Thermo-Reversible Protein Fibrillar Hydrogels
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0953-G04-02
Thermo-Reversible Protein Fibrillar Hydrogels Aline Miller1, Alberto Saiani2, and Hui Yan3 1 Chemical Engineering and Analytical Science, University of Manchester, Sackville Street, PO Box 88, University of Manchester, Manchester, M60 1QD, United Kingdom 2 University of Manchester, Manchester, M1 7HS, United Kingdom 3 University of Manchester, Manchester, M60 1QD, United Kingdom
ABSTRACT Hen egg white lysozyme (HEWL) was exposed to various physical and chemical denaturing environments to encourage protein denaturation and consequent gelation. Its phase behavior was examined as a function of pH, temperature and also in the presence of the reductant dithiothreitol (DTT). Transparent viscoelastic gels form at low pH values while opaque gels form under alkaline conditions. No increase in viscosity was observed for systems in pure water unless 20 mM of DTT was added, which is known to break the disulfide bridges present in HEWL. The microstructure of the gel was studied using transmission electron microscopy (TEM) and environmental scanning electron microscopy (ESEM). Gels formed at low pH contain fibrils ~10 nm in diameter with various lengths while at high pH the gels are dominated by particulate aggregates. Thinner fibrils that are 4-6 nm in diameter are observed in the gels formed in the presence of DTT. In this case the distinct feature of the gels is they are thermoreversible and can be melted and reformed easily by varying the temperature.
INTRODUCTION Hydrogels have recently attracted much interest in the biomaterials sector because of their ability to entrap large quantities of water or biological fluids. They are traditionally fabricated with high molecular weight amphiphilic polymers cross-linked through physical entanglements or covalent bonds. Recently the ability of proteins and peptides to self-assemble into ordered supramolecular architectures on the meso- to macroscopic length scales has attracted considerable attention in the development of novel biomaterials due to their potential biocompatibility and biodegradability [1-4]. In particular, the β-sheet motif is of most interest due to its important role in the formation of protein fibrils [5]. These fibrils have recently been shown to further self-organize into a three-dimensional network, i.e. a protein hydrogel that is able to retain up to 97% water or biological fluid [3]. As with natural globular proteins, it is known that mild denaturing conditions, such as low pH, elevated temperature and organic solvents encourage the formation of fibrils rich in β-sheet structures [6] and if the protein concentration is above a critical threshold, fibrils will self-organize to form a three-dimensional fibrillar network [4]. However, systematic studies on protein self-assembly in response to different destabilizing conditions and consequent effects of such destabilizing conditions on the morphology of resulting supramolecular structures are few in the literature. In this work, we have focused on the gelation behavior of the model protein hen egg wh
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