Shear properties of human brain tissue.

The objective of this study was to determine a relationship between shear stress and strain for 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 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. The average true shear stress and finite strain were calculated. A nonlinear, viscoelastic, standard solid model was fit to the constant rate test data and the material constants were determined.