Phase Conversion Of Ice-Templated Alpha-Tricalcium Phosphate Scaffolds Into Low-Temperature Calcium Phosphates With Anisotropic Open Porosity

The current study aims to extend the material platform for anisotropically structured calcium phosphates to low-temperature phases such as calcium-deficient hydroxyapatite (CDHA) or the secondary phosphates monetite and brushite. This is achieved by the phase conversion of highly porous alpha-tricalcium phosphate (alpha-TCP) scaffolds fabricated by ice-templating into the aforementioned phases by hydrothermal treatment or incubation in phosphoric acid. Prior to these steps, alpha-TCP scaffolds are either sintered for 8 h at 1400 degrees C or remain in their original state. Both nonsintered and sintered alpha-TCP specimens are converted into CDHA by hydrothermal treatment, while a transformation into monetite and brushite is achieved by incubation in phosphoric acid. Hydrothermal treatment for 72 h at 175 degrees C increases the porosity in nonsintered samples from 85% to 88% and from 75% to 88% in the sintered ones. An increase in the specific surface area from (1.102 +/- 0.005) to (9.17 +/- 0.01) m(2) g(-1) and from (0.190 +/- 0.004) to (2.809 +/- 0.002) m(2) g(-1) due to the phase conversion is visible for both the nonsintered and sintered samples. Compressive strength of the nonsintered samples increases significantly from (0.76 +/- 0.11) to (5.29 +/- 0.94) MPa due to incubation in phosphoric acid.