Transparent skull window has promise for brain condition diagnosis and treatment

People with a wide range of brain disorders could benefit from the development of a transparent material that can be implanted into the skull to allow lasers to be used in diagnostics and therapy without causing any adverse immune response.

Based on a ceramic used commonly in bone implants, the material has been developed by materials scientists at the University of California at Riverside (UC Riverside) as part of a ongoing international project called ‘Window on the Brain’, the purpose of which is to develop a system by which therapy can be applied to the brain without the need for repeated craniotomies, operations which involve the removal of part of the skull that are traumatic for he patient and can carry the serious risk of infections.

‘Window on the Brain’ is intended to help improve the care of people with brain tumours, damage from stroke and neurodegenerative disorders. Rather than having to perform a craniotomy to access brain tissue directly, the idea is to place a single transparent implant of a rigid material that can still perform the skull’s protective function but allow laser energy to be used to selectively heat tissue as part of a therapy programme, to destroy diseased or cancerous tissue or cauterise damaged blood vessels that could cause cerebral haemorrhage.

The UC Riverside team developed a nanocrystalline, transparent form of the ceramic yttria-stabilised zirconia, which is used in hip implants and dental crowns, and implanted it into the skull of a hamster, where, they report in a paper in the journal Nanomedicine, it fused with the living tissue and caused no immune response. The zirconia mineral is more impact-resistant and biocompatible then titanium, thermoplastic polymers and glass-based materials that have been developed by other members of the Windows consortium, making it “ the only implant material that could conceivably be used in humans,’ the researchers claim. The team performed a series of laser-based diagnostics, including transillumination and fluorescent microscopy, to measure   white blood cell adhesion to the implant, blood vessel size and blood flow rate directly from the living brain tissue with no ill-effects.

In another set of experiments, a team including Windows project leader Guillermo Aguilar, a mechanical engineer at Riverside, tested whether the implant could be used to fend off a common side-effect of skull implants, infections of Escherichia coli which grows in a biofilm on the inside of the implant.

“This was an important finding because it showed that the combination of our transparent implant and laser-based therapies enables us to treat not only brain disorders, but also to tackle bacterial infections that are common after cranial implants,” said UC Riverside neurosurgeon Devin Binder, who was part of the research team. “These infections are especially challenging to treat because many antibiotics do not penetrate the blood brain barrier.”

The experiment involved placing a zirconium window on top of a heated pad with a slice of agar jelly on which they cultured a fluorescent E. coli colony. In a paper in the journal Lasers in Surgery and Medicine they explain how used an infra-red laser with light wavelength 810nm, and how using a pulsed laser effectively kills the bacteria without increasing the temperature of the agar, indicating that it could be used to treat infection without damaging the brain.