Biobased Silica from Rice Husk and Straw for the Synthesis of Biocompatible Glasses

Abstract

The present work aims to investigate the preparation of bioactive glasses by using rice husk derived silica. The glasses have been synthesized by the traditional melt-quench method. The obtained glasses have been subsequently characterized in terms of their characteristic temperatures by Differential Thermal analysis (DTA/DSC), phase analysis by X-ray diffraction (XRD) and structural analysis through spectroscopic techniques (Scanning electron microscopy, energy dispersive X-ray spectroscopy and Fourier-transform infrared spectroscopy - FTIR). In addition, the obtained bioactive glasses were immersed in solutions similar to biological body fluid to investigate their bioactivity, evaluating pH of solution with time, ion release with the help of microwave plasma spectroscopy and hydroxyapatite formation. The findings suggested that incorporating different oxides (MoO3, SrO, MnO, CoO) into a bioactive glass does not give any negative effect. This provides beneficial role for the synthesis of a new class of bioactive glasses for drug delivery and antibacterial activities. The entire work in the thesis is presented in ten chapters. Chapter 1: This chapter includes a brief discussion on the glasses, their classification, structure and their properties. Further, a detailed description of biomaterials and an outline of bioactive glasses, their types, and their bioactivity assessment in simulated body fluid are given. Agriculture waste for SiO2 extraction has been discussed in brief. Chapter 2: This chapter summarizes the recent literature concerning to different extraction routes of silica utilizing rice husk and straw. Influence of fabrication route, type of silica extracted and their applications in various fields has been discussed in detail. Further, the literature includes the various bioactive glass compositions doped with different metal oxides. Based on the literature, the last section of this chapter reviews the gaps in study. On the basis of these literature gaps, the objectives to carry out the research present in the thesis are proposed. Chapter 3: This chapter describes the details of the experimental procedure followed to achieve the proposed objectives. The detailed methodology adopted for the extraction of silica and preparation of glasses are presented in this chapter. Also, the different characterization techniques used in this study has been discussed briefly. Chapter 4: This chapter describes the extraction of SiO2 from rice husk and straw through chemical and biological routes. The extracted SiO2 has been characterized. The results obtainedutilizing both routes have been discussed and compared with commercial SiO2. The yield of SiO2 is calculated for both methods (chemically and biological extracted silica). In addition to this, the as-obtained SiO2 is assessed for antibacterial activity against the growth of two bacterial strains Staphylococcus aureus and Escherichia coli. Chapter 5: This chapter provides the details about the utilization of biogenic silica in the synthesis of biocompatible glasses of general composition SiO2-P2O5-CaO-MgO-MoO3. In this glass series, P2O5 (5%) and CaO (25%) was kept constant whereas MgO and MoO3 were varied from 10% to 20% and 0% to 5%, respectively. The structural, morphological, elemental and functional properties of bioactive glasses were analyzed. The effect of MoO3 on the structural and thermal properties of synthesized glasses have been studied in details. The bioactivity of as-prepared glass samples was further evaluated after immersion in simulated body fluid solution. Chapter 6: This chapter reports on the synthesis and biocompatibility of SiO2-P2O5-MgO-CaO-SrO glass system. The MgO was partially replaced by the SrO to check its influence on the bioactivity of the glass samples. The bioactivity of the glasses was monitored by surface activity of the glass samples after treatment with the simulated body fluid. The evolution of the apatite layer was confirmed by observing variations in the crystal structures, morphological features, and evolution of new functional groups. The incorporation of SrO led to enhancement in the bioactivity of the glass samples as compared to the one without it. Chapter 7: This chapter describes the synthesis of alkali-free biocompatible glasses utilizing the agricultural waste rice husk and eggshells. A series of glasses with basic composition of SiO2-P2O5-MgO-CaO has been synthesized using melt-quench technique, where P2O5 is partially replaced by MnO. These glasses are assessed for their in-vitro reactivity with different characterization techniques before and after soaking in the simulated body fluid solution. These results designate that low-cost agro-waste-derived alkali-free glasses have potential in medical applications in drug delivery as well as it helps in environmental pollution management. Chapter 8: This chapter discusses two different categories of bioactive glasses prepared from biomass using SiO2 and P2O5 as glass formers. These glasses are prepared by melt-quench technique. The glasses are evaluated in-vitro for their bioactivity assessment with the help of simulated body fluid (SBF). These investigations proved that the as-prepared glass samples have high drug loading efficiency and antibacterial activity.Chapter 9 In this chapter a comparative analysis is presented for glasses made by using chemically extracted silica and biologically extracted silica. Considering the fact that yield of biologically extracted silica is less, the compositions which showed best results in case of chemical silica, are selected for glass preparation with biological extracted silica. The results for in-vitro bioactivity evaluation in the simulated body fluid (SBF) solution with different characterization are discussed here. Chapter 10 This chapter describes the conclusion drawn from above studies and scope for future work. It gives the structural, morphological, elemental and functional properties of agro-waste derived SiO2 and CaO. Utilization of agro-waste derived silica is highly useful as it forms glasses at much lower temperature as compared to commercial silica. Further, the incorporation of different oxides in the designed glass compositions has been studied in detail. It is found that the inclusion of MoO3, SrO, MnO, and CoO in the glass matrix has helped to enhance the bioactivity of the synthesized glasses. The formation of hydroxyapatite layer and drug loading properties along with the antibacterial studies of these glasses was better as compared to already reported glasses of similar categories. On the basis of the findings of the studied glass systems, further scope has been suggested.