Tissue micromotion induced stress around brain implants

The long-term consequences of tissue micromotion against stationary brain implants are poorly understood. Our aim here is to measure surface micromotion in the rodent somatosensory cortex and estimate mechanical stresses induced in the brain tissue due to micromotion against stationary implants. A differential variable reluctance transducer (DVRT) was used in adult rats to monitor micromotion normal to the somatosensory cortex surface. Using finite element models of the brain, we then estimated shear and normal stresses in the brain tissue in the vicinity of the brain implants. Surface micromotion was observed to be few tens of microns due to pressure changes during respiration and 2-4/spl mu/m due to vascular pulsatility. Maximum shear stress values of up to 2.5-3.5 KPa were estimated near the tip of a 50/spl mu/m diameter implant. Tissue micromotion on the surface of the somatosensory cortex can lead to significant shear and normal stress build-up in the brain tissue in the vicinity of cylindrical brain implants. The impact of the mechanical stress on brain tissue viability and function under chronic in-vivo conditions needs to be assessed in future studies.