THE LUBRICATING ABILITY OF BIOMEMBRANE MODELS WITH DIPALMITOYL PHOSPHATIDYLCHOLINE AND GAMMA-GLOBULIN

Two kinds of friction tests were conducted to investigate the lubricat ing effect of the injection of amphiphilies on the osteoarthritic join t. The effects of the addition of L alpha-dipalmitoyl phosphatidylchol ine (L alpha-DPPC) riposomes and gamma-globulin in a saline solution o f sodium hyaluronate (HA) were evaluated through pendulum friction tes ts. The frictional characteristics of pig shoulder joints were confirm ed to depend on the viscosity of the lubricants only in the physiologi cally low load condition and in the condition immediately after loadin g. Detergent (polyoxyethylene p-t-octylphenyl ether) was successfully used to remove adsorbed films from the articular surfaces. The frictio n coefficient of natural synovial joints was significantly increased i n a mode of mixed lubrication with the HA solution of 0.2 g/dl by the treatment of the surface with the detergent. The addition of L alpha-D PPC riposomes or gamma-globulin significantly improved the boundary lu bricating ability of the articular surfaces treated with the detergent , depending on the quantity of those additives. It appears that the L alpha-DPPC riposomes and gamma-globulin can form protective films on t he articular surfaces like a biomembrane. Moreover, the reciprocating frictional behaviour in sliding pairs of pig articular cartilages and glass plates was studied in order to elucidate the tribological role o f those constituents in the boundary lubricating film on the articular surface. Pig synovial fluid and water solutions of HA were used as lu bricants. The synovial fluid had superior lubricating ability compared to the HA solution of equivalent viscosity under a physiologically hi gh load condition. This fact seems to be responsible for the boundary lubricating ability of constituents other than hyaluronic acid. Langmu ir-Blodgett (LB) films of L alpha-DPPC on the glass plate were kept at a low and stable friction coefficient, depending on the number of fil m layers. In conditions of mixed films with L alpha-DPPC and gamma-glo bulin, the frictional behaviour was improved by increasing the quantit y of gamma-globulin. A model is proposed in which the effective adsorb ed films are composed of proteins, phospholipids and other conjugated constituents on the articular surfaces to be accurate in describing th e boundary lubricating mechanism. The mechanism is controlled by hydro phobic groups in those amphiphilies.