## 1 Introduction  
In many industrial systems, the final task of a robot is to grasp and reposition an object. Recent research and development efforts in the field of robotics have focused on designing grippers with high torque and accuracy for grabbing various objects and replacing humans with robotic systems in dangerous or difficult jobs [1]. Common types of robotic grippers in industries are vacuum grippers, pneumatic grippers, hydraulic grippers, and servo-electric grippers. Currently, the state of the art in compliant mechanisms, as seen in [2, 3], requires sophisticated control structures, as well as having a low torque motor that is able to only lift small and light objects. The major problem with using these grippers is related to their rigidity and limitation in grasping a variety of objects, specifically when we are dealing with objects with fragile or soft surfaces. One potential approach involves using pressure sensors to replicate a human-like sense of touch. However, due to cost-effectiveness and concerns regarding the reliability of the gripper's tip strength, alternative options need to be explored and taken into consideration [1; 4]. An alternative emerging technology that has significant potential is flexible and inexpensive materials that can be 3D-printed and used in designing robotic grippers [5]. One of these materials, thermoplastic polyurethane (TPU), is starting to become more available in the market, however, it is not being used in many gripper tasks effectively, as most grippers only use it as a finger cushion [6; 7]. TPU, because of its high resistance, is used in many grippers on the end-effectors to help in picking up objects [6]. This flexible material is also used on tactile sensors that can be implemented into robotic grippers or be designed in a way to create a compressible mechanic for the end of a gripper mechanism [7; 8]. With recent advancements in the technologies of electronic components like electrical motors and additive manufacturing, industrial grippers are continuously going to be better and cheaper [1]. Moreover, the increasing influence of automation and robots in various aspects of human life highlights the necessity of grippers with the capability to perform multiple tasks in a single setting. Many grippers already come equipped with a tactile end effector to increase friction and grip strength, however, to grab a wide variety of objects, the gripper needs compressible material on the surface of it [6; 7; 9]. Compressible material on the end-effector reduces the damage to the object being grasped while increasing the friction between the object and the surface of the robotic hand, allowing a variety of objects to be grabbed [9]. A compressible gripper can work in any condition or environment that is considered hostile to humans, as well as being able to grab any object [1]. One such example of a common commercial application would be the inspection of and work in radiation zones [10; 11]. Another example of a potential application is manufacturing production lines. Most of the current robotics grippers have been made for certain applications and are designed based on exact synthesis. Therefore, they can grasp only similar objects with minimal changes in the application, and even for that, they need readjusting (physical/program adjustment). This is not ideal for applications and industries that want to use robotic arms for grasping a variety of objects with different sizes, shapes, weights, etc., during a process without changing robotic grippers [12]. On the other hand, the total weight that a robot can lift is partially dependent on the gripper (end-effector) it is carrying. This is one of the main concerns of designers, which can be solved by minimizing the number of actuators, applying the optimization algorithms, and making the parts hollow [1; 4; 13; 14].