Spinal implants get inflated to treat pain
Researchers from the University of Cambridge, UK, are developing an ultra-thin, inflatable device to treat the most severe forms of pain in the spinal column without invasive surgery. The team has combined soft robotic fabrication techniques, ultra-thin electronics and microfluidics to create a device thin enough – 0.06mm thick – to be implanted into the epidural space of the spine column.
‘The device consists of an electrical interface, positioned on top of a flexible substrate which contains fluidic chambers. This part of the device is rolled up and packaged inside of a thin needle. Once the device is correctly placed by the surgeon these chambers are inflated, expanding the device inside of the body and covering the spinal cord,’ explains Ben Woodington, PhD Candidate at the University.
Made from parylene-C and silicone, the device is inflated once it has been inserted with water or air and then connected to a pulse generator. The ultra-thin electrodes start sending small currents to the spinal cord to disrupt pain signals. ‘This device can be rolled up into the shape of a percutaneous needle then implanted on the site of interest before being expanded in situ, unfurling into a paddle-type conformation,’ says Woodington. ‘The device and implantation procedure have been validated in vitro and on human cadaver models.
‘…Fluidic and electrical connections lead from the tail end of the device, the latter of which is connected to an implantable pulse generator and battery which sits further down the back, away from the spinal cord.’
The team uses parylene-C and silicone due to their biocompatibility and long history of use in implantable medical devices, as well as their intrinsic flexibility and ease of processing. ‘The electrical interface is made from gold, a material which we can use to microfabricate thin wires and electrodes,’ he adds. ‘This material is also well accepted in the body.’
According to the researchers, it is the incorporation of fluid chambers that separates the device from other thin-film electronics, allowing it to be inflated into a paddle-type shape once it is inside the patient.
‘Our earlier versions were actually so thin that they were invisible to X-rays, which the surgeon would need to use to confirm they’re in the right place before inflating the device,’ notes Woodington. ‘We added some bismuth particles to make it visible without increasing the thickness too much.’
The in vitro (bench testing) and human cadaver testing has helped refine both the device and the surgical procedure for implantation.
‘We were able to successfully implant the device through a standard Touhy needle (similar to an epidural needle), navigate the device up the spinal column, guided by X-ray, without damaging any of the structures. We were then able to actuate/unroll the device using air pressure from outside the body,’ Woodington explains. ‘The device was also mechanically and electrically characterised in the lab and was shown to perform as one would expect a standard spinal cord stimulation device would.’ The team is using materials, components and processes that are compatible with industrial manufacture, and are now working with a partner to identify how they can make further improvements to the design.
‘The next step for this project is to produce our first batch of devices from a contracted manufacturer,’ Woodington concludes. ‘After this we can start the preclinical and clinical testing required to bring such a device to the people who need it most.’