Wireless Optogenetic Nanonetworks for Brain Stimulation: Device Model and Charging Protocols

Functional nanotransducer-mediated wireless neural modulation techniques

Functional nanomaterials have emerged as versatile nanotransducers for wireless neural modulation because of their minimal invasion and high spatiotemporal resolution. The nanotransducers can convert external excitation sources (e.g. NIR light, x-rays, and magnetic fields) to visible light (or local heat) to activate optogenetic opsins and thermosensitive ion channels for neuromodulation. The present review provides insights into the fundamentals of the mostly used functional nanomaterials in wireless neuromodulation including upconversion nanoparticles, nanoscintillators, and magnetic nanoparticles. We further discussed the recent developments in design strategies of functional nanomaterials with enhanced energy conversion performance that have greatly expanded the field of neuromodulation. We summarized the applications of functional nanomaterials-mediated wireless neuromodulation techniques, including exciting/silencing neurons, modulating brain activity, controlling motor behaviors, and regulating peripheral organ function in mice. Finally, we discussed some key considerations in functional nanotransducer-mediated wireless neuromodulation along with the current challenges and future directions.

Feed-Forward and Feedback Control in Astrocytes for Ca 2+-Based Molecular Communications Nanonetworks

Synaptic plasticity depends on the gliotransmitters' concentration in the synaptic channel. And, an abnormal concentration of gliotransmitters is linked to neurodegenerative diseases, including Alzheimer's, Parkinson's, and epilepsy. In this paper, a theoretical investigation of the cause of the abnormal concentration of gliotransmitters and how to achieve its control is presented through a Ca ²⁺-signalling-based molecular communications framework. A feed-forward and feedback control technique is used to manipulate IP ₃ values to stabilize the concentration of Ca ²⁺ inside the astrocytes. The theoretical analysis of the given model aims i) to stabilize the Ca ²⁺ concentration around a particular desired level in order to prevent abnormal gliotransmitters' concentration (extremely high or low concentration can result in neurodegeneration), ii) to improve the molecular communication performance that utilizes Ca ²⁺ signalling, and maintain gliotransmitters' regulation remotely. It shows that the refractory periods from Ca ²⁺ can be maintained to lower the noise propagation resulting in smaller time-slots for bit transmission, which can also improve the delay and gain performances. The proposed approach can potentially lead to novel nanomedicine solutions for the treatment of neurodegenerative diseases, where a combination of nanotechnology and gene therapy approaches can be used to elicit the regulated Ca ²⁺ signalling in astrocytes, ultimately improving neuronal activity.

Analysis of Light Propagation on Physiological Properties of Neurons for Nanoscale Optogenetics

Miniaturization of implantable devices is an important challenge for future brain-computer interface applications, and in particular for achieving precise neuron stimulation. For stimulation that utilizes light, i.e., optogenetics, the light propagation behavior and interaction at the nanoscale with elements within the neuron is an important factor that needs to be considered when designing the device. This paper analyzes the effect of light behavior for a single neuron stimulation and focuses on the impact from different cell shapes. Based on the Mie scattering theory, the paper analyzes how the shape of the soma and the nucleus contributes to the focusing effect resulting in an intensity increase, which ensures that neurons can assist in transferring light through the tissue toward the target cells. At the same time, this intensity increase can in turn also stimulate neighboring cells leading to interference within the neural circuits. This paper also analyzes the ideal placements of the device with respect to the angle and position within the cortex that can enable axonal biophoton communications, which can contain light within the cell to avoid the interference.