Advancing McKibben artificial muscles: Bio-inspired design for complex motion

McKibben Artificial Muscles (AMs) are widely used in soft robotics as actuators due to their compliance and high force output. However, achieving complex motions with multiple AMs in different orientations remains challenging, as each requires a bulky pneumatic or hydraulic system, complicating assembly and increasing the risk of leaks. These limitations restrict their use in compact or lightweight applications. Inspired by natural muscle architectures that optimize force distribution and enable multidirectional motion, this study aims to integrate complex fiber arrangements into a single McKibben AM. A novel fabrication technique was developed using an interplay between multiple traditional Japanese Kumihimo braiding disks to create multi-directional AMs. Two case studies demonstrate the approach: (1) a bending actuator capable of achieving programed bending angles depending on actuation pressure and (2) a convergent actuator whose combined branches reconfigured output force direction to extend motion range. The resulting branched AMs locally encode complex motion within their structure, eliminating the need for complex actuator systems. This manufacturing strategy advances McKibben AM design toward more compact, adaptive and versatile systems for advanced soft robotic applications.