The dynamics of calcium phosphate precipitation studied with a new polyacrylamide steady state matrix-model: influence of pyrophosphate collagen and chondroitin sulfate.

A novel steady-state gel-matrix model system is described which facilitates the quantitative kinetic study of the influence of media and matrix composition on a precipitation process. The potentialities of the system are illustrated in experiments in which the precipitation of calcium phosphate in a polyacrylamide film is studied as a function of the calcium and phosphate concentration in the solutions flowing along opposite sides of the film. Addition of pyrophosphate to the reactant solutions was found to diminish the (calcium) x (phosphate) millimolar product at which precipitation starts, indicating a positive effect on nucleation. The slope of the curve was found to decrease, which points to a negative influence of pyrophosphate on the crystal growth process. Incorporation of collagen in the matrix did not change the curve, but incorporation of chondroitin sulfate decreased the formation product since the intercept of the curve was reduced. The usefulness of the system compared with test-tube and non-steady state gel experiments for calcium phosphate precipitation studies and its significance for the study of in vitro and in vivo precipitation processes in general, are discussed.