Biological systems often have multi-scale structures to achieve their functionality, e.g., tendons have a multi-scale structure composed of collagen fibers arranged hierarchically parallel to the long axis of the tendon. A tendon's J-curve usually represents the mechanical behaviour of such structures, which is divided into four regions: (I) toe region, (II) linear region, (III) plastic region, and (IV) failure region. The toe region represents the alignment of the collagen fibers. At 2% tension, all fibers are already out of their crimped state. In the linear region, the collagen fibers respond to the load in a linear fashion. The two subsequent regions (plastic and failure) represent the beginning and the total failure of the collagen fibers[1].

Inspired by the J-curve generated by the stretching of a tendon as a reference, 2D TPU structures have been created using additive manufacturing. Parallel elastic slats form the elements that induce the strain-stiffening effect (see Figure 1). Three designs: set of waves, waves, and tape were analysed, with the same thickness and length, but varying the design and the number of slats. As the structures are stretched, there is a longitudinal change in the structures, creating a unidirectional orientation, which causes them to become stiffer and more difficult to stretch at greater elongations similar to collagen fibres in the tendon. This work explores the relationship between the structural design and mechanical properties to enable mimicking the tendon motion.