This study describes the formation of a calcium polyacrylate-hydroxyap
atite cement. Our hypothesis was that calcium phosphates would rapidly
hydrolyze in the presence of polyacrylic acid (PAA) to form a cement.
PAA, tetracalcium phosphate (TetCP), and dicalcium phosphate (DCP) we
re reacted together and formed calcium polyacrylate (CPA) and hydroxya
patite (HAp) within 10 h at 38 degrees C, resulting in hardened masses
. Reaction times increased with decreasing (HAp reactants)/PAA ratios.
In the first of three reaction stages, the pH increased while CPA and
dicalcium phosphate dihydrate (DCPD) formed. Two steady-state pH cond
itions occurred during the second stage as TetCP reacted with DCPD and
DCP. The first steady-state pH was the result of DCPD and TetCP react
ing at near-equilibrium conditions. The second steady-state pH resulte
d as the reaction became limited by DCP dissolution. The third, diffus
ionally controlled, stage occurred as DCP and previously formed HAp re
acted to produce calcium-deficient HAp (Ca/P=1.5). The emphasis of thi
s investigation was to establish the mechanistic path involved and the
rate-limiting steps of the reaction.