  Silicon-substituted hydroxyapatite (SiHA) macroporous scaffolds have been
prepared by robocasting. In order to optimize their bone regeneration
properties, we have manufactured these scaffolds presenting different
microstructures: nanocrystalline and crystalline. Moreover, their surfaces have
been decorated with vascular endothelial growth factor (VEGF) to evaluate the
potential coupling between vascularization and bone regeneration. In vitro cell
culture tests evidence that nanocrystalline SiHA hinders pre-osteblast
proliferation, whereas the presence of VEGF enhances the biological functions
of both endothelial cells and pre-osteoblasts. The bone regeneration capability
has been evaluated using an osteoporotic sheep model. In vivo observations
strongly correlate with in vitro cell culture tests. Those scaffolds made of
nanocrystalline SiHA were colonized by fibrous tissue, promoted inflammatory
response and fostered osteoclast recruitment. These observations discard
nanocystalline SiHA as a suitable material for bone regeneration purposes. On
the contrary, those scaffolds made of crystalline SiHA and decorated with VEGF
exhibited bone regeneration properties, with high ossification degree, thicker
trabeculae and higher presence of osteoblasts and blood vessels. Considering
these results, macroporous scaffolds made of SiHA and decorated with VEGF are
suitable bone grafts for regeneration purposes, even in adverse pathological
scenarios such as osteoporosis.
