Opto‐electro‐thermal optimization of photonic probes for optogenetic neural stimulation

Abstract

Implantable photonic probes are of increasing interest to the field of biophotonics and in particular, optogenetic neural stimulation. Active probes with onboard light emissive elements allow for electronic multiplexing and can be manufactured through existing microelectronics methods. However, as the optogenetics field moves towards clinical practice, an important question arises as to whether such probes will cause excessive thermal heating of the surrounding tissue. Light emitting diodes typically produce more heat than light. The resultant temperature rise of the probe surface therefore needs to be maintained under the regulatory limit of 2°C. This work combines optical and thermal modelling, which have been experimental verified. Analysis has been performed on the effect of probe/emitter geometries, emitter, and radiance requirements. Finally, the effective illumination volume has been calculated within thermal limits for different probe emitter types and required thresholds.

The Neural Engine: A Reprogrammable Low Power Platform for Closed-Loop Optogenetics

“…The main purpose of this stage is to convert numerical outcomes from the suppressor into real-world optical intensities and waveforms. These need to take into account, light penetration [6] and Channelrhodopsin (ChR2) encoded cell performance [28]. Also, the efficiency of the LED drive circuit [12], LEDs and optrode electro-thermal-optical characteristics need to be taken into account [6].…”

“…6(b). The developed system was connected to the implantable electrodes with 130k ohm [30], and is enclosed in this holder. Data was recorded using an SD card on the control board.…”

“…Previously discussed implantable electronics have been constrained by battery capacities and thermal issues [6]. This places significant limits on the processing and stimulus.…”

“…To achieve this, there needs to be a platform which can implement closed-loop stimuli within both the constraints of battery operation and thermal output. For the latter, the surface of the implant should not exceed 2O C to stay within the regulatory limits [6]. For the former, the largest rechargeable medical-grade batteries at the time of writing are between 300-350 mAhr (e.g.…”

Nanoparticle-Mediated Upconversion of Near-Infrared Light: A Step Closer to Optogenetic Neuromodulation in Humans

“…Optogenetics has been successfully used to treat Parkinson’s disease, chronic pain, refractory epilepsy and retinitis pigmentosa in different animal models [2]. However, therapeutic deep brain optogenetic neuromodulation in humans is limited by a number of practical challenges, notably the long-term safety of viral vectors used for genetic engineering [8-11], the long-term expression of light-reactive channels in neurons [12], the effective delivery and diffusion of light through brain tissue [13, 14], tissue damage by light-related overheating [13, 14] and the still rudimentary understanding of network dynamics in the human brain [7, 8, 15]. …”