Wireless, battery-free subdermally implantable photometry systems for chronic recording of neural dynamics

Abstract

Recording cell-specific neuronal activity while monitoring behaviors of freely moving subjects can provide some of the most significant insights into brain function. Current means for monitoring calcium dynamics in genetically targeted populations of neurons rely on delivery of light and recording of fluorescent signals through optical fibers that can reduce subject mobility, induce motion artifacts, and limit experimental paradigms to isolated subjects in open, two-dimensional (2D) spaces. Wireless alternatives eliminate constraints associated with optical fibers, but their use of head stages with batteries adds bulk and weight that can affect behaviors, with limited operational lifetimes. The systems introduced here avoid drawbacks of both types of technologies, by combining highly miniaturized electronics and energy harvesters with injectable photometric modules in a class of fully wireless, battery-free photometer that is fully implantable subdermally to allow for the interrogation of neural dynamics in freely behaving subjects, without limitations set by fiber optic tethers or operational lifetimes constrained by traditional power supplies. The unique capabilities of these systems, their compatibility with magnetic resonant imaging and computed tomography and the ability to manufacture them with techniques in widespread use for consumer electronics, suggest a potential for broad adoption in neuroscience research.

A Review: Electrode and Packaging Materials for Neurophysiology Recording Implants

“…Metals are the most prevailing and common electrode materials for neural recording for nearly 50 years (Kim et al, 2018 ). Widely used metal electrode materials, such as Au, platinum (Pt), iridium (Ir), tungsten (W), and tantalum (Ta), offer a great number of desirable properties, including chemical inertness, high electrical conductivity, and excellent biocompatibility in biological environments (Barrese et al, 2016 ; Won et al, 2018 ; Burton et al, 2020 ). Au/Pt and Ir/Pt have been used as the electrode materials for “Utah array” and “Michigan Probe,” two of the most popular neural interface electrodes (House et al, 2006 ; Kim et al, 2010a ).…”

Multifunctional Flexible Biointerfaces for Simultaneous Colocalized Optophysiology and Electrophysiology

“…[ 1,2 ] Advances in microelectronics have allowed the development of high‐resolution microelectrode arrays for electrophysiological monitoring and stimulation. Recently, optical techniques with high spatial resolution such as optogenetics, [ 3 ] calcium imaging, [ 4 ] and photometry [ 5,6 ] have been developed, allowing for optophysiology to serve as an alternative to electrophysiology for biomedical research. For example, optogenetics is an emerging technique that uses light to control the activity of genetically modified cells, such as neurons and cardiomyocytes.…”

Advanced Electrical and Optical Microsystems for Biointerfacing

“…In addition to optogenetics, optical recording technologies represent crucial tools that are broadly adopted for monitoring of physiological information and improving diagnosis and treatment of diseases. Recent advances in flexible and stretchable optoelectronic devices enable comfortable and conformal attachment on the human skin [ 94,178 ] or minimally invasive implantable applications in the brain of animals [ 157,179 ] to achieve continuous and accurate optical measurements. Compared with electrical recording platforms, optical recording has unique features such as deeper penetration depths in tissues, higher spatial and spectral resolutions, etc.…”

“…More recently, we further developed a wireless, battery‐free fully implantable photometry system (Figure 10e). [ 179 ] The system avoids the use of head‐mounted batteries and is instead powered wirelessly by magnetic resonant coupling between a primary antenna in the environment and a secondary receiving antenna in the device. This feature reduces the overall device weight to 45 mg and allows chronic stable operations without concerns from the limited operational lifetimes associated with batteries.…”