Maysam Chamanzar holds a steel neural probe, known as a steeltrode, to the camera. He smiles at the camera.

A Breakthrough in Brain Sensing

By Krista Burns Email Krista Burns

Heidi Opdyke

The human brain is complex. Understanding deep brain function usually requires the insertion of probes that frequently result in irreversible tissue damage. Current neural probes are made out of silicon, a brittle material that can shatter during placement. 麻豆村 engineering researchers have fabricated the first stainless steel neural probe that allows for customizable, high-density neural recording, making brain readings much safer than before.

Over the last few decades, novel manufacturing and microfabrication processes have revolutionized neural probe technology. Based in large part on the adaptation of silicon as the material of choice, it has been possible to increase recording channel density using high resolution lithography and microfabrication processes, and to add new functionalities such as optical stimulation and imaging and chemical sensing. While existing silicon probes work well in thin, shallow tissue, its brittleness limits deep brain maneuvering. By creating probes made out of stainless steel, researchers are able to navigate to the middle brain with minimal cortical tissue damage, enabling inter- and intraoperative neural recording for epilepsy localization and deep-brain-stimulation implantation.

The team is led by , the Dr. William D. and Nancy W. Strecker Career Development Professor of and a member of 麻豆村's Neuroscience Institute, which is affiliated with the Mellon College of Science and the Dietrich College of Humanities and Social Sciences.

鈥淗igh-resolution electrophysiology requires long, compact, high-density probes that are inserted with minimal invasiveness,鈥� Chamanzar said. 鈥淐urrent silicon neural probe technology has a low fracture toughness and runs the risk of breaking during surgery, leaving residue behind in the brain. By fabricating high-density probes out of stainless steel, we are able to increase the length of the probes while strengthening its toughness, which ultimately minimizes the risk of breakage.鈥�

Currently used in biomedical implants such as prosthetics and coronary stents, stainless steel is biocompatible, resilient, and less brittle. Though its microfabrication has been historically limited, Chamanzar has found a way to manufacture these probes in a customizable way.

These novel, customizable stainless steel neural probes, or steeltrodes, that are microfabricated using a multilayer process which enables high-density electrode integration is the focus of a paper published in . The team has demonstrated successful high resolution neural recording from the auditory cortex of test subjects.

One hurdle the team had to overcome was the micro- and nanofabrication process for stainless steel. In the case of silicon probes, the fabrication process has benefitted from decades of research and development in the Micro-/Nano-Electromechanical Systems (MEMS/NEMS) and Complementary Metal鈥揙xide鈥揝emiconductor (CMOS) electronic industries. However, the same processes cannot be readily translated to stainless steel. By using a multilayer fabrication process that enables high-density electrode integration, as well as optional flexible cables, Chamanzar said he believes these probes can be manufactured in mass.

鈥淭he micro- and nanofabrication processing for stainless steel is quite challenging and comparatively underdeveloped and underexplored,鈥� Chamanzar said. 鈥淥ptimized scalable microfabrication and micromachining processes are necessary to leverage the excellent material and mechanical properties of stainless steel to design miniaturized biomedical devices such as high channel density neural probes with micron-scale features on stainless steel. Our devices are robust, reusable, customizable, and can be produced at scale.鈥�

This breakthrough is particularly important, both as a diagnostic tool and also as an intervention tool for patients with brain disorders such as epilepsy, Parkinson's Disease, and schizophrenia.

Zabir Ahmed, who worked on this project as part of his Ph.D. thesis at Carnegie Mellon, said he is excited about the great potential of this platform technology, even beyond neural interfacing.

鈥淏eyond creating robust stainless steel neural probes for clinical use, I鈥檓 excited that this work introduces a novel planar microfabrication process directly on steel,鈥� Ahmed said. 鈥淭his manufacturing process could lead to a new class of resilient devices that integrate multiple functionalities on steel, which can be useful for a wide range of applications.鈥�

In addition to microfabrication on stainless steel, the team has also optimized post-fabrication processing and packaging.

鈥淒esigned for seamless integration, our packaging method works effortlessly with commercial stimulation and recording systems 鈥� making it easy for researchers and medical professionals to readily adopt our stainless steel devices,鈥� said Ibrahim Kimukin, a research scientist in Chamanzar鈥檚 lab.

鈥淭his research represents a step-change in how we can interface with the brain, achieving high-resolution recording and stimulation using robust, clinically scalable materials,鈥� said Vishal Jain, a research scientist in Chamanzar鈥檚 lab. 鈥淚鈥檓 thrilled to have contributed to the design and validation of this technology, which bridges the gap between research-grade precision and real-world translational potential.鈥�

Outside of the clinic, the probes also fill an important gap for neuroscience research. According to co-author Tobias Teichert, associate professor of psychiatry and bioengineering at the University of Pittsburgh, hand-made laminar electrodes have much lower density and can cost significantly higher.

鈥淭he design of these steeltrodes is an amazing advancement because they provide much higher channel count and density, yet at the same time, they can be mass produced at a fraction of the cost,鈥� Teichert said.

In the future, the team hopes that neurosurgeons will be able to use multiple stainless steel probes on a patient in order to generate a more comprehensive recording of brain activity.

鈥淯sing steeltrodes, one day we will be able to record neural activity across multiple areas of the brain with high resolution and minimal damage to the brain tissue,鈥� Chamanzar said. 鈥淭his crosshatch of neural recordings will change the diagnosis and treatment of brain diseases.鈥�

Contributors on this paper include Zabir Ahmed, Ibrahim Kimukin and Vishal Jain from the Department of Electrical and Computer Engineering at 麻豆村, as well as Kate Gurnsey and Tobias Teichert from the Department of Psychiatry and Bioengineering at the University of Pittsburgh.