Wireless Magnetoelectrically-Driven Organic Light-Emitting Diodes for Optogenetic Stimulation

Current deep brain stimulation (DBS) devices are commonly based on tethered electrodes that are inserted into deep areas of the brain to treat a variety of different neurological diseases such as Parkinson’s or Alzheimer’s disease. The tethers required for energy transmission account for a large fraction of the volume these devices take up in the brain and thus greatly increase their invasiveness. Different approaches towards wireless implants are currently being pursued, but wireless energy transfer deep into the brain remains challenging due to size, absorption, and power constraints. Induction coils, RF-antennas and magnetoelectric power receivers are currently among the most promising strategies for wireless power supply, with the latter being of particular interest due to its potential for extremely small size.<br/>Although the non-specific stimulation of targeted brain areas through electrical signals can alleviate symptoms of patients for a variety of different diseases, its lack of spatial specificity hinders further understanding of the mechanisms of DBS. Optogenetics, the genetically targeted introduction of light-sensitive ion channels in specific neurons, can partially close this gap. However, targeted light delivery to specific areas of the brain remains an unsolved challenge, in particular for DBS. Recently, organic light-emitting diodes (OLEDs) have arisen as an alternative to the commonly used inorganic light sources [1]. OLEDs can be fabricated on a multitude of different substrates and in almost any shape due to the amorphous character of their constituent layers. While device stability has traditionally been an issue for OLEDs, recent advances in device encapsulation now allow their prolonged use in a biological environment [2].<br/>Here we propose a magnetoelectrically driven OLED that could allow targeted yet wireless light-delivery centimeters deep inside the brain. Red phosphorescent OLEDs with doped-charge transport layers are used to optimize for high-brightness at low power consumption. Furthermore, the OLED device structure is adjusted to efficiently handle the alternating voltage provided by the magnetoelectric supply. The ultrathin OLEDs add negligible volume and weight to the employed magnetoelectric power receivers. To provide sufficient power to drive the OLEDs, we have developed custom-designed hardware and software that generates high frequency magnetic fields, i.e., in the range of several milli tesla in the mid-kilohertz regime. We also optimized the multilayer magnetoelectric laminate structure. In the future, controlling the resonance frequency of the magnetoelectric power receivers will allow to specifically address individual OLEDs within a large ensemble of devices distributed throughout a region of the brain, and thus for spatially controlled light delivery.<br/><br/>[1] Murawski, C. et al. (2020). Segment-Specific Optogenetic Stimulation in Drosophila melanogaster with Linear Arrays of Organic Light-Emitting Diodes. <i>Nature Communications</i>, <i>11</i>(1), 6248.<br/>[2] Keum, C. et al. (2020). A substrateless, flexible, and water-resistant organic light-emitting diode. <i>Nature Communications</i>, <i>11</i>(1), 6250.