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Yang et al. Soft Sci. 2025, 5, 46 https://dx.doi.org/10.20517/ss.2025.44 Page 3 of 39

electromagnetic interference and have problems such as low sensitivity, high power usage, and susceptibility
to environmental interference [24,25] . For the mainstream electrical sensors, including the two types mentioned
above, invasive electrical sensors inevitably induce inflammatory reactions due to the implantation of
foreign bodies such as electrodes, whereas noninvasive electrical sensors also have safety concerns due to
electrical hazards, the inability to resist electromagnetic interference, and poor biocompatibility [26,27] . To
overcome these challenges, sensors composed of flexible optical waveguide systems, which operate on the
principle of optical modulation rather than electrical modulation, have emerged as safe and reliable
alternatives.

Flexible optical waveguides are well established in the sensing field for measuring various physical,
[30]
[29]
[28]
[31]
chemical, and biological quantities such as displacement , velocity , temperature , weight ,
[32]
[33]
[34]
pressure , strain , pH , humidity , and so on. In terms of performance, flexible optical waveguides can
[35]
achieve ≥ 30 V/m immunity to electromagnetic interference, exceeding the immunity of electrochemical
sensors; and even after prolonged physiological monitoring, flexible optical waveguides are generally offset
within < 0.5%, and their optical modulation principle eliminates electrochemical drift, a key limitation of
enzyme-based electrochemical sensors that require frequent recalibration . In addition, the waveguides
[26]
enable multiparameter sensing with a single device, reducing system complexity compared to hybrid
[36]
electrical arrays . Furthermore, due to their high biocompatibility, high sensitivity, and deep penetration
range, flexible optical waveguides possess unique advantages in human health monitoring and sensing [36-39] ,
and are commonly used for long-term monitoring of human physiological signals, disease prevention, and
clinical diagnosis [40-42] . In addition to sensing, owing to the biocompatibility of their materials and the
further development of photobiology, flexible optical waveguides can also be used for minimally invasive or
even noninvasive medical clinical treatment, and after surgery, they can also be used for rehabilitation,
assisted living support, etc., with a broad range of applications [43,44] .

In this work, based on a review of flexible optical waveguides for human health assistance, we systematically
classify and summarize the current development status and specific applications of flexible optical
waveguides in the field of human health assistance, as well as their possible future development trends, as
presented in Figure 1 [45-56] . We classify the materials commonly used for preparing flexible optical waveguide
systems, summarizing the basic properties and uniqueness of the three primary material types: hydrogels,
elastomers, and biodegradable materials. Building on this foundation, we will then examine the
fundamental principles that enable flexible optical waveguide systems to function in sensing applications,
offering readers deeper insight into how these systems are leveraged for practical use. To illustrate their
versatility, we further review and analyze concrete application examples across three key domains: invasive
biomedical diagnosis and therapy, contact-based physiological information monitoring, and interactive soft
robotics, highlighting their transformative potential in these fields.

MATERIALS FOR FLEXIBLE OPTICAL WAVEGUIDES
The advent of rapid material science advancements has facilitated the utilization of an array of innovative
materials in the fabrication and packaging of optical waveguides that impart enhanced flexibility.
Traditional rigid materials (such as silicon and carbon-based materials) have many advantages, such as anti-
electromagnetic interference, light weight, low optical loss, sensitive response, etc., and are widely used in
optical fiber communication, remote sensing, imaging, etc. [57-59] . However, these materials are not suitable
for preparing flexible optical waveguides. Specifically, first, such conventional materials are hard, brittle, and
sharp, making them unsuitable for use as wearable flexible optical waveguide materials; second, these
materials are not biocompatible, which can easily lead to inflammation and immune reactions if they are
used as implantable flexible optical waveguide materials.