Neural interfaces are medical devices that are designed to be surgically implanted into nerves after an amputation, to allow signals to be extracted from the nervous system in order to control artificial limbs. Several types of interface implant have been developed but none has reached clinical use yet, because although they may work well initially, they gradually cease to function because of the development of scarring around them, which until now could not be prevented.
'Scarring is a natural response of the body to artificial material, and happens around almost all types of implanted medical devices' said Dr James FitzGerald, a consultant neurosurgeon at NDS who led the study. 'It is a particular problem for nerve interfaces where the scar tissue gets in between nerve fibres and electrodes and pushes them apart, reducing signal strength. In some types of implant the scar tissue can actually strangulate the nerve fibres'.
Solving the scarring problem is a key requirement for long term function of nerve interfaces. - Dr James FitzGerald
The researchers constructed nerve implants containing tiny quantities of a steroid drug called dexamethasone. Tests showed drug release was sustained over a one year period and resulted in a dramatic reduction in scarring. The amount of drug released per day was equivalent to less than one thousandth of the body’s normal daily production of steroids. The challenge now will be to develop the technology to the point where drug release can be sustained for even longer periods.
Dr FitzGerald said: 'Solving the scarring problem is a key requirement for long term function of nerve interfaces. Drug elution allows scar suppression in the immediate vicinity of the implant using tiny quantities of drug that should have no side effects. Now we need to extend the period of anti-scarring protection, eventually to decades'.
The research is published in the Journal of Neural Engineering.