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Kim et al. Soft Sci 2023;3:18 https://dx.doi.org/10.20517/ss.2023.08 Page 7 of 19

Acute visual evoked potentialactivation test
The in vivo experiment was conducted in 6-week-old Sprague-Dawley rats. The rodents were first
anesthetized via an intramuscular injection of a ketamine/xylazine, and the head was fixated on a Model 900
stereotaxic instrument (David Kopf Instrument, Inc., Los Angeles, CA, USA) . The hair and scalp were
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shaved using a razor blade and incised using operating scissors, respectively. The skull was drilled into an
oval shape using an electrical tool (Strong 207s; Saeshin, Inc., Daegu, Korea), followed by removing the
trimmed fragment and securing the cortical area.

For the ECoG monitoring from visual evoked potential (VEP), the prepared ICH arrays coupled with a
customized adaptor were connected to a Digital Lynx SX neural recording instrument (Neuralynx, Inc.,
Bozeman, MT, USA). The soft device was conformally mounted onto the epidural surface area, and ICH
was injected into the four previously punched channels. Two stainless-steel screws were placed over the
frontal lobe as the reference and ground. Prior to VEP activation, baseline ECoG signals were sufficiently
accumulated for 5 min. After the baseline signal recordings, the anesthetized rodents were subjected to dark
adaptation for 5 min, followed by event-related potential activation from the visual cortex test for 5 min.

The VEP activation test in the left hemisphere is as follows: light stimulation was conducted at 0.2 Hz
frequency in the right eye of the rodent using a green LED with the left eye blinded by a black fabric sheet.
The documented neural signal data were processed and analyzed using MATLAB.

In vivo degradation of ICH
To evaluate the biodegradation of ICH in vivo, 1 mL of ICH was injected onto the surface of the secured left
hemisphere of anesthetized rodents. Immediately after the injection, the brain was sealed with the
previously cut skull to embed the hydrogel using UV-curable medical glue. The scalp was then sutured, and
the rodent was left to recover from sedation.

Magnetic resonance imaging of the device-implanted rodents
All MRI experiments were performed using a Bruker Biospec 9.4 T/30 cm bore (Bruker, Billerica, MA,
USA). The rodents were first sedated with isoflurane, and the head was positioned at the isocenter of the
magnet. A birdcage RF coil with an inner diameter of 86 mm was used to produce circular polarization, and
a Bruker planar surface coil with an inner diameter of 10 mm was mounted directly on the cradle and
positioned above the brain for detection. Magnetic resonance imaging (MRI) measurements were taken in
the axial and coronal planes, and the images were processed and evaluated using ImageJ for the qualitative
evaluation of the electrode array and the in vivo degradation of the ICH.

Brain extraction and histology
Four weeks after ICH implantation, the rodents were sedated with isoflurane. The completely anesthetized
rodents were then cut open below the diaphragm, and the rib cage was cut to expose the heart. A needle
mounted on a 50-mL syringe filled with saline solution was inserted into the left ventricle, and a small
incision was made in the right atrium. Perfusion was performed by injecting 150 mL of saline solution. The
head was then decapitated, and the bones and skin were carefully removed to extract the cerebral cortex.
The extracted brains were then fixed in 4% paraformaldehyde for 24 h at room temperature.

Next, the fixed brains were sliced and stained with hematoxylin and eosin (H&E) and Masson’s trichrome
(MT) staining at Genoss Co., Ltd. (Suwon, South Korea). The stained specimen was imaged using an optical
microscope for the evaluation of diseased cells, tissues, and fibrosis.