scCO2-foamed silk fibroin aerogel/poly(ε-caprolactone) scaffolds containing dexamethasone for bone regeneration

Bone scaffolds prepared with porogens and bioactive agents can accelerate bone tissue formation by providing a suitable 3D-porous structure that promotes cell colonization and differentiation towards the osteogenic lineage. In this work, scaffolds containing poly(ε-caprolactone) (PCL) as biopolymeric matrix, silk fibroin as cell adhesion promoter, and dexamethasone as osteogenic differentiation agent, were prepared by supercritical foaming (37 °C, 140 bar, 1 h), a solvent-free method providing a straightforward and effective route for the processing of bioactive grafts. Silk fibroin aerogels in the form of submicron-sized particles were herein developed for the first time and evaluated as porosity inducers. These aerogels incorporated in the scaffolds refined the porous structure and facilitated cell infiltration and the biological fluid transport. Dexamethasone was used in two different forms (base, DX and phosphate salt, DS) to unveil their role in bone regeneration. The morphology of the scaffolds was evaluated using mercury intrusion porosimetry, helium pycnometry and in silico structure modelling. Different release profiles were recorded when using DX or DS. The biological performance was assessed in in vivo tests in calvarial defects using a rat model. Results unveiled the interesting morphological properties of the scaffolds in terms of porosity, pore size distribution and interconnectivity, which are compatible with their application in bone repair. In vivo tests showed the importance of the dexamethasone form and release profile in promoting the bone tissue regeneration with a significant increase in the number of ossification foci and in bone repair extent 14 weeks post-implantation for certain formulations.