The Diels-Alder Cross-Linked Gelatin/Dextran Nanocomposite Hydrogels with Silver Nanoparticles for Wound Healing Applications: Synthesis, Characterization, and In Vitro Evaluation

Wound healing involves a sophisticated biological process that relies on ideal conditions to advance through various stages of repair. Modern wound dressings are designed to imitate the natural surroundings around cells and offer properties such as moisture regulation, strength, and antimicrobial defense to boost healing. A recent research project unveiled a new type of gelatin (Gel)/dextran (Dex) hydrogels, linked through Diels-Alder (D-A) reactions, loaded with silver nanoparticles (Ag-NPs) for cutting-edge wound treatment. Gel and Dex were chemically modified to form the hydrogels via the D-A reaction. The hydrogels were enriched with Ag-NPs at varying levels. Thorough analyses of the hydrogels using methods like NMR, FT-IR, and SEM were carried out to assess their structure and nanoparticle integration. Rheological tests displayed that the hydrogels had favorable mechanical attributes, particularly when Ag-NPs were included. The hydrogels demonstrated controlled swelling, responsiveness to pH changes, and were non-toxic. Testing against E. coli showcased the strong antibacterial activity of the nanocomposite hydrogels in a concentration-dependent manner. This investigation showcased the promise of these bioactive nanocomposite hydrogels in promoting speedy wound healing by maintaining a moist environment, offering an antimicrobial shield, and ensuring mechanical support at the wound site.

Polymer-Drug Conjugates Codeliver a Temozolomide Intermediate and Nitric Oxide for Enhanced Chemotherapy against Glioblastoma Multiforme

Polymer-drug conjugates (PDCs) provide possibilities for the development of multiresponsive drug delivery and release platforms utilized in cancer therapy. The delivery of Temozolomide (TMZ, a DNA methylation agent) by PDCs has been developed to improve TMZ stability under physiological conditions for the treatment of glioblastoma multiforme (GBM); however, with inefficient chemotherapeutic efficacy. In this work, we synthesized an amphiphilic triblock copolymer (P1-SNO) with four pendant functionalities, including (1) a TMZ intermediate (named MTIC) as a prodrug moiety, (2) a disulfide bond as a redox-responsive trigger to cage MTIC, (3) S-nitrosothiol as a light/heat-responsive donor of nitric oxide (NO), and (4) a poly(ethylene glycol) chain to enable self-assembly in aqueous media. P1-SNO was demonstrated to liberate MTIC in the presence of reduced glutathione and release gaseous NO upon exposure to light or heat. The in vitro results revealed a synergistic effect of released MTIC and NO on both TMZ-sensitive and TMZ-resistant GBM cells. The environment-responsive PDC system for codelivery of MTIC and NO is promising to overcome the efficacy issue in TMZ-based cancer therapy.

Therapeutic Delivery of Nitric Oxide Utilizing Saccharide-Based Materials

As a gasotransmitter, nitric oxide (NO) regulates physiological pathways and demonstrates therapeutic effects such as vascular relaxation, anti-inflammation, antiplatelet, antithrombosis, antibacterial, and antiviral properties. However, gaseous NO has high reactivity and a short half-life, so NO delivery and storage are critical questions to be solved. One way is to develop stable NO donors and the other way is to enhance the delivery and storage of NO donors from biomaterials. Most of the researchers studying NO delivery and applications are using synthetic polymeric materials, and they have demonstrated significant therapeutic effects of these NO-releasing polymeric materials on cardiovascular diseases, respiratory disease, bacterial infections, etc. However, some researchers are exploring saccharide-based materials to fulfill the same tasks as their synthetic counterparts while avoiding the concerns of biocompatibility, biodegradability, and sustainability. Saccharide-based materials are abundant in nature and are biocompatible and biodegradable, with wide applications in bioengineering, drug delivery, and therapeutic disease treatments. Saccharide-based materials have been implemented with various NO donors (like S-nitrosothiols and N-diazeniumdiolates) via both chemical and physical methods to deliver NO. These NO-releasing saccharide-based materials have exhibited controlled and sustained NO release and demonstrated biomedical applications in various diseases (respiratory, Crohn's, cardiovascular, etc.), skin or wound applications, antimicrobial treatment, bone regeneration, anticoagulation, as well as agricultural and food packaging. This review aims to highlight the studies in methods and progress in developing saccharide-based NO-releasing materials and investigating their potential applications in biomedical, bioengineering, and disease treatment.

NO-releasing polypeptide nanocomposites reverse cancer multidrug resistance via triple therapies

Multidrug resistance (MDR) induced by the overexpression of P-glycoprotein (P-gp) transporters mainly leads to chemotherapy (CT) failure. Herein, a NIR/pH dual-sensitive charge-reversal polypeptide nanocomposite (PDA-PLC) was developed for co-delivering a nitric oxide (NO) donor and doxorubicin (DOX). Under near-infrared (NIR) irradiation, the released high-concentration of NO gas inhibited the P-gp expression to sensitize the chemotherapeutic medicine DOX and assisted photothermal therapy (PTT) to eradicate cancer cells without skin scarring. Further, the distinctive charge-reversal capacity of PDA-PLC significantly facilitated cellular uptake in the tumor acidic microenvironment (pH 6.8) and enhanced its stability in the physiological environment (pH 7.4). This DOX-loading polypeptide nanocomposite (PDA-PLC/DOX) provides an effective strategy for the PTT-NO-CT triple-combination therapy to overcome MDR STATEMENT OF SIGNIFICANCE: Multidrug resistance (MDR) has been considered to be the paramount factor of chemotherapy (CT) failure in cancer. In this work, an NIR/pH dual-sensitive charge-reversal polypeptide nanomedicine (PDA-PLC/DOX) was developed to overcome MDR through the triple combination therapy of photothermal therapy (PTT), NO gas therapy, and CT. The distinctive charge-reversal capacity of PDA-PLC/DOX significantly facilitated cellular uptake in the tumor acidic microenvironment (pH 6.8) and enhanced its stability in the physiological environment (pH 7.4), while the NIR trigger-released NO gas greatly inhibited the expression of P-gp and synergistically enhanced PTT and CT efficacy. This polypeptide nanocomposite PDA-PLC/DOX provides an effective strategy of using the PTT-NO-CT triple combination therapy with charge-reversal property to completely eradicate the MCF-7/ADR tumor.

The evolving landscape for cellular nitric oxide and hydrogen sulfide delivery systems: A new era of customized medications

Nitric oxide (NO) and hydrogen sulfide (H2S) are industrial toxins or pollutants; however, both are produced endogenously and have important biological roles in most mammalian tissues. The recognition that these gasotransmitters have a role in physiological and pathophysiological processes has presented opportunities to harness their intracellular effects either through inhibition of their production; or more commonly, through inducing their levels and or delivering them by various modalities. In this review article, we have focused on an array of NO and H2S donors, their hybrids with other established classes of drugs, and the various engineered delivery platforms such a fibers, polymers, nanoparticles, hydrogels, and others. In each case, we have reviewed the rationale for their development.

Thiolated polymers: Bioinspired polymers utilizing one of the most important bridging structures in nature

Thiolated polymers designated "thiomers" are obtained by covalent attachment of thiol functionalities on the polymeric backbone of polymers. In 1998 these polymers were first described as mucoadhesive and in situ gelling compounds forming disulfide bonds with cysteine-rich substructures of mucus glycoproteins and crosslinking through inter- and intrachain disulfide bond formation. In the following, it was shown that thiomers are able to form disulfides with keratins and membrane-associated proteins exhibiting also cysteine-rich substructures. Furthermore, permeation enhancing, enzyme inhibiting and efflux pump inhibiting properties were demonstrated. Because of these capabilities thiomers are promising tools for drug delivery guaranteeing a strongly prolonged residence time as well as sustained release on mucosal membranes. Apart from that, thiomers are used as drugs per se. In particular, for treatment of dry eye syndrome various thiolated polymers are in development and a first product has already reached the market. Within this review an overview about the thiomer-technology and its potential for different applications is provided discussing especially the outcome of studies in non-rodent animal models and that of numerous clinical trials. Moreover, an overview on product developments is given.

NIR-Responsive Polypeptide Nanocomposite Generates NO Gas, Mild Photothermia, and Chemotherapy to Reverse Multidrug-Resistant Cancer

Multidrug resistance (MDR) of cancers that results from overexpression of a P-glycoprotein (P-gp) transporter mainly causes chemotherapy (CT) failure and hinders clinical transitions of current polypeptide nanomedicines. Herein, a novel polypeptide nanocomposite PNOC-PDA that integrates heat-sensitive NO gas delivery and photothermal conversion attributes can overcome MDR and maximize CT; meanwhile the optimized CT and intracellular high-concentration NO gas can assist a mild photothermal therapy (PTT) to eradicate cancer cells. The triple therapies produced a superior and synergistic effect on MDR-reversal and killing MCF-7/ADR in vitro, and the P-gp expression level was downregulated to 46%, as confirmed by means of MTT, Western blot, flow cytometry, and confocal laser scanning microscopy. Significantly, by using one intravenous injection of PNOC-PDA/DOX and a single near-infrared irradiation, the triple therapies of mild PTT, NO gas therapy, and CT achieved complete MCF-7/ADR tumor ablation without skin damage, scarring, and tumor recurrence within 30 days. This work provides a versatile method for the fabrication of NIR-responsive polypeptide nanocomposite with intrinsic photothermal conversion and NO-releasing attributes, opening up a new avenue for reversing MDR in tumors.

Nitric Oxide-Releasing Macromolecular Scaffolds for Antibacterial Applications

Exogenous nitric oxide (NO) represents an attractive antibacterial agent because of its ability to both disperse and directly kill bacterial biofilms while avoiding resistance. Due to the challenges associated with administering gaseous NO, NO-releasing macromolecular scaffolds are developed to facilitate NO delivery. This progress report describes the rational design and application of NO-releasing macromolecular scaffolds as antibacterial therapeutics. Special consideration is given to the role of the physicochemical properties of the NO storage vehicles on antibacterial or anti-biofilm activity.

Biodegradable crosslinked polyesters derived from thiomalic acid and S-nitrosothiol analogues for nitric oxide release

Crosslinked polyesters with Young's moduli similar to that of certain soft biological tissues were prepared via bulk polycondensation of thiomalic acid and 1,8-octanediol alone, and with citric or maleic acid. The copolymers were converted to nitric oxide (NO)-releasing S-nitrosothiol (RSNO) analogues by reaction with tert-butyl nitrite. Additional conjugation steps were avoided by inclusion of the thiolated monomer during the polycondensation to permit thiol conversion to RSNOs. NO release at physiological pH and temperature (pH 7.4, 37 °C) was determined by chemiluminescence-based NO detection. The average total NO content for poly(thiomalic-co-maleic acid-co-1,8-octanediol), poly(thiomalic-co-citric acid-co-1,8-octanediol), and poly(thiomalic acid-co-1,8-octanediol) was 130 ± 39 μmol g-1, 200 ± 35 μmol g-1, and 130 ± 11 μmol g-1, respectively. The antibacterial properties of the S-nitrosated analogues were confirmed against Escherichia coli and Staphylococcus aureus. The hydrolytic degradation products were analyzed by time-of-flight mass spectrometry after a 10-week study to investigate their composition. Tensile mechanical tests were performed on the non-nitrosated polymers as well as their S-nitrosated derivatives and suggested that the materials have appropriate Young's moduli and elongation values for biomedical applications.

Nitric oxide-releasing injectable hydrogels with high antibacterial activity through in situ formation of peroxynitrite

Nitric oxide (NO) is an endogenous molecule with many critical biological functions that depend on its concentration. At high levels, NO provides broad-spectrum antibacterial effects through both its pathogen inhibition and killing abilities. However, its short half-life has been a great challenge to its clinical application in pharmaceutical forms. In this study, we incorporated the NO donor S-nitrosothiolated gelatin (GelSNO) into injectable gelatin-based hydrogels (GHs) to controllably release NO. Under catalysis by horseradish peroxidase, H₂O₂ oxidizes phenol moieties functionalized on gelatin to quickly form phenol-phenol crosslinks that encapsulate GelSNO. Through thermal, visible light, and oxidizing agent-driven mechanisms, NO is released from the GH/GelSNO hydrogels. By varying the GelSNO concentration, the release of NO was controllable in a wide range, 0.054-2.050 μmol/mL, for up to 14 days. In addition, NO release was fine-tunable as a function of H₂O₂ concentration. Notably, the in situ formation of peroxynitrite (ONOO^-) that produces potent antibacterial effects originated from H₂O₂ residues and nitrous acid formed by NO and oxygen in aqueous solution. The Kirby-Bauer method indicated that there was an inhibition zone against both Escherichia coli and Staphylococcus aureus incubated with GH/GelSNO hydrogels. The AlarmaBlue assay showed that E. coli and S. aureus were completely killed at NO concentrations of 0.39 and 0.58 μmol/mL. Cytotoxicity tests of GH/GelSNO hydrogels on human dermal fibroblasts at the indicated bactericidal NO concentrations induced no cell toxicity. In summary, GH/GelSNO hydrogels may provide a new platform for topical delivery of NO in treating wound infections and for various biomedical applications.

STATEMENT OF SIGNIFICANCE

NO is an effective antibacterial agent even in cases of antibiotic-resistant bacteria. Moreover, its intermediate, peroxynitrite, has been reported to have a much higher ability to kill bacteria. In this study, we utilized injectable GH/GelSNO hydrogels formed by HRP/H₂O₂ reaction not only to control NO release but also to generate peroxynitrite in situ from released NO and H₂O₂ residues. The GH/GelSNO hydrogels showed significant antibacterial ability on both gram-positive and negative bacteria, while no cytotoxicity was induced on human dermal fibroblasts. In addition, their tunable chemico-physical properties and controllable NO release within a wide range but narrow scale will make the hydrogels useful in various biomedical applications.

Hollow double-layered polymer nanoparticles with S-nitrosothiols for tumor targeted therapy

Tumor targeted hollow double-layered polymer nanoparticles (HDPNs) withS-nitrosothiols for nitric oxide (NO)-release as chemotherapy were described.

Recent advances in thromboresistant and antimicrobial polymers for biomedical applications: just say yes to nitric oxide (NO)

Biomedical devices are essential for patient diagnosis and treatment; however, when blood comes in contact with foreign surfaces or homeostasis is disrupted, complications including thrombus formation and bacterial infections can interrupt device functionality, causing false readings and/or shorten device lifetime. Here, we review some of the current approaches for developing antithrombotic and antibacterial materials for biomedical applications. Special emphasis is given to materials that release or generate low levels of nitric oxide (NO). Nitric oxide is an endogenous gas molecule that can inhibit platelet activation as well as bacterial proliferation and adhesion. Various NO delivery vehicles have been developed to improve NO's therapeutic potential. In this review, we provide a summary of the NO releasing and NO generating polymeric materials developed to date, with a focus on the chemistry of different NO donors, the polymer preparation processes, and in vitro and in vivo applications of the two most promising types of NO donors studied thus far, N-diazeniumdiolates (NONOates) and S-nitrosothiols (RSNOs).

Bio-inspired strategies for designing antifouling biomaterials

Contamination of biomedical devices in a biological medium, biofouling, is a major cause of infection and is entirely avoidable. This mini-review will coherently present the broad range of antifouling strategies, germicidal, preventive and cleaning using one or more of biological, chemical and physical techniques. These techniques will be discussed from the point of view of their ability to inhibit protein adsorption, usually the first step that eventually leads to fouling. Many of these approaches draw their inspiration from nature, such as emulating the nitric oxide production in endothelium, use of peptoids that mimic protein repellant peptides, zwitterionic functionalities found in membrane structures, and catechol functionalities used by mussel to immobilize poly(ethylene glycol) (PEG). More intriguing are the physical modifications, creation of micropatterns on the surface to control the hydration layer, making them either superhydrophobic or superhydrophilic. This has led to technologies that emulate the texture of shark skin, and the superhyprophobicity of self-cleaning textures found in lotus leaves. The mechanism of antifouling in each of these methods is described, and implementation of these ideas is illustrated with examples in a way that could be adapted to prevent infection in medical devices.

Reprint of: Nitric oxide-releasing polysaccharide derivative exhibits 8-log reduction against Escherichia coli, Acinetobacter baumannii and Staphylococcus aureus

Health-care associated infections (HAIs) and the increasing number of antibiotic-resistant bacteria strains remain significant public health threats worldwide. Although the number of HAIs has decreased by using improved sterilization protocols, the cost related to HAIs is still quantified in billions of dollars. Furthermore, the development of multi-drug resistant strains is increasing exponentially, demonstrating that current treatments are inefficient. Thus, the quest for new methods to eradicate bacterial infection is increasingly important in antimicrobial, drug delivery and biomaterials research. Herein, the bactericidal activity of a water-soluble NO-releasing polysaccharide derivative was evaluated in nutrient broth media against three bacteria strains that are commonly responsible for HAIs. Data confirmed that this NO-releasing polysaccharide derivative induced an 8-log reduction in bacterial growth after 24h for Escherichia coli, Acinetobacter baumannii and Staphylococcus aureus. Additionally, the absence of bacteria after 72 h of exposure to NO illustrates the inability of the bacteria to recover and the prevention of biofilm formation. The presented 8-log reduction in bacterial survival after 24h is among the highest reduction reported for NO delivery systems to date, and reaches the desired standard for industrially-relevant reduction. More specifically, this system represents the only water-soluble antimicrobial to reach such a significant bacterial reduction in nutrient rich media, wherein experimental conditions more closely mimic the in vivo environment than those in previous reports. Furthermore, the absence of bacterial activity after 72 h and the versatility of using a water-soluble compound suggest that this NO-releasing polysaccharide derivative is a promising route for treating HAIs.

Preparation of Proteoglycan Mimetic Graft Copolymers

Proteoglycans are proteins with pendant glycosaminoglycan polysaccharide side chains. The method described here enables the preparation of graft copolymers with glycosaminoglycan side chains, which mimic the structure and composition of proteoglycans. By controlling the stoichiometry, graft copolymers can be obtained with a wide range of glycosaminoglycan side-chain densities. The method presented here uses a three-step reaction mechanism to first functionalize a hyaluronic acid backbone, followed by reductive amination to couple the glycosaminoglycan side chain to the backbone, by the reducing end. Proteoglycan mimics like the ones proposed here could be used to study the structure-property relationships of proteoglycans and to introduce the biochemical and biomechanical properties of proteoglycans into biomaterials and therapeutic formulations.

Biodegradable citrate-based polyesters with S-nitrosothiol functional groups for nitric oxide release

Nitric oxide (NO) is a biologically-active free radical involved in numerous physiological processes such as regulation of vasodilation, promotion of cell proliferation and angiogenesis, and modulation of the inflammatory and immune responses. Furthermore, NO has demonstrated the ability to mitigate the foreign body response that often results in the failure of implanted biomedical devices. Although NO has promising therapeutic value, the short physiological half-life of exogenous NO complicates its effective delivery. For this reason, the development of NO-releasing materials that permit the localized delivery of NO is an advantageous method of utilizing this molecule for biomedical applications. Herein, we report the synthesis and characterization of biodegradable NO-releasing polyesters prepared from citric acid, maleic acid, and 1,8-octanediol. NO release was achieved by incorporation of S-nitrosothiol donor groups through conjugation of cysteamine and ethyl cysteinate to the polyesters, followed by S-nitrosation with tert-butyl nitrite. The extent of NO loading and the release properties under physiological conditions (pH 7.4 PBS, 37 °C) were determined by chemiluminesence-based NO detection. The average total NO content of poly(citric-co-maleic acid-co-1,8-octanediol)-cysteamine was determined to be 0.45 ± 0.07 mol NO g^-1 polymer, while the NO content for poly(citric-co-maleic acid-co-1,8-octanediol)-ethyl cysteinate was 0.16 ± 0.04 mol NO g^-1 polymer. Continuous NO release under physiological conditions was observed for at least 6 days for the cysteamine analog and 4 days for the ethyl cysteinate analog. Cell viability assays and morphological studies with human dermal fibroblasts indicated an absence of toxic leachates at a cytotoxic level, and suggested that these citrate-based polyesters may be suitable for future biomedical applications.

Nitric oxide-releasing polysaccharide derivative exhibits 8-log reduction against Escherichia coli, Acinetobacter baumannii and Staphylococcus aureus

Health-care associated infections (HAIs) and the increasing number of antibiotic-resistant bacteria strains remain significant public health threats worldwide. Although the number of HAIs has decreased by using improved sterilization protocols, the cost related to HAIs is still quantified in billions of dollars. Furthermore, the development of multi-drug resistant strains is increasing exponentially, demonstrating that current treatments are inefficient. Thus, the quest for new methods to eradicate bacterial infection is increasingly important in antimicrobial, drug delivery and biomaterials research. Herein, the bactericidal activity of a water-soluble NO-releasing polysaccharide derivative was evaluated in nutrient broth media against three bacteria strains that are commonly responsible for HAIs. Data confirmed that this NO-releasing polysaccharide derivative induced an 8-log reduction in bacterial growth after 24h for Escherichia coli, Acinetobacter baumannii and Staphylococcus aureus. Additionally, the absence of bacteria after 72h of exposure to NO illustrates the inability of the bacteria to recover and the prevention of biofilm formation. The presented 8-log reduction in bacterial survival after 24h is among the highest reduction reported for NO delivery systems to date, and reaches the desired standard for industrially-relevant reduction. More specifically, this system represents the only water-soluble antimicrobial to reach such a significant bacterial reduction in nutrient rich media, wherein experimental conditions more closely mimic the in vivo environment than those in previous reports. Furthermore, the absence of bacterial activity after 72h and the versatility of using a water-soluble compound suggest that this NO-releasing polysaccharide derivative is a promising route for treating HAIs.

Cardiac catheterization: consequences for the endothelium and potential for nanomedicine

Cardiac catheterization results in interactions between the catheter and surfaces and the artery lumen, which is lined by the endothelium. These interactions can range from minor rubbing to severe mechanical injury. Further, in the case of radial access, even atraumatic interactions have consequences ranging from clinical complications, such as radial spasm and radial occlusion, to lasting endothelial cell dysfunction. These consequences may be underappreciated; however, endothelial cells play a central role in maintaining vascular homeostasis via nitric oxide production. Existing treatment paradigms do not address endothelial dysfunction or damage and, thus, novel therapeutic approaches are needed. Nanomedicine, in particular, offers great potential in the form of targeted drug delivery, via functionalized coatings or nanocarriers, aimed at increased nitric oxide bioavailability or reduced inflammation.

Anti-thrombogenic properties of a nitric oxide-releasing dextran derivative: evaluation of platelet activation and whole blood clotting kinetics

Controlling platelet activation and clotting initiated by cardiovascular interventions remains a major challenge in clinical practice. In this work, the anti-thrombotic properties of a polysaccharide-based nitric oxide (NO)-releasing dextran derivative are presented. Total platelet adhesion, platelet morphology and whole blood clotting kinetics were used as indicators to evaluate the anti-clotting properties of this material. With a total NO delivery of 0.203±0.003 μmol, the NO-releasing dextran derivative (Dex-SNO) mixed with blood plasma demonstrated a significantly lower amount of platelet adhesion and activation onto a surface and reduced whole blood clotting kinetics. Nearly 75% reduction in platelet adhesion and a significant retention of platelet morphology were observed with blood plasma treated with Dex-SNO, suggesting this to be a potential anti-platelet therapeutic agent for preventing thrombosis that does not have an adverse effect on circulating platelets.

Applications for nitric oxide in halting proliferation of tumor cells

Tumor resistance to cytotoxic therapeutics coupled with dose-limiting toxicity is a serious hurdle in the field of medical oncology. In the face of this obstacle, nitric oxide has emerged as a powerful adjuvant for the hypersensitization of tumors to more traditional chemo- and radio-therapeutics. Furthermore, emerging evidence indicates that nitric oxide donors have the potential to function independently in the clinical management of cancer. Herein, we discuss the role of nitric oxide in cancer and the potential for nitric oxide donors to support conventional therapeutics.