A window in the skull won’t let anyone read your mind, but it may give doctors on-demand access to take images of the brain or check the progress of cancer without repeated surgeries.
UC Riverside researchers say they have engineered the right material for a window that would be about 10 times stronger than glass and facilitate diagnosis of cancer, study of brain function or delivery of therapies aimed at neurological diseases and psychiatric disorders.
The team successfully imaged a mouse’s brain through the engineered pane using optical coherence tomography, the light-based equivalent of a sonogram that can produce minutely detailed images of soft tissue.
The technology, which is based on decoding the scattering of light or lasers into a coherent image, has been held back in some applications by the scattering properties of bone, such as a cranium. Doctors have resorted to thinning the cranial bone and other techniques.
Glass was an obvious candidate for opening a long-range window, but doctors and engineers alike cringed at the prospect of an easily breakable, shard-producing material close to the brain, even it it was covered with scalp tissue.
“Clearly, glass would not be a material that you would like to have as a window,” said UC Riverside mechanical engineer Guillermo Aguilar, lead author of the study published online Tuesday in the journal Nanomedicine. “But zirconia, on the other hand, is a very, very strong material.”
The problem with zirconia, even in the nano-engineered form commonly used in dental implants, is it’s about as transparent as white china.
Engineers took yttrium-stabilized zirconia and subjected it to massive heat and pressure changes that changed the shape of the crystals to such a small scale that light-scattering properties become negligible, said fellow UC Riverside mechanical engineer Javier Garay. The rest amounted to grinding and polishing, then using dental cement to affix it to a mouse’s skull.
“Typically when you look at a pieces of zirconia, it would look very much like your coffee cup, a white, non-transparent material," Garay said. "One of the breakthroughs here is we were able to make a material that is typically non-transparent and make it transparent. That was the enabling technology."
The team scanned the mouse, then compared the resolution of the image taken through the new zirconia port with one produced through the rodent’s cranial bone. The differences were startling.
Optical coherence tomography, however, is only one example of the type of observation, scanning and therapy that could be used more effectively with open access to the brain, a concept that the university is pursuing through a “Windows to the Brain” bioengineering initiative.
The UC Riverside team already has engineered ways to "inscribe" such a pane to allow use of more deeply penetrating waves, such as those used in the nascent field of optogentics, in which light stimulates or inhibits individual neurons.
The researchers also are working on optical clearing agents that can temporarily render skin transparent, a technique that could be combined with the zirconia port.
First, they will have to test whether the material is suitable for long-term use around live tissue and bone - a potentially serious impediment, even if Zirconia has been used extensively in dental and orthopedic applications.
“In a sense we have some certainty that the bio-compatibility is going to be OK," Aguilar said. "But we need to make sure that for this particular type of zirconia and for this particular application it’s also going to be bio-compatible. And if it’s not, we’re going to have to come up with a way to solve that problem.”
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