# Bioactive Glasses for Soft and Hard Tissue Healing Applications--A Short Review
## 4 Bioactive glasses  
It has been thoroughly demonstrated that specific BG compositions generate surface hydroxy-carbonate apatite (HCA) when in contact with biological fluids, which enhances their attachment to mineralized tissues, with minimal inflammation and toxicity for the host [16]. The interfacial HCA layer forms at a pace that has a high structural and chemical similarity to that of the mineral phase of bone [72]. The bioactivity of BGs is appropriate for applications in bone tissue regeneration as the formation of HA represents the marker which characterizes material-bone strong bonding. Unfortunately, BGs have poor mechanical strength and fracture toughness despite having excellent bioactive characteristics. Therefore, their use is often limited to non-load  
Figure 4: Surface reaction stages of BGs in hard tissue healing. Figure 3: General use of BGs in hard tissue healing. BG Thin Films  
The surface quality--in particular, the surface topography and the used material--influences bone healing and regeneration. Now, the majority of implantable materials are Ti alloys, stainless steel (SS), or Co-Cr alloy. The physiologically active surface that either promotes osteointegration or prevents infection is typically absent from these metals. Thus, efforts have been concentrated on creating different coatings to enhance the functionality of existing implants [73]. These coatings' construction must meet a number of crucial requirements: first, the coating must be biocompatible and not cause any immune or foreign body reaction; second, it must be osseeconductive in order to encourage osteoblasts to adhere to, proliferate, and grow on the surface in order to form a bone--implant linkage [73]. As mentioned in the previous sections, when BGs are used to coat metallic implants, a hydroxyapatite-like phase can form at the site where the implant meets the host tissue, aiding in the implant's better integration [74]. BGs of excellent bioactivity have been used by our group onto less biocompatible or biointer materials (such as titanium or steel) in the form of coatings [75; 76; 77; 78]. Our studies evidenced a transformation of BG into CHA in 28 days for BG57 (56.5% SiO\({}_{2}\), 15% CaO, 11% Na\({}_{2}\)O, 8.5% MgO, 6% P\({}_{2}\)O\({}_{5}\), and 3% K\({}_{2}\)O) or in 42 days in the case of BG61 (61.1 wt% SiO\({}_{2}\), 10.3 wt% Na\({}_{2}\)O, 2.8 wt% K\({}_{2}\)O, 12.6 wt% CaO, 7.2 wt% MgO, and 6 wt% P\({}_{2}\)O\({}_{5}\)) after immersion in SBF [75; 76; 77; 78]. One of the risks associated with the insertion of an implant into the human organism is the one represented by microbial infections. One effective way in fighting biofilm-associated infections is to prevent the adhesion and/or delay the growth of colonizing microorganisms via implant coating with bioactive films releasing antimicrobial drugs. Our group explored an innovative concept for implants coating based upon double layers of BG and antimicrobial plants extract/polymer deposited by Matrix Assisted Pulsed Laser Evaporation (MAPLE) onto different substrates. The BG dissolution resulted in the growth of a bioapatite layer with anti-corrosive protection of the substrate. Our layers proved bioactive action, antimicrobial effect, and strong shielding against metal ions release. Thin films of BG-PMMA-Doxycycline (Doxy) were deposited onto 316 LS substrates by means of MAPLE technique [79]. When in contact with simulated body fluids (SBF), the composite films demonstrated the ability to stimulate the progress of biological-like HA on their surface, validating the film bioactivity. A prolonged release of active Doxy molecules occurs together with the BG dissolution in SBF, which is beneficial for preventing local infections. Four weeks after the sample's immersion in SBF, apatite layers begin to form on the surface; the apatite layer together with the polymer provide excellent protection against deterioration and the release of dangerous metallic ions (Cr, Ni, Cu).