Mullins Effect in Soft Biological Tissues and Knitted Titanium Nickelide Under Cyclic Loading

The mechanical behavior of samples of skin, tendon, muscle, and knitted mesh made from TiNi wire was investigated employing uniaxial cyclic tension and tension to rupture. The cyclic tensile stress-strain curves of all biological tissues exhibited the Mullins softening effect, characteristic of cyclic tension of hyperelastic materials. The mechanical behavior of knitted TiNi mesh made of 40-100 μm diameter wire is similar to soft biological tissues. All samples under uniaxial cyclic tension have exhibited the softening and delay effects, and in each of the diagrams, one can distinguish low and high-modulus regions. The deformation of the wire in the loading-unloading cycle is characterized by a superelastic behavior, which did not manifest itself in knitted TiNi mesh made from it. The knitted mesh from TiNi 60 μm wire at a minimum pre-tension has shown a minimal softening effect and a minimal decrease in stress hysteresis after the first cycle of physiological deformation of 6%. The discovered effects of hyperelastic behavior will make it possible to develop criteria for the selection and evaluation of knitted materials made of titanium nickelide for soft tissue reconstructive surgery. In vivo studies have shown good integration of the knitted TiNi mesh into living biological tissues under normal physiological stress.