Carbon nanotube fibres could have role in treating neurological disorders
28 March 2015
New experiments show that bio-compatible carbon nanotube fibres are ideal candidates for small, safe electrodes that interact with the brain.
The fibres have proven superior to metal electrodes for deep brain stimulation and to read signals from a neuronal network. Because they provide a two-way connection, they show promise for treating patients with neurological disorders while monitoring the real-time response of neural circuits in areas that control movement, mood and bodily functions.
They could replace much larger electrodes currently used in devices for deep brain stimulation therapies in Parkinson’s disease patients.
They may also advance technologies to restore sensory or motor functions and brain-machine interfaces as well as deep brain stimulation therapies for other neurological disorders, including dystonia and depression, the researchers write.
The fibres, created by the Rice University lab of chemist and chemical engineer Matteo Pasquali, consist of bundles of long nanotubes originally intended for aerospace applications where strength, weight, and conductivity are paramount.
The individual nanotubes measure only a few nanometers across, but when millions are bundled in a process called wet spinning, they become thread-like fibres about a quarter the width of a human hair.
“We developed these fibres as high-strength, high-conductivity materials,” Pasquali says. “Yet, once we had them in our hand, we realized that they had an unexpected property: they are really soft, much like a thread of silk. Their unique combination of strength, conductivity, and softness makes them ideal for interfacing with the electrical function of the human body.”
The highly conductive carbon nanotube fibres also show much more favourable impedance than state-of-the-art metal electrodes, making for better contact at lower voltages over long periods. The working end of the fibre is the exposed tip, which is about the width of a neuron. The rest is encased with a three-micron layer of a flexible, biocompatible, insulating polymer.
The challenge is in placing the tips. Clinicians who implant deep brain stimulation devices start with a recording probe able to 'listen' to neurons that emit characteristic signals depending on their functions. Once a surgeon finds the right spot, the probe is removed and the stimulating electrode gently inserted. Rice carbon nanotube fibres that send and receive signals would simplify implantation, say the researchers.
The fibres could lead to self-regulating therapeutic devices for Parkinson’s and other patients. Current devices include an implant that sends electrical signals to the brain to calm the tremors that afflict Parkinson’s patients.
“But our technology enables the ability to record while stimulating,” says Flavia Vitale, a research scientist in Pasquali’s lab. “Current electrodes can only stimulate tissue. They’re too big to detect any spiking activity, so basically the clinical devices send continuous pulses regardless of the response of the brain.”
Caleb Kemere, an assistant professor who brought expertise in animal models of Parkinson’s disease to the project, forsees a closed-loop system that can read neuronal signals and adapt stimulation therapy in real time. He anticipates building a device with many electrodes that can be addressed individually to gain fine control over stimulation and monitoring from a small, implantable device.
“Interestingly, conductivity is not the most important electrical property of the nanotube fibres,” says Pasquali. “These fibres are intrinsically porous and extremely stable, which are both great advantages over metal electrodes for sensing electrochemical signals and maintaining performance over long periods of time.”