Background: Debonding of the stem-cement interface occurs inevitably in-vivo under physiological loading, and pseudo-synovial fluid is subsequently pumped into this interface, serving as the lubricant. However, the influence of protein adsorption onto the femoral stem surface has not been well taken into consideration in previous in vitro studies.
Materials and methods: The biotribological properties at the stem-cement interface were investigated through a series of fretting frictional tests using polished stainless steel 316L stem and smooth bone cement, lubricated by three different media at body temperature, i.e. 100% calf serum, 25% calf serum, and 0.9% saline solution. The surface characterization of the femoral stem was evaluated sequentially using optical microscope, optical interferometer, scanning electron microscope, and Raman spectroscopy.
Results: The friction coefficient generally kept stable during the test, and the minimum value (0.254) was obtained when 100% calf serum was used as the lubricant. Slight scratches were detected within the contact area for the stainless steel 316L stems lubricated by 100% calf serum and 25% calf serum, which was further surrounded by the adsorbed protein film with alveolate feature. Additionally, a wear scar was present within the contact area when 0.9% saline solution was used as the lubricant.
Conclusions: Protein adsorption onto the stainless steel 316L stem surface affected the biotribological properties at the stem-cement interface under oscillatory fretting mechanism. Generation of wear debris at the stem-cement interface may be postponed by modification of physicochemical properties of the femoral stem to promote protein adsorption.
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