Calcium phosphate cement containing resorbable fibers for short-term reinforcement and macroporosity

Calcium phosphate cement (CPC) sets to form hydroxyapatite and has been used in medical and dental procedures. However, the brittleness and low strength of CPC prohibit its use in many stress-bearing locations, unsupported defects, or reconstruction of thin bones. Recent studies incorporated fibers into CPC to improve its strength. In the present study, a novel methodology was used to combine the reinforcement with macroporosity: large-diameter resorbable fibers were incorporated into CPC to provide short-term strength, then dissolved to create macropores suitable for bone ingrowth. Two types of resorbable fibers with 322 microm diameters were mixed with CPC to a fiber volume fraction of 25%. The set specimens were immersed in saline at 37 degrees C for 1, 7, 14, 28 and 56d, and were then tested in three-point flexure. SEM was used to examine crack-fiber interactions. CPC composite achieved a flexural strength 3 times, and work-of-fracture (toughness) nearly 100 times, greater than unreinforced CPC. The strength and toughness were maintained for 2-4 weeks of immersion, depending on fiber dissolution rate. Macropores or channels were observed in CPC composite after fiber dissolution. In conclusion, incorporating large-diameter resorbable fibers can achieve the needed short-term strength and fracture resistance for CPC while tissue regeneration is occurring, then create macropores suitable for vascular ingrowth when the fibers are dissolved. The reinforcement mechanisms appeared to be crack bridging and fiber pullout, the mechanical properties of the CPC matrix also affected the composite properties.