Bacteria-responsive multifunctional nanogel for targeted antibiotic delivery

Microgels and hydrogels as delivery systems for antimicrobial peptides

Due to rapid development of bacterial resistance against antibiotics, an emerging health crisis is underway, where 'simple' infections may no longer be treatable. Antimicrobial peptides (AMPs) constitute a class of substances attracting interest in this context. So far, research on AMPs has primarily focused on the identification of potent and selective peptides, as well as on the action mode of such peptides. More recently, there has been an increasing awareness that the delivery of AMPs is challenging due to their size, net positive charge, amphiphilicity, and proteolytic susceptibility. Hence, successful development of AMP therapeutics will likely require also careful design of efficient AMP delivery systems. In the present brief review, we discuss microgels, as well as related polyelectrolyte complexes and macroscopic hydrogels, as delivery systems for AMPs. In doing so, key factors for peptide loading and release are outlined and exemplified, together with consequences of this for functional performance relating to antimicrobial effects and cell toxicity.

A New Antibiotic-Loaded Sol-Gel Can Prevent Bacterial Prosthetic Joint Infection: From in vitro Studies to an in vivo Model

The aim of this study was to evaluate the effect of a moxifloxacin-loaded organic-inorganic sol-gel with different antibiotic concentration in the in vitro biofilm development and treatment against Staphylococcus aureus, S. epidermidis, and Escherichia coli, cytotoxicity and cell proliferation of MC3T3-E1 osteoblasts; and its efficacy in preventing the prosthetic joint infection (PJI) caused by clinical strains of S. aureus and E. coli using an in vivo murine model. Three bacterial strains, S. epidermidis ATCC 35984, S. aureus 15981, and, E. coli ATCC 25922, were used for microbiological studies. Biofilm formation was induced using tryptic-soy supplemented with glucose for 24 h, and then, adhered and planktonic bacteria were estimated using drop plate method and absorbance, respectively. A 24-h-mature biofilm of each species growth in a 96-well plate was treated for 24 h using a MBECTM biofilm Incubator lid with pegs coated with the different types of sol-gel, after incubation, biofilm viability was estimated using alamrBlue. MC3T3-E1 cellular cytotoxicity and proliferation were evaluated using CytoTox 96 Non-Radioactive Cytotoxicity Assay and alamarBlue, respectively. The microbiological studies showed that sol-gel coatings inhibited the biofilm development and treated to a mature biofilm of three evaluated bacterial species. The cell studies showed that the sol-gel both with and without moxifloxacin were non-cytotoxic and that cell proliferation was inversely proportional to the antibiotic concentration containing by sol-gel. In the in vivo study, mice weight increased over time, except in the E. coli-infected group without coating. The most frequent symptoms associated with infection were limping and piloerection; these symptoms were more frequent in infected groups with non-coated implants than infected groups with coated implants. The response of moxifloxacin-loaded sol-gel to infection was either total or completely absent. No differences in bone mineral density were observed between groups with coated and non-coated implants and macrophage presence lightly increased in the bone grown directly in contact with the antibiotic-loaded sol-gel. In conclusion, moxifloxacin-loaded sol-gel coating is capable of preventing PJI caused by both Gram-positive and Gram-negative species.

Pillar[5]arene-based, dual pH and enzyme responsive supramolecular vesicles for targeted antibiotic delivery against intracellular MRSA

A rationally designed mannosylated amphiphilic pillar[5]arene (Man@AP5) self-assembles into supramolecular vesicles with encapsulated vancomycin (Man@AP5-Van), enhancing vancomycin's antibacterial efficacy against intracellular MRSA.

Role and modulation of the secondary structure of antimicrobial peptides to improve selectivity

Helix is a two-edged sword for AMPs, and conformational modulation of AMPs can control the balance between antimicrobial activity and toxicity.

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.

Overcoming Hurdles in Nanoparticle Clinical Translation: The Influence of Experimental Design and Surface Modification

Nanoparticles are becoming an increasingly popular tool for biomedical imaging and drug delivery. While the prevalence of nanoparticle drug-delivery systems reported in the literature increases yearly, relatively little translation from the bench to the bedside has occurred. It is crucial for the scientific community to recognize this shortcoming and re-evaluate standard practices in the field, to increase clinical translatability. Currently, nanoparticle drug-delivery systems are designed to increase circulation, target disease states, enhance retention in diseased tissues, and provide targeted payload release. To manage these demands, the surface of the particle is often modified with a variety of chemical and biological moieties, including PEG, tumor targeting peptides, and environmentally responsive linkers. Regardless of the surface modifications, the nano-bio interface, which is mediated by opsonization and the protein corona, often remains problematic. While fabrication and assessment techniques for nanoparticles have seen continued advances, a thorough evaluation of the particle's interaction with the immune system has lagged behind, seemingly taking a backseat to particle characterization. This review explores current limitations in the evaluation of surface-modified nanoparticle biocompatibility and in vivo model selection, suggesting a promising standardized pathway to clinical translation.

Carbohydrate-based nanocarriers and their application to target macrophages and deliver antimicrobial agents

Many deadly infections are produced by microorganisms capable of sustained survival in macrophages. This reduces exposure to chemadrotherapy, prevents immune detection, and is akin to criminals hiding in police stations. Therefore, the use of glyco-nanoparticles (GNPs) as carriers of therapeutic agents is a burgeoning field. Such an approach can enhance the penetration of drugs into macrophages with specific carbohydrate targeting molecules on the nanocarrier to interact with macrophage lectins. Carbohydrates are natural biological molecules and the key constituents in a large variety of biological events such as cellular communication, infection, inflammation, enzyme trafficking, cellular migration, cancer metastasis and immune functions. The prominent characteristics of carbohydrates including biodegradability, biocompatibility, hydrophilicity and the highly specific interaction of targeting cell-surface receptors support their potential application to drug delivery systems (DDS). This review presents the 21^st century development of carbohydrate-based nanocarriers for drug targeting of therapeutic agents for diseases localized in macrophages. The significance of natural carbohydrate-derived nanoparticles (GNPs) as anti-microbial drug carriers is highlighted in several areas of treatment including tuberculosis, salmonellosis, leishmaniasis, candidiasis, and HIV/AIDS.

Targeting of Nanotherapeutics to Infection Sites for Antimicrobial Therapy

Bacterial infections cause a wide range of host immune disorders, resulting in local and systemic tissue damage. Antibiotics are pharmacological interventions for treating bacterial infections, but increased antimicrobial resistance and the delayed development of new antibiotics have led to a major global health threat, the so-called "superbugs". Bacterial infections consist of two processes: pathogen invasion and host immune responses. Developing nanotherapeutics to target these two pathways may be effective for eliminating bacteria and restoring host homeostasis, thus possibly finding new treatments for bacterial infections. This review offers new approaches for developing nanotherapeutics based on the pathogenesis of infectious diseases. We have discussed how nanoparticles target infectious microenvironments (IMEs) and how they target phagocytes to deliver antibiotics to eliminate intracellular pathogens. We also review a new concept-host-directed therapy for bacterial infections, such as targeting immune cells for the delivery of anti-inflammatory agents and vaccine developments using bacterial membrane-derived nanovesicles. This review demonstrates the translational potential of nanomedicine for improving infectious disease treatments.

Recent Advances and Future Prospects on Adaptive Biomaterials for Antimicrobial Applications

Bacterial infection is becoming the biggest threat to human health. The scenario is partly due to the ineffectiveness of the conventional antibiotic treatments against the emergence of multidrug-resistant bacteria and partly due to the bacteria living in biofilms or cells. Adaptive biomaterials can change their physicochemical properties in the microenvironment of bacterial infection, thereby facilitating either their interactions with bacteria or drug release. The trends in treating bacterial infections using adaptive biomaterials-based systems are flourishing and generate innumerous possibility to design novel antimicrobial therapeutics. This feature article aims to summarize the recent developments in the formulations, mechanisms, and advances of adaptive materials in bacterial infection diagnosis, contact killing of bacteria, and antimicrobial drug delivery. Also, the challenges and limitations of current antimicrobial treatments based on adaptive materials and their clinical and industrial future prospects are discussed.

Endogenous stimulus-powered antibiotic release from nanoreactors for a combination therapy of bacterial infections

The use of an endogenous stimulus instead of external trigger has an advantage for targeted and controlled release in drug delivery. Here, we report on cascade nanoreactors for bacterial toxin-triggered antibiotic release by wrapping calcium peroxide (CaO2) and antibiotic in a eutectic mixture of two fatty acids and a liposome coating. When encountering pathogenic bacteria in vivo these nanoreactors capture the toxins, without compromising their structural integrity, and the toxins form pores. Water enters the nanoreactors through the pores to react with CaO2 and produce hydrogen peroxide which decomposes to oxygen and drives antibiotic release. The bound toxins reduce the toxicity and also stimulate the body's immune response. This works to improve the therapeutic effect in bacterially infected mice. This strategy provides a Domino Effect approach for treating infections caused by bacteria that secrete pore-forming toxins.

An AIEgen-Peptide Conjugate as a Phototheranostic Agent for Phagosome-Entrapped Bacteria

The detection and elimination of intracellular bacteria remain a major challenge. In this work, we report an aggregation-induced emission (AIE) bioprobe that can detect bacterial infection and kill bacteria surviving inside macrophages through a dynamic process, notably specific molecular tailoring of the probe by caspase-1 activation in infected macrophages and accumulation of the residue on phagosomes containing bacteria, leading to light-up fluorescent signals. Moreover, the AIEgen can serve as a photosensitizer for generation of reactive oxygen species (ROS); and the average ROS indicator fluorescent signal intensity per unit area in the bacterial phagosomes is approximately 2.7-fold higher than that in the cytoplasm. This, in turn, induces bacteria killing with high efficiency and minimal cytotoxicity towards macrophages. We envision that this specific light-up bioprobe may provide a new approach for selective and sensitive detection and eradication of intracellular bacterial infections.

Bioinspired Liposomes for Oral Delivery of Colistin to Combat Intracellular Infections by Salmonella enterica

Bacterial invasion into eukaryotic cells and the establishment of intracellular infection has proven to be an effective means of resisting antibiotic action, as anti-infective agents commonly exhibit a poor permeability across the host cell membrane. Encapsulation of anti-infectives into nanoscaled delivery systems, such as liposomes, is shown to result in an enhancement of intracellular delivery. The aim of the current work is, therefore, to formulate colistin, a poorly permeable anti-infective, into liposomes suitable for oral delivery, and to functionalize these carriers with a bacteria-derived invasive moiety to enhance their intracellular delivery. Different combinations of phospholipids and cholesterol are explored to optimize liposomal drug encapsulation and stability in biorelevant media. These liposomes are then surface-functionalized with extracellular adherence protein (Eap), derived from Staphylococcus aureus. Treatment of HEp-2 and Caco-2 cells infected with Salmonella enterica using colistin-containing, Eap-functionalized liposomes resulted in a significant reduction of intracellular bacteria, in comparison to treatment with nonfunctionalized liposomes as well as colistin alone. This indicates that such bio-invasive carriers are able to facilitate intracellular delivery of colistin, as necessary for intracellular anti-infective activity. The developed Eap-functionalized liposomes, therefore, present a promising strategy for improving the therapy of intracellular infections.

An enzyme-responsive membrane for antibiotic drug release and local periodontal treatment

Periodontitis is a chronic, destructive inflammatory disease that injures tooth- supporting tissues, eventually leading to tooth loss. Complete eradication of periodontal pathogenic microorganisms is fundamental to allow periodontal healing and commonly precedes periodontal tissue regeneration. To address this challenge, we report a strategy for developing an enzyme-mediated periodontal membrane for targeted antibiotic delivery into infectious periodontal pockets; the unique components of the membrane will also benefit periodontal alveolar bone repair. In this approach, a chitosan membrane containing polyphosphoester and minocycline hydrochloride (PPEM) was prepared. Physical, morphological, and ultrastructural analyses were carried out in order to assess cellular compatibility, drug release and antibacterial activity in vitro. Additionally, the functionality of the PPEM membrane was evaluated in vivo with a periodontal defect model in rats. The results confirm that the PPEM membrane exhibits good physical properties with excellent antibacterial activity and successfully promotes periodontal tissue repair, making it promising for periodontal treatment.

O-Mannosylation Affords a Glycopeptide Hydrogel with Inherent Antibacterial Activities against E. coli via Multivalent Interactions between Lectins and Supramolecular Assemblies

Multivalent carbohydrate-lectin interactions play a crucial role in bacterial infection. Biomimicry of multivalent glycosystems represents a major strategy in the repression of bacterial growth. In this study, a new kind of glycopeptide (Naphthyl-Phe-Phe-Ser-Tyr, NMY) scaffold with mannose modification is designed and synthesized, which is able to perform supramolecular self-assembly with the assistance of catalytic enzyme, and present multiple mannose ligands on its self-assembled structure to target mannose-binding proteins. Relying on multivalent carbohydrate-lectin interactions, the glycopeptide hydrogel is able to bind Escherichia coli (E. coli) in high specificity, and result in bacterial adhesion, membrane disruption and subsequent cell death. In vivo wound healing assays reveal that this glycopeptide hydrogel exhibits considerable potentials for promoting wound healing and preventing E. coli infection in a full-thickness skin defect mouse model. Therefore, through a specific mannose-lectin interaction, a biocompatible hydrogel with inherent antibacterial activity against E. coli is achieved without the need to resort to antibiotic or antimicrobial agent treatment, highlighting the potential role of sugar-coated nanomaterials in wound healing and control of bacterial pathogenesis.

Biodegradable Antibacterial Polymeric Nanosystems: A New Hope to Cope with Multidrug-Resistant Bacteria

The human society is faced with daunting threats from bacterial infections. Over decades, a variety of antibacterial polymeric nanosystems have exhibited great promise for the eradication of multidrug-resistant bacteria and persistent biofilms by enhancing bacterial recognition and binding capabilities. In this Review, the "state-of-the-art" biodegradable antibacterial polymeric nanosystems, which could respond to bacteria environments (e.g., acidity or bacterial enzymes) for controlled antibiotic release or multimodal antibacterial treatment, are summarized. The current antibacterial polymeric nanosystems can be categorized into antibiotic-containing and intrinsic antibacterial nanosystems. The antibiotic-containing polymeric nanosystems include antibiotic-encapsulated nanocarriers (e.g., polymeric micelles, vesicles, nanogels) and antibiotic-conjugated polymer nanosystems for the delivery of antibiotic drugs. On the other hand, the intrinsic antibacterial polymer nanosystems containing bactericidal moieties such as quaternary ammonium groups, phosphonium groups, polycations, antimicrobial peptides (AMPs), and their synthetic mimics, are also described. The biodegradability of the nanosystems can be rendered by the incorporation of labile chemical linkages, such as carbonate, ester, amide, and phosphoester bonds. The design and synthesis of the degradable polymeric building blocks and their fabrications into nanosystems are also explicated, together with their plausible action mechanisms and potential biomedical applications. The perspectives of the current research in this field are also described.

Functional selenium modified microgels: temperature-induced phase transitions and network morphology

Microgels that host selenium and mimic the structure of the enzyme glutathione peroxidase are of great interest for biotechnological and catalytic applications. For this purpose selenium-functionalized thermoresponsive poly(N-vinylcaprolactam) (PVCL) microgels with cleavable diselenide crosslinks have been investigated. Thermodynamic and morphological parameters characterizing the temperature-induced phase transitions of dual crosslinked PVCL microgels were obtained using dynamic light scattering (DLS), 1H high-resolution magic-angle sample-spinning (MAS) NMR spectroscopy, and transverse magnetization (T2) NMR relaxometry. Quantities obtained from Flory-Rehner theory, a two-state model and Boltzmann sigmoidal function were used to relate the phase transitions of the dual crosslinked microgels to the transition temperature, entropy, temperature width of the phase transition, Flory interaction parameters, average number of strands, polymer volume fraction of the collapsed microgels, core-corona fractions and chain dynamics. The morphology of the selenium modified microgels after the oxidation and reduction processes was investigated by 1H T2 NMR and further correlated with the crosslink density.

Nanoparticles: Antimicrobial Applications and Its Prospects

Nowadays, nanomaterials [NPs; size, 1–100 nm] have emerged as unique antimicrobial agents. Specially, several classes of antimicrobial NPs and nanosized carriers for antibiotic delivery have proven their efficacy for handling infectious diseases, including antibiotic-resistant ones, in vitro as well as in animal models, which can offer better therapy than classical drugs due to their high surface area-to-volume ratio, resulting in appearance of new mechanical, chemical, electrical, optical, magnetic, electro-optical, and magneto-optical properties, unlike from their bulk properties. Thus, scientifically NPs have been validated to be fascinating in fighting bacteria. In this chapter, we will discuss precise properties of microorganisms and their modifications among each strain specifically. The toxicity mechanisms vary from one stain to another. Even the NP’s efficacy to treat against bacteria and drug-resistant bacteria and their defense mechanisms change according to strains in particular composition of cell walls, the enzymic composition, and so on. Thus, we provide an outlook on NPs in the microbial world and mechanism to overcome the drug resistance by tagging antibiotics in NPs and its future prospects for the scientific world.

Bacteria-Responsive Single and Core-Shell Nanofibrous Membranes Based on Polycaprolactone/Poly(ethylene succinate) for On-Demand Release of Biocides

Traditional antibacterial dressings continuously elute biocides, even if there are no bacteria. This unneeded release can cause cytotoxicity, increase costs, and delay healing. We designed a bacteria-responsive nanofibrous wound dressing, which can be degraded in the presence of bacteria to release antimicrobial agents. A model biocide, benzyl dimethyl tetradecyl ammonium chloride (BTAC), was incorporated into bacteria-degradable polymers [polycaprolactone and poly(ethylene succinate)] in two ways: evenly distributed inside the polymers as single nanofibers and encapsulated in a core surrounded by the same polymers as core-shell nanofibers. Because of bacterial activity (both lipase secretion and acidic pH), degradation of the fibers was facilitated and caused the release of incorporated BTAC. BTAC-loaded single and core-shell nanofibers presented >1 log reduction of both Staphylococcus aureus and Escherichia coli within 2 h. Additionally, the core-shell structure provided a more controlled release of BTAC with prolonged antibacterial properties than single nanofibers. The core-shell nanofibers also exhibited minimal cytotoxicity against human fibroblast cells (>80% viable cells after 24 h contact). These nanofibrous mats have the potential to selectively release antibacterial agents to prevent wound infections without delaying wound healing.

Kill the Real with the Fake: Eliminate Intracellular Staphylococcus aureus Using Nanoparticle Coated with Its Extracellular Vesicle Membrane as Active-Targeting Drug Carrier

Staphylococcus aureus bacteremia is one of the most serious bacterial infections worldwide. Most complications of S. aureus bacteremia arise because the pathogen can survive inside host phagocytes, especially macrophages, which makes elimination of intracellular S. aureus key to clinical success. Unfortunately, most antibiotics have poor cellular penetration capacity, which necessitates intracellular delivery of antibiotics. We herein use nanoparticle coated with membrane of extracellular vesicle secreted by S. aureus (i.e., NP@EV) as active-targeting antibiotic carrier, with counterparts coated with PEGylated lipid bilayer (i.e., NP@Lipo; PEG = poly(ethylene glycol)) or with membrane of outer membrane vesicle secreted by Escherichia coli (i.e., NP@OMV) included as controls. NP@EV is internalized at higher efficiency by S. aureus-infected macrophage than by naïve counterpart, whereas NP@Lipo and NP@OMV are not; instead, NP@OMV, but neither NP@EV nor NP@Lipo, is internalized at higher efficiency by E. coli-infected macrophage than by naïve counterpart. Moreover, when injected intravenously into mouse models, NP@EV, but neither NP@OMV nor NP@Lipo, exhibits significantly higher accumulations within four major organs (kidney, lung, spleen, and heart) bearing metastatic S. aureus infections than within healthy counterparts. These observations suggest that EV membrane coating of NP@EV endows the particle with active targeting capacity both in vitro and in vivo. As a result, when preloaded with antibiotics and intravenously administered to alleviate metastatic infection in S. aureus bacteremia-bearing mouse model, NP@EV confers its cargoes with strikingly improved efficacy; in doing so, NP@EV is significantly more efficient than both NP@Lipo and NP@OMV in kidney and lung-which bear the highest metastatic bacterial burden and represent most common sites for S. aureus infection, respectively. Such an active-targeting delivery platform may have implications in promoting clinical success on intracellular pathogen-associated complications.

Promising Recent Strategies with Potential Clinical Translational Value to Combat Antibacterial Resistant Surge

Multiple drug resistance (MDR) for the treatment of bacterial infection has been a significant challenge since the beginning of the 21st century. Many of the small molecule-based antibiotic treatments have failed on numerous occasions due to a surge in MDR, which has claimed millions of lives worldwide. Small particles (SPs) consisting of metal, polymer or carbon nanoparticles (NPs) of different sizes, shapes and forms have shown considerable antibacterial effect over the past two decades. Unlike the classical small-molecule antibiotics, the small particles are less exposed so far to the bacteria to trigger a resistance mechanism, and hence have higher chances of fighting the challenge of the MDR process. Until recently, there has been limited progress of clinical treatments using NPs, despite ample reports of in vitro antibacterial efficacy. In this review, we discuss some recent and unconventional strategies that have explored the antibacterial efficacy of these small particles, alone and in combination with classical small molecules in vivo, and demonstrate possibilities that are favorable for clinical translations in near future.

Multifunctional Coatings and Nanotopographies: Toward Cell Instructive and Antibacterial Implants

In biomaterials science, it is nowadays well accepted that improving the biointegration of dental and orthopedic implants with surrounding tissues is a major goal. However, implant surfaces that support osteointegration may also favor colonization of bacterial cells. Infection of biomaterials and subsequent biofilm formation can have devastating effects and reduce patient quality of life, representing an emerging concern in healthcare. Conversely, efforts toward inhibiting bacterial colonization may impair biomaterial-tissue integration. Therefore, to improve the long-term success of medical implants, biomaterial surfaces should ideally discourage the attachment of bacteria without affecting eukaryotic cell functions. However, most current strategies seldom investigate a combined goal. This work reviews recent strategies of surface modification to simultaneously address implant biointegration while mitigating bacterial infections. To this end, two emerging solutions are considered, multifunctional chemical coatings and nanotopographical features.

Design of smart targeted and responsive drug delivery systems with enhanced antibacterial properties

The use of antibiotics has been an epoch-making invention in the past few decades for the treatment of infectious diseases. However, the intravenous injection of antibiotics lacking responsiveness and targeting properties has led to low drug utilization and high cytotoxicity. More importantly, it has also caused the development and spread of drug-resistant bacteria due to repeated medication and increased dosage. The differences in the microenvironments of the bacterial infection sites and normal tissues, such as lower pH, high expression of some special enzymes, hydrogen peroxide and released toxins, etc., are usually used for targeted and controlled drug delivery. In addition, bacterial surface charges, antigens and the surface structures of bacterial cell walls are all different from normal tissue cells. Based on the special bacterial infection microenvironments and bacteria surface properties, a series of drug delivery systems has been constructed for highly efficient drug release. This review summarizes the recent progress in targeted and responsive drug delivery systems for enhanced antibacterial properties.

Chemotaxis-Instructed Intracellular Staphylococcus aureus Infection Detection by a Targeting and Self-Assembly Signal-Enhanced Photoacoustic Probe

Intracellular invasion and the survival of Staphylococcus aureus in phagocytic cells has been regarded as one of the mechanisms that leads to the treatment failure of S. aureus infection and potential antibiotic resistance. The detection of infected phagocytic cells plays an important role in guiding antibiotic treatment and in reducing drug resistance. The development of a sensitive and specific imaging probe to visualize the intracellular bacteria is quite challenging. In this work, we report a photoacoustic agent (MPC) that is able to detect intracellular S. aureus infection through a dynamic process, including (i) active targeting and internalization into macrophage cells, (ii) specific molecular tailoring by caspase-1 in infected macrophage cells, and (iii) enhancement of the photoacoustic (PA) signal owing to molecular self-assembly. The PA signal per area of the "stimuli-induced assembly" agent (MPC) increases more than 2-fold over that of the active targeting control agent (MP_SC). Finally, based on this approach, the average PA signal in the infected site is enhanced by approximately 2.6-fold over that of the control site. We envision that this PA contrast agent may provide a new approach for the selective and sensitive diagnosis of an intracellular bacterial infection.

Bioresponsive Nanoparticles Targeted to Infectious Microenvironments for Sepsis Management

Sepsis is a life-threatening disease resulted from a dysregulated host immune response to bacterial infections, continuing to cause high morbidity and mortality worldwide. Despite discoveries of many potential therapeutic targets, effective treatments of sepsis are lacking. Here, a strategy is reported to target infectious microenvironments (IMEs) via bioresponsive nanoparticles that simultaneously eliminate bacteria and alleviate the host inflammation response, thus managing sepsis in mice. The nanoparticle is made of copolymers sensitive to pH and bacterial enzymes to self-assemble into a micelle loaded with both an antibiotic (ciprofloxacin) and an anti-inflammatory agent ((2-[(aminocarbonyl)amino]-5-(4-fluorophenyl)-3-thiophenecarboxamide). In addition, the nanoparticle is conjugated with intercellular adhesion molecule-1 antibodies to target IMEs. Nanoparticle targeting to IMEs and local cues as triggers to deliver therapeutics in on-demand manners is demonstrated using an acute lung bacterial infection mouse model. In the sepsis mouse model induced by peritonitis at a lethal dose of bacterial invasion, it is shown that concurrently targeting pathogens and excessive inflammation pathways is valuable to manage the sepsis. The study illustrates not only the development of a new delivery system but also the mechanism-based therapy of nanomedicine for infectious diseases.

Nanocarriers with conjugated antimicrobials to eradicate pathogenic biofilms evaluated in murine in vivo and human ex vivo infection models

Conventional antimicrobials are becoming increasingly ineffective for treating bacterial infection due to the emergence of multi-drug resistant (MDR) pathogens. In addition, the biofilm-mode-of-growth of infecting bacteria impedes antimicrobial penetration in biofilms. Here, we report on poly(ethylene)glycol-poly(β-amino esters) (PEG-PAE) micelles with conjugated antimicrobials, that can uniquely penetrate biofilms, target themselves to bacterial cell surfaces once inside the low-pH environment of a biofilm and release conjugated antimicrobials through degradation of their ester-linkage with PAE by bacterial lipases. In vitro, PEG-PAE micelles with conjugated Triclosan (PEG-PAE-Triclosan) yielded no inadvertent leakage of their antimicrobial cargo and better killing of MDR Staphylococcus aureus, Escherichia coli and oral streptococcal biofilms than Triclosan in solution. In mice, PEG-PAE-Triclosan micelles with conjugated Triclosan yielded better eradication efficacy towards a MDR S. aureus-infection compared with Triclosan in solution and Triclosan-loaded micelles at equal Triclosan-equivalent concentrations. Ex vivo exposure of multi-species oral biofilms collected from orthodontic patients to PEG-PAE-Triclosan micelles, demonstrated effective bacterial killing at 30-40 fold lower Triclosan-equivalent concentrations than achieved by Triclosan in solution. Importantly, Streptococcus mutans, the main causative organism of dental caries, was preferentially killed by PEG-PAE-Triclosan micelles. Thus PEG-PAE-Triclosan micelles present a promising addendum to the decreasing armamentarium available to combat infection in diverse sites of the body. STATEMENT OF SIGNIFICANCE: pH-adaptive polymeric micelles with conjugated antimicrobials can efficiently eradicate infectious biofilms from diverse body sites in mice and men. An antimicrobial was conjugated through an ester-linkage to a poly(ethylene glycol) (PEG)/poly(β-amino ester) block copolymer to create micellar nanocarriers. Stable micelle structures were formed by the hydrophobic poly(β-amino ester) inner core and a hydrophilic PEG outer shell. Thus formed PEG-PAE-Triclosan micelles do not lose their antimicrobial cargo underway to an infection site through the blood circulation, but penetrate and accumulate in biofilms to release antimicrobials once inside a biofilm through degradation of its ester-linkage by bacterial lipases, to kill biofilm-embedded bacteria at lower antimicrobial concentrations than when applied in solution. PEG-PAE-Triclosan micelles effectively eradicate biofilms of multi-drug-resistant pathogens and oral bacteria, most notably highly cariogenic Streptococcus mutans, in mice and men respectively, and possess excellent clinical translation possibilities.

Functional Microgels: Recent Advances in Their Biomedical Applications

Here, a spotlight is shown on aqueous microgel particles which exhibit a great potential for various biomedical applications such as drug delivery, cell imaging, and tissue engineering. Herein, different synthetic methods to develop microgels with desirable functionality and properties along with degradable strategies to ensure their renal clearance are briefly presented. A special focus is given on the ability of microgels to respond to various stimuli such as temperature, pH, redox potential, magnetic field, light, etc., which helps not only to adjust their physical and chemical properties, and degradability on demand, but also the release of encapsulated bioactive molecules and thus making them suitable for drug delivery. Furthermore, recent developments in using the functional microgels for cell imaging and tissue regeneration are reviewed. The results reviewed here encourage the development of a new class of microgels which are able to intelligently perform in a complex biological environment. Finally, various challenges and possibilities are discussed in order to achieve their successful clinical use in future.

Bone-targeting poly(ethylene sodium phosphate)

Poly(ethylene sodium phosphate) (PEP·Na) showed excellent cytocompatibility and in vivo bone affinity. Moreover, PEP·Na did not interact with thrombin, which is a coagulation-related protein. Because immobilization of therapeutic agents and imaging probes on PEP·Na is easily performed, PEP·Na is a promising polymer for bone-targeted therapies.

Intracellular GSH-activated galactoside photosensitizers for targeted photodynamic therapy and chemotherapy

Ligand-targeted cancer therapeutics has been developed to minimize non-specific cytotoxicity via ligand-drug conjugates during the past few decades. We present here the design and synthesis of a GSH-activated amphiphilic photosensitizer conjugated with galactose (TPP-S-S-Gal) for targeted photodynamic therapy. Furthermore, the galactoside photosensitizer as supramolecular amphiphiles can self-assemble into micelles, which can be applied in integrative cancer treatment with chemotherapy drugs such as camptothecin (CPT) encapsulated in the hydrophobic core of micelles. Upon reaction with free thiol GSH that is relatively abundant in tumor cells, disulfide bond cleavage occurs as well as the active photosensitizer TPP and chemotherapy drug CPT release, which can cause cell apoptosis. The in vitro biological assessment of TPP-S-S-Gal micelles against the A549 cell line was evaluated by MTT assay, flow cytometry and confocal scanning laser microscopy, respectively. According to the MTT assay, TPP-S-S-Gal micelles exhibited low dark toxicity and efficient integrative efficacy of PDT and chemotherapy towards A549 cells after light irradiation.

A review on core-shell structured unimolecular nanoparticles for biomedical applications

Polymeric unimolecular nanoparticles (NPs) exhibiting a core-shell structure and formed by a single multi-arm molecule containing only covalent bonds have attracted increasing attention for numerous biomedical applications. This unique single-molecular architecture provides the unimolecular NP with superior stability both in vitro and in vivo, a high drug loading capacity, as well as versatile surface chemistry, thereby making it a desirable nanoplatform for therapeutic and diagnostic applications. In this review, we surveyed the architecture of various types of polymeric unimolecular NPs, including water-dispersible unimolecular micelles and water-soluble unimolecular NPs used for the delivery of hydrophobic and hydrophilic agents, respectively, as well as their diverse biomedical applications. Future opportunities and challenges of unimolecular NPs were also briefly discussed.

Macrophage-Instructed Intracellular Staphylococcus aureus Killing by Targeting Photodynamic Dimers

The survival of Staphylococcus aureus inside phagocytes is considered to be the sticking point of long-term chronic inflammation. Here, we fabricate peptide-chlorophyll-based photodynamic therapy (PDT) agents with "sandwich" dimeric structure to enhance the PDT effect and active targeting property to eliminate intracellular infections, which could be seen as prospective antibacterial agents for inflammation.

Nanoparticle-based local antimicrobial drug delivery

Despite the wide success of antibiotics in modern medicine, the treatment of bacterial infections still faces critical challenges, especially due to the rapid emergence of antibiotic resistance. As a result, local antimicrobial treatment aimed at enhancing drug concentration at the site of infection while avoiding systemic exposure is becoming increasingly attractive, as it may alleviate resistance development. Meanwhile, therapeutic nanoparticles, especially liposomes, polymeric nanoparticles, dendrimers, and inorganic nanoparticles, are gaining traction to improve the therapeutic efficacy with many applications specifically focused on local antimicrobial treatment. This review highlights topics where nanoparticle-based strategies hold significant potential to advance treatment against local bacterial infections, including (1) promoting antibiotic localization to the pathogen, (2) modulating drug-pathogen interaction against antibiotic resistance, and (3) enabling novel anti-virulence approaches for 'drug-free' antimicrobial activity. In each area, we highlight the innovative antimicrobial strategies tailored for local applications and review the progress made for the treatment of bacterial infections.

Fabrication of Polymer-Protein Hybrids

Rapid developments in organic chemistry and polymer chemistry promote the synthesis of polymer-protein hybrids with different structures and biofunctionalities. In this feature article, recent progress achieved in the synthesis of polymer-protein conjugates, protein-nanoparticle core-shell structures, and polymer-protein nanogels/hydrogels is briefly reviewed. The polymer-protein conjugates can be synthesized by the "grafting-to" or the "grafting-from" approach. In this article, different coupling reactions and polymerization methods used in the synthesis of bioconjugates are reviewed. Protein molecules can be immobilized on the surfaces of nanoparticles by covalent or noncovalent linkages. The specific interactions and chemical reactions employed in the synthesis of core-shell structures are discussed. Finally, a general introduction to the synthesis of environmentally responsive polymer-protein nanogels/hydrogels by chemical cross-linking reactions or molecular recognition is provided.

Recent developments in smart antibacterial surfaces to inhibit biofilm formation and bacterial infections

Since their development over 70 years, antibiotics are still the most effective strategy to treat bacterial biofilms and infections.

High definition polyphosphoesters: between nucleic acids and plastics

Nucleic acids and synthetic polyphosphoester materials have been distinct fields – this review shows how these areas now comprise a continuum.

Responsive crosslinked polymer nanogels for imaging and therapeutics delivery

Nanogels are water-soluble crosslinked polymer networks with tremendous potential in targeted imaging and controlled drug and gene delivery.

Balancing antimicrobial activity with biological safety: bifunctional chitosan derivative for the repair of wounds with Gram-positive bacterial infections

Because of the balance between antimicrobial activity and biological safety, the bifunctional chitosan derivative could control infections and promote healing simultaneously.

Synchronous, efficient and fast removal of phosphate and organic matter by carbon-coated lanthanum nanorods

Both phosphate and organic carbon can serve as nutrients for microorganism growth. Simultaneous removal of both nutrients would realize the antibacterial strategy of nutrient starvation better to ensure water quality safety. In addition, a short treatment time is the premise for the application of a material in water treatment. Herein, carbon-coated lanthanum nanorods with a uniform distribution of La and C (C–La-MOF) were rationally prepared through glucose and La-MOF hydrothermal treatment and further carbonization to synchronously and rapidly remove phosphate and organic matter. The carbon layer thickness was tuned by varying the hydrothermal time to find the optimal balance between excellent phosphate intake and low lanthanum leakage. C–La-MOF had a strong anti-interference ability and high phosphate capture capacity over a wide pH range of 2–12. Impressively, when phosphate and organic carbon coexisted in solution, their removal performances remained relatively unchanged compared with that when the two nutrients existed independently, and their adsorption equilibriums could be easily reached within 10 min. All of the above results prove that C–La-MOF is a promising material for practical drinking water treatment.

The carbon-coated lanthanum nanorods with uniform distribution of La and C can synchronously remove phosphate and organic matter, efficiently and rapidly.

Surface engineering of titanium implants with enzyme-triggered antibacterial properties and enhanced osseointegrationin vivo

A catechol-functionalized coating on a Van-loaded Ti implant achieves enhanced osseointegration and effective inhibition of bacterial adhesion and enzyme-triggered antibacterial drug release.

Therapeutic nanoplatforms with bacteria-specific activation for directional transport of antibiotics

An entirely new strategy is explored for directional transport delivery of antibiotics to bacteria utilizing a bacteria-activated nanoplatform.

Acidity-triggered charge-reversible multilayers for construction of adaptive surfaces with switchable bactericidal and bacteria-repelling functions

Microenvironment acidity of infected sites was utilized to control the surface charge, and therefore, manipulate bacterial behavior.

In Situ Capture of Bacterial Toxins for Antivirulence Vaccination

Antivirulence vaccination is a promising strategy for addressing bacterial infection that focuses on removing the harmful toxins produced by bacteria. However, a major challenge for creating vaccines against biological toxins is that the vaccine potency is often limited by lack of antigenic breadth, as most formulations have focused on single antigens, while most bacteria secrete a plethora of toxins. Here, a facile approach for generating multiantigenic nanotoxoids for use as vaccines against pathogenic bacteria by leveraging the natural affinity of virulence factors for cellular membranes is reported. Specifically, multiple virulent toxins from bacterial protein secretions are concurrently and naturally entrapped using a membrane-coated nanosponge construct. The resulting multivalent nanotoxoids are capable of delivering virulence factors together, are safe both in vitro and in vivo, and can elicit functional immunity capable of combating live bacterial infections in a mouse model. Despite containing the same bacterial antigens, the reported nanotoxoid formulation consistently outperforms a denatured protein preparation in all of the metrics studied, which underscores the utility of biomimetic nanoparticle-based neutralization and delivery. Overall this strategy helps to address major hurdles in the design of antivirulence vaccines, enabling increased antigenic breadth while maintaining safety.

Selective cleavage of the polyphosphoester in crosslinked copper based nanogels: enhanced antibacterial performance through controlled release of copper

Polymeric architectures with controlled and well-defined structural features are required to render a sustainable antibacterial surface - a key requirement in the design of polymeric membranes for water purification. Herein, surface selective crosslinking of copper oxide-polyphosphoester (CuO-PPE) hybrid nanogels on to polyvinylidene fluoride-styrene maleic anhydride (PVDF/SMA) ultrafiltration membranes was developed. The hybrid nanogels, composed of PPE and CuO, with inherent antifouling and antibacterial properties, were crosslinked using a macroinitiator (polyethylene glycol, PEG) and subsequently grafted on to PVDF/SMA by alkyne-anhydride reaction. Partially hydrolysed SMA solubilizes membrane proteins and the phosphatase/phospholipase triggers the cleavage of PPE segments resulting in controlled release of Cu ions. This unique strategy renders the membrane surface antibacterial through sustained and controlled release of Cu ions thereby generating intracellular reactive oxygen species (ROS). In addition, the enhanced antibiofouling performance of these membranes is facilitated by the presence of the hydrophilic macroinitiator (PEG and PPE). The modified membranes designed in this study are durable and possess long-term stability due to strong covalent interaction between CuO-PPE and the PVDF/SMA membrane. Studies on the flux, porosity and protein adsorption of the membranes were performed. An enhanced flux recovery ratio was observed for the modified membrane due to the pendant PPE groups (from CuO-PPE) which prohibit irreversible protein adsorption on the PVDF surface. The cytotoxicity of CuO-PPE is greatly reduced because of an effective coverage of CuO by biocompatible PPEs. This study opens up new avenues of fabricating "smart" inorganic nanoparticles that can be confined in a soft hybrid polymeric gel network with controlled release of Cu ions thereby precluding ubiquitous bacterial treatment in water filtration systems.