A New Equipment to Measure the Viscoelastic Properties of Soft Materials and its Application to Articular Cartilage

Abstract

A new equipment to measure the viscoelastic properties of soft materials has been developed. The equipment has an advantage; the measurement of an acceleration and a collision velocity convey enough information to calculate a load and a deformation history of a specimen. The new equipment is applied to measure viscoelastic properties of articular cartilages. The specimens were taken from the proximal head of the avian tibia. In the first phase of the experiment, the specimens were filled with intercellular fluid. In the second phase, the intercellular fluid was partly exchanged with normal saline solution. The following results were obtained: (1) The collision between the impactor and the articular cartilage is not perfectly elastic, and energy is dissipated; (2) The dissipated energy is proportional to the square of the collision velocities; (3) No significant difference between the amounts of dissipated energy in the articular cartilages with the intercellular fluid and those with the normal saline solution was observed. The maximum displacement of the articular cartilages with the intercellular fluid is, however, smaller than those with the normal saline solution; (4) Intercellular fluid has the properties of a spring; (5) The articular cartilages can be approximated with a Kelvin model whose constants vary exponentially with depth; (6) The physical properties of intercellular fluid largely contribute to the physical properties of the articular cartilages.