Osteoporosis is a worldwide disease resulting in the increase of bone fragility and enhanced fracture risk in adults. In the context of osteoporotic fractures, bone tissue engineering (BTE), i.e., the use of bone substitutes combining biomaterials, cells, and bone inducers, is a potential alternative to conventional treatments. Pre-clinical testing of innovative scaffolds relies on in vitro systems where the simultaneous presence of osteoblasts (OBs) and osteoclasts (OCs) is required to mimic their crosstalk and molecular cooperation for bone remodelling. To this aim, two composite materials based on type I collagen were developed, containing either strontium-enriched mesoporous bioactive glasses or rod-like hydroxyapatite nanoparticles. Following chemical crosslinking with genipin, the nanostructured materials were tested for 2–3 weeks with an indirect co-culture of human trabecular bone-derived OBs and buffy coat-derived OC precursors. The favourable structural and biological properties of the materials proved to successfully support the viability, adhesion, and differentiation of bone cells, encouraging a further investigation of the two bioactive systems as biomaterial inks for the 3D printing of more complex scaffolds for BTE.

Mesoporous bioactive glasses (MBGs) have been widely studied as bone regeneration systems, due to their bioactivity and ability to store and release therapeutic agents with specific biological functions. The incorporation of these nanomaterials into a thermosensitive hydrogel (TSH), in which a solution undergoes a sol-gel transition under physiological conditions, represents a promising approach to design multifunctional devices able to deliver selected molecules to pathological sites. In fact, this system can perfectly fit the defect cavity shape prior to the complete gelation, and acts as a carrier for therapeutic agents prolonged release in situ. This challenging concept is the underlying idea of the MOZART project, whose objective was to develop a library of MBGs containing different therapeutic ions and drugs, to be used as a new, smart platform technology for highly targeted therapies to enhance bone healing. The aim of this work is to investigate the bone regeneration potential of MBGs containing strontium ions (pro-osteogenic) and incorporated into thermosensitive poly(etherurethane)(PEU) based on Poloxamer407. In order to further increase the pro-osteogenic response, MBGs were also loaded with N-acetylcysteine (NAC).

MBGs containing 2%mol of Sr²⁺ were prepared by an aerosol-assisted spray-drying method and NAC was loaded post-synthesis via an incipient wetness method. The PEU hydrogel (SHP407) was synthesized via a two-step procedure in nitrogen atmosphere. Particles were characterized (FE-SEM, N₂ adsorption-desorption analysis, TGA, DSC, FT-IR and XRD) and then incorporated into the hydrogel. The hybrid systems rheological properties and stability in aqueous environment at 37°C, and its ability to co-release Sr²⁺ and NAC were analysed. After preliminary biological in vitro tests, a proof-of-concept rodent study was run to assess the ability of the resulting formulation as bone healing device. X-ray at 2 and 4-weeks post-surgery and µCT-analysis were used to evaluate the healing results in a rat osteotomy model of biologically impaired healing. Then, bones were processed for histological evaluation.

Preliminary in vivo results demonstrated that incorporation of MBGs into a TSH is a promising strategy to design a multifunctional injectable formulation for in situ and sustained delivery of pro-osteogenic species enhancing bone regeneration.