DESIGNING OF GELLAN BASED ELECTROSPUN NANOFIBERS FOR BIOMEDICAL APPLICATIONS

Abstract

Gellan is a FDA-approved biocompatible polysaccharide which is composed of a linear chain of repeating tetrasaccharide units of D-glucose, D-glucuronic acid and L-rhamnose residues in 2:1:1 ratio. The significant structural features such as presence of free carboxylic group and bio-adhesiveness properties of gellan makes it a favorable candidate for drug delivery, tissue engineering and wound healing applications. A wide range of gellan based formulations (such as microsized fibers, nanoparticles, implanting hydrogels and thin film) have been in lime-light throughout the world. However, despite advantageous features of gellan, only limited studies regarding gellan based nano formulations have been scrutinized. The nano-sized formulations possess unique properties such as high surface area-to-volume ratio, which distinguish them from their macro-sized counterparts. This prompted us to fabricate the gellan based nanofibers using electrospinning technique. Electrospinning is as recognized and versatile technique to produce fibers of diameter ranging from nano to sub-micrometer with distinct properties such as high aspect ratio, porosity and special hierarchical features. Electrospun nanofibers synthesized from natural polymers such as alginate, hyaluronic acid, gelatin, chitosan and collagen, have been recognized as biocompatible materials for a number of applications. However, due to the limited solubility, highly coiled chain conformations and hydrodynamic reactions between the polyanions present in the solution, the fabrication of electrospun nanofibrous from these natural polymers, always remains a challenge which eventually restrict their practical applications. Like most of the natural polysaccharides, gellan also shows the complex sol-gel behavior and a non-typical solvation in water resulting in micro-aggregating gels which make the gellan aqueous solution very difficult to be electrospun. In this study, the above hurdle is overcome by preparing a blend solution of gellan with other water soluble, non-toxic, biocompatible and synthetic polymer i.e. PVA, which reduced the viscosity as well as the repulsive forces of resulted solution. In brief, Chapter 1 presents a detailed literature overview on properties and biomedical application of gellan gum in tissue engineering, drug delivery and wound healing area. Chapter 2 confined the optimization of process parameters for successful preparation of gellan based nanofibers. It concluded that the solution containing 1.5 wt% gellan and 10 wt% PVA in 1:1 ratio was found to be optimum for the obtaining stable nanofibers with uniform morphology and average diameter of 40 ± 15.8 nm. The fabricated nanofibers were then physio-chemically ii characterized using field emission electron microscopy (FESEM), Fourier transformed (FTIR) spectroscopy, X-ray diffraction (XRD), thermo-gravimetric (TGA) and differential scanning calorimetric (DSC) techniques to evaluate the morphology, compatibility, physical state and thermal stability of fabricated nanofibers. The IR spectra suggested the presence of weak molecular interaction and crosslinking within the gellan and PVA whereas XRD confirmed the highly crystalline nature of gellan-PVA nanofibers as compared to raw polymers. Conversely, the fabricated gellan/PVA nanofibers showed lack of integrity/stability in aqueous environment which is a primary requisite for its application in biomedical sector. Therefore, in Chapter 3, a number of crosslinking (physical, chemical, ionic and vapor crosslinking) methods were explored for gellan/PVA nanofibers to provide them mechanical strength as well as water stability. The crosslinking conditions were optimized with regards to its effects on substantial properties of materials and its biocompatibility. Results obtained, showed that heat crosslinked nanofibers exhibited good uniformity, structural integrity and cytocompatibility and hence were further evaluated for their potential biomedical applications. In Chapter 4, these electrospun nanofibers were used as a hydrophilic scaffolding material for skin tissue regeneration. The cell culture studies using human dermal fibroblast (3T3L1) cells established that these gellan based nanofibrous scaffold could induce improved cell adhesion as well as enhanced cell growth than conventionally proposed gellan based hydrogels and dry films. Importantly, the nanofibrous scaffolds are biodegradable and could be potentially used as a temporary substrate/ or biomedical graft to induce skin tissue regeneration. Chapter 5 presents the gastroretentive/mucoadhesive drug delivery potential of fabricated gellan/PVA nanofibers which was validated by examining the drug release profiles of ofloxacin drug from gellan/PVA nanofibers. The average diameters of ofloxacin loaded gellan/PVA nanofibers were recorded to be approximately 30 nm as compared to blank gellan/PVA nanofibers (approximately 40 nm), suggested that drug encapsulation significantly reduced the fiber diameter. In Chapter 6, we investigated the wound healing potential of electrospun gellan/PVA nanofibers. In this context, a preliminary in vivo study was performed on rat skin excision wound model. For neo-tissue regeneration in a sterilized environment and to combat microbial infection at wound site, amoxicillin (a broad spectrum antibiotic) was entrapped within these nanofibers. Entrapment of amoxicillin in the composite nanofibers was confirmed by the FESEM, FTIR and XRD analysis. Quick re-epithelializationin and collagen deposition was observed in case of gellan/PVA nanofibers which confirmed the candidature of such scaffolds for tissue regeneration and faster skin restoration