Controlled light-induced gas phase nitric oxide release from S-nitrosothiol-doped silicone rubber films

Nitric Oxide Photorelease from Silicone Films Doped with N-Nitroso BODIPY

Nitric oxide (NO) is a unique biochemical mediator involved in the regulation of vital processes. Light-controllable NO releasers show promise in the development of smart therapies. Here, we present a novel biocompatible material based on polydimethylsiloxane (PDMS) doped with BODIPY derivatives containing an N-nitroso moiety that is capable of the photoinduced generation of NO. We study the green-light-induced NO-release properties with the following three methods: electrochemical gas-phase sensor, liquid-phase sensor, and the Griess assay. Prolonged release of NO from the polymer films after short irradiation by narrow-band LED light sources and a laser beam is demonstrated. Importantly, this was accompanied by no or little release of the parent compound (BODIPY-based photodonor). Silicone films with the capability of controllable and clean NO release can potentially be used as a highly portable NO delivery system for different therapeutic applications.

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

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

Peroxynitrite-Scavenging Organosilica Nanomedicines for Light-Controllable NO Release and Precision On-Demand Glaucoma Therapy

Nitric oxide (NO) is a promising approach for treating ocular hypertension and glaucoma. However, its clinical application is limited by its uncontrollable release and the unwanted overproduction of peroxynitrite. Herein, a denitrifying hollow mesoporous organosilica nanoparticle (HMMN) with framework cohybridization is first constructed to encapsulate S-nitroso-N-acetyl-d,l-penicillamine (SNAP) to produce SNAP@HMMN with dual capacities of selective peroxynitrite removal and controllable NO release. Featuring a large corneal permeability, the well-designed SNAP@HMMN can achieve trans-corneal delivery to reach the target trabecular meshwork (TM)/Schlemm's canal (SC) site. Upon light irradiation, the intraocular pressure (IOP) is appropriately lowered in an adjustable and long-lasting manner while the outflow tissues are protected from nitrative damage, which is expected to realize precision on-demand glaucoma therapy with little biosafety concern, promising significant clinical translational potential.

Nitric Oxide: Physiological Functions, Delivery, and Biomedical Applications

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

Recent Developments in Multifunctional Antimicrobial Surfaces and Applications toward Advanced Nitric Oxide-Based Biomaterials

Implant-associated infections arising from biofilm development are known to have detrimental effects with compromised quality of life for the patients, implying a progressing issue in healthcare. It has been a struggle for more than 50 years for the biomaterials field to achieve long-term success of medical implants by discouraging bacterial and protein adhesion without adversely affecting the surrounding tissue and cell functions. However, the rate of infections associated with medical devices is continuously escalating because of the intricate nature of bacterial biofilms, antibiotic resistance, and the lack of ability of monofunctional antibacterial materials to prevent the colonization of bacteria on the device surface. For this reason, many current strategies are focused on the development of novel antibacterial surfaces with dual antimicrobial functionality. These surfaces are based on the combination of two components into one system that can eradicate attached bacteria (antibiotics, peptides, nitric oxide, ammonium salts, light, etc.) and also resist or release adhesion of bacteria (hydrophilic polymers, zwitterionic, antiadhesive, topography, bioinspired surfaces, etc.). This review aims to outline the progress made in the field of biomedical engineering and biomaterials for the development of multifunctional antibacterial biomedical devices. Additionally, principles for material design and fabrication are highlighted using characteristic examples, with a special focus on combinational nitric oxide-releasing biomedical interfaces. A brief perspective on future research directions for engineering of dual-function antibacterial surfaces is also presented.

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

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

Long-Term Storage Stability and Nitric Oxide Release Behavior of (N-Acetyl-S-nitrosopenicillaminyl)-S-nitrosopenicillamine-Incorporated Silicone Rubber Coatings

Physical incorporation of nitric oxide (NO) releasing materials in biomedical grade polymer matrices to fabricate antimicrobial coatings and devices is an economically viable process. However, achieving long-term NO release with a minimum or no leaching of the NO donor from the polymer matrix is still a challenging task. Herein, (N-acetyl-S-nitrosopenicillaminyl)-S-nitrosopenicillamine (SNAP-SNAP), a penicillamine dipeptide NO-releasing molecule, is incorporated into a commercially available biomedical grade silicone rubber (SR) to fabricate a NO-releasing coating (SNAP-SNAP/SR). The storage stabilities of the SNAP-SNAP powder and SNAP-SNAP/SR coating were analyzed at different temperatures. The SNAP-SNAP/SR coatings with varying wt % of SNAP-SNAP showed a tunable and sustained NO release for up to 6 weeks. Further, S-nitroso-N-acetylpenicillamine (SNAP), a well-explored NO-releasing molecule, was incorporated into a biomedical grade silicone polymer to fabricate a NO-releasing coating (SNAP/SR) and a comparative analysis of the NO release and S-nitrosothiol (RSNO) leaching behavior of 10 wt % SNAP-SNAP/SR and 10 wt % SNAP/SR was studied. Interestingly, the 10 wt % SNAP-SNAP/SR coatings exhibited ∼36% higher NO release and 4 times less leaching of NO donors than the 10 wt % SNAP/SR coatings. Further, the 10 wt % SNAP-SNAP/SR coatings exhibited promising antibacterial properties against Staphylococcus aureus and Escherichia coli due to the persistent release of NO. The 10 wt % SNAP-SNAP/SR coatings were also found to be biocompatible against NIH 3T3 mouse fibroblast cells. These results corroborate the sustained stability and NO-releasing properties of the SNAP-SNAP in a silicone polymer matrix and demonstrate the potential for the SNAP-SNAP/SR polymer in the fabrication of long-term indwelling biomedical devices and implants to enhance biocompatibility and resist device-related infections.

Nitric oxide releasing halloysite nanotubes for biomedical applications

Halloysite nanotubes (HNTs) are natural aluminosilicate clay that have been extensivelyexplored fordelivery of bioactive agents in biomedical applications because of their desirable features including unique hollow tubular structure, good biocompatibility, high mechanical strength, and extensive functionality. For the first time, in this work, functionalized HNTs are developed as a delivery platform for nitric oxide (NO), a gaseous molecule, known for its important roles in the regulation of various physiological processes. HNTs were first hydroxylated and modified with an aminosilane crosslinker, (3-aminopropyl) trimethoxysilane (APTMS), to enable the covalent attachment of a NO donor precursor, N-acetyl-d-penicillamine (NAP). HNT-NAP particles were then converted to NO-releasing S-nitroso-N-acetyl-penicillamine HNT-SNAP by nitrosation. The total NO loading on the resulting nanotubes was 0.10 ± 0.07 μmol/mg which could be released using different stimuli such as heat and light. Qualitative (Fourier-transform infrared spectroscopy and Nuclear magnetic resonance) and quantitative (Ninhydrin and Ellman) analyses were performed to confirm successful functionalization of HNTs at each step. Field emission scanning electron microscopy (FE-SEM) showed that the hollow tubular morphology of the HNTs was preserved after modification. HNT-SNAP showed concentration-dependent antibacterial effects against Gram-positive Staphylococcus aureus (S. aureus), resulting in up to 99.6% killing efficiency at a concentration of 10 mg/mL as compared to the control. Moreover, no significant cytotoxicity toward 3T3 mouse fibroblast cells was observed at concentrations equal or below 2 mg/mL of HNT-SNAP according to a WST-8-based cytotoxicity assay. The SNAP-functionalized HNTs represent a novel and efficient NO delivery system that holds the potential to be used, either alone or in combination with polymers for different biomedical applications.

Design and Characteristics of an Optofluidic Phase Modulator Based on Dielectrowetting

In this paper, an optofluidic phase modulator based on dielectrowetting is designed and fabricated to adjust the optical phase. Two liquids are filled in the device, and a transparent sheet is employed at the liquid interface to keep the interface flat. When different voltages are applied to the modulator, the flat interface moves up and down, leading to the variation of the optical phase. A theoretical model is constructed to predict the optical phase shift quantitatively, and the phase regulation ability is also tested experimentally. Our modulator realizes continuous adjustment of the optical phase in a certain range by the operation of voltage adjustment. When the voltage is increased to 150 V, the optical phase modulation range of our proposed modulator can reach 9.366 π.

Nitric Oxide-Releasing Insert for Disinfecting the Hub Region of Tunnel Dialysis Catheters

The use of tunneled dialysis catheters (TDCs) for patients in need of hemodialysis treatments (HDs) causes a significant number of bloodstream infections (BSIs), with very few viable preventative/treatment methods. Use of antibiotics is relatively ineffective due to the development of multidrug-resistant bacterial strains and the inability to penetrate bacterial biofilms. Nitric oxide (NO) is an endogenous gas molecule that has broad-spectrum antimicrobial/antibiofilm activity. In this study, the potential of creating a NO-releasing insert device that is attached onto the hub region cap of TDCs and locally releases NO within the TDC hub is evaluated for its antimicrobial/antibiofilm effectiveness. The NO-releasing insert contains the natural NO donor S-nitrosoglutathione (GSNO), along with zinc oxide (ZnO) nanoparticles to accelerate NO release from the GSNO, within a short silicone tube that is sealed at both ends and attached to the catheter cap. An in vitro 3-d-long antimicrobial study using catheter hubs yielded >6.6 log reductions of both Pseudomonas aeruginosa and Staphylococcus aureus for the NO-releasing insert device compared to controls. Two 14-d-long sheep studies demonstrated that the NO-releasing insert devices are exceptionally potent at preventing bacteria/biofilm growth on the inner lumen walls of TDCs compared to controls that have no preventative treatment devices as well as implanted TDCs that have commercially available chlorhexidine-treated insert devices placed within the hub regions.

Enhanced Hemocompatibility and In Vivo Analytical Accuracy of Intravascular Potentiometric Carbon Dioxide Sensors via Nitric Oxide Release

In this letter, the innate ability of nitric oxide (NO) to inhibit platelet activation/adhesion/thrombus formation is employed to improve the hemocompatibility and in vivo accuracy of an intravascular (IV) potentiometric PCO₂ (partial pressure of carbon dioxide) sensor. The catheter-type sensor is fabricated by impregnating a segment of dual lumen silicone tubing with a proton ionophore, plasticizer, and lipophilic cation-exchanger. Subsequent filling of bicarbonate and strong buffer solutions and placement of Ag/AgCl reference electrode wires within each lumen, respectively, enables measurement of the membrane potential difference across the inner wall of the tube, with this potential changing as a function of the logarithm of sample PCO₂. The dual lumen device is further encapsulated within a S-nitroso-N-acetyl-DL-penicillamine (SNAP)-doped silicone tube that releases physiological levels of NO. The NO releasing sensor exhibits near-Nernstian sensitivity toward PCO₂ (slope = 59.31 ± 0.78 mV/decade) and low drift rates (<2 mV/24 h after initial equilibration). In vivo evaluation of the NO releasing sensors, performed in the arteries and veins of anesthetized pigs for 20 h, shows enhanced accuracy (vs non-NO releasing sensors) when benchmarked to measurements of discrete blood samples made with a commercial blood gas analyzer. The accurate, continuous monitoring of blood PCO₂ levels achieved with this new IV NO releasing PCO₂ sensor configuration could help better manage hospitalized patients in critical care units.

Clinical use of inhaled nitric oxide: Local and systemic applications

Upon the FDA approval for inhaled nitric oxide (iNO) in 1999 to treat persistent pulmonary hypertension in neonates, iNO has proven to be a beneficial therapeutic in multiple diseases. We aim to review applications of iNO that have modeled its protective and therapeutic attributes, as well as highlight preliminary studies that could allude to future avenues of use. Numerous publications have reported specific incidences where iNO therapy has proved advantageous, while some applications have potential after further validation. Establishing guidelines on dosing, duration, and defined clinical uses are crucial for the future of iNO. Delivery of iNO has been controlled by a sole distributor, and comes with high cost, and lack of portability. A shift in patents has allowed for new designs for iNO device synthesis, with many new developments of iNO medical devices that will likely change the future of iNO in a medical setting.

Nanoscale lipid vesicles functionalized with a nitro-aniline derivative for photoinduced nitric oxide (NO) delivery

Nanoscale vesicles functionalized with a nitric oxide (NO) releasing molecule 4-nitro-3-(trifluoromethyl)aniline have been reported. The new NO-nano-vesicular donor material shows an effective photo-release of NO upon irradiation with blue light at 410 nm. The kinetics of NO release has been monitored by using simple spectroscopic techniques such as UV-Vis and fluorescence methods. Colorimetric Griess assay and fluorescence DAF assay have been used for the detection and quantification of NO released from vesicles. This new vesicular nanoscale NO donor has the advantages of facile preparation in water, capable of releasing NO in a pure aqueous medium, photo-controlled NO release, bio-compatibility and capacity to modulate the NO donor loading to achieve an essential amount of NO.

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

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

Comparison of electrochemical nitric oxide detection methods with chemiluminescence for measuring nitrite concentration in food samples

Nitrite is a naturally occurring species present in various food samples and also present in our bodies as a product of nitric oxide (NO) oxidation. Considering the ubiquity of nitrite, its determination is of great importance in both biological and food samples. Herein, a very facile indirect method of nitrite determination in meat samples via selective reduction to nitric oxide (NO) is presented. The resulting gaseous product is quantified via portable and cost-effective electrochemical sensors. Both a novel laboratory prepared Pt-Nafion based NO sensor and a commercially available amperometric NO sensor are compared. Excellent correlations between the nitrite amount found in tested samples using both of the electrochemical sensors and a reference chemiluminescence method are demonstrated (r = 0.997 and r = 0.999 for Pt-Nafion based and commercially available NO-B4 electrochemical sensors, respectively, n = 12). Moreover, the slope of the linear regression curves are very close to unity for the comparison of the three systems tested. The amperometric sensors compared within this work exhibit good precision and accuracy and are shown to be an attractive alternative to the costly chemiluminescence detection method for accurately determining nitrite levels in food samples.