Compressive properties of commercially available polyurethane foams as mechanical models for osteoporotic human cancellous bone

<p>Abstract</p> <p>Background</p> <p>Polyurethane (PU) foam is widely used as a model for cancellous bone. The higher density foams are used as standard biomechanical test materials, but none of the low density PU foams are universally accepted as models for osteoporotic (OP) bone. The aim of this study was to determine whether low density PU foam might be suitable for mimicking human OP cancellous bone.</p> <p>Methods</p> <p>Quasi-static compression tests were performed on PU foam cylinders of different lengths (3.9 and 7.7 mm) and of different densities (0.09, 0.16 and 0.32 g.cm^-3), to determine the Young's modulus, yield strength and energy absorbed to yield.</p> <p>Results</p> <p>Young's modulus values were 0.08–0.93 MPa for the 0.09 g.cm^-3foam and from 15.1–151.4 MPa for the 0.16 and 0.32 g.cm^-3foam. Yield strength values were 0.01–0.07 MPa for the 0.09 g.cm^-3foam and from 0.9–4.5 MPa for the 0.16 and 0.32 g.cm^-3foam. The energy absorbed to yield was found to be negligible for all foam cylinders.</p> <p>Conclusion</p> <p>Based on these results, it is concluded that 0.16 g.cm^-3PU foam may prove to be suitable as an OP cancellous bone model when fracture stress, but not energy dissipation, is of concern.</p

Fatigue characterization of a polymer foam to use as a cancellous bone analog material in the assessment of orthopaedic devices

Analog materials are used as a substitute to cancellous bone for in vitro biomechanical tests due to their uniformity, consistency in properties and availability. To date, only the static material properties of these materials have been assessed, although they are often used in fatigue tests. Cancellous bone exhibits complex material behavior when subjected to fatigue loads, including modulus degradation, accumulation of permanent strain and increasing hysteresis. Analog materials should exhibit similar fatigue behavior to cancellous bone if they are to be used in cyclic loading tests. In our study, a polymer foam (commercial name HEREX® C70.55) has been studied for its static and fatigue behavior and compared with that of cancellous bone. In compression, the foam exhibited qualitatively similar mechanical behavior, but the degree of modulus degradation and accumulation of permanent strain was lower than expected for cancellous bone. In general, the tensile properties of the foam were greater than found in compression, the opposite to the mechanical behavior of cancellous bone. The methodology employed here could form the basis of selecting suitable analog materials for cancellous bone in the future