High early strength calcium phosphate bone cement: Effects of dicalcium phosphate dihydrate and absorbable fibers

Calcium phosphate cement (CPC) sets in situ to form resorbable hydroxyapatite with chemical and crystallographic similarity to the apatite in human bones, hence it is highly promising for clinical applications. The objective of the present study was to develop a CPC that is fast setting and has high strength in the earl), stages of implantation. Two approaches were combined to impart high early strength to the cement: the use of dicalcium phosphate dihydrate with a high Solubility (which formed the cement CPC,,) instead of anhydrous dicalcium phosphate (which formed the conventional cement CPCA), and the incorporation of absorbable fibers. A 2 X 8 design was tested with two materials (CPCA and CPC,,) and eight levels of cement reaction time: 15 min, 30 min, I h, 1.5 h, 2 h, 4 h, 8 h, and 24 h. An absorbable Suture fiber was incorporated into cements at 25%, Volume fraction. The Gilmore needle method measured a hardening time of 15.8 min for CPCD, five-fold faster than 81.5 min for CPCA, at a powder:liquid ratio of 3:1. Scanning electron microscopy revealed the formation of nanosized rod-like hydroxyapatite crystals and platelet crystals in the cements. At 30 min, the flexural strength (mean +/- standard deviation; n = 5) was 0 MPa for CPCA (the paste did not set), (4.2 +/- 0.3) MPa for CPCD, and (10.7 +/- 2.4) MPa for CPCD-fiber specimens, significantly different from each other (Tukey's at 0.95). The work of fracture (toughness) was increased by two orders of magnitude for the CPCD-fiber cement. The high early strength matched the reported strength for cancellous bone and sintered porous hydroxyapatite implants. The composite strength S. was correlated to the matrix strength S-m: S-c = 2.16S(m). In summary, substantial early strength was imparted to a moldable, self-hardening and resorbable hydroxyapatite via two synergistic approaches: dicalcium phosphate dihydrate, and absorbable fibers. The new fast-setting and strong cement may help prevent catastrophic fracture or disintegration in moderate stress-bearing bone repairs. (c) 2005 Wiley Periodicals, Inc.