Sol-Gel Synthesis and in Vitro Characterization of Bioactive Glass Ceramics using Rice Husk Ash Waste Material

Abstract

Glass-ceramics materials share many properties with both glass and more traditional crystalline ceramics. It is formed as a glass, and then made to crystallize partly by heat treatment. . Bioactive glass-ceramics describes the beneficial or adverse effects of glass-ceramic with living tissue , when placed in body.
Bioactive glasses and glass-ceramics are more and more studied because of their surface chemical reactivity when in contact with body fluids [1–3]; by a complex mechanism of ions leaching and partial dissolution of the glass surface, the precipitation of bone-like apatite from the solution provides a strong chemical bonding with tissues. Since bioactive glasses and glass-ceramic are brittle materials, they are especially used in the field of small bone defects reconstruction, or as coatings on inert substrates for load-bearing prostheses.
Since the discovery of bioglass by Hench et al. [4] in the early 1970s, various types of ceramic, glass and glass–ceramic have been proposed and used as bone replacement biomaterials [5-7]. Specifically, these biomaterials have found clinical applications as coating for prostheses, bone filler, vertebral substitution and, in a porous form, as bone substitutes [8-15]. Most of them are based on the SiO2–P2O5–CaO–Na2O system. Bonding between bioactive glass or glass–ceramic and the surrounding tissues takes place through the formation of a hydroxyapatite layer, which is very similar to the mineral phase of bone. When the bioactive glass is placed in contact with physiological fluids, this layer is formed through a complex ion-exchange mechanism with the surrounding fluids, known as bioactivity.
This biologically-active layer of hydroxyapatite can form on the surface of glasses having a wide compositional range, and is considered as self by the surrounding living tissue; its presence is widely recognized to be a sufficient requirement for the implant to chemically bond with the living bone. Kokubo et al. [16] proposed the Tris-buffered simulated body fluid (SBF) for the in vitro study of bioactive glass and glass–ceramic, since its ion concentration is almost equal to that of human blood plasma. Since then, in vitro tests in SBF have been widely used as preliminary tests on new candidate materials showing bioactive properties. The ion leaching phenomenon involves the exchange of monovalent cations from the glass, such as Na+ or K+, with H3O+ from the solution, and thus causes an increase in the pH of the solution. It is known that osteoblasts prefer a slightly alkaline medium [17, 18], but it is also known that severe changes in pH can inhibit osteoblast activity and cause cell necrosis or apoptosis [19-21].
Different bioactive glass and glass ceramics have been synthesized in order to get desired mechanical, chemical properties by obtaining required microstructure. Some of common components used are Na2O, CaO, P2O5, SiO2 for synthesis of 45S5 and S53P4. In addition to these above components, varying composition of K2O, MgO , B2O3 are used to get 13-93, 3-04, 18-04, 23-04. There are some other glass and glass ceramics which also include ZnO, Ag and Al2O3.
In current study of bioactive glass ceramic we are using rice husk ash as raw material for synthesis of silica, which is amorphous in nature. It is cheap, easily available source with high content of silica