Adaptive optical waveguide system for large-area and overheating-preventing phototherapy in deep tissue.

Phototherapy, valued for its non-toxicity, selectivity, and minimal trauma, is predominantly applied to treat superficial diseases due to the limited penetration of light through tissues. While optical-fiber-assisted interventional phototherapy addresses this limitation, it lacks an immediate mechanism to mitigate overheating of surrounding healthy tissues. To improve the biosafety of interventional phototherapy, we develop an adaptive optical waveguide system (AOWS) based on a negative feedback modulation mechanism. The AOWS employs a thermally responsive liquid as the waveguide gating material, characterized by a precisely tunable low critical solution temperature (LCST). When the temperature surpasses the LCST, one-dimensional light propagation is scattered, providing effective thermal regulation. Furthermore, the design supports adjustable optical fiber outlets, with convex or concave configurations and varied curvatures, enabling precise control of the divergence angle. Superior to conventional optical fibers with smaller divergence angles, the AOWS facilitates closer placement to the lesion site, delivering a larger illumination area while significantly reducing the light pathway through normal tissue. More importantly, it provides thermal protection almost like an "on-off" switch without relying on irradiation power, ensuring enhanced safety and efficacy.