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Page 22 of 39 Yang et al. Soft Sci. 2025, 5, 46 https://dx.doi.org/10.20517/ss.2025.44

et al. developed a method of delivering near-infrared light to deeper structures of the spinal column using
flexible optical fibers and verified that the fiber-diffused light had no side effects on normal tissues in a
piglet model [193,194] .

Optogenetics
Optogenetic therapy involves the use of light to control cells within living tissue that have been genetically
[195]
modified to express light-sensitive ion channels . The advantages of optogenetic therapy over other
techniques include small wounds and high temporal and spatial resolution . Flexible optical waveguides
[196]
provide a minimally invasive means to deliver precise light pulses, facilitating control of neuronal activity
for research and potential treatment of neurological disorders. Systems that utilize optical waveguides for
optogenetic applications can be broadly classified into two categories: wired optogenetic systems and
wireless optogenetic systems . Gutierrez et al. completed an optogenetic study on a mouse model using an
[197]
optical fiber-based wired system . However, owing to the fixed light source and the limited length of the
[198]
optical fiber, this wired optogenetic system could limit the subject’s range of motion during the
experiment . Recent studies have demonstrated the feasibility of wireless optogenetic systems that
[199]
combine the three procedures of light-activated retinoid delivery, photo delivery, and subsequent electrical
recording in a miniature, flexible, all-polymer waveguide device [195,200,201] . The multifunctional neural probe
introduced by Park et al. consists of an optical waveguide, six electrodes, and two microfluidic channels
fabricated by fiber-optic drawing . The flexible probe is made entirely of polymers and polymer
[200]
composites that minimize the tissue response, enabling long-term, multimodal, high-fidelity detection of
brain circuits.

Contact physiological information monitoring
Long-term monitoring of physiological information is a key application area of flexible optical waveguides
beyond invasive biomedical diagnostics. Researchers are developing a wide range of photonic textiles,
wearable devices, and Internet of Things (IoT) furniture for long-term monitoring using various flexible
optical waveguides. In this section, we report research advances in contact physiological monitoring devices
based on four different usage scenarios: motion pattern recognition, cardiorespiratory function assessment,
sleep state recording, and pronunciation detection.

Motion pattern recognition
Several physiological changes can occur when the human body moves, the most intuitive of which can
involve joint movement, muscle contraction, and plantar pressure. Monitoring these physiological signals
for motion pattern recognition can help the public better understand their exercise health status and
support specific scenarios, such as athlete training and physician diagnosis.

Gait
Gait is an important indicator for assessing human health, and people with conditions such as Parkinson’s
disease, diabetes, and stroke often exhibit unique gait characteristics, which can be used to analyze details
such as the plantar pressure, step count, and walking speed. Therefore, developing devices for gait
monitoring is promising for preventing falls in elderly individuals, assisting athletes in training, and
improving shoe design. Domingues et al. designed an insole with an FBG network for remote gait analysis,
and the study showed that this IoT monitoring device successfully enabled monitoring and analysis of the
plantar pressure in the standing and walking phases of gait . However, the FBG optical fiber used in this
[202]
study may present potential safety hazards because of its insufficient flexibility. Recently, the POF-based
[49]
smart insole [Figure 9A ] developed by Xiang et al. demonstrated good performance in gait monitoring .
[49]
Avellar et al. demonstrated smart pants for biomechanical and activity recognition by developing a POF to