Phosphorescent Microneedle Array for the Measurement of Oxygen Partial Pressure in Tissue

Oxygen-Sensitive Optical Nanosensors: Current Advances and Future Perspectives

Oxygen sensing is essential across a wide range of fields, from understanding cellular metabolism and disease mechanisms to optimizing industrial and environmental processes. In this Perspective, we highlight key developments in optical architectures (at the nanometer to sub-micrometer scale), including their transduction methods and applications to in vitro, in vivo/in situ, and nonbiological systems. We also discuss future directions for the field in the domain of expanding extra/intracellular and nonbiological sensing. We address improving accessibility for nonexpert users through the need for standardized protocols and scalable production methods. Furthermore, we advocate for fostering interdisciplinary collaborations through academic incubators, conference networking, and strategic citation practices to bridge gaps between fundamental research and applied science to expand the impact of these tools to researchers outside the sensing field. Addressing these challenges will help drive the development of more versatile and widely accessible oxygen sensors, thus advancing innovation across diverse disciplines.

Microneedle-Based Electrochemical Array Patch for Ultra-Antifouling and Ultra-Anti-Interference Monitoring of Subcutaneous Oxygen

Oxygen saturation is a crucial indicator in the management of various diseases and in preoperative diagnosis, and the detection of oxygen content is valuable in guiding clinical treatment. However, as the classical and dominant oxygen detection strategies, current photoelectric oximeters and electrochemical-based blood gas analyzers often suffer from significant interindividual variation and poor compliance, respectively. In recent years, wearable microneedles (MNs) for analyzing biomarkers in interstitial fluid (ISF) have received great attention and recognition mainly for the reason that the content of the substances distributed in ISF has a better correlation with that in blood circulation compared with other body fluids such as sweat and saliva. Herein, an MN-based electrochemical array system was developed for continuous subcutaneous oxygen sensing, in which gold-modified commercial acupuncture MNs were used as the sensing units, and a tailored mini-workstation, a nonwoven fabric, and a water and air isolation membrane were integrated to fabricate a wearable array patch. Notably, a multifunctional swelling resin with good biocompatibility was adopted to decorate the MN surface as a protective layer and as an electrolyte gel. The swelling resin featured the ability to reduce epidermis secretions during the sensor array penetrating the skin and to decrease the interference of other biomolecules in ISF for oxygen assay during measurement. This proposed array patch can perform the subcutaneous oxygen analysis in the physiological range of 6-150 mmHg with high sensitivity (0.3817 μA/mmHg) and low theoretical limit of detection (5.06 mmHg). It also showed decent stability and selectivity in the presence of several kinds of exogenous and endogenous substances. Finally, the patch accomplished continual monitoring of the subcutaneous oxygen content during long-term physical exercise, showing great potential in providing warning about the hypoxia status of the human body. It could be foreseen that this high-performance patch will play an active role in respiratory disease evaluation, surgical monitoring, and public health care.

TiMON: a real-time integrated monitor for improving the placement and wear of emergency tourniquets

BACKGROUND

The use of emergency tourniquets among military personnel has helped to dramatically reduce battlefield deaths and has recently gained popularity in the civilian sector. Yet, even well-trained individuals can find it difficult to assess proper tourniquet application. Emergency tourniquets are typically deemed sufficiently tightened through cursory visual confirmation or pulse assessment. These indicators are not always accurate and are difficult to assess during chaotic events where fast and effective tourniquet application by both trained and untrained personnel can contribute significantly to saving lives. Towards addressing these issues, we have developed the Tourniquet Integrated Monitor (TiMON) as an easy-to-use real-time pressure sensing device designed to seamlessly integrate with pre-existing emergency tourniquets. Here, we present the results of two studies in which the TiMON was tested among a group of soldiers participating in the Army Expeditionary Warrior Experiments (AEWE) as well as in a group of untrained civilians from Massachusetts General Hospital.

METHODS

In the first study, 30 soldiers with prior tourniqueting experience were asked to apply a TiMON equipped CAT tourniquet onto a leg mannequin with (unblinded) and without (blinded) assistance from the TiMON's output. In the second study, 30 lay volunteers from Massachusetts General Hospital with no prior tourniquet training were recruited and taught how to apply a tourniquet under normal conditions prior to being asked to perform the same exercises as the soldiers. In both studies, data collected for statistical analysis consisted of the real-time applied pressure along with the elapsed time for each subject to finish applying the emergency tourniquet.

RESULTS

Subjects in both groups utilizing the TiMON had greater success in applying emergency tourniquets at the civilian clinically recommended occlusion range of 180 to 300 mmHg (soldiers: 86.67% assisted vs 33.33% unassisted; untrained volunteers: 93.33% assisted vs 40.00% unassisted). In terms of applied pressure, no significant mean differences were observed in either group (soldiers p-value = 0.13; untrained volunteers p-value = 0.26), however the unblinded subjects were found to exhibit significantly lower variances in applied pressure compared to those who were blinded (soldiers p-value < 0.0001; untrained volunteers p-value < 0.0001). In terms of application speeds, no significant differences in means and variances were observed in the soldiers (p-values = 0.85 and 0.61, respectively), while mildly significant increases in application times were observed in the untrained volunteers (p-value = 0.036).

CONCLUSION

Trained soldiers and lay volunteers using the TiMON were able to consistently apply tourniquets at clinically recommended occlusion pressures between 180 and 300 mmHg with significantly less under and over tightening while minimizing any negative effects to their application speeds. Despite it being their first time using the TiMON, both groups were able to quickly apply emergency tourniquets at significantly improved and consistent success rates regardless of prior training and experience.

Recent advances in fluorescent probes for ATP imaging

Adenosine-5'-triphosphate (ATP) is a critical biological molecule that functions as the primary energy currency within cells. ATP synthesis occurs in the mitochondria, and variations in its concentration can significantly influence mitochondrial and cellular performance. Prior studies have established a link between ATP levels and a variety of diseases, such as cancer, neurodegenerative conditions, ischemia, and hypoglycemia. Consequently, researchers have developed many fluorescent probes for ATP detection, recognizing the importance of monitoring intracellular ATP levels to understand cellular processes. These probes have been effectively utilized for visualizing ATP in living cells and biological samples. In this comprehensive review, we categorize fluorescent sensors developed in the last five years for ATP detection. We base our classification on fluorophores, structure, multi-response channels, and application. We also evaluate the challenges and potential for advancing new generations of fluorescence imaging probes for monitoring ATP in living cells. We hope this summary motivates researchers to design innovative and effective probes tailored to ATP sensing. We foresee imminent progress in the development of highly sophisticated ATP probes.

Continuous oxygen monitoring to enhance ex-vivo organ machine perfusion and reconstructive surgery

Continuous oxygenation monitoring of machine-perfused organs or transposed autologous tissue is not currently implemented in clinical practice. Oxygenation is a critical parameter that could be used to verify tissue viability and guide corrective interventions, such as perfusion machine parameters or surgical revision. This work presents an innovative technology based on oxygen-sensitive, phosphorescent metalloporphyrin allowing continuous and non-invasive oxygen monitoring of ex-vivo perfused vascularized fasciocutaneous flaps. The method comprises a small, low-energy optical transcutaneous oxygen sensor applied on the flap's skin paddle as well as oxygen sensing devices placed into the tubing. An intermittent perfusion setting was designed to study the response time and accuracy of this technology over a total of 54 perfusion cycles. We further evaluated correlation between the continuous oxygen measurements and gold-standard perfusion viability metrics such as vascular resistance, with good agreement suggesting potential to monitor graft viability at high frequency, opening the possibility to employ feedback control algorithms in the future. This proof-of-concept study opens a range of research and clinical applications in reconstructive surgery and transplantation at a time when perfusion machines undergo rapid clinical adoption with potential to improve outcomes across a variety of surgical procedures and dramatically increase access to transplant medicine.

Microneedles-Based Theranostic Platform: From the Past to the Future

Fully integrated theranostic devices are highly esteemed in clinical applications, offering immense potential in real-time disease monitoring and personalized care. Microneedles (MNs), as innovative and wearable devices, boast important advantages in biosensing and therapy, thus holding significant promise in the advancement of diagnostic and therapeutic platforms. Encouragingly, advancements in electrochemical sensing technology, micronano fabrication, and biocompatible materials are propelling momentum for MNs-based closed-loop systems, enhancing detection capabilities, biocompatibility, and cost-effectiveness. Moreover, the notable progress in integrating MN chips with other biochips signifies a frontier for growth. Successful clinical trials in target molecule monitoring and drug delivery domains herald excellent clinical translational prospects for the aforementioned theranostic platform. Finally, we delineate both challenges and opportunities in the development of integrated diagnostic and therapeutic MN systems, including continuous monitoring, intelligent control algorithms, safety, and regulatory considerations.

Integrating microneedles and sensing strategies for diagnostic and monitoring applications: The state of the art

Microneedles (MNs) offer minimally-invasive access to interstitial fluid (ISF) - a potent alternative to blood in terms of monitoring physiological analytes. This property is particularly advantageous for the painless detection and monitoring of drugs and biomolecules. However, the complexity of the skin environment, coupled with the inherent nature of the analytes being detected and the inherent physical properties of MNs, pose challenges when conducting physiological monitoring using this fluid. In this review, we discuss different sensing mechanisms and highlight advancements in monitoring different targets, with a particular focus on drug monitoring. We further list the current challenges facing the field and conclude by discussing aspects of MN design which serve to enhance their performance when monitoring different classes of analytes.

Demonstrating the Analytical Potential of a Wearable Microneedle-Based Device for Intradermal CO2 Detection

Monitoring of carbon dioxide (CO2) body levels is crucial under several clinical conditions (e.g., human intensive care and acid-base disorders). To date, painful and risky arterial blood punctures have been performed to obtain discrete CO2 measurements needed in clinical setups. Although noninvasive alternatives have been proposed to assess CO2, these are currently limited to benchtop devices, requiring trained personnel, being tedious, and providing punctual information, among other disadvantages. To the best of our knowledge, the literature and market lack a wearable device for real-time, on-body monitoring of CO2. Accordingly, we have developed a microneedle (MN)-based sensor array, labeled as CO2-MN, comprising a combination of potentiometric pH- and carbonate (CO32-)-selective electrodes together with the reference electrode. The CO2-MN is built on an epidermal patch that allows it to reach the stratum corneum of the skin, measuring pH and CO32- concentrations directly into the interstitial fluid (ISF). The levels for the pH-CO32- tandem are then used to estimate the PCO2 in the ISF. Assessing the response of each individual MN, we found adequate response time (t95 < 5s), sensitivity (50.4 and -24.6 mV dec-1 for pH and CO32-, respectively), and stability (1.6 mV h-1 for pH and 2.1 mV h-1 for CO32-). We validated the intradermal measurements of CO2 at the ex vivo level, using pieces of rat skin, and then, with in vivo assays in anesthetized rats, showing the suitability of the CO2-MN wearable device for on-body measurements. A good correlation between ISF and blood CO2 concentrations was observed, demonstrating the high potential of the developed MN sensing technology as an alternative to blood-based analysis in the near future. Moreover, these results open new horizons in the noninvasive, real-time monitoring of CO2 as well as other clinically relevant gases.

Performance gain and electro-mechanical design optimization of microneedles for wearable sensor systems

Minimally invasive microneedle (MN) is an emerging technology platform for wearable and implantable diagnostics and therapeutics systems. These short MNs offer pain-free insertion and simple operation. Among the MN technologies proposed to enhance interstitial fluid (ISF) extraction, porous and swellable (P-S) hydrogels absorb analyte molecules across the entire lateral surface. Currently, the design, development, and optimization of the MNs rely on empirical, iterative approaches. Based on theory of fluid flow and analyte diffusion through geometrically complex biomimetic systems, here we derive a generalized physics-guided model for P-S MN sensors. The framework (a) quantifies MN extracting efficiency [Formula: see text] in terms of its geometric and physical properties, and (b) suggests strategies to optimize sensor response while satisfying the mechanical constraints related to various skin-types (e.g., mouse, pig, humans, etc.). Our results show that, despite the differences in geometry and composition, P-S MNs obey a universal scaling response, [Formula: see text] with [Formula: see text] being MN length, diffusivity, and radius, respectively, and [Formula: see text], [Formula: see text] and [Formula: see text] are the ratio between approximate vs. exact analytical solutions, the effective biofluid transfer coefficient between dermis and skin, and the exponent for the power-law approximation, respectively. These parameters quantify the biomolecule transfer through the dermis-to-MN interface at different scaling limits. P-S MNs outperform hollow MNs by a 2-6x enhancement factor; however, the buckling-limit of insertion defines the maximized functionality of the sensor. Our model, validated against experimental results and numerical simulations, offers a predictive design framework to significantly reduce the optimization time for P-S MN-based sensor platforms.

Development and in-vivo validation of a portable phosphorescence lifetime-based fiber-optic oxygen sensor

Oxygenation is a crucial indicator of tissue viability and function. Oxygen tension ([Formula: see text]), i.e. the amount of molecular oxygen present in the tissue is a direct result of supply (perfusion) and consumption. Thus, measurement of [Formula: see text] is an effective method to monitor tissue viability. However, tissue oximetry sensors commonly used in clinical practice instead rely on measuring oxygen saturation ([Formula: see text]), largely due to the lack of reliable, affordable [Formula: see text] sensing solutions. To address this issue we present a proof-of-concept design and validation of a low-cost, lifetime-based oxygen sensing fiber. The sensor consists of readily-available off-the shelf components such as a microcontroller, a light-emitting diode (LED), an avalanche photodiode (APD), a temperature sensor, as well as a bright in-house developed porphyrin molecule. The device was calibrated using a benchtop setup and evaluated in three in vivo animal models. Our findings show that the new device design in combination with the bright porphyrin has the potential to be a useful and accurate tool for measuring [Formula: see text] in tissue, while also highlighting some of the limitations and challenges of oxygen measurements in this context.

Calculation of Tissue Oxygenation via an Inverse Boundary Problem for Transcutaneous Oxygenation Wearable Applications

In this article, we present a toolset to fully leverage a previously developed transcutaneous oxygenation monitor (TCOM) wearable technology to accurately measure skin oxygenation values. We describe numerical models and experimental characterization techniques that allow for the extraction of precise tissue oxygenation measurements. The numerical model is based on an inverse boundary problem of the parabolic equation with Dirichlet boundary conditions. To validate this model and characterize the diffusion of oxygen through the oxygen sensing materials, we designed a series of control/calibration experiments modeled after the device's clinical application using oxygenation values in the physiological range expected for healthy tissue. Our results demonstrate that it is possible to obtain accurate tissue pO2 measurements without the need for long equilibration times with a small wearable device.

Gold Nanocluster-Based Fluorescent Microneedle Platform toward Visual Detection of ATP

Adenosine triphosphate (ATP) participates in the regulation of most biological processes, and the ATP level is closely associated with many diseases. However, it still remains challenging to achieve on-site monitoring of ATP in an equipment-free and efficient way. Microneedles, a minimally invasive technology that can extract biomarkers from liquid biopsies, have recently emerged as useful tools for early diagnosis of a broad range of diseases. In this work, we developed hydrogel microneedles that are loaded with ATP-specific dual-emitting gold nanoclusters (RhE-AuNCs) for fast sampling and on-needle detection of ATP. These RhE-AuNCs were photo-crosslinked to the hydrogel matrix to form a fluorescent microneedle patch. Based on the ATP-induced Förster resonance energy transfer in RhE-AuNCs, a highly selective, sensitive, and reliable ATP sensor was developed. Moreover, simultaneous capture and visual detection of ATP was achieved by the AuNC-loaded microneedle sensing platform, which exhibits promising sensing performance. This work provides a new approach to design a point-of-care ATP sensing platform, which also holds great potential for the further development of microneedle-based analytical devices.

Oxygen-releasing biomaterials for regenerative medicine

Oxygen is critical to the survival, function and fate of mammalian cells. Oxygen tension controls cellular behavior through metabolic programming, which in turn controls tissue regeneration. A variety of biomaterials with oxygen-releasing capabilities have been developed to provide oxygen supply to ensure cell survival and differentiation for therapeutic efficacy, and to prevent hypoxia-induced tissue damage and cell death. However, controlling the oxygen release with spatial and temporal accuracy is still technically challenging. In this review, we provide a comprehensive overview of organic and inorganic materials available as oxygen sources, including hemoglobin-based oxygen carriers (HBOCs), perfluorocarbons (PFCs), photosynthetic organisms, solid and liquid peroxides, and some of the latest materials such as metal-organic frameworks (MOFs). Additionally, we introduce the corresponding carrier materials and the oxygen production methods and present state-of-the-art applications and breakthroughs of oxygen-releasing materials. Furthermore, we discuss the current challenges and the future perspectives in the field. After reviewing the recent progress and the future perspectives of oxygen-releasing materials, we predict that smart material systems that combine precise detection of oxygenation and adaptive control of oxygen delivery will be the future trend for oxygen-releasing materials in regenerative medicine.