LUBRICATING ABILITY OF LANGMUIR-BLODGETT-FILMS AS BOUNDARY LUBRICATING FILMS ON ARTICULAR SURFACES

Frictional behavior in sliding pairs of pig articular cartilage and gl ass plate has been studied to elucidate the tribological role of const ituents in a synovial fluid and a surface layer of the articular carti lage. Pig synovial fluid and water solution of hyaluronic acid were us ed as lubricants, The synovial fluid had a significantly superior lubr icating ability to a sodium hyaluronate solution of equivalent viscosi ty under physiologically high load condition. The superiority of the s ynovial fluid seems to be responsible for the boundary lubricating abi lity of constituents other than hyaluronic acid, Langmuir-Blodgett fil ms of phospholipid (L alpha-dipalmitoyl phosphatidylcholine, L alpha-D PPC) on the glass plate maintained low and stable friction, depending on the number of film layers. In conditions of mixed films containing gamma-globulin and L alpha-DPPC, the frictional behavior was improved by increasing the quantity of gamma-globulin. A model of the boundary lubricating mechanism is proposed in which the effective adsorbed film is composed of proteins, phospholipids and other conjugated constitue nts on the articular surfaces, and controlled by hydrophobic groups in those amphiphiles.