Transition-Metal-Mediated Release of Nitric Oxide (NO) from S-Nitroso-N-acetyl-d-penicillamine (SNAP): Potential Applications for Endogenous Release of NO at the Surface of Stents Via Corrosion Products

Verifying the cytotoxicity of a biodegradable zinc alloy with nanodiamond sensors

Metals are widely utilized as implant materials for bone fixtures as well as stents. Biodegradable versions of these implants are highly desirable since patients do not have to undergo a second surgery for the materials to be removed. Attractive options for such materials are zinc silver alloys since they also offer the benefit of being antibacterial. However, it is important to investigate the effect of the degradation products of such alloys on the surrounding cells, taking into account silver cytotoxicity. Here we investigated zinc alloyed with 1 % of silver (Zn1Ag) and how differently concentrated extracts (1 %-100 %) of this material impact human umbilical vein endothelial cells (HUVECs). More specifically, we focused on free radical generation and oxidative stress as well as the impact on cell viability. To determine free radical production we used diamond-based quantum sensing as well as conventional fluorescent assays. The viability was assessed by observing cell morphology and the metabolic activity via the MTT assay. We found that 1 % and 10 % extracts are well tolerated by the cells. However, at higher extract concentrations we observed severe impact on cell viability and oxidative stress. We were also able to show that quantum sensing was able to detect significant free radical generation even at the lowest tested concentrations.

Nitric oxide-triggering activity of gold-, platinum- and cerium oxide-nanozymes from S-nitrosothiols and diazeniumdiolates

Cardiovascular diseases pose a significant global health challenge, contributing to high mortality rates and impacting overall well-being and quality of life. Nitric oxide (NO) plays a pivotal role as a vasodilator, regulating blood pressure and enhancing blood flow-crucial elements in preventing cardiovascular diseases, making it a prime therapeutic target. Herein, metal-based nanozymes (NZs) designed to induce NO release from both endogenous and exogenous NO-donors are investigated. Successful synthesis of gold, platinum (Pt) and cerium oxide NZs is achieved, with all three NZs demonstrating the ability to catalyze the NO release from various NO sources, namely S-nitrosothiols and diazeniumdiolates. Pt-NZs exhibit the strongest performance among the three NZ types. Further exploration involved investigating encapsulation and coating techniques using poly(lactic-co-glycolic acid) nanoparticles as experimental carriers for Pt-NZs. Both strategies showed efficiency in serving as platforms for Pt-NZs, successfully showing the ability to trigger NO release.

Thrombogenicity of biodegradable metals

Biodegradable metals offer a promising means to ameliorate many of the long-term risks associated with vascular devices made of conventional biostable stent metals. While numerous biodegradable metal alloys have been developed and characterized in animal models, knowledge of their blood reactivity and thrombogenicity remains unknown. Metal hemocompatibility is particularly valuable because current generation drug-eluting stents pose a significant long-term thrombosis risk. In this study, four pure metals, widely used as degradable base materials (Fe, Zn, Mg, and Mo), and three alloys commonly used in cardiovascular devices [NiTi, CoCr, and stainless steel (SS)] were evaluated. This work examined how each of these metals activate platelets, coagulation factors, and inflammation using in vitro hemocompatibility assays and a clinically relevant ex vivo non-human primate arteriovenous shunt model. Testing found that while all metals promoted a downstream activation of platelets and coagulation in flowing whole blood, platelet and fibrin attachment to Mg was markedly reduced. Additionally, Fe and Mo trended toward higher platelet attachment and contact pathway activation. Overall, the results suggest that Mg may delay clot initiation, but not eliminate clot formation, indicating the importance of understanding thrombosis in Mg alloys that are currently being developed for clinical use as biodegradable stents.

A CO-releasing coating based on carboxymethyl chitosan-functionalized graphene oxide for improving the anticorrosion and biocompatibility of magnesium alloy stent materials

Due to its biofunctions similar to NO, the CO gas signaling molecule has gradually shown great potential in cardiovascular biomaterials for regulating the in vivo performances after the implantation and has received increasing attention. To construct a bioactive surface with CO-releasing properties on the surface of magnesium-based alloy to augment the anticorrosion and biocompatibility, graphene oxide (GO) was firstly modified using carboxymethyl chitosan (CS), and then CO-releasing molecules (CORM401) were introduced to synthesize a novel biocompatible nanomaterial (GOCS-CO) that can release CO in the physiological environments. The GOCS-CO was further immobilized on the magnesium alloy surface modified by polydopamine coating with Zn2+ (PDA/Zn) to create a bioactive surface capable of releasing CO in the physiological environment. The outcomes showed that the CO-releasing coating can not only significantly enhance the anticorrosion and abate the corrosion degradation rate of the magnesium alloy in a simulated physiological environment, but also endow it with good hydrophilicity and a certain ability to adsorb albumin selectively. Owing to the significant enhancement of anticorrosion and hydrophilicity, coupled with the bioactivity of GOCS, the modified sample not only showed excellent ability to prevent platelet adhesion and activation and reduce hemolysis rate but also can promote endothelial cell (EC) adhesion, proliferation as well as the expression of nitric oxide (NO) and vascular endothelial growth factor (VEGF). In the case of CO release, the hemocompatibility and EC growth behaviors were further significantly improved, suggesting that CO molecules released from the surface can significantly improve the hemocompatibility and EC growth. Consequently, the present study provides a novel surface modification method that can simultaneously augment the anticorrosion and biocompatibility of magnesium-based alloys, which will strongly promote the research and application of CO-releasing bioactive coatings for surface functionalization of cardiovascular biomaterials and devices.

Nanomaterials-Induced Redox Imbalance: Challenged and Opportunities for Nanomaterials in Cancer Therapy

Cancer cells typically display redox imbalance compared with normal cells due to increased metabolic rate, accumulated mitochondrial dysfunction, elevated cell signaling, and accelerated peroxisomal activities. This redox imbalance may regulate gene expression, alter protein stability, and modulate existing cellular programs, resulting in inefficient treatment modalities. Therapeutic strategies targeting intra- or extracellular redox states of cancer cells at varying state of progression may trigger programmed cell death if exceeded a certain threshold, enabling therapeutic selectivity and overcoming cancer resistance to radiotherapy and chemotherapy. Nanotechnology provides new opportunities for modulating redox state in cancer cells due to their excellent designability and high reactivity. Various nanomaterials are widely researched to enhance highly reactive substances (free radicals) production, disrupt the endogenous antioxidant defense systems, or both. Here, the physiological features of redox imbalance in cancer cells are described and the challenges in modulating redox state in cancer cells are illustrated. Then, nanomaterials that regulate redox imbalance are classified and elaborated upon based on their ability to target redox regulations. Finally, the future perspectives in this field are proposed. It is hoped this review provides guidance for the design of nanomaterials-based approaches involving modulating intra- or extracellular redox states for cancer therapy, especially for cancers resistant to radiotherapy or chemotherapy, etc.

Bilayer vascular grafts with on-demand NO and H2S release capabilities

Nitric oxide (NO) and hydrogen sulfide (H2S) gasotransmitters exhibit potential therapeutic effects in the cardiovascular system. Herein, biomimicking multilayer structures of biological blood vessels, bilayer small-diameter vascular grafts (SDVGs) with on-demand NO and H2S release capabilities, were designed and fabricated. The keratin-based H2S donor (KTC) with good biocompatibility and high stability was first synthesized and then electrospun with poly (l-lactide-co-caprolactone) (PLCL) to be used as the outer layer of grafts. The electrospun poly (ε-caprolactone) (PCL) mats were aminolyzed and further chelated with copper (II) ions to construct glutathione peroxidase (GPx)-like structural surfaces for the catalytic generation of NO, which acted as the inner layer of grafts. The on-demand release of NO and H2S selectively and synergistically promoted the proliferation and migration of human umbilical vein endothelial cells (HUVECs) while inhibiting the proliferation and migration of human umbilical artery smooth muscle cells (HUASMCs). Dual releases of NO and H2S gasotransmitters could enhance their respective production, resulting in enhanced promotion of HUVECs and inhibition of HUASMCs owing to their combined actions. In addition, the bilayer grafts were conducive to forming endothelial cell layers under flow shear stress. In rat abdominal aorta replacement models, the grafts remained patency for 6 months. These grafts were capable of facilitating rapid endothelialization and alleviating neointimal hyperplasia without obvious injury, inflammation, or thrombosis. More importantly, the grafts were expected to avoid calcification with the degradation of the grafts. Taken together, these bilayer grafts will be greatly promising candidates for SDVGs with rapid endothelialization and anti-calcification properties.

A nitric oxide-catalytically generating carboxymethyl chitosan/sodium alginate hydrogel coating mimicking endothelium function for improving the biocompatibility

Thanks to their outstanding mechanical properties and corrosion resistance in physiological environments, titanium and its alloys are broadly explored in the field of intravascular devices. However, the biocompatibility is insufficient, causing thrombus formation and even implantation failure. In this study, inspired by the functions of endothelial glycocalyx and the NO-releasing of endothelial cells (ECs), a biomimetic coating (TNTA-Se) with three-dimensional gel-like structures and NO-catalytically generating ability was constructed on the titanium surface. To this end, the titanium alloy was firstly anodized and then annealed to form nanotube structures imitating the three-dimensional villous of glycocalyx, followed by the preparation of the Cu2+-loaded polydopamine intermediate layer for the immobilization of carboxymethyl chitosan and sodium alginate to form the hydrogel structure. Finally, an organoselenium compound (selenocystamine) as an active catalyst was covalently immobilized on the surface to develop a bioactive coating mimicking endothelial function with NO-generating activity. The surface morphologies and chemical structures of the biomimetic coating were characterized by scanning electron microscopy (SEM), energy dispersion X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), and the results indicated that the NO-catalytically generating hydrogel coating was successfully constructed. The results of water contact angle and protein adsorption suggested that the TNTA-Se coating exhibited excellent hydrophilicity, the promotion of bovine serum albumin (BSA) adsorption while the inhibition of fibrinogen (FIB) adsorption. Upon the addition of NO donor S-nitroso glutathione (GSNO) and reducing agent glutathione (GSH), the surface (TNTA-NO) displayed excellent blood compatibility and cytocompatibility to ECs. Compared with other surfaces, the TNTA-NO coating can not only further promote BSA adsorption and inhibit the adhesion and activation of platelets as well as hemolysis, but also significantly enhance ECs adhesion and proliferation and up-regulate VEGF and NO expression of ECs. The current study demonstrated that the NO-catalytically generating hydrogel coating on the titanium alloy can mimic the glycocalyx structure and endothelium function to catalyze a large number of NO donors in human blood to produce NO, and thus simultaneously enhance the surface hemocompatibility and endothelialization, representing a promising strategy for long-term cardiovascular implants of titanium-based devices.

Biomimetic catheter surface with dual action NO-releasing and generating properties for enhanced antimicrobial efficacy

Infection of indwelling catheters is a common healthcare problem, resulting in higher morbidity and mortality. The vulnerable population reliant on catheters post-surgery for food and fluid intake, blood transfusion, or urinary incontinence or retention is susceptible to hospital-acquired infection originating from the very catheter. Bacterial adhesion on catheters can take place during the insertion or over time when catheters are used for an extended period. Nitric oxide-releasing materials have shown promise in exhibiting antibacterial properties without the risk of antibacterial resistance which can be an issue with conventional antibiotics. In this study, 1, 5, and 10 wt % selenium (Se) and 10 wt % S-nitrosoglutathione (GSNO)-incorporated catheters were prepared through a layer-by-layer dip-coating method to demonstrate NO-releasing and NO-generating capability of the catheters. The presence of Se on the catheter interface resulted in a 5 times higher NO flux in 10% Se-GSNO catheter through catalytic NO generation. A physiological level of NO release was observed from 10% Se-GSNO catheters for 5 d, along with an enhanced NO generation via the catalytic activity as Se was able to increase NO availability. The catheters were also found to be compatible and stable when subjected to sterilization and storage, even at room temperature. Additionally, the catheters showed a 97.02% and 93.24% reduction in the adhesion of clinically relevant strains of Escherichia coli and Staphylococcus aureus, respectively. Cytocompatibility testing of the catheter with 3T3 mouse fibroblast cells supports the material's biocompatibility. These findings from the study establish the proposed catheter as a prospective antibacterial material that can be translated into a clinical setting to combat catheter-related infections.

Catalytic effect of transition metal-doped medical grade polymer on S-nitrosothiol decomposition and its biological response

Nitric oxide (NO)-release from polymer metal composites is achieved through the incorporation of NO donors such as S-nitrosothiols (RSNO). Several studies have shown that metal nanoparticles catalytically decompose RSNO to release NO. In polymer composites, the NO surface flux from the surface can be modulated by the application of metal nanoparticles with a varying degree of catalytic activity. In this study, we compare the NO-releasing polymer composite design strategy - demonstrating how different ways of incorporating RSNO and metal nanoparticles can affect NO flux, donor leaching, or biological activity of the films. The first approach included blending both the RSNO and metal nanoparticle in the matrix (non-layered), while the second approach involved dip-coating metal nanoparticle/polymer layer on the RSNO-containing polymer composite (layered). Secondly, we compare both designs with respect to metal nanoparticles, including iron (Fe), copper (Cu), nickel (Ni), zinc (Zn), and silver (Ag). Differential NO surface flux is observed for each metal nanoparticle, with the Cu-containing polymer composites showing the highest flux for layered composites, whereas Fe demonstrated the highest NO flux for non-layered composites in 24 h. Additionally, a comparative study on NO flux modulation via the choice of metal nanoparticles is shown. Furthermore, mouse fibroblast cell viability when exposed to leachates from the polymer metal composites was dependent on (1) the design of the polymer composite where the layered approach performed better than non-layered composites (2) diffusion of metal nanoparticles from the composites plays a key role. Antibacterial activity on methicillin-resistant Staphylococcus aureus was also dependent on individual metal nanoparticles and flux levels in a 24 h in vitro CDC bioreactor study. Therefore, the study establishes the need for a layered polymer metal composite strategy that synergizes NO flux without negatively affecting biocompatibility.

Silk fibroin/chitosan coating with tunable catalytic nitric oxide generation for surface functionalization of cardiovascular stents

Developing a functional coating for vascular stents with sustainable and tunable NO release remains challenging. In this work, we report a silk fibroin/chitosan-based biopolymer coating incorporating copper ions as a catalyst for NO generation and demonstrate its potential for the surface functionalization of cardiovascular stents. Based on the differences in silk fibroin and chitosan coordinating with copper ions, the loading, bonding, and release of copper ions could be precisely regulated over a wide range by controlling the ratio of silk fibroin and chitosan. This system shows good cytocompatibility for endothelial cells and tunable catalytic activity to decompose S-nitroso-N-acetyl-D-penicillamine (SNAP) for NO generation. Consequently, a functionalized coating with sustainable and tunable NO catalysis generation was developed on the metallic stent. Based on good biocompatibility, tunable NO release, and simple processing, the coating is expected to have great promise in the field of intervention therapy of cardiovascular disease.

Nitric Oxide-Releasing Bioinspired Scaffold for Exquisite Regeneration of Osteoporotic Bone via Regulation of Homeostasis

Osteoporotic bone regeneration is a challenging process which involves the occurrence of sophisticated interactions. Although various polymeric scaffolds have been proposed for bone repair, research on osteoporotic bone regeneration remains practically limited. In particular, achieving satisfactory bone regeneration when using osteoporotic drugs is challenging including bisphosphonates. Here, a novel nitric oxide-releasing bioinspired scaffold with bioactive agents for the exquisite regeneration of osteoporotic bone is proposed. The bone-like biomimetic poly(lactic-co-glycolic acid) scaffold is first prepared in combination with organic/inorganic ECM and magnesium hydroxide as the base implant material. Nanoparticles containing bioactive agents of zinc oxide (ZO), alendronate, and BMP2 are incorporated to the biomimetic scaffold to impart multifunctionality such as anti-inflammation, angiogenesis, anti-osteoclastogenesis, and bone regeneration. Especially, nitric oxide (NO) generated from ZO stimulates the activity of cGMP and protein kinase G; in addition, ZO downregulates the RANKL/osteoprotegerin ratio by suppressing the Wnt/β-catenin signaling pathway. The new bone is formed much better in the osteoporotic rat model than in the normal model through the regulation of bone homeostasis via the scaffold. These synergistic effects suggest that such a bioinspired scaffold could be a comprehensive way to regenerate exceptionally osteoporotic bones.

Moving research direction in the field of metallic bioresorbable stents-A mini-review

In contrast to polymer bioresorbable stents (BRS) that exhibited suboptimal performance in clinical trials due to their deficient mechanical properties, metallic BRS with improved mechanical strength have made their way into the clinic and have demonstrated more promising results. In the roadmap of research and development of metallic BRS, magnesium and iron based biodegradable metal stents had been clinically used, and the zinc based biodegradable metal stents had been trailed in Mini-Pigs. In this mini-review paper, we demonstrate the current technology levels and point out the future R&D direction of metallic BRS. Magnesium based BRS should target for decreasing struct thickness meanwhile balancing with enough supporting strength. Iron based BRS should move towards high efficient absorption, conversion, metabolism, elimination of its degradation products. Zn based BRS should strive to improve mechanical stability, creep resistance and biocompatibility. Future R&D directions of metallic BRS should move towards new materials such as Molybdenum, intelligent stent integrated with degradable biosensors, and new stent with multiple biofunctions, such as NO release.

Roles and current applications of S-nitrosoglutathione in anti-infective biomaterials

Bacterial infections can compromise the physical and biological functionalities of humans and pose a huge economical and psychological burden on infected patients. Nitric oxide (NO) is a broad-spectrum antimicrobial agent, whose mechanism of action is not affected by bacterial resistance. S-nitrosoglutathione (GSNO), an endogenous donor and carrier of NO, has gained increasing attention because of its potent antibacterial activity and efficient biocompatibility. Significant breakthroughs have been made in the application of GSNO in biomaterials. This review is based on the existing evidence that comprehensively summarizes the progress of antimicrobial GSNO applications focusing on their anti-infective performance, underlying antibacterial mechanisms, and application in anti-infective biomaterials. We provide an accurate overview of the roles and applications of GSNO in antibacterial biomaterials and shed new light on the avenues for future studies.

Recent progress in nitric oxide-generating nanomedicine for cancer therapy

Nitric oxide (NO) is an endogenous, multipotent biological signaling molecule that participates in several physiological processes. Recently, exogenous supplementation of tumor tissues with NO has emerged as a potential anticancer therapy. In particular, it induces synergistic effects with other conventional therapies (such as chemo-, radio-, and photodynamic therapies) by regulating the activity of P-glycoprotein, acting as a vascular relaxant to relieve tumor hypoxia, and participating in the metabolism of reactive oxygen species. However, NO is highly reactive, and its half-life is relatively short after generation. Meanwhile, NO-induced anticancer activity is dose-dependent. Therefore, the targeted delivery of NO to the tumor is required for better therapeutic effects. In the past decade, NO-generating nanomedicines (NONs), which enable sustained and specific NO release in tumor tissues, have been developed for enhanced cancer therapy. This review describes the recent efforts and preclinical achievements in the development of NON-based cancer therapies. The chemical structures employed in the fabrication of NONs are summarized, and the strategies involved in NON-based cancer therapies are elaborated.

In situ synthesis of ultrafine Cu2O on layered double hydroxide for electrochemical detection of S-nitrosothiols

The identification and quantitation of S-nitrosothiols (RSNO) has aroused enormous levels of attention, due to RSNO have many roles in vivo. Here, we synthesized the nanocomposites of ultrafine Cu₂O/layered double hydroxide (u-Cu₂O/LDH) by the in situ topotactic reduction of a Cu²⁺-containing LDH with ascorbic acid under gentle conditions and applied these u-Cu₂O/LDH to detect and monitor RSNO. Electrochemical signals of u-Cu₂O/LDH exhibited a wide N-acetyl-S-nitrosopenicillamine detection range from 5.0 nM-4.0 μM and 4.0 μM-400 μM, with a low detection limit of 1.58 nM. The sensor also exhibited good performance for other RSNO, such as S-nitrosoglutathione, S-nitrosocysteine, and S-nitrosohomocysteine with corresponding limits of detection at 1.94 nM, 1.23 nM and 1.62 nM, respectively. The high levels of selectivity and sensitivity to RSNO in complex biological environments can be attributed to the abundance of exposed active sites, and the underlying support structure. In addition, u-Cu₂O/LDH also exhibited dynamic nitric oxide (NO) monitoring ability from living cells. Collectively, these results reveal that u-Cu₂O/LDH exhibit a remarkable ability to quantify RSNO levels in complex samples, and could therefore provide new tools for exploring ultrafine nanomaterials as a potential biosensor to investigate biological events.

Improved biocompatibility of Zn-Ag-based stent materials by microstructure refinement

The metallurgical engineering of bioresorbable zinc (Zn)-based medical alloys would greatly benefit from clarification of the relationships between material properties and biological responses. Here we investigate the biocompatibility of three Zn-based silver (Ag)-containing alloys, ranging from binary to quinary alloy systems. Selected binary and quinary Zn-Ag-based alloys underwent solution treatment (ST) to increase the solubility of Ag-rich phases within the Zn bulk matrix, yielding two different microstructures (one without ST and a different one with ST) with the same elemental composition. This experimental design was intended to clarify the relationship between elemental profile/microstructure and biocompatibility for the Zn-Ag system. We found that the quinary alloy system (Zn-4Ag-0.8Cu-0.6Mn-0.15Zr) performed significantly better, in terms of histomorphometry, than any alloy system we have evaluated to date. Furthermore, when solution treated to increase strength and ductility and reduce the fraction of Ag-rich phases, the quinary alloy's biocompatibility further improved. In vitro corrosion testing and metallographic analysis of in vivo implants demonstrated a more uniform mode of corrosion for the solution treated alloy. We conclude that Zn-Ag alloys can be engineered through alloying to substantially reduce neointimal growth. The positive effect on neointimal growth can be further enhanced by dissolving the AgZn₃ precipitates in the Zn matrix to improve the corrosion uniformity. These findings demonstrate that neointimal-forming cells can be regulated by elemental additions and microstructural changes in degradable Zn-based implant materials. STATEMENT OF SIGNIFICANCE: The metallurgical engineering of bioresorbable zinc (Zn)-based medical alloys would greatly benefit from clarification of the relationships between material properties and biological responses. Here, selected binary and quinary Zn-Ag-based alloys underwent solution treatment (ST) to increase the solubility of Ag-rich phases within the Zn bulk matrix, yielding two different microstructures (one without ST and a different one with ST) with the same elemental composition. We found that applying a thermal treatment restores mechanical strength and mitigates the strain rate sensitivity of Zn-Ag alloys by dissolving AgZn₃ precipitates. Ag-rich nano-precipitates in Zn decrease biocompatibility, a phenomenon that can be counteracted by dissolving the AgZn₃ precipitates in the bulk Zn matrix.

Cu(II)-functionalized silk fibroin films for the catalytic generation of nitric oxide

In situ release of nitric oxide (NO) has been suggested to be a potential functionalization strategy for blood-contacting implants. In this study, the NO generation capability catalyzed by the copper ion-incorporated silk fibroin (SF) films in the presence of S-nitroso-N-acetyl-dl-penicillamine (SNAP) is demonstrated. Cu(II) is effectively bound to the surface of the SF film based on metal-protein coordination. The x-ray photoelectron spectroscopy results indicate that copper ions may exist on the surface of the SF film in the form of Cu(II)/Cu(I) coexistence. The degradation behavior showed that the bound copper ions on the surface of the SF films can maintain a slow release in phosphate-buffered saline (PBS) or collagenase IA solution for 7 days. There was no significant difference in the release of copper ions between PBS degradation and enzyme degradation. The loading of copper ions significantly improved the release of NO from SNAP through catalysis. Based on the biological effects of copper ions and the ability to catalyze the release of NO from S-nitrosothiols, copper ion loading provides an option for the construction of bioactive SF biomaterials.

A nitric oxide-eluting and REDV peptide-conjugated coating promotes vascular healing

Drug-eluting stents (DESs) placement remarkably reduces the over-proliferation of smooth muscle cells (SMCs) and thus neointimal hyperplasia. However, the pharmacological agent also slows down the re-endothelization, delays injury vascular healing and increases the risk of in-stent restenosis (ISR). Here, inspired by mussel foot proteins (Mfps), a mimicking endothelium functional stent coating was efficiently fabricated by thiol-ene "click" reaction, consisting of catechol grafted chitosan (CS-C), zinc sulfate, and Arg-Glu-Asp-Val (REDV) peptide. The mimicking endothelium coating could continuously catalyze endogenous nitric oxide (NO) gas and maintain the bioactivity of REDV peptide. Compared with bare stents, the mimicking coatings significantly inhibited the acute thrombosis for the first 1-week, accelerated re-endothelization and decreased in-stent restenosis for 1- and 3-month after implantation. In addition, the synergistic effect of NO and REDV peptide also regulated inflammation response and promoted the expression of muscle fiber.

Ceria Nanoparticles as an Unexpected Catalyst to Generate Nitric Oxide from S-Nitrosoglutathione

Ceria nanoparticles (NPs) are widely reported to scavenge nitric oxide (NO) radicals. This study reveals evidence that an opposite effect of ceria NPs exists, that is, to induce NO generation. Herein, S-nitrosoglutathione (GSNO), one of the most biologically abundant NO donors, is catalytically decomposed by ceria NPs to produce NO. Ceria NPs maintain a high NO release recovery rate and retain their crystalline structure for at least 4 weeks. Importantly, the mechanism of this newly discovered NO generation capability of ceria NPs from GSNO is deciphered to be attributed to the oxidation of Ce³⁺ to Ce⁴⁺ on their surface, which is supported by X-ray photoelectron spectroscopy and density functional theory analysis. The prospective therapeutic effect of NO-generating ceria NPs is evaluated by the suppression of cancer cells, displaying a significant reduction of 93% in cell viability. Overall, this report is, to the authors' knowledge, the first study to identify the capability of ceria NPs to induce NO generation from GSNO, which overturns the conventional concept of them acting solely as a NO-scavenging agent. This study will deepen our knowledge about the therapeutic effects of ceria NPs and open a new route toward the NO-generating systems for biomedical applications.

Understanding the Performance of Metal-Organic Frameworks for Modulation of Nitric oxide Release from S-nitrosothiols

S-Nitrosothiols (RSNOs) which were important intermediates in circulating reservoirs of nitric oxide (NO), transport and numerous NO signaling pathway plays intricate roles in the etiology of several pathologies. However, it is still a challenge to control release of NO from nitrosylated compounds under physiological pH. In this paper, for the first time, we report the catalytic activity and kinetic study for modulation of NO release from RSNOs by an array of metal-organic frameworks (MOFs) (M-MOF (M'); M = Zr, Cu; and M' = Cu, Pd, no metal) under physiological conditions via time-dependent absorbance spectra. The result showed that metal active site and the morphology and pore size of MOFs exhibited different activities toward RSNOs. The order of catalytic activity of these MOFs toward RSNOs is ordered in the decreasing sequence: Cu-MOF(Pd) ˃ Cu-MOF(Cu) ˃ Cu-MOF(no metal) ˃ Zr-MOF(Pd) ˃ Zr-MOF(Cu) ˃ Zr-MOF(no metal). In addition, Zr-MOF(Pd) was as model for cell experiment, demonstrated Zr-MOF(Pd) could react with RSNOs to generate NO in the complex environment of cell. Collectively, these findings establish a platform for MOFs-based, highly catalyze RSNOs in biological samples, a powerful tool for expanding the knowledge of the biology and chemistry of NO-mediated phenomena.

SMA-BmobaSNO: an intelligent photoresponsive nitric oxide releasing polymer for drug nanoencapsulation and targeted delivery

Nitric oxide (NO) is an important biological signalling molecule that acts to vasodilate blood vessels and change the permeability of the blood vessel wall. Due to these cardiovascular actions, co-administering NO with a therapeutic could enhance drug uptake. However current NO donors are not suitable for targeted drug delivery as they systemically release NO. To overcome this limitation we report the development of a smart polymer, SMA-BmobaSNO, designed to release NO in response to a photostimulus. The polymer's NO releasing functionality is an S-nitrosothiol group that, at 10 mg ml^-1, is highly resistant to both thermal (t_1/216 d) and metabolic (t_1/232 h) decomposition, but rapidly brakes down under photoactivation (2700 W m^-2, halogen source) to release NO (t_1/225 min). Photoresponsive NO release from SMA-BmobaSNO was confirmed in a cardiovascular preparation, where irradiation resulted in a 12-fold decrease in vasorelaxation EC₅₀(from 5.2μM to 420 nM). To demonstrate the polymer's utility for drug delivery we then used SMA-BmobaSNO to fabricate a nanoparticle containing the probe Nile Red (NR). The resulting SMA-BmobaSNO-NR nanoparticle exhibited spherical morphology (180 nm diameter) and sustained NR release (≈20% over 5 d). Targeted delivery was characterised in an abdominal preparation, where photoactivation (450 W m^-2) caused localized increases in vasodilation and blood vessel permeability, resulting in a 3-fold increase in NR uptake into photoactivated tissue. Nanoparticles fabricated from SMA-BmobaSNO therefore display highly photoresponsive NO release and can apply the Trojan Horse paradigm by using endogenous NO signalling pathways to smuggle a therapeutic cargo into target tissue.

Surface engineering and the application of laser-based processes to stents - A review of the latest development

Late in-stent thrombus and restenosis still represent two major challenges in stents’ design. Surface treatment of stent is attracting attention due to the increasing importance of stenting intervention for coronary artery diseases. Several surface engineering techniques have been utilised to improve the biological response in vivo on a wide range of biomedical devices. As a tailorable, precise, and ultra-fast process, laser surface engineering offers the potential to treat stent materials and fabricate various 3D textures, including grooves, pillars, nanowires, porous and freeform structures, while also modifying surface chemistry through nitridation, oxidation and coatings. Laser-based processes can reduce the biodegradable materials' degradation rate, offering many advantages to improve stents’ performance, such as increased endothelialisation rate, prohibition of SMC proliferation, reduced platelet adhesion and controlled corrosion and degradation. Nowadays, adequate research has been conducted on laser surface texturing and surface chemistry modification. Laser texturing on commercial stents has been also investigated and a promotion of performance of laser-textured stents has been proved.

In this critical review, the influence of surface texture and surface chemistry on stents performance is firstly reviewed to understand the surface characteristics of stents required to facilitate cellular response. This is followed by the explicit illustration of laser surface engineering of stents and/or related materials. Laser induced periodic surface structure (LIPSS) on stent materials is then explored, and finally the application of laser surface modification techniques on latest generation of stent devices is highlighted to provide future trends and research direction on laser surface engineering of stents.

•

Compared conventional surface engineering with laser-based methods for biomedical devices.

•

Explained the influence of texture geometry and surface chemistry on stents biological response.

•

Reviewed state of the art in laser surface engineering of stents for improved biological response.

•

Reviewed state of the art in laser surface engineering to control degradation of bioresorbable stents.

•

Highlighted novel laser surface engineering designs for improved stents'performance.

A Synergistic New Approach Toward Enhanced Antibacterial Efficacy via Antimicrobial Peptide Immobilization on a Nitric Oxide-Releasing Surface

Despite technological advancement, nosocomial infections are prevalent due to the rise of antibiotic resistance. A combinatorial approach with multimechanistic antibacterial activity is desired for an effective antibacterial medical device surface strategy. In this study, an antimicrobial peptide, nisin, is immobilized onto biomimetic nitric oxide (NO)-releasing medical-grade silicone rubber (SR) via mussel-inspired polydopamine (PDA) as a bonding agent to reduce the risk of infection. Immobilization of nisin on NO-releasing SR (SR-SNAP-Nisin) and the surface characteristics were characterized by Fourier transform infrared spectroscopy and scanning electron microscopy with energy-dispersive X-ray spectroscopy and contact angle measurements. The NO release profile (7 days) and diffusion of SNAP from SR-SNAP-Nisin were quantified using chemiluminescence-based nitric oxide analyzers and UV-vis spectroscopy, respectively. Nisin quantification showed a greater affinity of nisin immobilization toward SNAP-doped SR. Matrix-assisted laser desorption/ionization mass spectrometry analysis on surface nisin leaching for 120 h under physiological conditions demonstrated the stability of nisin immobilization on PDA coatings. SR-SNAP-Nisin shows versatile in vitro anti-infection efficacy against Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus in the planktonic and adhered states. Furthermore, the combination of NO and nisin has a superior ability to impair biofilm formation on polymer surfaces. SR-SNAP-Nisin leachates did not elicit cytotoxicity toward mouse fibroblast cells and human umbilical vein endothelial cells, indicating the biocompatibility of the material in vitro. The preventative and therapeutic potential of SR-SNAP-Nisin dictated by two bioactive agents may offer a promising antibacterial surface strategy.

Polydopamine/poly(sulfobetaine methacrylate) Co-deposition coatings triggered by CuSO4/H2O2 on implants for improved surface hemocompatibility and antibacterial activity

Implanted biomaterials such as medical catheters are prone to be adhered by proteins, platelets and bacteria due to their surface hydrophobicity characteristics, and then induce related infections and thrombosis. Hence, the development of a versatile strategy to endow surfaces with antibacterial and antifouling functions is particularly significant for blood-contacting materials. In this work, CuSO4/H2O2 was used to trigger polydopamine (PDA) and poly-(sulfobetaine methacrylate) (PSBMA) co-deposition process to endow polyurethane (PU) antibacterial and antifouling surface (PU/PDA(Cu)/PSBMA). The zwitterions contained in the PU/PDA(Cu)/PSBMA coating can significantly improve surface wettability to reduce protein adsorption, thereby improving its blood compatibility. In addition, the copper ions released from the metal-phenolic networks (MPNs) imparted them more than 90% antibacterial activity against E. coli and S. aureus. Notably, PU/PDA(Cu)/PSBMA also exhibits excellent performance in vivo mouse catheter-related infections models. Thus, the PU/PDA(Cu)/PSBMA has great application potential for developing multifunctional surface coatings for blood-contacting materials so as to improve antibacterial and anticoagulant properties.

Electrochemically deposition of catechol-chitosan hydrogel coating on coronary stent with robust copper ions immobilization capability and improved interfacial biological activity

Establishing a facile and versatile strategy to confer coronary stent with improved interfacial biological activity is crucial for novel cardiovascular implants. Developing a coating with NO release ability catalyzed by metal ions, such as copper, will be highly advantageous for the functionalized surface modification of metal stents. However, most available strategies involve drawbacks of low efficiency, complex processes, and toxic chemicals. Therefore, in this study, we report a green and facile electrobiofabrication method to construct the bioactive hydrogel coating by combining chitosan, catechol groups and copper ions on coronary stent and titanium surfaces. Experimental results demonstrated that the chitosan hydrogel coating can be precisely controlled synthesis via electrochemical deposition and serves as a versatile platform for copper ions immobilization. Additionally, mussel-inspired catechol groups could be chemically grafted on chitosan chains to further enhance the film mechanical properties and binding abilities of copper ions. Moreover, in vitro cell biocompatibility and catalyzed NO-generation activity have also been accessed and which suggesting great possibilities for biomedical applications. Therefore, by coupling the electrobiofabrication approach and multi-functionalities of the hybrid film, this report would advance the development of biomimetic hydrogel coating for vascular engineering (e.g., coronary stent) and other biomedical devices.

Highly hydrophobic polytetrafluoroethylene particle immobilization via polydopamine anchor layer on nitric oxide releasing polymer for biomedical applications

Biomedical surface-associated infections and thrombus formation are two major clinical issues that challenge patient safety and patient the fate of a medical device in the body . Single platform multifunctional surfaces are critical to address both these indwelling medical device-related problems. In this work, bio-inspired approaches are employed to fabricate a polymer composite with a versatile surface that can reduce bacterial infections and platelet adhesion in vitro. In the first bio-inspired approach, the functionality of nitric oxide (NO) produced by endothelial cell lining of blood vessels is mimicked through incorporation of S-nitroso-N-acetylpenicillamine (SNAP) within a CarboSil-2080A™ (CarboSil) polymer composite matrix. The second approach involves utilizing mussel adhesive chemistry, via polydopamine (PDA) to immobilize polytetrafluoroethylene (PTFE) particles on the polymer composite surface. The PTFE coating facilitates a decrease in wettability by making the polymer composite surface highly hydrophobic (contact angle ca. 120°). The surface of the fabricated polymer composite , CarboSil SNAP-PTFE, had a cobblestone-like structured appearance as characterized through scanning electron microscopy (SEM). Water contact angle (WCA) and surface tension measurements indicated no significant coating losses after 24 h under physiological conditions. NO surface flux was measured and analyzed for 5 days using a chemiluminescence-based nitric oxide analyzer and was found to be within the physiological range. CarboSil SNAP-PTFE reduced adhered bacteria (99.3 ± 0.5% for Gram-positive S. aureus and 99.1 ± 0.4% for Gram-negative E. coli) in a 24 h in vitro study. SEM analysis showed the absence of biofilm formation on CarboSil SNAP-PTFE polymer composites, while present on CarboSil in 24 h exposure to S. aureus. Platelet adhesion was reduced by 83.3 ± 4.5%. Overall, the results of this study suggest that a combination of NO-releasing CarboSil with PTFE coating can drastically reduce infection and platelet adhesion.

Analysis of vascular inflammation against bioresorbable Zn-Ag based alloys

Zinc (Zn) has emerged as a promising bioresorbable stent material due to its satisfactory corrosion behavior and excellent biocompatibility. However, for load bearing implant applications, alloying is required to boost its mechanical properties as pure Zn exhibits poor strength. Unfortunately, an increase in inflammation relative to pure Zn is a commonly observed side-effect of Zn alloys. Consequently, the development of a Zn-based alloy that can simultaneously feature improved mechanical properties and suppress inflammatory responses is a big challenge. Here, a bioresorbable, biocompatible Zn-Ag-based quinary alloy was comprehensively evaluated in vivo, in comparison to reference materials. The inflammatory and smooth muscle cellular response was characterized and correlated to metrics of neointimal growth. We found that implantation of the quinary alloy was associated with significantly improved inflammatory activities relative to the reference materials. Additionally, we found that inflammation, but not smooth muscle cell hyperplasia, significantly correlates to neointimal growth for Zn alloys. The results suggest that inflammation is the main driver of neointimal growth for Zn-based alloys and that the quinary Zn-Ag-Mn-Zr-Cu alloy may impart inflammation-resistance properties to arterial implants.

Nitric Oxide-Producing Cardiovascular Stent Coatings for Prevention of Thrombosis and Restenosis

Cardiovascular stenting is an effective method for treating cardiovascular diseases (CVDs), yet thrombosis and restenosis are the two major clinical complications that often lead to device failure. Nitric oxide (NO) has been proposed as a promising small molecule in improving the clinical performance of cardiovascular stents thanks to its anti-thrombosis and anti-restenosis ability, but its short half-life limits the full use of NO. To produce NO at lesion site with sufficient amount, NO-producing coatings (including NO-releasing and NO-generating coatings) are fashioned. Its releasing strategy is achieved by introducing exogenous NO storage materials like NO donors, while the generating strategy utilizes the in vivo substances such as S-nitrosothiols (RSNOs) to generate NO flux. NO-producing stents are particularly promising in future clinical use due to their ability to store NO resources or to generate large NO flux in a controlled and efficient manner. In this review, we first introduce NO-releasing and -generating coatings for prevention of thrombosis and restenosis. We then discuss the advantages and drawbacks on releasing and generating aspects, where possible further developments are suggested.

Multifunctional S-Nitroso-N-acetylpenicillamine-Incorporated Medical-Grade Polymer with Selenium Interface for Biomedical Applications

Modern crises in implantable or indwelling blood-contacting medical devices are mainly due to the dual problems of infection and thrombogenicity. There is a paucity of biomaterials that can address both problems simultaneously through a singular platform. Taking cues from the body's own defense mechanism against infection and blood clotting (thrombosis) via the endogenous gasotransmitter nitric oxide (NO), both of these issues are addressed through the development of a layered S-nitroso-N-acetylpenicillamine (SNAP)-doped polymer with a blended selenium (Se)-polymer interface. The unique capability of the SNAP-Se-1 polymer composites to explicitly release NO from the SNAP reservoir as well as generate NO via the incorporated Se is reported for the first time. The NO release from the SNAP-doped polymer increased substantially in the presence of the Se interface. The Se interface was able to generate NO in the presence of S-nitrosoglutathione (GSNO) and glutathione (GSH), demonstrating the capability of generating NO from endogenous S-nitrosothiols (RSNO). Scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) traced distribution of elemental Se nanoparticles on the interface and the surface properties were evaluated by surface wettability and roughness. The SNAP-Se-1 efficiently inhibited the growth of bacteria and reduced platelet adhesion while showing minimal cytotoxicity, thus potentially eliminating the risks of systemic antibiotic and blood coagulation therapy. The SNAP-Se-1 exhibited antibacterial activity of ∼2.39 and ∼2.25 log reductions in the growth of clinically challenging adhered Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli. SNAP-Se-1 also significantly reduced platelet adhesion by 85.5% compared to corresponding controls. A WST-8-based cell viability test performed on NIH 3T3 mouse fibroblast cells provided supporting evidence for the potential biocompatibility of the material in vitro. These results highlight the prospective utility of SNAP-Se-1 as a blood-contacting infection-resistant biomaterial in vitro which can be further tuned by application specificity.

Nitric oxide-releasing vascular grafts: A therapeutic strategy to promote angiogenic activity and endothelium regeneration

Small-diameter vascular grafts (SDVGs) are associated with a high incidence of failure due to infection and obstruction. Although several vascular grafts are commercially available, specific anatomical differences of defect sites require patient-based design and fabrication. Design and fabrication of such custom-tailored grafts are possible with 3d-printing technology. The aim of this study is to develop 3d-printed SDVGs with a nitric oxide (NO)-releasing coating to improve the success rate of implantation. The SDVGs were printed from polylactic acid and coated with blending of 10 wt% S-nitroso-N-acetyl-D-penicillamine into the polymeric substrate consisting of poly (ethylene glycol) and polycaprolactone. Our results show that NO is released in the physiological range (0.5-4 × 10^-10 mol·cm^-2·min^-1) for 14 days and NO-releasing coating showed significant antibacterial potential against Gram-positive and Gram-negative strains. It was shown that both NO-releasing and control grafts are biocompatible in-vitro and in-vivo. Interestingly, the NO-releasing SDVGs dramatically enhanced ECs proliferation and significantly enhanced ECs migration in-vitro compared to control grafts. In addition, the NO-releasing SDVGs showed angiogenic potential in-vivo which can further prove the results of our in-vitro study. These findings are expected to facilitate tissue regeneration and integration of custom-made vascular implants with enhanced clinical success. STATEMENT OF SIGNIFICANCE: A series of 3d-printed small-diameter vascular grafts (SDVGs, <6 mm) with controlled release of nitric oxide (NO) were prepared to combine the advantages of 3D printing technology and NO-releasing systems. The resulting NO-releasing grafts were promisingly showing sustained NO release in the physiological range over a two weeks period. In addition to the evaluation of endothelial cell migration in-vitro, we implanted for the first time the NO-releasing vascular grafts in a chick chorioallantoic membrane (CAM) to investigate the effect of the prepared grafts on the angiogenesis in-vivo. The fabricated grafts also exhibited bactericidal properties which prevent the formation of a biofilm layer and can thereby enhance the chance of endothelialization on the surface. Taken together, the innovative combination of rapid and highly accurate 3d-printing technology as a patient-specific fabrication method with NO-releasing coating represents a promising approach to develop bactericidal SDVGs with improved endothelialization.

Zinc-oxide nanoparticles act catalytically and synergistically with nitric oxide donors to enhance antimicrobial efficacy

The development of infection-resistant materials is of substantial importance as seen with an increase in antibiotic resistance. In this project, the nitric oxide (NO)-releasing polymer has an added topcoat of zinc oxide nanoparticle (ZnO-NP) to improve NO-release and match the endogenous NO flux (0.5-4 × 10-10 mol cm-2 min-1 ). The ZnO-NP is incorporated to act as a catalyst and provide the additional benefit of acting synergistically with NO as an antimicrobial agent. The ZnO-NP topcoat is applied on a polycarbonate-based polyurethane (CarboSil) that contains blended NO donor, S-nitroso-N-acetylpenicillamine (SNAP). This sample, SNAP-ZnO, continuously sustained NO release above 0.5 × 10-10 mol cm-2 min-1 for 14 days while samples containing only SNAP dropped below physiological levels within 24 h. The ZnO-NP topcoat improved NO release and reduced the amount of SNAP leached by 55% over a 7-day period. ICP-MS data observed negligible Zn ion release into the environment, suggesting longevity of the catalyst within the material. Compared to samples with no NO-release, the SNAP-ZnO films had a 99.03% killing efficacy against Staphylococcus aureus and 87.62% killing efficacy against Pseudomonas aeruginosa. A cell cytotoxicity study using mouse fibroblast 3T3 cells also noted no significant difference in viability between the controls and the SNAP-ZnO material, indicating no toxicity toward mammalian cells. The studies indicate that the synergy of combining a metal ion catalyst with a NO-releasing polymer significantly improved NO-release kinetics and antimicrobial activity for device coating applications. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 00A: 000-000, 2019.

Crystal-facet-dependent denitrosylation: modulation of NO release from S-nitrosothiols by Cu2O polymorphs

Nitric oxide (NO), a gaseous small molecule generated by the nitric oxide synthase (NOS) enzymes, plays key roles in signal transduction. The thiol groups present in many proteins and small molecules undergo nitrosylation to form the corresponding S-nitrosothiols. The release of NO from S-nitrosothiols is a key strategy to maintain the NO levels in biological systems. However, the controlled release of NO from the nitrosylated compounds at physiological pH remains a challenge. In this paper, we describe the synthesis and NO releasing ability of Cu2O nanomaterials and provide the first experimental evidence that the nanocrystals having different crystal facets within the same crystal system exhibit different activities toward S-nitrosothiols. We used various imaging techniques and time-dependent spectroscopic measurements to understand the nature of catalytically active species involved in the surface reactions. The denitrosylation reactions by Cu2O can be carried out multiple times without affecting the catalytic activity.

Catalyzed Nitric Oxide Release Via Cu Nanoparticles Leads to an Increase in Antimicrobial Effects and Hemocompatibility for Short Term Extracorporeal Circulation

Devices used for extracorporeal circulation are met with two major medical concerns: thrombosis and infection. A device that allows for anticoagulant-free circulation while reducing risk of infection has yet to be developed. We report the use of a copper nanoparticle (Cu NP) catalyst for the release of nitric oxide (NO) from the endogenous donor S-nitrosoglutathione (GSNO) in a coating applied to commercial Tygon S3^™ E-3603 poly(vinyl chloride) tubing in order to reduce adhered bacterial viability and the occurrence thrombosis for the first time in an animal model. Cu GSNO coated material demonstrated a nitric oxide (NO) release flux ranging from an initial flux of 6.3 ± 0.9 ×10^-10 mol cm^-2 min^-1 to 7.1 ± 0.4 ×10^-10 mol cm^-2 min^-1 after 4 h of release, while GSNO loops without Cu NPs only ranged from an initial flux of 1.1 ± 0.2 ×10^-10 mol cm^-2 min^-1 to 2.3 ± 0.2 ×10^-10 mol cm^-2 min^-1 after 4 h of release, indicating that the addition of Cu NPs can increase NO flux up to five times in the same 4 h period. Additionally, a 3-log reduction in S. aureus and 1-log reduction in P. aeruginosa was observed in viable bacterial adhesion over a 24 h period compared to control loops. A Cell Counting Kit-8 (CCK-8) assay was used to validate no overall cytotoxicity towards 3T3 mouse fibroblasts. Finally, extracorporeal circuits were coated and exposed to 4 h of blood flow under an in vivo rabbit model. The Cu GSNO combination was successful in maintaining 89.3% of baseline platelet counts, while the control loops were able to maintain 67.6% of the baseline. These results suggest that the combination of Cu NPs with GSNO increases hemocompatibility and antimicrobial properties of ECC loops without any cytotoxic effects towards mammalian cells.

Urban Particulate Matter-Induced Decomposition of S-Nitrosoglutathione Relevant to Aberrant Nitric Oxide Biological Signaling

Exposure to airborne particulate matter (PM) is associated with hazardous effects on human health. Soluble constituents of PM may be released in biological fluids and disturb the precisely tuned nitric oxide signaling processes. The influence of aqueous extracts from two types of airborne urban PM (SRM 1648a, a commercially available sample, and KR PM2.5, a sample collected "in-house" in Krakow, Poland) on the stability of S-nitrosoglutathione (GSNO) was investigated. The particle interfaces had no direct effect on the studied reaction, but extracts obtained from both samples facilitated NO release from GSNO. The effectiveness of NO release was significantly affected by glutathione (GSH) and ascorbic acid (AscA). Examination of the combined influence of Cu²⁺ , Fe³⁺ , and reductants on GSNO stability revealed copper to be the main GSNO decomposing species. Computational models of nitrosothiols interacting with metal oxide substrates and solvated metal ions support these claims. The study stresses the importance of the interplay between metal ions and biological reductants in S-nitrosothiols decomposition.

Development of an Injectable Nitric Oxide Releasing Poly(ethylene) Glycol-Fibrin Adhesive Hydrogel

Fibrin microparticles were incorporated into poly(ethylene) glycol (PEG)-fibrinogen hydrogels to create an injectable, composite that could serve as a wound healing support and vehicle to deliver therapeutic factors for tissue engineering. Nitric oxide (NO), a therapeutic agent in wound healing, was loaded into fibrin microparticles by blending S-Nitroso-N-acetyl penicillamine (SNAP) with a fibrinogen solution. The incorporation of microparticles affected swelling behavior and improved tissue adhesivity of composite hydrogels. Controlled NO release was induced via photolytic and thermal activation, and modulated by weight percent of particles incorporated. These NO-releasing composites were non-cytotoxic in culture. Cells maintained morphology, viability, and proliferative character. Fibrin microparticles loaded with SNAP and incorporated into a PEG-fibrinogen matrix, creates a novel injectable composite hydrogel that offers improved tissue adhesivity and inducible NO-release for use as a regenerative support for wound healing and tissue engineering applications.

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.

Platinum nanoparticles: an avenue for enhancing the release of nitric oxide from S-nitroso-N-acetylpenicillamine and S-nitrosoglutathione

Nitric oxide (NO) is an endogenous bioregulator with established roles in diverse fields. The difficulty in the modulation of NO release is still a significant obstacle to achieving successful clinical applications. We report herein our initial work using electron spin resonance (ESR) spectroscopy to detect NO generated from S-nitroso-N-acetylpenicillamine (SNAP) and S-nitrosoglutathione (GSNO) donors catalyzed by platinum nanoparticles (Pt NPs, 3 nm) under physiological conditions. With ESR spectroscopy coupled with spin trapping and spin labeling techniques, we identified that Pt NPs can significantly promote the generation of NO from SNAP and GSNO under physiological conditions. A classic NO colorimetric detection kit was also employed to verify that Pt NPs truly triggered the release of NO from its donors. Pt NPs can act as promising delivery vehicles for on-demand NO delivery based on time and dosage. These results, along with the detection of the resulting disulfide product, were confirmed with mass spectrometry. In addition, cellular experiments provided a convincing demonstration that the triggered release of NO from its donors by Pt NPs is efficient in killing human cancer cells in vitro. The catalytic mechanism was elucidated by X-ray photo-electron spectroscopy (XPS) and ultra-high performance liquid chromatography/high-resolution mass spectrometry (UHPLC-HRMS), which suggested that Pt-S bond formation occurs in the solution of Pt NPs and NO donors. Identification of Pt NPs capable of generating NO from S-nitrosothiols (RSNOs) is an important step in harnessing NO for investigations into its clinical applications and therapies.

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.

Substrate mediated enzyme prodrug therapy

Substrate mediated enzyme prodrug therapy (SMEPT) is a biomedical platform developed to perform a localized synthesis of drugs mediated by implantable biomaterials. This approach combines the benefits and at the same time offers to overcome the drawbacks for traditional pill-based drug administration and site-specific, implant mediated drug delivery. Specifically, SMEPT offers the flexibility of delivering multiple drugs - individually as monotherapy, in sequence, or as a combination therapy, all of which is also accomplished in a site-specific manner. This technology is also unique for site-specific synthesis of drugs with short half-life, such as nitric oxide. This review presents historical development of SMEPT from early reports to the most recent examples, and also outlines potential avenues for subsequent development of this platform.

Tunable Nitric Oxide Release from S-Nitroso-N-acetylpenicillamine via Catalytic Copper Nanoparticles for Biomedical Applications

The quest for novel therapies to prevent bacterial infections and blood clots (thrombosis) is of utmost importance in biomedical research due to the exponential growth in the cases of thrombosis and blood infections and the emergence of multi-drug-resistant strains of bacteria. Endogenous nitric oxide (NO) is a cellular signaling molecule that plays a pivotal role in host immunity against pathogens, prevention of clotting, and regulation of systemic blood pressure, among several other biological functions. The physiological effect of NO is dose dependent, which necessitates the study of its tunable release kinetics, which is the objective of this study. In the present study, polymer composites were fabricated by incorporating S-nitroso-N-acetylpenicillamine (SNAP) in a medical-grade polymer, Carbosil, and top-coated with varying concentrations of catalytic copper nanoparticles (Cu-NPs). The addition of the Cu-NPs increased the NO release, as well as the overall antimicrobial activity via the oligodynamic effect of Cu. SNAP (10 wt %) composites without Cu-NP coatings showed a NO flux of 1.32 ± 0.6 × 10^-10 mol min^-1 cm^-2, whereas Cu-NP-incorporated SNAP films exhibited fluxes of 4.48 ± 0.5 × 10^-10, 4.84 ± 0.3 × 10^-10, and 11.7 ± 3.6 × 10^-10 mol min^-1 cm^-2 with 1, 3, and 5 wt % Cu-NPs, respectively. This resulted in a significant reduction (up to 99.8%) in both gram-positive and gram-negative bacteria, with very low platelet adhesion (up to 92% lower) as compared to that of the corresponding controls. Copper leachates from the SNAP films were detected using the inductively coupled plasma-mass spectrometry technique and were found to be significantly lower in concentration than the recommended safety limit by the FDA. The cell viability test performed on mouse fibroblast 3T3 cells provided supportive evidence for the biocompatibility of the material in vitro.

Design Considerations for Silica-Particle-Doped Nitric-Oxide-Releasing Polyurethane Glucose Biosensor Membranes

Nitric oxide (NO)-releasing polymers have proven useful for improving the biocompatibility of in vivo glucose biosensors. Unfortunately, leaching of the NO donor from the polymer matrix remains a critical design flaw of NO-releasing membranes. Herein, a toolbox of NO-releasing silica nanoparticles (SNPs) was utilized to systematically evaluate SNP leaching from a diverse selection of biomedical-grade polyurethane sensor membranes. Glucose sensor analytical performance and NO-release kinetics from the sensor membranes were also evaluated as a function of particle and polyurethane (PU) chemistries. Particles modified with N-diazeniumdiolate NO donors were prone to leaching from PU membranes due to the zwitterionic nature of the NO donor modification. Leaching was minimized (<5% of the entrapped silica over 1 month) in low water uptake PUs. However, SNP modification with neutral S-nitrosothiol (RSNO) NO donors lead to biphasic leaching behavior. Particles with low alkanethiol content (<3.0 wt % sulfur) leached excessively from a hydrogel PU formulation (HP-93A-100 PU), while particles with greater degrees of thiol modification did not leach from any of the PUs tested. A functional glucose sensor was developed using an optimized HP-93A-100 PU membrane doped with RSNO-modified SNPs as the outer, glucose diffusion-limiting layer. The realized sensor design responded linearly to physiological concentrations of glucose (minimum 1-21 mM) over 2 weeks incubation in PBS and released NO at >0.8 pmol cm-2 s-1 for up to 6 days with no detectable (<0.6%) particle leaching.