Clinical evaluation of stretchable and wearable inkjet-printed strain gauge sensor for respiratory rate monitoring at different measurements locations

The respiration rate (RR) is a vital sign in physiological measurement and clinical diagnosis. RR can be measured using stretchable and wearable strain gauge sensors which detect the respiratory movements in the abdomen or thorax areas caused by volumetric changes. In different body locations, the accuracy of RR detection might differ due to different respiratory movement amplitudes. Few studies have quantitatively investigated the effect of the measurement location on the accuracy of new sensors in RR detection. Using a stretchable and wearable inkjet-printed strain gauge (IPSG) sensor, RR was measured from five body locations (umbilicus, upper abdomen, xiphoid process, upper thorax, and diagonal) on 30 healthy test subjects while sitting on an armless chair. At each location, reference RR was simultaneously detected by the e-Health sensor, and the measurement was repeated twice. Subjects were asked about the comfortableness of locations. Based on Levene's test, ANOVA was performed to investigate if there is a significant difference in RR between sensors, measurement locations, and two repeated measurements. Bland-Altman analysis was applied to the RR measurements at different locations. The effects of measurement site and measurement trials on RR difference between sensors were also investigated. There was no significant difference between IPSG and reference sensors, between any locations, and between the two measurements (all p > 0.05). As to the RR deviation between IPSG and reference sensors, there was no significant difference between any locations, or between two measurements (all p > 0.05). All the 30 subjects agreed that diagonal and upper thorax positions were the most uncomfortable and most comfortable locations for measurement, respectively. The IPSG sensor could accurately detect RR at five different locations with good repeatability. Upper thorax was the most comfortable location.

Optimization of Geometry Parameters of Inkjet-Printed Silver Nanoparticle Traces on PDMS Substrates Using Response Surface Methodology

Inkjet printing is an emerging technology with key advantages that make it suitable for the fabrication of stretchable circuits. Specifically, this process is cost-effective and less complex compared to conventional fabrication technologies. Inkjet printing has several process and geometry parameters that significantly affect the electromechanical properties of the printed circuits. This study aims to optimize the geometry parameters of inkjet-printed silver nanoparticle traces on plasma-treated polydimethylsiloxane (PDMS) substrates. The optimization process was conducted for two printed shapes, namely straight line and horseshoe patterns. The examined input factors for the straight line traces were: the number of inkjet-printed layers and line width. On the other hand, the number of cycles and amplitude were the examined input parameters for the horseshoe shape. First, the optimal number of layers and line width were found from the straight line analysis and subsequently were used in the optimization of the horseshoe pattern parameters. The optimization of the input parameters was carried out using the response surface methodology (RSM), where the objective of the optimization was to maximize the breakdown strain of the traces while maximizing the gauge factor and minimizing the ink cost. The results indicate that a 1.78 mm line width and one layer are the optimal geometry parameters for the straight line traces, while for the horseshoe pattern, the optimal parameters are one layer, a line width of 1.78 mm, amplitude of 4 mm and one cycle. The optimal straight line was designed to sustain up to 10% strain while the horseshoe pattern was designed to sustain up to 15% strain.

Enhanced inertial focusing of microparticles and cells by integrating trapezoidal microchambers in spiral microfluidic channels

In this work, manipulating width and equilibrium position of fluorescent microparticles in spiral microchannel fractionation devices by embedding microchambers along the last turn of a spiral is reported. Microchambers with different shapes and sizes were tested at Reynolds numbers between 15.7 and 156.6 (100–1000 μL min⁻¹) to observe focusing of 2, 5 and 10 μm fluorescent microparticles. This paper also discusses the fabrication process of the microfluidic chips with femtosecond laser ablation on glass wafers, as well as a particle imaging velocimetry (μPIV) study of microparticle trajectories inside a microchamber. It could be demonstrated with an improved final design with inclined microchamber side walls, that the 2 μm particle equilibrium position is shifted towards the inner wall by ∼27 μm and the focusing line's width is reduced by ∼18 μm. Finally, Saccharomyces cerevisiae yeast cells were tested in the final chip and a cell focusing efficiency of 99.1% is achieved.

In this work, manipulating width and equilibrium position of fluorescent microparticles in spiral microchannel fractionation devices by embedding microchambers along the last turn of a spiral is reported.

Sheath-less high throughput inertial separation of small microparticles in spiral microchannels with trapezoidal cross-section

Various mechanisms of different designs have emerged for the purpose of microparticle separation and cell sorting. The main goals behind such designs are to create high throughput and high purity sample isolation. In this study, high efficiency, high throughput and precise separation of microparticles under inertial lift and drag forces induced by trapezoidal curvilinear channels are reported. This work is the first to focus and recover 2 from 5 μm and 2 from 10 μm particles in spiral channels in a sheath-less flow device, which reduces the overall complexity of the system and allows for higher throughput. The new microfluidic chip design is fabricated in glass using femtosecond laser ablation. In addition, mathematical force calculations were conducted during the design phase of the microfluidic channels and compared with experiments. The results show a close prediction of the equilibrium position of the tested microparticles.

This work is the first to focus and recover 2 from 5 μm and 2 from 10 μm particles in spiral channels in a sheath-less flow device, which reduces the overall complexity of the system and allows for higher throughput.

Experimental Characterization of Inkjet-Printed Stretchable Circuits for Wearable Sensor Applications

This paper introduces a cost-effective method for the fabrication of stretchable circuits on polydimethylsiloxane (PDMS) using inkjet printing of silver nanoparticle ink. The fabrication method, presented here, allows for the development of fully stretchable and wearable sensors. Inkjet-printed sinusoidal and horseshoe patterns are experimentally characterized in terms of the effect of their geometry on stretchability, while maintaining adequate electrical conductivity. The optimal fabricated circuit, with a horseshoe pattern at an angle of 45°, is capable of undergoing an axial stretch up to a strain of 25% with a resistance under 800 Ω. The conductivity of the circuit is fully reversible once it is returned to its pre-stretching state. The circuit could also undergo up to 3000 stretching cycles without exhibiting a significant change in its conductivity. In addition, the successful development of a novel inkjet-printed fully stretchable and wearable version of the conventional pulse oximeter is demonstrated. Finally, the resulting sensor is evaluated in comparison to its commercially available counterpart.

New generation of spinning systems for robust active mixing on microfluidic CDs: oil/water emulsion as an evaluation test

Microfluidic CDs (or Lab-on-Disc) continue to emerge in various applications of real life sciences, including biomedical and pharmaceutical fields. However, microfluidic CDs with advanced and efficient unit operation tools, such as pumping, valving, and mixing, need to be implemented to achieve the required applications in these fields. In this work, a novel generation of a spinning system to perform robust active mixing is developed for microfluidic CDs. The developed system is equipped with a dual-motor and dual-CD configuration to perform magnetically driven active mixing. The results show that the developed spinning system can provide a wide range of mixing frequencies independent of the spinning speed of the microfluidic CD. To evaluate the performance of this system under extreme conditions, an emulsion process of oil and water was conducted. Although the oil produced high drag force on the mixing magnet, the emulsion process successfully reached a steady state of mixing within a few seconds (approximately 3.5 s), and the mixture became homogeneous at 75 seconds. To demonstrate one of the potential applications of the proposed developed spinning setup, microparticles were successfully extracted from water to oil using water/oil emulsion on the microfluidic CD. In conclusion, mixing can be performed without influencing the integrated microfluidic components such as valves or pumps. This improvement can widen the range of applicability of microfluidic CDs in multi-step and complex processes where mixing is essential.

Low Cost Lab on Chip for the Colorimetric Detection of Nitrate in Mineral Water Products

The diagnostics of health status and the quality of drinking water are among the most important United Nations sustainable development goals. However, in certain areas, wars and instability have left millions of people setting in refugee camps and dangerous regions where infrastructures are lacking and rapid diagnostics of water quality and medical status are critical. In this work, microfluidic testing chips and photometric setups are developed in cheap and portable way to detect nitrate concentrations in water. The performed test is designed to work according to the Griess procedure. Moreover, to make it simple and usable in areas of low resource settings, commercially available Arduino mega and liquid crystal display (LCD) shield are utilized to process and display results, respectively. For evaluation purposes, different local products of tap water, bottled drinking water, and home-filter treated water samples were tested using the developed setup. A calibration curve with coefficient of determination (R²) of 0.98 was obtained when absorbance of the prepared standard solutions was measured as a function of the concentrations. In conclusion, this is the first step towards a compact, portable, and reliable system for nitrate detection in water for point-of-care applications.

LEGO Mindstorms NXT for elderly and visually impaired people in need: A platform

This paper presents the employment of LEGO Mindstorms NXT robotics as core component of low cost multidisciplinary platform for assisting elderly and visually impaired people. LEGO Mindstorms system offers a plug-and-play programmable robotics toolkit, incorporating construction guides, microcontrollers and sensors, all connected via a comprehensive programming language. It facilitates, without special training and at low cost, the use of such device for interpersonal communication and for handling multiple tasks required for elderly and visually impaired people in-need. The research project provides a model for larger-scale implementation, tackling the issues of creating additional functions in order to assist people in-need. The new functions were built and programmed using MATLAB through a user friendly Graphical User Interface (GUI). Power consumption problem, besides the integration of WiFi connection has been resolved, incorporating GPS application on smart phones enhanced the guiding and tracking functions. We believe that developing and expanding the system to encompass a range of applications beyond the initial design schematics to ease conducting a limited number of pre-described protocols. However, the beneficiaries for the proposed research would be limited to elderly people who require assistance within their household as assistive-robot to facilitate a low-cost solution for a highly demanding health circumstance.

An in-line photonic biosensor for monitoring of glucose concentrations

This paper presents two PDMS photonic biosensor designs that can be used for continuous monitoring of glucose concentrations. The first design, the internally immobilized sensor, consists of a reactor chamber, micro-lenses and self-alignment structures for fiber optics positioning. This sensor design allows optical detection of glucose concentrations under continuous glucose flow conditions of 33 µL/h based on internal co-immobilization of glucose oxidase (GOX) and horseradish peroxidase (HRP) on the internal PDMS surface of the reactor chamber. For this design, two co-immobilization methods, the simple adsorption and the covalent binding (PEG) methods were tested. Experiments showed successful results when using the covalent binding (PEG) method, where glucose concentrations up to 5 mM with a coefficient of determination (R2) of 0.99 and a limit of detection of 0.26 mM are detectable. The second design is a modified version of the internally immobilized sensor, where a microbead chamber and a beads filling channel are integrated into the sensor. This modification enabled external co-immobilization of enzymes covalently onto functionalized silica microbeads and allows binding a huge amount of HRP and GOX enzymes on the microbeads surfaces which increases the interaction area between immobilized enzymes and the analyte. This has a positive effect on the amount and rate of chemical reactions taking place inside the chamber. The sensor was tested under continuous glucose flow conditions and was found to be able to detect glucose concentrations up to 10 mM with R2 of 0.98 and a limit of detection of 0.7 mM. Such results are very promising for the application in photonic LOC systems used for online analysis.

Vertical microbubble column-A photonic lab-on-chip for cultivation and online analysis of yeast cell cultures

This paper presents a vertically positioned microfluidic system made of poly(dimethylsiloxane) (PDMS) and glass, which can be applied as a microbubble column (μBC) for biotechnological screening in suspension. In this μBC, microbubbles are produced in a cultivation chamber through an integrated nozzle structure. Thus, homogeneous suspension of biomass is achieved in the cultivation chamber without requiring additional mixing elements. Moreover, blockage due to produced carbon dioxide by the microorganisms-a problem predominant in common, horizontally positioned microbioreactors (MBRs)-is avoided, as the gas bubbles are released by buoyancy at the upper part of the microsystem. The patterned PDMS layer is based on an optimized two-lithographic process. Since the naturally hydrophobic PDMS causes problems for the sufficient production of microbubbles, a method based on polyelectrolyte multilayers is applied in order to allow continuous hydrophilization of the already bonded PDMS-glass-system. The μBC comprises various microelements, including stabilization of temperature, control of continuous bubble formation, and two optical configurations for measurement of optical density with two different sensitivities. In addition, the simple and robust application and handling of the μBC is achieved via a custom-made modular plug-in adapter. To validate the scalability from laboratory scale to microscale, and thus to demonstrate the successful application of the μBC as a screening instrument, a batch cultivation of Saccharomyces cerevisiae is performed in the μBC and compared to shake flask cultivation. Monitoring of the biomass growth in the μBC with the integrated online analytics resulted in a specific growth rate of 0.32 h(-1), which is almost identical to the one achieved in the shake flask cultivation (0.31 h(-1)). Therefore, the validity of the μBC as an alternative screening tool compared to other conventional laboratory scale systems in bioprocess development is proven. In addition, vertically positioned microbioreactors show high potential in comparison to conventional screening tools, since they allow for high density of integrated online analytics and therefore minimize time and cost for screening and guarantee improved control and analysis of cultivation parameters.