Trabecular bone modulus

Inspired by the hierarchical structures that enable bone function, Deng et al. recently developed a mechanically competent 3D scaffold mimicking the bone marrow cavity and the lamellar structure of bone by orienting electrospun polyphosphazene-polyester blend nanofibers in a concentric manner with an open central cavity (Figure 11.9b and c) [66]. The 3D biomimetic scaffold exhibited mechanical characteristic similar to native bone. Compressive modulus of the scaffold was found to be within the range of human trabecular bone. When tuned to have desired properties, the concentric open macrostructures of nanofibers that structurally and mechanically mimic the native bone can be a potential scaffold design for accelerated bone healing. 

Zysset, P. K., Edward Guo, X., Edward Hoffler, C., Moore, K. E. Goldstein, S. A. Elastic modulus and hardness of cortical and trabecular bone lamellae measured by nanoindentation in the human femur. Journal of Biomechanics 32, 1005-1012, doi 10.1016/s0021-9290(99)00111-6(1999). 

Interestingly, the failure (yield and ultimate) strains of human trabecular bone have only a weak dependence, if any, on apparent density and modulus." - - - A recent study designed to test for intersite differences found that yield strains were approximately uniform within anatomic sites, with standard deviations on the order of one-tenth the mean value, but mean values could vary across sites" (Fig. 8.13). Thus, for analysis purposes, yield strains can be considered constant wiAin sites but heterogeneous across sites. Regardless of anatomic site, however, yield stains are higher in compression than in tension." Ultimate strains are typically in the range of 1.0 to 2.5 percent. Evidence from experiment on bovine bone indicates that yield strains are also isotropic - despite substantial anisotropy of modulus and strength. 

TABLE 8.4 Power-Law Regressions Between Modulus E (in MPa) and Apparent Density p (in g/cm ) for Human Trabecular Bone Specimens from a Range of Anatomic Sites... 

When trabecular bone is loaded in compression beyond its elastic range, unloaded, and reloaded, it displays loss of stiffness and development of permanent strains (Fig. 8.14). In particular, it reload with an initial modulus close to its intact Young s modulus but then quickly loses stiffness. The residual modulus is statistically similar to the perfect-damage modulus (a secant modulus from the origin to the point of unloading). In general, the reloading stress-strain curve... 

FIGURE 8.14 Compressive load-unload-reload behavior of human vertebral trabecular bone. Similar to cortical bone tested in tension, an initial overload causes residual strains and a reloading curve whose modulus quickly reduces from a value similar to the intact modulus to a value similar to the perfect damage modulus. (From Ref. 105.)... 

Keaveny, T. M., Wachtel, E. F., Ford, C. M., and Hayes, W. C. (1994), Differences between the tensile and compressive strengths of bovine tibial trabecular bone dqioid on modulus,/. Biomech. 27 1137-1146. 

Ladd, A. J., Kinney, J. H., Haupt, D. L., and Goldstein, S. A. (1998), Finite-element modeling of trabecular bone Comparison with mechanical testing and determination of tissue modulus, J. Orthop. Res. 16(5) 622-628. 

The relationships between the static mechanical properties of trabecular bone and apparent density vary for the different types of trabecular bone because of the anatomic site-, age-, and disease-related variations in trabecular architecture. Both linear and power-law relationships can be used to describe the dependence of modulus and compressive strength on apparent density (Tables A2.2, A2.3), with typical coefficients of determination (r values) in the range 0.5-0.9. Differences in the predictive... 

Yaszemski, M.J., Mikos, A.G., Payne, R.G. and Hayes, W.C. (1994) Biodegradable Polymer Composites for Temporary Replacement of Trabecular Bone The Effect of Polymer Molecular Weight on Composite Strength and Modulus, In Biomatetials for Drug and Cell Delivery, Mikos. A.G., Murphy R., Bernstein H., Peppas N..V., eds., 331, Pittsburgh Materials Research Society) 251-256. 

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