Reinforcement of alpha-tricalcium phosphate-based cement by incorporation of rod-shaped hydroxyapatite

摘要

Calcium phosphate cement (CPC) is an injectable bioactive ceramic applicable in orthopedic fields such as fillers in bone defects. Alpha-tricalcium phosphate (α-TCP, Ca_3(PO_4)_2) is known as a major component of CPC, since it transforms into hydroxyapatite (HAp, Ca_(10)(PO_4)_6(OH)_2) through reaction with H2O. The transformation from α-TCP into HAp leads setting of CPC. Improvement of the mechanical strength of CPC is expected by addition of HAp crystals with unique morphology. This study is focused on fabrication of α-TCP-based cements with incorporation of rod-shaped HAp, to evaluate their setting properties and mechanical properties. Two types of rod-shaped HAp were prepared through hydrothermal processing from different starting materials, i.e. one was calcium-chelated ethylenediamine tetraacetic acid (Ca-EDTA) in phosphate solution, and the other was beta-tricalcium phosphate ((S-TCP). Rod-shaped crystals with ca. 6 and 25 μm in length were obtained through the hydrothermal processing from Ca-EDTA and β-TCP, respectively. Both of them were identified to be HAp by X-ray diffraction. Irregular-shaped HAp particles with ca. 3 μm in size were used as a control. The HAp crystals were mixed with powder of α-TCP in the range from 0 to 15 mass%. The powder and ultrapure water was mixed at powder/liquid mass ratio of 2/1 to results in a paste, followed by shaped with a cylindrical mold with 5 in dimeter and 10 mm in length. Setting time of the cement was measured according to the international standard ISO 9917. Compressive strength of the specimens was measured after incubation in 100% humidity at 36.5°C for 1 hour. The setting time of the prepared paste was shortened with increasing the amounts of added HAp, irrespective of their morphology. The reduced setting time might be caused by enhancement of HAp formation. The prepared cylindrical specimens with 5 mass% of rod-shaped HAp with 25 μm in length showed the compressive strength of 50 MPa, while that without addition of HAp was 35 MPa. The compressive strength of the specimens prepared with addition of rod-shaped HAp with 6 μm in length or with irregular-shaped HAp particles of 3 μm in size showed similar compressive strength of the cements without HAp. The rod-shaped HAp crystals with longer length distinctly contributed to improvement of mechanical strength, while setting reaction of the paste was accelerated by addition of HAp crystals.