Dynamic Response Study of Piezoresistive Ti3C2-MXene Sensor for Structural Impacts.

MXenes are a new family of two-dimensional (2D) nanomaterials. They are inorganic compounds of metal carbides/nitrides/carbonitrides. Titanium carbide MXene (Ti3C2-MXene) was the first 2D nanomaterial reported in the MXene family in 2011. Owing to the good physical properties of Ti3C2-MXenes (e.g., conductivity, hydrophilicity, film-forming ability, elasticity) various applications in wearable sensors, energy harvesters, supercapacitors, electronic devices, etc., have been demonstrated. This paper presents the development of a piezoresistive Ti3C2-MXene sensor followed by experimental investigations of its dynamic response behavior when subjected to structural impacts. For the experimental investigations, an inclined ball impact test setup is constructed. Stainless steel balls of different masses and radii are used to apply repeatable impacts on a vertical cantilever plate. The Ti3C2-MXene sensor is attached to this cantilever plate along with a commercial piezoceramic sensor, and their responses for the structural impacts are compared. It is observed from the experiments that the average response times of the Ti3C2-MXene sensor and piezoceramic sensor are 1.28±0.24µs and 31.19±24.61µs, respectively. The fast response time of the Ti3C2-MXene sensor makes it a promising candidate for monitoring structural impacts.

Flexible strain sensor with high sensitivity, fast response, and good sensing range for wearable applications.

Flexible strain sensors are emerging rapidly and overcoming the drawbacks of traditional strain sensors. However, many flexible sensors failed to balance the sensitivity, response time, and the desired sensing range. This work proposes a novel and cost-effective strain sensor which simultaneously achieved high sensitivity, fast response, and a good sensing range. It illustrates a prototype strain sensor realized with a nanocomposite constituting reduced graphene oxide and palladium as the primary sensing elements. These sensors were fabricated with manual screen-printing technology. The sensor exhibited an outstanding performance for the different strains ranging from 0.1% to 45%. As a result, a substantially high gauge factor around 1523 at a strain of as high as 45% and a rapid response time of 47 ms was obtained. This work demonstrated potential applications like real-time monitoring of pulse and respiration, and other physical movement detection, which become crucial parameters to be measured continuously during the COVID-19 pandemic.

Correction: Dynamic response study of Ti3C2-MXene films to shockwave and impact forces.

[This corrects the article DOI: 10.1039/D0RA04879H.].

Dynamic response study of Ti3C2-MXene films to shockwave and impact forces.

MXenes (Titanium Carbide, Ti3C2-MXene) are two-dimensional nanomaterials that are known for their conductivity, film-forming ability, and elasticity. Though literature reports the possibility of usage of Ti3C2-MXenes for sensor development, the material properties and response need be studied in detail for designing sensors to measure dynamic variables like force, displacement, etc., in a dynamic environment. Ti3C2-MXenes due to their good electro-mechanical properties can be used for manufacturing sensing elements for engineering and biomedical applications. This paper focuses on an investigation of the dynamic response properties of Ti3C2-MXenes subjected to shockwave and impact forces. A supersonic shockwave (Mach number: 1.68, peak overpressure: 234.3 kPa) produced in a shock tube acts as an external force on the Ti3C2-MXene film placed inside the shock tube. In the experiment performed, the response time of the Ti3C2-MXene film sample has been observed to be in the range of few microseconds (∼7 µs) for the high-velocity shock. In a separate experiment, Ti3C2-MXene film samples are subjected to low-velocity impact forces through a ball drop test. The results from the ball drop test provide a response time in the range of few milliseconds (average ∼1.5 ms). In this novel demonstration, the Ti3C2-MXene film sample responds well for both low-velocity mechanical impact as well as high-velocity shockwave impact. Further, the repeatability of the dynamic response of the Ti3C2-MXene film sample is discussed along with its significant piezoresistive behavior. This work provides the basis for sensor development to measure the dynamic phenomena of pressure changes, acoustic emissions, structural vibrations, etc.

Highly sensitive, scalable reduced graphene oxide with palladium nano-composite as strain sensor.

We report a novel strain sensor based on reduced graphene oxide (rGO) with palladium (Pd) nano-composite. The sensor was fabricated on the SS304 stainless-steel substrate using a screen-printing method. Graphene oxide was synthesized using a modified Hummer's method and reduced using a chemical route. Field emission-scanning electron microscope, x-ray diffraction and Raman spectroscopy were used to characterize the as-synthesized nano-composite. The as-fabricated strain sensor was tested for tensile strain using Micro-universal Test Machine and the change in resistance for different strains was recorded. The sensor response was observed to be stable and linear within the applied strain range of 0-3000 microstrains, and an average gauge factor of 42.69 was obtained in this range.

High-range noise immune supersensitive graphene-electrolyte capacitive strain sensor for biomedical applications.

This paper presents development and performance assessment of an innovative and a highly potent graphene-electrolyte capacitive sensor (GECS) based on the supercapacitor model. Although graphene has been widely researched and adapted in supercapacitors as electrode material, this combination has not been applied in sensor technology. A low base capacitance, generally the impeding factor in capacitive sensors, is addressed by incorporating electric double layer capacitance in GECS, and a million-fold increase in base capacitance is achieved. The high base capacitance (∼22.0 µF) promises to solve many inherent issues pertaining to capacitive sensors. GECS is fabricated by using thermally reduced microwave exfoliated graphene oxide material to form interdigitated electrodes coated with solid-state electrolyte which forms the double layer capacitance. The capacitance response of GECS on subjecting to strain is examined and an enormous operating range (∼300 nF) is seen, which is the salient feature of this sensor. The GECS showed an impressive device sensitivity of 11.24 nF kPa-1 and good immunity towards noise i.e. lead capacitance and stray capacitance. Two regimes of operation are identified based on the procedure of device fabrication. The device can be applied to varied applications and one such biomedical application of breath pattern monitoring is demonstrated.

Tailoring Thin-Film Piezoelectrics for Crash Sensing.

Crash sensing and its assessment play a pivotal role in autonomous vehicles for preventing fatal casualties. Existing crash sensors are severely bottlenecked by sluggish response time, rigid mechanical components, and space constraints. Miniaturized sensors embedded with custom-tailored nanomaterials upholds potential to overcome these limitations. In this article, piezoelectric Zinc-Oxide thin film as a crash sensing layer is integrated onto a flexible metal-alloy cantilever. Material characterization studies are conducted to confirm piezoelectric property of sputtered ZnO film. The piezoelectric d 31 coefficient value of ZnO film was 7.2 pm V-1 . The ZnO sensing element is firmly mounted on a scaled car model and used in a crash sensing experimental set-up. A comprehensive theoretical analysis for two different real scenarios (nearly elastic and nearly inelastic collision) of crash events followed by experimental study is discussed. The crash sensor's output exhibits a linear relationship with magnitude of impact forces experienced at crash events. The response time of ZnO crash sensor is 18.2 ms, and it exhibits a sensitivity of 28.7 mV N-1 . The developed crash sensor has potential to replace bulk material sensors owing to its faster response time, high sensitivity, and compactness as the demand for crash sensors in next-generation automobile industries is progressively growing.

Packaged peristaltic micropump for controlled drug delivery application.

Micropump technology has evolved significantly in the last two decades and is finding a variety of applications ranging from µTAS (micro Total Analysis System) to drug delivery. However, the application area of the micropump is limited owing to: simple pumping mechanism, ease of handling, controlled (microliter to milliliter) delivery, continuous delivery, and accuracy in flow rate. Here, the author presents the design, development, characterization, and precision flow controlling of a DC-motor driven peristaltic pump for controlled drug delivery application. All the micropump components were fabricated using the conventional fabrication technique. The volume flow variation of the pump has been characterized for different viscous fluids. The change in volume flow due to change in back pressure has been presented in detail. The fail-safe mode operation of the pump has been tested and leak rate was measured (∼0.14% leak for an inlet pressure of 140 kPa) for different inlet pressures. The precision volume flow of the pump has been achieved by measuring the pinch cam position and load current. The accuracy in the volume flow has been measured after 300 rotations. Finally, the complete system has been integrated with the necessary electronics and an android application has been developed for the self-administration of bolus and basal delivery of insulin.

Experts' perspectives on the role of medical marijuana in oncology: A semistructured interview study.

BACKGROUND: Expansion of medical marijuana (MM) laws in the United States may offer oncology new therapeutic options. However, the scientific evidence for MM remains in infancy. This study qualitatively explored professional opinion around the role of MM in cancer care. METHODS: Semistructured interviews were administered to a sample of individuals with expertise at the interface of MM and oncology nationally. Key informant criteria included an oncologic clinical or research background and any of the following: publications, research, or lectures on cannabinoids or cancer symptoms; involvement in the development of MM dispensaries or legislation; and early adoption of state MM certification procedures. A gold standard, grounded, inductive approach was used to identify underlying themes. RESULTS: Participants (N = 15) were predominantly male, in their sixth decade, working in academic settings. Themes ranged from strong beliefs in marijuana's medical utility to reservations about this notion, with calls for expansion of the scientific evidence base and more stringent MM production standards. All participants cited nausea as an appropriate indication, and 13 of 15 pain. Over one-third believed MM to have a more attractive risk profile than opioids and benzodiazepines. CONCLUSIONS: Expert opinion was divided between convictions in marijuana's medicinal potential and guardedness in this assertion, with no participant refuting MM's utility outright. Emergent themes included that MM ameliorates cancer-related pain and nausea and is safer than certain conventional medications. Participants called for enhanced purity and production standards, and further research on MM's utility.

Peristaltic pump-based low range pressure sensor calibration system.

Peristaltic pumps were normally used to pump liquids in several chemical and biological applications. In the present study, a peristaltic pump was used to pressurize the chamber (positive as well negative pressures) using atmospheric air. In the present paper, we discuss the development and performance study of an automatic pressurization system to calibrate low range (millibar) pressure sensors. The system includes a peristaltic pump, calibrated pressure sensor (master sensor), pressure chamber, and the control electronics. An in-house developed peristaltic pump was used to pressurize the chamber. A closed loop control system has been developed to detect and adjust the pressure leaks in the chamber. The complete system has been integrated into a portable product. The system performance has been studied for a step response and steady state errors. The system is portable, free from oil contaminants, and consumes less power compared to existing pressure calibration systems. The veracity of the system was verified by calibrating an unknown diaphragm based pressure sensor and the results obtained were satisfactory.

Polyvinylidene fluoride film based nasal sensor to monitor human respiration pattern: an initial clinical study.

Design and development of a piezoelectric polyvinylidene fluoride (PVDF) thin film based nasal sensor to monitor human respiration pattern (RP) from each nostril simultaneously is presented in this paper. Thin film based PVDF nasal sensor is designed in a cantilever beam configuration. Two cantilevers are mounted on a spectacle frame in such a way that the air flow from each nostril impinges on this sensor causing bending of the cantilever beams. Voltage signal produced due to air flow induced dynamic piezoelectric effect produce a respective RP. A group of 23 healthy awake human subjects are studied. The RP in terms of respiratory rate (RR) and Respiratory air-flow changes/alterations obtained from the developed PVDF nasal sensor are compared with RP obtained from respiratory inductance plethysmograph (RIP) device. The mean RR of the developed nasal sensor (19.65 ± 4.1) and the RIP (19.57 ± 4.1) are found to be almost same (difference not significant, p > 0.05) with the correlation coefficient 0.96, p < 0.0001. It was observed that any change/alterations in the pattern of RIP is followed by same amount of change/alterations in the pattern of PVDF nasal sensor with k = 0.815 indicating strong agreement between the PVDF nasal sensor and RIP respiratory air-flow pattern. The developed sensor is simple in design, non-invasive, patient friendly and hence shows promising routine clinical usage. The preliminary result shows that this new method can have various applications in respiratory monitoring and diagnosis.

Cerebrospinal fluid pressure changes during the induction phase of anaesthesia.

Cerebrospinal fluid pressure (CSFP) by lumbar puncture, systemic blood pressure (BP) and pulse rate (PR) were measured for 15 minutes during the induction phase of general anaesthesia in seven groups of six healthy female patients each. Intravenous drugs, thiopentopne 5 mg . kg-1, alfathesin 50 microliters . kg-1 and diazepam 0.5 mg . kg-1 given in 10 to 20 seconds caused a fall of CSFP and BP, whereas ketamine 2 mg . kg-1 and a three-minute induction with halothane three per cent, trichloroethylene one per cent, or methoxyflurane 0.75 per cent caused a sharp highly significant but short-lived rise of CSFP. Unlike ketamine, trichlorethylene and methoxyflurane, halothane caused a simultaneous significant fall of BP. To rule out apprehension as the cause of the rise of CSFP with inhalation agents a second challenge was given with similar concentrations of the vapours while patients were asleep. These still produced a sharp and significant rise of CSFP.