# A State-of-the-Art Review on Robots and Medical Devices Using Smart Fluids and Shape Memory Alloys
## 3 Robots Using SMA
### SMA-Based Robots
The SMA wires, with 35 routine pulleys were used as the skull actuators [51]. Recently, the majority of SMA robotic researchers have been more interested in biologically inspired (or biometric) robotics, as these robots are useful in solving problems that are challenging for humans by providing pertinent information from underwater, space, air, and land. The state-of-the-art robotic applications using SMA wire actuators are summarized in Table 3, while emphasizing biomimetic robot applications. Over the last decades, SMAs have been utilized as alternative actuators for underwater robots due to their ability to perform flexible and complex movements, inspired by biological mechanisms [52]. [PERSON] et al. [53; 54] designed a micro-robot fish driven by a flexible actuated biomimetic fin thatsimulates the musculature, and flexible bending, of a squid/cuttlefish. [PERSON] et al. [55] suggested a new concept, using V-shape configured SMA actuators to bend a continuous flexible structure, representing the backbone of a robot fish. A small crawling robot has been developed by mimicking the model organism of _Caenorhabditis elegans_[56]. A thermal SMA was selected as an actuator because of having properties similar to those of _C. elegans_ muscles. The starfish robot has a number of tentacles or arms extending from its central body in the form of a disk, like the topology of a real starfish. The arm is a soft and composite structure, generating a planar reciprocal motion with a fast response speed upon actuation provided by the SMA wires [57; 58]. An SMA composite-based soft actuator was designed to provide a large deformation profile inspired by the contraction of a jellyfish bell, utilizing the rowing mechanism for locomotion (e.g., buoyancy) [59]. This actuator was found to achieve 80% of maximum deformation, consuming 7.9 J/cycle when driven at 16.2 V/0.98 A and a frequency of 0.25 Hz [59]. [PERSON] et al. [60] designed another type of jellyfish-inspired jet propulsion robot (JetPRo) mimicking the proficient jetting propulsion mechanism (iris mechanism) used by the hydromedusa _Sarsia tubulosa_. A biomimetic swimming robot, based on the locomotion of a marine turtle and SMA wire, was developed by [PERSON] et al. to perform the smooth, soft flapping motions of this type of turtle [61]. The motion of such a structure can be designed by specifying the angle between a filament of the scaffold structure, and a shape-memory alloy (SMA) wire. Based on the analysis of the _Chelonia mydas_ turtle, using two swimming gaits (routine and vigorous swimming gaits), the flipper actuator was designed to be divided into three segments, containing a scaffold structure fabricated with a 3-D printer [62]. A soft-bodied robot was proposed using an SMA-based soft composite with inchworm-inspired locomotion, capable of both two-way linear and turning movement [63]. The centimeter-scale work-like robot, inspired by a helical kirigami-enabled parallel structure, was designed using an SMA coil spring actuator [64]. Unlike the inchworm-inspired locomotion, a quick actuation mechanism for a flytrap-inspired robot has been studied by using SMAs [65], which actuates artificial leaves made from asymmetrically laminated carbon fiber. Similar to the flytrap-inspired robot, a novel direction-changing concept for miniature jumping robots, inspired by Froghopper, has been developed by using a coil spring actuator for triggering the jumping [66]. SMAs acting as artificial biceps and triceps are used for mimicking the morphing wing mechanism of the bat [67], or dragonfly [68]. Although SMA actuators provide several attractive advantages over traditional actuators, including silent and smooth operation, direct actuation, simple driving circuitry, and high-power density, it is well-known that there are some technical limitations, such as low energy efficiency, associated with the energy conversion of heat to mechanical work, slow response, and difficulties in positional control [69].