Thanks to their high biocompatibility and bioactivity, bioactive glasses are very promising materials for soft and hard tissue repair and engineering. Because bioactivity and specific surface area intrinsically linked, the last decade has seen a focus on the development of highly porous and/or nano-sized materials. This review emphasizes the synthesis of bioactive glass nanoparticles and materials design strategies. The first part comprehensively covers mainly soft chemistry processes, which aim to obtain dispersible and monodispersed nanoparticles. The second part discusses the use of bioactive glass nanoparticles for medical applications, highlighting the design of materials. Mesoporous nanoparticles for drug delivery, injectable systems and scaffolds consisting of bioactive glass nanoparticles dispersed in a polymer, implant coatings and particle dispersions will be presented.

There is accumulating evidence that strontium-containing biomaterials have positive effects on bone tissue repair. We investigated the in vitro effect of a new Sr-doped bioactive glass manufactured by the sol-gel method on osteoblast viability and differentiation. Osteoblasts isolated from foetal mouse calvaria were cultured in the presence of bioactive glass particles; particles were undoped (B75) or Sr-doped with 1 wt.% (B75-Sr1) and 5 wt.% (B75-Sr5). Morphological analysis was carried out by contrast-phase microscopy and scanning electron microscopy (SEM). Cell viability was evaluated by the MTS assay at 24 h, 48 h and 72 h. At 24 h, day 6 and day 12, osteoblast differentiation was evaluated by assaying alkaline phosphatase (ALP) activity, osteocalcin (OC) secretion and gene expression of various bone markers, using Real-Time-PCR. Alizarin Red staining and ALP histoenzymatic localisation were performed on day 12. Microscopic observations and MTS showed an absence of cytotoxicity in the three investigated bioactive glasses. B75-Sr5 particles in cell cultures, in comparison with those of B75 and B75-Sr1, resulted in a significant up-regulation of Runx2, Osterix, Dlx5, collagen I, ALP, bone sialoprotein (BSP) and OC mRNA levels on day 12, which was associated with an increase of ALP activity on day 6 and OC secretion on day 12. In conclusion, osteoblast differentiation of foetal mouse calvarial cells was enhanced in the presence of bioactive glass particles containing 5 wt.% strontium. Thus, B75-Sr5 may represent a promising bone-grafting material for bone regeneration procedures.

Bacterial cellulose (BC) aerogels, which are fragile, ultra-lightweight, open-porous and transversally isotropic materials, have been reinforced with the biocompatible polymers polylactic acid (PLA), polycaprolactone (PCL), cellulose acetate (CA), and poly(methyl methacrylate) (PMMA), respectively, at varying BC/polymer ratios. Supercritical carbon dioxide anti-solvent precipitation and simultaneous extraction of the anti-solvent using scCO2 have been used as core techniques for incorporating the secondary polymer into the BC matrix and to convert the formed composite organogels into aerogels. Uniaxial compression tests revealed a considerable enhancement of the mechanical properties as compared to BC aerogels. Nitrogen sorption experiments at 77K and scanning electron micrographs confirmed the preservation (or even enhancement) of the surface-area-to-volume ratio for most of the samples. The formation of an open-porous, interpenetrating network of the second polymer has been demonstrated by treatment of BC/PMMA hybrid aerogels with EMIM acetate, which exclusively extracted cellulose, leaving behind self-supporting organogels.