Wuyang Yu

Highly Stretchable and Sensitive Unidirectional Strain Sensor via Laser Carbonization

In this paper, we present a simple and low-cost technique for fabricating highly stretchable (up to 100% strain) and sensitive (gauge factor of up to 20 000) strain sensors. Our technique is based on transfer and embedment of carbonized patterns created through selective laser pyrolization of thermoset polymers, such as polyimide, into elastomeric substrates (e.g., PDMS or Ecoflex). Embedded carbonized materials are composed of partially aligned graphene and carbon nanotube (CNT) particles and show a sharp directional anisotropy, which enables the fabrication of extremely robust, highly stretchable, and unidirectional strain sensors. Raman spectrum of pyrolized carbon regions reveal that under optimal laser settings, one can obtain highly porous carbon nano/microparticles with sheet resistances as low as 60 Ω/□. Using this technique, we fabricate an instrumented latex glove capable of measuring finger motion in real-time.

A sewing-enabled stitch-and-transfer method for robust, ultra-stretchable, conductive interconnects

Fabricating highly stretchable and robust electrical interconnects at low-cost remains an unmet challenge in stretchable electronics. Previously reported stretchable interconnects require complicated fabrication processes with resulting devices exhibiting limited stretchability, poor reliability, and large gauge factors. Here, we demonstrate a novel sew-and-transfer method for rapid fabrication of low-cost, highly stretchable interconnects. Using a commercial sewing machine and double-thread stitch with one of the threads being water soluble polyvinyl alcohol (PVA), thin zigzag-pattern metallic wires are sewn into a polymeric film and are subsequently transferred onto a stretchable elastomeric substrate by dissolving PVA in warm water. The resulting structures exhibit extreme stretchability (exceeding 500% strain for a zigzag angle of 18 °) and robustness (capable of withstanding repeated stretch-and-release cycles of 15000 at 110% strain, 50000 at 55% strain, and > 120000 at 30% strain without any noticeable change in resistance even at maximum strain levels). Using this technique, we demonstrate a stretchable inductive strain sensor for monitoring balloon expansion in a Foley urinary catheter capable of detecting the balloon diameter change from 9 mm to 38 mm with an average sensitivity of 4 nH/mm.

A Smart Capsule With GI-Tract-Location-Specific Payload Release

In this paper, we present a smart capsule for location-specific drug release in the gastrointestinal tract. Once activated through a magnetic proximity fuse, the capsule opens up and releases its powdered payload in a location specified by an implanted miniature magnetic marker or an externally worn larger magnet. The capsule (9 mm × 26 mm) comprises of two compartments: one contains a charged capacitor and a reed switch, while the second one houses the drug reservoir capped by a taut nylon thread intertwined with a nichrome wire. The nichrome wire is connected to the capacitor through the reed switch. The capacitor is charged to 2.7 V before ingestion and once within the proximity of the permanent magnet; the reed switch closes, discharging the capacitor through the nichrome wire, melting the nylon thread, detaching the cap, and emptying the drug reservoir.

A low-cost fabrication technique for direct sewing stretchable interconnetions for wearable electronics

Here, we present a facile method for rapid fabrication of low-cost, stretchable electrical interconnections for wearable electronics. Using a commercial sewing machine, thin metallic wires are sewn onto the wearable materials in a double-stitch zigzag pattern, with the second stitch being a water-soluble polyvinyl alcohol (PVA) thread. The stretchable pattern is secured onto a clothing (e.g., a glove) with a stretchable elastomer coating followed by dissolution of the PVA thread in water. The interconnections maintain a constant electrical conductivity for strains up to 50 % and bending cycles over 15000. As a proof of concept implementation, we sewed interconnects and a soft capacitive force sensor onto a latex glove to create a wearable tactile sensor with a linear sensitivity of 96 fF/N.

Diaper-embedded urinary tract infection monitoring system powered by a urine-powered battery

Urinary tract infection (UTI) is one of the most common infections accounting for more than 7 million office visits per year. Although mostly uncomplicated and easily treatable, if identified early, UTI can be a major source of morbidity and mortality in geriatric patients, in particular, those suffering from neurodegenerative diseases, and in infants who have difficulties in communicating symptoms, making early identification of UTIs crucial. In this paper, we present a diaper-embedded, wireless, self-powered, and autonomous UTI monitoring sensor module that allows an effortless early detection of UTIs. The sensor module consists of a paper-based colorimetric nitrite sensor, urine-powered batteries, a boost converter, a low-power sensor interface utilizing pulse width modulation (PWM), and a Bluetooth low energy (BLE) module for wireless transmission. Experimental results show a better detection of nitrite, a surrogate of UTI, than conventional dipstick testing. The sensor module achieves a sensitivity of 1.35 ms/(mg/L) and a detection limit of 4 mg/L for nitrite.

A diaper-embedded disposable nitrite sensor with integrated on-board urine-activated battery for UTI screening

This paper reports a low-cost solution to the early detection of urinary nitrite, a common surrogate for urinary tract infection (UTI). We present a facile method to fabricate a disposable and flexible colorimetric [1] nitrite sensor and its urine-activated power source [2] on a hydrophobic (wax) paper through laser-assisted patterning and lamination. Such device, integrated with interface circuitry and a Bluetooth low energy (BLE) module can be embedded onto a diaper, and transmit semi-quantitative UTI monitoring information in a point-of-care and autonomous fashion. The proposed nitrite sensing platform achieves a sensitivity of 1.35 ms/(mg/L) and a detection limit of 4 mg/L.

A highly stretchable pH sensor array using elastomer-embedded laser carbonized patterns

This paper reports on a facile and low cost method to fabricate highly stretchable potentiometric pH sensor arrays for biomedical and wearable applications. The technique uses laser carbonization of a thermoset polymer followed by transfer and embedment of carbonized nanomaterial onto an elastomeric matrix. The process combines selective laser pyrolization/carbonization with meander interconnect methodology to fabricate stretchable conductive composites with which pH sensors can be realized. The stretchable pH sensors display a sensitivity of -51 mV/pH over the clinically-relevant range of pH 4-10. The sensors remain stable for strains of up to 50 %.

Flexible supercapacitor based on MnO2 coated laser carbonized electrodes

This paper presents a facile, low-cost approach for fabrication of flexible hybrid carbon/ MnO2 pseudo-capacitors. The highly porous carbon electrodes of the supercapacitor are fabricated by laser pyrolysis of polyimide-laminated copper sheet and subsequently coated with a uniform thin layer of MnO2. The porous laser carbonized polyimide provides a high effective surface area for the MnO2 coating, resulting in an increase of 55% in the electrochemical performance of the supercapacitor. The fabricated device exhibits a specific capacitance of 7.1mFcm-2 at a scan rate of 40mVs-1. Moreover, the copper backing film provides a proper electrical contact to the high surface area carbon/ MnO2 composite for stability under mechanical deformation and low internal resistance.

Diaper-Embedded Urinary Tract Infection Monitoring Sensor Module Powered by Urine-Activated Batteries

Urinary tract infection (UTI) is one of the most common infections in humans. UTI is easily treatable using antibiotics if identified in early stage. However, without early identification and treatment, UTI can be a major source of serious complications in geriatric patients, in particular, those suffering from neurodegenerative diseases. Also, for infants who have difficulty in describing their symptoms, UTI may lead to serious development of the disease making early identification of UTI crucial. In this paper, we present a diaper-embedded, wireless, self-powered, and autonomous UTI monitoring sensor module that allows an early detection of UTI with minimal effort. The sensor module consists of a paper-based colorimetric nitrite sensor, urine-activated batteries, a boost dc–dc converter, a low-power sensor interface utilizing pulse width modulation, and a Bluetooth low energy module for wireless transmission. Experimental results show a better detection of nitrite, a surrogate of UTI, than that of conventional dipstick testing. The proposed sensor module achieves a sensitivity of 1.35 ms/(mg/L) and a detection limit of 4 mg/L for nitrite.

A facile fabrication technique for stretchable interconnects and transducers via laser carbonization

This paper presents a facile, low-cost approach for fabricating highly-porous conductive carbon patterns on elastomeric substrates using laser carbonization of polyimide and its subsequent transfer onto a PDMS sheet. Using this technique, we fabricated stretchable interconnects and an array of piezoresistive tactile sensors. Raman spectra of pyrolyzed carbon regions revealed that under optimal laser settings, one can obtain highly porous carbon particles, nanotubes, and graphite sheets with sheet resistances as low as 50 Ω/. Characterizations of the stretchable patterns showed linear sensitivities of 8.912 kΩ/ε% and 518Ω/N in response to strain and normal force, respectively.