Are Flexible Optical Waveguides the Future of Biomedical Sensors and Wearable Tech?

High-tech robotic biomedical research facility (AI generated) © julija -stock.adobe.com

In a review article published in Advanced Intelligent Systems, researchers Xuechun Wang, Zilong Li, and Lei Su from the School of Engineering and Materials Science at Queen Mary University of London delve into the latest advancements in soft optical waveguides (1–3). Their study highlights how these innovative optical systems could transform biomedical applications, wearable devices, and soft robotics by offering high flexibility, durability, and immunity to electromagnetic interference (1–3).

The Growing Need for Soft Optical Waveguides

As technology advances, the demand for flexible, biocompatible, and precise sensors has surged in fields such as healthcare, wearable electronics, and robotics. Traditional electronic sensors rely on electrical properties such as piezoelectric, capacitive, or resistive changes (1–3). While effective, these methods suffer from electromagnetic interference and limited biocompatibility. Soft optical waveguides, on the other hand, offer a promising alternative by utilizing light as an information carrier, ensuring enhanced sensitivity and durability while maintaining flexibility (1–3).

Material Innovations and Fabrication Techniques

Soft optical waveguides are primarily constructed from hydrogels, naturally derived polymers, and elastomers. Hydrogels, known for their high water content and flexibility, provide excellent optical properties for implantable biomedical sensors. Meanwhile, naturally derived polymers such as silk, agarose, and cellulose present biodegradable options that eliminate the need for surgical removal. Elastomers, highly stretchable and transparent, serve as protective layers for these waveguides (1–3).

In addition to solid-core waveguides, liquid-core optical waveguides have emerged as a cutting-edge innovation. These waveguides, composed of a liquid core encapsulated by a polymer cladding, allow for fine-tuned optical properties and increased adaptability. Fabrication techniques such as soft lithography and photocurable liquid core–fugitive shell printing enable the precise development of these flexible optical systems (1–3).

Spectroscopic Sensing and Actuation Mechanisms

One of the most significant advantages of soft optical waveguides is their ability to perform multimodal sensing through spectroscopic techniques. Sensors utilizing light intensity, pattern shifts, wavelength variations, and phase changes allow for highly sensitive detection of environmental stimuli. For instance, researchers have developed hydrogel-based waveguides doped with carbon dots to detect heavy metal ions such as Hg²⁺ and Pb²⁺, revealing their potential for environmental and biochemical monitoring (1). Soft optical waveguides are also adaptable to 3D printing for rapid customized configurations (3).

Bragg grating-based sensors, another key advancement in optical waveguides, function by embedding fiber Bragg gratings (FBGs) into flexible materials. This technique allows for strain-sensitive sensors that can detect mechanical deformations with high accuracy. One innovative example includes an artificial skin made from stretchable polydimethylsiloxane (PDMS), capable of monitoring compression forces and strain through colorimetric wavelength shifts (1).

Applications in Medicine, Wearables, and Soft Robotics

Soft optical waveguides are poised to redefine several industries. In the biomedical field, they enable real-time physiological monitoring through implantable sensors that minimize immune responses. Wearable technology also benefits from these materials, as flexibility allows integration into clothing or directly onto the skin for continuous health tracking.

Soft robotics is another promising field where optical waveguides enhance sensory feedback and control. By incorporating light-based actuation mechanisms, robots equipped with these waveguides can achieve more natural and adaptive movements, closely mimicking biological organisms (1–3).

Future Challenges and Opportunities

Despite their immense potential, soft optical waveguides face challenges related to manufacturing scalability, optical loss reduction, and multimodal sensing integration. Compared to traditional glass fiber optics, these materials still exhibit higher optical transmission losses, necessitating further optimization of fabrication techniques. Additionally, improving machine learning (ML) algorithms for real-time analysis and adaptive sensing will be critical for their widespread adoption (1–3).

Another major hurdle is durability. Soft materials are more susceptible to environmental fluctuations and mechanical stress, potentially leading to failure. However, advancements in self-healing materials offer a promising solution by allowing these waveguides to recover functionality even after sustaining damage. Such developments could significantly extend the lifespan of soft optical waveguides in real-world applications (1–3).

The research conducted by Wang, Li, and Su highlights the transformative potential of soft optical waveguides in biomedical applications, wearable technology, and robotics. By overcoming current limitations in fabrication, sensing capabilities, and durability, these materials could soon become the foundation for next-generation smart sensors and actuation systems. With ongoing innovations in material science and spectroscopic analysis, soft optical waveguides are set to play a pivotal role in the evolution of flexible and biocompatible technologies (1).

References

(1) Wang, X.; Li, Z.; Su, L. Soft Optical Waveguides for Biomedical Applications, Wearable Devices, and Soft Robotics: A Review. Adv. Intell. Syst. 2024, 6 (1), 2300482. DOI: 10.1002/aisy.202300482

(2) Zhong, L.; Tian, X.; Wang, J. Y.; Wang, J. X.; Nie, Z.; Chen, X.; Peng, Y. Calibration-Free Optical Waveguide Bending Sensor for Soft Robots. Soft Sci. 2025, 5 (1), N-A. DOI: 10.20517/ss.2024.52

(3) Trunin, P.; Cafiso, D.; Beccai, L. Design and 3D Printing of Soft Optical Waveguides Towards Monolithic Perceptive Systems. Addit. Manuf. 2025, 104687. DOI: 10.1016/j.addma.2025.104687