Flexible multimaterial polymer fiber implants for integrated brain interrogation: enlarged illumination, bidirectional interfaces, and deep-brain temperature sensing

Neural interfaces capable of efficient simultaneous modulation and sensing in neural circuits remain constrained by inadequate mechanical compliance and limited multifunctional integration within a single implant. Here, we present an overview of unified neurophotonic platform based on soft, thermally drawn multimaterial polymer optical fibers (POFs). The platform enables high-numerical aperture (NA) optical neuromodulation, bidirectional optoelectronic interfacing, and deep-tissue physiological sensing. The large refractive index contrast between the core and cladding materials results in an ultra-high NA in the step-index fibers, leading to expanded illumination profiles. Embedded microfluidic channels enable controlled drug delivery, while integrated tungsten or liquid-metal electrodes allow concurrent electrophysiological recording. In addition, polymer fiber Bragg gratings inscribed in the fiber core enable high-resolution deep-tissue temperature sensing. The functionality of the interface has been validated in rodents. This approach provides a scalable strategy for minimally invasive and localized interrogation of neural circuits in deep tissue.