Hyperelastic Behavior of Knitted TiNi Mesh under Uniaxial Tension

TiNi-based alloys belong to the class of materials with shape memory effects and superelasticity, which are currently being actively studied and successfully used in engineering and medicine. In these alloys, their natural ability to undergo large inelastic deformations and return to their original shape by increasing temperature or relieving stress takes place. The key characteristic of these phenomena is thermoelastic martensitic transformations (MT). The problem of biocompatibility of implants is relevant, as the number of operations using implants in various fields of medicine is growing rapidly. Currently, several studies are underway on the deformation behavior of biological tissues and various implant materials. Wires made of TiNi are one of the most important metal biomedical materials used in endovascular surgery, orthodontics, soft tissue plastics in the form of stents, catheters, orthodontic archwires, metal-knitted materials. Textile implants should be singled out from a wide range of structures made of thin TiNi wire, with the help of which complex surgical problems are solved. A variety of mesh structures made of titanium nickelide are characterized by a particular complexity of deformation characteristics, the manifestation of which in the implant-bio-tissue interface is difficult to predict. To create the appropriate mechanical behavior of an implant in the form of mesh structures, it is necessary to study their deformation behavior. Therefore, to describe the functioning of a superelastic implant in the interface with a biological tissue, the aim of this work is to study the deformation behavior of wire samples 40, 60, and 90 µm thick from the TiNi alloy and metal knit made from them by the method of uniaxial tension. TiNi wires exhibit the effect of superelasticity at a relative strain of 4-6%. Under uniaxial tension of knitted mesh made of these wires, the effect of superelasticity was not detected. It has been found that the cyclic tension diagrams of knitted mesh show behavior inherent in hyperelastic materials. The total tensile load is unevenly distributed in the knitwear, in contrast to the uniformly distributed load when testing the wire.