SEEDED GROWTH OF HYDROXYAPATITE IN THE PRESENCE OF DISSOLVED ALBUMIN AT CONSTANT COMPOSITION

Hydroxyapatite (HAP) crystals were grown from a supersaturated solution by the addition of seed crystals at a temperature of 37 degrees C. Throughout the experiment, the pH and calcium ion concentration were monitored by electrodes in the solution, and maintained at constant values by the addition of ammonia solution (maintaining a pH value of 7.4 during HAP precipitation) and calcium nitrate solution. Triammonium orthophosphate solution was added at the same time as calcium nitrate, so that the ratio of calcium to phosphate ions in the solution was appropriate to the precipitation of HAP. The volume of calcium nitrate solution which needed to be added was used as a measure of HAP crystal growth. Albumin was added to some of the supersaturated solutions to give a concentration in the range 50-250 mu g cm(-3). HAP crystals grown at different albumin concentrations were examined by scanning electron microscopy. After an initial period of 30 min, the growth of HAP crystals increased linearly with time. This behavior was attributed to initial growth healing such dislocations as steps and kinks; growth at screw dislocations was considered to occur throughout the period of the experiment and to give rise to the linear growth phase. The linear growth rate decreased linearly with the albumin concentration. HAP crystals grown in the absence of albumin formed spherical aggregates; the size of these aggregates decreased with the albumin concentration.