Abstract
The discovery of bioactive glasses (BGs) in the late 1960s by Larry Hench et al. was driven by the need for implant materials with an ability to bond to living tissues, which were intended to replace inert metal and plastic implants that were not well tolerated by the body. Among a number of tested compositions, the one that later became designated by the well-known trademark of 45S5 Bioglass® excelled in its ability to bond to bone and soft tissues. Bonding to living tissues was mediated through the formation of an interfacial bone-like hydroxyapatite layer when the bioglass was put in contact with biological fluids in vivo. This feature represented a remarkable milestone, and has inspired many other investigations aiming at further exploring the in vitro and in vivo performances of this and other related BG compositions. This paradigmatic example of a target-oriented research is certainly one of the most valuable contributions that one can learn from Larry Hench. Such a goal-oriented approach needs to be continuously stimulated, aiming at finding out better performing materials to overcome the limitations of the existing ones, including the 45S5 Bioglass®. Its well-known that its main limitations include: (i) the high pH environment that is created by its high sodium content could turn it cytotoxic; (ii) and the poor sintering ability makes the fabrication of porous three-dimensional (3D) scaffolds difficult. All of these relevant features strongly depend on a number of interrelated factors that need to be well compromised. The selected chemical composition strongly determines the glass structure, the biocompatibility, the degradation rate, and the ease of processing (scaffolds fabrication and sintering). This manuscript presents a first general appraisal of the scientific output in the interrelated areas of bioactive glasses and glass-ceramics, scaffolds, implant coatings, and tissue engineering. Then, it gives an overview of the critical issues that need to be considered when developing bioactive glasses for healthcare applications. The aim is to provide knowledge-based tools towards guiding young researchers in the design of new bioactive glass compositions, taking into account the desired functional properties.
Highlights
The structure of a glass could be quantified by the pair distribution function (PDF) or radial distribution function (RDF), given by g(r), which is related to the probability of finding another atom at a distance r from a central atom
It was observed that in both of the cell culture media tested (Dulbecco’s modified Eagle’s medium, and osteogenesis differentiation medium), alkali-free bioactive glasses clearly induced the appearance of more calcium deposits than 45S5 Bioglass®, indicating their greater ability to induce cell differentiation. These results clearly demonstrated the superiority of alkali-free bioactive glasses in stimulating the differentiation of human mesenchymal stem cells (hMSCs) into bone-forming cells, making them a safe and better alternative materials for dental, orthopaedic, and maxillofacial surgery applications in comparison to 45S5 Bioglass® [277]
The pertinence in further exploring this perspective is quite questionable, as the degree of novelty is not clear, and it seems to go beyond science and towards advertisement
Summary
The atoms constituting the glass are organised in a short-range order that depends on the glass composition, i.e., glass seems to be a liquid, but behaves similar to a solid in human time scales [4,5]. The properties of a glass can be adjusted by doping, i.e., adding small amounts of other oxides to the glass composition, allowing the controlled release of ionic species. This feature is of great importance in bioactive glasses, conferring them with potential therapeutic actions upon releasing suitable ions that might stimulate cells’ differentiation (osteoinduction), or act as antimicrobial or neuroprotective agents, etc. Tg is an interval of temperatures that depends significantly on the composition and thermal history of the material (e.g., melting temperature, cooling rate, and the subsequent heat-treatment schedules)
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