Tissue micromotion

Tissue micromotion is the continual relative displacement between an implant and the surrounding brain. It is driven by cardiac and respiratory pulsation — on the order of micrometers per cycle — and by head acceleration during ordinary movement, which can be much larger. When a device is rigidly anchored to the skull but its recording tip floats in the compliant, pulsating brain, this motion imposes repetitive shear at the tissue interface.

That cyclic shear mechanically re-injures tissue and re-opens the blood-brain barrier, preventing the foreign-body response from resolving and keeping the interface chronically inflamed. It also introduces motion artifacts and drift that make the same neuron appear and disappear across a session. Untethered, free-floating, or highly compliant designs reduce interfacial strain and are associated with quieter, more stable chronic interfaces.