Polymyxin B-Polysaccharide Polyion Nanocomplex with Improved Biocompatibility and Unaffected Antibacterial Activity for Acute Lung Infection Management

Catalase-templated nanozyme-loaded microneedles integrated with polymyxin B for immunoregulation and antibacterial activity in diabetic wounds

Diabetic wounds are characterized by chronic trauma, with long-term non-healing attributed to persistent inflammation and recurrent bacterial infections. Exacerbation of the inflammatory response is largely due to increased levels of reactive oxygen species (ROS). In this study, catalase (CAT) was used as a biological template to synthesize nanozyme-supported natural enzymes (CAT-Mn(SH)x) using a biomimetic mineralization method. Subsequently, polymyxin B (CAT-Mn(SH)x@PMB) was immobilized on its surface through electrostatic assembly. CAT-Mn(SH)x@PMB demonstrates the ability for slow and sustained release of hydrogen sulfide (H2S). Finally, CAT-Mn(SH)x@PMB loaded microneedles (MNs) substrate were synthesized using polyvinyl alcohol (PVA) and hydroxyethyl methacrylate (HEMA), and named CAT-(MnSH)x@PMB-MNs. It exhibited enhanced enzyme and antioxidant activities, along with effective antibacterial properties. Validation findings indicate that it can up-regulate the level of M2 macrophages and reduce the level of pro-inflammatory cytokine tumor necrosis factor-α (TNF-α). Additionally, it promotes angiogenesis and rapid nerve regeneration, thereby facilitating wound healing through its dual anti-inflammatory and antibacterial effects. Hence,this study introduces a time-space tissue-penetrating and soluble microneedle patch with dual anti-inflammatory and antibacterial effects for the treatment of diabetic wounds.

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.

Lipase and pH-responsive diblock copolymers featuring fluorocarbon and carboxyl betaine for methicillin-resistant staphylococcus aureus infections

The emergence of multidrug-resistant bacteria along with their resilient biofilms necessitates the development of creative antimicrobial remedies. We designed versatile fluorinated polymer micelles with surface-charge-switchable properties, demonstrating enhanced efficacy against Methicillin-Resistant Staphylococcus Aureus (MRSA) in planktonic and biofilm states. Polymethacrylate diblock copolymers with pendant fluorocarbon chains and carboxyl betaine groups were prepared using reversible addition-fragmentation chain transfer polymerization. Amphiphilic fluorinated copolymers self-assembled into micelles, encapsulating ciprofloxacin in their cores (CIP@FCBMs) for antibacterial and antibiofilm applications. As a control, fluorine-free copolymer micelles loaded with ciprofloxacin (CIP@BCBMs) were prepared. Although both CIP@FCBMs and CIP@BCBMs exhibited pH-responsive surface charges and lipase-triggered drug release, CIP@FCBMs exhibited powerful antimicrobial and antibiofilm activities in vitro and in vivo, attributed to superior serum stability, higher drug loading, enhanced fluorination-facilitated cellular uptake, and lipase-triggered drug release. Collectively, reversing surface charge, on-demand antibiotic release, and fluorination-mediated nanoparticles hold promise for treating bacterial infections and biofilms.

Charge-Reversible Nanoparticles: Advanced Delivery Systems for Therapy and Diagnosis

The past two decades have witnessed a rapid progress in the development of surface charge-reversible nanoparticles (NPs) for drug delivery and diagnosis. These NPs are able to elegantly address the polycation dilemma. Converting their surface charge from negative/neutral to positive at the target site, they can substantially improve delivery of drugs and diagnostic agents. By specific stimuli like a shift in pH and redox potential, enzymes, or exogenous stimuli such as light or heat, charge reversal of NP surface can be achieved at the target site. The activated positive surface charge enhances the adhesion of NPs to target cells and facilitates cellular uptake, endosomal escape, and mitochondrial targeting. Because of these properties, the efficacy of incorporated drugs as well as the sensitivity of diagnostic agents can be essentially enhanced. Furthermore, charge-reversible NPs are shown to overcome the biofilm formed by pathogenic bacteria and to shuttle antibiotics directly to the cell membrane of these microorganisms. In this review, the up-to-date design of charge-reversible NPs and their emerging applications in drug delivery and diagnosis are highlighted.

Cell-Selective Binding Zwitterionic Polymeric Micelles Boost the Delivery Efficiency of Antibiotics

Effective accumulation and penetration of antibiotics in the biofilm are critical issues for bacterial infection treatment. Red blood cells (RBCs) have been widely utilized to hitchhike nanocarriers for drug delivery. It is vital and challenging to find a nanocarrier with an appropriate affinity toward RBCs and bacteria for selective hitchhiking and release that determines the drug delivery efficiency and specificity. Herein, we report a zwitterionic polymer poly(2-(N-oxide-N,N-diethylamino)ethyl methacrylate) (OPDEA)-based micelle, which can hitchhike on RBCs in blood and preferentially release in the infection site. We found that OPDEA could bind to the RBCs cell membrane via phospholipid-related affinity and transfer to Gram-positive bacteria due to nearly an order of magnitude stronger interaction with the bacteria cell wall. The zwitterionic surface and cell-wall affinity of OPDEA-based micelles also promote their penetration in biofilm. The clarithromycin-loaded OPDEA micelles show efficient drug delivery into the infection site, resulting in excellent therapeutic performance in both peritonitis and pneumonia models by intravenous or spray administration. This simple RBC-selective hitchhiking and releasing antibiotic delivery system provides a promising strategy for the design of antibacterial nanomedicines.

Facile Synthesis of Self-Targeted Zn2+ -Gallic acid Nanoflowers for Specific Adhesion and Elimination of Gram-Positive Bacteria

Transition metal ions are served as disinfectant thousand years ago. However, the in vivo antibacterial application of metal ions is strongly restricted due to its high affinity with proteins and lack of appropriate bacterial targeting method. Herein, for the first time, Zn2+ -gallic acid nanoflowers (ZGNFs) are synthesized by a facile one-pot method without additional stabilizing agents. ZGNFs are stable in aqueous solution while can be easily decomposed in acidic environments. Besides, ZGNFs can specifically adhere onto Gram-positive bacteria, which is mediated by the interaction of quinone from ZGNFs and amino groups from teichoic acid of Gram-positive bacteria. ZGNFs exhibit high bactericidal effect toward various Gram-positive bacteria in multiple environments, which can be ascribed to the in situ Zn2+ release on bacterial surface. Transcriptome studies reveal that ZGNFs can disorder basic metabolic processes of Methicillin-resistant Staphylococcus aureus (MRSA). Moreover, in a MRSA-induced keratitis model, ZGNFs exhibit long-term retention in the infected corneal site and prominent MRSA elimination efficacy due to the self-targeting ability. This research not only reports an innovative method to prepare metal-polyphenol nanoparticles, but also provides a novel nanoplatform for targeted delivery of Zn2+ in combating Gram-positive bacterial infections.

Counterion-induced antibiotic-based small-molecular micelles for methicillin-resistant Staphylococcus aureus infections

A new counterion-induced small-molecule micelle (SM) with surface charge-switchable activities for methicillin-resistant Staphylococcus aureus (MRSA) infections is proposed. The amphiphilic molecule formed by zwitterionic compound and the antibiotic ciprofloxacin (CIP), via a "mild salifying reaction" of the amino and benzoic acid groups, can spontaneously assemble into counterion-induced SMs in water. Through vinyl groups designed on zwitterionic compound, the counterion-induced SMs could be readily cross-linked using mercapto-3, 6-dioxoheptane by click reaction, to create pH-sensitive cross-linked micelles (CSMs). Mercaptosuccinic acid was also decorated on the CSMs (DCSMs) by the same click reaction to afford charge-switchable activities, resulting in CSMs that were biocompatible with red blood cells and mammalian cells in normal tissues (pH 7.4), while having strong retention to negatively charged bacterial surfaces at infection sites, based on electrostatic interaction (pH 5.5). As a result, the DCSMs could penetrate deep into bacterial biofilms and then release drugs in response to the bacterial microenvironment, effectively killing the bacteria in the deeper biofilm. The new DCSMs have several advantages such as robust stability, a high drug loading content (∼ 30%), easy fabrication, and good structural control. Overall, the concept holds promise for the development of new products for clinical application. STATEMENT OF SIGNIFICANCE: We fabricated a new counterion-induced small-molecule micelle with surface charge-switchable activities (DCSMs) for methicillin-resistant Staphylococcus aureus (MRSA) infections. Compared with reported covalent systems, the DCSMs not only have improved stability, high drug loading content (∼ 30%), and good biosafety, but also have the environmental stimuli response, and antibacterial activity of the original drugs. As a result, the DCSMs exhibited enhanced antibacterial activities against MRSA both in vitro and in vivo. Overall, the concept holds promise for the development of new products for clinical application.

A clinical perspective of chitosan nanoparticles for infectious disease management

Infectious diseases and their effective management are still a challenge in this modern era of medicine. Diseases, such as the SARS-CoV-2, Ebola virus, and Zika virus, still put human civilization at peril. Existing drug banks, which include antivirals, antibacterial, and small-molecule drugs, are the most advocated method for treatment, although effective but they still flounder in many instances. This calls for finding more effective alternatives for tackling the menace of infectious diseases. Nanoformulations are progressively being implemented for clinical translation and are being considered a new paradigm against infectious diseases. Natural polymers like chitosan are preferred to design nanoparticles owing to their biocompatibility, biodegradation, and long shelf-life. The chitosan nanoparticles (CNPs) being highly adaptive delivers contemporary prevention for infectious diseases. Currently, they are being used as antibacterial, drug, and vaccine delivery vehicles, and wound-dressing materials, for infectious disease treatment. Although the recruitment of CNPs in clinical trials associated with infectious diseases is minimal, this may increase shortly due to the sudden emergence of unknown pathogens like SARS-CoV-2, thus turning them into a panacea for the management of microorganisms. This review particularly focuses on the all-around application of CNPs along with their recent clinical applications in infectious disease management.

Recent nanotechnology-based strategies for interfering with the life cycle of bacterial biofilms

Biofilm formation plays an important role in the resistance development in bacteria to conventional antibiotics. Different properties of the bacterial strains within biofilms compared with their planktonic states and the protective effect of extracellular polymeric substances contribute to the insusceptibility of bacterial cells to conventional antimicrobials. Although great effort has been devoted to developing novel antibiotics or synthetic antibacterial compounds, their efficiency is overshadowed by the growth of drug resistance. Developments in nanotechnology have brought various feasible strategies to combat biofilms by interfering with the biofilm life cycle. In this review, recent nanotechnology-based strategies for interfering with the biofilm life cycle according to the requirements of different stages are summarized. Additionally, the importance of strategies that modulate the bacterial biofilm microenvironment is also illustrated with specific examples. Lastly, we discussed the remaining challenges and future perspectives on nanotechnology-based strategies for the treatment of bacterial infection.

Dual-stimuli responsive smart nanoprobe for precise diagnosis and synergistic multi-modalities therapy of superficial squamous cell carcinoma

BACKGROUND

Although the promising advancements of current therapeutic approaches is available for the squamous cell carcinoma (SCC) patients, the clinical treatment of SCC still faces many difficulties. The surgical irreparable disfigurement and the postoperative wound infection largely hamper the recovery, and the chemo/radiotherapy leads to toxic side effects.

RESULTS

Herein, a novel pH/Hyaluronidase (HAase) dual-stimuli triggered smart nanoprobe Fe^IIITA@HA has been designed through the biomineralization of Fe³⁺ and polyphenol tannic acid (TA) under the control of hyaluronic acid (HA) matrix. With the HA residues on the outer surface, Fe^IIITA@HA nanoprobes can specifically target the SCC cells through the over-expressed CD44, and accumulate in the carcinoma region after intravenously administration. The abundant HAase in carcinoma microenvironment will trigger the degradation of HA molecules, thereby exposing the Fe^IIITA complex. After ingesting by tumor cells via CD44 mediated endocytosis, the acidic lysosomal condition will further trigger the protonation of TA molecules, finally leading to the Fe³⁺ release of nanoprobe, and inducing a hybrid ferroptosis/apoptosis of tumor cells through peroxidase activity and glutathione depletion. In addition, Owing to the outstanding T₁ magnetic resonance imaging (MRI) performance and phototermal conversion efficiency of nanoprobes, the MRI-guided photothermal therapy (PTT) can be also combined to complement the Fe³⁺-induced cancer therapy. Meanwhile, it was also found that the nanoprobes can promote the recruitment of CD4⁺ and CD8⁺ T cells to inhibit the tumor growth through the cytokines secretion. In addition, the Fe^IIITA@HA nanoprobes can be eliminated from the body and no obvious adverse side effect can be found in histological analysis, which confirmed the biosafety of them.

CONCLUSION

The current Fe^IIITA@HA nanoprobe has huge potential in clinical translation in the field of precise diagnosis and intelligent synergistic therapy of superficial SCC. This strategy will promisingly avoid the surgical defects, and reduce the systemic side effect of traditional chemotherapy, paving a new way for the future SCC treatment.

Recent Progress in Type I Aggregation-Induced Emission Photosensitizers for Photodynamic Therapy

In modern medicine, precision diagnosis and treatment using optical materials, such as fluorescence/photoacoustic imaging-guided photodynamic therapy (PDT), are becoming increasingly popular. Photosensitizers (PSs) are the most important component of PDT. Different from conventional PSs with planar molecular structures, which are susceptible to quenching effects caused by aggregation, the distinct advantages of AIE fluorogens open up new avenues for the development of image-guided PDT with improved treatment accuracy and efficacy in practical applications. It is critical that as much of the energy absorbed by optical materials is dissipated into the pathways required to maximize biomedical applications as possible. Intersystem crossing (ISC) represents a key step during the energy conversion process that determines many fundamental optical properties, such as increasing the efficiency of reactive oxygen species (ROS) production from PSs, thus enhancing PDT efficacy. Although some review articles have summarized the accomplishments of various optical materials in imaging and therapeutics, few of them have focused on how to improve the phototherapeutic applications, especially PDT, by adjusting the ISC process of organic optics materials. In this review, we emphasize the latest advances in the reasonable design of AIE-active PSs with type I photochemical mechanism for anticancer or antibacterial applications based on ISC modulation, as well as discuss the future prospects and challenges of them. In order to maximize the anticancer or antibacterial effects of type I AIE PSs, it is the aim of this review to offer advice for their design with the best energy conversion.

Nanomaterials for Delivering Antibiotics in the Therapy of Pneumonia

Bacterial pneumonia is one of the leading causes of death worldwide and exerts a significant burden on health-care resources. Antibiotics have long been used as first-line drugs for the treatment of bacterial pneumonia. However, antibiotic therapy and traditional antibiotic delivery are associated with important challenges, including drug resistance, low bioavailability, and adverse side effects; the existence of physiological barriers further hampers treatment. Fortunately, these limitations may be overcome by the application of nanotechnology, which can facilitate drug delivery while improving drug stability and bioavailability. This review summarizes the challenges facing the treatment of bacterial pneumonia and also highlights the types of nanoparticles that can be used for antibiotic delivery. This review places a special focus on the state-of-the-art in nanomaterial-based approaches to the delivery of antibiotics for the treatment of pneumonia.

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.

An inflammation-targeted nanoparticle with bacteria forced release of polymyxin B for pneumonia therapy

The epidemic of multidrug-resistant Gram-negative bacteria is an ever-growing global concern. Polymyxin B (PMB), a kind of "old fashioned" antibiotic, has been revived in clinical practice and mainly used as last-line antibiotics for otherwise untreatable serious infections because the incidence of the resistance to PMB is currently relatively low in comparison with other antibiotics in vivo owing to the unique bactericidal mechanism of PMB. However, serious adverse side effects, including nephrotoxicity and neurotoxicity, hamper its clinical application. Herein, we describe the development of a nanoparticle that can target sites of inflammation and forcedly release PMB specifically in the area of Gram-negative bacteria. This particle was constructed through the electrostatic self-assembly of hyaluronic acid (HA) and PMB molecules in order to realize the safe and effective treatment of pneumonia. After systemic administration, PMB-HA nanoparticles were found to actively accumulate in the lungs, precisely target the CD44 receptors over-expressed on the membrane of activated endothelial cells in inflammatory sites, and then come into contact with the bacteria resident in the damaged alveolar-capillary membrane. Due to the electrostatic and hydrophobic interactions between PMB and the lipopolysaccharide (LPS) in the outer membranes of bacteria, the PMB molecules in the PMB-HA nanoparticles are expected to escape from the nanoparticles to insert into the bacteria via competitive binding with LPS. Through shielding the cationic nature of PMB, PMB-HA nanoparticles also possess outstanding biosafety performance in comparison to free PMB. It is thus believed that this smart delivery system may pave a new way for the resurrection of PMB in the future clinical treatment of bacterial inflammatory diseases.

AIEgen Intercalated Nanoclay-Based Photodynamic/Chemodynamic Theranostic Platform for Ultra-Efficient Bacterial Eradication and Fast Wound Healing

With the emergence and global spread of bacterial resistance, pathogenic bacterial infections have become a serious threat to human health. Thus, therapeutic strategies with highly antibacterial efficacy and a low tendency to induce drug resistance are strongly desired to combat bacterial infections. Here, an ultra-efficient photodynamic/chemodynamic theranostics platform is developed by intercalating an aggregation-induced emission (AIE) photosensitizer, TPCI, into the nanolayers of iron-bearing montmorillonite (MMT). The formed TPCI/MMT composite can not only perform efficient photodynamic therapy (PDT) through a burst generation of singlet oxygen (¹O₂) upon white light illumination but also continuously implement chemodynamic therapy (CDT) by converting endogenous hydrogen peroxide into highly toxic hydroxyl radicals (^•OH) due to iron release. In addition, the fluorescence of TPCI/MMT can be activated due to the AIE feature of TPCI, which helps guide the location of the antimicrobials. The combination of such powerful bombs (PDT) and unremitting ambushes (CDT) in TPCI/MMT can synergistically and effectively eliminate bacteria and promote faster wound healing in vivo with good biocompatibility and low side effects. The smart and simple design of TPCI/MMT provides a representative paradigm for achieving efficient antimicrobials to combat the coming resistance crisis.

Nanostructure Control of an Antibiotic-based Polyion Complex Using a Series of Polycations with Different Side-chain Modification Rates

Developing nanovehicles for delivering antibiotics is a promising approach to overcome the issue of antibiotic resistance. This study aims to utilize a polyion complex (PICs) system for developing novel nanovehicles for polymyxin-type antibiotics, which are known as last resort drugs. The formation of antibiotic-based PIC nanostructures was investigated using colistimethate sodium (CMS), an anionic cyclic short peptide, and a series of block catiomers bearing different amounts of guanidinium moieties on their side chains. In addition, only the modified catiomer, and not the unmodified catiomer, self-assembles with CMS, implying the importance of the guanidine moieties for enhancing the interaction between the catiomer and CMS via the formation of multivalent hydrogen bonding. Moreover, micellar and vesicular PIC nanostructures are selectively formed depending on the ratio of the guanidine residues. Size-exclusion chromatography revealed that the encapsulation efficiency of CMS is dependent on the guanidinium modification ratio. The antimicrobial activity of the PIC nanostructures is also confirmed, indicating that the complexation of CMS in the PICs and further release from the PICs successfully occurs. This article is protected by copyright. All rights reserved.

Water soluble organometallic small molecules as promising antibacterial agents: synthesis, physical-chemical properties and biological evaluation to tackle bacterial infections

The Na[3,3'-Fe(8-I-1,2-C₂B₉H₁₀)₂] and Na[2,2'-M(1,7-C₂B₉H₁₁)] (M = Co³⁺, Fe³⁺) small molecules are synthesized and the X-ray structures of [(H₃O)(H₂O)₅][2,2'-Co(1,7-C₂B₉H₁₁)₂] and [Cs(MeCN)][8,8'-I₂-Fe(1,2 C₂B₉H₁₀)₂], both displaying a transoid conformation of the [M(C₂B₉)₂]^- framework, are reported. Importantly, the supramolecular structure of [(H₃O)(H₂O)₅][2,2'-Co(1,7-C₂B₉H₁₁)₂] presents 2D layers leading to a lamellar arrangement of the anions while the cation layers form polymeric water rings made of six- and four-membered rings of water molecules connected via OH⋯H hydrogen bonds; B-H⋯O contacts connect the cationic and anionic layers. Herein, we highlight the influence of the ligand isomers (ortho-/meta-), the metal effect (Co³⁺/Fe³⁺) on the same isomer, as well as the influence of the presence of the iodine atoms on the physical-chemical and biological properties of these molecules as antimicrobial agents to tackle antibiotic-resistant bacteria, which were tested with four Gram-positive bacteria, five Gram-negative bacteria, and three Candida albicans strains that have been responsible for human infections. We have demonstrated an antimicrobial effect against Candida species (MIC of 2 and 3 nM for Na[3,3'-Co(8-I-1,2-C₂B₉H₁₀)₂] and Na[2,2'-Co(1,7-C₂B₉H₁₁)₂], respectively), and against Gram-positive and Gram-negative bacteria, including multiresistant MRSA strains (MIC of 6 nM for Na[3,3'-Co(8-I-1,2-C₂B₉H₁₀)₂]). The selectivity index for antimicrobial activity of Na[3,3'-Co(1,2-C₂B₉H₁₁)₂] and Na[3,3'-Co(8-I-1,2-C₂B₉H₁₀)₂] compounds is very high (165 and 1180, respectively), which reveals that these small anionic metallacarborane molecules may be useful to tackle antibiotic-resistant bacteria. Moreover, we have demonstrated that the outer membrane of Gram-negative bacteria constitutes an impermeable barrier for the majority of these compounds. Nonetheless, the addition of two iodine groups in the structure of the parent Na[3,3'-Co(1,2-C₂B₉H₁₁)₂] had an improved effect (3-7 times) against Gram-negative bacteria. Possibly the changes in their physical-chemical properties make the meta-isomers and the ortho-di-iodinated small molecules more permeable for crossing this barrier. It should be emphasized that the most active metallabis(dicarbollide) small molecules are both transoid conformers in contrast to the ortho- [3,3'-Co(1,2-C₂B₉H₁₁)₂]^- that is cisoid. The fact that these small molecules cross the mammalian membrane and have antimicrobial properties but low toxicity for mammalian cells (high selectivity index, SI) represents a promising tool to treat infectious intracellular bacteria. Since there is an urgent need for antibiotic discovery and development, this study represents a relevant advance in the field.

Stimuli-responsive nanoplatforms for antibacterial applications

The continuously increasing bacterial resistance has become a big threat to public health worldwide, which makes it urgent to develop innovative antibacterial strategies. Nanotechnology-based drug delivery systems are considered as promising strategies in combating bacterial infections which are expected to improve the therapeutic efficacy and minimize the side effects. Unfortunately, the conventional nanodrug delivery systems always suffer from practical dilemmas, including incomplete and slow drug release, insufficient accumulation in infected sites, and weak biofilm penetration ability. Stimuli-responsive nanoplatforms are hence developed to overcome the disadvantages of conventional nanoparticles. In this review, we provide an extensive review of the recent progress of endogenous and exogenous stimuli-responsive nanoplatforms in the antibacterial area, including planktonic bacteria, intracellular bacteria, and bacterial biofilms. Taking advantage of the specific infected microenvironment (pH, enzyme, redox, and toxin), the mechanisms and strategies of the design of endogenous stimuli-responsive nanoplatforms are discussed, with an emphasis on how to improve the therapeutic efficacy and minimize side effects. How to realize controlled drug delivery using exogenous stimuli-responsive nanoplatforms especially light-responsive nanoparticles for improved antibacterial effects is another topic of this review. We especially highlight photothermal-triggered drug delivery systems by the combination of photothermal agents and thermo-responsive materials. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease Therapeutic Approaches and Drug Discovery > Emerging Technologies.

Charge reversal nano-systems for tumor therapy

Surface charge of biological and medical nanocarriers has been demonstrated to play an important role in cellular uptake. Owing to the unique physicochemical properties, charge-reversal delivery strategy has rapidly developed as a promising approach for drug delivery application, especially for cancer treatment. Charge-reversal nanocarriers are neutral/negatively charged at physiological conditions while could be triggered to positively charged by specific stimuli (i.e., pH, redox, ROS, enzyme, light or temperature) to achieve the prolonged blood circulation and enhanced tumor cellular uptake, thus to potentiate the antitumor effects of delivered therapeutic agents. In this review, we comprehensively summarized the recent advances of charge-reversal nanocarriers, including: (i) the effect of surface charge on cellular uptake; (ii) charge-conversion mechanisms responding to several specific stimuli; (iii) relation between the chemical structure and charge reversal activity; and (iv) polymeric materials that are commonly applied in the charge-reversal delivery systems.

Molecular Engineering of Polymyxin B for Imaging and Treatment of Bacterial Infections

The emergence of multi-drug resistant bacteria and the lack of novel antibiotics to combat them have led to the revival of polymyxin B, a previously abandoned antibiotic due to its potential nephrotoxicity and neurotoxicity. To facilitate its widely clinical applications, increasing effort has been devoted to molecularly engineer polymyxin B for the targeted imaging and effective treatment of bacterial infections. Herein, the molecular engineering strategies will be summarized in this mini review, with selected recent advances for illustration. Perspective of the challenges and trends in this exciting and eagerly anticipated research area will also be provided in the end. We hope this mini review will inspire researchers from diverse fields to bring forward the next wave of exploiting molecular engineering approaches to propel the “old” polymyxin B to “new” clinical significance in combating bacterial infections.

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...

Visualizing the Potential Impairment of Polymyxin B to Central Nervous System Through MR Susceptibility-Weighted Imaging

Polymyxin B (PMB) exert bactericidal effects on the cell wall of Gram-negative bacteria, leading to changes in the permeability of the cytoplasmic membrane and resulting in cell death, which is sensitive to the multi-resistant Gram-negative bacteria. However, the severe toxicity and adverse side effects largely hamper the clinical application of PMB. Although the molecular pathology of PMB neurotoxicity has been adequately studied at the cellular and molecular level. However, the impact of PMB on the physiological states of central nervous system in vivo may be quite different from that in vitro, which need to be further studied. Therefore, in the current study, the biocompatible ultra-uniform Fe3O4 nanoparticles were employed for noninvasively in vivo visualizing the potential impairment of PMB to the central nervous system. Systematic studies clearly reveal that the prepared Fe3O4 nanoparticles can serve as an appropriate magnetic resonance contrast agent with high transverse relaxivity and outstanding biosafety, which thus enables the following in vivo susceptibility-weighted imaging (SWI) studies on the PMB-treated mice models. As a result, it is first found that the blood-brain barrier (BBB) of mice may be impaired by successive PMB administration, displaying by the discrete punctate SWI signals distributed asymmetrically across brain regions in brain parenchyma. This result may pave a noninvasive approach for in-depth studies of PMB medication strategy, monitoring the BBB changes during PMB treatment, and even assessing the risk after PMB successive medication in multidrug-resistant Gram-negative bacterial infected patients from the perspective of medical imaging.

Aggregation-Induced Emission-Based Platforms for the Treatment of Bacteria, Fungi, and Viruses

The prevention and control of pathogenic bacteria, fungi, and viruses is a herculean task for all the countries since they greatly threaten global public health. Rapid detection and effective elimination of these pathogens is crucial for the treatment of related diseases. It is urgently demanded to develop new diagnostic and therapeutic strategies to combat bacteria, fungi, and viruses-induced infections. The emergence of aggregation-induced emission (AIE) luminogens (AIEgens) is a revolutionary breakthrough for the treatment of many diseases, including pathogenic infections. In this review, the main focus is on the applications of AIEgens for theranostic treatment of pathogenic bacteria, fungi, and viruses. Due to the AIE characteristic, AIEgens are promising fluorescent probes for the detection of bacteria, fungi, and viruses with excellent sensitivity and photostability. Moreover, AIEgen-based theranostic platforms can be fabricated by introducing bactericidal moieties or designing AIE photosensitizers and AIE photothermal agents. The current strategies and ongoing developments of AIEgens for the treatment of pathogenic bacteria, fungi, and viruses will be discussed in detail.

Current Advances in Lipid and Polymeric Antimicrobial Peptide Delivery Systems and Coatings for the Prevention and Treatment of Bacterial Infections

Bacterial infections constitute a threat to public health as antibiotics are becoming less effective due to the emergence of antimicrobial resistant strains and biofilm and persister formation. Antimicrobial peptides (AMPs) are considered excellent alternatives to antibiotics; however, they suffer from limitations related to their peptidic nature and possible toxicity. The present review critically evaluates the chemical characteristics and antibacterial effects of lipid and polymeric AMP delivery systems and coatings that offer the promise of enhancing the efficacy of AMPs, reducing their limitations and prolonging their half-life. Unfortunately, the antibacterial activities of these systems and coatings have mainly been evaluated in vitro against planktonic bacteria in less biologically relevant conditions, with only some studies focusing on the antibiofilm activities of the formulated AMPs and on the antibacterial effects in animal models. Further improvements of lipid and polymeric AMP delivery systems and coatings may involve the functionalization of these systems to better target the infections and an analysis of the antibacterial activities in biologically relevant environments. Based on the available data we proposed which polymeric AMP delivery system or coatings could be profitable for the treatment of the different hard-to-treat infections, such as bloodstream infections and catheter- or implant-related infections.

Synthetic Mimics of Antimicrobial Peptides for the Targeted Therapy of Multidrug-Resistant Bacterial Infection

Antibacterial materials are highly demanded in treatment of bacterial infection, especially severe ones with multidrug-resistance. Herein, pH-responsive polypeptide, i.e., poly-L-lysine modified by 1-(propylthio)acetic acid-3-octylimidazolium and citraconic anhydride (PLL-POIM-CA), is synthesized by post-polymerization modification of poly-L-lysine (PLL) with 1-(propylthio)acetic acid-3-octylimidazolium (POIM) and citraconic anhydride (CA). It is observed that PLL-POIM-CA is stable under normal physiological condition, while CA cleaves rapidly at weakly acidic environment like bacterial infectious sites. The hydrolyzed PLL-POIM-CA exhibits excellent broad-spectrum antibacterial activities against Gram-negative bacteria of Escherichia coli and Gram-positive bacteria of Staphylococcus aureus and methicillin-resistant Staphylococcus aureus (MRSA). In particular, the minimum inhibitory concentration (MIC) against multidrug-resistant bacteria like MRSA is as low as 7.8 µg mL^-1 . Moreover, PLL-POIM-CA exhibits good biocompatibility with mouse fibroblast cells (L929) in vitro and improved hemocompatibility with an HC₅₀ exceeding 5000 µg mL^-1 . Therefore, PLL-POIM-CA displays an excellent bacteria versus cells selectivity (HC₅₀ /MIC) over 534, which is 53 times higher than natural antimicrobial peptide of indolicidin. It is further demonstrated in vivo that the antimicrobial polypeptide effectively accelerates MRSA-infected wound healing by relieving local inflammatory response. Therefore, this targeted antimicrobial polypeptide has broad application prospects for the treatment of multidrug-resistant bacterial infection.

In vitro/vivo antitumor study of modified-chitosan/carboxymethyl chitosan "boosted" charge-reversal nanoformulation

Major obstacles in the development of nanoformulations as efficient drug delivery systems are the rapid clearance from blood circulation and lysosomal entrapment. To overcome these problems, a polysaccharide-based core-shell type charge-switchable nanoformulation (CS-LA-DMMA/CMCS/PAMAM@DOX) is constructed to improve antitumor efficacy of DOX. By applying carboxymethyl chitosan (CMCS) as bridge polymer and negatively charged chitosan-derivative as outer shell, the stability and pH-sensitivity of this nanoformulation is promisingly enhanced. Furthermore, the positively charged PAMAM@DOX could escape from lysosomes via "proton sponge effect" and "cationic-anionic interaction with lysosome membranes". Admirable cellular uptake and high apoptosis/necrosis rate were detected in this study. In vitro assays demonstrate that the CS-LA-DMMA/CMCS/PAMAM@DOX was internalized into HepG2 cells predominantly via the clathrin-mediated endocytosis pathway. Excitingly, in vivo studies showed that high accumulation of CS-LA-DMMA/CMCS/PAMAM@DOX in tumor tissue led to enhanced tumor inhibition. Compared with free DOX, the tumor inhibition rate of nanoformulation was improved up to 226%.

Nanoparticles Enable Efficient Delivery of Antimicrobial Peptides for the Treatment of Deep Infections

Abstract Antimicrobial peptides (AMPs) have emerged as promising alternatives of traditional antibiotics against drug-resistant bacteria owing to their broad-spectrum antimicrobial properties and low tendency to drug resistance. However, their therapeutic efficacy in vivo, especially for infections in deep organs, is limited owing to their systemic toxicity and low bioavailability. Nanoparticles-based delivery systems offer a strategy to increase the therapeutic index of AMPs by preventing proteolysis, increasing the accumulation at infection sites, and reducing toxicity. Herein, we will discuss the current progress of using nanoparticles as delivery vehicles for AMPs for the treatment of deep infections.Statement of significanceAntimicrobial peptides (AMPs) are rarely directly used to treat deep infections due to their systemic toxicity and low bioavailability. This review summarizes recent progress that researchers employed nanoparticles-based delivery systems to deliver AMPs for the treatment of deep infections. Nanoparticles-based delivery systems offer a strategy to increase the therapeutic index of AMPs by preventing proteolysis, increasing the accumulation at infection sites, and reducing toxicity. Especially, the development of intelligent nanocarriers can achieve selective activation and active target in the infectious sites, thus improving the therapeutic efficacy against bacterial infection and reducing the toxicity against normal tissues.

Phenylboronic acid-conjugated chitosan nanoparticles for high loading and efficient delivery of curcumin

In order to achieve high loading and efficient delivery of curcumin, phenylboronic acid-conjugated chitosan nanoparticles were prepared by a simple desolvation method. These nanoparticles exhibited a regular spherical shape with the average size about 200-230 nm and narrow size distribution, which were kinetically stable under physiological condition. Due to boronate ester formation between curcumin and phenylboronic acid groups in the nanoparticles, and the hydrogen bonding interactions between curcumin and nanocarriers, curcumin was successfully loaded into the nanoparticles with high drug loading content. These curcumin-loaded nanoparticles showed pH and reactive oxygen species (ROS)-triggered drug release behavior. In vitro cell experiments revealed that the blank nanoparticles were completely nontoxic to cultured cells, and the curcumin-loaded nanoparticles exhibited efficient antitumor efficiency against cancer cells. Moreover, the drug-loaded nanoparticles performed an enhanced growth inhibition in three-dimensional multicellular tumor spheroids. Thus, these nanocarriers would be a promising candidate for curcumin delivery in tumor treatment.

Lactobionic acid-modified thymine-chitosan nanoparticles as potential carriers for methotrexate delivery

In order to achieve efficient delivery of methotrexate (MTX), thymine-chitosan nanoparticles (Thy-Cs NPs) were prepared, and further decorated with lactobionic acid (LA) to obtain tumor-targeting nanoparticles (LA-Thy-Cs NPs). These nanoparticles possessed a regular spherical structure with the average size about 190-250 nm and narrow size distribution, which were kinetically stable in the physiological environment. Due to electrostatic interactions and multiple hydrogen-bonding interactions between MTX and carriers, MTX was loaded into Thy-Cs NPs with high drug loading content (~20%). MTX release from Thy-Cs NPs was significantly accelerated in the mildly acidic environment due to the destruction of two types of non-covalent interactions. In vitro cell experiments demonstrated that LA-Thy-Cs NPs could be efficiently internalized into hepatoma carcinoma cells, leading to higher cytotoxicity. Moreover, MTX-loaded LA-Thy-Cs NPs performed an enhanced growth inhibition in three-dimensional multicellular tumor spheroids. Thus, the LA decorated thymine-chitosan nanocarriers can be a promising candidate for efficient delivery of MTX.

An overview of chitosan and its application in infectious diseases

Infectious diseases, such as the coronavirus disease-19, SARS virus, Ebola virus, and AIDS, threaten the health of human beings globally. New viruses, drug-resistant bacteria, and fungi continue to challenge the human efficacious drug bank. Researchers have developed a variety of new antiviral and antibacterial drugs in response to the infectious disease crisis. Meanwhile, the development of functional materials has also improved therapeutic outcomes. As a natural material, chitosan possesses good biocompatibility, bioactivity, and biosafety. It has been proven that the cooperation between chitosan and traditional medicine greatly improves the ability of anti-infection. This review summarized the application and design considerations of chitosan-composed systems for the treatment of infectious diseases, looking forward to providing the idea of infectious disease therapy.

Functionalized biomaterials to combat biofilms

Pathogenic microbial biofilms that readily form on implantable medical devices or human tissues have posed a great threat to worldwide healthcare. Hopes are focused on preventive strategies towards biofilms, leaving a thought-provoking question: how to tackle the problem of established biofilms? In this review, we briefly summarize the functionalized biomaterials to combat biofilms and highlight current approaches to eradicate pre-existing biofilms. We believe that all of these strategies, alone or in combination, could represent a blueprint for fighting biofilm-associated infections in the postantibiotic era.

Recent advances: peptides and self-assembled peptide-nanosystems for antimicrobial therapy and diagnosis

Bacterial infections, especially the refractory treatment of drug-resistant bacteria, are one of the greatest threats to human health. Self-assembling peptide-based strategies can specifically detect the bacteria at the site of infection in the body and kill it.

Emerging antibacterial nanomedicine for enhanced antibiotic therapy

This review highlights the different mechanisms of current nano-antibiotic systems for combatting serious antibiotic resistance of bacteria.