The compliant, continuum, and configurable robotics field in general has gained growing interest in the past years especially with the exciting advances in artificial intelligence technology, [1] which could enable various valuable applications ranging from manufacturing to safety and healthcare. [2,3] Soft robots are of notable interest because, unlike their rigid counterpart, they can easily deform while being mechanically resilient, [4,5] adapt to the outer environment without harm to humans, [6] and finally, enable low-cost manufacturing. [7] For robots to interact with the outer environment and complete tasks, a set of sensors and actuators need to be integrated into the system. Soft robots, in specific, present additional challenges because their sensing and actuation devices are generally highly integrated within the body of the robot and its whole functionality. These challenges become even more critical when the soft robot is scaled down to sub-centimeter size as the sensing, power, and data analysis units are moved off-board. As a result, miniaturized soft actuators that respond to various stimuli and show large deformations in addition to mechanical resilience are crucial. These would be particularly promising for application in artificial muscles, microrobots, and micro-manipulators. [8-10] Active and soft materials are promising for this task as they can be actuated through various external stimuli, such as photons, thermal, magnetic and/or electric field. Such materials range from particles, to polymers (either electroactive or shape memory), papers, fluids, shape memory alloys (SMAs), liquid metals, hydrogels, 2D materials, or a combination of these. [6-25] Nevertheless, some materials can be more suitable for a specific set of applications than others; for instance, materials stimulated by the near-infrared (NIR) spectrum are promising for biomedical applications, whereas sunlight-stimulated materials are suitable for nature-inspired soft robots used in outside environments. Various useful metrics are generally used to assess the performance of the actuators; these include the generated stress and strain, Young's modulus or measured stiffness, in addition to their power, work, energy, and force density. In this Review article, however, we focus on the application of the soft actuators in soft robotics where the reported metrics include mode and speed of actuation (or locomotion), power, voltage, current (of the driving signal), lifting force, and weight among others. In this Review article, different active materials that have been developed and used in soft actuators for soft robotics are discussed and grouped by the stimulus that generates the actuation response as shown in Figure 1. The physics of operation, resulting deformations, mechanical resilience, and their pros and cons are presented with a focus on the applications of the different soft

Soft Robotics In article number http://doi.wiley.com/10.1002/aisy.202000128, Muhammad Mustafa Hussain and co‐workers present a comprehensive review on soft robots which are paving the way towards a wide range of vital applications such as drug delivery, among others. Various state‐of‐the‐art soft actuators which respond to different stimuli, including light, heat, and applied electric field with a focus on their various applications in soft robotics, are discussed.

Point-of-care testing (POC) has the ability to detect chronic and infectious diseases early or at the time of occurrence and provide a state-of-the-art personalized healthcare system. Recently, wearable and flexible sensors have been employed to analyze sweat, glucose, blood, and human skin conditions. However, a flexible sensing system that allows for the real-time monitoring of throat-related illnesses, such as salivary parotid gland swelling caused by flu and mumps, is necessary. Here, for the first time, a wearable, highly flexible, and stretchable piezoresistive sensing patch based on carbon nanotubes (CNTs) is reported, which can record muscle expansion or relaxation in real-time, and thus act as a next-generation POC sensor. The patch offers an excellent gauge factor for in-plane stretching and spatial expansion with low hysteresis. The actual extent of muscle expansion is calculated and the gauge factor for applications entailing volumetric deformations is redefined. Additionally, a bluetooth-low-energy system that tracks muscle activity in real-time and transmits the output signals wirelessly to a smartphone app is utilized. Numerical calculations verify that the low stress and strain lead to excellent mechanical reliability and repeatability. Finally, a dummy muscle is inflated using a pneumatic-based actuator to demonstrate the application of the affixed wearable next-generation POC sensor.

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Structural engineering plays an essential role in designing, improving, and optimizing an electromechanical system, instinctively affecting its performance. In this study, design optimization, finite element analysis, and experimental evaluation of capacitive pressure sensors were conducted. The air pressure sensing application was demonstrated to characterize different sensors, which include a combination of multiple rectangular cantilevers and diaphragms (square and circular-shaped). After the design improvement, we found that the square and circular diaphragms each with two trapezoidal cantilevers exhibited highest sensitivity to air pressure monitoring among the different investigated designs which combine the square and circular diaphragms with cantilevers. These designs were then selected for further analysis for acoustic pressure monitoring. The sensors were fabricated using the doit-yourself technique with household materials such as post-it paper, posted tape, and foil. Our approach offers an alternative to the conventional cleanroom fabrication technique and uses easily available materials to fabricate affordable sensors. Therefore, this is the first step toward the development of democratized and sustainable electronic devices that are affordable and available to everyone on the internet.

Commercial Silver and Silver Chloride (Ag/AgCl) wet electrodes are used to monitor electrocardiogram (ECG) signals in numerous bioimpedance applications. These electrodes are single-use components that irritate the skin during the replacement and removal of electrodes, making the process uncomfortable for the patient. This study introduces the use of a copper-based filament with the highest reported conductivity (0.006 Ω.cm) in biomedical applications, showcasing the process parameters of 3D printed, semi-flexible and wearable dry electrodes to monitor ECG signals. The effect of the printing-process parameters on the electrical performance is thoroughly investigated (10 parameters and >100 electrode samples) to find the printed electrodes’ highest conductivity and lowest impedance. The results showed the concentric and flat dry electrode structures of Tbed = 80 °C and Tnozzle = 140 and 150 °C with the best performance, confirming that different electrode structures and printing parameters significantly influence electrodes' functionality, conductivity, and impedance measurements.

Commercial wet Silver and Silver Chloride electrodes are used to monitor electrocardiogram (ECG) signals in numerous bioimpedance applications. These electrodes are frequently single-use components that adhere to the skin through an adhesive surface. This sticky surface is infamous for generating skin irritations during the replacement and removal of electrodes, making the process uncomfortable for the patient. Because this type of electrodes is inappropriate in many measuring situations, the applicability of dry electrodes is investigated. This study introduces the use of a copper-based filament (Electrifi) with the highest reported conductivity (0.006 Ω.cm) in biomedical applications, showcasing the process parameters of 3D printed, semi-flexible and wearable dry electrodes to monitor ECG signals. The effect of the printing-process parameters (bed and nozzle temperatures, surface infill pattern) on the electrical performance is thoroughly investigated (10 parameters and >100 electrode samples) to find the highest conductivity and lowest impedance of the printed electrodes. The influence of ten process parameters on the resistivity of printed electrode samples with three different surface structures (namely concentric, rough, and flat as shown in Fig. 1a) and different thicknesses have been experimented. The analyzed parameters play a significant role in the electrodes’ impedance and conductivity values. Choosing a proper setup of these parameters can enhance the bio-impedance measurements of dry electrodes similar to ranges of wet electrodes and even below. The flow of this study was divided into two main stages. First, electrodes of 15 mm diameter and 2 mm thickness were 3D printed with three surface structures, each with six temperature settings, including two nozzle temperatures (140 and 150 °C) and three bed temperatures (40, 60, and 80 °C). At this point, non-optimized electrodes are recognized. Second, another optimization strategy was presented, which involves experimenting with electrodes of 15 mm diameter and 0.5 mm thickness with two surface structures (concentric and flat), each with two temperature settings, including two nozzle temperatures (140 and 150 °C) and one bed temperature (80 °C). A 2D profilometry is provided, showcasing the effect of printing parameters on the electrodes' surface roughness. Keithley and Agilent semiconductor device analyzers were used to record the impedance measurements; both can acquire complex impedance spectra per second in a frequency range from 20 kHz to 400 kHz. The excitation current was set to 20 µA. This study investigates the behavior of 2 stacked electrodes. For this purpose, two binder clips were used to securely hold the two electrodes, resulting in uniform force distribution. The resistance measurements are performed using the same equipment under a fixed frequency at 400 kHz that is then converted into conductivity given the electrodes' cross-sectional area and thickness to be 177 mm2 and 2 mm (or 0.5 mm), respectively. The process parameters significantly affect the electrodes surface structures, specifically the bed temperature (Tbed). The roughness of the structured surfaces (concentric and rough) was observed to be increasing with the increase in bed temperature. However, the roughness of the flat surface remained unchanged under all temperature parameters. The impedance measurements of the 2 mm thick electrodes decreased significantly over frequency, showing a capacitive behavior (Fig. 1b). This is due to the air gap created between the structured electrodes, parasitic factors from the devices themselves, and external factors such as light, airflow, and movement that influenced the measurement. The conductivity measurements are depicted in Fig. 1c, unlike the rough surface electrode, which uses additional ironing parameters, the flat and concentric surface electrodes are printed with the same process parameters, resulting in equivalent resistance and conductivity values. Thus, the concentric and flat structures of Tbed = 80 °C and Tnozzle = 140 and 150 °C showed the best performance among all samples. Decreasing the thickness to 0.5 mm of the concentric and flat structures and using the optimum bed and nozzle temperatures generated better and stable results with higher sensitivity and lower impedance measurements. In conclusion, this study confirms that different electrode structures and printing temperatures significantly influence the electrodes' functionality, conductivity, and impedance measurements. Defining the optimum printing parameters for the electrodes' material is fundamental to obtain stable and reliable measurements. With a new insight into the electrical behavior of the copper-based Electrifi filament, process optimization and new printing strategies can be studied for the single-process fused filament fabrication (FFF) 3D printing to create functional and sensitive electrodes. Figure 1. A) Images of the three 3D printed electrodes surfaces: flat (left), concentric (middle), and rough (right). B) Impedance measurement of the concentric structure at different frequencies. C) Conductivity measurements of the electrodes with three different surfaces. Figure 1

In this work, soft actuators made of shape memory polymers (SMPs) are used to actuate and control a solar tracker in response to heat generated by sunlight. To achieve this, a thermo-mechanical design of a solar tracker is 4D printed. The results show that the black-colored elliptical-shaped solar tracker can shrink and tilt by up to 30° when exposed to sunlight with a response time of 30 s, enabling the solar cell to remain exposed to the highest light intensity and therefore, allowing for continuously optimizing the solar cell power output.