A more efficient way to ease chronic pain
Chronic pain is one of the most widespread and devastating conditions worldwide. Every year in the United States, for example, around 100 million adults suffer from chronic pain1, lasting longer than 12 weeks. In most cases, it can be treated with medication; but for people whose pain fails to respond to drugs, spinal-cord stimulation (SCS) offers a last resort to ease their daily agony. The procedure involves implanting tiny, electrode-covered wires alongside the spinal cord, which are connected to a battery implanted below the skin. When activated, usually by remote control, these electrodes send electrical impulses that can quell the sensation of pain.
Leads and paddles
The most common SCS procedure involves ‘lead-type’ devices: thin wires that are coated with electrodes at one end. These wires can be threaded up alongside the spine under local anaesthetic while the physician carefully tracks their location using X-rays. It’s a relatively simple procedure, with a high success rate; but one downside is that the cylindrical shape of the wire means it can occasionally be dislodged away from the spinal cord, a phenomenon known as migration.
The other, less frequently used method of SCS involves ‘paddle-type’ devices. A paddle-type device consists of a wire with a rectangle-shaped, flattened end that can be up to 12 millimetres across and 67 millimetres long. The large, flat paddle shape means that migration is rarely a problem, and it can also carry many more electrodes than a lead-type SCS device – sometimes as many as 32 – thus providing greater electrical stimulation. Furthermore, all of the electrodes face towards the spine, meaning the device is more energy efficient. Implantation, however, is more invasive than ‘lead-type’ devices and requires open spinal surgery, says Damiano Giuseppe Barone, clinical lecturer in neurosurgery at the University of Cambridge, UK2.
We were having the laboratory's cake club, and we started talking about previous experiences.
Best of both worlds
A few years ago, a chance meeting at a laboratory social event laid the foundation for a device that could combine the strengths of both lead-type and paddle-type SCS devices. “This project was completely serendipitous,” says Barone. “I was working on my own thing, and Chris [Proctor] was working on a completely different project. I think we were having the laboratory’s cake club, and we started talking about previous experiences.” Chris Proctor had just published a paper on a neural probe that used microfluidics (tiny channels full of gas or liquid) to deliver drugs for treating epilepsy3, while Barone was working on peripheral nerve implants. Their conversation led to an idea that combined their areas of study – a spinal implant that could be inflated using microfluidics.
Along with their co-authors, the pair published a paper earlier this year4 describing an SCS implant that can be rolled up to less than 2 millimetres in diameter. But when air is pumped into the microfluidic channels of the device using a syringe, it unfurls to a width of 12 millimetres inside the body. Dubbed MI-SCS by the authors, the novel implant has the advantages of a lead-type device in that it can be easily threaded into position in a patient under local anaesthetic, but it also has the advantages of a paddle-type device in that it can provide electrical stimulation over a wider area and is less likely to slip out of place.
The authors were able to fabricate incredibly thin electrodes using photolithography and soft lithography, methods for printing patterns on to extremely thin materials. And to prevent rejection by the body, the device is made entirely from biocompatible substances such as parylene-C, silicone, polyethylene, polyimide and gold.
“We went through different iterations of different methods to reach the right shape for the unrolling,” says Barone. “Then the challenge was how to roll it to reach the dimension of the cylindrical device, then to unroll to reach the dimension of a paddle device.” In terms of making the device pliable enough to roll and unroll, he says that the engineering background of team members Proctor and George Malliaras was invaluable, and made for smooth progress when it came to creating flexible electronics. “That was the easiest bit,” he says. “The rest was challenging.”
So far, the team has successfully implanted MI-SCS into cadavers, but Barone says the next big step will be to test the system in large animals, and then in humans in around three years’ time. It could be ready for market in as soon as five years.
The lab has got the full range: We've got biologists, neuroscientists, engineers, physicists, computer scientists...
Barone thinks that his multidisciplinary background has been an important contributor to his work on MI-SCS. He gained a medical degree specialising in neurosurgery, then went on to do a PhD in neuroscience and neuroprosthetics, before studying electrical engineering as a postdoctoral researcher, which is when he met Proctor. He thinks that being in contact with people from various disciplines is a key driver of innovation. “The Bioelectronic lab I co-lead with Prof. Malliaras has got the full range: we’ve got biologists, neuroscientists, engineers, physicists, computer scientists…,” he says, adding that integrating the knowledge from different fields is the key to coming up with new concepts. “Otherwise, single fields reach their limits. It’s about talking to each other. Being more multidisciplinary means really working together, rather than just asking for an opinion.”
Holmes, D. The pain drain. Nature 2016;535:S2–S3.
Interview with Damiano Giuseppe Barone, October 2021.
Proctor, CM et al. Electrophoretic drug delivery for seizure control. Sci Adv. 2018;4: eaau1291.
Woodington BJ, et al. Electronics with shape actuation for minimally invasive spinal cord stimulation. Sci Adv. 2021;7:eabg7833.