Carbonated calcium phosphates are suitable pH-stabilising fillers for biodegradable polyesters.

Carbonated amorphous calcium phosphates were prepared with different carbonate content. Their ability to neutralise acidity was probed by time-resolved titration experiments with lactic acid, the monomer that results from degradation of polylactide. The results show that although calcium phosphate as such can reduce acidity, their buffering range lies at a pH of about 4, i.e. outside the physiological range. This is not related to the rate of dissolution. Carbonated calcium phosphates as well as calcium carbonate (calcite) alone are able to keep the pH around 7.4. Consequently, carbonated calcium phosphates are suitable basic filler materials as they are able to compensate acidity, and to buffer within the physiological pH-range.