Programmable, Soft Optical Waveguide for Optogenetics

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Project Summary The proposed project aims at developing a programmable and soft optical waveguide which will enable precise and uniform light delivery, provide large lateral access, and minimize inflammatory response in the brain tissue. Combination of these functions in one device is highly demanded for maximizing potentials of optogenetics in studying brain functions and treating human’s neurological diseases, but it is still not accessible in current optogenetic probes and their integrated optoelectronic devices. The proposed waveguide will be made of interconnected shanks whose core is a biocompatible shape memory polymer (SMP) cladded by alginate hydrogel layers, which has a lower refractive index (RI) than that of the SMP. This RI mismatch will help to realize total internal reflection of light in the interface of the SMP and the hydrogel layers. Above the phase transition temperature (< 37 ℃), the SMP will become highly transparent and show soft-robotic actuation. This actuation force will drive the highly compact optical waveguide—for easy insertion to the brain tissue—to form a preprogrammed three-dimensional (3D) wavy and expanding shape. With defined optical apertures along the individual shank, the light can be uniformly and precisely delivered to the brain tissue. The inherited biocompatibility and softness of the SMP and the hydrogel will cause little or no inflammatory response to the brain tissue. To our knowledge, it will be the first attempt of developing such a type of optical waveguide. To accomplish the proposed goal optical and mechanical structures of the waveguide will be first designed. Then numerical models will be developed to optimize the static and dynamic actuation processes, which will serve as the sophisticated design principles for the experiments. The optical waveguide will be fabricated, programmed. Its light transport and shape actuation performance will be evaluated. The resulting SMP and alginate hydrogel will have the optimum refractive indices and mechanical properties. Their interface will be strong and smooth for minimizing the light scattering. The waveguide is expected to show satisfactory shape actuation and little light loss in 0.6% agarose hydrogel that mimics the viscoelastic environment of brain tissue. If success, this proposed technology will be transformative. First of all, it will pave the intellectual and technological way to provide a novel platform for implantable devices with new functionalities which other ordinary devices cannot offer, such as truly 3D interfaces, precise and uniform light delivery, minimized damage to the brain. All of them will help to deepen the understanding of brain functions. Moreover, integration of the microelectrodes that can do signal recording with the waveguide will empower the devices the functions of stimulation and recording. They can be further developed into optogenetics-based neuromodulation therapies for treating human’s neurological diseases such as Parkinson’s disease and epilepsy, which are highly relevant to public health. Finally, concepts and technologies of this 3D neural interface introduced here may result in bio- electronic-optoelectronic systems that will show responsive and adaptive features in future.