Self-setting Collagen-Calcium Phosphate Bone Cement: Mechanical and Cellular Properties

Calcium phosphate cement (CPC) can conform to complex bone cavities and set in situ to form bioresorbable hydroxapatite. OBJECTIVES: To develop a CPC-collagen composite with improved fracture resistance, and to investigate the effects of collagen on mechanical and cellular properties. METHODS: A type I bovine collagen was incorporated into CPC. MC3T3-E1 osteoblast cells were cultured on the composite. Work of fracture, flexural strength, cell attachment, and number of live cells per specimen area were compared. CPC without collagen served as the control for physical property studies and tissue culture polystyrene served as the control for cell studies. RESULTS: At a CPC powder/liquid mass ratio of 3/1, the work of fracture (mean ± sd; n = 6) was increased from (22 ± 4) J/m² at 0% collagen, to (381 ± 119) J/m² at 5% collagen (p < 0.05). At 2.5 – 5% of collagen, the flexural strength at powder/liquid ratios of 3/1 and 3.5/1 was 8 – 10 MPa. They matched the previously reported 2 – 11 MPa of sintered porous hydroxyapatite impants. SEM revealed that the collagen fibers were covered with nano-apatite crystals and bonded to the CPC matrix. Higher collagen content increased the osteoblast cell attachment (p < 0.05). The number of live cells per specimen area was (382 ± 99) cells/mm² on CPC containing 5% collagen, higher than (173 ± 42) cells/mm² at 0% collagen (p < 0.05). The cytoplasmic extensions of the cells anchored to the nano-apatite crystals of the CPC matrix. CONCLUSIONS: Collagen was incorporated into in situ setting nano-apatite CPC, achieving a 10-fold increase in work of fracture (toughness) and 2-fold increase in osteoblast cell attachment. This moldable/injectable, mechanically strong, nano-apatite-collagen composite may enhance bone regeneration in moderate stress bearing applications.

Supported by NIH/NIDCR R01 grant DE14190.