Bioactive Glass Scaffolds with Hierarchical Structure and their 3D Characterization
Bone tissue has evolved into hierarchical three-dimensional structures with dimensions ranging from nanometres to metres. The structure varies depending on the site in the body, which is dictated by the loading environment. Medically, bone is one of the most replaced body parts (second only to blood) but replicating these complex living hierarchical structures for the purpose of regenerating defective bone is a challenge that has yet to be overcome. A temporary template (scaffold) is needed that matches the hierarchical structure of native bone as closely as possible that is available ‘off the shelf’ for surgeons to use. After implantation the scaffold must bond to bone and stimulate not only three dimensional (3D) bone growth, but also vascularisation to feed the new bone. There are many engineering design criteria for a successful bone scaffold and bioactive glass foam scaffolds have been developed that can fulfil most of them, as they have a hierarchical porous structure, they can bond to bone, and they release soluble silica species and calcium ions that have been found to up-regulate seven families of genes in osteogenic cells. Other ions have also been incorporated to combat infection and to counteract osteoporosis. Their tailorable hierarchical structure consists of highly interconnected open spherical macropores, further, because the glass is sol-gel derived, the entire structure is nanoporous. The macropores are critical for bone and blood vessel growth, the nanopores for tailoring degradation rates and protein adsorption and for cell attachment. This chapter describes the optimised sol-gel foaming process and how bone cells respond to them. Whatever type of scaffold is used for bone regeneration, it is critically important to be able to quantify the hierarchial pore structure. The nanopore size can be quantified using gas sorption, but to obtain full information of the macropore structure, imaging must be done using X-ray microtomography and the resulting images must be quantified via 3D image analysis. These techniques are reviewed.
M. Vallet-Regí and M. Vila
J. R. Jones and P. D. Lee, "Bioactive Glass Scaffolds with Hierarchical Structure and their 3D Characterization", Key Engineering Materials, Vol. 441, pp. 123-137, 2010