Viscoelastic behaviour of novel PCL/hydroxyapatite nanocomposites for bone regeneration

Bone is a true nanocomposite consisting of nanocrystalline hydroxyapatite (HA) dispersed in a collagen-rich matrix. Nanocrystalline HA promotes osteoblast cell adhesion, differentiation and proliferation better than microcrystalline HA. Consequently, there is an increasing demand for novel nanocomposites containing nanocrystalline HA, which act as a support for cell growing. Among the different materials proposed for bone regeneration (ceramics, metals and polymers), biodegradable polyesters have acquired a particular niche of interest, since they contain unstable bonds that are hydrolytically cleaved and release degradation products that are normal intermediates of metabolic pathways. Poly(?-caprolactone) (PCL) based materials are widely investigated for bone regeneration techniques. PCL is highly biocompatible and degrades slowly, thus providing, in the long time of the degradation, adequate support until bone regeneration is completed. Two major limitations of the PCL are the strong hydrophobic character and the poor mechanical behaviour. With respect to the first aspect, the functionalization is a particularly relevant approach in order to reduce hydrophobicity by introduction of hydrophilic groups. In previous papers [1,2] we reported how functionalization of PCL through radical grafting is a powerful tool to modulate properties of interest, such as crystallinity, hydrophilicity, degradation rate and interaction with hydrophilic fillers. In particular, we found that its derivative PCL-MAGMA shows homogeneous dispersion of HA and better HA/polymer interface. We also showed how addition of low amount of HA strongly influences the biological interaction of the material with cells in terms of adhesion and proliferation [3]. In this paper, we investigated the morphology and the rheological behaviour of PCL and PCL-MAGMA nanocomposites with different amount of HA.