The role of SAPL as a boundary lubricant in prosthetic joints

The purpose of this study was to test the potential of the bodyʹs natural lubricant, surface-active phospholipids (SAPL), to decrease friction in prosthetic joints by acting as a boundary lubricant, and to test the interaction of SAPL with Pyrolytic Carbon (PyC), a new material used in artificial heart valves and joint replacements of the upper limb. Initial testing [Coller R, Hargreaves DJ, Hills BA, Crawford RW. Is SAPL the boundary lubricant in prosthetic joints: friction testing and surface rinsing. Australian Journal of Mechanical Engineering 2004;1:63–71] slid ultra-high molecular weight polyethylene (UHMWPE) pins against highly polished stainless steel plates (surface roughness of 0.01 μm). This second series of tests was a continuation of previous research, validating the results and expanding the experiments to investigate the interaction of SAPL with PyC. In both cases, a Hounsfield test rig was used to perform the tests at ambient room conditions and at 37 °C. In both series of tests, comparative friction measurements were made using a synthetic SAPL, dipalmitoyl phosphatidylcholine (DPPC) with saline and saline only as the lubricants. When DPPC was used, the friction was reduced by 50% for the UHMWPE/SS combination, and was reduced by more than 75% for the UHMWPE/PyC combination, suggesting that DPPC acts as an effective boundary lubricant. This recent study, along with previous testing [Coller R, Hargreaves DJ, Hills BA, Crawford RW. Is SAPL the boundary lubricant in prosthetic joints: friction testing and surface rinsing. Australian Journal of Mechanical Engineering 2004;1:63–71], strongly suggests that SAPL has the ability to decrease friction in prosthetic joints by acting as a boundary lubricant, and that SAPL interacts favourably with PyC.