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Lu et al. Soft Sci 2024;4:36 https://dx.doi.org/10.20517/ss.2024.29 Page 3 of 20

resolution in near-surface depth measurement and minute deformation measurement of soft tissues
through methods such as piezoelectric actuation [28,29] , ultrasound arrays [18,20] , and optical coherence
elastography (OCE) [30,31] .

Understanding the generation and feedback of signals in superficial tissues can aid in evaluating the health
status of deeper tissue organs. Firstly, it offers a better understanding of the biomechanical responses of
tissues under conditions of both health and degradation, contributing to the explanation of tissue
behavior [2,32] . For example, changes in skin mechanical signals can be used to monitor skin diseases such as
scleroderma and psoriasis. Secondly, it helps characterize the mechanical properties of soft tissues, which
play a crucial role in physiology and disease . Lastly, it enables the evaluation of tissue characteristics at
[33]
[34]
different scales , such as detecting changes in intraocular pressure through eye monitoring signals and
reflecting cardiovascular status by seizing blood pressure (BP) waveforms from deep-seated vessels [35-40] .
Overall, mechanical measurement of biological tissues is crucial for advancing the understanding of tissue
mechanics, disease processes, and treatment strategies.

In this review, we discuss essential strategies for soft wearable devices for the evaluation of biological tissue
mechanics, which are focused on characterizing the mechanical properties of soft biological tissues in
various locations [Figure 1]. The emphasis is on the systematic properties of engineering designs and
methodologies, which possess diagnostic utility across varying measurement depths. This article
commences with an outline of multiple categories of wearable devices, ranging from flexible threads to
stretchable devices and three-dimensional (3D) circuit integrators. Secondly, microelectromechanical
devices are utilized for profound analysis of soft tissue biomechanics at adjustable characteristic depths,
ranging from shallow skin to mid to deep organ signal acquisition. Finally, examples will be given to explain
its applications, such as monitoring alterations in tissue mechanical properties and targeting anomalous
areas related to various diseases. These applications include voice code recognition , dermatologic
[41]
[20]
[20]
malignancy evaluation , arterial stiffness measurement , neonatal physiological monitoring , and more.
[29]
Recent advancements in these areas have the potential to transform tissue mechanics monitoring into a
significant aspect of healthcare and biomedical research, which are crucial for early diagnosis, monitoring
disease progression, and guiding treatment strategies in various medical fields.
EMERGING CLASSES OF SOFT WEARABLE DEVICES TO CAPTURE HUMAN BODY
MECHANICS
Overview of different sensing platforms for biological tissue mechanics with unique form factors
This section focuses on the biomechanics-sensing strategies of wearable microsystem technology for
mechanical measurement in biological tissues, which rely on small deformations of tissues, such as
intraocular pressure [10,11] , vocal cord vibration , heartbeat , muscle movement , changes in biological
[43]
[42]
[44]
[20]
tissue mechanical properties [28,29] , and pulse pulsation [Figure 1A]. When designing for clinical or home
use, reliability and high measurement accuracy are essential considerations. The goal of wearable
engineering is often to miniaturize size, conform to design and tissue mechanics, and match or
continuously connect with biological targets within short time intervals. The focus here is on providing a
measurement platform for mechanical compliance for the target organization.

[10]
Recent examples include strain gauges with filaments [Figure 1B] , stretchable electronic platforms with
biological compliance [Figure 1C] , and 3D circuit integrations for deep tissue characterization
[45]
[Figure 1D] . Conventional rigid devices rely on numerous displacement measurements in response to
[46]
large applied loads, leading to uncertainties during measurement and challenges when applied to bending
tissue surfaces that change over time. These microsystems, characterized by tissue-like mechanics, possess a