Needle-like ion doped hydroxyapatitecrystals influence osteogenic properties of PCL composite scaffolds

Surface topography and chemistry both play a crucial role on influencing cell response in three dimensional porous scaffolds in terms of osteogenesis. Inorganic materials with peculiar morphology and chemical functionalities may be proficiently used to improve scaffold properties - in the bulk and along pore surface - promoting in vitro and in vivo osseous tissue in-growth. The present study is aimed at investigating how bone regenerative properties of composite scaffolds made of poly(?-caprolactone) (PCL) can be augmented by the peculiar properties of ion doped hydroxyapatite (dHA) crystals, mainly emphasizing the role of crystal shape on cell activities mediated by microstructural properties. At the first stage, the study of mechanical response by crossing experimental compression tests and theoretical simulation via empirical models, allow recognizing a significant contribution of dHA shape factor on scaffold elastic moduli variation as a function of the relative volume fraction. Secondly, the peculiar needle-like shape of dHA crystals concurs to influence microscopic (i.e., crystallinity, adhesion forces) and macroscopic (i.e, roughness) properties with relevant effects on biological response of the composite scaffold: DSC clearly indicate a reduction of crystallization heat - from 66,75 to 43.05 J/g - while AFM analyses show a significant increase of roughness - from (78.15 ± 32.71) to (136.13 ± 63.21) nm - and of pull- off forces - from 33.7% to 48.7%. Accordingly, experimental studies with MG-63 osteoblast-like cells show a more efficient in vitro secretion of ALP and collagen I and a more copious in vivo formation of new bone trabeculae, thus suggesting a relevant role of dHA to support the main mechanisms involved in bone regeneration.