09 September 2013

Transparent skull implant for easier, cheaper laser-based brain scanning

Only a short-sighted curmudgeon could deny that optical technologies are set to revolutionize therapeutic brain stimulation and monitoring. Insofar as the retina is part of the brain, it already has. A little-known technique known as optical computed tomography (OCT) makes use of some fancy interferometric techniques to create high-resolution scans of retinal structure, in particular, when imaging in the depth, or “Z” plane. A group from the University of California at Riverside has recently proved themselves as international thought leaders in the field by extending this technique to optically image the brain through the skull.

With a single paper, published in the access-challenged journal Nanomedicine: Nanotechnology, Biology and Medicine, they have made what amounts to the most important fashion statement of the year. To paraphrase their central tentant, “Windows to the brain are cool.” In fact, the authors introduce the short form, “WttB,” as a descriptor for their new technology. As fascinating as OCT may be, this new research is not really about Mach-Zhender fiber optic scan heads, its about a new zirconia-based material they developed — nanocrystalline yttria-stabilized zirconia (ncYSZ).
By recasting ordinarily opaque, but biocompatible, dental cement into a formulation with a nano-sized crystal structure, the researchers were able to create a transparent new wonder material. They then implanted a small window made from ncYZS into the skull of a mouse, and created an OCT image of part of its brain. While the research is not often glamorized, “breaking the skull barrier” is a significant technical challenge for realizing technologies like optogenetics, or other possible incarnations of light-based stimulation and imaging devices. Various skull-thinning methods combined with glass-based implants have been used in the lab to image through the skull, but these methods would expose a human to significant mechanical risk in the course of daily activity.

While the low fracture toughness of typical glasses (KIC = 0.7 – 0.9 MPa·m1/2) would present a clear problem for spearhead NFL tackles far greater then the expected concussion, that of ncYSZ (KIC ~ 8 MPa·m1/2) might compare favorably with any polymer helmet. As alluded to above, the real power in what these researchers now propose is not just that the rapidly maturing field of laser-based diagnostics and therapeutics might soon be made available to the infirm, but that it could potentially at some time be available in acceptable form to the masses.

The researchers call the device a “calvarium prosthesis” in their title — calvarium meaning simply, skull. We have previous discussed the virtues of 3D-printed skulls, and have also noted that transparency need not always mean it has to be invisible. We are not necessarily saying society is ready for everyone to go all barreleye right now (see video above), but wish to note that a more discrete version of a cranial WttB might balance with the merits of the occasional cerebral check or tune-up.

The researchers note that the advantages of their new skull option would extend to chronic monitoring of cerebral edema or swelling, and for more precise targeting of therapies for residual gliomas. I asked Guillermo Aguilar, one of the authors on the study, about other biocompatible material possibilities. Sapphire, while costly to secure, form, and machine, has some fantastic physical specs which could come in handy. It has high transparency across a wide range of wavelengths and finds use in many exotic applications like X-ray windows. He said simply that in mass production scale, this ncYSZ would be even cheaper than the titanium implants that are currently used as skull replacements. When it comes to bringing new technologies to the table on a scale where they can be fully vetted for widespread, and possibly elective use, perhaps affordability is the most important driver.

Now Read: MIT creates glucose fuel cell to power implanted brain-computer interfaces

Research paper: dx.doi.org/10.1016/j.nano.2013.08.002 – “Transparent Nanocrystalline Yttria-Stabilized-Zirconia Calvarium Prosthesis”


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