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Yang et al. Soft Sci. 2025, 5, 46 https://dx.doi.org/10.20517/ss.2025.44 Page 17 of 39

enable diagnosis or monitoring of the above human health signals. To provide readers with a clear overview
before delving into detailed case studies, we summarize in Table 2 the representative categories of flexible
optical waveguides, their performance indicators, and specific biomedical applications. This comparative
summary highlights not only the material and performance characteristics but also examples of how each
category is being applied in invasive biomedical diagnosis and therapy, contact physiological information
monitoring, and interactive soft robots.

This comparative framework not only clarifies the trade-offs among different waveguide platforms in terms
of optical, mechanical, and biological performance but also highlights their translational relevance across
diverse biomedical scenarios. Guided by this framework, the following subsections provide a detailed
analysis of the state-of-the-art applications of flexible optical waveguides in invasive biomedical diagnosis
and therapy, contact physiological information monitoring, and interactive soft robots.

Invasive biomedical diagnosis and therapy
The human immune system is highly exclusive, making biocompatibility or biodegradability crucial for
modern medical devices. Within tissues, photons interact with biological matter through various processes,
[160]
producing various effects on tissues and cells . In this context, flexible optical waveguides fabricated from
different materials for use in invasive biomedical devices have been extensively explored, opening new
possibilities for biomedical applications. Researchers have made notable progress in the use of flexible
optical waveguides for drug delivery, in situ analytical detection, and biomedical therapy.

Drug delivery
Conventional drug delivery systems for tumors and many chronic diseases rely primarily on the passive
transport of small-molecule drugs through the body. The effectiveness of this transport is closely related to
the physicochemical properties of the drug molecule, such as the drug solubility and drug dissociation
constant . However, these physicochemical properties of drugs may lead to limitations in the therapeutic
[161]
[162]
[163]
efficacy for the disease and to excessive accumulation in nontarget organs . Thus, flexible optical
waveguide-based intelligent drug delivery systems that enable controlled release of drugs in the body have
been developed in recent years.

When light is used as a stimulus, optical fibers can be used to remotely manipulate drug release. In addition,
spatial and temporal control of drug release can be achieved by varying the light intensity and exposure time
[45]
to precisely regulate the corresponding dose [164,165] . As shown in Figure 7A , Kurochkin et al. presented a
method for photothermally activating and releasing encapsulated substances from the surface of a
photosensitive polymer 3D microstructured film (PTMF) in picogram quantities in different environments
using laser radiation delivered by multimode optical fibers . Sui et al. presented a novel structured polymer
[45]
optical fiber (POFs) with an ultrahigh numerical aperture (NA) for drug delivery and neuromodulation
field . The optical waveguide developed was made of three polymer materials-polycarbonate (PC),
[156]
polysulfone (PSU), and fluorinated ethylene propylene (FEP)-and had improved flexibility and fiber
lighting angle compared with traditional silicon optical fibers, making it suitable for use as an implantable
material.

In situ analytical detection
In-situ analytical detection plays a crucial role in biomedical diagnostics by enabling real-time monitoring
of analytes such as blood glucose, blood oxygen, and various biomarkers. These analytes provide valuable
insights into the state of health and disease, facilitating early detection and management of conditions such
as diabetes, respiratory distress, and cardiovascular diseases. By integrating waveguides into sensors and