A NOVEL SKELETAL DRUG-DELIVERY SYSTEM USING SELF-SETTING CALCIUM-PHOSPHATE CEMENT .6. EFFECT OF PARTICLE-SIZE OF METASTABLE CALCIUM PHOSPHATES ON MECHANICAL STRENGTH OF A NOVEL SELF-SETTING BIOACTIVE CALCIUM-PHOSPHATE CEMENT

Resistance to compressive strength after setting of the calcium phosph ate cement consisting of tetracalcium phosphate (TECP), dicalcium phos phate dihydrate (DCPD), and 40 wt/wt% of a synthetic hydroxyapatite (H AP) was tested. An equimolar mixture of the calcium phosphate powder c ontaining DCPD (particle diameter [D] 0.52-3.33 mu m) and TECP (D, 1.1 -13.1 mu m) transformed into HAP at 37 degrees C, 100% RH after being mixed with 25 mM phosphoric acid. X-ray diffraction suggested that the cement containing fine particles of DCPD and TECP completely transfor med to HAP, but that mixtures containing larger particles did not. Bec ause particle size of both DCPD and TECP affected the compressive stre ngth of the cement, the crystal growth of HAP during cement formation depended on the specific surface area (Sw) of the raw materials. The c rystallite size of transformed HAP was estimated based on X-ray diffra ction peaks at 25.8 and 32.8 degrees attributable to the 002 and 300 p lanes. The crystallite size attributable to the 300 plane decreased wi th increasing Sw, but that attributable to the 002 plane showed no sig nificant relationship. The compressive strength of the cement after ha rdening increased with an increase of its Sw. This suggested that the harder calcium phosphate cement was (derived) from the smaller particl e size of the raw materials. (C) 1995 John Wiley and Sons, Inc.