Lubricating Ability of Langmuir-Blodgett Films as Boundary Lubricating Films on Articular Surfaces

Abstract

Frictional behavior in sliding pairs of pig articular cartilage and glass plate has been studied to elucidate the tribological role of constituents in a synovial fluid and a surface layer of the articular cartilage. Pig synovial fluid and water solution of hyaluronic acid were used as lubricants. The synovial fluid had a significantly superior lubricating ability to a sodium hyaluronate solution of equivalent viscosity under physiologically high load condition. The superiority of the synovial fluid seems to be responsible for the boundary lubricating ability of constituents other than hyaluronic acid. Langmuir-Blodgett films of phospholipid (Lα-dipalmitoyl phosphatidylcholine, Lα-DPPC) on the glass plate maintained low and stable friction, depending on the number of film layers. In conditions of mixed films containing γ-globulin and Lα-DPPC, the frictional behavior was improved by increasing the quantity of γ-globulin. A model of the boundary lubricating mechanism is proposed in which the effective adsorbed film is composed of proteins, phospholipids and other conjugated constituents on the articular surfaces, and controlled by hydrophobic groups in those amphiphiles.