Nature BE: Shengxing team at Tsinghua University and others found that thin-film silicon photodiodes can selectively activate or inhibit neural activity

The development of new neural regulation technologies to activate and/or inhibit the activity of individual neurons or specific neural networks in real time and accurately is of great significance
for in-depth understanding of the working mechanism of the brain and the development of neurological disease treatment methods.
Compared with biochemical methods such as drugs, neural regulation methods based on physical fields such as photoelectric signals have the advantages of wireless control, high spatiotemporal resolution, fast response and low side effects, and have also been a research hotspot
in the field of brain-computer interface in recent years.

Recently, Tsinghua University, Tsinghua University Department of Electronics, Tsinghua-IDG/McGovern Institute of Brain Science Associate Professor Sheng Xing, Chinese Academy of Sciences Shenzhen Institute of Advanced Technology, Shenzhen-Hong Kong Institute of Brain Science Innovation Institute Li Xiaojian, researcher Li Xiaojian, Beijing Institute of Technology Associate Researcher Wang Shirong, as co-corresponding authors, published in Nature Biomedical Engineering title: Bioresorbable thin-film silicon diodes for the optoelectronic excitation and inhibition of neural activities
.

The study uses a flexible thin film single crystal silicon diode integrated with the nervous system to generate a polarized electric field under illumination to selectively activate and suppress
in vitro and in vivo neural signals.
At the same time, the thin film silicon structure can be safely degraded in vivo and has good biocompatibility
.
This bio-friendly, non-genetic, wireless remote operation, activation-inhibition bidirectional photoelectric control implantable device can provide effective technical support
for basic neuroscience research and clinical applications.

Silicon-based semiconductors are the cornerstone of the information industry, and the PN diode structure, as the basic unit of electronic engineering, is widely used in microelectronic chips, photoelectric detection and imaging, photovoltaic cells and other systems
.
In biological systems, when silicon-based diodes bind to neurons, the basic unit of the nervous system, how do their photoelectric properties affect the activity and function of the nervous system?

The research team found that when the flexible thin film silicon-based diode structure is integrated with neural tissue, it generates a polarized photogenerated electric field at the semiconductor-solution interface under light conditions, and can selectively activate and inhibit the activity of
nerve signals without introducing gene coding tools such as optogenetics.

Figure 1.
Degradable silicon thin-film diodes generate photoelectric signals to activate and inhibit neural activity (schematic)

In ex vivo experiments, by cultivating dorsal root ganglion (DRG) on the surface of thin-film silicon diode structures (p+n-type and n+p-type) with different polarities, the polarized photogenerated electric field of silicon devices can correspondingly raise or decrease the membrane potential of cells, cause depolarization or hyperpolarization of neurons, further activate or inhibit the release of action potentials, and cause the rise or fall
of calcium activity signals.

Figure 2.
Photovoltage polarity-dependent activation and inhibition of ex vivo neuronal activity in silicon thin-film diodes

The patterned silicon-based thin film devices prepared by micro-nano process can be conformally attached to the surface of living biological tissues for remote photoelectric regulation
of in vivo biological nerve signals.
The silicon-based diode film is coated in the sciatic ganglia of mice, and the motor amplitude
of the hind limbs of mice can be selectively enhanced or weakened by polarity-dependent photogenerated electric fields.
By attaching a silicon-based diode film to the mouse cerebral cortex, the photogenerated electric field can also activate or inhibit the electrical activity
of the cortex accordingly.

Figure 3.
Photovoltage-dependent activation and inhibition of the in vivo nerves of silicon thin-film diodes: (a) regulation of activation and inhibition of sciatic nerve activities and (b) regulation of activation and inhibition of activities in neural regions within the cerebral cortex

In addition, silicon-based semiconductors also have good biosafety and degradable characteristics, the silicon thin film device is combined with a degradable substrate, it is coated in the sciatic nerve of animals or attached to the cerebral cortex, through long-term experimental records, the natural dissolution and disappearance process
of silicon film in the organism can be observed.
This degradable property, which avoids the risks associated with introducing secondary surgical removal of implants, offers potential prospects
for specific medical applications.

Image

Figure 4.
Biodegradability test of silicon films on the sciatic nerve and cerebral cortex

Huang Yunxiang, former postdoctoral fellow of Tsinghua University, Cui Yuting, postdoctoral fellow of Beijing Institute of Biological Sciences, and Deng Hanjie, technician of Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, are the co-first authors
of the paper.
Associate Professor Sheng Xing, Department of Electronics, Tsinghua University, Tsinghua-IDG/McGovern Institute of Brain Science, Li Xiaojian, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen-Hong Kong Institute of Brain Science Innovation, and Wang Shirong, associate researcher of Beijing Institute of Technology, are the co-corresponding authors
of the paper.

Original source:

Huang， Y.
， Cui， Y.
， Deng， H.
et al.
Bioresorbable thin-film silicon diodes for the optoelectronic excitation and inhibition of neural activities.
Nat.
Biomed.
Eng (2022).
https：//doi.
org/10.
1038/s41551-022-00931-0.