Extended Data Fig. 2: Fabrication and design specifications of the in-ear integrated sensors. | Nature Biomedical Engineering

Extended Data Fig. 2: Fabrication and design specifications of the in-ear integrated sensors.

From: In-ear integrated sensor array for the continuous monitoring of brain activity and of lactate in sweat

Extended Data Fig. 2

a–l. Fabrication procedure. (a) Print and cure (60 °C for 10 minutes) the stretchable Ag interconnection layer with the corresponding stencil. (b) Print and cure (60 °C for 10 minutes) the SEBS insulation layer with the corresponding stencil. (c) Print and cure (60 °C for 10 minutes) the stretchable PB layer for lactate sensing WE and CE with the corresponding stencil. (d) Mold and cure (room temperature for 30 minutes) the 3D electrophysiological electrodes with a 3D printed PLA mold. (e) Drop cast and fill the 3D electrophysiological electrode back holes with the SEBS. (f) Adhere a piece of double-sided medical tape onto the back of the sensor enclosing the SEBS backing. (g) Cut the profile of the sensor. (h) Align and adhere the flexible PCB to the bonding pads. (i) Fill silver epoxy onto a piece of Kapton tape with openings aligned to the sensor’s bonding pads. (j) Release the Kapton tape to cure and pattern the silver epoxy onto corresponding bonding pads. (k) Peel off the release liner of the medical tape at the back, assemble the sensor onto the targeted location of the earphone, and install the earphone hook as fixation. (l) Adhere the PVA hydrogel and modify the lactate electrodes with LOx. m–p. Pattern design of each layer. (m) Substrate TPU layer. (n) Interconnection stretchable Ag layer. (o) Insulation SEBS layer. (p) Electrochemical electrode stretchable PB layer. q–s. 3D electrophysiological electrode design. (q) Air gap observed for the earphone’s silicone tip to the ear canal. (r) Design principle of the 3D electrophysiological electrode with ‘spring-loaded’ backing. (s) Finite element simulation of the 3D electrophysiological electrode structure showing the curved back hole formation via thermal expansion coefficient mismatch between the TPU and the stretchable Ag ink. t. 3D printed PLA mold structure. u–v. Molded 3D electrophysiological electrode (u) before and (v) after curing. w–x. Silicone earphone hook stretchable Ag ink modification, (w) REF and DRL exposed wire location. (x) Cured stretchable Ag electrodes on the earphone hook. y. Connecting flexible PCB layer by layer design.

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