You are presented with multiple paper abstracts, alongside the associated literature review and chapter titles. Given the provided information, you are going to do a literature review. Please generate a coherent literature review that synthesizes the content, draws connections between different works, highlights major findings, and identifies any gaps in the existing research.

Literature Review Title: Various Robots Made from Piezoelectric Materials and Electroactive Polymers: A Review 
Chapter Title:  Electroactive Polymers Property overview 
1. Abstract of Cited Paper (BIB001):  Electroactive polymers (EAP) are an emerging class of functional materials that respond to electrical stimulation with large displacement. This attractive characteristic earned them the name artificial muscles. Even though the actuation force and robustness of existing EAP materials require further improvement, there has already been a series of reported successes. The successful applications that were demonstrated include catheter steering element, miniature manipulator, dust wiper, miniature robotic arm, and grippers. Some of the currently considered applications may be difficult to accomplish, and it is important to examine the requirements to the level that current materials can address. Using EAP to replace existing actuators may be a difficult challenge, and therefore it is highly desirable to identify a niche application where it would not need to compete with existing capabilities. The field involves multidisciplines that include materials, chemistry, electromechanics, computers, electronics, etc. A review of the state of the art and some of the challenges to the application of these materials are provided. 
2. Abstract of Cited Paper (BIB002):  Human-like robots are increasingly becoming an engineering reality thanks to recent technology advances. These robots, which are inspired greatly by science fiction, were originated from the desire to reproduce the human appearance, functions and intelligence and they may become our household appliance or even companion. The development of such robots is greatly supported by emerging biologically inspired technologies. Potentially, electroactive polymer (EAP) materials are offering actuation capabilities that allow emulating the action of our natural muscles for making such machines perform lifelike. There are many technical issues related to making such robots including the need for EAP materials that can operate as effective actuators. Beside the technology challenges these robots also raise concerns that need to be addressed prior to forming super capable robots. These include the need to prevent accidents, deliberate harm, or their use in crimes. In this paper, the potential EAP actuators and the challenges that these robots may pose will be reviewed.

Literature Review:
For decades, attention has been focused on polymer actuators for the design and control of smart systems. Electroactive polymer (EAP) is a kind of active polymer that can produce a significant shape change in response to external electrical stimulation. The EAP has attractive properties, being flexible, lightweight, and soft compared with other smart materials. There are many different types of EAPs and they can be classified into two categories according to their activation mechanisms, electronic EAPs and ionic EAPs. Electronic EAPs, such as dielectric elastomers (DEs) and liquid crystal elastomers (LCEs), are driven by electric field or Maxwell forces. These EAPs have fast response time and high mechanical energy density. In addition, they can generate a large actuating force under high voltage input (higher than 100 V). Since electronic EAPs can be made to hold the induced strain under activation of a certain DC voltage input, they can be used in robotic applications. However, they have mostly mono-polar actuating because of electrostriction effect caused by independence of the voltage polarity. On the other hand, ionic EAPs, such as conductive polymers (CPs) and ionic polymer metallic composites (IPMCs), are driven by the ionic movements (diffusion of ions) and they can be activated by a low voltage input (1 or 2 V). These EAPs has inherent bi-directional actuation that depends on the voltage polarity. The significant disadvantage of Ionic EAPs is that they require encapsulation or protective layer to operate in open-air condition. Moreover, they have low electro-mechanical coupling efficiency and slow response time. The advantages and disadvantages of the different EAPs have been well addressed in BIB001 BIB002 BIB003 .