A The research presented has the aim to show that better optimized systems based on Shape Memory Alloys (SMAs) can be designed using https://isbndirect.com/ muscles working as biomimetic model. In particular the Skeletal muscles and the antagonistic pairs have been used as biomechanical model, they are the voluntary muscles that allow the body to move and they make up 40% of an organism’s body mass (Lindstedt, 2016).

Skeletal muscles are held to the bones by tendons, which role is to transfer the force generated by the muscles contraction to the bone joint. Tendons are made of robust tissue and they work as special viscoelastic connectors between bone and muscle. For an adduction movement in a joint, contraction and shortening of the muscle generates a force that is applied on a lever system that causes the joint adduction movements. To recover its initial position, the reciprocal muscle on the other side of the joint contracts and shortens. As described by Biewener and Roberts (2000), muscles are normally coupled in opposition so that movements of joints are driven by a mechanism in which one group of muscles contracts while another group relaxes or lengthens (Aversa et al., 2017 a-e, 2016 a-o; Petrescu et al., 2017, 2016 a-e; Petrescu and Petrescu; Petrescu).

Basically antagonistic pairs are muscles where one moves the bone in one direction and the other moves it back the other way in transmission of nerve impulses to the muscles. In the adduction movement of a human arm, the agonist biceps shortens and bends the forearm on the elbow joint, conversely, on arm abduction movement; the antagonist triceps shortens and returns the forearm to its original position. In general, the muscle that applies the force needed for a movement is only one of agonist-antagonistic pairs and, in particular, there is always a selective stimulation driven by the brain that acts on the muscle that contracts or shortens (agonist), while the behaviour of the reciprocal is passive, it works roughly like a brake (antagonist). The active muscle for a specific movement is always the one that contracts (Yang et al., 2013).

A unique class of Smart Materials that has in common with muscles the capability to react to an impulse (thermal in this case) with a change of shape and thus also with a contracting movement if necessary is that of Shape Memory Alloys (Van Humbeeck, 2010; Meisel et al., 2014; Melton and Mercier, 1980).

This analogy between muscles contraction and extension and the ability of this class of intermetallic alloys to undergo contraction and extension (superelasticity) under the effect of thermal and mechanical stimulation, allow us to derive a biomechanically inspired machine based on these materials.

U.S. Naval Ordnance Laboratory discovered shape Memory Effect for the first time during 1960s. The researcher of the Laboratory found this effect in a 1 to 1 alloy of Nickel and Titanium, but only nowadays, a higher spread for biomedical field, actuators, couplings and surgical instruments. Anyhow, applications of SMAs for industrial or product design are still so poorly spread and SMAs potentialities are only rarely and weakly exploited.

Nickel-Titanium alloys are intermetallic compounds (Otsuka and Ren, 1999) and they able to show thermal shape memory effect, namely, to return to their original shape on heating even when largely deformed (up to 10%).