies that influence the properties and biological activity of peptides as pharmaceuticals. It also assesses how physicochemical factors affect the application of peptide drugs in disease treatment and the effectiveness of chemical strategies in disease therapy. Concurrently, this review discusses the prospective advancements in therapeutic peptide development, with the goal of offering guidance for designing and optimizing therapeutic peptides and to delve deeper into the therapeutic potential of peptides for disease intervention.

Amphiphilic polymer coated carbon nanotubes: A promising platform against Salmonella typhi

Carbon nanotubes (CNTs) are an excellent example of new nanostructures that can penetrate bacterial cell walls. Its remarkable physical features and potent antibacterial activity make it a promising candidate for various applications. However, two significant barriers currently limit the antibacterial potential of CNTs in medical devices: cell toxicity and CNTs aggregation within a polymer matrix. In this study, a simple and cost-effective method was proposed to synthesize multi-walled carbon nanotubes-g-[poly(ethylene glycol)-bpoly(ε-caprolactone)] (PEG-PCL@CNTs) using biocompatible amphiphilic PEG-PCL diblock copolymer via non-covalent functionalization. Furthermore, time-killing kinetic, ROS generation experiments and SEM analysis demonstrated that PEG-PCL@CNTs exhibited antibacterial activities against S. typhi strains through cell membrane disruption with the release of cellular contents and ROS generation. Excellent hemocompatibility with decreased hemolysis ratios was demonstrated by the PEG-PCL@CNTs nanohybrid materials. Thus, PEG-PCL incorporation may successfully lessen both bacterial adhesion and the toxicity of CNT to human cells. These findings suggest a new avenue for rational design of polymer-functionalization of carbon nanomaterials as therapeutic agents for bacterial infections.

Host Defense Peptide-Mimicking Poly(2-oxazoline)s Displaying Potent Activities toward Phytopathogens to Alleviate Antimicrobial Resistance in Agriculture

Given the limited types of agricultural bactericides and the rapid emergence of antimicrobial resistance, bacterial plant diseases pose a serious threat to agricultural production, which calls for effective antimicrobial agents with a low propensity for resistance. Host defense peptides (HDPs) have drawn significant attention for their broad-spectrum antimicrobial activity. In this study, we found that HPD-mimicking poly(2-oxazoline) Gly-POX20 exhibits potent activity against bacterial phytopathogens, with superior antibacterial selectivity and proteolytic stability compared to the natural HDP melittin. Compared to commonly used agricultural bactericides, Gly-POX20 displays more efficient antibiofilm activity and a lower propensity for resistance than does the antibiotic streptomycin, likely due to its antibacterial mechanism, which involves DNA interaction and generating lethal doses of ROS. In vivo studies reveal that Gly-POX20 is effective in preventing and treating phytopathogens without observable damage to plant tissues, suggesting that poly(2-oxazoline) could be a promising bactericide for agricultural applications.

Presenting Antimicrobial Peptides on Poly(ethylene glycol): Star-Shaped vs Comb-Like Architectures

Conjugating antimicrobial peptides (AMPs) to nonlinear polymers is a promising strategy to overcome the translational challenges of AMPs toward treating infections caused by antibiotic-resistant bacteria. Nonlinear polymers, and therefore conjugates, can be prepared with various architectures (e.g., star-shaped, comb-like, hyperbranched, etc.), however, the effects of polymer architecture on antimicrobial performance and related properties, like size and morphology in solution and secondary structure, are not yet well-understood. Here, we compare conjugates of the human chemokine-derived AMP stapled P9 with poly(ethylene glycol) (PEG) prepared in two of the major nonlinear architectures: star-shaped and comb-like. At comparable molecular weights and compositions (peptide wt %), comb-like conjugates afford increased helicity, solubility, antimicrobial activity, and proteolytic stability compared to star-shaped analogs. We then leveraged the expansive design space of comb-like architectures to prepare conjugates with different backbone lengths and PEG side chain lengths, with shorter PEG side chains leading to increased helicity, yet potentially less shielding from proteolytic degradation and the longest backbone lengths furnishing the most potent antimicrobial activity. Both comb-like and star-shaped conjugates display high zeta potential, indicating that the cationic AMPs were accessible for electrostatic interactions with bacterial membranes. Yet, the comb-like conjugates showed a higher fraction of unimolecular structures indicative of a lower propensity for supramolecular assembly that could be encumbering the desired AMP-bacteria interactions in the star-shaped conjugates. Together, our work shows comb-like AMP-polymer conjugates to outperform analogous star-shaped conjugates, while adding design flexibility to access an expansive range of monomer chemistries, monomer distributions, and backbone lengths to modulate performance-determining properties and ultimately furnish an effective suite of AMP-polymer materials as alternatives to conventional antibiotics for combatting bacterial infections.

Synergistic Enhancement of Antibacterial and Osteo-Immunomodulatory Activities of Titanium Implants via Dual-Responsive Multifunctional Surfaces

Bone implant-associated infections and inflammations, primarily caused by bacteria colonization, frequently result in unsuccessful procedures and pose significant health risks to patients. To mitigate these challenges, the development of engineered implants with spatiotemporal regulation capabilities, designed to inhibit bacterial survival and modulate immune responses in the early stage, while promoting bone defect healing in the late stage is proposed. The implants are functionalized with ε-poly-l-lysine-phenylboronic acid (PP) via dynamic boronic ester bonds, which facilitate its release through a reactive oxygen species (ROS) and pH-responsive strategy, thereby establishing an antibacterial microenvironment on and around the implants. Additionally, the dynamic metal coordination interaction facilitates the loading and sustained release of Sr2+ under an acidic environment, providing immunomodulatory and osteogenic effects. The ROS/pH-responsive feature, coupled with the implant-bone tissue integration process, affords precise spatiotemporal regulation of the Ti-TA-Sr-PP implants. This strategy represents a promising approach for the preparation of advanced bone implants.

Chitosan microflower-embedded gelatin sponges for advanced wound management and hemostatic applications

The study explored the antimicrobial, antibiofilm, and hemostatic properties of chitosan microflowers (CMF) in sponge form. The main objective was to enhance the preparation of CMF by employing varying quantities of calcium chloride (CaCl2) and tripolyphosphate (TPP). CMF was then combined with gelatin (GE) in different proportions to produce three sponge samples: CMF0@GE, CMF1@GE, and CMF2@GE. The CMF had a morphology like that of a flower and produced surfaces with a porous sponge-like structure. The antibacterial activity, as determined by the zone of inhibition (ZOI), increased with greater doses of CMF. Among the tested samples, CMF2@GE had the greatest activity against Pseudomonas aeruginosa, Klebsiella pneumoniae, Staphylococcus aureus, and Enterococcus faecium. CMF2@GE successfully suppressed biofilm formation, decreased clotting time to an average of 212.67 s, and exhibited excellent biocompatibility by preserving over 90 % viability of human skin fibroblast cells at dosages below 100 μg/mL. The results indicated that gelatin sponges filled with CMF have considerable promise as flexible medical instruments for wound healing and infection control.

Fluoroamphiphilic polymers exterminate multidrug-resistant Gram-negative ESKAPE pathogens while attenuating drug resistance

ESKAPE pathogens are a panel of most recalcitrant bacteria that could "escape" the treatment of antibiotics and exhibit high incidence of drug resistance. The emergence of multidrug-resistant (MDR) ESKAPE pathogens (particularly Gram-negative bacteria) accounts for high risk of mortality and increased resource utilization in health care. Worse still, there has been no new class of antibiotics approved for exterminating the Gram-negative bacteria for more than 50 years. Therefore, it is urgent to develop novel antibacterial agents with low resistance and potent killing efficacy against Gram-negative ESKAPE pathogens. Herein, we present a class of fluoropolymers by mimicking the amphiphilicity of cationic antimicrobial peptides. Our optimal fluoroamphiphilic polymer (PD45HF5) displayed selective antimicrobial ability for all MDR Gram-negative ESAKPE pathogens, low resistance, high in vitro cell selectivity, and in vivo curative efficacy. These findings implied great potential of fluoroamphiphilic cationic polymers as promising antibacterial agents against MDR Gram-negative ESKAPE bacteria and alleviating antibiotic resistance.

A multifunctional nanoplatform for precision-guided therapeutic intervention in bacterial infection

Skin wound infection has become a global clinical problem in recent years. Curcumin (Cur) and polylysine (PLL) are natural products with strong antibacterial properties. However, the poor water solubility and low stability of Cur and the cationic toxicity of PLL limit their application. In this study, we synthesized a macromolecular hyaluronic acid (HA)-curcumin drug (HC) via esterification. HC was attracted by electrostatic interactions with positively charged PLL to form a spherical nanocomplex (HCP) with hyaluronidase (HAase) and pH dual response under ultrasonication. HCP was found to target the bacterial infection microenvironment and release Cur and PLL for synergistic antibacterial action. In addition, HCP was proven to exhibit good biocompatibility and broad spectrum antibacterial activity to bacterial strains S. aureus and E. coli and antibacterial biofilm activities in vitro. In vivo experiments showed that HCP could inhibit pathogens and promote wound healing. These results prove that HCP can be used as a new strategy for the treatment and management of infected wounds.

AMP-Mimetic Antimicrobial Polymer-Involved Synergic Therapy with Various Coagents for Improved Efficiency

The misuse of antibiotics contributes to the emergence of multidrug-resistant (MDR) bacteria. Infections caused by MDR bacteria are rapidly evolving into a significant threat to global healthcare due to the lack of effective and safe treatments. Antimicrobial peptides (AMPs) with broad-spectrum antibacterial activity kill bacteria generally through a membrane disruption mechanism; hence, they tend not to induce resistance readily. However, AMPs exhibit disadvantages, such as high cost and susceptibility to proteolytic degradation, which limit their clinical application. AMP-mimetic antimicrobial polymers, with low cost, stability to proteolysis, broad-spectrum antimicrobial activity, negligible antimicrobial resistance, and rapid bactericidal effect, have received extensive attention as a new type of antibacterial drugs. Lately, AMP-mimetic polymer-involved synergic therapy provides a superior alternative to combat MDR bacteria by distinct mechanisms. In this Review, we summarize the AMP-mimetic antimicrobial polymers involved in synergic therapy, particularly focusing on the different combinations between the polymers with commercially available antimicrobials, organic small molecule photosensitizers, inorganic nanomaterials, and nitric oxide.

Antibacterial polylysine-containing hydrogels for hemostatic and wound healing applications: preparation methods, current advances and future perspectives

The treatment of various types of wounds such as dermal wounds, multidrug resistant bacteria-infected wounds, and chronic diabetic wounds is one of the critical challenges facing healthcare systems. Delayed wound healing can impose a remarkable burden on patients and health care professionals. In this case, given their unique three-dimensional porous structure, biocompatibility, high hydrophilicity, capability to provide a moist environment while absorbing wound exudate, permeability to both gas and oxygen, and tunable mechanical properties, hydrogels with antibacterial function are one of the most promising candidates for wound healing applications. Polylysine is a cationic polymer with the advantages of inherent antibacterial properties, biodegradability, and biocompatibility. Therefore, its utilization to engineer antibacterial hydrogels for accelerating wound healing is of great interest. In this review, we initially discuss polylysine properties, and then focus on the most recent advances in polylysine-containing hydrogels (since 2016) prepared using various chemical and physical crosslinking methods for hemostasis and wound healing applications. Finally, the challenges and future directions in the engineering of these antibacterial hydrogels for wound healing are discussed.

Synthesis and Synergistic Antimicrobial Efficacy of Covalent Conjugates Composed of Epsilon-Poly-l-lysine and Beta-Lactam Antibiotics

The increasing severity of problems posed by drug-resistant pathogens has compelled researchers to explore innovative approaches for infection prevention. Among these strategies, conjugation methods stand out for their convenience and high efficacy. In this study, multiple covalent conjugates were synthesized, incorporating the natural antimicrobial peptide epsilon-poly-l-lysine (EPL) and two commonly used β-lactam antibiotics: penicillin G or ampicillin. Enhanced antimicrobial efficacy against typical Gram-negative pathogens, along with faster kill kinetics compared to combination approaches, was demonstrated by the EPL-Ampicillin covalent conjugates. Their antimicrobial mechanism was also substantiated through SEM and fluorescence tests in this work, confirming the inheritance of membrane-disrupting properties from EPL. Furthermore, the excellent biocompatibility of the raw materials was reserved in the covalent conjugates. This simplified conjugation method holds promise for the development of infection therapeutic drugs and potentially restores the sensitivity of conventional antibiotics to drug-resistant pathogens by introducing membrane-disrupting mechanisms.

Stimuli-triggered multilayer films in response to temperature and ionic strength changes for controlled favipiravir drug release

The block copolymer micelles and natural biopolymers were utilized to form layer-by-layer (LbL) films via electrostatic interaction, which were able to effectively load and controllably release favipiravir, a potential drug for the treatment of coronavirus epidemic. The LbL films demonstrated reversible swelling/shrinking behavior along with the manipulation of temperature, which could also maintain the integrity in the structure and the morphology. Due to dehydration of environmentally responsive building blocks, the drug release rate from the films was decelerated by elevating environmental temperature and ionic strength. In addition, the pulsed release of favipiravir was observed from the multilayer films under the trigger of temperature, which ensured the precise control in the content of the therapeutic reagents at a desired time point. The nanoparticle-based LbL films could be used for on-demandin vitrorelease of chemotherapeutic reagents.

Current status of development and biomedical applications of peptide-based antimicrobial hydrogels

Microbial contamination poses a serious threat to human life and health. Through the intersection of material science and modern medicine, advanced bionic hydrogels have shown great potential for biomedical applications due to their unique bioactivity and ability to mimic the extracellular matrix environment. In particular, as a promising antimicrobial material, the synthesis and practical biomedical applications of peptide-based antimicrobial hydrogels have drawn increasing research interest. The synergistic effect of peptides and hydrogels facilitate the controlled release of antimicrobial agents and mitigation of their biotoxicity while achieving antimicrobial effects and protecting the active agents from degradation. This review reports on the progress and trends of researches in the last five years and provides a brief outlook, aiming to provide theoretical background on peptide-based antimicrobial hydrogels and make suggestions for future related work.

Structural Element of Vitamin U-Mimicking Antibacterial Polypeptide with Ultrahigh Selectivity for Effectively Treating MRSA Infections

Antimicrobial peptides (AMPs) exhibit mighty antibacterial properties without inducing drug resistance. Achieving much higher selectivity of AMPs towards bacteria and normal cells has always been a continuous goal to be pursued. Herein, a series of sulfonium-based polypeptides with different degrees of branching and polymerization were synthesized by mimicking the structure of vitamin U. The polypeptide, G2 -PM-1H+ , shows both potent antibacterial activity and the highest selectivity index of 16000 among the reported AMPs or peptoids (e.g., the known index of 9600 for recorded peptoid in "Angew. Chem. Int. Ed., 2020, 59, 6412."), which can be attributed to the high positive charge density of sulfonium and the regulation of hydrophobic chains in the structure. The antibacterial mechanisms of G2 -PM-1H+ are primarily ascribed to the interaction with the membrane, production of reactive oxygen species (ROS), and disfunction of ribosomes. Meanwhile, altering the degree of alkylation leads to selective antibacteria against either gram-positive or gram-negative bacteria in a mixed-bacteria model. Additionally, both in vitro and in vivo experiments demonstrated that G2 -PM-1H+ exhibited superior efficacy against methicillin-resistant Staphylococcus aureus (MRSA) compared to vancomycin. Together, these results show that G2 -PM-1H+ possesses high biocompatibility and is a potential pharmaceutical candidate in combating bacteria significantly threatening human health.

Brush Polymer Coatings with Hydrophilic Main-Chains for Improving Surface Antibacterial Properties

Polymer coatings with improved surface antibacterial properties are of great importance for the application and development of implantable medical devices. Herein, we report the design, preparation, and antibacterial properties of a series of brush polymers (Dex-KEs) with hydrophilic dextran main-chains and mixed-charge polypeptide (KE) side-chains. Dex-KEs showed higher bactericidal activity and antifouling and antibiofilm properties than maleic acid modified dextran (Dex-Ma), KE, Dex-Ma/KE blend coatings, and brush polymer coatings with hydrophobic main-chains (AcDex-KEs). They also showed negligible in vitro cytotoxicity toward different mammalian cells and good in vivo biocompatibility. Dex-KE-coated implants exhibited potent in vivo resistance to bacterial infection before or after implantation.

Protein-directed synthesis of ZIF-8 functionalized with a polymer as core-shell drug coatings with antibacterial and anti-inflammatory properties

We developed a strategy to use lysozyme (Lys) as a template to produce mesoporous zeolitic imidazolate framework (ZIF-8) structures under physiological conditions. Thereafter, an amphiphilic triblock copolymer, PEG-PPG-PEG, was used to form protective core-shell ZIF-8 nanocomposite coatings to protect the encapsulated drug epigallocatechin-3-gallate (EGCG), to achieve notable antibacterial properties against E. coli, S. aureus and MRSA strains. Moreover, nanocomposites exhibited anti-inflammatory activity by counteracting the secretion of cytokines in THP-1 macrophages.

Antimicrobial Peptide Octominin-Encapsulated Chitosan Nanoparticles Enhanced Antifungal and Antibacterial Activities

Antimicrobial peptides (AMPs) have become a key solution for controlling multi-drug-resistant (MDR) pathogens, and the nanoencapsulation of AMPs has been used as a strategy to overcome challenges, such as poor stability, adverse interactions, and toxicity. In previous studies, we have shown the potent antimicrobial activity of Octominin against Candida albicans and Acinetobacter baumannii. This study is focused on the nanoencapsulation of Octominin with chitosan (CS) and carboxymethyl chitosan (CMC) as a drug delivery system using the ionotropic gelation technique. Octominin-encapsulated CS nanoparticles (Octominin-CNPs) had an average diameter and zeta potential of 372.80 ± 2.31 nm and +51.23 ± 0.38 mV, respectively, while encapsulation efficiency and loading capacity were 96.49 and 40.20%, respectively. Furthermore, Octominin-CNPs showed an initial rapid and later sustained biphasic release profile, and up to 88.26 ± 3.26% of the total Octominin release until 96 h. Transmission electron microscopy data showed the irregular shape of the Octominin-CNPs with aggregations. In vitro and in vivo toxicity of Octominin-CNPs was significantly lower than the Octominin at higher concentrations. The antifungal and antibacterial activities of Octominin-CNPs were slightly higher than those of Octominin in both the time-kill kinetic and microbial viability assays against C. albicans and A. baumannii, respectively. Mode of action assessments of Octominin-CNPs revealed that morphological alterations, cell membrane permeability alterations, and reactive oxygen species generation were slightly higher than those of Octominin at the tested concentrations against both C. albicans and A. baumannii. In antibiofilm activity assays, Octominin-CNPs showed slightly higher biofilm inhibition and biofilm eradication activities compared to that of Octominin. In conclusion, Octominin was successfully encapsulated into CS, and Octominin-CNPs showed lower toxicity and greater antimicrobial activity against C. albicans and A. baumannii compared to Octominin.

Enzyme-triggered smart antimicrobial drug release systems against bacterial infections

The rapid emergence and spread of drug-resistant bacteria, as one of the most pressing public health threats, are declining our arsenal of available antimicrobial drugs. Advanced antimicrobial drug delivery systems that can achieve precise and controlled release of antimicrobial agents in the microenvironment of bacterial infections will retard the development of antimicrobial resistance. A variety of extracellular enzymes are secreted by bacteria to destroy physical integrity of tissue during their invasion of host body, which can be utilized as stimuli to trigger "on-demand" release of antimicrobials. In the past decade, such bacterial enzyme responsive drug release systems have been intensively studied but few review has been released. Herein, we systematically summarize the recent progress of smart antimicrobial drug delivery systems triggered by bacteria secreted enzymes such as lipase, hyaluronidase, protease and antibiotic degrading enzymes. The perspectives and existing key issues of this field will also be discussed to fuel the innovative research and translational application in the future.

M, Zarrintaj P, Formela K, Saeb MR, Bencherif SA. Clickable Polysaccharides for Biomedical Applications: A Comprehensive Review

Recent advances in materials science and engineering highlight the importance of designing sophisticated biomaterials with well-defined architectures and tunable properties for emerging biomedical applications. Click chemistry, a powerful method allowing specific and controllable bioorthogonal reactions, has revolutionized our ability to make complex molecular structures with a high level of specificity, selectivity, and yield under mild conditions. These features combined with minimal byproduct formation have enabled the design of a wide range of macromolecular architectures from quick and versatile click reactions. Furthermore, copper-free click chemistry has resulted in a change of paradigm, allowing researchers to perform highly selective chemical reactions in biological environments to further understand the structure and function of cells. In living systems, introducing clickable groups into biomolecules such as polysaccharides (PSA) has been explored as a general approach to conduct medicinal chemistry and potentially help solve healthcare needs. De novo biosynthetic pathways for chemical synthesis have also been exploited and optimized to perform PSA-based bioconjugation inside living cells without interfering with their native processes or functions. This strategy obviates the need for laborious and costly chemical reactions which normally require extensive and time-consuming purification steps. Using these approaches, various PSA-based macromolecules have been manufactured as building blocks for the design of novel biomaterials. Clickable PSA provides a powerful and versatile toolbox for biomaterials scientists and will increasingly play a crucial role in the biomedical field. Specifically, bioclick reactions with PSA have been leveraged for the design of advanced drug delivery systems and minimally invasive injectable hydrogels. In this review article, we have outlined the key aspects and breadth of PSA-derived bioclick reactions as a powerful and versatile toolbox to design advanced polymeric biomaterials for biomedical applications such as molecular imaging, drug delivery, and tissue engineering. Additionally, we have also discussed the past achievements, present developments, and recent trends of clickable PSA-based biomaterials such as 3D printing, as well as their challenges, clinical translatability, and future perspectives.

Self-Assembled Cationic Nanoparticles Combined with Curcumin against Multidrug-Resistant Bacteria

The overuse of antibiotics exacerbates the development of antibiotic-resistant bacteria, threatening global public health, while most traditional antibiotics act on specific targets and sterilize through chemical modes. Therefore, it is a desperate need to design novel therapeutics or extraordinary strategies to overcome resistant bacteria. Herein, we report a positively charged nanocomposite PNs-Cur with a hydrodynamic diameter of 289.6 nm, which was fabricated by ring-opening polymerization of ε-caprolactone and Z-Lys-N-carboxyanhydrides (NCAs), and then natural curcumin was loaded onto the PCL core of PNs with a nanostructure through self-assembly, identified through UV-vis, and characterized by scanning electron microscopy (SEM) and dynamic light scattering (DLS). Especially, the self-assembly dynamics of PNs was simulated through molecular modeling to confirm the formation of a core-shell nanostructure. Biological assays revealed that PNs-Cur possessed broad-spectrum and efficient antibacterial activities against both Gram-positive and Gram-negative bacteria, including drug-resistant clinical bacteria and fungus, with MIC values in the range of 8-32 μg/mL. Also, in vivo evaluation showed that PNs-Cur exhibited strong antibacterial activities in infected mice. Importantly, the nanocomposite did not indeed induce the emergence of drug-resistant bacterial strains even after 21 passages, especially showing low toxicity regardless of in vivo or in vitro. The study of the antibacterial mechanism indicated that PNs-Cur could indeed destruct membrane potential, change the membrane potential, and cause the leakage of the cytoplasm. Concurrently, the released curcumin further plays a bactericidal role, eventually leading to bacterial irreversible apoptosis. This unique bacterial mode that PNs-Cur possesses may be the reason why it is not easy to make the bacteria susceptible to easily produce drug resistance. Overall, the constructed PNs-Cur is a promising antibacterial material, which provides a novel strategy to develop efficient antibacterial materials and combat increasingly prevalent bacterial infections.

Addressing a future pandemic: how can non-biological complex drugs prepare us for antimicrobial resistance threats?

Loss of effective antibiotics through antimicrobial resistance (AMR) is one of the greatest threats to human health. By 2050, the annual death rate resulting from AMR infections is predicted to have climbed from 1.27 million per annum in 2019, up to 10 million per annum. It is therefore imperative to preserve the effectiveness of both existing and future antibiotics, such that they continue to save lives. One way to conserve the use of existing antibiotics and build further contingency against resistant strains is to develop alternatives. Non-biological complex drugs (NBCDs) are an emerging class of therapeutics that show multi-mechanistic antimicrobial activity and hold great promise as next generation antimicrobial agents. We critically outline the focal advancements for each key material class, including antimicrobial polymer materials, carbon nanomaterials, and inorganic nanomaterials, and highlight the potential for the development of antimicrobial resistance against each class. Finally, we outline remaining challenges for their clinical translation, including the need for specific regulatory pathways to be established in order to allow for more efficient clinical approval and adoption of these new technologies.

Environment tolerant, adaptable and stretchable organohydrogels: preparation, optimization, and applications

Multiple stretchable materials have been successively developed and applied to wearable devices, soft robotics, and tissue engineering. Organohydrogels are currently being widely studied and formed by dispersing immiscible hydrophilic/hydrophobic polymer networks or only hydrophilic polymer networks in an organic/water solvent system. In particular, they can not only inherit and carry forward the merits of hydrogels, but also have some unique advantageous features, such as anti-freezing and water retention abilities, solvent resistance, adjustable surface wettability, and shape memory effect, which are conducive to the wide environmental adaptability and intelligent applications. This review first summarizes the structure, preparation strategy, and unique advantages of the reported organohydrogels. Furthermore, organohydrogels can be optimized for electro-mechanical properties or endowed with various functionalities by adding or modifying various functional components owing to their modifiability. Correspondingly, different optimization strategies, mechanisms, and advanced developments are described in detail, mainly involving the mechanical properties, conductivity, adhesion, self-healing properties, and antibacterial properties of organohydrogels. Moreover, the applications of organohydrogels in flexible sensors, energy storage devices, nanogenerators, and biomedicine have been summarized, confirming their unlimited potential in future development. Finally, the existing challenges and future prospects of organohydrogels are provided.

Antimicrobial Peptides and Macromolecules for Combating Microbial Infections: From Agents to Interfaces

Bacterial resistance caused by the overuse of antibiotics and the shelter of biofilms has evolved into a global health crisis, which drives researchers to continuously explore antimicrobial molecules and strategies to fight against drug-resistant bacteria and biofilm-associated infections. Cationic antimicrobial peptides (AMPs) are considered to be a category of potential alternative for antibiotics owing to their excellent bactericidal potency and lesser likelihood of inducing drug resistance through their distinctive antimicrobial mechanisms. In this review, the hitherto reported plentiful action modes of AMPs are systematically classified into 15 types and three categories (membrane destructive, nondestructive membrane disturbance, and intracellular targeting mechanisms). Besides natural AMPs, cationic polypeptides, synthetic polymers, and biopolymers enable to achieve tunable antimicrobial properties by optimizing their structures. Subsequently, the applications of these cationic antimicrobial agents at the biointerface as contact-active surface coatings and multifunctional wound dressings are also emphasized here. At last, we provide our perspectives on the development of clinically significant cationic antimicrobials and related challenges in the translation of these materials.

Versatile polymer-based strategies for antibacterial drug delivery systems and antibacterial coatings

Human health damage and economic losses due to bacterial infections are very serious worldwide. Excessive use of antibiotics has caused an increase in bacterial resistance. Fortunately, various non-antibiotic antibacterial materials...

Chitosan with pendant (E)-5-((4-acetylphenyl) diazenyl)-6-aminouracil groups as synergetic antimicrobial agents

Conventional antimicrobial agents are losing the war against drug resistance day-by-day. Chitosan biopolymer is one of the alternative materials that lends itself well to this application by fine-tuning its bioactivity...

Contributions of photochemistry to bio-based antibacterial polymer materials

Surgical site infections constitute a major health concern that may be addressed by conferring antibacterial properties to surgical tools and medical devices via functional coatings. Bio-sourced polymers are particularly well-suited to prepare such coatings as they are usually safe and can exhibit intrinsic antibacterial properties or serve as hosts for bactericidal agents. The goal of this Review is to highlight the unique contribution of photochemistry as a green and mild methodology for the development of such bio-based antibacterial materials. Photo-generation and photo-activation of bactericidal materials are illustrated. Recent efforts and current challenges to optimize the sustainability of the process, improve the safety of the materials and extend these strategies to 3D biomaterials are also emphasized.

Antimicrobial Properties of Chitosan and Chitosan Derivatives in the Treatment of Enteric Infections

Antibiotics played an important role in controlling the development of enteric infection. However, the emergence of antibiotic resistance and gut dysbiosis led to a growing interest in the use of natural antimicrobial agents as alternatives for therapy and disinfection. Chitosan is a nontoxic natural antimicrobial polymer and is approved by GRAS (Generally Recognized as Safe by the United States Food and Drug Administration). Chitosan and chitosan derivatives can kill microbes by neutralizing negative charges on the microbial surface. Besides, chemical modifications give chitosan derivatives better water solubility and antimicrobial property. This review gives an overview of the preparation of chitosan, its derivatives, and the conjugates with other polymers and nanoparticles with better antimicrobial properties, explains the direct and indirect mechanisms of action of chitosan, and summarizes current treatment for enteric infections as well as the role of chitosan and chitosan derivatives in the antimicrobial agents in enteric infections. Finally, we suggested future directions for further research to improve the treatment of enteric infections and to develop more useful chitosan derivatives and conjugates.

Chemical syntheses of bioinspired and biomimetic polymers toward biobased materials

The rich structures and hierarchical organizations in nature provide many sources of inspiration for advanced material designs. We wish to recapitulate properties such as high mechanical strength, colour-changing ability, autonomous healing and antimicrobial efficacy in next-generation synthetic materials. Common in nature are non-covalent interactions such as hydrogen bonding, ionic interactions and hydrophobic effects, which are all useful motifs in tailor-made materials. Among these are biobased components, which are ubiquitously conceptualized in the space of recently developed bioinspired and biomimetic materials. In this regard, sustainable organic polymer chemistry enables us to tune the properties and functions of such materials that are essential for daily life. In this Review, we discuss recent progress in bioinspired and biomimetic polymers and provide insights into biobased materials through the evolution of chemical approaches, including networking/crosslinking, dynamic interactions and self-assembly. We focus on advances in biobased materials; namely polymeric mimics of resilin and spider silk, mechanically and optically adaptive materials, self-healing elastomers and hydrogels, and antimicrobial polymers.

Membrane-disruptive peptides/peptidomimetics-based therapeutics: Promising systems to combat bacteria and cancer in the drug-resistant era

Membrane-disruptive peptides/peptidomimetics (MDPs) are antimicrobials or anticarcinogens that present a general killing mechanism through the physical disruption of cell membranes, in contrast to conventional chemotherapeutic drugs, which act on precise targets such as DNA or specific enzymes. Owing to their rapid action, broad-spectrum activity, and mechanisms of action that potentially hinder the development of resistance, MDPs have been increasingly considered as future therapeutics in the drug-resistant era. Recently, growing experimental evidence has demonstrated that MDPs can also be utilized as adjuvants to enhance the therapeutic effects of other agents. In this review, we evaluate the literature around the broad-spectrum antimicrobial properties and anticancer activity of MDPs, and summarize the current development and mechanisms of MDPs alone or in combination with other agents. Notably, this review highlights recent advances in the design of various MDP-based drug delivery systems that can improve the therapeutic effect of MDPs, minimize side effects, and promote the co-delivery of multiple chemotherapeutics, for more efficient antimicrobial and anticancer therapy.

Molecular engineering of antimicrobial peptide (AMP)-polymer conjugates

As antimicrobial resistance becomes an increasing threat, bringing significant economic and health burdens, innovative antimicrobial treatments are urgently needed. While antimicrobial peptides (AMPs) are promising therapeutics, exhibiting high activity against resistant bacterial strains, limited stability and toxicity to mammalian cells has hindered clinical development. Attaching AMPs to polymers provides opportunities to present AMPs in a way that maximizes bacterial killing while enhancing compatibility with mammalian cells, stability, and solubility. Conjugation of an AMP to a linear hydrophilic polymer yields the desired improvements in stability, mammalian cell compatibility, and solubility, yet often markedly reduces bactericidal effects. Non-linear polymer architectures and supramolecular assemblies that accommodate multiple AMPs per polymer chain afford AMP-polymer conjugates that strike a superior balance of antimicrobial activity, mammalian cell compatibility, stability, and solubility. Therefore, we review the design criteria, building blocks, and synthetic strategies for engineering AMP-polymer conjugates, emphasizing the connection between molecular architecture and antimicrobial performance to inspire and enable further innovation to advance this emerging class of biomaterials.

Chemically modified and conjugated antimicrobial peptides against superbugs

Antimicrobial resistance (AMR) is one of the greatest threats to human health that, by 2050, will lead to more deaths from bacterial infections than cancer. New antimicrobial agents, both broad-spectrum and selective, that do not induce AMR are urgently required. Antimicrobial peptides (AMPs) are a novel class of alternatives that possess potent activity against a wide range of Gram-negative and positive bacteria with little or no capacity to induce AMR. This has stimulated substantial chemical development of novel peptide-based antibiotics possessing improved therapeutic index. This review summarises recent synthetic efforts and their impact on analogue design as well as their various applications in AMP development. It includes modifications that have been reported to enhance antimicrobial activity including lipidation, glycosylation and multimerization through to the broad application of novel bio-orthogonal chemistry, as well as perspectives on the direction of future research. The subject area is primarily the development of next-generation antimicrobial agents through selective, rational chemical modification of AMPs. The review further serves as a guide toward the most promising directions in this field to stimulate broad scientific attention, and will lead to new, effective and selective solutions for the several biomedical challenges to which antimicrobial peptidomimetics are being applied.

Novel Diabetic Foot Wound Dressing Based on Multifunctional Hydrogels with Extensive Temperature-Tolerant, Durable, Adhesive, and Intrinsic Antibacterial Properties

Diabetic foot ulcers (DFUs) are hard-healing chronic wounds and susceptible to bacterial infection. Conventional hydrogel dressings easily lose water at high temperature or freeze at low temperature, making them unsuitable for long-term use or in extreme environments. Herein, a temperature-tolerant (-20 to 60 °C) antibacterial hydrogel dressing is fabricated by the assembly of polyacrylamide, gelatin, and ε-polylysine. Owing to the water/glycerin (Gly) binary solvent system, the resultant hydrogel (G-PAGL) displayed good heat resistance and antifreezing properties. Within the wide temperature range (-20 to 60 °C), all the desirable features of the hydrogel, including superstretchability (>1400%), enduring water retention, adhesiveness, and persistent antibacterial property, are quite stable. Remarkably, the hydrogel wound dressing displayed lasting and broad antibacterial activity against Gram-positive and Gram-negative bacteria. Satisfactorily, the double-network (DN) G-PAGL hydrogel dressing could effectively promote the healing of DFUs by accelerating collagen deposition, promoting angiogenesis, and inhibiting bacterial breed. As far as we know, this is the first time that the extensive temperature-tolerant DN hydrogel with antibacterial ability is developed to use as DFU wound dressing. The G-PAGL hydrogel provides more choices for DFU wound dressings that could be used in extreme environments.

A multifunctional shape-adaptive and biodegradable hydrogel with hemorrhage control and broad-spectrum antimicrobial activity for wound healing

Hemorrhage is the leading cause of preventable death of injured military and civilian patients, and subsequent infection risks endanger their lives or impede the healing of their wounds. Here, we report an injectable biodegradable hydrogel with hemostatic, antimicrobial, and healing-promoting properties. The hydrogel was prepared by dynamic cross-linking of a natural polysaccharide (dextran) with antimicrobial peptide ε-poly-l-lysine (EPL) and encapsulating base fibroblast growth factor (bFGF). The amino groups of EPL were allowed to react with the aldehyde of oxidized dextran (OD) through the Schiff-base reaction for the generation of hydrogels that have fast self-healing and injectable characteristics and adapt to the shapes of wounds. The prepared OD/EPL hydrogels promoted blood clotting in vitro and stopped bleeding in a rat liver injury model within 6 min through their platelet-aggregating ability and sealing effect. These hydrogels exhibited inherent antimicrobial effects without the use of antibiotics and effectively killed a broad spectrum of pathogenic microbes, including Gram-positive methicillin-resistant Staphylococcus aureus (MRSA), Gram-negative Escherichia coli, and Pseudomonas aeruginosa and fungus Candida albicans in vitro. Moreover, these OD/EPL hydrogels were compatible with mammalian cells in vitro and in vivo and biodegradable in the mouse body. The loaded bFGF can be released sustainably, and it can promote angiogenesis, endothelial cell migration, and consequently accelerate the healing of wounds. The OD/EPL hydrogel inhibited MRSA infection in a rat full-thickness skin wound model and promoted healing. This kind of multifunctional hydrogel is a promising wound dressing for the emergency treatment of acute deep or penetrating injuries.

Design of nanoengineered antibacterial polymers for biomedical applications

Pathogenic bacteria have become global threats to public health. Since the advent of antibiotics about 100 years ago, their use has been embraced with great enthusiasm because of their effective treatment of bacterial infections. However, the evolution of pathogenic bacteria with resistance to conventional antibiotics has resulted in an urgent need for the development of a new generation of antibiotics. The use of antimicrobial polymers offers the promise of enhancing the efficacy of antimicrobial agents. Of the various antibacterial polymers that effectively eradicate pathogenic bacteria, those that are nanoengineered have garnered significant research interest in their design and biomedical applications. Because of their high surface area and high reactivity, these polymers show greater antibacterial activity than conventional antibacterial agents, by inhibiting the growth or destroying the cell membrane of pathogenic bacteria. This review summarizes several strategies for designing nanoengineered antibacterial polymers, explores the factors that affect their antibacterial properties, and examines key features of their design. It then comments briefly on the future prospects for nanoengineered antibacterial polymers. This review thus provides a feasible guide to developing nanoengineered antibacterial polymers by presenting both broad and in-depth bench research, and it offers suggestions for their potential in biomedical applications.

Advances of peptides for antibacterial applications

In the past few decades, peptide antibacterial products with unique antibacterial mechanisms have attracted widespread interest. They can effectively reduce the probability of drug resistance of bacteria and are biocompatible, so they possess tremendous development prospects. This review provides recent research and analysis on the basic types of antimicrobial peptides (including poly (amino acid)s, short AMPs, and lipopeptides) and factors to optimize antimicrobial effects. It also summarizes the two most important modes of action of antimicrobial peptides and the latest developments in the application of AMPs, including antimicrobial agent, wound healing, preservative, antibacterial coating and others. Finally, we discuss the remaining challenges to improve the antibacterial peptides and propose prospects in the field.

Imminent antimicrobial bioink deploying cellulose, alginate, EPS and synthetic polymers for 3D bioprinting of tissue constructs

3D printing, one of its kinds has been a recent technological trend to fabricate complex and patterned biomaterial with controlled precision. With the conventional kick-start of printing metals and plastics, advancements in printing viable cells, polysaccharides or microbes themselves have been achieved. The additive antimicrobial properties in bioinks sourced from organic and inorganic materials have profound implications in tissue engineering. Cellulose, alginate, exopolysaccharides, ceramics and synthetic polymers are integrated as a viable component in inks and used for bio-printing. To date, bacterial infection and immunogenicity pose a potential health risk during a tissue implant or bone substitution. In order to mitigate microbial infection, antimicrobial bioinks with significant antimicrobial potential have been the much sought after strategies. This approach could be an effective frontline defense against microbial interference in tissue engineering and biomedical applications. An overview on the antimicrobial potential of polysaccharides as bioinks for 3D bioprinting has been critically reviewed.

Applications of Thiol-Ene Chemistry for Peptide Science

Radical thiol-ene chemistry has been demonstrated for a range of applications in peptide science, including macrocyclization, glycosylation and lipidation amongst a myriad of others. The thiol-ene reaction offers a number of advantages in this area, primarily those characteristic of "click" reactions. This provides a chemical approach to peptide modification that is compatible with aqueous conditions with high orthogonality and functional group tolerance. Additionally, the use of a chemical approach for peptide modification affords homogeneous peptides, compared to heterogeneous mixtures often obtained through biological methods. In addition to peptide modification, thiol-ene chemistry has been applied in novel approaches to biological studies through synthesis of mimetics and use in development of probes. This review will cover the range of applications of the radical-mediated thiol-ene reaction in peptide and protein science.

Ultra-efficient Antibacterial System Based on Photodynamic Therapy and CO Gas Therapy for Synergistic Antibacterial and Ablation Biofilms

In recent years, with the emergence of various kinds of drug-resistant bacteria, existing antibiotics have become inefficient in killing these bacteria, and the formation of biofilms has further weakened the therapeutic effect. More problematically, the massive use and abuse of antibiotics have caused severe side effects. Thus, the development of ultra-efficient and safe antibacterial systems is urgently needed. Herein, a photodynamic therapy (PDT)-driven CO-controlled delivery system (Ce6&CO@FADP) is developed for synergistic antibacterial and ablation biofilms. Ce6&CO@FADP is constructed using a fluorinated amphiphilic dendritic peptide (FADP) and physically loaded with Ce6 and CORM-401. After efficiently entering the bacteria, Ce6&CO@FADP can rapidly release CO intracellularly by the massive consumption of the H₂O₂ generated during the PDT process, without affecting the generation of singlet oxygen (¹O₂). As such, the combination of CO and ¹O₂ exerts notable synergistic antibacterial and biofilm ablation effects both in vitro and in vivo (including subcutaneous bacterial infection and biofilm catheter models) experiments. More importantly, all biosafety assessments suggest the good biocompatibility of Ce6&CO@FADP. Together, these results reveal that Ce6&CO@FADP is an efficient and safe antibacterial system, which has essential application prospects for the treatment of bacterial infections and ablation of biofilms in vivo.

Antibacterial and hydroxyapatite-forming coating for biomedical implants based on polypeptide-functionalized titania nanospikes

Titanium (Ti)-based implants often suffer from detrimental bacterial adhesion and inefficient healing, so it is crucial to design a dual-functional coating that prevents bacterial infection and enhances bioactivity for a successful implant. Herein, we successfully devised a cationic polypeptide (Pep)-functionalized biomimetic nanostructure coating with superior activity, which could not only kill pathogenic bacteria rapidly and inhibit biofilm formation for up to two weeks, but also promote in situ hydroxyapatite (HAp) formation. Specifically, a titania (TiO2) nanospike coating (TNC) was fabricated by alkaline hydrothermal treatment firstly, followed by immobilization of rationally synthesized Pep via robust coordinative interactions, named TNPC. This coating was able to effectively kill (>99.9%) both Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli) bacteria, while being non-toxic to murine MC3T3-E1 osteoblastic cells. Furthermore, the in vivo infection studies denoted that the adherent bacteria numbers on the TNPC implants were significantly reduced by 6 orders of magnitude than those on the pure Ti implants (p < 0.001). Importantly, in the presence of cationic amino groups and residual Ti-OH groups, substantial HAp deposition on the TNPC surface in Kokubo's simulated body fluid (SBF) occurred after 14 days. Altogether, our results support the clinical potential of this biomimetic dual-functional coating as a new approach with desirable antibacterial properties and HAp-forming ability in orthopedic and dental applications.

Combating Pseudomonas aeruginosa Biofilms by a Chitosan-PEG-Peptide Conjugate via Changes in Assembled Structure

Pseudomonas aeruginosa (P. aeruginosa) biofilms are associated with a wide range of infections, from chronic tissue diseases to implanted medical devices. In a biofilm, the extracellular polymeric substance (EPS) causes an inhibited penetration of antibacterial agents, leading to a 100-1000 times tolerance of the bacteria. In view of the water-filled channels in biofilms and the highly negative charge of EPS, we design a chitosan-polyethylene glycol-peptide conjugate (CS-PEG-LK₁₃) in this study. The CS-PEG-LK₁₃ prefers a neutrally charged assembly at a size of ∼100 nm in aqueous environment, while undergoes disassembly to expose the α-helical peptide at the bacterial cell membrane. This behavior provides CS-PEG-LK₁₃ superiorities in both penetrating the biofilms and inactivating the bacteria. At a concentration of 8 times the minimum inhibitory concentration, CS-PEG-LK₁₃ has a much higher antibacterial efficiency (72.70%) than LK₁₃ peptide (15.24%) and tobramycin (33.57%) in an in vitro P. aeruginosa biofilm. Moreover, CS-PEG-LK₁₃ behaves comparable capability of combating an implanted P. aeruginosa biofilm to highly excess tobramycin. This work has implications for the design of new antibacterial agents in biofilm combating.

Structural design and antimicrobial properties of polypeptides and saccharide–polypeptide conjugates

The development and progress of antimicrobial polypeptides and saccharide–polypeptide conjugates in regards to their structural design, biological functions and antimicrobial mechanism.

Combinations of Antimicrobial Polymers with Nanomaterials and Bioactives to Improve Biocidal Therapies

The rise of antibiotic-resistant microorganisms has become a critical issue in recent years and has promoted substantial research efforts directed to the development of more effective antimicrobial therapies utilizing different bactericidal mechanisms to neutralize infectious diseases. Modern approaches employ at least two mixed bioactive agents to enhance bactericidal effects. However, the combinations of drugs may not always show a synergistic effect, and further, could also produce adverse effects or stimulate negative outcomes. Therefore, investigations providing insights into the effective utilization of combinations of biocidal agents are of great interest. Sometimes, combination therapy is needed to avoid resistance development in difficult-to-treat infections or biofilm-associated infections treated with common biocides. Thus, this contribution reviews the literature reports discussing the usage of antimicrobial polymers along with nanomaterials or other inhibitors for the development of more potent biocidal therapies.