Window to the Nervous System

New material developed in a joint study between the Technion and the University of Chicago paves the way for restoring damaged nerve tissue and heart pacing through an external light source on the body. It is based on the concept that light projected into the body (near-infrared) will hit a membrane made of the new material, which will photo-activate the damaged nerve tissue or heart. The study, published in Nature Materials, was led by Assistant Professor Hemi Rotenberg of the Faculty of Biomedical Engineering at the Technion and Professor Bozhi Tian of the University of Chicago.

Nerve tissues are the biological platform that transmits information between different areas of the body. Most of them are found in the two control centers of the central nervous system: the brain and spinal cord. The peripheral nervous system stems from the central nervous system, controlling many physical activities, including muscle activation and the transmission of sensory information.

Damage to the peripheral nervous system can lead to limitations such as paralysis, numbness and chronic pain. Although peripheral nerves can undergo regeneration, this is a slow process with limited outcome. However, some medical interventions may enhance rehabilitation.

One solution for the treatment of damaged nerves is electrical stimulation, the effectiveness of which has been demonstrated in many studies. The problem is that this method usually involves invasive procedures that can damage the body’s tissues. The development by Prof. Rotenberg may eliminate the need for electrode transplantation.

Researchers at the Technion and the University of Chicago created a new semiconductor device in a flexible, ultra-thin membrane configuration that interfaces well with biological tissues. The idea is to use this membrane to wrap the damaged nerve tissue or in the case of heart pacing – wrap the heart itself. This step will be carried out as part of the surgery that is necessary in any case in the event of such vulnerabilities.

Asst. Prof. Hemi Rotenberg

“Our development is a photovoltaic material, that is, material that converts light energy into electrical energy that affects nerve tissue,” explained Prof. Rotenberg. “In the article, we demonstrate the efficacy of the new substance in two different contexts – heart pacing and the activation of the peripheral nervous system. In the context of heart treatments, for example, such a device can allow temporary cardiac pacing for post-operative rehabilitation and avoid the use of a temporary electrode to be inserted into the heart. Because the membrane we developed is made of a silicon-based material, which absorbs in the body without any toxic effect whatsoever, there is no need for further surgical action to remove it from the body.”

The uniqueness of the material developed by the researchers is the formation of a semiconducting diode junction from a single type of silicon. This is highly unusual, as diodes are usually made by interfacing two types of silicon. Semiconductors are based on energetic gaps that determine their level of conductivity; they are usually made up of n-type materials, which contribute an electron to the material, and p-type materials that take an electron from the material (leaving a hole instead). The connection between the two materials creates an efficient interface called p-n junction, the building block of electronic devices and solar cells.

The silicon membrane as seen before wrapping it around the heart or nerve tissue. The color you see is due to the porosity of the surface – pores that reflect and absorb the different wavelengths of light in a non-homogeneous way, causing the different colors of the rainbow to appear

The connection between the two different materials is a very complex technological challenge, hence the importance of the discovery presented in the new article; a diode made only of p-type silicon, and the junction is built of ordinary silicon and porous silicon.

According to Prof. Rotenberg, the creation of the new material was unexpected. “I accidentally used a metal tweezer in the laboratory, which provided iron ions to the solution – something I did not plan to happen. The iron ions turned out to catalyze the creation of nanopores on the surface of silicon.”

He also says the new material is a window that allows the medical team to have an external impact on the tissues of the patient’s body. Outside the medical field, the new development is expected to contribute greatly to various applications, for example, in the field of renewable energies. Since renewable energy sources such as the sun are volatile and do not operate at constant intensity throughout the day, energy storage becomes a major challenge in promoting the use of these energies. One of the trends in this regard is the production of hydrogen using the decomposition of water by the power of solar radiation, because the hydrogen produced is a storable energy source. Prof. Rotenberg estimates and hopes that the new material he developed with his colleagues will accelerate the development of more advanced and efficient solar devices.

Video: An isolated heart that spontaneously contracts. On the wall of the heart, you can see the silicon membrane (on the right). By projecting light on the membrane, you can change the heart rate in case of an arrhythmia (for the video we used a green light because infrared light does not show up well to the human eye). Similarly, limb movements can be affected by pulses of light.

For the full article in Nature Materials click here.