Bioactive Glasses

The principle of "biological inertia" has long governed the design of materials intended for implantation in the living environment: this principle advocates minimizing the response generated by the introduction of a foreign body into the organism. However, to enhance integration, it may be desirable for the implant to interact positively with the host tissue. Such is the case with bioactive materials, capable of accelerating tissue repair. At the forefront of bioactivity are bioactive glasses.

Bioactive glasses or bioverres are mainly used in bone tissue repair. In this field, the main limitation of implants is the low mechanical strength of the interface with the surrounding tissue. Bioactive glasses provide an elegant solution to this problem, by establishing continuity with the tissue through physico-chemical reactions, thus recreating a natural interface. Bioactive glasses are also resorbable, disappearing as they are replaced by neoformed tissue. What's more, the ionic products produced by their dissolution can have a beneficial effect on bone cell repair mechanisms. This combination of features demonstrates the remarkable osseointegration capabilities of bioveres, which are sometimes even superior to autografts.

We'll look in detail at the factors determining bioactivity in glasses, which is linked as much to their structure and morphology as to their composition. As these parameters can be easily adjusted by the melting process, and even more so by the sol-gel process, bioactivity in glasses can be finely controlled and adapted to a wide variety of applications. In spite of this, and despite some significant clinical and commercial successes, bioactive lenses are still only moderately used by practitioners, mainly for processing reasons which will be discussed in this article.

Nevertheless, the future of bone regeneration is partly linked to the development of bioactive glasses, whether as supports for in vitro tissue graft reconstruction, or as constituents of new composite and hybrid materials that increasingly mimic bone.

In the first paragraph of this article, we will define the concept of bioactivity (§ 1.1 ) and explain the mechanisms involved in the case of bioveres (§