Viscoelastic properties of the nucleus pulposus of the intervertebral disk in compression

The viscoelastic properties of the nucleus pulposus were measured in compression for 35 specimens dissected from 9 sheep. Measurements on 19 specimens were made on the day of slaughter; the remaining 16 specimens were stored frozen and thawed before testing. A preload of 0.2 N was applied to each specimen and a cyclic compression of 10 mum applied at eight frequencies in the range 0.1-10 Hz at a temperature of 37 degreesC. Freezing appeared to increase the storage modulus, E', but not the loss modulus, E', or tan delta =E"/E'. These parameters, E', E" and tan delta, had values of 64 +/- 28 kPa, 24 +/- 11 and 0.33 kPa +/-0.07, respectively. The value of tan delta passed through a minimum at a loading frequency of 0.9 +/-0.2 Hz. The water content of the specimens was 80 +/-2%. (C) 2001 Kluwer Academic Publishers.