Self‐setting collagen‐calcium phosphate bone cement: Mechanical and cellular properties

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Abstract
Calcium phosphate cement (CPC) can conform to complex bone cavities and set in-situ to form bioresorbable hydroxyapatite. The aim of this study was to develop a CPC-collagen composite with improved fracture resistance, and to investigate the effects of collagen on mechanical and cellular properties. A type-I bovine-collagen was incorporated into CPC. MC3T3-E1 osteoblasts were cultured. At CPC powder/liquid mass ratio of 3, 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 and 3.5 was 8–10 MPa. They matched the previously reported 2–11 MPa of sintered porous hydroxyapatite implants. 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. In summary, collagen was incorporated into in situ-setting, nano-apatitic CPC, achieving a 10-fold increase in work-of-fracture (toughness) and two-fold increase in osteoblast cell attachment. This moldable/injectable, mechanically strong, nano-apatite-collagen composite may enhance bone regeneration in moderate stress-bearing applications. © 2008 Wiley Periodicals, Inc. J Biomed Mater Res 2009