A snug fit for neurological device
Delivering a flexible implant through a catheter to electronically monitor neurological diseases is the ultimate goal for a team of scientists in the USA.
The concept is making headway, claim the researchers involved at Tufts University, and the Universities of Pennsylvania and Illinois.
They have applied a dissolvable film of silk as a mechanical support for ultra-thin open-mesh electrode pads and electrical traces (about two micrometres thick). This could be used, for example, to detect when epileptic seizures begin and deliver pulses to shut the seizures down.
Professor John Rogers at Illinois explains, ‘Two classes of devices exist today. The first uses arrays of sharp needle-shaped electrodes that penetrate the brain tissue. These provide high resolution, high fidelity coupling, but damage tissue during insertion and continue to over time’.
The second device, he says, comprises electrode pads that are placed on the brain’s surface. Their contact area (about 3.5mm diameter), however, is too large for high spatial resolution signal monitoring, and reducing their size would require better conformal coverage of the brain for direct coupling with the tissue. The current thicknesses achievable for these pads (about 700µm), without losing their stability in fabrication and implantation, are said to be too rigid for conformal coverage.
‘Our technology attempts to combine the advantages of these two technologies to provide a high fidelity coupling, high spatial resolution, non-invasive, non-penetrating design that wraps and gently conforms to the curves and folds of the brain,’ says Rogers.
Dr Brian Litt at Pennsylvania adds, ‘The brain moves with each heartbeat. We need devices that stay still relative to targets in the moving liquid environment’.
The result is a base material made from silk, purified from silkworm cocoons at Tufts University. This biocompatible and bioresorbable film, which acts as a substrate for the more compliant electronic components, is mounted on the brain. It then dissolves, leaving the mesh electrode system to ‘shrink wrap’ the brain.
The silk processing conditions are said to be customisable for programming dissolution rates, from a few seconds to a few days. Rogers says, ‘The silk must be sufficiently thin to provide some degree of bending to conform and to facilitate rapid, complete dissolution. At the same time, it must be sufficiently thick to allow easy manipulation’. A thickness of about 20-50µm has been found most appropriate for this application.
The metal electrodes, which are about 500µm2 in size, are bonded to an anisotropic conductive film at one end of the arrays to connect to an external recording system. The arrays are made from gold and coated in polyimide to protect them from contact with the tissue or bodily fluids. The implant is said to have achieved improved spatial resolution recordings at micrometre level, with in vivo trials conducted with invasive implantation.
Professors Chris McLeod and Tony Cass at the Institute of Biomedical Engineering at Imperial College London, UK, welcome the development. In a joint statement, they say, ‘It looks like a good idea to have a flexible substrate for electrode arrays which will dissolve (controllably) in time – a useful step in chronic implant development and not controversial’.
The US team certainly believe in the potential for monitoring the brain, as well as other parts of the body, by pursuing wireless communication, non-invasive delivery systems and further in vivo testing.Materials World Magazine, 01 May 2010
The concept is making headway, claim the researchers involved at Tufts University, and the Universities of Pennsylvania and Illinois.
They have applied a dissolvable film of silk as a mechanical support for ultra-thin open-mesh electrode pads and electrical traces (about two micrometres thick). This could be used, for example, to detect when epileptic seizures begin and deliver pulses to shut the seizures down.
Professor John Rogers at Illinois explains, ‘Two classes of devices exist today. The first uses arrays of sharp needle-shaped electrodes that penetrate the brain tissue. These provide high resolution, high fidelity coupling, but damage tissue during insertion and continue to over time’.
The second device, he says, comprises electrode pads that are placed on the brain’s surface. Their contact area (about 3.5mm diameter), however, is too large for high spatial resolution signal monitoring, and reducing their size would require better conformal coverage of the brain for direct coupling with the tissue. The current thicknesses achievable for these pads (about 700µm), without losing their stability in fabrication and implantation, are said to be too rigid for conformal coverage.
‘Our technology attempts to combine the advantages of these two technologies to provide a high fidelity coupling, high spatial resolution, non-invasive, non-penetrating design that wraps and gently conforms to the curves and folds of the brain,’ says Rogers.
Dr Brian Litt at Pennsylvania adds, ‘The brain moves with each heartbeat. We need devices that stay still relative to targets in the moving liquid environment’.
The result is a base material made from silk, purified from silkworm cocoons at Tufts University. This biocompatible and bioresorbable film, which acts as a substrate for the more compliant electronic components, is mounted on the brain. It then dissolves, leaving the mesh electrode system to ‘shrink wrap’ the brain.
The silk processing conditions are said to be customisable for programming dissolution rates, from a few seconds to a few days. Rogers says, ‘The silk must be sufficiently thin to provide some degree of bending to conform and to facilitate rapid, complete dissolution. At the same time, it must be sufficiently thick to allow easy manipulation’. A thickness of about 20-50µm has been found most appropriate for this application.
The metal electrodes, which are about 500µm2 in size, are bonded to an anisotropic conductive film at one end of the arrays to connect to an external recording system. The arrays are made from gold and coated in polyimide to protect them from contact with the tissue or bodily fluids. The implant is said to have achieved improved spatial resolution recordings at micrometre level, with in vivo trials conducted with invasive implantation.
Professors Chris McLeod and Tony Cass at the Institute of Biomedical Engineering at Imperial College London, UK, welcome the development. In a joint statement, they say, ‘It looks like a good idea to have a flexible substrate for electrode arrays which will dissolve (controllably) in time – a useful step in chronic implant development and not controversial’.
The US team certainly believe in the potential for monitoring the brain, as well as other parts of the body, by pursuing wireless communication, non-invasive delivery systems and further in vivo testing.Materials World Magazine, 01 May 2010
- Login or register to post comments
- Printer-friendly version