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

Achieving Biomedically Desirable Nitric Oxide Release from Glucose Monitor Surfaces Via a Cu-Based Catalyst Coating

We report the design of a blood-contacting glucose monitor with a nitric oxide (NO)-releasing metal-organic framework (MOF) embedded within the outer polymer layer of a glucose sensor to promote the release of NO from endogenous NO donors. The sensors were tested by using amperometry across a range of glucose concentrations to assess whether the presence of either the MOF or NO decreased the performance of the glucose monitor. Even though signal response was diminished, the sensors maintained a good regression fit (R2 = 0.9944) and a similar dynamic range and reproducibility in the presence of S-nitrosoglutathione.

Recent Development of Implantable Chemical Sensors Utilizing Flexible and Biodegradable Materials for Biomedical Applications

Implantable chemical sensors built with flexible and biodegradable materials exhibit immense potential for seamless integration with biological systems by matching the mechanical properties of soft tissues and eliminating device retraction procedures. Compared with conventional hospital-based blood tests, implantable chemical sensors have the capability to achieve real-time monitoring with high accuracy of important biomarkers such as metabolites, neurotransmitters, and proteins, offering valuable insights for clinical applications. These innovative sensors could provide essential information for preventive diagnosis and effective intervention. To date, despite extensive research on flexible and bioresorbable materials for implantable electronics, the development of chemical sensors has faced several challenges related to materials and device design, resulting in only a limited number of successful accomplishments. This review highlights recent advancements in implantable chemical sensors based on flexible and biodegradable materials, encompassing their sensing strategies, materials strategies, and geometric configurations. The following discussions focus on demonstrated detection of various objects including ions, small molecules, and a few examples of macromolecules using flexible and/or bioresorbable implantable chemical sensors. Finally, we will present current challenges and explore potential future directions.

Miniaturized Capsule System Toward Real-Time Electrochemical Detection of H2 S in the Gastrointestinal Tract

Hydrogen sulfide (H2 S) is a gaseous inflammatory mediator and important signaling molecule for maintaining gastrointestinal (GI) homeostasis. Excess intraluminal H2 S in the GI tract has been implicated in inflammatory bowel disease and neurodegenerative disorders; however, the role of H2 S in disease pathogenesis and progression is unclear. Herein, an electrochemical gas-sensing ingestible capsule is developed to enable real-time, wireless amperometric measurement of H2 S in GI conditions. A gold (Au) three-electrode sensor is modified with a Nafion solid-polymer electrolyte (Nafion-Au) to enhance selectivity toward H2 S in humid environments. The Nafion-Au sensor-integrated capsule shows a linear current response in H2 S concentration ranging from 0.21 to 4.5 ppm (R2 = 0.954) with a normalized sensitivity of 12.4% ppm-1 when evaluated in a benchtop setting. The sensor proves highly selective toward H2 S in the presence of known interferent gases, such as hydrogen (H2 ), with a selectivity ratio of H2 S:H2 = 1340, as well as toward methane (CH4 ) and carbon dioxide (CO2 ). The packaged capsule demonstrates reliable wireless communication through abdominal tissue analogues, comparable to GI dielectric properties. Also, an assessment of sensor drift and threshold-based notification is investigated, showing potential for in vivo application. Thus, the developed H2 S capsule platform provides an analytical tool to uncover the complex biology-modulating effects of intraluminal H2 S.

Photo-controlled and photo-calibrated nanoparticle enabled nitric oxide release for anti-bacterial and anti-biofilm applications

After numerous efforts to elucidate the biological role of nitric oxide (NO), NO treatments have become a hotspot at the forefront of medicine. NO-releasing substances are constantly needed, while the direct use of NO gas is unattainable in bio-systems. An ideal NO donor should possess controllable and visible NO-release capability. The reported NO donating nanoparticles, prepared via encapsulating a hydrophobic NO-releasing compound into DSPE-PEG₂₀₀₀, meet the criteria mentioned previously. The localization and flux of NO released from these nanoparticles could be manipulated by UV or blue light. Meanwhile, NOD-NPs emit a dose-dependent fluorescence intensity to calibrate the generation of NO. While the good biocompatibility of NOD-NPs has been validated, the NO from our nanoparticles demonstrates efficient anti-bacterial and anti-biofilm effects toward Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). Therefore, the NOD-NPs developed in this work have potential application in evaluating the regulation of microbes by NO.

Facile Synthesis of Conductive Metal-Organic Frameworks Nanotubes for Ultrahigh-Performance Flexible NO Sensors

Cu-benzenehexathiol (Cu-BHT) has attracted significant attention due to its record high electrical conductivity and crystal defects Cu_2c . However, the nonporous structure and small specific surface area of Cu-BHT with two-dimensional kagome lattice invariably limit its practical application in sensing and catalysis. In this work, Cu-BHT nanotubes (Cu-BHT-NTs) are designed and prepared via a facile homogeneous reaction to solve these problems. Compared with the traditional nanorod-like structure, the Cu-BHT-NTs not only have a higher specific surface area but also possess a higher proportion of crystal defects (66.6%). The successfully configured DPPTT/Cu-BHT-NTs heterostructure organic field-effect transistor (OFET)-based sensor exhibits excellent sensitivity as high as 13 610%, a minimum detection limits down to 5 ppb, and exceptional selectivity to nitric oxide (NO) toxic gases. Theoretical analysis systematically shows that Cu_2c sites in the Cu-BHT-NTs increase the number of electrons transferred from the heterostructure to NO molecules, confirming that the high sensitivity and selectivity result from the high binding between Cu-BHT-NTs and NO molecules. Furthermore, a fully flexible device based on the heterojunction OFET sensor is prepared to ensure the convenience of wearing and carrying gas sensors, opening up a new avenue for the next generation of wearable intelligent electronics.

3D Printing of Antibacterial Polymer Devices Based on Nitric Oxide Release from Embedded S-Nitrosothiol Crystals

Controlled release of drugs from medical implants is an effective approach to reducing foreign body reactions and infections. We report here on a one-step 3D printing strategy to create drug-eluting polymer devices with a drug-loaded bulk and a drug-free coating. The spontaneously formed drug-free coating dramatically reduces the surface roughness of the implantable devices and serves as a protective layer to suppress the burst release of drugs. A high viscosity liquid silicone that can be extruded based on its shear-thinning property and quickly vulcanize upon exposure to ambient moisture is used as the ink for 3D printing. S-Nitrosothiol type nitric oxide (NO) donors in their crystalline forms are selected as model drugs because of the potent antimicrobial, antithrombotic, and anti-inflammatory properties of NO. Direct ink writing of the homogenized polymer-drug mixtures generates rough and ill-defined device surfaces because of the exposed S-nitrosothiol microparticles. When a low-viscosity silicone (polydimethylsiloxane) is added into the ink, this silicone diffuses outward upon deposition to form a drug-free outermost layer without compromising the integrity of the printed structures. S-Nitrosoglutathione (GSNO) or S-nitroso-N-acetylpenicillamine (SNAP) embedded in the printed silicone matrix releases NO under physiological conditions from days to about one month. The microsized drug crystals are well-preserved in the ink preparation and printing processes, which is one reason for the sustained NO release. Biofilm and cytotoxicity experiments confirmed the antibacterial property and safety of the printed NO-releasing devices. This additive manufacturing platform does not require dissolution of drugs and involves no thermal or UV processes and, therefore, offers unique opportunities to produce drug-eluting silicone devices in a customized manner.

Tumor-Penetrable Nitric Oxide-Releasing Nanoparticles Potentiate Local Antimelanoma Therapy

Although nitric oxide (NO) has been emerging as a novel local anticancer agent because of its potent cytotoxic effects and lack of off-target side effects, its clinical applications remain a challenge because of the short effective diffusion distance of NO that limits its anticancer activity. In this study, we synthesized albumin-coated poly(lactic-co-glycolic acid) (PLGA)-conjugated linear polyethylenimine diazeniumdiolate (LP/NO) nanoparticles (Alb-PLP/NO NPs) that possess tumor-penetrating and NO-releasing properties for an effective local treatment of melanoma. Sufficient NO-loading and prolonged NO-releasing characteristics of Alb-PLP/NO NPs were acquired through PLGA-conjugated LP/NO copolymer (PLP/NO) synthesis, followed by nanoparticle fabrication. In addition, tumor penetration ability was rendered by the electrostatic adsorption of the albumin on the surface of the nanoparticles. The Alb-PLP/NO NPs showed enhanced intracellular NO delivery efficiency and cytotoxicity to B16F10 murine melanoma cells. In B16F10-tumor-bearing mice, the Alb-PLP/NO NPs showed improved extracellular matrix penetration and spatial distribution in the tumor tissue after intratumoral injection, resulting in enhanced antitumor activity. Taken together, the results suggest that Alb-PLP/NO NPs represent a promising new modality for the local treatment of melanoma.

Modulating the foreign body response of implants for diabetes treatment

Diabetes Mellitus is a group of diseases characterized by high blood glucose levels due to patients' inability to produce sufficient insulin. Current interventions often require implants that can detect and correct high blood glucose levels with minimal patient intervention. However, these implantable technologies have not reached their full potential in vivo due to the foreign body response and subsequent development of fibrosis. Therefore, for long-term function of implants, modulating the initial immune response is crucial in preventing the activation and progression of the immune cascade. This review discusses the different molecular mechanisms and cellular interactions involved in the activation and progression of foreign body response (FBR) and fibrosis, specifically for implants used in diabetes. We also highlight the various strategies and techniques that have been used for immunomodulation and prevention of fibrosis. We investigate how these general strategies have been applied to implants used for the treatment of diabetes, offering insights on how these devices can be further modified to circumvent FBR and fibrosis.

Continuous Glucose Monitoring Devices: Past, Present, and Future Focus on the History and Evolution of Technological Innovation

The concept of implantable glucose sensors has been promulgated for more than 40 years. It is now accepted that continuous glucose monitoring (CGM) increases quality of life by allowing informed diabetes management decisions as a result of more optimized glucose control. The focus of this article is to provide a brief overview of the CGM market history, emerging technologies, and the foreseeable challenges for the next CGM generations as well as proposing possible solutions in an effort to advance the next generation of implantable sensor.

Visible light-responsive micelles enable co-delivery of nitric oxide and antibiotics for synergistic antibiofilm applications

Tetraphenylethylene (TPE) moieties have been employed as a light-absorbing antenna for the activation of photoresponsive N-nitrosamine derivatives, enabling visible light-triggered NO release and efficient biofilm dispersal.

Recent Progress and Perspectives on Polyurethane Membranes in the Development of Gas Sensors

In today's technology, gas sensors are of great importance in areas such as assessing environmental impacts, monitoring gas production facilities, measuring natural gas, controlling mines and gas leaks. Improving sensor sensitivity and decreasing the determination time is among the subjects that are continuously investigated. The use of polymeric membranes to make such improvements is common practice in the gas sensor field. By the development of polymeric membrane-based gas sensors and increasing the measurement sensitivity, accurate, sensitive, precise and fast measurements of toxic gases, volatile organic gases, and trace gases have been possible. Therefore, polyurethane membranes have been promising in the development of next-generation gas sensors based on membrane diffusion to ensure real-time and continuous monitoring of gases in industry and academic studies. This study aims to evaluate, compare and discuss the recent developments in the use of polyurethane membranes in existing gas detection technologies with chemical, electrical and optical measurement methods. In these measurement methods, polyurethane structures act as a selectively permeable membrane, an ideal matrix material for conductive additives or a suitable film structure for coating the conductive polymeric films. Conductive additives or conductive film structures for gas sensors play an important role in the detection of the gas structure with the change in electrical properties during the passage of gas molecules. This review has focused on important properties such as selectivity, detection time and measurement sensitivity concerning gas detection technology containing polyurethane, which has been used so far.

Studies of combined NO-eluting/CD47-modified polyurethane surfaces for synergistic enhancement of biocompatibility

The blood compatibility of various intravascular (IV) devices (e.g., catheters, sensors, etc.) is compromised by activation of platelets that can cause thrombus formation and device failure. Such devices also carry a high risk of microbial infection. Recently, nitric oxide (NO) releasing polymers/devices have been proposed to reduce these clinical problems. CD47, a ubiquitously expressed transmembrane protein with proven anti-inflammation/anti-platelet properties when immobilized on polymeric surfaces, is a good candidate to complement NO release in both effectiveness and longevity. In this work, we successfully appended CD47 peptides (pepCD47) to the surface of biomedical grade polyurethane (PU) copolymers. SIRPα binding and THP-1 cell attachment experiments strongly suggested that the pepCD47 retains its biological properties when bound to PU films. In spite of the potentially high reactivity of NO toward various amino acid residues in CD47, the efficacy of surface-immobilized pepCD47 to prevent inflammatory cell attachment was not inhibited after being subjected to a high flux of NO for three days, demonstrating excellent compatibility of the two species. We further constructed a CD47 surface immobilized silicone tubing filled with NO releasing S-nitrosoglutathione/ascorbic acid (GSNO/AA) solution for synergistic biocompatibility evaluation. Via an ex vivo Chandler loop model, we demonstrate for the first time that NO release and CD47 modification could function synergistically at the blood/material interface and produce greatly enhanced anti-inflammatory/anti-platelet effects. This concept should be readily implementable to create a new generation of thromboresistant/antimicrobial implantable devices.

Nitric oxide-releasing semi-crystalline thermoplastic polymers: preparation, characterization and application to devise anti-inflammatory and bactericidal implants

Semi-crystalline thermoplastics are an important class of biomaterials with applications in creating extracorporeal and implantable medical devices. In situ release of nitric oxide (NO) from medical devices can enhance their performance via NO's potent anti-thrombotic, bactericidal, anti-inflammatory, and angiogenic activity. However, NO-releasing semi-crystalline thermoplastic systems are limited and the relationship between polymer crystallinity and NO release profile is unknown. In this paper, the functionalization of poly(ether-block-amide) (PEBA), Nylon 12, and polyurethane tubes, as examples of semi-crystalline polymers, with the NO donor S-nitroso-N-acetylpenicillamine (SNAP) within, is demonstrated via a polymer swelling method. The degree of crystallinity of the polymer plays a crucial role in both SNAP impregnation and NO release. Nylon 12, which has a relatively high degree of crystallinity, exhibits an unprecedented NO release duration of over 5 months at a low NO level, while PEBA tubing exhibits NO release over days to weeks. As a new biomedical application of NO, the NO-releasing PEBA tubing is examined as a cannula for continuous subcutaneous insulin infusion. The released NO is shown to enhance insulin absorption into the bloodstream probably by suppressing the tissue inflammatory response, and thereby could benefit insulin pump therapy for diabetes management.

Biomaterials: Foreign Bodies or Tuners for the Immune Response?

The perspectives of regenerative medicine are still severely hampered by the host response to biomaterial implantation, despite the robustness of technologies that hold the promise to recover the functionality of damaged organs and tissues. In this scenario, the cellular and molecular events that decide on implant success and tissue regeneration are played at the interface between the foreign body and the host inflammation, determined by innate and adaptive immune responses. To avoid adverse events, rather than the use of inert scaffolds, current state of the art points to the use of immunomodulatory biomaterials and their knowledge-based use to reduce neutrophil activation, and optimize M1 to M2 macrophage polarization, Th1 to Th2 lymphocyte switch, and Treg induction. Despite the fact that the field is still evolving and much remains to be accomplished, recent research breakthroughs have provided a broader insight on the correct choice of biomaterial physicochemical modifications to tune the reaction of the host immune system to implanted biomaterial and to favor integration and healing.

JS-K as a nitric oxide donor induces apoptosis via the ROS/Ca2+/caspase-mediated mitochondrial pathway in HepG2 cells

JS-K, (O²-(2, 4-dinitrophenyl) 1-[(4-ethoxycarbonyl) piperazin-1-yl] diazen 1-ium-1, 2-diolate), is a novel diazeniumdiolate-based nitric oxide donor prodrug. The present study investigated the relationship between reactive oxygen species (ROS) elevation, Ca²⁺ overload and mitochondrial disruption in JS-K-induced apoptosis. JS-K could significantly inhibit cell growth and induce apoptosis in a dose-dependent manner. Meanwhile, JS-K caused the accumulation of ROS, overload of Ca²⁺, decrease of mitochondrial membrane potential, release of cytochrome c (Cyt c) from mitochondria to the cytoplasm, increase of Bax-to-Bcl-2 ratio and activation of caspase- 9/3. NAC (an antioxidant) or BAPTA (an intracellular Ca²⁺ chelator) could partially reverse the above events, while BAPTA had little effect on the levels of ROS. Furthermore, pre-treatment with Carboxy-PTIO (a NO scavenger) significantly blocked the increasing of ROS, cytosolic Ca²⁺ and reversed the loss of mitochondrial membrane potential in JS-K-induced apoptosis. Taken together, the results suggested that NO released from JS-K could significantly induce HepG2 cell apoptosis through a ROS/Ca²⁺/caspase-mediated mitochondrial pathway.