Bioactive Glass-Based Scaffolds for Bone Tissue Engineering - Tissue Engineering: Cell-Surface Interactions for Tissue Culture - page 207

Fig. 6 SEM image of osteoblasts cultured for 2 days on bioactive glass stored under dry
conditions [ 136 ]. The osteoblasts mainly exhibit a ''stand-off'' morphology (C) with many dorsal
ruffles (r) and filapodia (f). Cell divisions (m) are also relatively often seen. Cracks on the glass
surface are due to dehydration of the top layer during critical point drying. (Figure reprinted with
permission of Springer)

bone [ 125 , 126 ]. Therefore, trabecular bone is more important in phosphate and
calcium homeostasis than compact bone. The unique hierarchical structure of bone
enables its self-repairing properties; bone can alter its geometry and material
properties in response to changing external stimuli (e.g., mechanical stresses), and
it undergoes a continuous remodeling process [ 121 , 127 ]. Bone grows in response
to load, so that the density of trabecular bone depends on the magnitude of the
loads and the orientation of the trabeculae depends on the loading direction.
Analyzing experimental results from the literature [ 72 , 91 , 94 , 113 ], a linear
relationship between scaffold porosity and compressive strength is found, with
coefficients of determination R 2

between 0.80 and 0.99, as reported elsewhere

[ 128 ].
For human bone, different functional relationships between bone volume
fraction (i.e., porosity) and mechanical properties have been observed. On the
basis of image-guided failure assessment (IGFA), Nazarian et al. [ 117 ] found
highly positive linear correlations (R 2 = 0.8-0.9) between bone volume fraction
and compressive yield strength as well as between bone volume fraction and
elastic modulus. Other authors reported quadratic [ 129 ] or power-law relationships
[ 114 ] between bone volume fraction (relative density) and compressive strength,
as well as between bone volume fraction and Young's modulus of human bone
[ 129 , 130 ]. Moreover, a second-order polynomial relationship between porosity
and Young's modulus has been found in the modeling of the mechanical properties
of a face-centered cubic scaffold microstructure [ 131 , 132 ].