Mesoporous hydroxyapatite and mesoporous bioactive glasses, a new strategy to mimic the inorganic component of bone

Human bone is a composite material composed of an organic matrix (mainly collagen) and an inorganic phase made up by nanometric crystals of hydroxyapatite. The aim of the present work is to fabricate a smart scaffold that mimics the natural bone chemistry, structure and topography for the treatment of osteoporotic fracture. The starting material chosen for this purpose is a composite matrix made of collagen, mesoporous hydroxyapatite (MHA) and/or mesoporous bioactive glasses (MBG). Mesoporous materials have exceptional textural characteristics (high surface area, high pore volume and highly ordered mesoporosity) that lead to an improved reactivity in body fluids, making these materials particularly suitable for bone tissue regeneration. MBG has been synthesised through an aerosol-assisted spray-drying process in mild acidic aqueous environment, obtaining spherical microparticles with highly controlled shape and dimensions. They belong to the system 85%SiO2/15%CaO (mol %) and have been doped with therapeutic ions to further increase their regenerative potential. In particular Sr has been chosen for its osteogenic and bone antiresorptive properties (Sr_MBG_SD) whereas copper for its antibacterial and angiogenetic behaviour (Cu_MBG_SD). MHA will be prepared through a modified co-precipitation method, using an elevated concentration of templating agent based on the work of Zhao and Ma. The aim is to obtain a rod-like shape with dimensions similar to bone hydroxyapatite. These two materials have been characterized through FESEM coupled with EDXS and through adsorption and desorption of nitrogen to evaluate their mesoporous structure. In particular, bioactivity and ion release tests have been carried out on MBGs to investigate their behaviour in a physiologic-like fluid. MHA has been analysed with XRD to investigate its crystalline structure and the size of nanocrystals.