Bioactive Glass System Research Articles

An in vitro biological and anti-bacterial study on a sol–gel derived silver-incorporated bioglass system

Objectives The purpose of this study was to evaluate the in vitro antibacterial and biological activity of silver-incorporated bioactive glass system SiO 2–CaO–P 2O 5–Ag 2O (AgBG). The bacteriostatic and bactericidal properties of this new quaternary glass system along with the ternary sol–gel glass system SiO 2–CaO–P 2O 5 (BG) have been studied using Escherichia coli as a test micro-organism. The AGBG system thus appears to be a promising material for dental applications, since similar effects might be produced on a film of bacteria and mucous that grows on the teeth. Methods The SiO 2–CaO–P 2O 5–Ag 2O and SiO 2–CaO–P 2O 5 glass systems were synthesized by the sol–gel technique and characterized for their physicho-chemical properties. The antibacterial activity and biological properties were evaluated by determining the minimum inhibitory concentrations (MICs). Release of Ag + into the culture medium was measured by inductively coupled plasma (ICP) analysis. Results The in vitro antibacterial action of the SiO 2–CaO–P 2O 5–Ag 2O was compared with that of its ternary counterpart glass system. The concentrations of Ag-bioglass, in the range of 0.02–0.20 mg of Ag-bioglass per millilitre of culture medium, were found to inhibit the growth of these bacteria. The Ag-bioglass not only acts bacteriostatically but it also elicited a rapid bactericidal action. A complete bactericidal effect was elicited in the early stages of the incubation at Ag-bioglass concentration of 20 mg/ml and the ternary glass system had no effect on bacterial growth or viability. The antibacterial action of Ag-bioglass was exclusively attributed to the leaching of Ag + ions from the glass matrix. Significance One of the major advantages of incorporating silver ions into a gel glass system is that the porous glass matrix can allow for controlled sustained delivery of the antibacterial agent to dental material, used even under anaerobic conditions such as deep in the periodontal pocket. This glass system also provides long-term action required for systems which are constantly at risk of microbial contamination.

Influence of particle size on the crystallization process and the bioactive behavior of a bioactive glass system

Bioactive glasses have attracted considerable interest in recent years, due to their technological application, especially in biomaterials research. Differential scanning calorimetry (DSC) has been used in the study of the crystallization mechanism in the SiO2–Na2O–CaO–P2O5 glass system, as a function of particle size. The curve of the bulk glass presents a slightly asymmetric crystallization peak that could be deconvoluted into two separate peaks, their separation being followed in the form of powder glasses. Also, a shift of the crystallization peaks to lower temperatures was observed with the decrease of the particle size. FTIR studies – that are confirmed by XRD measurements – proved that the different peaks could be attributed to different crystallization mechanisms. Moreover, it is presented the bioactive behavior of the specific glass as a function of particle size. The study of bioactivity is performed through the process of its immersion in simulated human blood plasma (simulated body fluid, SBF) and the subsequent examination of the development of carbonate-containing hydroxyapatite layer on the surface of the particles. The bioactive response is improved with the increase of the particle size of powders up to 80 μm and remains almost unchanged for further increase, following the specific surface to volume ratio decrease.

Self-Setting Paste Model in Bioactive Glass Systems

Self-setting paste model in bioactive glass systems was investigated. Particulate glasses based on the systems CaO-SiO2-P2O5 and Na2O-CaO-SiO2 were combined with sodium phosphate solution to constitute paste models. Setting behavior of these pastes, i.e., workability and setting within 30 min were obtained by controlled composition-mass conditions. Specifically, it was found that the setting behavior could be controlled by glass compositions as well as mixing ratios of solids and solutions. These suggest new concept of bioactive cement for various biomedical applications.

Mechanistic Study of Apatite Formation on Bioactive Glass Surface Using 31P Solid-State NMR Spectroscopy

The molecular mechanism of apatite formation on bioactive glass surface is studied using the techniques of XRD, EDX, SEM, FT-IR, and solid-state 31P NMR. Using the sol−gel method a bioactive glass system containing glass beads of 2 to 3 microns in size is prepared with the composition containing 30% CaO − 70% SiO2. Our experimental data support the apatite formation mechanism proposed by Hench concerning the precipitation and crystallization of calcium phosphate. The phosphate ions initially deposited on the glass surface are largely in amorphous phase and have substantial amount of water molecules in the surrounding. As the soaking time in simulated body fluid increases, some of the water molecules diffuse out of the phosphate lattice, leading to the formation of a crystalline phase. Our data show that the structure of the crystalline phase is different from type B carbonate apatite but similar to hydroxyapatite.

Fibrin glue as an osteoinductive protein in a mouse model

Fibrin sealant or fibrin glue (FG) has been found to be effective as a wound-healing substance in surgery. However, its role in bone fracture healing and osseous tissue response is not fully understood. This ambiguity questions the potential of FG as an inductive protein. The present study was undertaken to evaluate the osteoinductive property of FG when coated with calcium phosphate and glass ceramics and implanted in the extraskeletal site of male Swiss albino mice. Implant materials used for this study were hydroxyapatite (HA) porous granules (300–350 μm), bioactive glass system (BGS)-AW type and calcium phosphate calcium silicate system (HABGS) non-porous granules (300–350 μm). Uncoated granules (control) and coated granules with 2.5 mg FG and 5 mg FG were implanted in the quadriceps muscle of mice and sacrificed after 28 days. Histologically, HA, BGS and HABGS implanted animal groups showed good healing response. However, neo-osteogenesis was observed only in the BGS and HABGS granules impregnated with FG. Furthermore, bone formation was observed to be more conspicuous in 5 mg FG coated BGS and HABGS granules when compared with 2.5 mg FG coated BGS and HABGS granules. Fluorochrome labeling proved that mineralization had already started by day 15 with FG preadsorbed BGS and HABGS granules. On the contrary, the uncoated granules did not show any de novo bone formation. This experimental study provides an evidence of the positive role of FG as a potential osteoinductive biologic tissue adhesive.

Analysis by nuclear magnetic resonance and raman spectroscopies of the structure of bioactive alkaline-earth silicophosphate glasses

Structural knowledge of bioactive glass systems is necessary to understand their biological properties and improve their mechanical and clinical performance. In this work, the local structure of P and Si in bioactive glasses of the system CaO-SiO 2-P 2O 5-CaF 2 with different Mg or Sr contents was determined, by means of 31P and 29Si magic-angle sample-spinning nuclear magnetic resonance (MASS NMR) and Raman spectroscopies. The results show that phosphorus is located in calcium-orthophosphate domains, surrounded by silicate species containing 1, 2 and 3 bridging-oxygens per SiO 4 tetrahedra. The type and relative distribution of the silicate units do not depend on the nature of the alkaline earth cations present in the system. However, the increase of RO content decreases the degree of polymerization of silicon tetrahedra, while PO 4 monomeric units remain unchanged. An interpretation of the medium-range structure of the glass is suggested.