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A novel porous polydimethylsiloxane (PDMS)-based capacitive pressure sensor was fabricated by optimizing the dielectric layer porosity for wide-range pressure sensing applications in the sports field. The pressure sensor consists of a porous PDMS dielectric layer and two fabric-based conductive electrodes. The porous PDMS dielectric layer was fabricated by introducing nitric acid (HNO3) into a mixture of PDMS and sodium hydrogen bicarbonate (NaHCO3) to facilitate the liberation of carbon dioxide (CO2) gas, which induces the creation of porous microstructures within the PDMS dielectric layer. Nine different pressure sensors (PS1, PS2,..., PS9) were fabricated in which the porosity (pore size, thickness) and dielectric constant of the PDMS dielectric layers were varied by changing the curing temperature, the mixing proportions of the HNO3/PDMS concentration, and the PDMS mixing ratio. The response of the fabricated pressure sensors was investigated for the applied pressures ranging from 0 to 1000 kPa. A relative capacitance change of ∼100, ∼323, and ∼485% was obtained by increasing the curing temperature from 110 to 140 to 170 °C, respectively. Similarly, a relative capacitance change of ∼170, ∼282, and ∼323% was obtained by increasing the HNO3/PDMS concentration from 10 to 15 to 20%, respectively. In addition, a relative capacitance change of ∼94, ∼323, and ∼460% was obtained by increasing the PDMS elastomer base/curing agent ratio from 5:1 to 10:1 to 15:1, respectively. PS9 exhibited the highest sensitivity over a wide pressure sensing range (low-pressure ranges (<50 Pa), 0.3 kPa-1; high-pressure ranges (0.2-1 MPa), 3.2 MPa-1). From the results, it was observed that the pressure sensors with dielectric layers prepared at relatively higher curing temperatures, higher HNO3 concentrations, and higher PDMS ratios resulted in increased porosity and provided the highest sensitivity. As an application demonstrator, a wearable fit cap was developed using an array of 16 pressure sensors for measuring and mapping the applied pressures on a player's head while wearing a helmet. The pressure mapping aids in observing and understanding the proper fit of the helmet in sports applications.

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RESUMEN

Photonic curing has shown great promise in maintaining the integrity of flexible thin polymer substrates without structural degradation due to shrinkage, charring or decomposition during the sintering of printed functional ink films in milliseconds at high temperatures. In this paper, single-step photonic curing of screen-printed nickel (Ni) electrodes is reported for sensor, interconnector and printed electronics applications. Solid bleached sulphate paperboard (SBS) and polyethylene terephthalate polymer (PET) substrates are employed to investigate the electrical performance, ink transfer and ink spreading that directly affect the fabrication of homogeneous ink films. Ni flake ink is selected, particularly since its effects on sintering and rheology have not yet been examined. The viscosity of Ni flake ink yields shear-thinning behavior that is distinct from that of screen printing. The porous SBS substrate is allowed approximately 20% less ink usage. With one-step photonic curing, the electrodes on SBS and PET exhibited electrical performances of a minimum of 4 Ω/sq and 16 Ω/sq, respectively, at a pulse length of 1.6 ms, which is comparable to conventional thermal heating at 130 °C for 5 min. The results emphasize the suitability of Ni flake ink to fabricate electronic devices on flexible substrates by photonic curing.

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Chronic wounds affect over 6.5 million Americans and are notoriously difficult to treat. Suboptimal oxygenation of the wound bed is one of the most critical and treatable wound management factors, but existing oxygenation systems do not enable concurrent measurement and delivery of oxygen in a convenient wearable platform. Thus, we developed a low-cost alternative for continuous O2 delivery and sensing comprising of an inexpensive, paper-based, biocompatible, flexible platform for locally generating and measuring oxygen in a wound region. The platform takes advantage of recent developments in the fabrication of flexible microsystems including the incorporation of paper as a substrate and the use of a scalable manufacturing technology, inkjet printing. Here, we demonstrate the functionality of the oxygenation patch, capable of increasing oxygen concentration in a gel substrate by 13% (5 ppm) in 1 h. The platform is able to sense oxygen in a range of 5-26 ppm. In vivo studies demonstrate the biocompatibility of the patch and its ability to double or triple the oxygen level in the wound bed to clinically relevant levels.

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A novel and flexible oxygen sensing patch was successfully developed for wearable, industrial, food packaging, pharmaceutical and biomedical applications using a cost-efficient and rapid prototypable additive inkjet print manufacturing process. An oxygen sensitive ink was formulated by dissolving ruthenium dye and ethyl cellulose polymer in ethanol in a 1 : 1 : 98 (w/w/w) ratio. The patch was fabricated by depositing the oxygen sensitive ink on a flexible parchment paper substrate using an inkjet printing process. A maximum absorbance from 430 nm to 480 nm and a fluorescence of 600 nm was observed for the oxygen sensitive ink. The capability of the oxygen sensitive patch was investigated by measuring the fluorescence quenching lifetime of the printed dye for varying oxygen concentration levels. A fluorescence lifetime decay (τ) from ≈4 µs to ≈1.9 µs was calculated for the printed oxygen sensor patch, for oxygen concentrations varying from ≈5 mg L-1 to ≈25 mg L-1. A sensitivity of 0.11 µs mg L-1 and a correlation coefficient of 0.9315 was measured for the printed patches. The results demonstrated the feasibility of employing an inkjet printing process for the rapid prototyping of flexible and moisture resistant oxygen sensitive patches which facilitates a non-invasive method for monitoring oxygen and its concentration levels.

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A hexaazatriphenylene (HAT) derivative, naphtho[2,3-h]naphtho[2',3':7,8]quinoxalino[2,3-a]naphtho[2',3':7,8]quinoxalino[2,3-c]phenazine-5,10,15,20,25,30-hexaone (NQH) was synthesized, characterized, and found to have novel properties in being selective toward the detection of copper (Cu2+) ions. The capability of NQH to be employed as a colorimetric, chemo-fluorescence and electrochemical sensor for the detection of Cu2+ was demonstrated by performing UV-Vis absorbance, fluorescence intensity, and cyclic voltammetry (CV) measurements. The interaction between NQH and Cu2+ was initially observed with an obvious color change from yellow to brown upon the addition of Cu2+ ions to NQH. The interaction was also confirmed by UV-Vis absorbance, fluorescence intensity, and mass spectroscopy (MS/MS) measurements. UV absorbance, fluorescence and CV of NQH toward Cu2+ showed good linearity with a detection limit of 3.32 µM, 2.20 µM and 0.78 µM, respectively, which are lower than the toxicity levels of copper in drinking water (20-30 µM) set by the U.S. Environmental Protection Agency (EPA) and World Health Organization (WHO). A 1 : 2 stoichiometry complexation between NQH and Cu2+ was confirmed by Job's plot and MS/MS. In addition, the selectivity and sensitivity of the NQH compound towards Cu2+ ions were further confirmed by performing CV on a screen printed flexible and planar electrochemical sensor.

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A novel functionalized multi-walled carbon nanotube (FMWCNT)/hydroxyethyl cellulose (HEC) composite-based humidity sensor was successfully developed for humidity monitoring applications. FMWCNTs were synthesized by covalently functionalizing multi-walled carbon nanotubes (MWCNTs) in a mixture of sulfuric and nitric acid to enhance their hydrophilicity. The FMWCNTs were characterized using transmission electron microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy and dispersion analysis to verify the presence of functional hydroxyl and carboxyl groups. A FMWCNT/HEC (1 : 6 w/w) composite ink was formulated using the solution blending technique with 2.5 wt% FMWCNTs. A multi-layered humidity sensor was fabricated using additive print manufacturing processes on a flexible polyethylene terephthalate (PET) substrate. Screen printing and gravure printing processes were used to deposit the bottom silver (Ag) electrode and FWMCNT/HEC sensing layers, respectively. The capability of the fabricated humidity sensor was investigated by measuring its resistive response towards relative humidity (RH) varying from 20% RH to 80% RH. As the RH was increased from 20% RH to 80% RH in steps of 10% RH at 25 °C, it was observed that the resistance of the printed sensor increased linearly. The printed sensor demonstrated resistance changes as high as ≈290% at 80% RH, when compared to its base resistance at 20% RH. A sensitivity and a response time of 0.048/%RH and ≈20 s were obtained for the printed sensor, respectively. The results thus demonstrated the feasibility of employing additive print manufacturing processes to develop a highly sensitive sensor for humidity monitoring applications.

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Advancements in the field of printed electronics can be applied to the field of diabetes testing. A brief history and some new developments in printed electronics components applicable to personal test devices, including circuitry, batteries, transmission devices, displays, and sensors, are presented. Low-cost, thin, and lightweight materials containing printed circuits with energy storage or harvest capability and reactive/display centers, made using new printing/imaging technologies, are ideal for incorporation into personal-use medical devices such as glucose test meters. Semicontinuous rotogravure printing, which utilizes flexible substrates and polymeric, metallic, and/or nano "ink" composite materials to effect rapidly produced, lower-cost printed electronics, is showing promise. Continuing research advancing substrate, "ink," and continuous processing development presents the opportunity for research collaboration with medical device designers.

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