Nanomachining for high-resolution scanning of mammalian brain microstructure

The paper discusses how ultra precision nanomachining can provide a breakthrough in reconstructing the neuronal networks of mammalian brains. To explore this unknown territory a new instrument developed at Texas A&M, the Knife-Edge Scanning Microscope (KESM), will be presented. The instrument comprises four major subsystems: precision positioning stage, microscope/knife assembly, imaging system, and cluster computer. The specimen (a whole mouse brain) is embedded in a plastic block and mounted atop a three-axis precision positioning stage. The instrument uses diamond knife sectioning of the plastic-embedded brain, with layers typically a few hundred nm thick. Sectioning at 300nm resolution allows to create an aligned volume data set of ∼12 terabytes representing the tissue microstructure of entire brain. Preliminary cutting tests have shown that the major obstacle to obtain robust data are self-excited oscillations (chatter) generated during the cutting process, when sequential layers are being removed from the sample. It is clear now, that the regeneration effect and free oscillations caused by the sudden nature of the tool engagement into the sample, play paramount roles. Slight alterations of the cutting velocity for each pass have partially suppressed the chatter, however, not to extend that KESM can be used effectively unmodified. The main modifications to the current design are aimed to produce a chatter free operation. This can be achieved by employing an ultra-precision three-axis CNC lathe designed for single point diamond turning, and featuring the angular and axial motion accuracy of 8nm and and subnanometer slide feedback resolution.