Shear properties of human brain tissue

The objective of this study was to determine the shear stress versus strain relationship of human brain tissue by performing transient, single pulse, high rate, shear displacement tests. A constant velocity, parallel plate shear test device was designed and fabricated. This equipment utilized a computer interfaced, servo controlled linear motor to displace the lower shear plate horizontally with respect to the upper shear plate at a predetermined velocity. This equipment generated constant rate shear strains in cylindrical tissue samples mounted between the shear plates. The transverse reaction force at the upper end of the sample was measured during the event with a sensitive quartz piezoelectric force transducer thus obtaining the force associated with the displacement versus time ramp. Shear tests were performed on 125 tissue samples taken from twelve fresh cadaver brain specimens. Brain tissue samples were approximately two centimeters in diameter and one centimeter in length. The average true shear stress was calculated and cross plotted with the finite strain to obtain shear stress versus strain curves for each test. A nonlinear, standard solid, viscoelastic model was fit to the constant rate test data and utilized to develop a general shear stress versus strain relationship.