Polyurethane with tethered copper(II)-cyclen complex: preparation, characterization and catalytic generation of nitric oxide from S-nitrosothiols

Surface Modification of Oxygenator Fibers with a Catalytically Active Metal-Organic Framework to Generate Nitric Oxide: An Ex Vivo Pilot Study

Coating all portions of an extracorporeal membrane oxygenation (ECMO) circuit with materials exhibiting inherent, permanent antithrombotic properties is an essential step to prevent thrombus-induced complications. However, developing antithrombotic coatings for oxygenator fibers within membrane oxygenators of ECMO systems has proven challenging. We have used polydopamine (PDA) to coat oxygenator fibers and immobilize a Cu-based metal-organic framework (MOF) on the surface to act as a nitric oxide (NO) catalyst. Importantly, the PDA/MOF coating will produce NO indefinitely from endogenous S-nitrosothiols and it has not previously been applied to ECMO oxygenator fibers.

Copper and Zinc Co-doped Titanium Dioxide Nanotubes Arrays on Controlling Nitric Oxide Releasing and Regulating the Inflammatory Responses for Cardiovascular Biomaterials

BACKGROUND

Titanium dioxide (TiO₂) nanotubes arrays have shown tremendous application foreground due to their unique characters of structure and performance. However, the single bio-function is still the limit on cardiovascular biomaterials.

METHODS

The loadability function provides the possibility for the TiO₂ nanotubes arrays to realize composite multifunction. The copper can catalyze the release of nitric oxide to promote the proliferation of endothelium cells and improve the anticoagulant. Also, zinc can adjust the inflammatory responses to improve anti-inflammation.

RESULTS

In this patent work, we co-doped the copper and zinc onto TiO₂ nanotubes arrays to estimate the hemocompatibility, cytocompatibility and responses of inflammation. The results showed that copper and zinc could introduce better multi-biofunctions to the TiO₂ nanotubes arrays for the application in cardiovascular biomaterials.

CONCLUSION

In summary, the NTs@Cu/Zn sample as a new composite material in this study had significant biocompatibility in vascular implantation and can be used as a potential material for polymer- free drug-eluting stents.

Opportunities for Nitric Oxide in Potentiating Cancer Immunotherapy

Despite nearly 30 years of development and recent highlights of nitric oxide (NO) donors and NO delivery systems in anticancer therapy, the limited understanding of exogenous NO's effects on the immune system has prevented their advancement into clinical use. In particular, the effects of exogenously delivered NO differing from that of endogenous NO has obscured how the potential and functions of NO in anticancer therapy may be estimated and exploited despite the accumulating evidence of NO's cancer therapy-potentiating effects on the immune system. After introducing their fundamentals and characteristics, this review discusses the current mechanistic understanding of NO donors and delivery systems in modulating the immunogenicity of cancer cells as well as the differentiation and functions of innate and adaptive immune cells. Lastly, the potential for the complex modulatory effects of NO with the immune system to be leveraged for therapeutic applications is discussed in the context of recent advancements in the implementation of NO delivery systems for anticancer immunotherapy applications. SIGNIFICANCE STATEMENT: Despite a 30-year history and recent highlights of nitric oxide (NO) donors and delivery systems as anticancer therapeutics, their clinical translation has been limited. Increasing evidence of the complex interactions between NO and the immune system has revealed both the potential and hurdles in their clinical translation. This review summarizes the effects of exogenous NO on cancer and immune cells in vitro and elaborates these effects in the context of recent reports exploiting NO delivery systems in vivo in cancer therapy applications.

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.

Facile fabrication of copper-incorporating poly(ε-caprolactone)/keratin mats for tissue-engineered vascular grafts with the potential of catalytic nitric oxide generation

Tissue-engineered vascular grafts (TEVGs) provide a new alternative for vascular construction. Nitric oxide (NO) is capable of promoting vascular tissue regeneration and reducing restenosis caused by vascular implantation. Therefore, in situ production of NO by catalytic decomposition of the endogenous donor is a promising strategy to fabricate a TEVG. In this study, poly(ε-caprolactone) (PCL) was first electrospun with keratin (Ker) to afford PCL/Ker mats and then incorporated with Cu(II) ions through multiple interactions. This strategy is very simple, green, and facile. Particularly, the incorporated Cu(II) ions were partially reduced to Cu(I) ions due to the reducibility of keratin. The chelated copper ions were expected to catalyze the generation of NO from endogenous S-nitrosothiol (RSNO). As a result, PCL/Ker-Cu mats selectively accelerated the adhesion, migration, and growth of human umbilical vein endothelial cells (HUVECs), while inhibiting the proliferation of human umbilical artery smooth muscle cells (HUASMCs). Furthermore, these mats exhibited excellent blood compatibility and significant antibacterial activity. Vascular implantation in vivo indicated that the tubular mats could inhibit thrombus formation and retain patency for 3 months after implantation in the rabbit carotid artery. More importantly, vascular remodeling was observed during follow-up, including a complete endothelium and smooth muscle layer. Taken together, the PCL/Ker-Cu mats have great potential application in vascular tissue regeneration.

Nitric Oxide-Releasing Platforms for Treating Cardiovascular Disease

Cardiovascular disease (CVD) is the first leading cause of death globally. Nitric oxide (NO) is an important signaling molecule that mediates diverse processes in the cardiovascular system, thereby providing a fundamental basis for NO-based therapy of CVD. At present, numerous prodrugs have been developed to release NO in vivo. However, the clinical application of these prodrugs still faces many problems, including the low payloads, burst release, and non-controlled delivery. To address these, various biomaterial-based platforms have been developed as the carriers to deliver NO to the targeted tissues in a controlled and sustained manner. This review aims to summarize recent developments of various therapeutic platforms, engineered to release NO for the treatment of CVD. In addition, two potential strategies to improve the effectiveness of existing NO therapy are also discussed, including the combination of NO-releasing platforms and either hydrogen sulfide-based therapy or stem cell therapy. Hopefully, some NO-releasing platforms may provide important therapeutic benefits for CVD.

Endogenous nitric oxide-generating surfaces via polydopamine-copper coatings for preventing biofilm dispersal and promoting microbial killing

INTRODUCTION

Peri-implantitis is a bacterially induced inflammatory disease which affects the hard and soft tissues around a dental implant. Microbial biofilm formation is an important causative factor in peri-implantitis. The aim of this study is to develop an effective multifunctional surface coating for antimicrobial property and to counteract oral biofilm-associated infections via a single polydopamine copper coating (PDAM@Cu) on titanium implant surface to regulate endogenous nitric oxide (NO) generation.

METHODS

PDAM@Cu coatings were made with different concentrations of CuCl₂ on titanium surfaces with a simple dip coating technique. Coatings were characterised to evaluate Cu concentrations as well as NO release rates from the coatings. Further, salivary biofilms were made on the coatings using Brain Heart Infusion (BHI) media in an anaerobic chamber. Biofilms were prepared with three different mixtures, one of which was saliva only, the second had an addition of sheep's blood, and the third was prepared with NO donors S-nitrosoglutathione (GSNO) and L-glutathione (GSH) in the mixture of saliva and blood to evaluate the effects of endogenously produced NO on biofilms. The effectiveness of coated surfaces on biofilms were assessed using four different methods, namely, crystal violet assay, scanning electron microscopy imaging, 2,3-bis (2-methoxy-4-nitro-5-sulfophenyl)-5-[(phenylamino) carbonyl]-2H-tetrazolium hydroxide (XTT) metabolic assay, and live/dead staining.

RESULTS

NO release rates could be controlled with different Cu concentration in PDAM@Cu coatings. NO generated from the PDAM@Cu coatings effectively induced dispersal of biofilms shown by the reduction in biofilm biomass as well as reduced biofilm attachment in samples prepared with blood and NO donors. Cu ions released from the PDAM@Cu coatings resulted in killing of the dispersed bacteria, which was evidenced by the live/dead cell staining and reduced metabolic activity noted from the XTT assay. In contrast, samples prepared with saliva showed no significant reduction in biofilms, indicating the important effect of endogenously generated NO on biofilm dispersal.

CONCLUSION

In conclusion, PDAM@Cu coatings with NO generating surfaces have a dual anti-biofilm function, with a synergistic effect on biofilm dispersal from regulated NO generation and bactericidal effects from Cu ions from the coatings.

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.

Single and multi-functional coating strategies for enhancing the biocompatibility and tissue integration of blood-contacting medical implants

Device-associated clot formation and poor tissue integration are ongoing problems with permanent and temporary implantable medical devices. These complications lead to increased rates of mortality and morbidity and impose a burden on healthcare systems. In this review, we outline the current approaches for developing single and multi-functional surface coating techniques that aim to circumvent the limitations associated with existing blood-contacting medical devices. We focus on surface coatings that possess dual hemocompatibility and biofunctionality features and discuss their advantages and shortcomings to providing a biocompatible and biodynamic interface between the medical implant and blood. Lastly, we outline the newly developed surface modification techniques that use lubricant-infused coatings and discuss their unique potential and limitations in mitigating medical device-associated complications.

Recent developments in nitric oxide-releasing biomaterials for biomedical applications

Nitric oxide (NO) is an endogenous gas with several physiological activities. Owing to the NO physiological functions, such as inhibition of platelet aggregation and adhesion, vascular muscle relaxation, modulation of inflammation and immune response, antibacterial and anticancer activity, increasing attensions have been paid to the development of biomaterials with the ability to release this medical gas. Nowadays, numerous prodrugs have been developed to release NO in vivo. However, due to the low payloads and non-controlled delivery of the prodrug, the NO-releasing devices do not fulfil the expectations, which restricts their widespread application. Recently, several methods have been proposed to address the issue above, including physical and chemical methods and specific designs. This review aims to briefly introduce the latest achievements with recent 3 years involving coatings which mimic the vascular endothelium to treat atherosclerosis, nanocarriers which generate NO for a sustained anticancer treatment, and a framework which modifies the prodrug as a stable cardiovascular stent or as an anticancer targeted drug.

Biomimetic nano-NOS mediated local NO release for inhibiting cancer-associated platelet activation and disrupting tumor vascular barriers

Platelets attribute to the hypercoagulation of blood and maintenance of the tumor vascular integrity, resulting in limited intratumoral perfusion of nanoparticle into solid tumors. To overcome these adversities, we herein present an antiplatelet strategy based on erythrocyte membrane-enveloped proteinic nanoparticles that biomimic nitric oxide synthase (NOS)with co-loading of l-Arginine (LA) and photosensitizer IR783 for local NO release and inhibition of the activation of tumor-associated platelets specifically, thereby enhancing vascular permeability and accumulation of the nanoparticles in tumors. A cRGD-immobolized membrane structure is constructed to actively target platelets and cancer cells respectively, through overexpressed integrin receptors such as integrin α_IIbβ₃ and α_vβ₃, accelerating the inhibition of platelet activation and endocytosis of nanoparticles by tumor cells. Bio-mimicking the arginine/NO pathway in vivo, synergistical delivery of LA and IR783 enables LA molecules readily oxidize to NO with O₂ that is mediated by activated IR783, the resulted NO not only retards the activity of platelets to disrupt the vascular integrity of tumor but also enhances toxicity to cancer cells. In addition, NIR-controlled release localizes the NO spatiotemporally to tumor-associated platelets and prevents undesirable systemic bleeding substantially. The reduction of the hypercoagulable state is further demonstrated by the down-regulation of tissues factor (TF) expression in tumor cells. Our study describes a promising approach to combat cancer, which advances the biomimetic NOS system as the potent therapeutic forces toward clinic applications.

Polydopamine-Modified Copper-Doped Titanium Dioxide Nanotube Arrays for Copper-Catalyzed Controlled Endogenous Nitric Oxide Release and Improved Re-Endothelialization

The controllable release is necessary for ideal drug delivery technologies. Because of their high specific surface area and high porosity, titanium dioxide nanotubes (TNTs) have been widely used as drug carriers in medical devices. By loading copper as the catalyst, nitric oxide (NO) generation was facilitated by catalyzing the decomposition of renewable endogenous NO donors in vivo. Herein, the long-term controllable release profile of NO is highlighted owing to the multilayer polydopamine (PDA) cap structure. Different layers of PDA are used to adjust the NO release behavior, and the results show that three layers of PDA can not only effectively prevent the burst release of NO but also maintain long-term stable release of copper ion and NO. The bioactivity of the NO generated from three-layer PDA-modified copper-loaded TNTs (PDA-3L-NTCu2) and unmodified copper-loaded TNTs (NTCu2) are verified by our work, indicating effective inhibition of platelet activation, thrombosis, inflammation, and intimal hyperplasia. Importantly, the PDA-3L-NTCu2 show selectively promote the growth of endothelial cells in vitro and outstanding re-endothelialization for 4 weeks in vivo, as compared to NTCu2, TNTs, and 316L stain steel. This study suggests that copper-loaded with PDA modification helps us achieve controlled long-term stable local NO release with well-retained bioactivity and enhanced re-endothelialization.

Cu∥-loaded polydopamine coatings with in situ nitric oxide generation function for improved hemocompatibility

NO is the earliest discovered gas signal molecule which is produced by normal healthy endothelial cells, and it has many functions, such as maintaining cardiovascular homeostasis, regulating vasodilation, inhibiting intimal hyperplasia and preventing atherosclerosis in the blood system. Insufficient NO release is often observed in the pathological environment, for instance atherosclerosis. It was discovered that NO could be released from the human endogenous NO donor by many compounds, and these methods can be used for the treatment of certain diseases in the blood system. In this work, a series of copper-loaded polydopamine (PDA) coatings were produced through self-polymerization time for 24, 48 and 72 h. The chemical composition and structure, coating thickness and hydrophilicity of the different copper-loaded PDA coatings surfaces were characterized by phenol hydroxyl quantitative, X-ray photoelectron spectroscopy, ellipsometry atomic force microscopy and water contact angles. The results indicate that the thickness and the surface phenolic hydroxyl density of the PDA coatings increased with the polymerization time.This copper-loaded coating has glutathione peroxidase-like activity, and it has the capability of catalyzing NO releasing from GSNO. The surface of the coating showed desirable hemocompatibility, the adhesion and activation of platelets were inhibited on the copper-loaded coatings. At the same time, the formation of the thrombosis was also suppressed. These copper-loaded PDA coatings could provide a promising platform for the development of blood contact materials.

A Versatile Surface Bioengineering Strategy Based on Mussel-Inspired and Bioclickable Peptide Mimic

In this work, we present a versatile surface engineering strategy by the combination of mussel adhesive peptide mimicking and bioorthogonal click chemistry. The main idea reflected in this work derived from a novel mussel-inspired peptide mimic with a bioclickable azide group (i.e., DOPA₄-azide). Similar to the adhesion mechanism of the mussel foot protein (i.e., covalent/noncovalent comediated surface adhesion), the bioinspired and bioclickable peptide mimic DOPA₄-azide enables stable binding on a broad range of materials, such as metallic, inorganic, and organic polymer substrates. In addition to the material universality, the azide residues of DOPA₄-azide are also capable of a specific conjugation of dibenzylcyclooctyne- (DBCO-) modified bioactive ligands through bioorthogonal click reaction in a second step. To demonstrate the applicability of this strategy for diversified biofunctionalization, we bioorthogonally conjugated several typical bioactive molecules with DBCO functionalization on different substrates to fabricate functional surfaces which fulfil essential requirements of biomedically used implants. For instance, antibiofouling, antibacterial, and antithrombogenic properties could be easily applied to the relevant biomaterial surfaces, by grafting antifouling polymer, antibacterial peptide, and NO-generating catalyst, respectively. Overall, the novel surface bioengineering strategy has shown broad applicability for both the types of substrate materials and the expected biofunctionalities. Conceivably, the "clean" molecular modification of bioorthogonal chemistry and the universality of mussel-inspired surface adhesion may synergically provide a versatile surface bioengineering strategy for a wide range of biomedical materials.

Nitric-Oxide-Releasing Biomaterial Regulation of the Stem Cell Microenvironment in Regenerative Medicine

Stem cell therapy has proven to be an attractive solution for the treatment of degenerative diseases or injury. However, poor cell engraftment and survival within injured tissues limits the successful use of stem cell therapy within the clinical setting. Nitric oxide (NO) is an important signaling molecule involved in various physiological processes. Emerging evidence supports NO's diverse roles in modulating stem cell behavior, including survival, migration, differentiation, and paracrine secretion of proregenerative factors. Thus, there has been a shift in research focus to concentrate efforts on the delivery of therapeutic concentration ranges of NO to the target tissue sites. Combinatory therapies utilizing biomaterials that control NO generation and support stem cell delivery can be holistic and synergistic approaches to significantly improve tissue regeneration. Here, the focus is on recent developments of various therapeutic platforms, engineered to both transport NO and to enhance stem-cell-mediated regeneration of damaged tissues. New and emerging revelations of how the stem cell microenvironment can be regulated by NO-releasing biomaterials are also highlighted.

Nanosized copper(ii) oxide/silica for catalytic generation of nitric oxide from S-nitrosothiols

The findings of this study suggest that copper(ii) oxide–silica nanoparticles produce NO from the GSNO species at physiological conditions in situ and could be used for designing biomedical materials with NO generating activity.

Micelle-embedded coating with ebselen for nitric oxide generation

Nitric oxide generation is considered to be a key factor to mimic endothelial function in terms of anti-coagulation and anti-hyperplasia. Herein, ebselen which could play the similar role as glutathion peroxidase-like was loaded into micelles and was further assembled into a layer-by-layer coating. The ability of nitric oxide generation and corresponding biological effect were investigated. Endothelial-mimetic surface has now attracted huge attention in blood-contacting materials, due to its inherent ability of secreting nitric oxide. Among those categories, nitric oxide generation surface is considered to be safe and tunable in the modification of vascular biomedical devices. How to adsorb or immobilize glutathion peroxidase-like catalyst and maintain sustained/safe nitric oxide generation is full of interest. This study aimed at developing a functional coating constructed via layer-by-layer assembly to introduce the catalyst into the coating by pre-loading ebselen in micelles. We firstly introduced phenylboronic acid moiety into the micelle molecule backbone and grafted catechol moiety to chitosan backbone. Then, chitosan, micelles (containing ebselen) and heparin were adopted as polyelectrolytes and then alternatively assembled onto the substrate via layer-by-layer protocol. The catechol was conjugated to the amine groups of chitosan by Schiff base reaction to synthesize chitosan-catechol. The hydrophobic cholesterol was conjugated to the one end of the hydrophilic hyaluronic acid, and the hydroxymethylphenylboronic acid was conjugated to the other end via the esterification of carboxyl (-COOH) and hydroxyl (-OH). The modified hyaluronic acid could spontaneously form micelles in aqueous solution. Ebselen was the loaded into the as-prepared micelles. Chitosan-catechol, heparin, and micelles were alternatively assembled onto the substrate layer by layer to form a micelle-embedded coating. The micelle-embedded coating with ebselen was successfully obtained and the nitric oxide generation ability was in a safe level which was close to healthy endothelial cells. The coating could effectively inhibit platelet adhesion and smooth muscle cell proliferation. The use of ebselen preloaded into micelles could provide a sustained release of catalyst for in situ nitric oxide generation. Besides, this method could also be used to load diverse drugs and regulate desired properties. The study was approved by the Institutional Review Board of the West China Hospital in Sichuan University on March 3, 2018, with approval No. K2018044.

Development of Cu-Modified PVC and PU for Catalytic Generation of Nitric Oxide

Nitric oxide (NO) generating surfaces are potentially promising for improving haemocompatibility of blood-contacting biomaterials. In the present report, Cu-modified poly(vinyl chloride) (PVC) and polyurethane (PU) were prepared via polydopamine (pDA)-assisted chelation. The copper content on the PVC and PU modified surfaces, assessed by inductively coupled plasma - optical emission spectrometry (ICP-OES), were about 3.86 and 6.04 nmol·cm−2, respectively. The Fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) data suggest that copper is attached to the polymer surface through complex formation with pDA. The cumulative leaching of copper from modified PVC and PU during the five day incubation in phosphate buffered saline (PBS), measured by inductively coupled plasma mass spectrometry (ICP-MS), was about 50.7 ppb and 48 ppb, respectively which is within its physiological level. Modified polymers were tested for their ability to catalytically generate NO by decomposing of endogenous S-nitrosothiol (GSNO). The obtained data show that Cu-modified PVC and PU exhibited the capacity to generate physiological levels of NO which could be a foundation for developing new biocompatible materials with NO-based therapeutics.

Selenium-containing polyurethane with elevated catalytic stability for sustained nitric oxide release

Stable and controllable nitric oxide (NO) release at the physiological level from biomedical materials remains a challenge for NO-based therapy. NO-generating polymers have great potential to achieve this goal because they can catalytically decompose endogenous S-nitrosothiols (RSNOs) into NO. However, the current catalytic surfaces based on such polymers often suffer from loss of catalytic sites, which can influence the stability of NO release in their long-term application. In this work, we proposed a novel strategy to enhance the catalytic stability of NO-catalytic materials by incorporating catalytic sites into the polymer backbone. Selenium-containing polyurethane (PU-Se) was synthesized by using the catalyst 2,2'-diselenodiethanol (SeDO) as the chain extender. A series of PU/PU-Se blend films were prepared to investigate the effect of PU-Se content on the catalytic properties. The blend films exhibited excellent catalytic activity, and also showed outstanding catalytic stability in comparison with PU coated by diselenide/dopamine (PU-PDA-Se). Among these blend films, PU-Se-10 exhibited a stable NO release rate of 5.05 × 10^-10 mol cm^-2 min^-1 after exposure to PBS buffer for 30 days. Moreover, the PU/PU-Se films exhibited decreased platelet activation/adhesion, low hemolysis ratio, excellent biocompatibility, and similar mechanical properties to PU. It is expected that the newly designed PU-Se has great potential in generating stable NO release at the physiological level for the long-term application of blood-contacting medical devices.

Novel Surfaces in Extracorporeal Membrane Oxygenation Circuits

The balance between systemic anticoagulation and clotting is challenging. In normal hemostasis, the endothelium regulates the balance between anticoagulant and prothrombotic systems. It becomes particularly more challenging to maintain this physiologic hemostasis when we are faced with extracorporeal life support therapies, where blood is continuously in contact with a foreign extracorporeal circuit surface predisposing a prothrombotic state. The blood-surface interaction during extracorporeal life support therapies requires the use of systemic anticoagulation to decrease the risk of clotting. Unfractionated heparin is the most common anticoagulant agent widely used in this setting. New trends include the use of direct thrombin inhibitor agents for systemic anticoagulation; and surface modifications that aim to overcome the blood-biomaterial surface interaction by modifying the hydrophilicity or hydrophobicity of the polymer surface; and coating the circuit with substances that will mimic the endothelium or anti-thrombotic agents. To improve hemocompatibility in an extracorporeal circuit, replication of the anti-thrombotic and anti-inflammatory properties of the endothelium is ideal. Surface modifications can be classified into three major groups: biomimetic surfaces (heparin, nitric oxide, and direct thrombin inhibitors); biopassive surfaces [phosphorylcholine, albumin, and poly- 2-methoxyethylacrylate]; and endothelialization of blood contacting surface. The focus of this paper will be to review both present and future novel surface modifications that can obviate the need for systemic anticoagulation during extracorporeal life support therapies.

The grafts modified by heparinization and catalytic nitric oxide generation used for vascular implantation in rats

Small-diameter (<6 mm) vascular grafts are increasingly needed in peripheral vascular surgery but have few successes because of acute thrombosis, incomplete endothelialization and intimal hyperplasia after implantation. This study used electrospun poly(ε-caprolactone) as the matrix material. Heparin and selenium-containing catalyst-organoselenium modified polyethyleneimine were introduced through layer-by-layer assembly in order to build a vascular graft with in situ nitric oxide (NO) generation. The aim of this study was to explore the application of the graft with improved histocompatibility and biological function for vascular implantation in rats. After implantation in rats, compared to poly(ε-caprolactone), the modified grafts could promote the adhesion and proliferation of endothelial cells, and inhibit the adhesion of smooth muscle cells. The modified grafts remarkably promoted endothelialization, inhibited intimal hyperplasia and increased the ratio of alternatively activated macrophages (M2) to classical activated macrophages (M1). This work constructed a vascular graft with heparinization and catalytic NO generation for improving the vascularization, and accelerating the tissue regeneration by regulating the inflammatory response. The present study indicates that it is a promising method for regulating response and tissue regeneration of small diameter vascular grafts by a novel approach of combining heparinization and catalytic NO generation.

Nitric Oxide Release for Improving Performance of Implantable Chemical Sensors - A Review

Over the last three decades, there has been extensive interest in developing in vivo chemical sensors that can provide real-time measurements of blood gases (oxygen, carbon dioxide, and pH), glucose/lactate, and potentially other critical care analytes in the blood of hospitalized patients. However, clot formation with intravascular sensors and foreign body response toward sensors implanted subcutaneously can cause inaccurate analytical results. Further, the risk of bacterial infection from any sensor implanted in the human body is another major concern. To solve these issues, the release of an endogenous gas molecule, nitric oxide (NO), from the surface of such sensors has been investigated owing to NO's ability to inhibit platelet activation/adhesion, foreign body response and bacterial growth. This paper summarizes the importance of NO's therapeutic potential for this application and reviews the publications to date that report on the analytical performance of NO release sensors in laboratory testing and/or during in vivo testing.

Nitric Oxide Generation from Endogenous Substrates Using Metal-Organic Frameworks: Inclusion within Poly(vinyl alcohol) Membranes To Investigate Reactivity and Therapeutic Potential

Cu-BTTri (H₃BTTri = 1,3,5-tris[1H-1,2,3-triazol-5-yl]benzene) is a water-stable, copper-based metal-organic framework (MOF) that exhibits the ability to generate therapeutic nitric oxide (NO) from S-nitrosothiols (RSNOs) available within the bloodstream. Immobilization of Cu-BTTri within a polymeric membrane may allow for localized NO generation at the blood-material interface. This work demonstrates that Cu-BTTri can be incorporated within hydrophilic membranes prepared from poly(vinyl alcohol) (PVA), a polymer that has been examined for numerous biomedical applications. Following immobilization, the ability of the MOF to produce NO from the endogenous RSNO S-nitrosoglutathione (GSNO) is not significantly inhibited. Poly(vinyl alcohol) membranes containing dispersions of Cu-BTTri were tested for their ability to promote NO release from a 10 μM initial GSNO concentration at pH 7.4 and 37 °C, and NO production was observed at levels associated with antithrombotic therapeutic effects without significant copper leaching (<1%). Over 3.5 ± 0.4 h, 10 wt % Cu-BTTri/PVA membranes converted 97 ± 6% of GSNO into NO, with a maximum NO flux of 0.20 ± 0.02 nmol·cm^-2·min^-1. Furthermore, it was observed for the first time that Cu-BTTri is capable of inducing NO production from GSNO under aerobic conditions. At pH 6.0, the NO-forming reaction of 10 wt % Cu-BTTri/PVA membrane was accelerated by 22%, while an opposite effect was observed in the case of aqueous copper(II) chloride. Reduced temperature (20 °C) and the presence of the thiol-blocking reagent N-ethylmaleimide (NEM) impair the NO-forming reaction of Cu-BTTri/PVA with GSNO, with both conditions resulting in a decreased NO yield of 16 ± 1% over 3.5 h. Collectively, these findings suggest that Cu-BTTri/PVA membranes may have therapeutic utility through their ability to generate NO from endogenous substrates. Moreover, this work provides a more comprehensive analysis of the parameters that influence Cu-BTTri efficacy, permitting optimization for potential medical applications.

Drug eluting antimicrobial vascular catheters: Progress and promise

Vascular catheters are critical tools in modern healthcare yet present substantial risks of serious bloodstream infections that exact significant health and economic burdens. Drug-eluting antimicrobial vascular catheters have become important tools in preventing catheter-related bloodstream infections and their importance is expected to increase as significant initiatives are expanded to eliminate and make the occurrence of these infections unacceptable. Here we review clinically significant and emerging drug-eluting antimicrobial catheters within the categories of antibiotic, antiseptic, novel bioactive agents and energy-enhanced drug eluting antimicrobial catheters. Important representatives of each category are reviewed from the standpoints of mechanisms of action, physical-chemical properties, safety, in vitro and clinical effectiveness.

Metal-Organic Framework/Chitosan Hybrid Materials Promote Nitric Oxide Release from S-Nitrosoglutathione in Aqueous Solution

It has been previously demonstrated that copper-based metal-organic frameworks (MOFs) accelerate formation of the therapeutically active molecule nitric oxide (NO) from S-nitrosothiols (RSNOs). Because RSNOs are naturally present in blood, this function is hypothesized to permit the controlled production of NO through use of MOF-based blood-contacting materials. The practical implementation of MOFs in this application typically requires incorporation within a polymer support, yet this immobilization has been shown to impair the ability of the MOF to interact with the NO-forming RSNO substrate. Here, the water-stable, copper-based MOF H3[(Cu4Cl)3-(BTTri)8] (H3BTTri = 1,3,5-tris(1H-1,2,3-triazol-5-yl)benzene), or Cu-BTTri, was incorporated within the naturally derived polysaccharide chitosan to form membranes that were evaluated for their ability to enhance NO generation from the RSNO S-nitrosoglutathione (GSNO). This is the first report to evaluate MOF-induced NO release from GSNO, the most abundant small-molecule RSNO. At a 20 μM initial GSNO concentration (pH 7.4 phosphate buffered saline, 37 °C), chitosan/Cu-BTTri membranes induced the release of 97 ± 3% of theoretical NO within approximately 4 h, corresponding to a 65-fold increase over the baseline thermal decomposition of GSNO. Furthermore, incorporation of Cu-BTTri within hydrophilic chitosan did not impair the activity of the MOF, unlike earlier efforts using hydrophobic polyurethane or poly(vinyl chloride). The reuse of the membranes continued to enhance NO production from GSNO in subsequent experiments, suggesting the potential for continued use. Additionally, the major organic product of Cu-BTTri-promoted GSNO decomposition was identified as oxidized glutathione via mass spectrometry, confirming prior hypotheses. Structural analysis by pXRD and assessment of copper leaching by ICP-AES indicated that Cu-BTTri retains crystallinity and exhibits no significant degradation following exposure to GSNO. Taken together, these findings provide insight into the function and utility of polymer/Cu-BTTri systems and may support the development of future MOF-based biomaterials.

Electrospun poly-ε-caprolactone scaffold modified with catalytic nitric oxide generation and heparin for small-diameter vascular graft

Vascular grafts are significantly needed in peripheral vascular surgery; however, small diameter grafts are not always available, and synthetic grafts perform poorly because of acute thrombosis and neointimal proliferation after implantation.

Iron Complex Facilitated Copper Redox Cycling for Nitric Oxide Generation as Nontoxic Nitrifying Biofilm Inhibitor

In this study, we developed poly(vinyl chloride) (PVC)-solvent casted mixed metal copper and iron complexes capable of catalytic generation of the antibiofilm nitric oxide (NO) from endogenous nitrite. In the absence of additional reducing agent, we demonstrated that the presence of iron complex facilitates a redox cycling, converting the copper(II) complex to active copper(I) species, which catalyzes the generation of NO from nitrite. Assessed by protein assay and surface coverage analyses, the presence of the mixed metal complexes in systems containing water industry-relevant nitrite-producing nitrifying biofilms was shown to result in a "nontoxic mode" of biofilm suppression, while confining the bacterial growth to the free-floating planktonic phase. Addition of an NO scavenger into the mixed metal system eliminated the antibiofilm effects, therefore validating first, the capability of the mixed metal complexes to catalytically generate NO from the endogenously produced nitrite and second, the antibiofilm effects of the generated NO. The work highlights the development of self-sustained antibiofilm materials that features potential for industrial applications. The novel NO-generating antibiofilm technology diverts from the unfavorable requirement of adding a reducing agent and importantly, the less tendency for development of bacterial resistance.

Influence of chirality on catalytic generation of nitric oxide and platelet behavior on selenocystine immobilized TiO2 films

As nitric oxide (NO) plays vital roles in the cardiovascular system, incorporating this molecule into cardiovascular stents is considered as an effective method. In the present study, selenocystine with different chirality (i.e., l- and d-selenocystine) was used as the catalytic molecule immobilized on TiO2 films for decomposing endogenous NO donor. The influences of surface chirality on NO release and platelet behavior were evaluated. Results show that although the amount of immobilized l-selenocystine on the surface was nearly the same as that of immobilized d-selenocystine, in vitro catalytic NO release tests showed that l-selenocystine immobilized surfaces were more capable of catalyzing the decomposition of S-nitrosoglutathione and thus generating more NO. Accordingly, l-selenocystine immobilized surfaces demonstrated significantly increased inhibiting effects on the platelet adhesion and activation, when compared to d-selenocystine immobilized ones. Measurement of the cGMP concentration of platelets further confirmed that surface chirality played an important role in regulating NO generation and platelet behaviors. Additionally, using bovine serum albumin and fibrinogen as model proteins, the protein adsorption determined with quartz crystal microbalance showed that the l-selenocystine immobilized surface enhanced protein adsorption. In conclusion, surface chirality significantly influences protein adsorption and NO release, which may have significant implications in the design of NO-generating cardiovascular stents.

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).

Nitric oxide-generatingl-cysteine-grafted graphene film as a blood-contacting biomaterial

With polyethylenimine molecules as the linker,l-cysteine was grafted on the surface of graphene nanosheets, endowing the functionalized graphene film with the ability to catalytically decompose nitric oxide donors to reduce platelet adhesion.

A new high-capacity metal ion-complexing gel containing cyclen ligands

“Hairy” nano-scale objects cross-linked into a high-capacity metal-binding hydrogel.

Integration of molecular and enzymatic catalysts on graphene for biomimetic generation of antithrombotic species

The integration of multiple synergistic catalytic systems can enable the creation of biocompatible enzymatic mimics for cascading reactions under physiologically relevant conditions. Here we report the design of a graphene-haemin-glucose oxidase conjugate as a tandem catalyst, in which graphene functions as a unique support to integrate molecular catalyst haemin and enzymatic catalyst glucose oxidase for biomimetic generation of antithrombotic species. Monomeric haemin can be conjugated with graphene through π-π interactions to function as an effective catalyst for the oxidation of endogenous L-arginine by hydrogen peroxide. Furthermore, glucose oxidase can be covalently linked onto graphene for local generation of hydrogen peroxide through the oxidation of blood glucose. Thus, the integrated graphene-haemin-glucose oxidase catalysts can readily enable the continuous generation of nitroxyl, an antithrombotic species, from physiologically abundant glucose and L-arginine. Finally, we demonstrate that the conjugates can be embedded within polyurethane to create a long-lasting antithrombotic coating for blood-contacting biomedical devices.

Evaluation of experimental methods for nitric oxide release from cardiovascular implants; bypass grafts as an exemplar

BACKGROUND

There is a great potential for nitric oxide (NO) eluting biomaterials in biomedical applications. These include the development of cardiovascular implants, wound healing products, or applications in cancer and respiratory therapy. While the potential of these materials as a therapy is becoming clearer, the real-time monitoring of NO is not easy and the success in the development of such materials depends on the accurate quantification of NO release.

METHOD

To emphasize on the importance of a measurement technique on the outcome of an experiment, we compared total NO released from S-nitroso-N-acetyl-d-penicillamine (SNAP) incorporated nanocomposite polymer in the form of bypass grafts under simulated physiological conditions using amperometric and chemiluminescence techniques.

RESULTS

We found that the total amount of NO measured by the amperometric technique was 35.8% of the theoretical amount. Similarly, on measuring NO release from the bypass grafts, we demonstrated that the chemiluminesence technique detected NO at a relatively higher level.

CONCLUSIONS

The results of this study clearly demonstrate the relative difference between analysis techniques for accurate NO detection that can be applied to distinct experimental models associated with NO-eluting cardiovascular implants.

Time lasting S-nitrosoglutathione polymeric nanoparticles delay cellular protein S-nitrosation

Physiological S-nitrosothiols (RSNO), such as S-nitrosoglutathione (GSNO), can be used as nitric oxide (NO) donor for the treatment of vascular diseases. However, despite a half-life measured in hours, the stability of RSNO, limited by enzymatic and non-enzymatic degradations, is too low for clinical application. So, to provide a long-lasting effect and to deliver appropriate NO concentrations to target tissues, RSNO have to be protected. RSNO encapsulation is an interesting response to overcome degradation and provide protection. However, RSNO such as GSNO raise difficulties for encapsulation due to its hydrophilic nature and the instability of the S-NO bound during the formulation process. To our knowledge, the present study is the first description of the direct encapsulation of GSNO within polymeric nanoparticles (NP). The GSNO-loaded NP (GSNO-NP) formulated by a double emulsion process, presented a mean diameter of 289 ± 7 nm. They were positively charged (+40 mV) due to the methacrylic acid and ethylacrylate polymer (Eudragit® RL) used and encapsulated GSNO with a satisfactory efficiency (i.e. 54% or 40 mM GSNO loaded in the NP). In phosphate buffer (37 °C; pH 7.4), GSNO-NP released 100% of encapsulated GSNO within 3h and remained stable still 6h. However, in contact with smooth muscle cells, maximum protein nitrosation (a marker of NO bioavailability) was delayed from 1h for free GSNO to 18h for GSNO-NP. Therefore, protection and sustained release of NO were achieved by the association of a NO donor with a drug delivery system (such as polymeric NP), providing opportunities for vascular diseases treatment.

Nitric oxide donors for cardiovascular implant applications

In an era of increased cardiovascular disease burden in the ageing population, there is great demand for devices that come in to contact with the blood such as heart valves, stents, and bypass grafts that offer life saving treatments. Nitric oxide (NO) elution from healthy endothelial tissue that lines the vessels maintains haemostasis throughout the vasculature. Surgical devices that release NO are desirable treatment options and N-diazeniumdiolates and S-nitrosothiols are recognized as preferred donor molecules. There is a keen interest to investigate newer methods by which NO donors can be retained within biomaterials so that their release and kinetic profiles can be optimized. A range of polymeric scaffolds incorporating microparticles and nanomaterials are presenting solutions to current challenges, and have been investigated in a range of clinical applications. This review outlines the application of NO donors for cardiovascular therapy using biomaterials that release NO locally to prevent thrombosis and intimal hyperplasia (IH) and enhance endothelialization in the fabrication of next generation cardiovascular device technology.

Preparation and characterization of an improved Cu(2+)-cyclen polyurethane material that catalyzes generation of nitric oxide from S-nitrosothiols

A new, stable and highly efficient Cu(2+)-cyclen-polyurethane material is described and shown to exhibit improved performance compared to prior materials for the catalytic decomposition of S-nitrosothiols to physiologically active nitric oxide.

Nitric oxide-generating silicone as a blood-contacting biomaterial

Coagulation upon blood-contacting biomaterials remains a problem for short- and long-term clinical applications. This study examined the ability of copper(II)-doped silicone surfaces to generate nitric oxide (NO) and locally inhibit coagulation. Silicone was doped with 3-μm copper [Cu(0)] particles yielding 3 to 10 weight percent (wt%) Cu in 70-μm thick Cu/silicone polymeric matrix composites (Cu/Si PMCs). At 3, 5, 8, and 10 wt% Cu doping, the surface expression of Cu was 12.1% ± 2.8%, 19.7% ± 5.4%, 29.0% ± 3.8%, and 33.8% ± 6.5%, respectively. After oxidizing Cu(0) to Cu(II) by spontaneous corrosion, NO flux, J(NO) (mol · cm(-2) · min(-1)), as measured by chemiluminescence, increased with surface Cu expression according to the relationship J(NO) = (1.63%SA(Cu) - 0.81) × 10(-11), R(2) = 0.98, where %SA(Cu) is the percentage of surface occupied by Cu. NO flux at 10 wt% Cu was 5.35 ± 0.74 × 10(-10) mol · cm(-2) · min(-1). The clotting time of sheep blood exposed to these surfaces was 80 ± 13 seconds with pure silicone and 339 ± 44 seconds when 10 wt% Cu(II) was added. Scanning electron microscopies (SEMs) of coatings showed clots occurred away from exposed Cu dendrites. In conclusion, Cu/Si PMCs inhibit coagulation in a dose-dependent fashion related to the extent of copper exposure on the coated surface.

Polymer-Based Nitric Oxide Therapies: Recent Insights for Biomedical Applications

Since the discovery of nitric oxide (NO) in the 1980s, this cellular messenger has been shown to participate in diverse biological processes such as cardiovascular homeostasis, immune response, wound healing, bone metabolism, and neurotransmission. Its beneficial effects have prompted increased research in the past two decades, with a focus on the development of materials that can locally release NO. However, significant limitations arise when applying these materials to biomedical applications. This Feature Article focuses on the development of NO-releasing and NO-generating polymeric materials (2006-2011) with emphasis on recent in vivo applications. Results are compared and discussed in terms of NO dose, release kinetics, and biological effects, in order to provide a foundation to design and evaluate new NO therapies.

The hemocompatibility of a nitric oxide generating polymer that catalyzes S-nitrosothiol decomposition in an extracorporeal circulation model

Nitric oxide (NO) generating (NOGen) materials have been shown previously to create localized increases in NO concentration by the catalytic decomposition of blood S-nitrosothiols (RSNO) via copper (Cu)-containing polymer coatings and may improve extracorporeal circulation (ECC) hemocompatibility. In this work, a NOGen polymeric coating composed of a Cu⁰-nanoparticle (80 nm)-containing hydrophilic polyurethane (SP-60D-60) combined with the intravenous infusion of an RSNO, S- nitroso-N-acetylpenicillamine (SNAP), is evaluated in a 4 h rabbit thrombogenicity model and the anti-thrombotic mechanism is investigated. Polymer films containing 10 wt.% Cu⁰-nanoparticles coated on the inner walls of ECC circuits are employed concomitantly with systemic SNAP administration (0.1182 μmol/kg/min) to yield significantly reduced ECC thrombus formation compared to polymer control + systemic SNAP or 10 wt.% Cu NOGen + systemic saline after 4 h blood exposure (0.4 ± 0.2 NOGen/SNAP vs 4.9 ± 0.5 control/SNAP or 3.2 ± 0.2 pixels/cm² NOGen/saline). Platelet count (3.9 ± 0.7 NOGen/SNAP vs 1.8 ± 0.1 control/SNAP or 3.0 ± 0.2 × 10⁸/ml NOGen/saline) and plasma fibrinogen levels were preserved after 4 h blood exposure with the NOGen/SNAP combination vs either the control/SNAP or the NOGen/saline groups. Platelet function as measured by aggregometry (51 ± 9 NOGen/SNAP vs 49 ± 3% NOGen/saline) significantly decreased in both the NOGen/SNAP and NOGen/saline groups while platelet P-selectin mean fluorescence intensity (MFI) as measured by flow cytometry was not decreased after 4 h on ECC to ex vivo collagen stimulation (26 ± 2 NOGen/SNAP vs 29 ± 1 MFI baseline). Western blotting showed that fibrinogen activation as assessed by Aγ dimer expression was reduced after 4 h on ECC with NOGen/SNAP (68 ± 7 vs 83 ± 3% control/SNAP). These results suggest that the NOGen polymer coating combined with SNAP infusion preserves platelets in blood exposure to ECCs by attenuating activated fibrinogen and preventing platelet aggregation. These NO-mediated platelet changes were shown to improve thromboresistance of the NOGen polymer-coated ECCs when adequate levels of RSNOs are present.

The artificial endothelium

As the world of critical care medicine advances, extracorporeal therapies (ECC) have become commonplace in the management of the high risk intensive care patient. ECC encompasses a wide variety of technologies from hemodialysis, continuous renal replacement therapy (CRRT) and plasmapheresis, to cardiopulmonary bypass (CPB), extracorporeal life support (ECLS) and hepatic support. The development of internal man made organs is the next step with ventricular assist devices and artificial lungs. As we advance the technologies with smaller devices, and more intricate circuitry, we lack the keystone necessary to control the blood-biomaterial interface. For the last 50 years much has been learned about surface induced thrombosis and attempts have been made to prevent it with alternative systemic anticoagulation, circuitry surface modifications, or a combination of both. Despite these efforts, systemic or regional anticoagulation remain necessary for both laboratory and clinical application of ECC. As such, the development of an endothelial-like, biomimetic surface to reduce or perhaps even eliminate the blood activation/thrombus formation events that occur upon exposure to artificial surfaces is paramount.