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Issue 6, 2008
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Thermoreversible lysozyme hydrogels: properties and an insight into the gelation pathway

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Abstract

The gelation behaviour of aqueous solutions of hen egg white lysozyme (HEWL) in the presence of 20 mM DTT in the concentration range 0.7 to 4.0 mM has been investigated using microDSC, FTIR, cryoTEM, SANS and oscillatory rheology. The macroscopic critical gelation concentration, Cgel, was found to be ∼ 3.0 mM. The disruption of the disulfide bonds by the DTT and the destabilisation of the protein were found to be a prerequisite for the formation of β-sheet rich fibrils under the mild conditions used in this work. Using our methodology the hydrogels obtained have a pH of 7, hence are suitable for cell culture, and are also thermoreversible. The hydrogel melting temperature was found to increase with increasing concentration and a similar structure was observed across the concentration range investigated. Our results suggest these systems are composed of a well defined regular network where single β-sheet rich fibrils (∼ 3 nm diameter) form initially, then two of these fibrils associate two-by-two to form junctions (∼ 6 nm diameter) and then on cooling further aggregate to form larger bundles of fibres. The network mesh size was found to decrease with increasing concentration. Our results suggest that below Cgel small unconnected gel-like aggregates exist that have a similar structure to the hydrogels obtained above Cgel. Using our data we propose a model for the denaturation and gelation behaviour of our system. During the first heating an α-helix to β-sheet molecular transition for the protein conformation occurs resulting in β-sheet rich fibrils forming through the self-assembly of β-sheet rich denaturated proteins. At high temperature the solution contains β-sheet rich fibrils with dissolved protein. On cooling an increase in the amount of β-sheet was observed viaFTIR suggesting that as the temperature is decreased more and more protein forms β-sheet rich fibrils. At the gelation temperature these fibrils associate two-by-two to form the network junctions resulting in the macroscopic gelation of the sample. Our results suggest the network junctions are formed via specific hydrophobic interactions. The hydrogels elastic modulus was found to scale as C2.45 for C > Cgel.

Graphical abstract: Thermoreversible lysozyme hydrogels: properties and an insight into the gelation pathway

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Supplementary files

Article information


Submitted
02 Nov 2007
Accepted
21 Feb 2008
First published
31 Mar 2008

Soft Matter, 2008,4, 1313-1325
Article type
Paper

Thermoreversible lysozyme hydrogels: properties and an insight into the gelation pathway

H. Yan, H. Frielinghaus, A. Nykanen, J. Ruokolainen, A. Saiani and A. F. Miller, Soft Matter, 2008, 4, 1313
DOI: 10.1039/B716966C

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