Wearable Sensor Platform Research Articles

Nerve-Agent Selective Chemiresistors Fabricated by Oxime Decorated Polypyrrole Layer on Cellulose Paper

In continuous research of detecting highly toxic chemical warfare agents to ensure preparedness for the future battlefield, flexible and wearable sensor platforms with high sensitivity are still demanding. Herein we demonstrate a facile fabrication of polypyrrole-based chemiresistors on cellulose paper for the detection of nerve gas simulants. In order to optimize electrical properties of sensor platform, conducting polymer made of polypyrrole were first synthesized on flexible cellulose paper and interdigitated electrodes were formed thereon. Following confirmation of polypyrrole and/or oxime moiety through FT-IR analyses, electrical characteristics were measured in the various ratio of monomers between simple pyrrole and oxime-modified one. Typically for the optimized chemiresistor(2:8 molar ratio of simple pyrrole and oxime-modified one), eleven species of chemical warfare agents were examined and enhanced conductivity(10<sup>4</sup>~10<sup>5</sup> order) was observed for three simulants(diethyl cyanophosphonate, diisopropyl fluorophosphonate and diethyl chlorophosphonate), which was mainly attributed to intermolecular hydrogen bonding, while no significant responses was recorded against sixteen common volatile organic chemicals.

Superlative and Selective Sensing of Serotonin in Undiluted Human Serum Using Novel Polystyrene Sulfonate Conductive Polymer.

In the past 5 years, real-time health monitoring has become ubiquitous with the development of watches and rings that can measure and report on the physiological state. As an extension, real-time biomarker sensors, such as the continuous glucose monitor, are becoming popular for both health and performance monitoring. However, few real-time sensors for biomarkers have been made commercially available; this is primarily due to problems with cost, stability, sensitivity, selectivity, and reproducibility of biosensors. Therefore, simple, robust sensors are needed to expand the number of analytes that can be detected in emerging and existing wearable platforms. To address this need, we present a simple but novel sensing material. In short, we have modified the already popular PEDOT/PSS conductive polymer by completely removing the PEDOT component and thus have fabricated a polystyrene sulfonate (PSS) sensor electrodeposited on a glassy carbon (GC) base (GC-PSS). We demonstrate that coupling the GC-PSS sensor with differential pulse voltammetry creates a sensor capable of the selective and sensitive detection of serotonin. Notably, the GC-PSS sensor has a sensitivity of 179 μA μM-1 cm-2 which is 36x that of unmodified GC and an interferent-free detection limit of 10 nM, which is below the concentrations typically found in saliva, urine, and plasma. Notably, the redox potential of serotonin interfacing with the GC-PSS sensor is at -0.188 V versus Ag/AgCl, which is significantly distanced from peaks produced by common interferants found in biofluids, including serum. Therefore, this paper reports a novel, simple sensor and polymeric interface that is compatible with emerging wearable sensor platforms.

Flexible and transparent humidity sensors based on hyperbranched poly(ionic liquid)s for wearable sensing

The rapid development of wearable electronics is driving the exploration of flexible and transparent humidity sensors. However, the limited humidity response and mechanical flexibility of sensitive materials hinder the normal operation of the device. In this research, flexible humidity sensors with a fast response time (1 s) were prepared using transparent imidazolium-based hyperbranched poly(ionic liquid)s (HPIL). The sensor performance was improved by regulating the counter anions with different hydrophobicity, such as trifluoromethanesulfonimide ion (TFSI-). The HPIL-TFSI sensor featured an improved response under low humidity condition (6%∼33% RH) with good linearity, excellent bending humidity response, mechanical stability, and long-term stability over a wide humidity range from 6% to 98% RH. Moreover, accurate sensing was achieved for respiratory monitoring, non-contact sensing, and detecting moisture on patched skin. The HPIL-TFSI sensor paves the way for the production of high-performance wearable sensor platforms.

Smart Wearable Nanopaper Patch for Continuous Multiplexed Optical Monitoring of Sweat Parameters.

Notwithstanding the substantial progress in optical wearable sensing devices, developing wearable optical sensors for simultaneous, real-time, and continuous monitoring of multiple biomarkers is still an important, yet unmet, demand. Aiming to address this need, we introduced for the first time a smart wearable optical sensor (SWOS) platform combining a multiplexed sweat sensor sticker with its IoT-enabled readout module. We employed our SWOS system for on-body continuous, real-time, and simultaneous fluorimetric monitoring of sweat volume (physical parameter) and pH (chemical marker). Herein, a variation in moisture (5-45 μL) or pH (4.0-7.0) causes a color/fluorescence change in the copper chloride/fluorescein immobilized within a transparent chitin nanopaper (ChNP) in a selective and reversible manner. Human experiments conducted on athletic volunteers during exercise confirm that our developed SWOS platform can be efficiently exploited for smart perspiration analysis toward personalized health monitoring. Moreover, our system can be further extended for the continuous and real-time multiplexed monitoring of various biomarkers (metabolites, proteins, or drugs) of sweat or other biofluids (for example, analyzing exhaled breath by integrating onto a facemask).

Design of an energy-efficient IOT device-assisted wearable sensor platform for healthcare data management

Advances in health-related behaviors, technical breakthroughs, and the spread of healthy living activities have expanded personal health evaluation on a broad scale. In medical applications, networks, data, and communication systems are extensively utilized and further expanding. Real-time applications for remote health monitoring generate massive amounts of data in a short period. Internet of Things (IoT) and cloud systems, resulting in unprocessed and inadequate data for end-users. Since cloud technology is a dispersed intermediary layer between the edge network and the cloud infrastructure, the delay is significantly decreased, and reliable communications can be established using cloud computing on an IoT-enabled healthcare device. This study presents an Energy Efficient Healthcare Data Management Method (EE-HDMM), which enhances health monitoring using an IoT-assisted wearable sensor infrastructure. The difficulty of constrained sources and the energy consumption is minimized by proposing the optimum energy resource allocation method. Wearable sensor technology supported by cloud computing is the ideal and dependable platform for powerful life-critical systems that are unlikely to have communication delays. Compared to conventional techniques, the suggested EE-HDMM has a high precision rate of 97%, a sensitivity rate of 94%, and a system efficiency of 96%.

A wearable device-enabled therapeutic approach to improve joint attention in autism spectrum disorder: a prospective pilot study.

It has been previously proposed that interventions aimed at integrating and co-activating music processing and motor control systems could have therapeutic potential for priming social skill development in children with autism spectrum disorder (ASD). In this study, we assessed this hypothesis through a wearable sensor platform called Ambulosono ("Ambulo"-walk; "sono"-sound) in which pleasurable children's musical stimuli are contingently linked to effortful motor action (locomotor step size), thus creating a motivational state proposed to be conducive to joint attention (JA) operation. Five participants were recruited from a community-based partner and were assessed by scoring responses following therapist-directed bids for JA. Multiple assessment sessions through a repeated time-series design were conducted to determine baseline and post-intervention scores. The intervention session consisted of approximately 15min of Ambulosono exposure. Baseline and post-intervention data were aggregated and analyzed using a linear mixed-effect model. The wearable sensor and wireless headphones of the Ambulosono system were tolerated by the participants, and there were no adverse effects associated with the use of the device. We found an increase in the average responses to bids for JA during the Ambulosono intervention phase compared to baseline across participants. This increase did not appear to result from enhanced general arousal. Our pilot data support feasibility and further testing of Ambulosono as a therapeutic aid for integration into community-based ASD programs to augment shared child-therapist social interactions.

Recent Advances in Multiplexed Wearable Sensor Platforms for Real-Time Monitoring Lifetime Stress: A Review

Researchers are interested in measuring mental stress because it is linked to a variety of diseases. Real-time stress monitoring via wearable sensor systems can aid in the prevention of stress-related diseases by allowing stressors to be controlled immediately. Physical tests, such as heart rate or skin conductance, have recently been used to assess stress; however, these methods are easily influenced by daily life activities. As a result, for more accurate stress monitoring, validations requiring two or more stress-related biomarkers are demanded. In this review, the combinations of various types of sensors (hereafter referred to as multiplexed sensor systems) that can be applied to monitor stress are discussed, referring to physical and chemical biomarkers. Multiplexed sensor systems are classified as multiplexed physical sensors, multiplexed physical-chemical sensors, and multiplexed chemical sensors, with the effect of measuring multiple biomarkers and the ability to measure stress being the most important. The working principles of multiplexed sensor systems are subdivided, with advantages in measuring multiple biomarkers. Furthermore, stress-related chemical biomarkers are still limited to cortisol; however, we believe that by developing multiplexed sensor systems, it will be possible to explore new stress-related chemical biomarkers by confirming their correlations to cortisol. As a result, the potential for further development of multiplexed sensor systems, such as the development of wearable electronics for mental health management, is highlighted in this review.

A Comparison of Inertial Measurement Units and Overnight Videography to Assess Sleep Biomechanics.

The assessment of sleep biomechanics (comprising movement and position during sleep) is of interest in a wide variety of clinical and research settings. However, there is no standard method by which sleep biomechanics are measured. This study aimed to (1) compare the intra- and inter-rater reliability of the current clinical standard, manually coded overnight videography, and (2) compare sleep position recorded using overnight videography to sleep position recorded using the XSENS DOT wearable sensor platform. Ten healthy adult volunteers slept for one night with XSENS DOT units in situ (on their chest, pelvis, and left and right thighs), with three infrared video cameras recording concurrently. Ten clips per participant were edited from the video. Sleeping position in each clip was coded by six experienced allied health professionals using the novel Body Orientation During Sleep (BODS) Framework, comprising 12 sections in a 360-degree circle. Intra-rater reliability was assessed by calculating the differences between the BODS ratings from repeated clips and the percentage who were rated with a maximum of one section of the XSENS DOT value; the same methodology was used to establish the level of agreement between the XSENS DOT and allied health professional ratings of overnight videography. Bennett's S-Score was used to assess inter-rater reliability. High intra-rater reliability (90% of ratings with maximum difference of one section) and moderate inter-rater reliability (Bennett's S-Score 0.466 to 0.632) were demonstrated in the BODS ratings. The raters demonstrated high levels of agreement overall with the XSENS DOT platform, with 90% of ratings from allied health raters being within the range of at least 1 section of the BODS (as compared to the corresponding XSENS DOT produced rating). The current clinical standard for assessing sleep biomechanics, manually rated overnight videography (as rated using the BODS Framework) demonstrated acceptable intra- and inter-rater reliability. Further, the XSENS DOT platform demonstrated satisfactory levels of agreement as compared to the current clinical standard, providing confidence for its use in future studies of sleep biomechanics.

Fully Transparent and Highly Sensitive pH Sensor Based on an a-IGZO Thin-Film Transistor with Coplanar Dual-Gate on Flexible Polyimide Substrates

In this paper, we propose a fully transparent and flexible high-performance pH sensor based on an amorphous indium gallium zinc oxide (a-IGZO) thin-film transistor (TFT) transducer with a coplanar dual-gate structure on polyimide substrates. The proposed pH sensor system features a transducer unit consisting of a floating gate (FG), sensing gate (SG), and control gate (CG) on a polyimide (PI), and an extended gate (EG) sensing unit on a separate glass substrate. We designed a capacitive coupling between (SG) and (CG) through the FG of an a-IGZO TFT transducer to contribute to sensitivity amplification. The capacitance ratio (CSG/CCG) increases linearly with the area ratio; therefore, the amplification ratio of the pH sensitivity was easily controlled using the area ratio of SG/CG. The proposed sensor system improved the pH sensitivity by up to 359.28 mV/pH (CSG/CCG = 6.16) at room temperature (300 K), which is significantly larger than the Nernstian limit of 59.14 mV/pH. In addition, the non-ideal behavior, including hysteresis and drift effects, was evaluated to ensure stability and reliability. The amplification of sensitivity based on capacitive coupling was much higher than the increase in the hysteresis voltage and drift rate. Furthermore, we verified the flexibility of the a-IGZO coplanar dual-gate TFT transducer through a bending test, and the electrical properties were maintained without mechanical damage, even after repeated bending. Therefore, the proposed fully transparent and highly sensitive a-IGZO coplanar dual-gate TFT-based pH sensor could be a promising wearable and portable high-performance chemical sensor platform.

Wearable sensor platforms for real-time monitoring and early warning of metabolic disorders in humans.

Nowadays, the prevalence of metabolic syndromes (MSs) has attracted increasing concerns as it is closely related to overweight and obesity, physical inactivity and overconsumption of energy, making the diagnosis and real-time monitoring of the physiological range essential and necessary for avoiding illness due to defects in the human body such as higher risk of cardiovascular disease, diabetes, stroke and diseases related to artery walls. However, the current sensing techniques are inconvenient and do not continuously monitor the health status of humans. Alternatively, the use of recent wearable device technology is a preferable method for the prevention of these diseases. This can enable the monitoring of the health status of humans in different health domains, including environment and structure. The use wearable devices with the purpose of facilitating rapid treatment and real-time monitoring can decrease the prevalence of MS and long-time monitor the health status of patients. This review highlights the recent advances in wearable sensors toward continuous monitoring of blood pressure and blood glucose, and further details the monitoring of abnormal obesity, triglycerides and HDL. We also discuss the challenges and future prospective of monitoring MS in humans.

Bioadhesive Gauze Embedded with Chitosan-Butein Bioconjugate: A Redox-Active pH Sensor Platform

With the ever-growing global wound care market, demand for robust redox-active healthcare material is obvious for the construction of wearable sensor platforms. Surface reactive functional group-rich material like chitosan holds huge potential for electrochemical biosensor application. Herein, a metal-free redox-active chitosan-butein (CSB) bioconjugate is processed into epidermal bioadhesive electrode material useful for pH sensors promising toward wound site analysis. A two-electrode system devised for conducting carbon-reinforced silver chloride paste and CSB-modified carbon/silver chloride matrix was used as a reference and working electrodes, respectively. Dimensions of working and reference electrodes (4 mm) were designed by 2D cutter plotter-assisted stenciling. The cross-sectional topology of the constructed adhesive CSB-sensor platform exhibits an average surface thickness of 183 ± 2 μm. Cyclic voltammetric analysis revealed the inherent 2e-/2H+ transfer attributed to the catechol OH groups of graft polymerized CSB modified on adhesive gauze. As-fabricated modified electrode substrates exhibit distinguishable potential differences with respect to electrolytes of varied pH (between 5 to 9), promising for wound site analysis.

Graphene woven fabric-polydimethylsiloxane piezoresistive films for smart multi-stimuli responses

The outstanding properties of graphene, including its electromechanical property, could be engineered for wearable electronic sensor platforms. The tubular graphene weaved into a mesh or graphene woven fabrics (GWF) has been reported as one of the most sensitive materials for deformation detection, as well as a promising temperature sensor. Herein, we present the performance of our developed flexible, stretchable, and multiple sensitive sensors fabricated from GWF embedded in polydimethylsiloxane (PDMS) film substrate. The GWF/PDMS sensor shows a pressure sensitivity of 0.0142 kPa−1 in a wide linearity range of 0–20 kPa, an outstanding Gauge factor (GF) of 582 at a strain of 6.2 %, and a very high positive sensitivity of 0.0238 °C−1 in the temperature range of 25–80 °C. A practical application as a high sensitivity air pressure sensor able to measure low pressures (in the range of Pa to kPa) was also demonstrated. This sensor platform having desirable performance characteristics is an excellent candidate for wearable devices in the healthcare sector.

Cutting-edge Piezo/Triboelectric-based Wearable Physical Sensor Platforms

Cutting-edge Piezo/Triboelectric-based Wearable Physical Sensor Platforms

Integrated Aptasensor Array for Sweat Drug Analysis.

Drug abuse is seriously endangering human health and jeopardizing society. There is an urgent need for rapid, sensitive, portable, and easy-to-operate methods for the daily detection of drugs in biological matrices. However, current drug detection methods based on chromatography, spectroscopy, immunosorbent assays, etc. are limited by the requirements of high logistical instruments and laboratory. Herein, we proposed a wearable electrochemical aptasensor with high sensitivity and specificity for the direct capture and rapid detection of multiple drugs in sweat. The single aptamer and dual aptamers with different base compositions were designed to compose the aptasensor array. Molecular docking simulations demonstrated different binding affinities between bioamines and aptamers. The developed aptasensor array is shown to be sufficient to generate distinct electrochemical fingerprints for different psychoactive drugs and interfering substances by extracting variable features from electrochemical signals. Sixteen analytes in the same concentration or gradient concentrations were identified with 100% accuracy. In addition, the wearable sensor platform was demonstrated to discriminate various drugs with similar chemical structures in artificial sweat and human sweat samples. The sensor array not only provided a new rapid method for the detection of drugs but also served as a reference for developing wearable sensors for onsite and daily testing of human biochemical information.

Preparation and Characterization of PEDOT:PSS/TiO2 Micro/Nanofiber-Based Gas Sensors.

In this study, we employed electrospinning technology and in situ polymerization to prepare wearable and highly sensitive PVP/PEDOT:PSS/TiO2 micro/nanofiber gas sensors. PEDOT, PEDOT:PSS, and TiO2 were prepared via in situ polymerization and tested for characteristic peaks using energy-dispersive X-ray spectroscopy (EDS) and Fourier transform infrared spectroscopy (FT-IR), then characterized using a scanning electron microscope (SEM), a four-point probe resistance measurement, and a gas sensor test system. The gas sensitivity was 3.46–12.06% when ethanol with a concentration between 12.5 ppm and 6250 ppm was measured; 625 ppm of ethanol was used in the gas sensitivity measurements for the PEDOT/composite conductive woven fabrics, PVP/PEDOT:PSS nanofiber membranes, and PVP/PEDOT:PSS/TiO2 micro/nanofiber gas sensors. The latter exhibited the highest gas sensitivity, which was 5.52% and 2.35% greater than that of the PEDOT/composite conductive woven fabrics and PVP/PEDOT:PSS nanofiber membranes, respectively. In addition, the influence of relative humidity on the performance of the PVP/PEDOT:PSS/TiO2 micro/nanofiber gas sensors was examined. The electrical sensitivity decreased with a decrease in ethanol concentration. The gas sensitivity exhibited a linear relationship with relative humidity lower than 75%; however, when the relative humidity was higher than 75%, the gas sensitivity showed a highly non-linear correlation. The test results indicated that the PVP/PEDOT:PSS/TiO2 micro/nanofiber gas sensors were flexible and highly sensitive to gas, qualifying them for use as a wearable gas sensor platform at room temperature. The proposed gas sensors demonstrated vital functions and an innovative design for the development of a smart wearable device.

Wearable electrochemical microneedle sensing platform for real-time continuous interstitial fluid monitoring of apomorphine: Toward Parkinson management

Parkinson’s disease (PD) is a progressive neurodegenerative disorder, impacting millions of people across the globe. For its management, pro-neurotransmitters or agonists are commonly being prescribed, which help to mitigate the symptoms. However, the progressiveness of PD and narrowing down of the drug therapeutic window eventually led to its ineffective management. Therefore, the requirement of continuous monitoring of administered drugs is of utmost need. In view of this, here, we demonstrate a microneedle-based wearable electrochemical sensor platform for the continuous monitoring of apomorphine (APO), a widely used therapeutic drug for Parkinson’s management. The APO sensor relies on a metallized carbon-paste packed hollow microneedle, operated using the square wave voltammetry (SWV) and chronoamperometry (CA) based transduction modes. Under the optimal conditions, the microneedle sensor offers sensitive detection of micromolar APO concentrations in artificial interstitial fluid (ISF) through the monitoring of the two oxidation peaks of the APO catechol and tertiary amine moieties (at 0.1 V and 0.7 V, respectively). The microneedle sensor exhibited a detection limit of 0.6 and 0.75 μM with the transduction techniques SWV and CA, respectively, and good operational stability as well as anti-biofouling protection in artificial-ISF medium. The specificity has been tested for the developed sensor in the presence of potential interfering molecules, where the developed sensor showed the selectivity towards APO. The attractive analytical performance demonstrated in the skin mimic environment makes the new wearable APO microneedle sensor a powerful candidate for continuous APO detection in PD management.

High Energy Density Li-Ion Capacitor for Use in Wearable Health Sensor Platforms

Lithium ion capacitors with their high energy density, high power density and good cycle life can offer potential standalone energy storage solution when combined with renewable energy harvesting technologies to power wearable health sensor or Internet of things platform. In this study, we demonstrate fabrication of 13 Wh/L packaged Li-ion capacitor 2016 coincell prototype that can be charged using harvested solar energy from indoor lighting to power wearable health sensor platforms. The capacitor with its extremely low self-discharge rate, high load carrying capability and cycle life can provide significant advantages relative to rechargeable batteries of similar form factor. The study provides a comparison of performance of Li-ion rechargeable battery against the fabricated capacitor to continuously power wearable heath sensor platform.

Real-World Evidence for a Smartwatch-Based Parkinson’s Motor Assessment App for Patients Undergoing Therapy Changes

Introduction: Parkinson’s disease (PD) is poorly quantified by patients outside the clinic, and paper diaries have problems with subjective descriptions and bias. Wearable sensor platforms; however, can accurately quantify symptoms such as tremor, dyskinesia, and bradykinesia. Commercially available smartwatches are equipped with accelerometers and gyroscopes that can measure motion for objective evaluation. We sought to evaluate the clinical utility of a prescription smartwatch-based monitoring system for PD utilizing periodic task-based motor assessment. Methods: Sixteen patients with PD used a smartphone- and smartwatch-based monitoring system to objectively assess motor symptoms for 1 week prior to instituting a doctor recommended change in therapy and for 4 weeks after the change. After 5 weeks the participants returned to the clinic to discuss their results with their doctor, who made therapy recommendations based on the reports and his clinical judgment. Symptom scores were synchronized with the medication diary and the temporal effects of therapy on weekly and hourly timescales were calculated. Results: Thirteen participants successfully completed the study and averaged 4.9 assessments per day for 3 days per week during the study. The doctor instructed 8 participants to continue their new regimens and 5 to revert to their previous regimens. The smartwatch-based assessments successfully captured intraday fluctuations and short- and long-term responses to therapies, including detecting significant improvements (p < 0.05) in at least one symptom in 7 participants. Conclusions: The smartwatch-based app successfully captured temporal trends in symptom scores following application of new therapy on hourly, daily, and weekly timescales. These results suggest that validated smartwatch-based PD monitoring can provide clinically relevant information and may reduce the need for traditional office visits for therapy adjustment.

High-performance textile piezoelectric pressure sensor with novel structural hierarchy based on ZnO nanorods array for wearable application

With the increasing demand for smart wearable clothing, the textile piezoelectric pressure sensor (T-PEPS) that can harvest mechanical energy directly has attracted significant attention. However, the current challenge of T-PEPS lies in remaining the outstanding output performance without compromising its wearing comfort. Here, a novel structural hierarchy T-PEPS based on the single-crystalline ZnO nanorods are designed. The T-PEPS is constructed with three layers mode consisting of a polyvinylidene fluoride (PVDF) membrane, the top and bottom layers of conductive rGO polyester (PET) fabrics with self-orientation ZnO nanorods. As a result, the as-fabricated T-PEPS shows low detection limit up to 8.71 Pa, high output voltage to 11.47 V and superior mechanical stability. The sensitivity of the sensor is 0.62 V·kPa−1 in the pressure range of 0–2.25 kPa. Meanwhile, the T-PEPS is employed to detect human movements such as bending/relaxation motion of the wrist, bending/stretching motion of each finger. It is demonstrated that the T-PEPS can be up-scaled to promote the application of wearable sensor platforms and self-powered devices.

Finger Gesture Tracking for Interactive Applications

This paper presents FinGTrAC, a system that shows the feasibility of fine grained finger gesture tracking using low intrusive wearable sensor platform (smart-ring worn on the index finger and a smart-watch worn on the wrist). The key contribution is in scaling up gesture recognition to hundreds of gestures while using only a sparse wearable sensor set where prior works have been able to only detect tens of hand gestures. Such sparse sensors are convenient to wear but cannot track all fingers and hence provide under-constrained information. However application specific context can fill the gap in sparse sensing and improve the accuracy of gesture classification. Rich context exists in a number of applications such as user-interfaces, sports analytics, medical rehabilitation, sign language translation etc. This paper shows the feasibility of exploiting such context in an application of American Sign Language (ASL) translation. Noisy sensor data, variations in gesture performance across users and the inability to capture data from all fingers introduce non-trivial challenges. FinGTrAC exploits a number of opportunities in data preprocessing, filtering, pattern matching, context of an ASL sentence to systematically fuse the available sensory information into a Bayesian filtering framework. Culminating into the design of a Hidden Markov Model, a Viterbi decoding scheme is designed to detect finger gestures and the corresponding ASL sentences in real time. Extensive evaluation on 10 users shows a recognition accuracy of 94.2% for 100 most frequently used ASL finger gestures over different sentences. When the size of the dictionary is extended to 200 words, the accuracy is degrades gracefully to 90% thus indicating the robustness and scalability of the multi-stage optimization framework.