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Lu et al. Soft Sci 2024;4:36 https://dx.doi.org/10.20517/ss.2024.29 Page 13 of 20

A wearable ultrasound array capable of continuously capturing real-time images of the heart and assessing
its function would be a remarkable advancement in the field of healthcare. The device combines several
components: piezoelectric transducer arrays, composite electrodes of liquid metal, and encapsulation of
triblock copolymer [Figure 3F] . Together, the anisotropic 1-3 piezoelectric composite and the silver-
[74]
epoxy-based backing layer form a transducer element capable of sensing or actuation. Employing a smaller
array pitch of 0.4 mm (0.78 ultrasonic wavelengths) in an ultrasonic imaging system can improve lateral
resolution and reduce grating lobes. High-density multilayer stretchable electrodes (8 μm thick) based on a
composite of eutectic gallium indium liquid metal and styrene-ethylene-butylene-styrene (SEBS) can
provide a solution for individually addressing each element in a tight array. Incorporating electromagnetic
shielding into ultrasound devices, such as using composite materials with great electromagnetic shielding
properties, can help minimize the interference from external electromagnetic waves and maintain the
integrity of ultrasonic RF signal, so as to improve the image quality. The described device possesses
exceptional electromechanical properties, including low dielectric loss, wide bandwidth, a high
electromechanical coupling coefficient, and negligible crosstalk, contributing to its excellent performance
and versatility in various fields such as telecommunications, medical imaging, sensing technologies, and
more. motion-mode (M-mode) imaging is a technique commonly used in medical ultrasound to monitor
[75]
activities over time within a target region in one dimension . It is particularly useful in cardiac imaging to
evaluate the movement and functional properties of the heart. By analyzing the M-mode images, clinicians
can assess various aspects of the motion of the target area, such as the one shown in Figure 3G, which
extracts the primary targets in the M-type images including the left ventricular ventricle, the septum and the
mitral/aortic valves from parasternal long-axis view B-mode images. The distance between feature
boundaries, such as the thickness of myocardium and the diameter of left ventricular, can be tracked using
M-mode. Analyzing the changes in the position of these boundaries over time, various measurements can
be obtained to assess cardiac structure and function. Besides, it is possible to correlate mechanical exercises
observed in M-mode visuals with the electrical signals recorded in an electrocardiogram (ECG) throughout
various stages of the cardiac cycle (the lower inset of Figure 3G). This information helps in diagnosing
cardiac abnormalities, evaluating heart function, and monitoring treatment progress.

Active semiconductor-based MEMS devices offer improved performance, miniaturization, integration, and
adaptability compared to traditional measurement approaches, making them highly suitable for evaluating
deep-tissue biomechanics, enabling more precise and efficient studies in biomedical applications. As shown
in Figure 3H, the UoC integrated a two-dimensional array of 8,690 MEMS transducers in a 140 × 64
configuration (area of 30 mm × 13.3 mm, spacing pitch of 200 µm) with complementary metal-oxide-
semiconductor (CMOS) control and processing electronics has significant potential for development as an
[65]
inexpensive whole body imaging probe . By combining a UoC platform with a portable system and an
artificial intelligence system, it becomes possible to perform quantitative measurements and obtain high-
quality clinical visuals of deep tissues throughout the human body, such as the abdominal UoC ultrasound
image: blood vessel flow in the kidney shown in Figure 3I. Excitingly, the proliferation of portable and low-
cost ultrasound imaging has the potential to revolutionize global health and make a significant impact on
the fields of medicine.

CLINICAL APPLICATIONS OF WEARABLE DEVICES FOR TISSUE MECHANICS
CHARACTERIZATION
Assessment of biological tissue mechanics across multiple dimensions offers a wealth of human-computer
interaction applications and clinical practices. This multidimensional analysis can lead to improvements in