STUDIES ON BIOACTIVE GLASS MATERIALS FOR BROAD SPECTRUM APPLICATIONS

Abstract

The function of biomaterials is to replace infected, injured or damage tissues. The first used biomaterials are bioinert, thus minimizing the formation of scar tissue at implant tissue interface. Bioglass was discovered by Dr. Larry Hench in 1969, which has the capability to bond with bone without encapsulated by fibrous tissues. It has been discovered that bioglass has a far higher bonding capacity than any other biomaterial. Its ability to form hydroxyapatite with body fluid makes it undefendable compared to virgin hydroxyapatite crystals. In addition to providing a surface for cell development, the presence of Si ions acts as a catalyst to speed up cellular proliferation. Recently, it has been discovered that bioglass is not only a good candidate for hard tissue regeneration but can also be used beyond bone regeneration such as soft tissue engineering applications. Since the late 1960s, many techniques have been developed and used to create bioglass, including the melt-quench method, the sol-gel method, flame spray synthesis, microwave synthesis, and others. Apart from these methods, a new cost effective, green synthetic route called bioinspired route has been reported by Santhiya et al in 2013. This approach was developed on admiring naturally synthesized nano-structured materials such as silica in diatoms by the guidance of bio macromolecular templates. In last two decades, the bio-inspired synthesis of nanostructured ceramic oxides below 100 C has been well established using organic templates. Santhiya et al. explored the effect of various templates on the textural and morphological properties of the bioglass particles. In the present investigation, the bio medical application of bioglass materials as inorganic-organic hybrid composites are explored. Herein, bioinspired method was adopted for in-situ mineralization of bioglass particles. Initially, the bioglass particles were synthesized using small molecules i.e., a Abstract monomer instead of high molecular weight synthetic polymers. Further, we have developed a new sustainable green synthetic method for the synthesis of bioglass particles directly utilising a natural plant extract as both a template and a source of a few inorganic metal ions. In this thesis, considering the huge importance of bioactive glass hybrid materials for both soft and hard tissue engineering applications, various in-situ mineralized bioactive glass hybrid materials are synthesized and characterized in detail. This thesis has been summarized in 6 chapters. Chapter 1 provides a general overview on soft and hard tissue engineering, generations of biomaterials, bioactive glass as third generation biomaterial and application of bioglass beyond bone regeneration. Additionally, a thorough overview of studies on the synthesis of bioactive glass and the mechanism of bioactivity in simulated body fluid is reviewed in detail. Bioactive glass hybrid materials' significance in biological applications is briefly discussed. Chapter 2 explains the fundamentals of numerous methods used to characterise bioglass materials. These tools help us to determine their structural, morphological, thermal and mechanical properties like size, charge, surface area, surface functional groups, morphology, and molecular structure. In Chapter 3, bioinspired synthesis method for mesoporous L-lysine-bioactive glass (LBG) hybrid xerogels at ambient conditions was discussed in details. L-lysine molecules were incorporated in bioactive glass (BG) network through physiochemical interaction. The step-wise addition of various BG precursors with L-lysine took place at its three pKa (2.18, 8.94, 10.54) and pI (9.74) values respectively. These LBG hybrid xerogels were thoroughly characterized before and after interaction with simulated body Abstract fluid (SBF). Interestingly, elemental analysis on xerogels reported 45S5 composition for inorganic contents of LBG_8.94 and LBG_9.74. In contrast, LBG_2.18 and LBG_10.54 contained higher SiO2 and corroborating discrete bioactivity behaviour of xerogels. Nitrogen sorption analysis confirmed the mesoporous nature of all four LBG xerogels with different pore size, pore volume and surface area. Importantly, distinctively controlled 7-Dehydrocholesterol release pattern of each LBG xerogels highlighted the importance of their tuneable textural property. Reported viscoelastic nature of freshly prepared LBG xerogels by rheological analysis promised its non invasive injectability. These new generation materials not only promise to serve nutrients for cell growth but also contain tailored textural as well as rheological characteristics for targeted bone engineering applications. In Chapter 4, we report for the first time, BGNPs synthesized using Trigonella foenum-graecum (TFG) leaf extract (TFGL_EX). Bioactive glass nanoparticles (BGNPs) have been reported in various biomedical applications such as tissue engineering, dental and bone repair, drug and gene delivery, tumour therapy and skincare. The requirement of sustainable synthesis methods is pertinent for large-scale manufacture of such popular materials. Currently, green synthesis methods have gained popularity in various nanoparticle synthesis as it is considered environmentally benign with minimal waste generation. To our knowledge, we report synthesis of BGNPs for the first time using Trigonella foenum-graecum (TFG) leaf extract (TFGL_EX). The TFGL_EX can be used both as a template and precursor for synthesizing BGNPs. The influence of the leaf extract on the composition, particle size and porosity of BGNPs has been determined using characterization techniques like ICP-MS, HR-TEM and nitrogen sorption analysis. Further, bioactivity and biocompatibility of the synthesized BGNPs could be successfully demonstrated through in-vitro studies in Simulated Body Abstract Fluid (SBF) and on model bone cell line, respectively. Native BGNPs as well as model antibacterial drug loaded counterparts demonstrates significant antibacterial properties and sustained drug release profiles. Overall, the study reports a sustainable property dependent synthesis methodology for BGNPs by utilizing organic and inorganic constitutes of TFGL_EX. In chapter 5, we address the design of a novel collagen/pectin (CP) hybrid composite hydrogel (CPBG) containing in-situ mineralized bioactive glass (BG) particles to simulate an integrative 3D cell environment. Systematic analysis of the CP sol revealed that collagen and pectin molecules interacted despite having comparable net negative charges through the mechanism of surface patch binding interaction. FTIR and TGA analysis confirmed this associative interaction resulting in the formation of a hybrid crosslinked network with the BG nanoparticles acting as pseudo crosslink junctions. SEM, EDX and TEM results confirmed uniform mineralization of BG particles, and their synergetic interaction with the network. The in-vitro bioactivity tests on CPBG indicated the formation of bone-like hydroxyapatite (Ca10(PO4)6(OH)2) microcrystals on its surface after interaction with simulated body fluid. This hydrogel was tested against Candida albicans when infused with the model antifungal medication amphotericin-B (AmB). The AmB release kinetics of the hydrogel followed the Fickian diffusion release mechanism demonstrating direct proportionality to gel swelling behaviour. Rheological analysis revealed the viscoelastic compatibility of CPBG for mechanical load bearing applications. Cell viability tests indicated appreciable compatibility of the hydrogel against U2OS and HaCaT cell lines. FDA/PI on the hydrogel portrayed preferential U2OS cell adhesion on hydrophobic hydroxyapatite layer compared to hydrophilic surfaces, thereby promising the regeneration of both soft and hard tissues. Abstract In Chapter 6, ultrafine fibers and a bioactive glass mineralized fibrous mat of gelatin pectin blends were produced by electrospinning in an aqueous phase. Herein, the gelatin-pectin blend was used as a template for the in-situ mineralization of bioactive glass particles during electrospinning of gelatin-pectin based hybrid composite fiber matrix. Additionally, in-situ mineralized bioactive glass along with the fibrous mat served as a site for 7-dehydrocholesterol, i.e., a vitamin-D precursor. This engineered fibrous mat resulted in the sustained release of the drug, which is essential for fortifying the neo regenerated bones. The fibrous mat also exhibited excellent bioactivity in simulated body fluid. Additionally, hybrid composite fibre mat displayed cell proliferation on the surface of fibrous mat and had outstanding cytocompatibility with osteoblast cells.