Ultra-small implant to improve muscle stimulation

A tiny new spinal implant could allow paraplegics to regain more muscle function in their lower body than ever before.

Existing technology that helps paralysed people to move their legs involves multiple implants or electrodes attached to the outside of the body, whereas the new ‘Active Book’ device combines several components in a chip the size of a child’s fingernail.

This could allow one person to have several units placed in their spinal canal to stimulate multiple muscle groups, meaning greater leg movement and the possibility of restoring bladder and bowel control.

A diagram of the Active Book
A diagram of the Active Book

Researchers from University College London (UCL) developed the device with engineers from Freiburg University, Germany, and the Tyndall Institute in Cork, Ireland, as part of a £500,000 ESPRC-funded project.

‘There are devices that use electrodes in the spinal canal but the muscle stimulators are implanted in the abdomen in the front,’ UCL project leader Prof Andreas Demosthenous told The Engineer.

Conventional spinal canal electrodes have wires coming out of them and the surgery needed to implant them risks fluid leakage, so surgeons have been reluctant to place more than one unit.

‘We have made an “active” device that contains both the electrodes and the stimulator,’ said Demosthenous.

‘Our method should allow them to have more flexibility by having more electrodes in the spinal canal without this problem.’

The technology doesn’t give the user brain control over the muscles, as other research is attempting to do, but it allows them to move their legs for exercises such as cycling or rowing.

How many units could be implanted has yet to be determined but the university is hoping to make the device available for pilot studies sometime next year.

To manufacture the Active Book, the team had to develop a new way of packaging the components.

‘It’s a combination of advances in integrated circuit design, semiconductor technology, micro-packaging and electro-fabrication,’ said Demosthenous.

Laser processing technology is used to cut tiny electrodes from platinum foil. These are then folded into a 3D shape that looks like the pages of a book, which close in around the nerve roots.

The electrodes are micro-welded to a silicon chip that is hermetically sealed to protect against water penetration, which can lead to electrolysis corrosion of the electronics.

‘We had to make the stimulator very small by putting in an integrated circuit with built-in features that allow it to be electrically safe, so in the case of semiconductor failure it wouldn’t cause current to flow to the electrodes,’ added Demosthenous.

The implant site on the spinal canal
The implant site on the spinal canal