Strong and macroporous calcium phosphate cement: Effects of porosity and fiber reinforcement on mechanical properties

Because of its excellent osteoconductivity and bone-replacement capability, self-setting calcium phosphate cement (CPC) has been used in a number of c linical procedures. For more rapid resorption and concomitant osseointegrat ion, methods were desired to build macropores into CPC; however, this decre ased its mechanical properties. The aims of this study, therefore, were to use fibers to strengthen macroporous CPC and to investigate the effects of the pore volume fraction on its mechanical properties. Water-soluble mannit ol crystals were incorporated into CPC paste; the set CPC was then immersed in water to dissolve mannitol, producing macropores. Mannitol/(mannitol CPC powder) mass fractions of 0, 10, 20, 30, and 40% were used. An aramid f iber volume fraction of 6% was incorporated into the CPC-mannitol. specimen s, which were set in 3 mm x 4 mm x 25 mm. molds and then fractured in three -point flexure to measure the strength, work of fracture, and modulus. The dissolution of mannitol created well-formed macropores, with CPC at 40% man nitol having a total porosity of a 70.8% volume fraction. Increasing the ma nnitol content significantly decreased the properties of CPC without fibers (analysis of variance; p < 0.001). The strength (mean standard deviation; n = 6) of CPC at 0% mannitol was 15.0 +/- 1.8 MPa; at 40% mannitol, it decr eased to 1.4 +/- 0.4 MPa. Fiber reinforcement improved the properties, with the strength increasing threefold at 0% mannitol, sevenfold at 30% mannito l, and nearly fourfold at 40% mannitol. The work of fracture increased by 2 orders of magnitude, but the modulus was not changed as a result of fiber reinforcement. A scanning electron microscopy examination of specimens indi cated crack deflection and bridging by fibers, matrix multiple cracking, an d frictional pullout of fibers as the reinforcement mechanisms. Macroporous CPCs were substantially strengthened and toughened via fiber reinforcement . This may help extend the use of CPCs with macropores for bony ingrowth to the repair of larger defects in stress-bearing locations. (C) 2001 John Wi ley & Sons, Inc.