# A State-of-the-Art Review on Robots and Medical Devices Using Smart Fluids and Shape Memory Alloys
## 4 Medical and Rehabilitation Applications  
In recent years, robots are being actively studied for utilization in biomedical fields. Especially, various efforts have been made to apply smart fluid to the rehabilitation robot based on the characteristic that the torque can be controlled continuously with a simple system. In 2007, [PERSON] et al. [82; 83] reported for design and test of ER brake-based active knee rehabilitation orthotic device. The knee brace provides variable and controllable damping that foster motor recovery in stroke patients. An electrorheological fluid-based brake component is used to facilitate knee flexion during stance by providing resistance to knee buckling. The schematic diagrams of the proposed orthotic device and ER fluid-based brake are shown in Figure 8. In the early 2000s, [PERSON] and [PERSON] [84] developed an above knee prosthesis using a rotary MR damper and its effectiveness was evaluated by using leg simulator. It was reported that by controlling the damping force of MR damper, the desired knee joint angle can be accurately achieved. [PERSON] et al. [85] designed and manufactured a prosthetic leg for above-knee amputees using MR damper and control performance was evaluated experimentally. The proposed device includes the wearable connector, encoder, flat motor, planetary gear head, gyro sensor, hinge, and MR damper. The MR damper generates reaction force, while the electronically commutated motor actively controls the knee joint angle during gait cycle. The configuration of the proposed above knee prosthesis and photograph of the fabricated above knee prosthesis are presented in Figure 9. [PERSON] et al. [86] proposed an ankle-foot orthosis using controllable MR brake in 2007. They fabricated two different prototypes by applying shear mode MR brakes with maximum torque of 0.71 Nm and 11.8 Nm, respectively. It is observed that the subject could maintain the dorsal flexion and prevent the drop foot in swing phase that by controlling the ankle torque using MR brake. Additionally, it is demonstrated that the higher bending moment and shorter walking cycle could be achieved by activating MR brake that in turn can prevent drop foot in swing phase and slap foot at heel strike. [PERSON] et al. [87] improved the model developed by [PERSON] et al. by adopting a newly proposed compact size MR brake with enhanced maximum torque of 10 Nm. [PERSON] et al. [88] proposed portable smart wrist rehabilitation device with rotational MR fluid brake actuator for telemedicine application as shown in Figure 10. They designed a novel T-shaped MR fluid brake that can generate output torque of 22.5 Nm and adopted to the proposed portable wrist rehabilitation system. [PERSON] et al. [89] recently developed and tested a wearable haptic device with pneumatic artificial muscles and MR brake for the application of upper limb rehabilitation. It is observed that this haptic device can render various force senses such as elasticity, friction, and viscosity. Figure 8: ER brake for active knee rehabilitation orthotic device [83]. Figure 9: The configuration of above knee prosthesis using MR damper [85]. Research on the application of biomedical field using shape memory alloys is also proceeding variously. To take advantage of the shape memory effect that can generate a motion similar to human muscle behavior, many studies have been reported for SMA actuation mechanism in the prosthetic hand application. [PERSON] et al. [90] reported a new prosthetic hand using SMA artificial muscles. It is demonstrated that the proposed device could grasp an object with the motion of the prosthetic finger. The photographs of the fabricated prosthetic hand and test result are presented in Figure 11. [PERSON] [91] proposed a tendon-driven SMA actuated finger for the prosthetic hand development that activates SMA actuation using an electro-myographic signal.