# Development, Experimental Assessment, and Application of a Vacuum-Driven Soft Bending Actuator
## 1 Introduction  
Soft pneumatic actuators are versatile and flexible components that use compressed air to perform functional tasks, enabling multi-axis motion. Their ability to adapt to the object's shape makes them especially well-suited for precise and delicate tasks in industrial manipulation and medical robotics. Current advancements in soft pneumatic actuators focus on addressing two major challenges: developing innovative design solutions and utilizing new soft materials with state-of-the-art manufacturing technologies [1, 2, 3, 4, 5]. In the pursuit of developing more flexible and lightweight actuators, various design solutions for soft pneumatic actuators have been proposed. These solutions are generally categorized into actuators that use positive or negative (vacuum) pressure or both simultaneously [6]. Soft pneumatic actuators using positive pressure can generate substantially higher forces due to their ability to operate with higher pressure values [7]. However, higher pressure increases the risk of material fatigue and actuator explosion due to thelimited material strength [8; 9; 10]. To address this issue, soft pneumatic actuators utilizing vacuum pressure have been developed, with a maximum value of \(-1\) bar [11; 12; 13]. Furthermore, design solutions of the soft pneumatic actuators vary depending on the type of motion they are intended to perform. Depending on application requirements, they can be designed for linear motion, bending, twisting, or a combination of these motions. Linear motion is typically achieved through the linear expansion or contraction of the actuator, driven by positive pressure [14; 15] or vacuum pressure [16; 17]. In contrast, angular bending involves two-axis or multi-axis motion and can be accomplished using various design approaches [18; 19]. For two-axis bending motion, one approach utilizes an asymmetric actuator geometry that enables bending under positive pressure [20] or vacuum pressure [21; 22; 23]. Angular motion can also be achieved with a symmetric actuator design incorporating a flexible limiting element [24], which restricts contraction on one side, causing the actuator to bend. A key factor in advancing soft pneumatic actuators is the selection of soft materials, which, when combined with innovative manufacturing techniques, significantly accelerates their development [25]. Silicone rubber, one of the most widely used materials, offers exceptional elasticity, allowing actuators to be fabricated by casting into custom molds to achieve desired shapes and dimensions. For example, studies [26; 27] employed this method to produce multi-chamber soft pneumatic bending actuators integrated into the soft robotic gripper. Similar results were reported in [28; 29], highlighting the conclusion that silicone rubber-based actuators typically operate at pressures under \(1\) bar, as higher pressures pose a risk of actuator explosion. Another method for fabricating soft pneumatic actuators is 3D printing with flexible materials. In the study [30], flexible thermoplastic elastomers (TPE) were used to fabricate a cell-based soft bending actuator. Furthermore, ref. [31] showed that pneumatic actuators of similar shape made from thermoplastic polyurethane (TPU) exhibited superior resistance to fatigue compared to those made from silicone rubber, withstanding up to 6400 cycles. However, ensuring actuator durability for real mechatronic systems requires materials with proven long-term performance. In [32; 33], commercially available ribbed rubber bellows, certified for durability by the manufacturer, were employed in the design of soft pneumatic actuators. Similarly, ref. [34] fabricated a soft pneumatic actuator using a heat-shrinkable material, with experimental results indicating the ability to achieve up to 150,000 operational cycles with minimal material degradation.