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Page 24 of 39 Yang et al. Soft Sci. 2025, 5, 46 https://dx.doi.org/10.20517/ss.2025.44

device design, Leal-Junior et al. proposed a 3D printing-supported gait assistive and rehabilitation device
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with embedded POFs, enabling pressure and microclimate change assessment .
Joint movement
In addition to the gait information reflected by the plantar pressure and changes in the leg muscles when
standing, the movement of the joints (knees, elbows, etc.) of the human body when walking also contains
much health information. Wang et al. proposed a wearable D-shaped POF sensing system based on
machine learning for human motion recognition . The designed wearable sports cuffs were worn on the
[153]
elbow and knee joints of the human body, and good results were achieved in the recognition of six types of
movement, such as walking, running, and climbing stairs. As shown in Figure 9B, Jiang et al. recently
proposed self-powered mechanoluminescent elastic optical waveguides combined with flexible circuits,
which were successfully applied in the monitoring of the bending motions of fingers, wrists, and elbows,
showing excellent sensing performance . The stretchable TPE optical fibers proposed by Leber et al. can
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reliably assess extreme mechanical stimuli, and their utility was demonstrated in a scaffold used for tracking
motion tracking . Zhou et al. reported a self-powered stretchable fiber-optic strain sensor with a
[114]
distributed sensing capability based on mechanoluminescent optical fibers, in which mechanoluminescent
phosphors that emitted light of different colors were discretely integrated into the housing of an elastomeric
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fiber . The sensor acquired bending information from different parts of the finger joints and used it for
complex gesture judgment.

Micromotion
Micromotion of the body, such as throat vibrations, muscle twitches, and teeth clenching, plays an equally
important role in physiological health monitoring. As shown in Figure 9C , Wang et al. proposed a novel
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wearable optical microfiber smart sensor based on wavy polymer optical microfibers (WPOMF) and
successfully conducted behavioral detection experiments with this sensor . With the assistance of artificial
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intelligence (AI), the WPOMF sensor placed on the larynx achieved articulatory recognition of key medical
monitoring words. Qian et al. presented a flexible and sensitive mechanoluminescent device with an elastic
modulus modified by a nano-dopant, which enabled light emission driven by muscle movement, i.e., the
[112]
photonic skin phenomenon . An interactive mouthguard based on a mechanoluminescence-driven
optical fiber sensor can be used for the operation of an occlusal control device, as proposed by Hou
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et al. . The sensor can be used to operate computers, smartphones, and wheelchairs through occlusion,
showing great promise for applications.

Cardiorespiratory function assessment
Cardiorespiratory function is one of the most important indicators of human health. Many diseases,
although difficult to detect in the early stages, can be detected based on subtle changes in cardiorespiratory
function. Thus, flexible optical waveguide devices to monitor physiological information over long periods
have been developed, offering significant potential for health monitoring. This section reports advanced
cases of flexible optical waveguide applications in pulse wave, heartbeat, and respiration monitoring.

Pulse waves
Monitoring pulse waves is essential for assessing cardiovascular health. Koyama et al. reported the use of a
plastic FBG optical sensor to measure pulsating strain at the fingertip . They successfully applied this
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sensor to pulse rate estimation, overcoming the safety hazards of quartz fiber grating sensors. Li et al.
developed a microfiber optical sensor with a PDMS hybrid plasmonic microfiber knot resonator PDMS
sandwich structure for monitoring clinical physiological signals . The sensor was successfully used for
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wrist pulse wave and finger pulse wave monitoring, showing excellent sensitivity. Liang et al. presented a