Design and fabrication of degradation resistant hydrogel optical fibers for potential long-term usage of photomedicine in deep-tissue

Hydrogel optical fiber has attracted attention in the fields of photomedicine in deep-tissue due to its biocompatibility, such as soft wet nature, tissue-like modulus, and low toxicity. Owing to its distinctive optical properties and the ease of crosslinking, PEGDA is commonly employed in the fabrication of hydrogel optical fibers with high light-guiding efficiency. However, due to the hydrolysis susceptibility of ester bonds, these hydrogel optical fibers tend to degrade rapidly in physiological environments, which may compromise their long-term functionality. Additionally, the development of a light transmission device that can operate long-term, efficiently and stably in the internal environment is expected to further promote the progress of photomedicine. In this work, we introduce a degradation-resistant hydrogel optical fiber (DRHOF) with high optical transmission. In the preparation process, we replace the ester bond in the polymer molecular chain with an amide bond with higher activation energy to achieve a longer degradation period. In addition, the sheath/core structured hydrogel fiber is prepared continuously by a coaxial needle, and the refractive index (RI) of the sheath/core spinning liquid is regulated to achieve low optical attenuation (0.12 ± 0.01 dB cm⁻¹ with 650 nm laser). It has lower cytotoxicity and causes less tissue inflammation after implantation than conventional polymer fibers. In terms of mechanical properties, its Young's modulus is adjustable between 0.08 MPa ∼ 0.41 MPa, which is similar to the modulus of the soft tissue. Thus, the DRHOF demonstrates the great potential being used as a highly effective tool for application in the field of photomedicine.

Statement of significance

The fabricated DRHOF exhibits resistance to degradation and biocompatibility, which can maintain the structural integrity within the muscle tissue without causing severe inflammation for at least three months.

The fabricated DRHOF shows a light attenuation of 0.12 ± 0.01 dB cm⁻¹ (λ=650 nm).

After three months in a simulated human body environment, light attenuation remained at 0.156 dB cm⁻¹, showing that DRHOF is suitable for long-term photomedicine in deep tissues.