Bacteria-responsive multifunctional nanogel for targeted antibiotic delivery

Stimuli‐Responsive Hydrogels for Antibacterial Applications

Hydrogels have emerged as promising candidates for biomedical applications, especially in the field of antibacterial therapeutics, due to their unique structural properties, highly tunable physicochemical properties, and excellent biocompatibility. The integration of stimuli-responsive functions into antibacterial hydrogels holds the potential to enhance their antibacterial properties and therapeutic efficacy, dynamically responding to different external or internal stimuli, such as pH, temperature, enzymes, and light. Therefore, this review describes the applications of hydrogel dressings responsive to different stimuli in antibacterial therapy. The collaborative interaction between stimuli-responsive hydrogels and antibacterial materials is discussed. This synergistic approach, in contrast to conventional antibacterial materials, not only amplifies the antibacterial effect but also alleviates adverse side effects and diminishes the incidence of multiple infections and drug resistance. The review provides a comprehensive overview of the current challenges and outlines future research directions for stimuli-responsive antibacterial hydrogels. It underscores the imperative for ongoing interdisciplinary research aimed at unraveling the mechanisms of wound healing. This understanding is crucial for optimizing the design and implementation of stimuli-responsive antibacterial hydrogels. Ultimately, this review aims to offer scientific guidance for the development and practical clinical application of stimuli-responsive antibacterial hydrogel dressings.

Diving into drug-screening: zebrafish embryos as an in vivo platform for antimicrobial drug discovery and assessment

The rise of multidrug-resistant bacteria underlines the need for innovative treatments, yet the introduction of new drugs has stagnated despite numerous antimicrobial discoveries. A major hurdle is a poor correlation between promising in vitro data and in vivo efficacy in animal models, which is essential for clinical development. Early in vivo testing is hindered by the expense and complexity of existing animal models. Therefore, there is a pressing need for cost-effective, rapid preclinical models with high translational value. To overcome these challenges, zebrafish embryos have emerged as an attractive model for infectious disease studies, offering advantages such as ethical alignment, rapid development, ease of maintenance, and genetic manipulability. The zebrafish embryo infection model, involving microinjection or immersion of pathogens and potential antibiotic hit compounds, provides a promising solution for early-stage drug screening. It offers a cost-effective and rapid means of assessing the efficacy, toxicity and mechanism of action of compounds in a whole-organism context. This review discusses the experimental design of this model, but also its benefits and challenges. Additionally, it highlights recently identified compounds in the zebrafish embryo infection model and discusses the relevance of the model in predicting the compound's clinical potential.

Polymeric Nanoparticles for Drug Delivery

The recent emergence of nanomedicine has revolutionized the therapeutic landscape and necessitated the creation of more sophisticated drug delivery systems. Polymeric nanoparticles sit at the forefront of numerous promising drug delivery designs, due to their unmatched control over physiochemical properties such as size, shape, architecture, charge, and surface functionality. Furthermore, polymeric nanoparticles have the ability to navigate various biological barriers to precisely target specific sites within the body, encapsulate a diverse range of therapeutic cargo and efficiently release this cargo in response to internal and external stimuli. However, despite these remarkable advantages, the presence of polymeric nanoparticles in wider clinical application is minimal. This review will provide a comprehensive understanding of polymeric nanoparticles as drug delivery vehicles. The biological barriers affecting drug delivery will be outlined first, followed by a comprehensive description of the various nanoparticle designs and preparation methods, beginning with the polymers on which they are based. The review will meticulously explore the current performance of polymeric nanoparticles against a myriad of diseases including cancer, viral and bacterial infections, before finally evaluating the advantages and crucial challenges that will determine their wider clinical potential in the decades to come.

Rifampicin-Loaded Polyelectrolyte Complex Eliminates Intracellular Bacteria through Thiol-Mediated Cellular Uptake and Oxidative Stress Enhancement

The poor accumulation of antibiotics in the cytoplasm leads to the poor eradication of intracellular bacteria. Herein, a polyelectrolyte complex (PECs@Rif) allowing direct cytosolic delivery of rifampicin (Rif) was developed for the treatment of intracellular infections by complexation of poly(α-lipoic acid) (pLA) and oligosaccharide (COS) in water and loading Rif. Due to the thiol-mediated cellular uptake, PECs@Rif delivered 3.9 times higher Rif into the cytoplasm than that of the free Rif during 8 h of incubation. After entering cells, PECs@Rif released Rif by dissociating pLA into dihydrolipoic acid (DHLA) in the presence of intracellular thioredoxin reductase (TrxR). Notably, DHLA could reduce endogenous Fe(III) to Fe(II) and provide a catalyst for the Fenton reaction to produce a large amount of reactive oxygen species (ROS), which would assist Rif in eradicating intracellular bacteria. In vitro assay showed that PECs@Rif reduced almost 2.8 orders of magnitude of intracellular bacteria, much higher than 0.7 orders of magnitude of free Rif. The bacteremia-bearing mouse models showed that PECs@Rif reduced bacterial levels in the liver, spleen, and kidney by 2.2, 3.7, and 2.3 orders of magnitude, respectively, much higher than free Rif in corresponding tissues. The direct cytosolic delivery in a thiol-mediated manner and enhanced oxidative stress proposed a feasible strategy for treating intracellular bacteria infection.

Controlling the function of bioactive worm micelles by enzyme-cleavable non-covalent inter-assembly cross-linking

Drugs that form self-assembled supramolecular structures to be most-active is a promising way of creating new highly specific and active pharmaceuticals. Controlling the activity of bioactive supramolecular structures such as drug-loaded micelles is possible by both core/shell and inter-assembly cross-linking. However, if the flexibility of the assembly is mandatory for the activity cross-linking is not feasible. Thus, such structures cannot be manipulated in their activity. The present study demonstrates a novel concept to control the activity of not drug-releasing, non-cross-linked bioactive superstructures. This is achieved by formation of nanostructured nanoparticles derived by non-covalent inter-assembly cross-linking of the superstructures. This is shown on the example of amphiphilic diblock-copolymers conjugated with the antibiotic ciprofloxacin (CIP). These polymer-antibiotic conjugates form worm micelles, which greatly activate the conjugated antibiotic without releasing it. Non-covalent inter-assembly cross-linking of these CIP-worm-micelles with amphiphilic triblock copolymers terminated with lipase-cleavable esters leads to nanostructured nanoparticles that resemble cross-linked worm micelles and show an up to 135-fold lower activity than the free worm micelles. The activity of the worm-micelles can be fully recovered by cleaving the end groups of the polymeric cross-linker with lipase.

The epidermal lipid-microbiome loop and immunity: Important players in atopic dermatitis

BACKGROUND

The promotion of epidermal barrier dysfunction is attributed to abnormalities in the lipid-microbiome positive feedback loop which significantly influences the imbalance of the epithelial immune microenvironment (EIME) in atopic dermatitis (AD). This imbalance encompasses impaired lamellar membrane integrity, heightened exposure to epidermal pathogens, and the regulation of innate and adaptive immunity. The lipid-microbiome loop is substantially influenced by intense adaptive immunity which is triggered by abnormal loop activity and affects the loop's integrity through the induction of atypical lipid composition and responses to dysregulated epidermal microbes. Immune responses participate in lipid abnormalities within the EIME by downregulating barrier gene expression and are further cascade-amplified by microbial dysregulation which is instigated by barrier impairment.

AIM OF REVIEW

This review examines the relationship between abnormal lipid composition, microbiome disturbances, and immune responses in AD while progressively substantiating the crosstalk mechanism among these factors. Based on this analysis, the "lipid-microbiome" positive feedback loop, regulated by immune responses, is proposed.

KEY SCIENTIFIC CONCEPTS OF REVIEW

The review delves into the impact of adaptive immune responses that regulate the EIME, driving AD, and investigates potential mechanisms by which lipid supplementation and probiotics may alleviate AD through the up-regulation of the epidermal barrier and modulation of immune signaling. This exploration offers support for targeting the EIME to attenuate AD.

Bactericidal Biodegradable Linear Polyamidoamines Obtained with the Use of Endogenous Polyamines

The work presents the synthesis of a series of linear polyamidoamines by polycondensation of sebacoyl dichloride with endogenous polyamines: putrescine, spermidine, spermine, and norspermidine-a biogenic polyamine not found in the human body. During the synthesis carried out via interfacial reaction, hydrophilic, semi-crystalline polymers with an average viscosity molecular weight of approximately 20,000 g/mol and a melting point of approx. 130 °C were obtained. The structure and composition of the synthesized polymers were confirmed based on NMR and FTIR studies. The cytotoxicity tests performed on human fibroblasts and keratinocytes showed that the polymers obtained with spermine and norspermidine were strongly cytotoxic, but only in high concentrations. All the other examined polymers did not show cytotoxicity even at concentrations of 2000 µg/mL. Simultaneously, the antibacterial activity of the obtained polyamides was confirmed. These polymers are particularly active against E. Coli, and virtually all the polymers obtained demonstrated a strong inhibitory effect on the growth of cells of this strain. Antimicrobial activity of the tested polymer was found against strains like Staphylococcus aureus, Staphylococcus epidermidis, and Pseudomonas aeruginosa. The broadest spectrum of bactericidal action was demonstrated by polyamidoamines obtained from spermine, which contains two amino groups in the repeating unit of the chain. The obtained polymers can be used as a material for forming drug carriers and other biologically active compounds in the form of micro- and nanoparticles, especially as a component of bactericidal creams and ointments used in dermatology or cosmetology.

Enzymatically Activatable Polymers for Disease Diagnosis and Treatment

The irregular expression or activity of enzymes in the human body leads to various pathological disorders and can therefore be used as an intrinsic trigger for more precise identification of disease foci and controlled release of diagnostics and therapeutics, leading to improved diagnostic accuracy, sensitivity, and therapeutic efficacy while reducing systemic toxicity. Advanced synthesis strategies enable the preparation of polymers with enzymatically activatable skeletons or side chains, while understanding enzymatically responsive mechanisms promotes rational incorporation of activatable units and predictions of the release profile of diagnostics and therapeutics, ultimately leading to promising applications in disease diagnosis and treatment with superior biocompatibility and efficiency. By overcoming the challenges, new opportunities will emerge to inspire researchers to develop more efficient, safer, and clinically reliable enzymatically activatable polymeric carriers as well as prodrugs.

Bionanotechnology and bioMEMS (BNM): state-of-the-art applications, opportunities, and challenges

The development of micro- and nanotechnology for biomedical applications has defined the cutting edge of medical technology for over three decades, as advancements in fabrication technology developed originally in the semiconductor industry have been applied to solving ever-more complex problems in medicine and biology. These technologies are ideally suited to interfacing with life sciences, since they are on the scale lengths as cells (microns) and biomacromolecules (nanometers). In this paper, we review the state of the art in bionanotechnology and bioMEMS (collectively BNM), including developments and challenges in the areas of BNM, such as microfluidic organ-on-chip devices, oral drug delivery, emerging technologies for managing infectious diseases, 3D printed microfluidic devices, AC electrokinetics, flexible MEMS devices, implantable microdevices, paper-based microfluidic platforms for cellular analysis, and wearable sensors for point-of-care testing.

Inflammation-responsive drug delivery nanosystems for treatment of bacterial-induced sepsis

Sepsis, a complication of dysregulated host immune systemic response to an infection, is life threatening and causes multiple organ injuries. Sepsis is recognized by WHO as a big contributor to global morbidity and mortality. The heterogeneity in sepsis pathophysiology, antimicrobial resistance threat, the slowdown in the development of antimicrobials, and limitations of conventional dosage forms jeopardize the treatment of sepsis. Drug delivery nanosystems are promising tools to overcome some of these challenges. Among the drug delivery nanosystems, inflammation-responsive nanosystems have attracted considerable interest in sepsis treatment due to their ability to respond to specific stimuli in the sepsis microenvironment to release their payload in a precise, targeted, controlled, and rapid manner compared to non-responsive nanosystems. These nanosystems posit superior therapeutic potential to enhance sepsis treatment. This review critically evaluates the recent advances in the design of drug delivery nanosystems that are inflammation responsive and their potential in enhancing sepsis treatment. The sepsis microenvironment's unique features, such as acidic pH, upregulated receptors, overexpressed enzymes, and enhanced oxidative stress, that form the basis for their design have been adequately discussed. These inflammation-responsive nanosystems have been organized into five classes namely: Receptor-targeted nanosystems, pH-responsive nanosystems, redox-responsive nanosystems, enzyme-responsive nanosystems, and multi-responsive nanosystems. Studies under each class have been thematically grouped and discussed with an emphasis on the polymers used in their design, nanocarriers, key characterization, loaded actives, and key findings on drug release and therapeutic efficacy. Further, this information is concisely summarized into tables and supplemented by inserted figures. Additionally, this review adeptly points out the strengths and limitations of the studies and identifies research avenues that need to be explored. Finally, the challenges and future perspectives on these nanosystems have been thoughtfully highlighted.

Research progress of nanoparticle targeting delivery systems in bacterial infections

Bacterial infection is a huge threat to the health of human beings and animals. The abuse of antibiotics have led to the occurrence of bacterial multidrug resistance, which have become a difficult problem in the treatment of clinical infections. Given the outstanding advantages of nanodrug delivery systems in cancer treatment, many scholars have begun to pay attention to their application in bacterial infections. However, due to the similarity of the microenvironment between bacterial infection lesions and cancer sites, the targeting and accuracy of traditional microenvironment-responsive nanocarriers are questionable. Therefore, finding new specific targets has become a new development direction of nanocarriers in bacterial prevention and treatment. This article reviews the infectious microenvironment induced by bacteria and a series of virulence factors of common pathogenic bacteria and their physiological functions, which may be used as potential targets to improve the targeting accuracy of nanocarriers in lesions.

Nanoparticles-based therapeutics for the management of bacterial infections: A special emphasis on FDA approved products and clinical trials

Microbial resistance has increased in recent decades as a result of the extensive and indiscriminate use of antibiotics. The World Health Organization listed antimicrobial resistance as one of ten major global public health threats in 2021. In particular, six major bacterial pathogens, including third-generation cephalosporin-resistant Escherichia coli, methicillin-resistant Staphylococcus aureus, carbapenem-resistant Acinetobacter baumannii, Klebsiella pneumoniae, Streptococcus pneumoniae, and Pseudomonas aeruginosa, were found to have the highest resistance-related death rates in 2019. To respond to this urgent call, the creation of new pharmaceutical technologies based on nanoscience and drug delivery systems appears to be the promising strategy against microbial resistance in light of recent advancements, particularly the new knowledge of medicinal biology. Nanomaterials are often defined as substances having sizes between 1 and 100 nm. If the material is used on a small scale; its properties significantly change. They come in a variety of sizes and forms to help provide distinguishing characteristics for a wide range of functions. The field of health sciences has demonstrated a strong interest in numerous nanotechnology applications. Therefore, in this review, prospective nanotechnology-based therapeutics for the management of bacterial infections with multiple medication resistance are critically examined. Recent developments in these innovative treatment techniques are described, with an emphasis on preclinical, clinical, and combinatorial approaches.

Antifungal therapy: Novel drug delivery strategies driven by new targets

In patients with compromised immunity, invasive fungal infections represent a significant cause of mortality. Given the limited availability and drawbacks of existing first-line antifungal drugs, there is a growing interest in exploring novel targets that could facilitate the development of new antifungal agents or enhance the effectiveness of conventional ones. While previous studies have extensively summarized new antifungal targets inherent in fungi for drug development purposes, the exploration of potential targets for novel antifungal drug delivery strategies has received less attention. In this review, we provide an overview of recent advancements in new antifungal drug delivery strategies that leverage novel targets, including those located in the physio-pathological barrier at the site of infection, the infection microenvironment, fungal-host interactions, and the fungal pathogen itself. The objective is to enhance therapeutic efficacy and mitigate toxic effects in fungal infections, particularly in challenging cases such as refractory, recurrent, and drug-resistant invasive fungal infections. We also discuss the current challenges and future prospects associated with target-driven antifungal drug delivery strategies, offering important insights into the clinical implementation of these innovative approaches.

Multidrug-Resistant Pathogens in Burn Wound, Prevention, Diagnosis, and Therapeutic Approaches (Conventional Antimicrobials and Nanoparticles)

Multidrug-resistant pathogens are one of the common causes of death in burn patients and have a high risk of nosocomial infections, especially pneumonia, urinary tract infections, and cellulitis. The role of prolonged hospitalization and empirical antibiotics administration in developing multidrug-resistant pathogens is undeniable. In the early days of admitting burn patients, Gram-positive bacteria were the dominant isolates with a more sensitive antibiotic pattern. However, the emergence of Gram-negative bacteria that are more resistant later occurs. Trustworthy guideline administration in burn wards is one of the strategies to prevent multidrug-resistant pathogens. Also, a multidisciplinary therapeutic approach is an effective way to avoid antibiotic resistance that involves infectious disease specialists, pharmacists, and burn surgeons. However, the emerging resistance to conventional antimicrobial approaches (such as systemic antibiotic exposure, traditional wound dressing, and topical antibiotic ointments) among burn patients has challenged the treatment of multidrug-resistant infections, and using nanoparticles is a suitable alternative. In this review article, we will discuss different aspects of multidrug-resistant pathogens in burn wounds, emphasizing the full role of these pathogens in burn wounds and discussing the application of nanotechnology in dealing with them. Also, some advances in various types of nanomaterials, including metallic nanoparticles, liposomes, hydrogels, carbon quantum dots, and solid lipid nanoparticles in burn wound healing, will be explained.

Advances in Diagnostic Approaches and Therapeutic Management in Bovine Mastitis

Mastitis causes huge economic losses to dairy farmers worldwide, which largely negatively affects the quality and quantity of milk. Mastitis decreases overall milk production, degrades milk quality, increases milk losses because of milk being discarded, and increases overall production costs due to higher treatment and labour costs and premature culling. This review article discusses mastitis with respect to its clinical epidemiology, the pathogens involved, economic losses, and basic and advanced diagnostic tools that have been used in recent times to diagnose mastitis effectively. There is an increasing focus on the application of novel therapeutic approaches as an alternative to conventional antibiotic therapy because of the decreasing effectiveness of antibiotics, emergence of antibiotic-resistant bacteria, issue of antibiotic residues in the food chain, food safety issues, and environmental impacts. This article also discussed nanoparticles'/chitosan's roles in antibiotic-resistant strains and ethno-veterinary practices for mastitis treatment in dairy cattle.

Recent Advances in Pharmaceutical Approaches of Antimicrobial Agents for Selective Delivery in Various Administration Routes

Globally, the increase of pathogenic bacteria with antibiotic-resistant characteristics has become a critical challenge in medical treatment. The misuse of conventional antibiotics to treat an infectious disease often results in increased resistance and a scarcity of effective antimicrobials to be used in the future against the organisms. Here, we discuss the rise of antimicrobial resistance (AMR) and the need to combat it through the discovery of new synthetic or naturally occurring antibacterial compounds, as well as insights into the application of various drug delivery approaches delivered via various routes compared to conventional delivery systems. AMR-related infectious diseases are also discussed, as is the efficiency of various delivery systems. Future considerations in developing highly effective antimicrobial delivery devices to address antibiotic resistance are also presented here, especially on the smart delivery system of antibiotics.

Biodegradable Polymers and Polymer Composites with Antibacterial Properties

Antibiotic resistance is one of the greatest threats to global health and food security today. It becomes increasingly difficult to treat infectious disorders because antibiotics, even the newest ones, are becoming less and less effective. One of the ways taken in the Global Plan of Action announced at the World Health Assembly in May 2015 is to ensure the prevention and treatment of infectious diseases. In order to do so, attempts are made to develop new antimicrobial therapeutics, including biomaterials with antibacterial activity, such as polycationic polymers, polypeptides, and polymeric systems, to provide non-antibiotic therapeutic agents, such as selected biologically active nanoparticles and chemical compounds. Another key issue is preventing food from contamination by developing antibacterial packaging materials, particularly based on degradable polymers and biocomposites. This review, in a cross-sectional way, describes the most significant research activities conducted in recent years in the field of the development of polymeric materials and polymer composites with antibacterial properties. We particularly focus on natural polymers, i.e., polysaccharides and polypeptides, which present a mechanism for combating many highly pathogenic microorganisms. We also attempt to use this knowledge to obtain synthetic polymers with similar antibacterial activity.

AIEgen-Based Nanomaterials for Bacterial Imaging and Antimicrobial Applications: Recent Advances and Perspectives

Microbial infections have always been a thorny problem. Multi-drug resistant (MDR) bacterial infections rendered the antibiotics commonly used in clinical treatment helpless. Nanomaterials based on aggregation-induced emission luminogens (AIEgens) recently made great progress in the fight against microbial infections. As a family of photosensitive antimicrobial materials, AIEgens enable the fluorescent tracing of microorganisms and the production of reactive oxygen (ROS) and/or heat upon light irradiation for photodynamic and photothermal treatments targeting microorganisms. The novel nanomaterials constructed by combining polymers, antibiotics, metal complexes, peptides, and other materials retain the excellent antimicrobial properties of AIEgens while giving other materials excellent properties, further enhancing the antimicrobial effect of the material. This paper reviews the research progress of AIEgen-based nanomaterials in the field of antimicrobial activity, focusing on the materials' preparation and their related antimicrobial strategies. Finally, it concludes with an outlook on some of the problems and challenges still facing the field.

Dual-responsive antibiotic and baicalein co-delivery nanoparticles with enhanced synergistic antibacterial activity

Globally, due to the rapid development of bacterial resistance, bacterial infections lead to significant mortality and morbidity which require efficient strategies to eradicate these infections. Herein, we prepared a dual-responsive synergistic drug delivery nanoparticle carrier (NPS@Bai/Cip), which responds to sub-acid bacterial microenvironments and targets phosphatase or phospholipase at infection sites. Nanoparticles surfaces were positively (10.0 mV) charged under acidic conditions, leading to good bacterial adhesion and enhanced drug accumulation. NPS@Bai/Cip showed good antibacterial and anti-biofilm activity against drug-resistant Pseudomonas aeruginosa. NPS@Bai/Cip could inhibit the biofilm formation via affecting the swimming, swarming, and twitching motilities of P. aeruginosa. NPS@Bai/Cip was used to treat drug-resistance P. aeruginosa-induced infection in rats by improving wound healing and reducing inflammatory responses. Thus, NPS@Bai/Cip functioned as an antibacterial and antibiofilm agent with good potential for treating bacteria-induced infections.

Smart delivery systems for microbial biofilm therapy: Dissecting design, drug release and toxicological features

Bacterial biofilms are highly protected surface attached communities of bacteria that typically cause chronic infections. To address their recalcitrance to antibiotics and minimise side effects of current therapies, smart drug carriers are being explored as promising platforms for antimicrobials. Herein, we briefly summarize recent efforts and considerations that have been applied in the design of these smart carriers. We guide readers on a journey on how they can leverage the inherent biofilm microenvironment, external stimuli, or combine both types of stimuli in a predictable manner. The specific carrier features that are responsible for their 'on-demand' properties are detailed and their impact on antibiofilm property are further discussed. Moreover, an analysis on the impact of such features on drug release profiles is provided. Since nanotechnology represents a significant slice of the drug delivery pie, some insights on the potential toxicity are also depicted. We hope that this review inspires researchers to use their knowledge and creativity to design responsive systems that can eradicate biofilm infections.

Nanomedicine: New Frontiers in Fighting Microbial Infections

Microbes have dominated life on Earth for the past two billion years, despite facing a variety of obstacles. In the 20th century, antibiotics and immunizations brought about these changes. Since then, microorganisms have acquired resistance, and various infectious diseases have been able to avoid being treated with traditionally developed vaccines. Antibiotic resistance and pathogenicity have surpassed antibiotic discovery in terms of importance over the course of the past few decades. These shifts have resulted in tremendous economic and health repercussions across the board for all socioeconomic levels; thus, we require ground-breaking innovations to effectively manage microbial infections and to provide long-term solutions. The pharmaceutical and biotechnology sectors have been radically altered as a result of nanomedicine, and this trend is now spreading to the antibacterial research community. Here, we examine the role that nanomedicine plays in the prevention of microbial infections, including topics such as diagnosis, antimicrobial therapy, pharmaceutical administration, and immunizations, as well as the opportunities and challenges that lie ahead.

Quasi-opsonin conjugated lipase-sensitive micelles activate macrophages against facultative intracellular bacterial infection

Drug resistance caused by facultative intracellular bacteria such as Salmonella typhimurium (S. typhimurium) is still a tough challenge. Bacteria phagocytosed by macrophages have evolved a variety of mechanisms to defend against host attack, and the poor entry of antibiotics into infected macrophages is conducive to the survival of intracellular bacteria. In this report, we prepared a quasi-opsonized chloramphenicol (Chl)-loaded micellar system (B-mLBP-M/Chl) assembled by a bacterial lipase-sensitive polymer with a conjugate of lipopolysaccharide-binding protein (LBP) analog and biotin (B) as a ligand, which could eliminate drug-resistant S. typhimurium with quasi-opsonization via 3 steps: (i) target and release antibiotics on bacteria lipase, (ii) opsonize S. typhimurium to be digested by the macrophage, and (iii) activate the macrophage for fighting. The B-mLBP-M/Chl could target bacterial LPS through mLBP by simulating the N-terminal sequence of native LBP, exhibiting a high ability to target the localized infection site in mice. It could also activate the phagocytosis of macrophages via coupled biotin, cooperating with antibiotics and effectively improving the survival of mice with little pathological damage to tissues. Moreover, compared with native opsonin, B-mLBP does not cause an excessive inflammatory response and could recover homeostasis after exerting the quasi-opsonization by regulating the levels of pro-inflammatory cytokines and anti-inflammatory cytokines. With a universal target site for Gram-negative bacteria and macrophage activation, this B-mLBP-M/Chl could be applied to other bacterial infections in the future. In particular, this analog may also serve as a useful template to design safe artificial opsonin, which could be a ligand for drug delivery systems or prodrugs.

Targeted Drug Delivery Systems for Eliminating Intracellular Bacteria

The intracellular survival of pathogenic bacteria requires a range of survival strategies and virulence factors. These infections are a significant clinical challenge, wherein treatment frequently fails because of poor antibiotic penetration, stability, and retention in host cells. Drug delivery systems (DDSs) are promising tools to overcome these shortcomings and enhance the efficacy of antibiotic therapy. In this review, the classification and the mechanisms of intracellular bacterial persistence are elaborated. Furthermore, the systematic design strategies applied to DDSs to eliminate intracellular bacteria are also described, and the strategies used for internalization, intracellular activation, bacterial targeting, and immune enhancement are highlighted. Finally, this overview provides guidance for constructing functionalized DDSs to effectively eliminate intracellular bacteria.

Nanomaterials against intracellular bacterial infection: from drug delivery to intrinsic biofunction

Fighting intracellular bacteria with strong antibiotics evading remains a long-standing challenge. Responding to and regulating the infectious microenvironment is crucial for treating intracellular infections. Sophisticated nanomaterials with unique physicochemical properties exhibit great potential for precise drug delivery towards infection sites, along with modulating infectious microenvironment via their instinct bioactivity. In this review, we first identify the key characters and therapeutic targets of intracellular infection microenvironment. Next, we illustrate how the nanomaterials physicochemical properties, such as size, charge, shape and functionalization affect the interaction between nanomaterials, cells and bacteria. We also introduce the recent progress of nanomaterial-based targeted delivery and controlled release of antibiotics in intracellular infection microenvironment. Notably, we highlight the nanomaterials with unique intrinsic properties, such as metal toxicity and enzyme-like activity for the treatment of intracellular bacteria. Finally, we discuss the opportunities and challenges of bioactive nanomaterials in addressing intracellular infections.

Stimuli-Activable Metal-Bearing Nanomaterials and Precise On-Demand Antibacterial Strategies

Bacterial infections remain the leading cause of death worldwide today. The emergence of antibiotic resistance has urged the development of alternative antibacterial technologies to complement or replace traditional antibiotic treatments. In this regard, metal nanomaterials have attracted great attention for their controllable antibacterial functions that are less prone to resistance. This review discusses a particular family of stimuli-activable metal-bearing nanomaterials (denoted as SAMNs) and the associated on-demand antibacterial strategies. The various SAMN-enabled antibacterial strategies stem from basic light and magnet activation, with the addition of bacterial microenvironment responsiveness and/or bacteria-targeting selectivity and therefore offer higher spatiotemporal controllability. The discussion focuses on nanomaterial design principles, antibacterial mechanisms, and antibacterial performance, as well as emerging applications that desire on-demand and selective activation (i.e., medical antibacterial treatments, surface anti-biofilm, water disinfection, and wearable antibacterial materials). The review concludes with the authors' perspectives on the challenges and future directions for developing industrial translatable next-generation antibacterial strategies.

Hydrogen sulfide-sensitive Chitosan-SS-Levofloxacin micelles with a high drug content: Facile synthesis and targeted Salmonella infection therapy

The delivery system of antibiotics plays an important role in increasing the drug efficacy and reducing the risks of off-target toxicities and antibiotic resistance. The pathophysiology of bacterial infections is similar to that of tumor tissues, but only a few delivery systems have been able to target and release antibiotics on demand. Herein, we designed and developed a robust Chitosan-SS-Levofloxacin (CS-SS-LF) micelles for targeted antibiotic delivery, in which disulfide bond can be reduced by hydrogen sulfide (H₂S), a typical product of Salmonella, and subsequently released antibiotic to eradicate Salmonella infection. CS-SS-LF micelles showed uniform size and sharp response to H₂S. Compared with levofloxacin alone, these micelles possessed a better capacity in disrupting Salmonella biofilms and reducing bacterial burden in organs. The H2S-sensitive CS-SS-LF micelles might enable a new way to address bacterial infections.

Recent Advances in the Biomedical Applications of Functionalized Nanogels

Nanomaterials have been extensively used in several applications in the past few decades related to biomedicine and healthcare. Among them, nanogels (NGs) have emerged as an important nanoplatform with the properties of both hydrogels and nanoparticles for the controlled/sustained delivery of chemo drugs, nucleic acids, or other bioactive molecules for therapeutic or diagnostic purposes. In the recent past, significant research efforts have been invested in synthesizing NGs through various synthetic methodologies such as free radical polymerization, reversible addition-fragmentation chain-transfer method (RAFT) and atom transfer radical polymerization (ATRP), as well as emulsion techniques. With further polymeric functionalizations using activated esters, thiol-ene/yne processes, imines/oximes formation, cycloadditions, nucleophilic addition reactions of isocyanates, ring-opening, and multicomponent reactions were used to obtain functionalized NGs for targeted delivery of drug and other compounds. NGs are particularly intriguing for use in the areas of diagnosis, analytics, and biomedicine due to their nanodimensionality, material characteristics, physiological stability, tunable multi-functionality, and biocompatibility. Numerous NGs with a wide range of functionalities and various external/internal stimuli-responsive modalities have been possible with novel synthetic reliable methodologies. Such continuous development of innovative, intelligent materials with novel characteristics is crucial for nanomedicine for next-generation biomedical applications. This paper reviews the synthesis and various functionalization strategies of NGs with a focus on the recent advances in different biomedical applications of these surface modified/functionalized single-/dual-/multi-responsive NGs, with various active targeting moieties, in the fields of cancer theranostics, immunotherapy, antimicrobial/antiviral, antigen presentation for the vaccine, sensing, wound healing, thrombolysis, tissue engineering, and regenerative medicine.

Intracellular bacteriolysis contributes to pathogenicity of Staphylococcus aureus by exacerbating AIM2-mediated inflammation and necroptosis

Staphylococcus aureus can survive within phagocytes. Indeed, we confirm in this study that approximately 10% of population persists in macrophages during S. aureus infection, while the rest are eliminated due to bacteriolysis, which is of particular interest to us. Herein, we observe that the bacteriolysis is an early event accompanied by macrophage death during S. aureus infection. Furthermore, the cell death is significantly accelerated following increased intracellular bacteriolysis, indicating that intracellular bacteriolysis induces cell death. Subsequently, we establish that the cell death is not apoptosis or pyroptosis, but AIM2-mediated necroptosis, accompanied by AIM2 inflammasome activation. This finding challenges the classical model that the cell death that accompanies inflammasome activation is always pyroptosis. In addition, we observe that the apoptosis-associated genes are highly inhibited during S. aureus infection. Finally, we establish in vivo that increased bacteriolysis significantly enhances S. aureus pathogenicity by promoting its dissemination to kidney and leading to an inflammatory cytokine storm in AIM2-mediated manner. Collectively, our data demonstrate that bacteriolysis is detrimental when triggered in excess and its side effect is mediated by AIM2. Meanwhile, we propose a potential immune manipulation strategy by which S. aureus sacrifices the minority to trigger a limited necroptosis, thereby releasing signals from dead cells to inhibit apoptosis and other anti-inflammatory cascades of live cells, eventually surviving within host cells and establishing infection.

Stimuli-responsive and biomimetic delivery systems for sepsis and related complications

Sepsis, a consequence of an imbalanced immune response to infection, is currently one of the leading causes of death globally. Despite advances in the discoveries of potential targets and nanotechnology, sepsis still lacks effective drug delivery systems for optimal treatment. Stimuli-responsive and biomimetic nano delivery systems, specifically, are emerging as advanced bio-inspired nanocarriers for enhancing the treatment of sepsis. Herein, we present a critical review of different stimuli-responsive systems, including pH-; enzyme-; ROS- and toxin-responsive nanocarriers, reported in the delivery of therapeutics for sepsis. Biomimetic nanocarriers, utilizing natural pathways in the inflammatory cascade to optimize sepsis therapy, are also reviewed, in addition to smart, multifunctional vehicles. The review highlights the nanomaterials designed for constructing these systems; their physicochemical properties; the mechanisms of drug release; and their potential for enhancing the therapeutic efficacy of their cargo. Current challenges are identified and future avenues for research into the optimization of bio-inspired nano delivery systems for sepsis are also proposed. This review confirms the potential of stimuli-responsive and biomimetic nanocarriers for enhanced therapy against sepsis and related complications.

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.

The Potential of Antibiotics and Nanomaterial Combinations as Therapeutic Strategies in the Management of Multidrug-Resistant Infections: A Review

Antibiotic resistance has become a major public health concern around the world. This is exacerbated by the non-discovery of novel drugs, the development of resistance mechanisms in most of the clinical isolates of bacteria, as well as recurring infections, hindering disease treatment efficacy. In vitro data has shown that antibiotic combinations can be effective when microorganisms are resistant to individual drugs. Recently, advances in the direction of combination therapy for the treatment of multidrug-resistant (MDR) bacterial infections have embraced antibiotic combinations and the use of nanoparticles conjugated with antibiotics. Nanoparticles (NPs) can penetrate the cellular membrane of disease-causing organisms and obstruct essential molecular pathways, showing unique antibacterial mechanisms. Combined with the optimal drugs, NPs have established synergy and may assist in regulating the general threat of emergent bacterial resistance. This review comprises a general overview of antibiotic combinations strategies for the treatment of microbial infections. The potential of antibiotic combinations with NPs as new entrants in the antimicrobial therapy domain is discussed.

Smart Bacteria-Responsive Drug Delivery Systems in Medical Implants

With the rapid development of implantable biomaterials, the rising risk of bacterial infections has drawn widespread concern. Due to the high recurrence rate of bacterial infections and the issue of antibiotic resistance, the common treatments of peri-implant infections cannot meet the demand. In this context, stimuli-responsive biomaterials have attracted attention because of their great potential to spontaneously modulate the drug releasing rate. Numerous smart bacteria-responsive drug delivery systems (DDSs) have, therefore, been designed to temporally and spatially release antibacterial agents from the implants in an autonomous manner at the infected sites. In this review, we summarized recent advances in bacteria-responsive DDSs used for combating bacterial infections, mainly according to the different trigger modes, including physical stimuli-responsive, virulence-factor-responsive, host-immune-response responsive and their combinations. It is believed that the smart bacteria-responsive DDSs will become the next generation of mainstream antibacterial therapies.

Cell membrane-coated nanoparticles for the treatment of bacterial infection

Despite the enormous success of antibiotics in antimicrobial therapy, the rapid emergence of antibiotic resistance and the complexity of the bacterial infection microenvironment make traditional antibiotic therapy face critical challenges against resistant bacteria, antitoxin, and intracellular infections. Consequently, there is a critical need to design antimicrobial agents that target infection microenvironment and alleviate antibiotic resistance. Cell membrane-coated nanoparticles (CMCNPs) are biomimetic materials that can be obtained by wrapping the cell membrane vesicles directly onto the surface of the nanoparticles (NPs) through physical means. Incorporating the biological functions of cell membrane vesicles and the superior physicochemical properties of NPs, CMCNPs have shown great promise in recent years for targeting infections, neutralizing bacterial toxins, and designing bacterial infection vaccines. This review highlights topics where CMCNPs present great value in advancing the treatment of bacterial infections, including drug delivery, detoxification, and vaccination. Lastly, we discuss the future hurdles and prospects of translating this technique into clinical practice, providing a comprehensive review of the technological developments of CMCNPs in the treatment of bacterial infections. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease Therapeutic Approaches and Drug Discovery > Emerging Technologies Nanotechnology Approaches to Biology > Nanoscale Systems in Biology.

Isoquinoline Antimicrobial Agent: Activity against Intracellular Bacteria and Effect on Global Bacterial Proteome

A new class of alkynyl isoquinoline antibacterial compounds, synthesized via Sonogashira coupling, with strong bactericidal activity against a plethora of Gram-positive bacteria including methicillin- and vancomycin-resistant Staphylococcus aureus (S. aureus) strains is presented. HSN584 and HSN739, representative compounds in this class, reduce methicillin-resistant S. aureus (MRSA) load in macrophages, whilst vancomycin, a drug of choice for MRSA infections, was unable to clear intracellular MRSA. Additionally, both HSN584 and HSN739 exhibited a low propensity to develop resistance. We utilized comparative global proteomics and macromolecule biosynthesis assays to gain insight into the alkynyl isoquinoline mechanism of action. Our preliminary data show that HSN584 perturb S. aureus cell wall and nucleic acid biosynthesis. The alkynyl isoquinoline moiety is a new scaffold for the development of potent antibacterial agents against fatal multidrug-resistant Gram-positive bacteria.

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.

pH-Activatable Organic Nanoparticles for Efficient Low-Temperature Photothermal Therapy of Ocular Bacterial Infection

Low-temperature photothermal therapy (PTT) systems constructed by integrating organic photothermal agents with other bactericidal components that initiate bacterial apoptosis at low hyperthermia possess a promising prospect. However, these multicomponent low-temperature PTT nanoplatforms have drawbacks in terms of the tedious construction process, suboptimal synergy effect of diverse antibacterial therapies, and high laser dose needed, compromising their biosafety in ocular bacterial infection treatment. Herein, a mild PTT nanotherapeutic platform is formulated via the self-assembly of a pH-responsive phenothiazinium dye. These organic nanoparticles with photothermal conversion efficiency up to 84.5% necessitate only an ultralow light dose of 36 J/cm² to achieve efficient low-temperature photothermal bacterial inhibition at pH 5.5 under 650 nm laser irradiation. In addition, this intelligent mild photothermal nanoplatform undergoes negative to positive charge reversion in acid biofilms, exhibiting good penetration and highly efficient elimination of drug-resistant E. coli biofilms under photoirradiation. Further in vivo animal tests demonstrated efficient bacterial elimination and inflammatory mitigation as well as superior biocompatibility and biosafety of the photothermal nanoparticles in ocular bacterial infection treatment. Overall, this efficient single-component mild PTT system featuring simple construction processes holds great potential for wide application and clinical transformation.

Supramolecular Hydrogel Based on Pseudopolyrotaxanes Aggregation for Bacterial Microenvironment-Responsive Antibiotic Delivery

Due to the extensive use of antibiotics, the variety and number of drug-resistant pathogens have increased dramatically and have become a major global health problem. This imposes significant demands on the rational and effective use of antibiotics. To this end, a supramolecular hydrogel based on pseudopolyrotaxanes aggregation is proposed for antibiotic delivery. Supramolecular cross-linking strategies allow hydrogels to be obtained under mild conditions that facilitate the encapsulation of antibiotics. The presence of pH-sensitive imine bonds allows for the reversible detachment of PEG residues from the PEGylated hyaluronic acid backbone in an acidic environment, which leads to reversible changes in hydrogel crosslink density and thus controls antibiotic release behavior. Antimicrobial assessments indicated that the hydrogel exhibited good antimicrobial efficiency against both Gram-positive and negative bacteria, while responding to the bacterial microenvironment and enabling a burst release of antibiotics in severe infections. The proposed hydrogel also has excellent biocompatibility and thus possesses great potential for biomedical applications.

β-Lactamase-Responsive Hydrogel Drug Delivery Platform for Bacteria-Triggered Cargo Release

Antibiotic resistance is a growing public health threat that complicates the treatment of infections. β-Lactamase enzymes, which hydrolyze the β-lactam ring present in many common antibiotics, are a major cause of this resistance and are produced by a broad range of bacterial pathogens. Here, we developed hydrogels that degrade specifically in the presence of β-lactamases and β-lactamase-producing bacteria as a platform for bacteria-triggered drug delivery. A maleimide-functionalized β-lactamase-cleavable cephalosporin was used as a crosslinker in the fabrication of hydrogels through end-crosslinked polymerization with multiarm thiol-terminated poly(ethylene glycol) macromers via Michael-type addition. We demonstrated that only hydrogels containing the responsive crosslinker were degraded by β-lactamases and β-lactamase-producing bacteria in vitro and in an ex vivo porcine skin infection model. Fluorescent polystyrene nanoparticles, encapsulated in the hydrogels as model cargo, were released at rates that closely tracked hydrogel wet mass loss, confirming β-lactamase-triggered controlled cargo release. Nonresponsive hydrogels, lacking the β-lactam crosslinker, remained stable in the presence of β-lactamases and β-lactamase-producing bacteria and exhibited no change in mass or nanoparticle release. Furthermore, the responsive hydrogels remained stable in non-β-lactamase enzymes, including collagenases and lipases. These hydrogels have the potential to be used as a bacteria-triggered drug delivery system to control unnecessary exposure to encapsulated antimicrobials, which can provide effective infection treatment without exacerbating resistance.

Long-Lasting Chemiluminescence-Based POCT for Portable and Visual Pathogenic Detection and In Situ Inactivation

Bacterial infections seriously threaten human health and also bring huge financial burden. It is critical to construct multifunctional platforms for effectively inactivating bacteria right after point-of-care testing (POCT). Chemiluminescence (CL) bioassays are considered as powerful candidates for POCT as they are free from using an excitation light source, while the flash-type emission limits their further application. Herein, a CL system with long, persistent, and intensive intensity was constructed based on the peroxidase-like property of 4-mercaptophenylboronic acid (MPBA)-functionalized CuSe nanoprobes (CuSe_NPs@MPBA), which improved the detection accuracy and sensitivity. By further integrating a smartphone as an analyzer, quantitative POCT of bacteria was realized with high sensitivity. The limit of detection was as low as 1.25 and 1.01 cfu mL^-1 for Staphylococcus aureus and Escherichia coli detection, respectively. Specifically, bacteria can be eliminated with high efficiency due to excellent photothermal property of CuSe_NPs@MPBA. The developed multifunctional platform also has advantages of simple operation with low cost, suggesting its high potential for use in food safety, environment monitoring, and clinical applications.

Interpenetrating Polymer Network Hydrogels Formed Using Antibiotics as a Dynamic Crosslinker for Treatment of Infected Wounds

Antibacterial hydrogels, particularly antibiotic-loaded hydrogels, are promising wound dressing materials for treatment of bacteria-infected wound. However, it is challenging to achieve sustained release of antibiotics from hydrogels through physical encapsulation of the antibiotics. Herein, an interpenetrating polymer network P(AA-co-HEMA)_Gen hydrogel is reported with double crosslinking formed by free radical polymerization of 2-hydroxyethyl methacrylate (HEMA) and acrylic acid (AA), while using the antibiotic gentamicin (Gen) as the dynamic physical crosslinker. Gentamicin is incorporated into the hydrogel networks via electrostatic interaction between the carboxyl groups of poly(acrylic acid) and the amino groups of gentamicin, which leads to pH-responsive drug release and a significant increase in mechanical strength (i.e., elastic modulus, viscous modulus, and compressive modulus). More importantly, the hydrogels with optimal compositions demonstrate long-lasting antibacterial activity against both Gram-positive bacteria (Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli) over 28 d. The in vivo studies that are conducted in an S. aureus-infected full-thickness skin wound model demonstrate that the double crosslinking hydrogels loaded with gentamicin eliminate bacteria in the wounds more effectively and significantly accelerate wound healing as compared to 3M dressing and the control without any treatment. Taken together, this antibiotic-loaded interpenetrating polymer network hydrogel is potentially a promising wound dressing material for the treatment of bacteria-infected wound.

Antibacterial and Biofilm-Eradicating Activities of pH-Responsive Vesicles against Pseudomonas aeruginosa

The formation of biofilms by a microcolony of bacteria is a significant burden on the healthcare industry due to difficulty eradicating it. In this study, pH-responsive vesicles capable of releasing apramycin (APR), a model aminoglycoside antibiotic, in response to the low pH typical of establishedPseudomonas aeruginosa biofilms resulted in improved eradication of existing biofilms in comparison to the free drug. The amphiphilic polymeric vesicle (PV) comprised of block polymer poly (ethylene glycol)-block-poly 2-(dimethylamino) ethyl methacrylate (mPEG-b-pDEAEMA) averaged 128 nm. The drug encapsulation content of APR in PV/APR was confirmed to be 28.2%, and the drug encapsulation efficiency was confirmed to be 51.2%. At pH 5.5, PV/APR released >90% APR after 24 h compared to <20% at pH 7.4. At pH 5.5, protonation of the pDEAEMA block results in a zeta potential of +23 mV compared to a neutral zeta potential of +2.2 mV at pH 7.4. Confocal microscopy, flow cytometry, and scanning electron microscopy reveal that the positively charged vesicles can compromise the integrity of the planktonic bacterial membrane in a pH-dependent manner. In addition, PV/APR is able to diffuse into mature biofilms to release APR in the acidic milieu of biofilm bacteria, and PV/APR was more efficient at eliminating preexisting biofilms compared to free APR at 128 and 256 μg/mL. This study reveals that dynamic charge density in response to pH can lead to differential levels of interactions with the biofilm and bacterial membrane. This effectively results in enhanced antibacterial and antibiofilm properties against both planktonic and difficult-to-treat biofilm bacteria at concentrations significantly lower than those of the free drug. Overall, this pH-responsive vesicle could be especially promising for treating biofilm-associated infectious diseases.

Stimuli-Responsive Antibacterial Materials: Molecular Structures, Design Principles, and Biomedical Applications

Infections are regarded as the most severe complication associated with human health, which are urgent to be solved. Stimuli-responsive materials are appealing therapeutic platforms for antibacterial treatments, which provide great potential for accurate theranostics. In this review, the advantages, the response mechanisms, and the key design principles of stimuli-responsive antibacterial materials are highlighted. The biomedical applications, the current challenges, and future directions of stimuli-responsive antibacterial materials are also discussed. First, the categories of stimuli-responsive antibacterial materials are comprehensively itemized based on different sources of stimuli, including external physical environmental stimuli (e.g., temperature, light, electricity, salt, etc.) and bacterial metabolites stimuli (e.g., acid, enzyme, redox, etc.). Second, structural characteristics, design principles, and biomedical applications of the responsive materials are discussed, and the underlying interrelationships are revealed. The molecular structures and design principles are closely related to the sources of stimuli. Finally, the challenging issues of stimuli-responsive materials are proposed. This review will provide scientific guidance to promote the clinical applications of stimuli-responsive antibacterial materials.

Cascade-Targeting Poly(amino acid) Nanoparticles Eliminate Intracellular Bacteria via On-Site Antibiotic Delivery

Intracellular bacteria in latent or dormant states tolerate high-dose antibiotics. Fighting against these opportunistic bacteria has been a long-standing challenge. Herein, the design of a cascade-targeting drug delivery system (DDS) that can sequentially target macrophages and intracellular bacteria, exhibiting on-site drug delivery, is reported. The DDS is fabricated by encapsulating rifampicin (Rif) into mannose-decorated poly(α-N-acryloyl-phenylalanine)-block-poly(β-N-acryloyl-d-aminoalanine) nanoparticles, denoted as Rif@FAM NPs. The mannose units on Rif@FAM NPs guide the initial macrophage-specific uptake and intracellular accumulation. After the uptake, the detachment of mannose in acidic phagolysosome via Schiff base cleavage exposes the d-aminoalanine moieties, which subsequently steer the NPs to escape from lysosomes and target intracellular bacteria through peptidoglycan-specific binding, as evidenced by the in situ/ex situ co-localization using confocal, flow cytometry, and transmission electron microscopy. Through the on-site Rif delivery, Rif@FAM NPs show superior in vitro and in vivo elimination efficiency than the control groups of free Rif or the DDSs lacking the macrophages- or bacteria-targeting moieties. Furthermore, Rif@FAM NPs remodel the innate immune response of the infected macrophages by upregulating M1/M2 polarization, resulting in a reinforced antibacterial capacity. Therefore, this biocompatible DDS enabling macrophages and bacteria targeting in a cascade manner provides a new outlook for the therapy of intracellular pathogen infection.

Cell Membrane-Cloaked Nanotherapeutics for Targeted Drug Delivery

Cell membrane cloaking technique is bioinspired nanotechnology that takes advantage of naturally derived design cues for surface modification of nanoparticles. Unlike modification with synthetic materials, cell membranes can replicate complex physicochemical properties and biomimetic functions of the parent cell source. This technique indeed has the potential to greatly augment existing nanotherapeutic platforms. Here, we provide a comprehensive overview of engineered cell membrane-based nanotherapeutics for targeted drug delivery and biomedical applications and discuss the challenges and opportunities of cell membrane cloaking techniques for clinical translation.

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.

Injectable and pH-responsive self-assembled peptide hydrogel for promoted tumor cell uptake and enhanced cancer chemotherapy

Chemotherapy is the main treatment for cancer therapy. However, its anti-tumor efficiency is always impaired by the poor bioavailability and low tumor accumulation of chemotherapeutic drugs. The variation between the tumor microenvironment and normal tissue has been recognized as an effective tool to improve drug anti-tumor efficiency. Herein, we developed an injectable, pH-responsive, in situ self-assembled drug-peptide hydrogel (MTX-KKFKFEFEF(DA)) for highly efficient local tumor chemotherapy with few side effects. The small molecule drug, methotrexate (MTX), and pH-responsive linker, 2,3-dimethylmaleic anhydride (DA), were facilely conjugated onto the chain of the KKFKFEFEF peptide via an amidation reaction. The negatively charged drug-peptide (pH 7.4) can be activated to be positive and achieve a sol-gel phase transition under an acidic microenvironment (pH 6.5) both in vitro and in vivo, resulting in highly efficient cellular uptake and endocytosis capacities. Moreover, the in vivo anti-tumor therapeutic effect revealed that the MTX-KKFKFEFEF(DA) hydrogel exhibits long-term tumor retention time, much better tumor inhibition rate and negligible side effects after intratumoral injection into breast tumor-bearing mice. Therefore, this study reveals a versatile strategy for fabricating a pH-responsive drug-peptide hydrogel to improve the chemotherapeutic efficacy of drugs in cancer treatment.

Polymers as advanced antibacterial and antibiofilm agents for direct and combination therapies

The growing prevalence of antimicrobial drug resistance in pathogenic bacteria is a critical threat to global health. Conventional antibiotics still play a crucial role in treating bacterial infections, but the emergence and spread of antibiotic-resistant micro-organisms are rapidly eroding their usefulness. Cationic polymers, which target bacterial membranes, are thought to be the last frontier in antibacterial development. This class of molecules possesses several advantages including a low propensity for emergence of resistance and rapid bactericidal effect. This review surveys the structure-activity of advanced antimicrobial cationic polymers, including poly(α-amino acids), β-peptides, polycarbonates, star polymers and main-chain cationic polymers, with low toxicity and high selectivity to potentially become useful for real applications. Their uses as potentiating adjuvants to overcome bacterial membrane-related resistance mechanisms and as antibiofilm agents are also covered. The review is intended to provide valuable information for design and development of cationic polymers as antimicrobial and antibiofilm agents for translational applications.

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...

Surface-engineered liposomes for dual-drug delivery targeting strategy against Methicillin-resistant Staphylococcus aureus (MRSA)

This study focused on the encapsulation of vancomycin (VAN) into liposomes coated with a red blood cell membrane with a targeting ligand, daptomycin–polyethylene glycol–1,2-distearoyl-sn-glycero-3-phosphoethanolamine, formed by conjugation of DAPT and N-hydroxysuccinimidyl-polyethylene glycol-1,2-distearoyl-sn-glycero-3-phosphoethanolamine. This formulation is capable of providing controlled and targeted drug delivery to the bacterial cytoplasm. We performed MALDI-TOF, NMR and FTIR analyses to confirm the conjugation of the targeting ligand via the formation of amide bonds. Approximately 45% of VAN could be loaded into the aqueous cores, whereas 90% DAPT was detected using UV–vis spectrophotometry. In comparison to free drugs, the formulations controlled the release of drugs for > 72 h. Additionally, as demonstrated using CLSM and flow cytometry, the resulting formulation was capable of evading detection by macrophage cells. In comparison to free drugs, red blood cell membrane–DAPT–VAN liposomes, DAPT liposomes, and VAN liposomes reduced the MIC and significantly increased bacterial permeability, resulting in > 80% bacterial death within 4 h. Cytotoxicity tests were performed in vitro and in vivo on mammalian cells, in addition to hemolytic activity tests in human erythrocytes, wherein drugs loaded into the liposomes and RBCDVL exhibited low toxicity. Thus, the findings of this study provide insight about a dual antibiotic targeting strategy that utilizes liposomes and red blood cell membranes to deliver targeted drugs against MRSA.