Structure-function relationships for coralline hydroxyapatite bone substitute

To improve the understanding of the functional requirements of trabecular b one substitutes, the structure-function relationships of coralline hydroxya patite were determined and compared to those of trabecular bone from a vari ety of anatomic sites. Mechanical properties and permeability of cylindrica l coralline hydroxyapatite specimens were measured and related to various m orphological parameters that were obtained from analysis of high-resolution (20 mu m) computer reconstructions of each specimen. Results indicated the average (+/-SD) Young's modulus (2900 +/- 1290 MPa, n = 20) and permeabili ty (0.50 +/- 0.19 x 10(-9) m(2), n = 21) of the coralline hydroxyapatite we re within the range of values exhibited by high density trabecular bone; ul timate stress (5.87 +/- 1.92 MPa, n = 13), while in the range of mid-densit y trabecular bone, was low considering its high volume fraction (31.3 +/- 1 .9%, n = 49); and ultimate strain (0.22 +/- 0.03%, n = 13) was much lower t han that of trabecular bone from any anatomic site. The only correlation fo und between mechanical and morphological parameters was between Young's mod ulus and "fabric" (a scalar measure of architecture that combined the degre e of microstructural anisotropy with orientation). These results provide in sight into the in vivo performance of this implant, as well as the biomecha nical requirements for successful trabecular bone substitutes in general. ( C) 1999 John Wiley & Sons, Inc.