On Heterogeneous Protein Adsorption in the Thin Film Lubrication with Model Synovial Lubricants

Description

The research proposal addresses fundamental aspects of artificial implant tribology with the objective of increasing their functional life. The major challenge that confronts prosthetic implants today is the provision of adequate usable life so that patients need not undergo another joint replacement surgery in their remaining lifetime. The reasons for artificial joint failure are complex. One major factor contributing to implant failure is excessive wear and damage of the bearing surfaces. This is a tribology problem which must be addressed through improved lubrication and reduced surface wear. In recent years there has been extensive research into the materials for artificial implants with less emphasis on lubrication mechanism.In natural joint lubrication, the protein adsorption film plays a significant role. However, the formation of the protein adsorption film on the surface of lubricated prosthetic materials is not yet thoroughly understood especially under thin film lubrication. Considerable research on protein adsorption and its effects on the tribological performance of prosthetic materials has been carried out, and the studies are mainly along two parallel lines. One deals fundamentally with the physical chemistry and thermodynamics of adsorbed synovial fluid proteins on surfaces that are usually prepared under conditions that differ from those of a real joint. The other runs mainly with friction and wear tests to assess the effect of the protein adsorption film. Characterizing the adsorption film, which is cultivated out of the lubricated contact conditions, may provide insight into the experimental results on friction and wear. However, the findings of the two lines of research may not always be compatible with each other, and may even be contradictory. The properties of the adsorption film may be governed by lubricated running conditions. The proposed work thus aims to bridge the gap between the aforementioned lines of research. The originality and innovativeness of this study are the proposed new method for evaluating protein adsorption in real-time and lubrication of simulated synovial fluids on surfaces that actually run under real lubricating conditions.We have successfully developed a novel optical slider test device. The slider contact is conformal and provides a closer simulation to the contact of human joints. A transparent disc is used, which enables accurate determination of the film thickness by interferometry and the provision of real-time observation of the lubricated surfaces. Experiments using synthetic synovial fluids with the new test rig showed that the protein adsorption film formed on the surface is non-uniform in thickness and the location that it forms is selective. These preliminary results are promising, and they necessitate a more detailed and systematic experimental study on protein adsorption in this proposed work. A new method of using two light beams will be devised for determining simultaneously the refractive index and true thickness of the adsorption layer. Our main focus is to understand the growth characteristics of the adsorption film and to elucidate the lubrication mechanism of synthetic synovial fluids through a combined experimental and modeling study.The key deliverables of this project are: (a) a new experimental method which enables quantitative and qualitative studies of adsorbed film formation and distribution, including the film thickness and refractive index properties; (b) detailed understanding of the effect of contact conditions and synovial fluid chemistry on protein adsorption at the sliding surface; (c) improved strategies for implant design and material development to optimize protein lubrication effect and minimise wear. We believe that the new technique and know-how developed from this project will find applications in technologically important areas of protein adsorbance, for example biofouling and food processing technology. In longer term the work will contribute to innovations in implant surface properties and chemistry, as well as to industry such as lubrication strategy of low speed friction pairs by constructing protein-like macromolecules as additives in lubricants.