Characterizing the hierarchical structures of bioactive sol–gel silicate glass and hybrid scaffolds for bone regeneration

Abstract

Bone is the second most widely transplanted tissue after blood. Synthetic alternatives are needed that can reduce the need for transplants and regenerate bone by acting as active temporary templates for bone growth. Bioactive glasses are one of the most promising bone replacement/regeneration materials because they bond to existing bone, are degradable and stimulate new bone growth by the action of their dissolution products on cells. Sol-gel-derived bioactive glasses can be foamed to produce interconnected macropores suitable for tissue ingrowth, particularly cell migration and vascularization and cell penetration. The scaffolds fulfil many of the criteria of an ideal synthetic bone graft, but are not suitable for all bone defect sites because they are brittle. One strategy for improving toughness of the scaffolds without losing their other beneficial properties is to synthesize inorganic/organic hybrids. These hybrids have polymers introduced into the sol-gel process so that the organic and inorganic components interact at the molecular level, providing control over mechanical properties and degradation rates. However, a full understanding of how each feature or property of the glass and hybrid scaffolds affects cellular response is needed to optimize the materials and ensure long-term success and clinical products. This review focuses on the techniques that have been developed for characterizing the hierarchical structures of sol-gel glasses and hybrids, from atomicscale amorphous networks, through the covalent bonding between components in hybrids and nanoporosity, to quantifying open macroporous networks of the scaffolds. Methods for non-destructive in situ monitoring of degradation and bioactivity mechanisms of the materials are also included.

In vitro bioactivity of titanium-doped bioglass

“…The concentration trend observed was broadly the same for all samples. Initially a rapid drop in the concentration of sodium was observed as it dissolved into the surrounding media; this was consistent with bioactivity models where the first step is the ion exchange of the cation Na + from the glass with H + from the surrounding physiological fluid [23,24]. The concentration of calcium and phosphorous are also shown to drop initially although at a slower rate.…”

“…Samples were annealed overnight at 350°C before being allowed to cool slowly to room temperature. The compositions of the two glasses prepared were (SiO 2 ) 46.1 (CaO) 26.9 (Na 2 O) 24 The glass rods (10 mm diameter) were cut into 2mm thick discs using a low speed diamond saw (Isomet, Buehler, USA) with an ethanol based lubricant Dp-blue (Struers, Denmark) to minimise aqueous contact. Discs were ground and polished using a DAP-7 polishing machine (Struers, Denmark) using a series of silicon carbide papers (P800, P1000, P1200, P2400 and P4000) and Dp-blue as a lubricant, followed by a final polish using 0.06 micron colloidal silica.…”

3D printed PLA-based scaffolds

“…22,23 Indeed, several studies have demonstrated the relevant role of ions on tissue regeneration. 24,25 Given that the glass particles incorporated into the polymer scaffold are partially exposed in the surface, as demonstrated by an alizarin red assay (where only the calcified inorganic phase is stained in red color, Fig. 3D), their presence contribute both to modify surface chemistry and surface topography.…”

Hierarchically engineered fibrous scaffolds for bone regeneration

“…For bone regeneration, hybrid materials (materials composed of a mixture of inorganic components, organic components or both types of components, which usually interpenetrate on the submicrometre scale [3]) appear to be one of the most promising candidates for the design of new scaffolds, owing to their excellent bioactivity and suitable mechanical properties [4]. However, they generally lack strong chemical interactions between their constituents, resulting in their non-homogeneous and fast degradation in body fluid.…”