  The human joint is an open-type joint composed of bones, cartilage,
ligaments, synovial fluid, and joint capsule, having advantages of flexibility
and impact resistance. However, replicating this structure in robots introduces
friction challenges due to the absence of bearings. To address this, our study
focuses on mimicking the fluid-exuding function of human cartilage. We employ a
rubber-based 3D printing technique combined with absorbent materials to create
a versatile and easily designed cartilage sheet for biomimetic robots. We
evaluate both the fluid-exuding function and friction coefficient of the
fabricated flat cartilage sheet. Furthermore, we practically create a piece of
curved cartilage and an open-type biomimetic ball joint in combination with
bones, ligaments, synovial fluid, and joint capsule to demonstrate the utility
of the proposed cartilage sheet in the construction of such joints.
