The material selection plays a major role in the design of a patellofemoral joint (PFJ) replacement due to the reported damage of the femoral condyles in deep knee flexion using ultra-high molecular weight polyethylene for the patellar components. The use of softer materials such as PCU and PVA/PVP may induce fluid film lubrication and thus reduce the risk of cartilage damage. This research aims to investigate in-vitro tribological performance of the articulation of cartilage-on-PCU (Bionate® I 80A and Bionate® II 80A) and cartilage-on-PVA/PVP (different concentrations and PVA to PVP fractions) using a custom-designed multi-directional pin-on-plate rig.
PVA/PVP showed low COF values (between 0.12±0.01 and 0.14±0.02) which were closer to the cartilage-on-cartilage articulation (0.03±0.01) compared to PCUs (0.41±0.02 for Bionate® II 80A and 0.50±0.02 for Bionate® I 80A). However, these PVA/PVP hydrogels were worn massively after 15 h articulation against the condyles. On the other hand, the counter-face condyles of PCUs were severely damaged, similar to the damage observed in the cartilage-on-stainless steel articulation. Among the PCUs, Bionate® II 80A showed superior tribological performance without depending on the lubricant and surface roughness parameters. When a migrating cartilage contact was achieved by articulating PCU pins on cartilage plates, PCUs revealed similar COF values (0.04±0.01) to the cartilage-on-cartilage articulation.
This work has shown that PVA/PVP hydrogels require further development to enhance their wear resistance if they are to be used as part of a joint replacement. However, they have low COF against articular cartilage and so are attractive possibilities for the future. The tested PCU grades have shown PCUs (especially Bionate® II 80A) can work with acceptably low COF under the right articulating conditions and that they have low wear in those tests. Therefore, the work in this thesis supports the further development of patellofemoral joint prostheses which include PCU components.