The design and development of textile-based strain sensors has been a focus of research and many investigators have studied this subject. This paper presents a new textile-based strain sensor design and shows the effect of base fabric parameters on its sensing properties. Sensing fabric could be used to measure articulations of the human body in the real environment. The strain sensing fabric was produced by using electronic flat-bed knitting technology; the base fabric was produced with elastomeric yarns in an interlock arrangement and a conductive yarn was embedded in this substrate to create a series of single loop structures. Experimental results show that there is a strong relationship between base fabric parameters and sensor properties.

Textile-Based Weft Knitted Strain Sensors: Effect of Fabric Parameters on Sensor Properties

Soft sensors have been playing a crucial role in detecting different types of physical stimuli to part or the entire body of a robot, analogous to mechanoreceptors or proprioceptors in biology. Most of the currently available soft sensors with compact form factors can detect only a single deformation mode at a time due to the limitation in combining multiple sensing mechanisms in a limited space. However, realizing multiple modalities in a soft sensor without increasing its original form factor is beneficial, because even a single input stimulus to a robot may induce a combination of multiple modes of deformation. Here, we report a multifunctional soft sensor capable of decoupling combined deformation modes of stretching, bending, and compression, as well as detecting individual deformation modes, in a compact form factor. The key enabling design feature of the proposed sensor is a combination of heterogeneous sensing mechanisms: optical, microfluidic, and piezoresistive sensing. We characterize the performance on both detection and decoupling of deformation modes, by implementing both a simple algorithm of threshold evaluation and a machine learning technique based on an artificial neural network. The proposed soft sensor is able to estimate eight different deformation modes with accuracies higher than 95%. We lastly demonstrate the potential of the proposed sensor as a method of human-robot interfaces with several application examples highlighting its multifunctionality.

Heterogeneous sensing in a multifunctional soft sensor for human-robot interfaces

Unlike conventional antimicrobials, the study of bacterial resistance to silver nanoparticles (AgNPs) remains in its infancy and the mechanism(s) through which it evolves are limited and inconclusive. The central question remains whether bacterial resistance is driven by the AgNPs, released Ag(I) ions or a combination of these and other factors. Here, we show a specific resistance in an Escherichia coli K-12 MG1655 strain to subinhibitory concentrations of AgNPs, and not Ag(I) ions, as indicated by a statistically significant greater-than-twofold increase in the minimum inhibitory concentration occurring after eight repeated passages that was maintained after the AgNPs were removed and reintroduced. Whole-population genome sequencing identified a cusS mutation associated with the heritable resistance that possibly increased silver ion efflux. Finally, we rule out the effect of particle aggregation on resistance and suggest that the mechanism of resistance may be enhanced or mediated by flagellum-based motility. Bacterial motility may be used as an important predictor of whether a particular bacteria strain can develop AgNP resistance and could inform design of nanoenabled antimicrobials that mechanistically target specific types of bacteria.

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Role of bacterial motility in differential resistance mechanisms of silver nanoparticles and silver ions

The paper presents a substantial review on the different kinds of strain sensors that have been employed as wearable sensing prototypes. The importance of strain sensors lies in their low cost, high sensitivity and multifunctional applications. The flexible strain sensors have been developed with printing techniques that have generated prototypes with varied electrical, mechanical and thermal characteristics. These types of devices have been primarily used for biomedical applications, where a small amount of deflection holds a crucial worth to monitor acute and chronic anomalies in human beings. Among the major areas in healthcare applications where strain sensors have been utilized, wearable sensing holds a pivotal role due to their capability of ubiquitous monitoring. The wearable sensors have been designed and fabricated with a range of processing materials, based on their respective applications. Along with the significant research related to the fabrication and implementation of wearable strain sensors, explanation related to the challenges of the current sensors and their futuristic possibilities have also been showcased in the paper.

A review on fabrication, characterization and implementation of wearable strain sensors

Flexible transparent electrodes (FTEs) with embedded metal meshes play an indispensable role in many optoelectronic devices due to their excellent mechanical stability and environmental adaptability. However, low‐cost, simple, efficient, and environmental friendly integrated manufacturing of high‐performance embedded metal meshes remains a huge challenge. Here, a facile and novel fabrication method is proposed for FTEs with an embedded metal mesh via liquid substrateelectric‐field‐driven microscale 3D printing process. This direct printing strategy avoids tedious processes and offers low‐cost and high‐volume production, enabling the fabrication of high‐resolution, high‐aspect ratio embedded metal meshes without sacrificing transparency. The final manufactured FTEs with 80 mm × 80 mm embedded metal mesh offers excellent optoelectronic performance with a sheet resistance (Rs) of 6 Ω sq−1 and a transmittance (T) of 85.79%. The embedded metal structure still has excellent mechanical stability and good environmental suitability under different harsh working conditions. The practical feasibility of the FTEs is successfully demonstrated with a thermally driven 4D printing structure and a resistive transparent strain sensor. This method can be used to manufacture large areas with facile, high‐efficiency, low‐cost, and high‐performance FTEs.

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1002/advs.202105331

Directly Printed Embedded Metal Mesh for Flexible Transparent Electrode via Liquid Substrate Electric‐Field‐Driven Jet

In this paper, we present a new approach to realize flexible transparent strain sensors. It combines the use of transparent conductive fabric with polydimethylsiloxane (PDMS) through a simple and straightforward layer-by-layer assembly process. The conductive fabric is used to realize the transparent electrodes while the PDMS is utilized as both the substrate and encapsulation layers. As a concept demonstration, an interdigital capacitive sensor is designed and fabricated using the proposed approach. The fabricated sensor is then characterized in terms of its transparency and electro-mechanical nature. This is followed by the application of the sensor in several physiological sensing scenarios, including the sensing of various body-part movements and tactile sensing. Apart from a high optical transparency (~70%), the sensor shows promising sensing results which validate the applicability of the proposed approach for realization of flexible and transparent strain sensors for wearable sensing applications.

A Transparent Strain Sensor Based on PDMS-Embedded Conductive Fabric for Wearable Sensing Applications

The past decade has seen the incorporation of antimicrobial nanosilver (NAg) into medical devices, and, increasingly, in everyday ‘antibacterial’ products. With the continued rise of antibiotic resistant bacteria, there are concerns that these priority pathogens will also develop resistance to the extensively commercialized nanoparticle antimicrobials. Herein, this work reports the emergence of stable resistance traits to NAg in the WHO-listed priority pathogen Staphylococcus aureus, which has previously been suggested to have no, or very low, capacity for silver resistance. With no native presence of genetically encoded silver defence mechanisms, the work showed that the bacterium is dependent on mutation of physiologically essential genes, including those involved in nucleotide synthesis and oxidative stress defence. While some mutations were uniquely associated with resistance to NAg, the study also found common mutations that could be protective against both NAg and ionic silver. This is consistent with the observation of NAg/ionic silver cross-resistance. These mutations were detected following withdrawal of the silver exposure, denoting heritable characteristics that allow for spread of the resistance traits even with discontinued silver use. Heritable silver resistance in priority pathogen cautions that these nanoparticle antimicrobials should only be used as needed, to preserve their efficacy for treating infections.

Elizabeth Valentin

Papers

A Transparent Strain Sensor Based on PDMS-Embedded Conductive Fabric for Wearable Sensing Applications

Heritable nanosilver resistance in priority pathogen: a unique genetic adaptation and comparison with ionic silver and antibiotics.