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. 2023 Feb 18;14(2):476.
doi: 10.3390/mi14020476.

Fabrication and Assembly Techniques for Sub-mm Battery-Free Epicortical Implants

Adam Khalifa  1 , Mehdi Nasrollahpour  2 , Ali Nezaratizadeh  1 , Xiao Sha  3 , Milutin Stanaćević  3 , Nian X Sun  2 , Sydney S Cash  4
Affiliations

Fabrication and Assembly Techniques for Sub-mm Battery-Free Epicortical Implants

Adam Khalifa et al. Micromachines (Basel). .

Abstract

Over the past three decades, we have seen significant advances in the field of wireless implantable medical devices (IMDs) that can interact with the nervous system. To further improve the stability, safety, and distribution of these interfaces, a new class of implantable devices is being developed: single-channel, sub-mm scale, and wireless microelectronic devices. In this research, we describe a new and simple technique for fabricating and assembling a sub-mm, wirelessly powered stimulating implant. The implant consists of an ASIC measuring 900 × 450 × 80 µm3, two PEDOT-coated microelectrodes, an SMD inductor, and a SU-8 coating. The microelectrodes and SMD are directly mounted onto the ASIC. The ultra-small device is powered using electromagnetic (EM) waves in the near-field using a two-coil inductive link and demonstrates a maximum achievable power transfer efficiency (PTE) of 0.17% in the air with a coil separation of 0.5 cm. In vivo experiments conducted on an anesthetized rat verified the efficiency of stimulation.

Keywords: distributed; neural stimulation; wireless power transmission.

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Conflict of interest statement

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

Figures

Figure 1
Figure 1
A conceptual diagram of the distributed interface using epicortical, single-channel, wireless implants.
Figure 2
Figure 2
A schematic diagram of the entire system and a micrograph of the ASIC.
Figure 3
Figure 3
(a) HFSS simulation model of the wireless power link, (b) drawing/picture of the experimental setup used to measure the rectified voltage, and (c) drawing of the experimental setup used to measure the S12, S11, and S22 parameters. For both testbench setups, the Tx–Rx distance was set to 5 mm.
Figure 4
Figure 4
Detailed flowchart of the complete fabrication and assembly process flow of the epicortical IMD and pictures showing some of the steps. The scale bar measures 200 µm.
Figure 5
Figure 5
(Left) Measured rectified voltage and (Right) current through the load when the device is wirelessly powered at a distance of 5 mm and connected to an RC load (representing the microelectrode).
Figure 6
Figure 6
Measured S22 parameters plotted on a Smith chart without (a) and with (b) the SMD inductor. Z22 values are displayed for 1.17 GHz.
Figure 7
Figure 7
(a) Simulated and (b) measured S11, S12, S22 parameters of a 2-coil inductive link through air with 5 mm Tx–Rx separation. (c) Simulated and measured PTEmax as a function of Tx–Rx distance.
Figure 8
Figure 8
Impedance spectra comparing PEDOT-coated stainless steel electrode with the uncoated stainless steel electrode.
Figure 9
Figure 9
Technology validation using immunofluorescence imaging: Picture of the rat experiment during wireless stimulation. c-Fos expression in the left (control) and right (stimulated) hemispheres of a rat brain. Scale bar is 100 µm.
See this image and copyright information in PMC

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