# Review of Soft Actuators Controlled with Electrical Stimuli: IPMC, DEAP, and MRE
## 2 Recent Progress in Development and Applications of Soft Actuators
### Ionic Polymer Metal Composite (IPMC)
#### 2.1.2 Actual Trends in the Application of IMPCs in Soft Robotics  
An IPMC is an electrically driven material that undergoes bending deformations in the presence of relatively low external voltages, exhibiting great potential as an actuator for applications in soft robotics, bio-engineering, or micro-robotics. It is certainly clear that the extent of applications of IPMCs goes beyond the scope of this paper. However, it presents the spectrum of such applications of IMPCs as soft actuators. Most of the work reported in robotics uses the IPMC as a simple actuator while the robot body is made from other materials [33; 34; 35; 36; 37; 38].  
The most important advantage of such IPMC actuators over conventional actuators is the softness of the membrane material. IPMC actuators have the ability to bend to a very large range, which is over 360 degrees [3]. The features of IMPC actuators make them useful for receiving haptic feedback during actuation because they can actuate and then sense, while only requiring a small voltage (bio-friendly) while generating large output sensing signals [39]. The IPMC actuator application study for optical lenses describes an IPMC actuator integrated into an intraocular lens (IOL) system.  
The underwater microrobot is also a novel potential application of the IPMC. There are several studies on underwater propulsion robots using IPMC actuators. For example, in [40], the authors developed a propulsion robot using an IPMC actuator as a fin to generate a forward impelling force. Another work presents a fish-like microrobot that uses two actuators for right and left turns [41].  
Figure 3 shows a prototype hybrid underwater soft biomimetic IPMC microrobot. The robot body was built with eleven IPMC actuators (two IPMC fingers, one tail, and eight IPMC legs) [42]. To date, multi-finger grippers that consist of two, four, and eight fingers have been produced. In [43] the authors proposed a three-fingered gripper in which each finger was an actuator, and each finger was actuated individually. As soft actuators, IPMCs can be applied in robotic optical systems, such as an auto-focus compact camera module and a tilting actuator for an endoscope [44; 45]. Additionally, [PERSON] et al. [46] developed an IPMC actuator that was used as a prototype for an active catheter-guidewire maneuvering application. The IPMC has some excellent characteristics for robotic applications compared with other soft polymer actuators as follows [47]:  
* driven with low voltage (<3 V);
* low power consumption;
* fast response (>10 Hz in water);
* mechanically and chemically durable and stable;
* soft and compliant;
* works in wet conditions (or in water).  
While significant progress has been made on new materials for IPMC soft actuators, it is also necessary to develop electrical control strategies at the same time. Based on various studies, the properties of the IPMC material were determined and various control algorithms were proposed. However, some studies showed that these classic strategies were not effective for such a material with highly nonlinear properties. Therefore, various adaptive control systems have recently been designed based on existing models to capture their dynamics and compensate for their changes [48; 49; 50].