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A mechanical and biological evaluation of calcium polyphosphate as a structural bone scaffold in revision total hip replacement Siggers, Kevin

Abstract

Revision total hip replacement (THR) commonly uses the addition of morsellized cancellous bone (MCB) for filling bone defects and to encourage new bone growth, however problems associated with allograft include limited availability, disease transmission and implant migration. The use of synthetic scaffolds as a substitute material is attractive due to its availability and ease of sterilization, however due to the high loads associated with the hip and the need to promote bone growth the number of suitable materials is limited. The novel ceramic calcium polyphosphate (CPP) has been shown to have good mechanical and biological properties and may be a suitable scaffold material for revision THR. In the first part of this study particulate CPP is tested in compression and shear and its mechanical properties are compared to that of the gold standard graft of MCB. In addition, compression and shear tests are carried out on a number of spherical particles of varying size and material in order to determine a relationship between the particle and graft bed properties. The results show that CPP has similar mechanical properties to that of MCB in both compression and shear, making it a suitable substitute graft material. Furthermore a relationship between the particle modulus and graft bed modulus show minimal gain in bed stiffness with increased particle stiffness. The second aspect of the study is to determine the effect of substrate material on MSC expansion and differentiation. CPP, allogeneic bone and hydroxyapatite/tricalcium phosphate (HA/TCP) are seeded with marrow stromal cells (MSCs) and cultured in expansion conditions. At 0, 3, 7, 14 and 21 days cell numbers and gene expressions are evaluated. After an initial drop in cell numbers, CPP and bone supported an increase in proliferation activity and show no up-regulation of the mature bone markers on CPP and Bone, which suggests that these substrates support MSC expansion rather than differentiation. In contrast, MSC number on HA/TCP decreased with time and it showed a down regulation of early osteogenic markers. This along with a substantial increase in mature markers indicate that HA/TCP favours MSC differentiation and maturation along the osteogenic lineage.

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