Bioactive glass-ceramic scaffolds: Processing and properties
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Introduction Glass-ceramics are partially crystallized inorganic materials obtained by controlled heat treatment of the parent glass above its crystallization temperature.1–3 The resulting glass-ceramics contain one or more crystalline phases embedded in a residual glassy phase.4,5 In the late 1960s, Hench6 discovered the first bioactive glass with composition (wt%) 45SiO2-24.5CaO24.5Na2O-6P2O5, termed 45S5 bioactive glass. This was the first man-made material, which was shown to develop strong bonding to bone upon implantation, providing an alternative to inert materials in orthopedic and bone-replacement applications. Developing bioactive glass-ceramics has been a natural extension of the field of bioactive glasses in order to design bioactive materials with higher mechanical strength, but similar bioactivity to bioactive glass. Bioactive glass-ceramics are usually characterized by superior mechanical properties, including higher elastic modulus, failure strength, and hardness, than bioactive glasses.3,7 However, the brittleness and low fracture toughness of bioactive glass-ceramics have remained major obstacles for their applications in load-bearing sites.4,5 Bioactive glasses and bioactive glass-ceramics elicit specific biological reactions on their surfaces when in contact with the biological environment, which can stimulate cell attachment, proliferation, and differentiation.8,9 In particular, once in contact with biological fluids, bioactive glasses and bioactive glass-ceramics
develop a biological active hydrocarbonate apatite (HCA) layer, which is equivalent to the mineral phase of bone. This layer is essential for the binding of the material to bone.10,11 Bioactive glasses and bioactive glass-ceramics can also degrade over time, releasing biologically active ions that have positive specific effects on cells (e.g., increase proliferation of human osteoblasts (cells that are able to form new bone matrix), as well as angiogenesis (induction of new blood vessel formation), and antimicrobial and anti-inflammatory effects in vitro and in vivo).12 Investigations have started to emerge on the potential of bioactive glasses for the regeneration and repair of soft tissues.13 Several review papers are available covering the general field of bioactive glasses and bioactive glass-ceramics.3,5,8,9,14 An extensive review on bioactive glass-ceramics in monolithic form has recently been published.5 This article was designed to fill the specific lack of recent review articles concerning porous bioactive glass-ceramics intended for applications in bone-tissue engineering (i.e., scaffolds), discussing the latest achievements in processing methods, microstructure, and properties of such systems.
Current developments in porous bioactive glassceramic scaffolds Tissue-engineering strategies involve the development of biological substitutes capable of inducing the growth of new
Elena Boccardi, Friedrich-Alexander-Universität Erlangen-Nürnberg, Germany; [email protected] Francesca E. Ciraldo, Friedrich-Alexander-Universität Erlangen-
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