**3. Relevant studies**

Most of the commercial biomaterials (glass, ceramics, glass-ceramics and composites) are known that bind to bones, being called bioactive ceramics. Also other strictly specialized compositions of bioactive glasses bind to soft tissues. A common feature of bioactive glasses and ceramics is the change of the material surface after time-dependent implantation. On the surface it is formed a biologically active layer of hydroxycarbonate apatite (HCA), which provides the tissue-binding structure [4].

Many studies have shown bone-related bioactive implants with sufficient adhesion to the interface to withstand mechanical fracture. A failure never occurs at the interface, but either in the implant or in the bone.

Bone binding was initially demonstrated for some compositional domains of bioactive glasses, containing SiO2, Na2O, CaO and P2O5, in the proportions specified in **Table 2**.

During the years many types and variations of the composition were approved by FDA and named Bioglass.

When introducing a material into the living organism, a series of very complex interactions can appear, being able to identify four specific phenomena that are unitary in the so-called "concept of biocompatibility", namely:


Chemical interactions that occur at the surface are:

• Rapid exchange of Na + and Ca2 + ions with H + and HO- ions in solution, leading to hydrolysis of silica groups, with the formation of silanol groups;

$$\text{Si}\text{-}\text{O}-\text{Na}^+ + \text{H}^+ + \text{HO}^- \rightarrow \text{Si}\text{-}\text{-}\text{OH} + \text{Na}^+ + \text{HO}^-\tag{2}$$


