Material characterization of the pig kidney in relation with the biomechanical analysis of renal trauma

The objective of this study was an investigation of the material properties of the fresh pig kidney and parametric characterization of its elastic and inelastic material behavior. The material investigation included density m easurements, uniaxial as well as three-dimensional compression tests, tensi le tests, and shear tests on the samples extracted from the fresh pig kidne y. For comparison, density measurements on a number of soft synthetic mater ials were also performed. Compression tests on the radial and the tangentia l specimens from the cortex tissue were performed at various loading rates. 'Three-axial compression tests were performed on the cortex tissues placed in a compression chamber. Shear tests were performed by punching a cylinde r into a slice of the cortex. Tensile tests were carried out on the outer c apsule. For characterization of the material behavior, a non-linear theoret ical simulation based on a two parameter Blatz model was used. For characte rization of the time-dependent behavior of the pig kidney cortex, a four-pa rameter linear viscoelastic model was employed. From the present experiment al and theoretical studies, a number of conclusions were derived: (1) The general behavior of the pig kidney cortex samples under compression showed the general non-linear features typical of the soft tissues; the st ress strain diagram was composed of a very flat part at very low stress lev el to about 30% relative deformation which was followed by a steeply rising stiffening leading to the radial rupture of samples marked by a maximum no minal rupture strain of about 50%. (2) The uniaxial compression tests on the radial and the tangential samples from the cortex tissue showed an increase of the rupture stress with the i ncrease in the loading rate, but a decrease in the related rupture strain. (3) The long-term uniaxial compression tests on the cortex specimens under sustained constant load showed an instantaneous deformation followed by a c reep response which eventually approached an asymptote. (4) Simulation of the non-linear material behavior of the cortex tissue und er uniaxial compression by the Blatz model gave two pairs of material param eters for the cortex in the radial and the tangential directions. Furthermo re, fitting of the assumed four parameter linear viscoelastic model with th e experimental data resulted in the viscoelastic material parameters. (C) 1 999 Elsevier Science Ltd. All rights reserved.