Abstract: Naturally optimized successful synovial joints with lightweight, high load-carrying, ultra-low friction and wear have attracted tribological communities to constantly imitate and replicate. Despite impressive advances in cartilage lubrication, extending such extraordinary performance advantages to macroscale solid lubrication remains a challenge. Herein, inspired by the fascinating interplay of synovial joints, a novel kind of trans-scale hierarchical structured ceramic-based composite was developed. Introducing microscale Ag microspheres (AgMs) “cartilage” layer and nanoscale Ag quantum dots/MXene (AgQDs/MXene) “synovial fluid” into the interior and exterior of printed macroscale SiOC “hard bone” realistically restores the gradient structure of synovial joint prototype. The resulted composite with ideal compressive strength (70.44 MPa) can achieve a 60.53% friction reduction and a low wear rate (2.05 × 10^-6 mm³ N^-1 m^-1) in dry tribo-contact for 3600 sliding cycles, while also maintaining considerable low friction (∼ 0.11) over 10,000 sliding cycles and long-term stable lubrication (∼ 0.13) for up to 50,000 reciprocating cycles. Such extraordinary performance can be explained by the division of macro contacts, full loading of AgMs and AgQDs/MXene, abrasive debris capture and removal, as well as the shear rolling effect induced by friction process. This work opens a new avenue to develop structural lubricating materials for complex engineering applications.

Key words: 3D printing, Synovial joints trans-scale structure, AgQDs/MXene/SiOC, High lubrication, Superior wear resistance