A Guided Walk through the World of Mesoporous Bioactive Glasses (MBGs): Fundamentals, Processing, and Applications

Abstract

Bioactive glasses (BGs) are traditionally known to be able to bond to living bone and stimulate bone regeneration. The production of such materials in a mesoporous form allowed scientists to dramatically expand the versatility of oxide-based glass systems as well as their applications in biomedicine. These nanostructured materials, called mesoporous bioactive glasses (MBGs), not only exhibit an ultrafast mineralization rate but can be used as vehicles for the sustained delivery of drugs, which are hosted inside the mesopores, and therapeutic ions, which are released during material dissolution in contact with biological fluids. This review paper summarizes the main strategies for the preparation of MBGs, as well as their properties and applications in the biomedical field, with an emphasis on the methodological aspects and the promise of hierarchical systems with multiscale porosity.

Keywords: bioactive glass; bioactivity; mesoporous; nanomaterials; porosity; scaffold; sol–gel; tissue engineering.

Figure 1

Summary of mesoporous bioactive glass (MBG) properties that make these materials highly attractive for biotechnological and biomedical applications [20].

Figure 2

Production of MBGs by the so-called “wet” method. The image shows a gel-derived glass (left side) and mesoporous silica (right side) obtained by sol–gel and supramolecular arrangement routes, respectively. MBGs are produced by combining these two routes (middle image) [27].

Figure 3

Phase sequence of a water–surfactant binary system following surfactant concentration [12].

Figure 4

Ternary phase diagram of P123–water–ethanol system at T = 23 °C. L1 denotes the region with isotropic solution (water-rich), I1 refers to isotropic gels, H1 refers to cylindrical micelles arranged in a 2D hexagonal lattice, and Lα is the lamellar phase. The region boundaries are traced by solid lines [39].

Figure 5

Ternary phase diagram of F127–water–buthanol system. L1 denotes the region with isotropic solution (water-rich), I1 refers to isotropic gels, H1 refers to cylindrical micelles arranged in a 2D hexagonal lattice, Lα is the lamellar phase, and L2 is a reverse isotropic micellar phase. The region boundaries are traced by solid lines. The arrow indicates the delicate balance of these regions: for example, the rapid evaporation of solvent may occur during some processes, such as spin-coating, thereby producing a transition from lamellar to hexagonal phase [38].

Figure 6

Stages of the evaporation-induced self-assembly (EISA) process for the production of MBGs. Image adapted from [14].

Figure 7

Transmission electron microscopy images of (a) P123-templated MBG and (b) cetyltrimethylammonium bromide (CTAB)-templated MBG [7].

Figure 8

Typical TEM images of F127-induced MBGs (a), in which the pore and wall structures are indicated by white lines in (b) [49].

Figure 9

High-resolution transmission electron microscopy images and electron diffraction patterns of conventional sol–gel SiO₂–CaO–P₂O₅ glasses, SiO₂–CaO–P₂O₅ MBG, and pure mesoporous silica [42].

Figure 10

Nano-crystalline apatite mineralization on the surface of three-dimensional MBG scaffolds: (a) “cauliflower” globular agglomerates (low magnification image), (b) details of nano-crystals (high magnification image) [7].

Figure 11

Schematic concept of using MBGs for drug delivery and bone regeneration [70].

Figure 12

Photographs of (a) the polyurethane sponges used as macroporous templates and (b) the resulting hierarchical MBG scaffolds [56].

Figure 13

SEM analysis of polyurethane sponges (a,b) and macro-mesoporous scaffolds with composition (mol.%) 100SiO₂ (c,d), 90SiO₂–5CaO–5P₂O₅ (e,f), 80SiO₂–15CaO–5P₂O₅ (g,h), and 70SiO₂–25CaO–5P₂O₅ (i,j) [56].