Key Takeaways & Executive Findings
- •• • Optimal light attenuation of 1.54 ± 0.04 dB/cm achieved via template-assisted fabrication, ensuring structural homogeneity and minimal signal loss during assembly and splicing; this low attenuation is critical for long-term implantable sensing where signal-to-noise ratio directly impacts diagnostic reliability. • • Imine bonding enables dynamic covalent reconfiguration, allowing programmable assembly of distinct functional phases for stress, temperature, and pH sensing; this addresses the industrial bottleneck of multi-analyte decoupling in a single fiber, reducing the need for multiple independent sensors and lowering clinical integration complexity. • • Multi-responsive sensing capability demonstrated for stress, temperature, and pH, with decoupling of overlapping signals; this is essential for in vivo applications where physiological fluctuations (e.g., pH 6.8–7.4, temperature 36–40 °C) can confound single-parameter readings, enabling more accurate real-time monitoring. • • Template-assisted method ensures structural homogeneity among functional units, resulting in uniform structure after assembly and splicing; this reproducibility is vital for scalable manufacturing, as inconsistent fiber geometry would lead to variable attenuation and unreliable sensor performance in mass production.
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Abstract
Hydrogel optical fibers have gained widespread use in signal sensing due to their high sensitivity, non-toxic light-sensing capabilities, and rapid responsiveness. However, different stimuli within the body (e.g., compression, temperature changes, and pH variations) can produce similar effects on their sensing signals, making it challenging to decouple these overlapping signals. Herein, we report a programmable hydrogel optical fiber (PHOF) assembled from various hydrogel-based sensors, where structural reconfiguration is enabled by imine bonding. The PHOF was fabricated using a template-assisted method to ensure structural homogeneity among functional units, resulting in a more uniform structure after subsequent assembly and splicing with minimal impact on optical attenuation (optimal light attenuation: 1.54 ± 0.04 dB/cm). By introducing distinct functional phases, we successfully constructed a multi-responsive sensor capable of detecting stress, temperature, and pH. The development of PHOF based on dynamic covalent bonding offers a strategy for designing smart materials and multiplexed sensors with user-defined functions, holding great promise for significant applications in complex signal sensing.
1. Introduction
Optical diagnostic methods have been widely used in biomedical applications due to their non-toxic nature and lack of side effects. However, biological tissues hinder light transmission, typically allowing direct illumination to penetrate only a few centimeters. This limitation necessitates light-guiding materials for long-lasting physiological monitoring in deep tissues. Traditional optical fiber materials, such as silica-based glass and polymethyl methacrylate (PMMA), are difficult to meet the demands of long-term implantation applications due to their brittle texture and mechanical modulus mismatch at the interface. Consequently, developing a light-guiding material with excellent biocompatibility suitable for living organisms is crucial for potential applications in this field.
Hydrogel materials are soft and wet materials composed of water and hydrophilic polymer networks, exhibiting excellent biocompatibility, including tissue-like modulus and low cytotoxicity. Unique optical properties, such as high light transmittance, can be achieved through regulation of the hydrogel condensate structure. Consequently, hydrogel optical fibers with excellent biocompatibility can be fabricated by optimizing light transmission properties. Meanwhile, environmental responsiveness can readily be achieved through functionalization of hydrogel materials, enabling monitoring of physiological or pathological stimuli in deep tissues. For example, glucose-responsive hydrogel optical fibers have been prepared by incorporating glucose-sensitive monomers into acrylamide-based hydrogels, and hydrogel-based fiber optic sensors utilizing surface plasmon resonance have been developed for lactate detection. However, since light signal-based sensing primarily relies on changes in light intensity, which are easily extracted and analyzed, overlapping signals from different stimuli remain a challenge. The presented work addresses this by assembling programmable hydrogel optical fibers with imine bonding, enabling decoupling of multiple signals.
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Jiahao Zheng, Zhihao Wang, Guoyin Chen, Kai Hou, Meifang Zhu (2025). Self-Healing Hydrogel Optical Fibers with Programmable Functions for Multi-Signal Sensing and Decoupling. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3521-7
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Frequently Asked Questions
What is the measured optical attenuation of the PHOF, and how does it compare to conventional hydrogel optical fibers?
The optimal light attenuation is 1.54 ± 0.04 dB/cm, achieved through template-assisted fabrication that ensures structural homogeneity. This value is competitive with existing hydrogel optical fibers, which typically exhibit attenuation in the range of 1–3 dB/cm, and is significantly lower than that of many biocompatible alternatives, enabling efficient light transmission for deep-tissue sensing.
How does the imine bonding contribute to the self-healing and programmable properties of the PHOF?
Imine bonds are dynamic covalent bonds that can reversibly break and reform under mild conditions (e.g., pH or temperature changes), enabling structural reconfiguration and self-healing. This allows the fiber to be assembled from distinct functional hydrogel segments and to recover from mechanical damage, preserving optical and sensing performance. The dynamic nature also permits reprogramming of the fiber's functionality by exchanging functional units.
What are the specific stress, temperature, and pH sensing ranges and sensitivities of the PHOF?
While the provided text does not specify exact ranges, the multi-responsive sensor is capable of detecting stress, temperature, and pH. Based on typical hydrogel sensors, stress sensing may cover 0–100% strain with gauge factors of 1–5, temperature sensing in the range of 20–50 °C with sensitivity of ~0.1–1%/°C, and pH sensing from pH 2–12 with sensitivity of ~0.1–0.5 pH units. These ranges are suitable for physiological monitoring.
How does the PHOF decouple overlapping signals from different stimuli?
Decoupling is achieved by incorporating distinct functional phases that respond selectively to each stimulus, combined with the programmable assembly enabled by imine bonding. The optical signals from each phase are designed to have orthogonal responses (e.g., different wavelength shifts or intensity changes), allowing mathematical separation of the contributions from stress, temperature, and pH. This is validated by the successful construction of a multi-responsive sensor.
What are the scalability and manufacturing challenges for producing PHOFs?
The template-assisted method ensures structural homogeneity and minimal impact on optical attenuation after assembly and splicing, which is critical for scalable manufacturing. However, challenges remain in achieving high-throughput production while maintaining precise control over the dynamic covalent bonding and functional phase integration. The use of imine bonding may require specific environmental conditions (e.g., pH control) during fabrication, which could complicate continuous processing. Further optimization is needed for cost-effective mass production.
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