Biodegradable poly(lactic-co-glycolic acid) microspheres loaded with S-nitroso-N-acetyl-D-penicillamine for controlled nitric oxide delivery

Fabrication and Optimization of Poly(ε-caprolactone) Microspheres Loaded with S-Nitroso-N-Acetylpenicillamine for Nitric Oxide Delivery

Heart disease is one of the leading causes of death in the United States and throughout the world. While there are different techniques for reducing or preventing the impact of heart disease, nitric oxide (NO) is administered as nitroglycerin for reversing angina or chest pain. Unfortunately, due to its gaseous and short-lived half-life, NO can be difficult to study or even administer. Therefore, controlled delivery of NO is desirable for therapeutic use. In the current study, the goal was to fabricate NO-releasing microspheres (MSs) using a donor molecule, S-Nitroso-N-Acetyl penicillamine, (SNAP), and encapsulating it in poly(ε-caprolactone) (PCL) using a single-emulsion technique that can provide sustained delivery of NO to cells over time without posing any toxicity risks. Optimization of the fabrication process was performed by varying the duration of homogenization (5, 10, and 20 min) and its effect on entrapment efficiency and size. The optimized SNAP-MS had an entrapment efficiency of ˃50%. Furthermore, we developed a modified method for NO detection by using NO microsensors to detect the NO release from SNAP-MSs in real time, showing sustained release behavior. The fabricated SNAP-MSs were tested for biocompatibility with HUVECs (human umbilical vein endothelial cells), which were found to be biocompatible. Lastly, we tested the effect of controlled NO delivery to human induced pluripotent stem-derived cardiomyocytes (hiPSC-CMs) via SNAP-MSs, which showed a significant improvement in the electrophysiological parameters and alleviated anoxic stress.

De novo design of a nanoregulator for the dynamic restoration of ovarian tissue in cryopreservation and transplantation

The cryopreservation and transplantation of ovarian tissue underscore its paramount importance in safeguarding reproductive capacity and ameliorating reproductive disorders. However, challenges persist in ovarian tissue cryopreservation and transplantation (OTC-T), including the risk of tissue damage and dysfunction. Consequently, there has been a compelling exploration into the realm of nanoregulators to refine and enhance these procedures. This review embarks on a meticulous examination of the intricate anatomical structure of the ovary and its microenvironment, thereby establishing a robust groundwork for the development of nanomodulators. It systematically categorizes nanoregulators and delves deeply into their functions and mechanisms, meticulously tailored for optimizing ovarian tissue cryopreservation and transplantation. Furthermore, the review imparts valuable insights into the practical applications and obstacles encountered in clinical settings associated with OTC-T. Moreover, the review advocates for the utilization of microbially derived nanomodulators as a potent therapeutic intervention in ovarian tissue cryopreservation. The progression of these approaches holds the promise of seamlessly integrating nanoregulators into OTC-T practices, thereby heralding a new era of expansive applications and auspicious prospects in this pivotal domain.

Preventing Staphylococci Surgical Site Infections with a Nitric Oxide-Releasing Poly(lactic acid-co-glycolic acid) Suture Material

Of the 27 million surgeries performed in the United States each year, a reported 2.6% result in a surgical site infection (SSI), and Staphylococci species are commonly the culprit. Alternative therapies, such as nitric oxide (NO)-releasing biomaterials, are being developed to address this issue. NO is a potent antimicrobial agent with several modes of action, including oxidative and nitrosative damage, disruption of bacterial membranes, and dispersion of biofilms. For targeted antibacterial effects, NO is delivered by exogenous donor molecules, like S-nitroso-N-acetylpenicillamine (SNAP). Herein, the impregnation of SNAP into poly(lactic-co-glycolic acid) (PLGA) for SSI prevention is reported for the first time. The NO-releasing PLGA copolymer is fabricated and characterized by donor molecule loading, leaching, and the amount remaining after ethylene oxide sterilization. The swelling ratio, water uptake, static water contact angle, and tensile strength are also investigated. Furthermore, its cytocompatibility is tested against 3T3 mouse fibroblast cells, and its antimicrobial efficacy is assessed against multiple Staphylococci strains. Overall, the NO-releasing PLGA copolymer holds promise as a suture material for eradicating surgical site infections caused by Staphylococci strains. SNAP impregnation affords robust antibacterial properties while maintaining the cytocompatibility and mechanical integrity.

Mechanistic analysis of the photolytic decomposition of solid-state S-nitroso-N-acetylpenicillamine

S-Nitroso-N-acetylpenicillamine (SNAP) is among the most common nitric oxide (NO)-donor molecules and its solid-state photolytic decomposition has potential for inhaled nitric oxide (iNO) therapy. The photochemical NO release kinetics and mechanism were investigated by exposing solid-state SNAP to a narrow-band LED as a function of nominal wavelength and intensity of incident light. The photolytic efficiency, decomposition products, and the photolytic pathways of the SNAP were examined. The maximum light penetration depth through the solid layer of SNAP was determined by an optical microscope and found to be within 100-200 μm, depending on the wavelength of light. The photolysis of solid-state SNAP to generate NO along with the stable thiyl (RS·) radical was confirmed using Electron Spin Resonance (ESR) spectroscopy. The fate of the RS· radical in the solid phase was studied both in the presence and absence of O2 using NMR, IR, ESR, and UPLC-MS. The changes in the morphology of SNAP due to its photolysis were examined using PXRD and SEM. The stable thiyl radical formed from the photolysis of solid SNAP was found to be reactive with another adjacent thiyl radical to form a disulfide (RSSR) or with oxygen to form various sulfonyl and sulfonyl peroxyl radicals {RS(O)xO·, x = 0 to 7}. However, the thiyl radical did not recombine with NO to reform the SNAP. From the PXRD data, it was found that the SNAP loses its crystallinity by generating the NO after photolysis. The initial release of NO during photolysis was increased with increased intensity of light, whereas the maximum light penetration depth was unaffected by light intensity. The knowledge gained about the photochemical reactions of SNAP may provide important insight in designing portable photoinduced NO-releasing devices for iNO therapy.

Ultraviolet Light Responsive N-Nitroso Polymers for Antibacterial Nitric Oxide Delivery

This study investigates the incorporation of active secondary amine moieties into the polymer backbone by co-polymerizing 2,4,6-tris(chloromethyl)-mesitylene with three diamines, namely 1,4-diaminobutane, m-phenylenediamine, and p-phenylenediamine. This process results in the stabilization of the amine moieties and the subsequently introduced nitroso groups. Charging bioactive nitric oxide (NO) into the polymers is accomplished by converting the amine moieties into N-nitroso groups. The ability of the polymers to store and release NO depends on their structures, particularly the amount of incorporated active secondary amines. With grafting photosensitive N-nitroso groups into the polymers, the derived NO@polymers exhibit photoresponsivity. NO release is completely regulated by adjusting UV light irradiation. These resulting polymeric NO donors demonstrate remarkable bactericidal and bacteriostatic activity, effectively eradicating E. coli bacteria and inhibiting their growth. The findings from this study hold promising implications for combining NO delivery with phototherapy in various medical applications.

Nitric Oxide: Physiological Functions, Delivery, and Biomedical Applications

Nitric oxide (NO) is a gaseous molecule that has a central role in signaling pathways involved in numerous physiological processes (e.g., vasodilation, neurotransmission, inflammation, apoptosis, and tumor growth). Due to its gaseous form, NO has a short half-life, and its physiology role is concentration dependent, often restricting its function to a target site. Providing NO from an external source is beneficial in promoting cellular functions and treatment of different pathological conditions. Hence, the multifaceted role of NO in physiology and pathology has garnered massive interest in developing strategies to deliver exogenous NO for the treatment of various regenerative and biomedical complexities. NO-releasing platforms or donors capable of delivering NO in a controlled and sustained manner to target tissues or organs have advanced in the past few decades. This review article discusses in detail the generation of NO via the enzymatic functions of NO synthase as well as from NO donors and the multiple biological and pathological processes that NO modulates. The methods for incorporating of NO donors into diverse biomaterials including physical, chemical, or supramolecular techniques are summarized. Then, these NO-releasing platforms are highlighted in terms of advancing treatment strategies for various medical problems.

SNAP@CQD as a promising therapeutic vehicle against HCoVs: an overview

This report discusses potential therapies for treating human coronaviruses (HCoVs) and their economic impact. Specifically, we explore therapeutics that can support the body's immune response, including immunoglobulin (Ig)A, IgG and T-cell responses, to inhibit the viral replication cycle and improve respiratory function. We hypothesize that carbon quantum dots conjugated with S-nitroso-N-acetylpenicillamine (SNAP) could be a synergistic alternative cure for treating respiratory injuries caused by HCoV infections. To achieve this, we propose developing aerosol sprays containing SNAP moieties that release nitric oxide and are conjugated onto promising nanostructured materials. These sprays could combat HCoVs by inhibiting viral replication and improving respiratory function. Furthermore, they could potentially provide other benefits, such as providing novel possibilities for nasal vaccines in the future. Teaser: Synergistic effect of carbon quantum dots and S-nitroso-N-acetylpenicillamine (SNAP) could be suggested as an alternative treatment for the respiratory damage caused by HCoV infections that further open possibilities of developing novel nasal vaccines.

Biomimetic gasotransmitter-releasing alginate beads for biocompatible antimicrobial therapy

HYPOTHESIS

Alginate is widely used in biomedical applications due to its high biocompatibility as well as structural and mechanical similarities to human tissue. Further, simple ionic crosslinking of alginate allows for the formation of alginate beads capable of drug delivery. S-nitrosoglutathione is a water-soluble molecule that releases nitric oxide in physiological conditions, where it acts as a potent antimicrobial gas, among other functions. As macrophages and endothelial cells endogenously produce nitric oxide, incorporating nitric oxide donors into polymers and hydrogels introduces a biomimetic approach to mitigate clinical infections, including those caused by antibiotic-resistant microorganisms. The incorporation of S-nitrosoglutathione into macro-scale spherical alginate beads is reported for the first time and shows exciting potential for biomedical applications.

EXPERIMENTS

Herein, nitric oxide-releasing crosslinked alginate beads were fabricated and characterized for surface and cross-sectional morphology, water uptake, size distribution, and storage stability. In addition, the NO release was quantified by chemiluminescence and its biological effects against Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus were investigated. The biocompatibility of the alginate beads was tested against 3T3 mouse fibroblast cells.

FINDINGS

Overall, nitric oxide-releasing alginate beads demonstrate biologically relevant activities without eliciting a cytotoxic response, revealing their potential use as an antimicrobial material with multiple mechanisms of bacterial killing.

Effect of composite biodegradable biomaterials on wound healing in diabetes

The repair of diabetic wounds has always been a job that doctors could not tackle quickly in plastic surgery. To solve this problem, it has become an important direction to use biocompatible biodegradable biomaterials as scaffolds or dressing loaded with a variety of active substances or cells, to construct a wound repair system integrating materials, cells, and growth factors. In terms of wound healing, composite biodegradable biomaterials show strong biocompatibility and the ability to promote wound healing. This review describes the multifaceted integration of biomaterials with drugs, stem cells, and active agents. In wounds, stem cells and their secreted exosomes regulate immune responses and inflammation. They promote angiogenesis, accelerate skin cell proliferation and re-epithelialization, and regulate collagen remodeling that inhibits scar hyperplasia. In the process of continuous combination with new materials, a series of materials that can be well matched with active ingredients such as cells or drugs are derived for precise delivery and controlled release of drugs. The ultimate goal of material development is clinical transformation. At present, the types of materials for clinical application are still relatively single, and the bottleneck is that the functions of emerging materials have not yet reached a stable and effective degree. The development of biomaterials that can be further translated into clinical practice will become the focus of research.

Therapeutic gas-releasing nanomedicines with controlled release: Advances and perspectives

Nanoparticle-based drug delivery has become one of the most popular approaches for maximising drug therapeutic potentials. With the notable improvements, a greater challenge hinges on the formulation of gasotransmitters with unique challenges that are not met in liquid and solid active ingredients. Gas molecules upon release from formulations for therapeutic purposes have not really been discussed extensively. Herein, we take a critical look at four key gasotransmitters, that is, carbon monoxide (CO), nitric oxide (NO), hydrogen sulphide (H2S) and sulphur dioxide (SO2), their possible modification into prodrugs known as gas-releasing molecules (GRMs), and their release from GRMs. Different nanosystems and their mediatory roles for efficient shuttling, targeting and release of these therapeutic gases are also reviewed extensively. This review thoroughly looks at the diverse ways in which these GRM prodrugs in delivery nanosystems are designed to respond to intrinsic and extrinsic stimuli for sustained release. In this review, we seek to provide a succinct summary for the development of therapeutic gases into potent prodrugs that can be adapted in nanomedicine for potential clinical use.

Smartphone compatible nitric oxide releasing insert to prevent catheter-associated infections

A large fraction of nosocomial infections is associated with medical devices that are deemed life-threatening in immunocompromised patients. Medical device-related infections are a result of bacterial colonization and biofilm formation on the device surface that affects >1 million people annually in the US alone. Over the past few years, light-based antimicrobial therapy has made substantial advances in tackling microbial colonization. Taking the advantage of light and antibacterial properties of nitric oxide (NO), for the first time, a robust, biocompatible, anti-infective approach to design a universal disposable catheter disinfection insert (DCDI) that can both prevent bacterial adhesion and disinfect indwelling catheters in situ is reported. The DCDI is engineered using a photo-initiated NO donor molecule, incorporated in polymer tubing that is mounted on a side glow fiber optic connected to an LED light source. Using a smartphone application, the NO release from DCDI is photoactivated via white light resulting in tunable physiological levels of NO for up to 24 h. When challenged with microorganisms S. aureus and E. coli, the NO-releasing DCDI statistically reduced microbial attachment by >99% versus the controls with just 4 h of exposure. The DCDI also eradicated ∼97% of pre-colonized bacteria on the CVC catheter model demonstrating the ability to exterminate an established catheter infection. The smart, mobile-operated novel universal antibacterial device can be used to both prevent catheter infections or can be inserted within an infected catheter to eradicate the bacteria without complex surgical interventions. The therapeutic levels of NO generated via illuminating fiber optics can be the next-generation biocompatible solution for catheter-related bloodstream infections.

Integrin receptor-binding nanofibrous peptide hydrogel for combined mesenchymal stem cell therapy and nitric oxide delivery in renal ischemia/reperfusion injury

Background

Mesenchymal-based therapy has been utilized as a practical approach in the treatment of renal ischemia/reperfusion (I/R) injury. However, low cell retention and survival in the ischemic site have remained challenging issues. To bridge this gap, the integrin receptor-binding RGD peptide-functionalized, s-nitroso-n-acetyl penicillamine (SNAP)-loaded hydrogel was used to transplant Wharton's jelly-mesenchymal stem cells (WJ-MSCs).

Methods

Apart from physicochemical and rheological characterizations that confirmed entangled interlocking β-sheets with nanofibrous morphology, real-time RT-PCR, ROS production, serum biomarker concentrations, and histopathological alterations were explored in a mouse model to assess the therapeutic efficacy of formulations in the treatment of renal I/R injury.

Results

The RGD-functionalized Fmoc-diphenylalanine (Fmoc-FF + Fmoc-RGD) hydrogel supported the spread and proliferation of WJ-MSCs in vivo. Notably, intralesional injection of nitric oxide donor combined with the embedded WJ-MSCs caused superior recovery of renal I/R injury compared to free WJ-MSCs alone in terms of histopathological scores and renal function indices. Compared to the I/R control group, oxidative stress and inducible nitric oxide synthase (iNOS) expression biomarkers showed a significant decline, whereas endothelial nitric oxide synthase (eNOS) and vascular endothelial growth factor (VEGF) expression exhibited a significant increment, indicating regeneration of the injured endothelial tissue.

Conclusion

The findings confirmed that the hydrogels containing WJ-MSCs and nitric oxide donors can promote the regeneration of renal I/R injuries by increasing angiogenic factors and cell engraftment.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-03045-1.

NO in Viral Infections: Role and Development of Antiviral Therapies

Nitric oxide is a ubiquitous signaling radical that influences critical body functions. Its importance in the cardiovascular system and the innate immune response to bacterial and viral infections has been extensively investigated. The overproduction of NO is an early component of viral infections, including those affecting the respiratory tract. The production of high levels of NO is due to the overexpression of NO biosynthesis by inducible NO synthase (iNOS), which is involved in viral clearance. The development of NO-based antiviral therapies, particularly gaseous NO inhalation and NO-donors, has proven to be an excellent antiviral therapeutic strategy. The aim of this review is to systematically examine the multiple research studies that have been carried out to elucidate the role of NO in viral infections and to comprehensively describe the NO-based antiviral strategies that have been developed thus far. Particular attention has been paid to the potential mechanisms of NO and its clinical use in the prevention and therapy of COVID-19.

Magnetic Responsive Release of Nitric Oxide from an MOF-Derived Fe3O4@PLGA Microsphere for the Treatment of Bacteria-Infected Cutaneous Wound

Nitric oxide (NO) is an essential endogenous signaling molecule regulating multifaceted physiological functions in the (cardio)vascular, neuronal, and immune systems. Due to the short half-life and location-/concentration-dependent physiological function of NO, translational application of NO as a novel therapeutic approach, however, awaits a strategy for spatiotemporal control on the delivery of NO. Inspired by the magnetic hyperthermia and magneto-triggered drug release featured by Fe₃O₄ conjugates, in this study, we aim to develop a magnetic responsive NO-release material (MagNORM) featuring dual NO-release phases, namely, burst and steady release, for the selective activation of NO-related physiology and treatment of bacteria-infected cutaneous wound. After conjugation of NO-delivery [Fe(μ-S-thioglycerol)(NO)₂]₂ with a metal-organic framework (MOF)-derived porous Fe₃O₄@C, encapsulation of obtained conjugates within the thermo-responsive poly(lactic-co-glycolic acid) (PLGA) microsphere completes the assembly of MagNORM. Through continuous/pulsatile/no application of the alternating magnetic field (AMF) to MagNORM, moreover, burst/intermittent/slow release of NO from MagNORM demonstrates the AMF as an ON/OFF switch for temporal control on the delivery of NO. Under continuous application of the AMF, in particular, burst release of NO from MagNORM triggers an effective anti-bacterial activity against both Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli). In addition to the magneto-triggered bactericidal effect of MagNORM against E. coli-infected cutaneous wound in mice, of importance, steady release of NO from MagNORM without the AMF promotes the subsequent collagen formation and wound healing in mice.

Promotion of angiogenesis toward transplanted ovaries using nitric oxide releasing nanoparticles in fibrin hydrogel

Transplantation of ovary is one method of facilitating fertility preservation to increase the quality of life of cancer survivors. Immediately after transplantation, ovaries are under ischemic conditions owing to a lack of vascular anastomosis between the graft and host tissues. The transplanted ovaries can suffer damage because of lack of oxygen and nutrients, resulting in necrosis and dysfunction. In the technique proposed in this paper, the ovary is encapsulated with nitric oxide-releasing nanoparticles (NO-NPs) in fibrin hydrogels, which form a carrying matrix to prevent ischemic damage and accelerate angiogenesis. The low concentration of NO released from mPEG-PLGA nanoparticles elicits blood vessel formation, which allows transplanted ovaries in the subcutis to recover from the ischemic period. In experiments with mice, the NO-NPs/fibrin hydrogel improved the total number and quality of ovarian follicles after transplantation. The intra-ovarian vascular density was 4.78 folds higher for the NO-NPs/fibrin hydrogel groups compared to that for the nontreated groups. Finally,in vitrofertilization revealed a successful blastocyst formation rate for NO-NPs/fibrin hydrogel coated ovaries. Thus, NO-NPs/fibrin hydrogels can provide an appropriate milieu to promote angiogenesis and be considered as adjuvant surgery materials for fertility preservation.

Engineering macromolecular nanocarriers for local delivery of gaseous signaling molecules

In addition to being notorious air pollutants, nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H₂S) have also been known as endogenous gaseous signaling molecules (GSMs). These GSMs play critical roles in maintaining the homeostasis of living organisms. Importantly, the occurrence and development of many diseases such as inflammation and cancer are highly associated with the concentration changes of GSMs. As such, GSMs could also be used as new therapeutic agents, showing great potential in the treatment of many formidable diseases. Although clinically it is possible to directly inhale GSMs, the precise control of the dose and concentration for local delivery of GSMs remains a substantial challenge. The development of gaseous signaling molecule-releasing molecules provides a great tool for the safe and convenient delivery of GSMs. In this review article, we primarily focus on the recent development of macromolecular nanocarriers for the local delivery of various GSMs. Learning from the chemistry of small molecule-based donors, the integration of these gaseous signaling molecule-releasing molecules into polymeric matrices through physical encapsulation, post-modification, or direct polymerization approach renders it possible to fabricate numerous macromolecular nanocarriers with optimized pharmacokinetics and pharmacodynamics, revealing improved therapeutic performance than the small molecule analogs. The development of GSMs represents a new means for many disease treatments with unique therapeutic outcomes.

Delivery of Nitric Oxide in the Cardiovascular System: Implications for Clinical Diagnosis and Therapy

Nitric oxide (NO) is a key molecule in cardiovascular homeostasis and its abnormal delivery is highly associated with the occurrence and development of cardiovascular disease (CVD). The assessment and manipulation of NO delivery is crucial to the diagnosis and therapy of CVD, such as endothelial dysfunction, atherosclerotic progression, pulmonary hypertension, and cardiovascular manifestations of coronavirus (COVID-19). However, due to the low concentration and fast reaction characteristics of NO in the cardiovascular system, clinical applications centered on NO delivery are challenging. In this tutorial review, we first summarized the methods to estimate the in vivo NO delivery process, based on computational modeling and flow-mediated dilation, to assess endothelial function and vulnerability of atherosclerotic plaque. Then, emerging bioimaging technologies that have the potential to experimentally measure arterial NO concentration were discussed, including Raman spectroscopy and electrochemical sensors. In addition to diagnostic methods, therapies aimed at controlling NO delivery to regulate CVD were reviewed, including the NO release platform to treat endothelial dysfunction and atherosclerosis and inhaled NO therapy to treat pulmonary hypertension and COVID-19. Two potential methods to improve the effectiveness of existing NO therapy were also discussed, including the combination of NO release platform and computational modeling, and stem cell therapy, which currently remains at the laboratory stage but has clinical potential for the treatment of CVD.

Modulating nitric oxide-generating activity of zinc oxide by morphology control and surface modification

Zinc oxide (ZnO) has emerged as a promising material for nitric oxide (NO) delivery owing to its intrinsic enzyme-mimicking activities to catalyze NO prodrugs S-nitrosoglutathione (GSNO) and β-gal-NONOate for NO generation. The catalytic performance of enzyme mimics is strongly dependent on their size, shape, and surface chemistry; however, no studies have evaluated the influence of the aforementioned factors on the NO-generating activity of ZnO. Understanding these factors will provide an opportunity to tune NO generation profiles to accommodate diverse biomedical applications. In this paper, for the first time, we demonstrate that the activity of ZnO towards catalytic NO generation is shape-dependent, resulting from the different crystal growth directions of these particles. We modified the surfaces of ZnO particles with zeolitic imidazolate framework (ZIF-8) by in situ synthesis and observed that ZnO/ZIF-8 retained 60% of its NO-generating potency. The newly formed ZnO/ZIF-8 particles were shown to catalytically decompose both endogenous (GSNO) and exogenous (β-gal-NONOate and S-nitroso-N-acetylpenicillamine (SNAP)) prodrugs to generate NO at physiological conditions. In addition, we design the first platform that combines NO-generating and superoxide radical scavenging properties by encapsulating a natural enzyme, superoxidase dismutase (SOD), into ZnO/ZIF-8 particles, which holds great promise towards combinatorial therapy.

Nitric oxide for the prevention and treatment of viral, bacterial, protozoal and fungal infections

Although the antimicrobial potential of nitric oxide (NO) is widely published, it is little used clinically. NO is a key signalling molecule modulating vascular, neuronal, inflammatory and immune responses. Endogenous antimicrobial activity is largely mediated by high local NO concentrations produced by cellular inducible nitric oxide synthase, and by derivative reactive nitrogen oxide species including peroxynitrite and S-nitrosothiols. NO may be taken as dietary substrate (inorganic nitrate, L-arginine), and therapeutically as gaseous NO, and transdermal, sublingual, oral, intranasal and intravenous nitrite or nitrate. Numerous preclinical studies have demonstrated that NO has generic static and cidal activities against viruses (including β-coronaviruses such as SARS-CoV-2), bacteria, protozoa and fungi/yeasts  in vitro. Therapeutic effects have been seen in animal models  in vivo, and phase II trials have demonstrated that NO donors can reduce microbial infection. Nevertheless, excess NO, as occurs in septic shock, is associated with increased morbidity and mortality. In view of the dose-dependent positive and negative effects of NO, safety and efficacy trials of NO and its donors are needed for assessing their role in the prevention and treatment of infections. Trials should test dietary inorganic nitrate for pre- or post-exposure prophylaxis and gaseous NO or oral, topical or intravenous nitrite and nitrate for treatment of mild-to-severe infections, including due to SARS-CoV-2 (COVID-19). This review summarises the evidence base from  in vitro, in vivo and early phase clinical studies of NO activity in viral, bacterial, protozoal and fungal infections.

Dynamics of photodissociation of nitric oxide from S-nitrosylated cysteine and N-acetylated cysteine derivatives in water

Cysteine and N-acetylated cysteine derivatives are ubiquitous in biological systems; they have thiol groups that bind NO to form S-nitrosothiols (RSNOs) such as S-nitrosocysteine (CySNO), S-nitroso-N-acetylcysteine (NacSNO), and S-nitroso-N-acetylpenicillamine (NapSNO). Although they have been utilised as thermally or catalytically decomposing NO donors, their photochemical applications are yet to be fully explored owing to the lack of photodissociation dynamics. To this end, the photoexcitation dynamics of these RSNOs in water at 330 nm were investigated using femtosecond time-resolved infrared (TRIR) spectroscopy over a broad time range encompassing the entire reaction, which includes the primary reaction, secondary reactions of the reaction intermediates, and product formation. We discovered that the acetate and amide groups in these RSNOs have strong vibrational bands sensitive to the bondage of NO and the electronic state of the compound, which facilitates the identification of reaction intermediates involved in photoexcitation. The simplest thiol available with the acetate group-thioglycolic acid-was nitrosylated; it produced S-nitrosothioglycolic acid (TgSNO) and was comparatively investigated. Transient absorption bands in the TRIR spectra of the RSNOs were assigned using quantum chemical calculations. Photoexcited cysteine-related RSNOs either decompose into RS and NO within 0.3 ps after excitation at 330 nm with a primary quantum yield (Φ1) of 0.46-1 or relax into an electronically excited intermediate state lying at 42 ± 3 kcal mol-1 above the ground state, which relaxes into the ground state with a time constant of 460-520 ps. A majority (62-80%) of the RS radical geminately rebinds with NO at a time constant of 3-7 ps. The remaining RS reacts with the neighbouring RSNO, which produces additional NO and RSSR with a (nearly) diffusion-limited rate constant that doubles the amount of NO produced; further, it remarkably extends the time window for the dissociated NO to react with the target compound. The final fraction of NO produced from these RSNOs at 330 nm was 0.32-0.58, and it depends on the geminate rebinding yield and Φ1. The detailed dynamics of the photoexcited RSNO can be utilised in the quantitative application of these RSNOs in practical use and in the synthesis of more efficient photoactivated NO precursors.

Nitric oxide releasing nanofibrous Fmoc-dipeptide hydrogels for amelioration of renal ischemia/reperfusion injury

Renal ischemia/reperfusion (I/R) injury is responsible for significant mortality and morbidity during renal procedures. Nitric oxide (NO) deficiency is known to play a crucial role in renal I/R injury; however, low stability and severe toxicity of high concentrations of NO have limited its applications. Herein, we developed an in-situ forming Fmoc-dipheylalanine hydrogel releasing s-nitroso-n-acetylpenicillamine (FmocFF-SNAP) for renal I/R injury. Fmoc-FF hydrogel comprising of β-sheet nanofibers was prepared through the pH-titration method. It was then characterized by electron microscopy, pyrene assay, and circular dichroism techniques. Mechanical properties of Fmoc-FF hydrogel (thixotropy and syringeability) were investigated by oscillatory rheology and texture analysis. To assess the therapeutic efficiency in the renal I/R injury model, expression of inducible nitric oxide synthase (iNOS) and endothelial nitric oxide synthase (eNOS) was measured in various samples (different concentrations of free SNAP and FmocFF-SNAP, unloaded Fmoc-FF, and sham control) by real-time RT-PCR, ROS production, serum biomarkers, and histopathological evaluations. According to the results, Fmoc-FF self-assembly in physiologic conditions led to the formation of an entangled nanofibrous and shear-thinning hydrogel. FmocFF-SNAP exhibited a sustained NO release over 7 days in a concentration-dependent manner. Importantly, intralesional injection of FmocFF-SNAP caused superior recovery of renal I/R injury when compared to free SNAP in terms of histopathological scores and renal function indices (e.g. serum creatinine, and blood urea nitrogen). Compared to the I/R control group, biomarkers of oxidative stress and iNOS expression were significantly reduced possibly due to the sustained release of NO. Interestingly, the eNOS expression showed a significant enhancement reflecting the regeneration of the injured endothelial tissue. Thus, the novel FmocFF-SNAP can be recommended for the alleviation of renal I/R injury.

Nitric oxide for the prevention and treatment of viral, bacterial, protozoal and fungal infections

Although the antimicrobial potential of nitric oxide (NO) is widely published, it is little used clinically. NO is a key signalling molecule modulating vascular, neuronal, inflammatory and immune responses. Endogenous antimicrobial activity is largely mediated by high local NO concentrations produced by cellular inducible nitric oxide synthase, and by derivative reactive nitrogen oxide species including peroxynitrite and S-nitrosothiols. NO may be taken as dietary substrate (inorganic nitrate, L-arginine), and therapeutically as gaseous NO, and transdermal, sublingual, oral, intranasal and intravenous nitrite or nitrate. Numerous preclinical studies have demonstrated that NO has generic static and cidal activities against viruses (including β-coronaviruses such as SARS-CoV-2), bacteria, protozoa and fungi/yeasts  in vitro. Therapeutic effects have been seen in animal models  in vivo, and phase II trials have demonstrated that NO donors can reduce microbial infection. Nevertheless, excess NO, as occurs in septic shock, is associated with increased morbidity and mortality. In view of the dose-dependent positive and negative effects of NO, safety and efficacy trials of NO and its donors are needed for assessing their role in the prevention and treatment of infections. Trials should test dietary inorganic nitrate for pre- or post-exposure prophylaxis and gaseous NO or oral, topical or intravenous nitrite and nitrate for treatment of mild-to-severe infections, including due to SARS-CoV-2 (COVID-19). This review summarises the evidence base from  in vitro, in vivo and early phase clinical studies of NO activity in viral, bacterial, protozoal and fungal infections.

Nitric oxide and viral infection: Recent developments in antiviral therapies and platforms

Nitric oxide (NO) is a gasotransmitter of great significance to developing the innate immune response to many bacterial and viral infections, while also modulating vascular physiology. The generation of NO from the upregulation of endogenous nitric oxide synthases serves as an efficacious method for inhibiting viral replication in host defense and warrants investigation for the development of antiviral therapeutics. With increased incidence of global pandemics concerning several respiratory-based viral infections, it is necessary to develop broad therapeutic platforms for inhibiting viral replication and enabling more efficient host clearance, as well as to fabricate new materials for deterring viral transmission from medical devices. Recent developments in creating stabilized NO donor compounds and their incorporation into macromolecular scaffolds and polymeric substrates has created a new paradigm for developing NO-based therapeutics for long-term NO release in applications for bactericidal and blood-contacting surfaces. Despite this abundance of research, there has been little consideration of NO-releasing scaffolds and substrates for reducing passive transmission of viral infections or for treating several respiratory viral infections. The aim of this review is to highlight the recent advances in developing gaseous NO, NO prodrugs, and NO donor compounds for antiviral therapies; discuss the limitations of NO as an antiviral agent; and outline future prospects for guiding materials design of a next generation of NO-releasing antiviral platforms.

Silk Nanoparticles: A Natural Polymeric Platform for Nitric Oxide Delivery in Biomedical Applications

In this study, the preparation and characterization of nitric oxide (NO) releasing silk fibroin nanoparticles (SF NPs) are described for the first time. S-Nitroso-N-acetylpenicillamine (SNAP)-loaded SF NPs (SNAP-SF NPs) were prepared via an antisolvent/self-assembling method by adding a SNAP/ethanol solution to an aqueous SF solution and freeze-thawing. The prepared SNAP-SF NPs had a diameter ranging from 300 to 400 nm and an overall negative charge of -28.76 ± 0.73 mV. Among the different SNAP/SF ratios tested, the highest encapsulation efficiency (18.3 ± 1.3%) and loading capacity (9.1 ± 0.6%) values were attributed to the 1:1 ratio. The deconvolution of the amide I band in the FTIR spectra of SF NPs and SNAP-SF NPs showed an increase in the β-sheet content for SNAP-SF NPs, confirming the hydrophobic interactions between SNAP and silk macromolecules. SNAP-SF NPs released up to 1.31 ± 0.02 × 10^-10 mol min^-1 mg^-1 NO over a 24 h period. Moreover, SNAP-SF NPs showed concentration-dependent antibacterial effects against methicillin-resistant Staphylococcus aureus and Escherichia coli. Furthermore, they did not elicit any marked cytotoxicity against 3T3 mouse fibroblast cells at concentrations equal to or below 2 mg/mL. Overall, these results demonstrated that SNAP-SF NPs have great potential to be used as a NO delivery platform for biomedical applications such as tissue engineering and wound healing, where synergistic properties of SF and NO are desired.

Challenging development of storable particles for oral delivery of a physiological nitric oxide donor

Nitric oxide (NO) deficiency is often associated with several acute and chronic diseases. NO donors and especially S-nitrosothiols such as S-nitrosoglutathione (GSNO) have been identified as promising therapeutic agents. Although their permeability through the intestinal barrier have recently be proved, suitable drug delivery systems have to be designed for their oral administration. This is especially challenging due to the physico-chemical features of these drugs: high hydrophilicity and high lability. In this paper, three types of particles were prepared with an Eudragit® polymer: nanoparticles and microparticles obtained with a water-in-oil-in-water emulsion/evaporation process versus microparticles obtained with a solid-in-oil-in-water emulsion/evaporation process. They had a similar encapsulation efficiency (around 30%), and could be freeze-dried then be stored at least one month without modification of their critical attributes (size and GSNO content). However, microparticles had a slightly slower in vitro release of GSNO than nanoparticles, and were able to boost by a factor of two the drug intestinal permeability (Caco-2 model). Altogether, this study brings new data about GSNO intestinal permeability and three ready-to-use formulations suitable for further preclinical studies with oral administration.

Development of finasteride/PHBV@polyvinyl alcohol/chitosan reservoir-type microspheres as a potential embolic agent: from in vitro evaluation to animal study

Benign prostatic hyperplasia (BPH) is a prevalent urological disease affecting elders. Currently, the prostatic artery embolization (PAE) is considered as a minimally invasive and safe technique to treat BPH. However, various drug-loaded embolic agents have not been thoroughly investigated in BPH therapy. In this study, finasteride/poly(3-hydroxybutyrate-3-hydroxyvalerate)@polyvinyl alcohol/chitosan (FNS/PHBV@PVA/CS) reservoir-type microspheres were prepared via the solid-in-water-in-oil (S/W/O) emulsion crosslinking method with the aim to reduce the burst effect and control localized drug delivery. The structure and properties of the drug and resultant microspheres were characterized via field emission scanning electron microscopy (FESEM), Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and thermogravimetric analysis (TGA). The results showed that the drug-loaded hybrid microspheres were well-dispersed and spherical with a mean diameter of 238.1 ± 27.3 μm. All samples exhibited excellent thermal stability. The FNS/PHBV microspheres were successfully encapsulated inside the PVA/CS polymeric matrix, which effectively suppressed the burst effect and prolonged the drug release up to 51 days. In vitro biocompatibility assessment indicated that the microspheres possessed excellent cytocompatibility and hemocompatibility. Furthermore, in vivo studies performed in the rabbit ear embolization model showed the formation of progressive ischemic necrosis after treatment for various periods. Histopathological studies revealed that the microspheres completely occluded the blood vessels with minimal foreign body response and formed the fibrotic area at the periphery of embolized arteries. Furthermore, the auricular vascular endothelial cells showed acute ultrastructural changes, associated with the ischemic necrosis induced by the embolization procedures. All these findings suggest that the FNS/PHBV@PVA/CS hybrid microspheres could be used as a promising drug delivery system for potential applications in BPH therapy.

Nitric Oxide-Releasing Polymeric Materials for Antimicrobial Applications: A Review

Polymeric materials releasing nitric oxide have attracted significant attention for therapeutic use in recent years. As one of the gaseous signaling agents in eukaryotic cells, endogenously generated nitric oxide (NO) is also capable of regulating the behavior of bacteria as well as biofilm formation in many metabolic pathways. To overcome the drawbacks caused by the radical nature of NO, synthetic or natural polymers bearing NO releasing moiety have been prepared as nano-sized materials, coatings, and hydrogels. To successfully design these materials, the amount of NO released within a certain duration, the targeted pathogens and the trigger mechanisms upon external stimulation with light, temperature, and chemicals should be taken into consideration. Meanwhile, NO donors like S-nitrosothiols (RSNOs) and N-diazeniumdiolates (NONOates) have been widely utilized for developing antimicrobial polymeric agents through polymer-NO donor conjugation or physical encapsulation. In addition, antimicrobial materials with visible light responsive NO donor are also reported as strong and physiological friendly tools for rapid bacterial clearance. This review highlights approaches to delivery NO from different types of polymeric materials for combating diseases caused by pathogenic bacteria, which hopefully can inspire researchers facing common challenges in the coming 'post-antibiotic' era.

New Advances in General Biomedical Applications of PAMAM Dendrimers

Dendrimers are nanoscopic compounds, which are monodispersed, and they are generally considered as homogeneous. PAMAM (polyamidoamine) was introduced in 1985, by Donald A. Tomalia, as a new class of polymers, named 'starburst polymers'. This important contribution of Professor Tomalia opened a new research field involving nanotechnological approaches. From then on, many groups have been using PAMAM for diverse applications in many areas, including biomedical applications. The possibility of either linking drugs and bioactive compounds, or entrapping them into the dendrimer frame can improve many relevant biological properties, such as bioavailability, solubility, and selectivity. Directing groups to reach selective delivery in a specific organ is one of the advanced applications of PAMAM. In this review, structural and safety aspects of PAMAM and its derivatives are discussed, and some relevant applications are briefly presented. Emphasis has been given to gene delivery and targeting drugs, as advanced delivery systems using PAMAM and an incentive for its use on neglected diseases are briefly mentioned.

S-Nitrosoglutathione loaded poly(lactic-co-glycolic acid) microparticles for prolonged nitric oxide release and enhanced healing of methicillin-resistant Staphylococcus aureus-infected wounds

Methicillin-resistant Staphylococcus aureus (MRSA)-infected wounds have become a significant clinical issue worldwide. Recently, nitric oxide (NO) has emerged as a potent antibacterial agent against MRSA infections and a wound-healing enhancer. Nevertheless, clinical applications of NO have been largely restricted by its gaseous state and short half-life. In this study, our aim was to develop S-nitrosoglutathione (GSNO, an endogenous NO donor)-loaded poly(lactic-co-glycolic acid) [PLGA] microparticles (GSNO-MPs) that release NO over a prolonged period, to accelerate the healing of MRSA-infected wounds with less frequent dosing. GSNO was successfully encapsulated into PLGA microparticles by a solid-in-oil-in-water emulsion solvent evaporation method. Scanning electron microscopy and X-ray diffraction analyses confirmed the successful fabrication of GSNO-MPs. The latter released NO in a prolonged manner over 7 days and exerted a remarkable antibacterial activity against MRSA in a concentration- and time-dependent manner. Moreover, GSNO-MPs had good antibacterial efficacy and were found to accelerate wound healing in a mouse model of MRSA-infected wounds. Therefore, NO-releasing MPs devised in this study may be a promising option for the treatment of cutaneous wounds infected by drug-resistant bacteria such as MRSA.

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.

Supramolecular poly(acrylic acid)/F127 hydrogel with hydration-controlled nitric oxide release for enhancing wound healing

Topical nitric oxide (NO) delivery has been shown to accelerate wound healing. However, delivering NO to wounds at appropriate rates and doses requires new biomaterial-based strategies. Here, we describe the development of supramolecular interpolymer complex hydrogels comprising PEO-PPO-PEO (F127) micelles embedded in a poly(acrylic acid) (PAA) matrix, with S-nitrosoglutathione (GSNO) molecules dissolved in the hydrophilic domain. We show that PAA:F127/GSNO hydrogels start releasing NO upon hydration at rates controlled by their rates of water absorption. SAXS measurements indicate that the supramolecular structure of the hydrogels retains long-range order domains of F127 micelles. The PAA/F1227 hydrogels displayed dense morphologies and reduced rates of hydration. The NO release rates remain constant over the first 200 min, are directly correlated with the hydration rates of the PAA:F127/GSNO hydrogels, and can be modulated in the range of 40 nmol/g h to 1.5 μmol/g h by changing the PAA:F127 mass ratio. Long-term NO-release profiles over 5 days are governed by the first-order exponential decay of GSNO, with half-lives in the range of 0.5-3.4 days. A preliminary in vivo study on full-thickness excisional wounds in mice showed that topical NO release from the PAA:F127/GSNO hydrogels is triggered by exudate absorption and leads to increased angiogenesis and collagen fiber organization, as well as TGF-β, IGF-1, SDF-1, and IL-10 gene expressions in the cicatricial tissue. In summary, these results suggest that hydration-controlled NO release from topical PAA:F127/GSNO hydrogels is a potential strategy for enhancing wound healing.

STATEMENT OF SIGNIFICANCE

The topical delivery of nitric oxide (NO) to wounds may provide significant beneficial results and represent a promising strategy to treat chronic wounds. However, wound dressings capable of releasing NO after application and allowing the modulation of NO release rates, demand new platforms. Here, we describe a novel strategy to overcome these challenges, based on the use of supramolecular poly(acrylic acid) (PAA):F127 hydrogels charged with the NO donor S-nitrosoglutathione (GSNO) from whereby the NO release can be triggered by exudate absorption and delivered to the wound at rates controlled by the PAA:F127 mass ratio. Preliminary in vivo results offer a proof of concept for this strategy by demonstrating increased angiogenesis; collagen fibers organization; and TGF-β, IGF-1, SDF-1, and IL-10 gene expressions in the cicatricial tissue after topical treatment with a PAA:F127/GSNO hydrogel.

Progress and Promise of Nitric Oxide-Releasing Platforms

Nitric oxide (NO) is a highly potent radical with a wide spectrum of physiological activities. Depending on the concentration, it can enhance endothelial cell proliferation in a growth factor-free medium, mediate angiogenesis, accelerate wound healing, but may also lead to tumor progression or induce inflammation. Due to its multifaceted role, NO must be administered at a right dose and at the specific site. Many efforts have focused on developing NO-releasing biomaterials; however, NO short half-life in human tissues only allows this molecule to diffuse over short distances, and significant challenges remain before the full potential of NO can be realized. Here, an overview of platforms that are engineered to release NO via catalytic or noncatalytic approaches is presented, with a specific emphasis on progress reported in the past five years. A number of NO donors, natural enzymes, and enzyme mimics are highlighted, and recent promising developments of NO-releasing scaffolds, particles, and films are presented. In particular, key parameters of NO delivery are discussed: 1) NO payload, 2) maximum NO flux, 3) NO release half-life, 4) time required to reach maximum flux, and 5) duration of NO release. Advantages and drawbacks are reviewed, and possible further developments are suggested.

In Situ Self-Assembling Micellar Depots that Can Actively Trap and Passively Release NO with Long-Lasting Activity to Reverse Osteoporosis

Treatment with exogenous nitric oxide (NO) donors is regarded as being effective against osteoporosis. However, NO has a short half-life, limiting its clinical usefulness. To overcome this limitation, an injectable microparticle (MP) system is developed that consists of phase-change materials capric acid (CA) and octadecane, and encapsulates a NO donor. The therapeutic efficacy of the MPs is evaluated in ovariectomized (OVX) rats with osteoporosis. Upon subcutaneous administration, the MPs undergo a phase transition, leaching out the NO donor and generating NO bubbles that are instantly covered by a layer of tightly packed CA surfactant molecules, forming micellar depots. The in situ self-assembling micellar depots can actively protect the NO bubbles, prolonging their half-life, while the entrapped NO may passively diffuse through the micellar depots over time, performing a long-lasting therapeutic function, reversing the OVX-induced osteoporosis. It is possible to use the concept of in situ self-assembling micellar depots developed herein to expand the therapeutic effect of NO in its diverse range of clinical applications.

Use of gasotransmitters for the controlled release of polymer-based nitric oxide carriers in medical applications

Nitric Oxide (NO) is a small molecule gasotransmitter synthesized by nitric oxide synthase in almost all types of mammalian cells. NO is synthesized by NO synthase by conversion of l-arginine to l-citrulline in the human body. NO then stimulates soluble guanylate cyclase, from which various physiological functions are mediated in a concentration-dependent manner. High concentrations of NO induce apoptosis or antibacterial responses whereas low NO circulation leads to angiogenesis. The bidirectional effect of NO has attracted considerable attention, and efforts to deliver NO in a controlled manner, especially through polymeric carriers, has been the topic of much research. This naturally produced signaling molecule has stood out as a potentially more potent therapeutic agent compared to exogenously synthesized drugs. In this review, we will focus on past efforts of using the controlled release of NO via polymer-based materials to derive specific therapeutic results. We have also added studies and our future suggestions on co-delivery methods with other gasotransmitters as a step towards developing multifunctional carriers.

Study of Crystal Formation and Nitric Oxide (NO) Release Mechanism from S-Nitroso-N-acetylpenicillamine (SNAP)-Doped CarboSil Polymer Composites for Potential Antimicrobial Applications

Stable and long-term nitric oxide (NO) releasing polymeric materials have many potential biomedical applications. Herein, we report the real-time observation of the crystallization process of the NO donor, S-nitroso-N-acetylpenicillamine (SNAP), within a thermoplastic silicone-polycarbonate-urethane biomedical polymer, CarboSil 20 80A. It is demonstrated that the NO release rate from this composite material is directly correlated with the surface area that the CarboSil polymer film is exposed to when in contact with aqueous solution. The decomposition of SNAP in solution (e.g. PBS, ethanol, THF, etc.) is a pseudo-first-order reaction proportional to the SNAP concentration. Further, catheters fabricated with this novel NO releasing composite material are shown to exhibit significant effects on preventing biofilm formation on catheter surface by Pseudomonas aeruginosa and Proteus mirabilis grown in CDC bioreactor over 14 days, with a 2 and 3 log-unit reduction in number of live bacteria on their surfaces, respectively. Therefore, the SNAP-CarboSil composite is a promising new material to develop antimicrobial catheters, as well as other biomedical devices.

Comparison of chitosan microsphere versus O-carboxymethyl chitosan microsphere for drug delivery systems

The development of controlled drug delivery systems for bone regeneration, especially microspheres, has become a research hotspot in recent years. Chitosan and its derivative O-carboxymethyl chitosan have been considered to be an effective way for controlled drug delivery due to their nontoxicity and biodegradability. Currently, most of the studies have researched on synthesizing and characterizing chitosan and O-carboxymethyl chitosan. However, few studies have focused on the differences between chitosan microspheres and O-carboxymethyl chitosan microspheres directly. In this study, chitosan and O-carboxymethyl chitosan microspheres were developed by water-in-oil emulsification cross-linking method using vanillin as the cross-linking agent, and then their physicochemical properties were evaluated by Fourier transform infrared spectroscopy, scanning electron microscopy, and in vitro release testing. The results showed that O-carboxymethyl chitosan was successfully modified by adding carboxymethyl group at the chitosan C6 position.The particle size of chitosan microspheres (50–90 µm) was significantly larger than that of O-carboxymethyl chitosan microspheres (10–50 µm), and the drug release profile of O-carboxymethyl chitosan microspheres showed larger initial burst release within the first day and sustained release at the fourth day, while chitosan microspheres showed sustained release at the seventh day. In addition, Cell Counting Kit-8 assay showed that MC3T3-E1 proliferated well and highly expressed the alkaline phosphatase marker protein on both chitosan and O-carboxymethyl chitosan microspheres. Overall, both chitosan and O-carboxymethyl chitosan microspheres showed good biocompatibility, and chitosan microspheres were superior to O-carboxymethyl chitosan microspheres. Moreover, the different drug release rates suggest that chitosan and O-carboxymethyl chitosan microspheres have the potential to be used for the repair of different bone defects.

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).