Self-hardening calcium phosphate cement-mesh composite: reinforcement, macropores, and cell response

Calcium phosphate cement (CPC) self-hardens to form hydroxyapatite, has excellent osteoconductivity and bone-replacement ability, and is promising for craniofacial and orthopedic repair. However, its low strength limits CPC to only nonstress repairs. This study aimed to reinforce CPC with meshes to increase strength, and to form macropores in CPC for bone ingrowth after mesh dissolution. A related aim was to evaluate the biocompatibility of the new CPC-mesh composite. Absorbable polyglactin meshes, a copolymer of poly(glycolic) and poly(lactic) acids, were incorporated into CPC to provide strength and then form interconnected cylindrical macropores suitable for vascular ingrowth. The composite flexural strength, work-of-fracture, and elastic modulus were measured as a function of the number of mesh sheets in CPC ranging from 1 (a mesh on the tensile side of the specimen) up to 13 (mesh sheets throughout the entire specimen), and as a function of immersion time in a physiological solution from 1 to 84 days. Cell culture was performed with osteoblast-like cells and the cell viability was quantified using an enzymatic assay. The strengths (mean +/- SD; n = 6) of CPC containing 13 or 6 meshes were 24.5 +/- 7.8 and 19.7 +/- 4.3 MPa, respectively, not significantly different from each other; both were significantly higher than 8.8 +/- 1.9 MPa of CPC without mesh (Tukey's at 0.95). The work-of-fracture of CPC with 13 or 6 meshes was 3.35 +/- 0.80 and 2.95 +/- 0.58 kJ/m(2), respectively, two orders of magnitude higher than 0.021 +/- 0.006 kJ/m(2) of CPC without mesh. Interconnected macropores were formed in CPC at 84 days' immersion. The new CPC-mesh formulation supported the adhesion, spreading, proliferation, and viability of osteoblast-like cells in vitro. In conclusion, absorbable meshes in CPC increased the implant strength by three-fold and work-of-fracture by 150 times; interconnected macropores suitable for bone ingrowth were created in CPC after mesh dissolution. The higher strength may help extend the use of CPC to larger stress-bearing repairs, and the macropores may facilitate tissue ingrowth and integration of CPC with adjacent bone.