Researchers from the University of California, Riverside have advanced their progress for the “Window to the Brain” (WttB) transparent skull implant.  

The purpose of the transparent WttB implant is to enable optical diagnostic and therapeutic procedures to be conducted through the implant, instead of needing to open the skull for optical access to the brain. As part of this research, researchers are adapting several optical diagnostic and therapeutic procedures for use through the implant.Pictured here is a graduate student (Nami Davoodzadeh) conducting Laser Speckle Imaging(LSI) through the implant in a mouse, to measure the velocity of cortical blood flow in the brain. 

Note the differences between the regular white light image (bottom left) and LSI image (bottom right)  of the WttB implant.

When laser light is directed onto a material, it can either be absorbed, scattered in different directions, or transmitted straight through the material.  For transparent materials like the WttB implant, a significant portion of light is transmitted through to the other side.  However, some light is absorbed, and this absorbed light is converted into heat.  This so-called photothermal heating of the implant is important to study, so that laser-based therapeutic and diagnostic procedures performed through the implant can be designed to avoid excessive heating and damage to surrounding tissue.  This image (below-right) shows a thermal map of the sample during laser irradiation.

Conventional yttria-stabilizedzirconia (YSZ) is optically opaque.  Through a special densification method, researchers are able to compress YSZ nanopowder into a bulk material, while maintaining a nanocrystalline internal structure. This nanocrystallinity results in less light scattering and higher light transmittance, and thus optical transparency.  When the samples are first densified, they appear opaque due to rough surface finish, which causes scattering (example on right).  This is similar to how roughened glass does not appear transparent. After polishing the surfaces of the YSZ sample with diamond particles, the scattering is reduced and the transparent nature of the samples is revealed (example on left).