Proof-of-concept study of the TriBot: a robot-based test setup for biotribological analyses of curved articular surfaces

Luisa de Roy ¹ Roderigo Moritz ¹ Jonas Schwer ¹ Klaus Schlickenrieder² ² Anita Ignatius ¹ Andreas Martin Seitz ^1*

• ¹ Institute of Orthopedic Research and Biomechanics, Faculty of Medicine, University of Ulm, Ulm, Germany
• ² Ulm University of Applied Sciences, Ulm, Baden-Wurttemberg, Germany

Introduction: Investigations on the articular cartilage (AC) frictional properties contribute to a better understanding of knee joint functionality. We identified the need for a tribological setup that allows for friction measurements on curved AC surfaces, without disrupting its structural integrity, under orthogonal contact conditions and controlled normal force application. Therefore, a robotic-based tribometerthe TriBotwas developed and validated in a two-part proof-of-concept study.Methods: First, the friction coefficients of polyoxymethylene pins on three different polyamide (PA) shapes were determined for validation purposes. Second, the frictional properties on porcine tibial plateaus were investigated. Trajectories on the medial and the lateral tibial surface were tested in the intact cartilage state and after inducing an anteromedial local defect.Results: No significant differences in the friction coefficients of the PA samples were found. Inducing an anteromedial cartilage defect significantly increased friction on the affected trajectories (+ 30 %, p < 0.05). Discussion: Our findings showed that the robotic tribometer is suitable for friction measurements on complexly shaped samples and that the system can detect differences in cartilage friction due to structural tissue damage. Overall, the robotic tribometer has the potential to advance our understanding of the knee joint's friction-related functionality.