Fig. 3: Mechanical and thermal characteristics of soft wireless rechargeable optoelectronic implants.
a Schematic diagram of an implant encapsulated with soft biocompatible polymers (top) and its cross-sectional view (bottom). b Optical images of the implant conformally mounted on a rat skull (left) and a half-cylinder structure with a radius of curvature of 35 mm (right). The insets show the zoomed-in images of the device edge, highlighting perfect conformal integration with the curved surfaces. c Extent of conformal contact on half-cylinder structures with various radii of curvature (5–50 mm) for the devices with silicone gel encapsulation with different thicknesses (tshell = 0.4, 1.4, and 2.4 mm). d Mechanical stress as a function of compression for devices coated with silicone gel with different thicknesses (tshell = 0.4, 1.4, and 2.4 mm). e Transverse effective Young’s modulus (Eeff) of devices coated with three common elastomers (PDMS, Ecoflex, and Ecoflex GEL) as a function of the encapsulation thickness (left) (n = 3). The zoomed-in graph (right) highlights the significantly low effective Young’s modulus of a device with Ecoflex GEL encapsulation, compared with devices coated with PDMS or Ecoflex. Error bars indicate maximum and minimum values. f Infrared images showing surface temperature of devices without (top) and with (bottom) polymer encapsulation before (left) and during (right) wireless charging and μ-ILED operation (40 Hz, 10 ms pulse width). The measurement was made in an ambient environment at room temperature. g Temperature of explanted brain tissue with a μ-ILED operated at different pulse frequencies (5, 10, 20, and 40 Hz; 10 ms pulse width) at 1 mm beneath the tissue surface (inset). To mimic a biological environment, the baseline temperature of the explanted brain tissue was maintained at 36.5 °C using a heater. h Battery voltage level as a function of time during repeated device operation—that is, repetition of wireless charging (60 min) and μ-ILED operating (20 Hz, 10 ms pulse width)—after immersing the devices in saline water with temperatures of 37 °C and 90 °C.
