Streaming potentials in chemically modified bone

Direct streaming experiments with no significant mechanical deformation have been performed to determine the constituent or constituents of bovine tibia mainly responsible for the production of streaming potentials. Following the approach of Frank and Grodzinsky (5), selective removal of either main constituent--collagen or hydroxyapatite--of the tissue was performed by chemical means, and the streaming potential was remeasured. Demineralized samples were prepared by soaking in formic acid/sodium citrate, and anorganic samples were prepared by boiling and also by sodium hypochlorite treatment. Demineralized samples demonstrated zeta potentials close to those of whole bone samples, whereas anorganic samples had much smaller zeta potentials. Collagen rather than hydroxyapatite mineral is therefore implicated as the constituent of whole bone dominating the streaming potential, in agreement with the observation that collagenous tissues containing no mineral phase, i.e., tendon and cartilage, also exhibit streaming potentials. No sign change was observed in whole bone at high NaCl concentration in solutions containing calcium or at low pH. Although the sign of the signal for anorganic bone could be reversed by the addition of Ca2+ or PO4(3+) to the test solutions, the sign of the signal in neither whole bone nor demineralized bone could be so affected. Sign changes in whole bone were observed only with solutions containing basic organic molecules, e.g., protamine sulphates.