# Current State of Robotics in Hand Rehabilitation after Stroke: A Systematic Review
## 2 Materials and Methods
### Drive Mode of Hand Rehabilitation Robot
Piezoelectric ceramics is one of the new smart materials with more applications and is a new type of micro-displacement device [74]. Because of its small size, high displacement resolution, fast response, high output force and high transduction efficiency, it is widely used in the fields of precision positioning, microelectromechanical systems, micro and nanomanufacturing technology and nano bioengineering. It has piezoelectric properties, ie., it can convert electrical energy and mechanical energy to each other. In addition to piezoelectric properties, they also have many properties, such as elasticity and dielectric properties, but the high drive voltage and small maximum deformation rate limit their application in large stroke actuators. Shape-memory alloy wire (SMA) is a unique new intelligent material that possesses two unique properties: shape memory effect and superelasticity [75; 76]. After plastic deformation and permanent deformation of common metals, SMA wire can return to its original shape after heating to a certain temperature; at the same time, it can undergo great deformation and consume and absorb mechanical energy after applying a certain load to SMA wire under isothermal conditions, and it can return to its original shape after removing the load, showing a good damping effect. This is its superelasticity. In 2017, a wearable glove driven by shape memory alloy filaments was developed at Tehran University, Iran [77], as shown in Figure 12. Guides were set at the corresponding joints on the glove for fixing the SMA contraction path, and the force generated by the contraction of the SMA actuator was used to compensate for the lack of finger muscle force. Tests have shown that the glove can effectively achieve flexion-extension movements of the fingers within a certain range, with maximum flexion angles of 80\({}^{\circ}\), 90\({}^{\circ}\), and 70\({}^{\circ}\) at the DIP, PIP, and MCP joints. In addition, the glove can also effectively grip objects with a single fingertip force of 8 N or more during gripping. Figure 11: (**a**) The dielectric elastomer bionic skeletal muscle experiment; (**b**) IPMC bionic gripper [72; 73]. Figure 12: Experimental prototype of the wearable glove driven by shape memory alloy [77]. The most commonly used new drive modes in the field of hand rehabilitation robotics are pneumatic artificial muscle drive and shape memory alloy drive. Pneumatic artificial muscles are more widely studied and have been used in numerous applications. They can be used in a variety of harsh environments due to their clean seal and they also have excellent flexibility. The flexibility, high power density, and high output force of shape memory alloy wire all indicate that it is an excellent intelligent drive material. Both new drive modes are more outstanding in terms of comfort and are well suited for applications in hand rehabilitation. Relative to exoskeletons that use rigid links, soft Exo suits use low-modulus materials, often along with tendon actuation, to transmit movement assistance without imposing substantial movement constraints along non-actuated DOFs. The field has yet to fully establish corresponding best practices for providing gait assistance for poorly ambulatory individuals. In the future decade, scholars and researchers in the field of soft robotics will also continue to focus on innovative ways to apply new soft drive methods [78].