Protection of Cartilage in Natural Joints: Investigation of the Impact of Hyaluronic Acid and Polymeric Substitutes on the Structure and Stability of Surface-Bound Lipid Layers

• Applicant: Professor Dr. Reiner Dahint
• Subject Area: Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry ; Biophysics ; Physical Chemistry of Solids and Surfaces, Material Characterisation
• Term: from 2015 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 270667246

Osteoarthritis is the most common joint disease in the western world. It typically starts with a degeneration of the cartilage, leading to increased friction in the joint, stiffness, and inflammation. A much discussed treatment is the so-called viscosupplementation which is based on the intra-articular injection of hyaluronic acid (HA). HA is a negatively charged polysaccharide that forms an essential component of the joint fluid. At physiological conditions HA supposedly bears friction-reducing properties. It is further believed that HA, adsorbed to cartilage, forms a protective layer against wear under operational demands of the joint. The underlying mechanisms of viscosupplementation, however, are not known in detail and its effectiveness is subject of current medical research. A special focus lies on the dependence of a possible successful treatment on molecular weight and concentration of HA as well as on the exclusion of placebo effects.The aim of the research project is to systematically investigate the effects of HA on the layer formation in joints using a model system. Since the articular cartilage is covered by a lipid layer, which in turn is in contact with the joint fluid, the focus of the studies will be on the influence of HA on the structure and stability of surface-bound lipid films. In fact, a stabilizing effect of HA on lipid layers was observed in initial experiments. On basis of these results we will develop a detailed understanding of the mechanisms, which determine structure formation and promote stability. An important aspect will be to investigate which specific properties of HA contribute to the stability of the terminal lipid layers and whether polymeric substitutes for HA are as effective or even more appropriate for achieving the desired functionality. Of particular interest will be the question on the influence of molecular weight, concentration and charge of the polymer used, ionic strength and pH of the embedding aqueous solution as well as the response of the interfacial layers formed to mechanical load.Main characterization technique is a combination of in situ neutron reflectometry and infrared spectroscopy, which provides detailed information on both the internal structure and composition of the layers as well as on the molecular conformation. For this purpose a novel neutron reflectometer with integrated infrared analysis, which was built by us, is available at the Helmholtz-Zentrum Berlin. Pressure and shear cells have been developed for the experimental investigation of applied mechanical stresses in the model joint system, and will also be used in the stability tests. Additional structural investigations of the respective solid/liquid interfaces will be conducted with a suitable X-ray reflectometer. Above studies will be complemented by other surface analytical in situ techniques such as ellipsometry, quartz-crystal-microbalance measurements and atomic force microscopy in liquid phase.

• DFG Programme: Research Grants
• Co-Investigator: Dr. Roland Steitz
• Cooperation Partner: Professor Dr. Joachim Dzubiella