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3D imaging of hydrogels

Water-based gels (hydrogels) based on complex sugars (polysaccharides) have applications in protein separation and purification in biotechnology, and for drug delivery in medicine.

The chemistry of the component molecules and the solution in which they are formed control how the hydrogels assemble and their macroscopic properties. To determine the basis of the macroscopic properties of hydrogels, Dr Andrew Leis and his colleagues from the CSIRO visualised the gels at the nanoscale in 3D.

Many techniques are suitable for visualising ordered crystalline materials but do not cope with heterogeneous materials such as hydrogels. Therefore, the team used electron tomography in the AMMRF (now Microscopy Australia) Linked Laboratory at the CSIRO Australian Animal Health Laboratory to observe the gels in 3D. Visualising the actual gels is more informative than having to assume gel characteristics based on models.

They saw that the gels’ nanoscale structure had different degrees of disorder, but still had defining characteristics. When hydrogels form at different pHs or in the presence of different ions, their macroscopic properties, such as stiffness and opacity, reconciled perfectly with what they expected to see at the nanoscale.

The team can now refine the dynamic simulations of molecular structure and function, and test the assumptions upon which these simulations are based. Because heterogeneities at the nanoscale can now be studied, fundamental questions can be answered about how the hydrogels self-assemble and the structural hierarchies that exist within them. In potential applications of hydrogels, perfecting their structure is likely to result in improved industrial efficiencies.

In the video above the polysaccharide bundles are green.

Leis et al., Proceedings of the International Symposium on Computational Models for the Life Sciences, pp. 206–213, 2013.

3D tomographic reconstruction of hydrogel fibre bundles 1.8–2.4nm thick (purple), each comprising three or four aligned polysaccharide molecules.

October 24, 2014