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Page 28 of 43 Wang et al. Soft Sci 2024;4:41 https://dx.doi.org/10.20517/ss.2024.53

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positioning .

The need for miniature and flexible robots for precise instrument guidance in minimally invasive surgeries
is growing, and fiber robots present a viable solution. For instance, the ferromagnetic soft catheter robot
[214]
(FSCR) system enables minimally invasive in situ bioprinting within living organisms . By incorporating
ferromagnetic particles into a fiber-reinforced polymer matrix, the system successfully achieved in vivo
hydrogel printing in a rat model [Figure 12G]. Similarly, Abdelaziz et al. developed a polymer-based robotic
fiber using a fiber-drawing technique, with thermal actuation achieved through localized heating along the
fiber’s length. This fiber robot exhibits excellent motion accuracy and repeatability, making it a promising
tool for delicate surgical procedures [Figure 12H and I]. Overall, both sensors at the tips of surgical
[112]
instruments and fibric surgical robots have markedly enhanced the precision and safety of minimally
invasive surgery. This advancement reduces the risks associated with traditional surgical methods by
enabling real-time monitoring of the surgical environment and tool positioning.

Implantable probe bioelectronics
Implantable SEEG and DBS electrodes
Implantable neuroelectrodes refer to electrophysiological devices that are implanted within a biological
organism and connected to it for the purposes of recording and stimulation . They are particularly
[215]
valuable in the diagnosis and treatment of neurological disorders, including epilepsy, migraines, and other
related conditions . Implantable neuroelectrodes can be categorized based on their functions into two
[115]
main types: Recording Electrodes: These include SEEG electrodes, which capture electroencephalogram
signals through deep electrodes surgically implanted within brain tissue . Stimulation Electrodes: These
[37]
encompass DBS electrodes, which, following the recording of nervous system signals, provide electrical
[33]
stimulation aimed at treating neurological disorders .
SEEG electrodes are surgically implanted into brain tissue to record electroencephalography (EEG) signals,
which reflect collective transmembrane currents from multiple neurons, as well as action potentials from
individual neurons or single units . The basic dimensions of these electrodes range from 0.8 to 1.23 mm.
[37]
[49]
Fiath et al. employed a SEEG electrode fabricated based on the PI film . This micro-cylindrical SEEG
electrode, with a diameter of 800 μm, was created by depositing a metal layer, such as platinum (Pt), on its
surface and employing a thin-film convolution process [Figure 13A]. However, this SEEG electrode was
limited to only 32 channels, which is relatively low. Pothof et al. employed time-domain multiplexing
(TDM), reducing the number of leads by a 16:1 ratio while increasing the number of channels to 128 .
[216]
TDM allows external signals measured by multiple electrodes to be used as input signals and transmitted
from the same output channel, greatly compressing the position occupied by the electrode leads [216,217]
[Figure 13B and C]. Further, Steinmetz et al. proposed a neural pixel probe fabricated using complementary
metal-oxide-semiconductor (CMOS) technology, which combines TDM with a very high integration of
1,280 channels in a single shank . In addition to the number of electrodes, the density of SEEG electrodes
[218]
is also an important metric, and increasing the electrode density by decreasing the size of individual
electrodes can improve the resolution of SEEG monitoring and even sense the electrical activity of a single
neuron . In 2021, Gerbella et al. designed a neuroelectrode combining macroelectrodes and
[37]
microelectrodes , which saves the space occupied by the electrodes, improves the electrode density, and
[48]
enhances the limit of the electrode’s perceptual resolution. Recently, Liu et al. proposed a neural probe with
an extremely high number of channels (1024) , very high stability (> 105 weeks) and reusability
[32]
[Figure 13D and E]. Therefore, the current mainstream research direction of SEEG electrodes is to further
improve the number and density of recording sites on a single-shank probe, the recording accuracy of a
single recording site, and the stability and effectiveness of long-time recording of the probe by combining
multiple fabrication techniques.