Deep brain temperature sensing using polymer fiber Bragg grating implants

In this work, we developed a polymer fiber Bragg grating (FBG) based brain implant for in vivo local brain temperature sensing. The Poly(methyl methacrylate) (PMMA) fiber was fabricated with the thermal drawing method, and the Bragg grating structure was inscribed into the core of the fiber with the phase mask inscription technique. An ethylene propylene (FEP) tube was sleeved outside of the PMMA fibers to reduce the cross-sensitivity with humidity and strain during brain temperature measurements. The assembled FBG implant exhibited a sensitivity of 33 pm/°C. An in vivo experiment was carried out to differentiate the temperature of three brain regions. The results show that the rat brain temperature in the deep region is higher than its cortical region, with a linear relationship between temperature and depth. By comparing the brain temperature (sensed by the FBG implant) and body core temperature (measured by a standard rectal thermometer), we have found a time delay of the turning point between them when artificially inducing body heat loss and heat restoration. The experimental results on rodent models suggests that the proposed FBG implant can be used as an effective tool for temperature sensing in deep brain regions.