Antibacterial and Anti-Inflammatory Effects of Apolipoprotein E

Apolipoprotein E (APOE) is a lipid-transport protein that functions as a key mediator of lipid transport and cholesterol metabolism. Recent studies have shown that peptides derived from human APOE display anti-inflammatory and antimicrobial effects. Here, we applied in vitro assays and fluorescent microscopy to investigate the anti-bacterial effects of full-length APOE. The interaction of APOE with endotoxins from Escherichia coli was explored using surface plasmon resonance, binding assays, transmission electron microscopy and all-atom molecular dynamics (MD) simulations. We also studied the immunomodulatory activity of APOE using in vitro cell assays and an in vivo mouse model in combination with advanced imaging techniques. We observed that APOE exhibits anti-bacterial activity against several Gram-negative bacterial strains of Pseudomonas aeruginosa and Escherichia coli. In addition, we showed that APOE exhibits a significant binding affinity for lipopolysaccharide (LPS) and lipid A as well as heparin. MD simulations identified the low-density lipoprotein receptor (LDLR) binding region in helix 4 of APOE as a primary binding site for these molecules via electrostatic interactions. Together, our data suggest that APOE may have an important role in controlling inflammation during Gram-negative bacterial infection.

Bioactive Injectable Hydrogel Dressings for Bacteria-Infected Diabetic Wound Healing: A "Pull-Push" Approach

Chronic diabetic wound healing remains a challenge due to the existence of excessive danger molecules and bacteria in the inflammatory microenvironment. There is an urgent need for advanced wound dressings that target both inflammation and infection. Here, a bioactive hydrogel without loading any anti-inflammatory ingredients is rationally designed to achieve a "Pull-Push" approach for efficient and safe bacteria-infected diabetic wound healing by integrating danger molecule scavenging (Pull) with antibiotic delivery (Push) in the inflammatory microenvironment. The cationic hydrogel, termed the OCMC-Tob/PEI hydrogel, is fabricated by the conjugation of polyethylenimine (PEI) and tobramycin (Tob) on an oxidized carboxymethyl cellulose (OCMC) backbone via the Schiff base reaction with injectable, self-healing, and biocompatible properties. The OCMC-Tob/PEI hydrogel not only displays the remarkable capability of capturing multiple negatively charged danger molecules (e.g., cell-free DNA, lipopolysaccharides, and tumor necrosis factor-α) to ameliorate anti-inflammation effects but also achieves controllable long-term antibacterial activity by the pH-sensitive release of Tob. Consequently, this multifunctional hydrogel greatly expedites the wound closure rate with combined anti-inflammation and anti-infection effects on Pseudomonas aeruginosa-infected diabetic wounds. Our work provides a highly versatile treatment approach for chronic diabetic wounds and a promising dressing for regenerative medicine.

Conjugated Molecule-Assisted Supramolecular Hydrogel with Enhanced Antibacterial and Antibiofouling Properties

The hydrogel using natural and synthetic polymers to create a cross-linking network has drawn attention in diverse bioapplications. However, inhibition of bacterial infection is still a challenge for hydrogel's wide application. In this work, we reported a supramolecular hydrogel with a good antibacterial property built from conjugated molecules. The water-soluble molecular 4,7-bis[9,9-di(2-carboxy-ethyl)-fluoren-2-yl]-2,1,3-benzothiadiazole (OFBTCOOH) physically linked with monomers via hydrophobic interaction. The free-radical polymerized poly(N-acryloyl glycinamide) was hydrogen-bond cross-linked by dual amides in the side chains to form a hydrogel. An adjustable micro-network was obtained by increasing OFBTCOOH with evidence of enhanced intermolecular interaction. The successfully integrated OFBTCOOH could be excited upon light irradiation. The energy of triplet-state excitons of OFBTCOOH transferred to the ground-state oxygen to produce singlet oxygen, which endowed the hydrogel with the antibacterial property. Meanwhile, the superhydrophilic surface of the hydrogel can bind water molecules to form a stable hydration layer, which acted as barriers to resist protein and bacterial adsorption and achieve the anti-biofouling goal. The ease in introducing conjugated polyelectrolytes may provide a formulation to functionalize hydrogels via various physical interactions.

Antibacterial peptide NZ2114-loaded hydrogel accelerates Staphylococcus aureus-infected wound healing

Wound infection caused by Staphylococcus aureus (S. aureus) is a great challenge which has caused significant burden and economic loss to the medical system. NZ2114, a plectasin-derived peptide, is an antibacterial agent for preventing and treating S. aureus infection, especially for methicillin-resistant S. aureus (MRSA) infection. Here, three-dimensional reticulated antimicrobial peptide (AMP) NZ2114 hydrogels were developed based on hydroxypropyl cellulose (HPC) and sodium alginate (SA); they displayed sustained and stable release properties (97.88 ± 1.79% and 91.1 ± 10.52% release rate in 72 h, respectively) and good short-term cytocompatibility and hemocompatibility. But the HPC-NZ2114 hydrogel had a smaller pore size (diameter 0.832 ± 0.420 μm vs. 3.912 ± 2.881 μm) and better mechanical properties than that of the SA-NZ2114 hydrogel. HPC/SA-NZ2114 hydrogels possess efficient antimicrobial activity in vitro and in vivo. In a full-thickness skin defect model, the wound closure of the 1.024 mg/g HPC-NZ2114 hydrogel group was superior to those of the SA-NZ2114 hydrogel and antibiotic groups on day 7. The HPC-NZ2114 hydrogel accelerated wound healing by reducing inflammation and promoting the production of vascular endothelial growth factor (VEGF), endothelial growth factor (EGF) and angiogenesis (CD31) through histological and immunohistochemistry evaluation. These data indicated that the HPC-NZ2114 hydrogel is an excellent candidate for S. aureus infection wound dressing. KEY POINTS: •NZ2114 hydrogels showed potential in vitro bactericidal activity against S. aureus •NZ2114 hydrogels could release continuously for 72 h and had good biocompatibility •NZ2114 hydrogels could effectively promote S. aureus-infected wound healing.

Dissolving microneedles with a biphasic release of antibacterial agent and growth factor to promote wound healing

Infected wound healing is a complex and dynamic process affecting millions of people. Since wound healing contains multiple stages, it requires staged management to realize the early inhibition of infection and the subsequent promotion of wound healing. A key point is to design a biphasic release system with antibacterial agents and growth factors to promote wound regeneration. As a safe, efficient and painless transdermal drug delivery method, microneedles (MNs) have attracted widespread attention. Herein, we present dissolving MNs with the biphasic release of an antibacterial agent and a growth factor to promote wound healing. bFGF was first encapsulated in PLGA microspheres (bFGF@PLGA) and then co-loaded with free ofloxacin onto polyvinylpyrrolidone MNs. Owing to the fast dissolution of the substrate, ofloxacin was quickly released to rapidly inhibit infection, while the PLGA microspheres were left in the wound. Due to the slow degradation of PLGA, bFGF encapsulated in the PLGA microspheres was slowly released to further promote wound healing. In vivo studies demonstrated that the MNs with the biphasic release of antibacterial agent and growth factor exhibited a superior capability to promote wound healing. This biphasic release system combined with microneedles has a bright future in wound healing.

Light-triggered on-site rapid formation of antibacterial hydrogel dressings for accelerated healing of infected wounds

An optimal wound dressing can seal variously shaped wounds and provide a complete barrier to resist bacterial invasion; more importantly, the dressing can be stretched or compressed when the wounds are subjected to external forces and quickly return to its original state after the forces are withdrawn. Here, we designed dressings with light-triggered on-site rapid formation of antibacterial hydrogel for the accelerated healing of infected wounds. The pro-hydrogel, composed of acrylamide (AM) and dopamine-hyaluronic acid-ε-poly-l-lysine (DA-HA-EPL), was filled into the Vibrio vulnificus-infected wound. A 405-nm blue light was exerted on the wound to rapidly photopolymerize AM to its polymer, i.e., polyacrylamide (PAM). A hydrogel network of PAM/DA-HA-EPL immediately formed on site within several seconds to insulate the wound. PAM/DA-HA-EPL possessed adhesion performance to adapt to changes in wound morphologies due to external forces. Moreover, it presented high antibacterial ability due to the presence of EPL, in vitro biocompatibility and the ability to promote cell migration. Vibrio vulnificus-infected wounds were established on full-thickness mouse skin, and the hydrogel dressing exhibited high healing efficiency in terms of skin tissue regeneration, collagen deposition, and angiogenesis. PAM/DA-HA-EPL is a promising hydrogel dressing for the accelerated healing of infected wounds.

Smart Multifunctional Polymer Systems as Alternatives or Supplements of Antibiotics To Overcome Bacterial Resistance

In recent years, infectious diseases have again become a critical threat to global public health largely due to the challenges posed by antimicrobial resistance. Conventional antibiotics have played a crucial role in combating bacterial infections; however, their efficacy is significantly impaired by widespread drug resistance. Natural antimicrobial peptides (AMPs) and their polymeric mimics demonstrate great potential for killing bacteria with low propensity of resistance as they target the microbial membrane rather than a specific molecular target, but they are also toxic to the host eukaryotic cells. To minimize antibiotics systemic spread and the required dose that promote resistance and to advocate practical realization of the promising activity of AMPs and polymers, smart systems to target bacteria are highly sought after. This review presents bacterial recognition by various specific targeting molecules and the delivery systems of active components in supramolecules. Bacteria-induced activations of antimicrobial-based nanoformulations are also included. Recent advances in the bacteria targeting and delivery of synthetic antimicrobial agents may assist in developing new classes of highly selective antimicrobial systems which can improve bactericidal efficacy and greatly minimize the spread of bacterial resistance.

Reactive oxygen species-degradable polythioketal urethane foam dressings to promote porcine skin wound repair

Porous, resorbable biomaterials can serve as temporary scaffolds that support cell infiltration, tissue formation, and remodeling of nonhealing skin wounds. Synthetic biomaterials are less expensive to manufacture than biologic dressings and can achieve a broader range of physiochemical properties, but opportunities remain to tailor these materials for ideal host immune and regenerative responses. Polyesters are a well-established class of synthetic biomaterials; however, acidic degradation products released by their hydrolysis can cause poorly controlled autocatalytic degradation. Here, we systemically explored reactive oxygen species (ROS)-degradable polythioketal (PTK) urethane (UR) foams with varied hydrophilicity for skin wound healing. The most hydrophilic PTK-UR variant, with seven ethylene glycol (EG7) repeats flanking each side of a thioketal bond, exhibited the highest ROS reactivity and promoted optimal tissue infiltration, extracellular matrix (ECM) deposition, and reepithelialization in porcine skin wounds. EG7 induced lower foreign body response, greater recruitment of regenerative immune cell populations, and resolution of type 1 inflammation compared to more hydrophobic PTK-UR scaffolds. Porcine wounds treated with EG7 PTK-UR foams had greater ECM production, vascularization, and resolution of proinflammatory immune cells compared to polyester UR foam-based NovoSorb Biodegradable Temporizing Matrix (BTM)-treated wounds and greater early vascular perfusion and similar wound resurfacing relative to clinical gold standard Integra Bilayer Wound Matrix (BWM). In a porcine ischemic flap excisional wound model, EG7 PTK-UR treatment led to higher wound healing scores driven by lower inflammation and higher reepithelialization compared to NovoSorb BTM. PTK-UR foams warrant further investigation as synthetic biomaterials for wound healing applications.

Bioactive anti-inflammatory antibacterial metformin-contained hydrogel dressing accelerating wound healing

Highly efficient wound healing and skin regeneration remain a challenge. Long-term inflammation and bacterial infection can inhibit the healing process and lead to the scar formation. Here, we report a hydrogel (FEM) formed by self-assembly of ε-poly-l-lysine-F127-ε-poly-l-lysine (EPL-F127-EPL) and metformin for wound repair. Especially, the role of metformin-based antibacterial hydrogel in wound healing and repair was investigated for the first time. FEM has inherent multifunctional properties, including controlled metformin release, anti-inflammatory and antibacterial activity, temperature responsiveness, injectable and self-healing capabilities. The in vivo results showed that FEM dressings accelerated the wound healing by stimulating the angiogenesis process of the wound tissue and anti-inflammation. This study shows that the multifunctional metformin-contained hydrogel scaffolds could enhance the wound repair through the anti-inflammation and accelerated angiogenesis, which could also expand the biomedical applications of metformin-based biomaterials.

Self-Assembling Peptide-Based Hydrogels for Wound Tissue Repair

Wound healing is a long-term, multistage biological process that includes hemostasis, inflammation, proliferation, and tissue remodeling and requires intelligent designs to provide comprehensive and convenient treatment. The complexity of wounds has led to a lack of adequate wound treatment materials, which must systematically regulate unique wound microenvironments. Hydrogels have significant advantages in wound treatment due to their ability to provide spatiotemporal control over the wound healing process. Self-assembling peptide-based hydrogels are particularly attractive due to their innate biocompatibility and biodegradability along with additional advantages including ligand-receptor recognition, stimulus-responsive self-assembly, and the ability to mimic the extracellular matrix. The ability of peptide-based materials to self-assemble in response to the physiological environment, resulting in functionalized microscopic structures, makes them conducive to wound treatment. This review introduces several self-assembling peptide-based systems with various advantages and emphasizes recent advances in self-assembling peptide-based hydrogels that allow for precise control during different stages of wound healing. Moreover, the development of multifunctional self-assembling peptide-based hydrogels that can regulate and remodel the wound immune microenvironment in wound therapy with spatiotemporal control has also been summarized. Overall, this review sheds light on the future clinical and practical applications of self-assembling peptide-based hydrogels.

Design of therapeutic biomaterials to control inflammation

Inflammation plays an important role in the response to danger signals arising from damage to our body and in restoring homeostasis. Dysregulated inflammatory responses occur in many diseases, including cancer, sepsis and autoimmunity. The efficacy of anti-inflammatory drugs, developed for the treatment of dysregulated inflammation, can be potentiated using biomaterials, by improving the bioavailability of drugs and by reducing side effects. In this Review, we first outline key elements and stages of the inflammatory environment and then discuss the design of biomaterials for different anti-inflammatory therapeutic strategies. Biomaterials can be engineered to scavenge danger signals, such as reactive oxygen and nitrogen species and cell-free DNA, in the early stages of inflammation. Materials can also be designed to prevent adhesive interactions of leukocytes and endothelial cells that initiate inflammatory responses. Furthermore, nanoscale platforms can deliver anti-inflammatory agents to inflammation sites. We conclude by discussing the challenges and opportunities for biomaterial innovations in addressing inflammation.

Degradable Hydrogel Adhesives with Enhanced Tissue Adhesion, Superior Self-Healing, Cytocompatibility, and Antibacterial Property

Degradable hydrogel adhesives with multifunctional advantages are promising to be candidates as hemostatic agents, surgical sutures, and wound dressings. In this study, hydrogel adhesives are constructed by catechol-conjugated gelatin from natural resource, iron ions (Fe³⁺ ), and a synthetic polymer. Specifically, the latter is prepared by the radical ring-opening copolymerization of a cyclic ketene acetal monomer 5,6-benzo-2-methylene-1,3-dioxepane and N-(2-ethyl p-toluenesulfonate) maleimide. By the incorporation of ester bonds in the backbone and the combination with quaternary ammonium salt pendants in the polymer, it exhibits excellent degradability and antibacterial property. Remarkably, doping the synthetic polymer into the 3,4-dihydroxyphenylacetic acid-modified gelatin network forms a semi-interpenetrating polymer network which can effectively improve the rigidity, tissue adhesion, and antibacterial property of fabricated hydrogel adhesives. Moreover, non-covalent bonds from coordination interaction between catechol and Fe³⁺ contribute to the fast self-healing of the developed hydrogel adhesives. These hydrogel adhesives with the multiple merits including the degradability, enhanced tissue adhesion, superior self-healing, good cytocompatibility, and antibacterial property show the great potential to be used as tissue adhesives in biomedical fields.

Experimental Model of Pulmonary Inflammation Induced by SARS-CoV-2 Spike Protein and Endotoxin

COVID-19 is characterized by a dysregulated and excessive inflammatory response and, in severe cases, acute respiratory distress syndrome. We have recently demonstrated a previously unknown high-affinity interaction between the SARS-CoV-2 spike (S) protein and bacterial lipopolysaccharide (LPS), leading to the boosting of inflammation. Here we present a mouse inflammation model employing the coadministration of aerosolized S protein together with LPS to the lungs. Using NF-κB-RE-Luc reporter and C57BL/6 mice followed by combinations of bioimaging, cytokine, chemokine, fluorescence-activated cell sorting, and histochemistry analyses, we show that the model yields severe pulmonary inflammation and a cytokine profile similar to that observed in COVID-19. Therefore, the model offers utility for analyses of the pathophysiological features of COVID-19 and the development of new treatments.

Biomaterial-based delivery of antimicrobial therapies for the treatment of bacterial infections

The rise in antibiotic-resistant bacteria, including strains that are resistant to last-resort antibiotics, and the limited ability of antibiotics to eradicate biofilms, have necessitated the development of alternative antibacterial therapeutics. Antibacterial biomaterials, such as polycationic polymers, and biomaterial-assisted delivery of non-antibiotic therapeutics, such as bacteriophages, antimicrobial peptides and antimicrobial enzymes, have improved our ability to treat antibiotic-resistant and recurring infections. Biomaterials not only allow targeted delivery of multiple agents, but also sustained release at the infection site, thereby reducing potential systemic adverse effects. In this Review, we discuss biomaterial-based non-antibiotic antibacterial therapies for the treatment of community- and hospital-acquired infectious diseases, with a focus in in vivo results. We highlight the translational potential of different biomaterial-based strategies, and provide a perspective on the challenges associated with their clinical translation. Finally, we discuss the future scope of biomaterial-assisted antibacterial therapies.

WEB SUMMARY

The development of antibiotic tolerance and resistance has demanded the search for alternative antibacterial therapies. This Review discusses antibacterial biomaterials and biomaterial-assisted delivery of non-antibiotic therapeutics for the treatment of bacterial infectious diseases, with a focus on clinical translation.

A spatiotemporal release platform based on pH/ROS stimuli-responsive hydrogel in wound repairing

Fabricating injectable hydrogel with multifunctions that matchs the highly ordered healing process of skin regeneration has greatly desired in treatment of chronic diabetic wounds. Herein, a pH/reactive oxygen species (ROS) dual responsive injectable glycopeptide hydrogel based on phenylboronic acid-grafted oxidized dextran and caffeic acid-grafted ε-polylysine was constructed, which exhibited inherent antibacterial and antioxidant capacities. The mangiferin (MF) with the ability to promote angiogenesis was encapsulated into pH-responsive micelles (MIC). Subsequently, diclofenac sodium (DS) with anti-inflammatory activities and MIC@MF were embedded into the hydrogel. The hydrogel possessed good biodegradability, stable rheological property and self-healing ability, and could realize the spatiotemporal delivery of DS and MF. The in vitro and in vivo data showed that the hydrogel was biocompatible with effective anti-infection, anti-oxidation and anti-inflammation at early stages, then further promoted angiogenesis and accelerated wound repairing. Collectively, this novel glycopeptide hydrogel provides a facile and effective strategy for chronic diabetic wound repairing.

Thrombin-Derived C-Terminal Peptide Reduces Candida-Induced Inflammation and Infection In Vitro and In Vivo

Infections due to the opportunistic fungus Candida have been on the rise in the last decades, especially in immunocompromised individuals and hospital settings. Unfortunately, the treatments available today are limited. Thrombin-derived C-terminal peptide (TCP-25) is an antimicrobial peptide (AMP) with antibacterial and immunomodulatory effects. In this work, we, for the first time, demonstrate the ability of TCP-25 ability to counteract Candidain vitro and in vivo. Using a combination of viable count assay (VCA), radial diffusion assay (RDA), and fluorescence and transmission electron microscopy analyses, TCP-25 was found to exert a direct fungicidal activity. An inhibitory activity of TCP-25 on NF-κB activation induced by both zymosan alone and heat-killed C. albicans was demonstrated in vitro using THP-1 cells, and in vivo using NF-κB reporter mice. Moreover, the immunomodulatory property of TCP-25 was further substantiated in vitro by analyzing cytokine responses in human blood stimulated with zymosan, and in vivo employing a zymosan-induced peritonitis model in C57BL/6 mice. The therapeutic potential of TCP-25 was demonstrated in mice infected with luminescent C. albicans. Finally, the binding between TCP-25 and zymosan was investigated using circular dichroism spectroscopy and intrinsic fluorescence analysis. Taken together, our results show that TCP-25 has a dual function by inhibiting Candida as well as the associated zymosan-induced inflammation. The latter function is accompanied by a change in secondary structure upon binding to zymosan. TCP-25, therefore, shows promise as a novel drug candidate against Candida infections.

Conductive dual hydrogen bonding hydrogels for the electrical stimulation of infected chronic wounds

Electrical stimulation (ES) via rigid electrodes near the wound is one of the promising approaches for chronic wound treatment, but it is unable to stimulate the whole wound area and treat infected wounds. In this study, a tough conductive hydrogel was prepared by the copolymerization of N-acryloyl glycinamide (NAGA) with quaternized chitosan-g-polyaniline (QCSP). The hydrogel showed a similar conductivity to the human skin and robust mechanical properties due to the dual hydrogen bonding motifs. The grafted polyaniline segments and functionalized quaternary ammonium groups showed intense antimicrobial activity against Pseudomonas aeruginosa and Staphylococcus aureus biofilms. The in vivo assay in diabetic rats proves that the ES via the conductive hydrogel was more effective in promoting the healing of infected wounds than the conventional ES via rigid electrodes. Due to the excellent flexibility and antibacterial properties, this conductive hydrogel shows great promise for infected chronic wound treatment.

Antimicrobial peptides - Unleashing their therapeutic potential using nanotechnology

Antimicrobial peptides (AMPs) are potent, mostly cationic, and amphiphilic broad-spectrum host defense antimicrobials that are produced by all organisms ranging from prokaryotes to humans. In addition to their antimicrobial actions, they modulate inflammatory and immune responses and promote wound healing. Although they have clear benefits over traditional antibiotic drugs, their wide therapeutic utilization is compromised by concerns of toxicity, stability, and production costs. Recent advances in nanotechnology have attracted increasing interest to unleash the AMPs' immense potential as broad-spectrum antibiotics and anti-biofilm agents, against which the bacteria have less chances to develop resistance. Topical application of AMPs promotes migration of keratinocytes and fibroblasts, and contributes significantly to an accelerated wound healing process. Delivery of AMPs by employing nanotechnological approaches avoids the major disadvantages of AMPs, such as instability and toxicity, and provides a controlled delivery profile together with prolonged activity. In this review, we provide an overview of the key properties of AMPs and discuss the latest developments in topical AMP therapy using nanocarriers. We use chronic hard-to-heal wounds-complicated by infections, inflammation, and stagnated healing-as an example of an unmet medical need for which the AMPs' wide range of therapeutic actions could provide the most potential benefit. The use of innovative materials and sophisticated nanotechnological approaches offering various possibilities are discussed in more depth.

Tannic acid-inspired, self-healing, and dual stimuli responsive dynamic hydrogel with potent antibacterial and anti-oxidative properties

Due to their intrinsic injectable and self-healing characteristics, dynamic hydrogels, based on dynamic covalent bonds, have gained a great attention. In this study, a novel dynamic hydrogel based on the boronic ester dynamic covalent bond is facilely developed using phenylboronic acid-modified hyaluronic acid (HA-PBA) and plant-derived polyphenol-tannic acid (TA). The dynamic hydrogel gelated quickly under mild conditions and had favorable viscoelastic properties with good self-healing and shear-thinning capabilities. Moreover, the simultaneous utilization of TA as a reductant for the green synthesis of silver nanoparticles (AgNP) inspired the preparation of a TA-reduced AgNP hybrid dynamic hydrogel with potent and broad-spectrum antibacterial activities. The dynamic hydrogels could also be applied for pH- and reactive oxygen species (ROS)-responsive release of loaded protein molecules without showing evident cytotoxicity and hemolysis in vitro. In addition, the dynamic hydrogels showed the anti-oxidative properties of high free radical and ROS scavenging capacity, which was verified by the DPPH (2,2-diphenyl-1-picryl-hydrazyl-hydrate) free radical assay and ROS fluorescence staining. Overall, this novel class of cytocompatible, self-healing, dual stimuli responsive, antibacterial, anti-oxidative, and injectable hydrogels could be promising as a wound dressing for chronic wound healing.

Functional Hydrogels as Wound Dressing to Enhance Wound Healing

Hydrogels, due to their excellent biochemical and mechnical property, have shown attractive advantages in the field of wound dressings. However, a comprehensive review of the functional hydrogel as a wound dressing is still lacking. This work first summarizes the skin wound healing process and relates evaluation parameters and then reviews the advanced functions of hydrogel dressings such as antimicrobial property, adhesion and hemostasis, anti-inflammatory and anti-oxidation, substance delivery, self-healing, stimulus response, conductivity, and the recently emerged wound monitoring feature, and the strategies adopted to achieve these functions are all classified and discussed. Furthermore, applications of hydrogel wound dressing for the treatment of different types of wounds such as incisional wound and the excisional wound are summarized. Chronic wounds are also mentioned, and the focus of attention on infected wounds, burn wounds, and diabetic wounds is discussed. Finally, the future directions of hydrogel wound dressings for wound healing are further proposed.

Antimicrobial Peptides: The Promising Therapeutics for Cutaneous Wound Healing

Chronic wound infections have caused an increasing number of deaths and economic burden, which necessitates wound treatment options. Hitherto, the development of functional wound dressings has achieved reasonable progress. Antibacterial agents, growth factors, and miRNAs are incorporated in different wound dressings to treat various types of wounds. As an effective antimicrobial agent and emerging wound healing therapeutic, antimicrobial peptides (AMPs) have attracted significant attention. The present study focuses on the application of AMPs in wound healing and discusses the types, properties and formulation strategies of AMPs used for wound healing. In addition, the clinical trial and the current status of studies on "antimicrobial peptides and wound healing" are elaborated through bibliometrics. Also, the challenges and opportunities for further development and utilization of AMP formulations in wound healing are discussed.

Peptide-coated polyurethane material reduces wound infection and inflammation

There is an urgent need for treatments that not only reduce bacterial infection that occurs during wounding but that also target the accompanying excessive inflammatory response. TCP-25, a thrombin-derived antibacterial peptide, scavenges toll-like receptor agonists such as endotoxins and lipoteichoic acid and prevents toll-like receptor-4 dimerization to reduce infection-related inflammation in vivo. Using a combination of biophysical, cellular, and microbiological assays followed by experimental studies in mouse and pig models, we show that TCP-25, when delivered from a polyurethane (PU) material, exerts anti-infective and anti-inflammatory effects in vitro and in vivo. Specifically, TCP-25 killed the common wound pathogens, Pseudomonas aeruginosa and Staphylococcus aureus, in both in vitro and in vivo assays. Furthermore, after its release from the PU material, the peptide retained its capacity to induce its helical conformation upon endotoxin interaction, yielding reduced activation of NF-κB in THP-1 reporter cells, and diminished accumulation of inflammatory cells and subsequent release of IL-6 and TNF-α in subcutaneous implant models in vivo. Moreover, in a porcine partial thickness wound infection model, TCP-25 treated infection with S. aureus, and reduced the concomitant inflammatory response. Taken together, these findings demonstrate a combined antibacterial and anti-inflammatory effect of TCP-25 delivered from PU in vitro, and in mouse and porcine in vivo models of localized infection-inflammation. STATEMENT OF SIGNIFICANCE: Local wound infections may result in systemic complications and can be difficult to treat due to increasing antimicrobial resistance. Surgical site infections and biomaterial-related infections present a major challenge for hospitals. In recent years, various antimicrobial coatings have been developed for infection prevention and current concepts focus on various matrices with added anti-infective components, including various antibiotics and antiseptics. We have developed a dual action wound dressing concept where the host defense peptide TCP-25, when delivered from a PU material, targets both bacterial infection and the accompanying inflammation. TCP-25 PU showed efficacy in in vitro and experimental wound models in mouse and minipigs.

Core-Shell Structured Antimicrobial Nanofiber Dressings Containing Herbal Extract and Antibiotics Combination for the Prevention of Biofilms and Promotion of Cutaneous Wound Healing

Burn wounds are susceptible to microbial invasion from both resident and exogenous bacteria, which becomes a critical public health issue and causes substantial economic burden. There is a perceived demand to produce new antimicrobial wound dressings that hinder bacterial colonization while accelerating the healing process and hence would provide an improved standard of care for patients. Since ancient times, herbal extracts from medicinally important plants have extensively been used for treating burn injuries. This work reports the utility of electrospun nanofibers containing plant extracts and antibiotics combination as a multifunctional scaffold for treating second-degree burns. First, we determined the various components of plant extracts from Gymnema sylvestre by two different processing methods and their synergism with minocycline antibiotics. Then, we prepared core-shell nanofibrous dressings with poly-ε-caprolactone/gelatin laden with minocycline hydrochloride as a shell and gelatin infused with G. sylvestre extracts (ultrasound-assisted extracts and cold macerated extracts) as the core using coaxial electrospinning. The electrospun nanofibers displayed a smooth, continuous, and bead-free morphology with adequate wettability. The presence of extract components in the core-shell nanofibers resulted in enhanced mechanical properties when compared to pristine mats. The core-shell structures resulted in sustained release of the bioactive components when compared to nanofiber blends. Core-shell nanofiber mats containing plant extracts and antibiotic combinations displayed potent antimicrobial and antibiofilm properties while promoting the spread and proliferation of skin cells when compared to pristine mats. In a porcine model of cutaneous second-degree burns, we showed that wounds treated with the antimicrobial dressing improved re-epithelialization and collagen organization in comparison to untreated wounds.

High strength and strain alginate fibers by a novel wheel spinning technique for knitting stretchable and biocompatible wound-care materials

Alginate fibrous materials have been applied as wound dressing to enhance wound healing due to its nontoxic, biodegradable, and hemostatic nature. Conventional nonwoven fabrication tactics, however, showed weakness in inflammation, degradation stability and mechanical properties. Herein, the wet-spun alginate fibers were prepared by a novel wheel spinning technique, then knitted into wound dressing. Benefiting from optimized wet spinning parameters and the agglomeration of alginate multimers, the fibers were endowed with elevated mechanical performances and biodegradability, which allowed for the feasibility of knitting wound-care materials. Using the new wheel spinning technique, high strength alginate fibers with 173 MPa were produced with breaking strain up to 18% and toughness of 16.16 MJ*m^-3. Meanwhile, alginate fibers with high breaking strain reaching 35% were produced with tensile strength of 135 MPa and toughness of 37.47 MJ*m^-3. The overall mechanical performances of these alginate fibers with high breaking strain are significantly higher (up to 2 times) than those published in the literature in term of toughness. In vitro degradation evaluation revealed that this wet spun fibrous dressing had good aqueous absorbency (50%) and sustained biodegradation properties. Furthermore, the consequent cell viability study also proved that this alginate knitted fabric is biocompatible for being applied as wound dressing.

The role of full-length apoE in clearance of Gram-negative bacteria and their endotoxins

ApoE is a well-known lipid-binding protein that plays a main role in the metabolism and transport of lipids. More recently, apoE-derived peptides have been shown to exert antimicrobial effects. Here, we investigated the antibacterial activity of apoE using in vitro assays, advanced imaging techniques, and in vivo mouse models. The formation of macromolecular complexes of apoE and endotoxins from Gram-negative bacteria was explored using gel shift assays, transmission electron microscopy, and CD spectroscopy followed by calculation of the α-helical content. The binding affinity of apoE to endotoxins was also confirmed by fluorescent spectroscopy detecting the quenching and shifting of tryptophan intrinsic fluorescence. We showed that apoE exhibits antibacterial activity particularly against Gram-negative bacteria such as Pseudomonas aeruginosa and Escherichia coli. ApoE protein folding was affected by binding of bacterial endotoxin components such as lipopolysaccharide (LPS) and lipid A, yielding similar increases in the apoE α-helical content. Moreover, high-molecular-weight complexes of apoE were formed in the presence of LPS, but not to the same extent as with lipid A. Together, our results demonstrate the ability of apoE to kill Gram-negative bacteria, interact with their endotoxins, which leads to the structural changes in apoE and the formation of aggregate-like complexes.

Development of an Experimental Ex Vivo Wound Model to Evaluate Antimicrobial Efficacy of Topical Formulations

Wound infections are considered a major cause for wound-associated morbidity. There is a high demand for alternative, robust, and affordable methods that can provide relatable and reproducible results when testing topical treatments, both in research and in the pharmaceutical industry. Here we present an ex vivo wound infection model using porcine skin and a burn wounding method, allowing for the efficacy evaluation of topical antimicrobial formulations. Utilizing this model, we demonstrate the potential of topical treatments after infecting the wounds with clinically significant bacteria, P. aeruginosa and S. aureus. We show that the method is compatible with several analytical tools used to analyze infection and antimicrobial effects. Both bacterial strains successfully infected the wound surface, as well as deeper regions of the tissue. Quantification of viable bacteria on the wound surface and in the tissue, longitudinal measurements of bioluminescence, fluorescence microscopy, and scanning electron microscopy were used to confirm the effects of antibacterial treatments. Furthermore, we show that biofilms are formed on the wound surface, indicating that the demonstrated method mirrors typical in vivo infections.

Ultrabroad-spectrum, multidrug resistant bacteria-killing, and biocompatible quaternized chitin derivative for infected wound healing

Wound infections have consistently been recognized as serious threats to human. The design of antimicrobial and biocompatible wound dressings for infected wounds is an area of constant research. Herein, we homogeneously synthesized an ultrabroad-spectrum antimicrobial and biocompatible quaternized chitin derivative (QC-4) in a high-efficiency and sustainable route using aqueous KOH/urea solution. Particularly, QC-4 displayed powerful multidrug resistant bacteria-killing activities even at a very low antimicrobial concentration range from 500 ng/mL to 5 μg/mL, including clinically prevalent multidrug-resistant Escherichia coli (MDR-E. coli), methicillin resistant Staphylococcus aureus (MRSA), multidrug-resistant Pseudomonas aeruginosa (MRPA), and multidrug-resistant Acinetobacter baumannii (MDR-A. baumannii). With the aim to facilitate clinical translation, we validated the biocompatibility and safety of QC-4 both in vitro and in vivo, and further assessed the effects of QC-4 on infected wound healing in a porcine infectious full-thickness skin wound model. QC-4 demonstrated significant reduction of microbial aggregates and enhanced wound-healing effects by promoted re-epithelialization and collagen deposition, which were quite comparable to that of commercial Alginate-Ag dressing and absolutely superior to commercial Chitoclot Bandage dressing. Additionally, we provided clear evidences that QC-4 had a unique mechanism of action by attracting electrostatically to the negatively charged microbial surface, thus damaging the microbial cell wall and membrane. Findings of this work provided robust preclinical rationale for the future translational applications of QC-4 as a novel ultrabroad-spectrum and multidrug resistant bacteria-killing antimicrobial wound dressing for clinical wound management.

Near-Infrared Light-Activatable Dual-Action Nanoparticle Combats the Established Biofilms of Methicillin-Resistant Staphylococcus aureus and Its Accompanying Inflammation

Clinically, inhibition of both bacterial infection and excessive inflammation is a crucial step for improved wound treatments. Herein, the fabrication of near-infrared-light (NIR)-activatable deoxyribonuclease (DNase)-carbon monoxide (CO)@mesoporous polydopamine nanoparticles (MPDA NPs) is demonstrated for efficient elimination of methicillin-resistant Staphylococcus aureus (MRSA) biofilms and the following anti-inflammatory activity. Specifically, thermosensitive CO-gas-releasing donors (CO releasing molecules, FeCO) are first encapsulated into MPDA NPs, followed by covalently immobilizing deoxyribonuclease I (DNase I) on the surfaces of MPDA NPs. DNase I can degrade the extracellular DNA in biofilms, which site specifically destroys the compactness of the biofilms. With NIR irradiation, DNase-CO@MPDA NPs display great photothermal ability, and further trigger on-demand delivery of bactericidal CO gas that can adequately permeate the impaired biofilms. Eventually, they achieve effective MRSA biofilm elimination in virtue of the synergistic effects of both DNase I participation and CO-gas-potentiated photothermal therapy. Importantly, the inflammatory responses of DNase-CO@MPDA NPs and NIR-treated wounds are simultaneously alleviated owing to the anti-inflammatory features of released CO. Finally, NIR-activatable DNase-CO@MPDA NPs accelerate the healing process of MRSA-biofilm-infected cutaneous wounds. Taken together, this phototherapeutic strategy displays great therapeutic potential in treating the formidable clinical problems caused by MRSA biofilms and the accompanying inflammation.

SARS-CoV-2 spike protein binds to bacterial lipopolysaccharide and boosts proinflammatory activity

There is a link between high lipopolysaccharide (LPS) levels in the blood and the metabolic syndrome, and metabolic syndrome predisposes patients to severe COVID-19. Here, we define an interaction between SARS-CoV-2 spike (S) protein and LPS, leading to aggravated inflammation in vitro and in vivo. Native gel electrophoresis demonstrated that SARS-CoV-2 S protein binds to LPS. Microscale thermophoresis yielded a KD of ∼47 nM for the interaction. Computational modeling and all-atom molecular dynamics simulations further substantiated the experimental results, identifying a main LPS-binding site in SARS-CoV-2 S protein. S protein, when combined with low levels of LPS, boosted nuclear factor-kappa B (NF-κB) activation in monocytic THP-1 cells and cytokine responses in human blood and peripheral blood mononuclear cells, respectively. The in vitro inflammatory response was further validated by employing NF-κB reporter mice and in vivo bioimaging. Dynamic light scattering, transmission electron microscopy, and LPS-FITC analyses demonstrated that S protein modulated the aggregation state of LPS, providing a molecular explanation for the observed boosting effect. Taken together, our results provide an interesting molecular link between excessive inflammation during infection with SARS-CoV-2 and comorbidities involving increased levels of bacterial endotoxins.

Covalent immobilization of DJK-5 peptide on porous titanium for enhanced antibacterial effects and restrained inflammatory osteoclastogenesis

Currently, implant-related bone infection characterized by aggravated infection-induced inflammatory responses and osteolysis, remains a severe challenge in orthopedic surgery, especially in patients with osteoporosis. Attempts to control such responses using biomaterials with combined immunomodulatory and anti-bacterial properties may provide novel strategies. Herein, DJK-5, a class of host defense peptides (HDPs) with established antimicrobial and immunomodulatory functions, was introduced into porous Ti alloy. Our results indicated that the DJK-5 immobilized surfaces showed intrinsically multifunctional properties, including antibacterial ability, anti-inflammation, biocompatibility and osteolysis-inhibiting properties. The results demonstrated that the antibacterial efficiency of DJK-5 functionalized surfaces was over 90 % for both Gram-positive and Gram-negative bacteria. Specifically, DJK-5 functionalized samples also possessed the excellent anti-bacterial activity against a mixture of bacterial strains, including S. aureus, S. epidermidis and P. aeruginosa, with an antibacterial rate against mixed bacteria reaching 91.36 %, as well as reduced biofilm formation. The remarkable anti-bacterial efficacy was likely based on the direct anti-bacterial effect of DJK-5, which destroyed the integrity of bacteria membranes, leading to the leakage of intracellular materials. Additionally, the immobilized DJK-5 surfaces could indirectly kill bacteria through promoted macrophage capacity to bacteria uptake. Furthermore, DJK-5 functionalized surfaces suppressed inflammatory reaction by decreasing the release of pro-inflammatory factors and increasing the secretions of anti-inflammatory factors, and thereby impeded the activation of NF-κB signal pathway, which resulted in the disruption of the actin rings and decreased Tracp5b expressions. Based on these promising findings, the multi-functional DJK-5 immobilized titanium represents an efficient alternative to realize better osseointegration in sever implant-associated bacterial infections.

Cell-Free DNA Promotes Thrombin Autolysis and Generation of Thrombin-Derived C-Terminal Fragments

Cell-free DNA (cfDNA) is the major structural component of neutrophil extracellular traps (NETs), an innate immune response to infection. Antimicrobial proteins and peptides bound to cfDNA play a critical role in the bactericidal property of NETs. Recent studies have shown that NETs have procoagulant activity, wherein cfDNA triggers thrombin generation through activation of the intrinsic pathway of coagulation. We have recently shown that thrombin binds to NETs in vitro and consequently can alter the proteome of NETs. However, the effect of NETs on thrombin is still unknown. In this study, we report that DNA binding leads to thrombin autolysis and generation of multiple thrombin-derived C-terminal peptides (TCPs) in vitro. Employing a 25-residue prototypic TCP, GKY25 (GKYGFYTHVFRLKKWIQKVIDQFGE), we show that TCPs bind NETs, thus conferring mutual protection against nuclease and protease degradation. Together, our results demonstrate the complex interplay between coagulation, NET formation, and thrombin cleavage and identify a previously undisclosed mechanism for formation of TCPs.

Nanodefensin-encased hydrogel with dual bactericidal and pro-regenerative functions for advanced wound therapy

Background: Host defense peptides (HDPs) have emerged as a novel therapeutic paradigm for wound management; however, their clinical applications remain a challenge owing to their poor pharmacological properties and lack of suitable pharmaceutical formulations. Nanodefensin (ND), a nanoengineered human α-defensin 5 (HD5), has shown improved pharmacological properties relative to the parent compound. In this study, we engineered a nanodefensin-encased hydrogel (NDEFgel), investigated the effects of NDEFgel on wound healing, and elucidated underlying mechanisms. Method: ND was chemically synthesized and tested functions by in vitro antimicrobial and scratch assays and western blotting. Different NDEFgels were evaluated by in vitro characterizations including degradation, drug release and antimicrobial activity. In full-thickness excisional murine models, the optimal NDEFgel was directly applied onto wound sites, and the efficacy was assessed. Moreover, the underlying mechanisms of pro-regenerative effect developed by NDEFgel were also explored. Results: Apart from bactericidal effects, ND modulated fibroblast behaviors by promoting migration and differentiation. Among the tested hydrogels, the Pluronic F127 (Plu) hydrogel represented the most desirable carrier for ND delivery owing to its favorable controlled release and compatibility with ND. Local treatment of NDEFgel on the wound bed resulted in accelerated wound regeneration and attenuated bacterial burden. We further demonstrated that NDEFgel therapy significantly upregulated genes related to collagen deposition and fibroblasts, and increased the expression of myofibroblasts and Rac1. We therefore found that Rac1 is a critical factor in the ND-induced modulation of fibroblast behaviors in vitro through a Rac1-dependent cytoskeletal rearrangement. Conclusion: Our results indicate that NDEFgel may be a promising dual-action therapeutic option for advanced wound management in the future.

Concentration- and pH-Dependent Oligomerization of the Thrombin-Derived C-Terminal Peptide TCP-25

Peptide oligomerization dynamics affects peptide structure, activity, and pharmacodynamic properties. The thrombin C-terminal peptide, TCP-25 (GKYGFYTHVFRLKKWIQKVIDQFGE), is currently in preclinical development for improved wound healing and infection prevention. It exhibits turbidity when formulated at pH 7.4, particularly at concentrations of 0.3 mM or more. We used biochemical and biophysical approaches to explore whether the peptide self-associates and forms oligomers. The peptide showed a dose-dependent increase in turbidity as well as α-helical structure at pH 7.4, a phenomenon not observed at pH 5.0. By analyzing the intrinsic tryptophan fluorescence, we demonstrate that TCP-25 is more stable at high concentrations (0.3 mM) when exposed to high temperatures or a high concentration of denaturant agents, which is compatible with oligomer formation. The denaturation process was reversible above 100 µM of peptide. Dynamic light scattering demonstrated that TCP-25 oligomerization is sensitive to changes in pH, time, and temperature. Computational modeling with an active 18-mer region of TCP-25 showed that the peptide can form pH-dependent higher-order end-to-end oligomers and micelle-like structures, which is in agreement with the experimental data. Thus, TCP-25 exhibits pH- and temperature-dependent dynamic changes involving helical induction and reversible oligomerization, which explains the observed turbidity of the pharmacologically developed formulation.

Real-time in vivo Imaging of LPS-induced Local Inflammation and Drug Deposition in NF-κB Reporter Mice

Wound, biomaterial, and surgical infections are all characterized by a localized and excessive inflammation, motivating the development of in vivo methods focused on the analysis of local immune events. However, current inflammation models, such as the commonly used in vivo models of endotoxin-induced inflammation are based on systemic, usually intraperitoneal, administration of lipopolysaccharide (LPS), causing endotoxin shock. Here, we describe a model of LPS-induced local inflammation in NF-κB-RE-Luc reporter mice. LPS, alone or with added therapeutic substances, is delivered locally via a hydrogel which is deposited subcutaneously, providing a spatially defined environment, enabling in vivo bioimaging analyses of local NF-κB activation. Evaluation of drug efficacy can be analyzed longitudinally in the same mouse, and using fluorescently labeled drugs, local drug deposition can be simultaneously analyzed, and correlated to the site of inflammation. Finally, the protocol can also be used to study retention and systemic release of the drug from locally deposited gels and other biomaterials.

Natural Polymer-Based Antimicrobial Hydrogels without Synthetic Antibiotics as Wound Dressings

Wound healing is usually accompanied by bacterial infection. The excessive use of synthetic antibiotics leads to drug resistance, posing a significant threat to human health. Hydrogel-based wound dressings aimed at mitigating bacterial infections have emerged as an effective wound treatment. The review presented herein particularly focuses on the hydrogels originating from natural polymers. To further enhance the performance of wound dressings, various strategies and approaches have been developed to endow the hydrogels with excellent broad-spectrum antibacterial activity. Those that are summarized in the current review are the hydrogels with intrinsic or stimuli-triggered bactericidal properties and others that serve as vehicles for loading antibacterial agents without synthetic antibiotics. Specific attention is paid to antimicrobial mechanisms and the antibacterial performance of hydrogels. Practical antibacterial applications to accelerate the wound healing employing these antibiotic-free hydrogels are also introduced along with the discussion on the current challenges and perspectives leading to new technologies.

Novel Anti-Inflammatory Approaches for Cystic Fibrosis Lung Disease: Identification of Molecular Targets and Design of Innovative Therapies

Cystic fibrosis (CF) is the most common genetic disorder among Caucasians, estimated to affect more than 70,000 people in the world. Severe and persistent bronchial inflammation and chronic bacterial infection, along with airway mucus obstruction, are hallmarks of CF lung disease and participate in its progression. Anti-inflammatory therapies are, therefore, of particular interest for CF lung disease. Furthermore, a better understanding of the molecular mechanisms involved in airway infection and inflammation in CF has led to the development of new therapeutic approaches that are currently under evaluation by clinical trials. These new strategies dedicated to CF inflammation are designed to treat different dysregulated aspects such as oxidative stress, cytokine secretion, and the targeting of dysregulated pathways. In this review, we summarize the current understanding of the cellular and molecular mechanisms that contribute to abnormal lung inflammation in CF, as well as the new anti-inflammatory strategies proposed to CF patients by exploring novel molecular targets and novel drug approaches.

Thrombin-derived C-terminal fragments aggregate and scavenge bacteria and their proinflammatory products

Thrombin-derived C-terminal peptides (TCPs), including a major 11-kDa fragment (TCP96), are produced through cleavage by human neutrophil elastase and aggregate lipopolysaccharide (LPS) and the Gram-negative bacterium Escherichia coli. However, the physiological roles of TCP96 in controlling bacterial infections and reducing LPS-induced inflammation are unclear. Here, using various biophysical methods, in silico molecular modeling, microbiological and cellular assays, and animal models, we examined the structural features and functional roles of recombinant TCP96 (rTCP96) in the aggregation of multiple bacteria and the Toll-like receptor (TLR) agonists they produce. We found that rTCP96 aggregates both Gram-negative and Gram-positive bacteria, including Staphylococcus aureus and Pseudomonas aeruginosa, and their cell-wall components LPS, lipid A, and lipoteichoic acid (LTA). The Gram-negative bacteria E. coli and P. aeruginosa were particularly sensitive to aggregation-induced bacterial permeabilization and killing. As a proof of concept, we show that rTCP96 reduces LPS-induced NF-κB activation in human monocytes, as well as in mouse models of LPS-induced subcutaneous inflammation. Moreover, in a mouse model of subcutaneous inoculation with P. aeruginosa, rTCP96 reduced bacterial levels. Together, these results link TCP-mediated aggregation of endotoxins and bacteria in vitro to attenuation of inflammation and bacterial levels in vivo.