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Entropic trapping of macromolecules by mesoscopic periodic voids in a polymer hydrogel

Nature volume 397, pages 141–144 (1999)Cite this article

Abstract

The separation of macromolecules such as polymers and DNA by means of electrophoresis, gel permeation chromatography or filtration exploits size-dependent differences in the time it takes for the molecules to migrate through a random porous network. Transport through the gel matrices, which usually consist of full swollen crosslinked polymers1,2,3,4,5,6,7,8,9,10,11, depends on the relative size of the macromolecule compared with the pore radius. Sufficiently small molecules are thought to adopt an approximately spherical conformation when diffusing through the gel matrix1, whereas larger ones are forced to migrate in a snake-like fashion3,4,5. Molecules of intermediate size, however, can get temporarily trapped in the largest pores of the matrix, where the molecule can extend and thus maximize its conformational entropy. This ‘entropic trapping’ is thought to increase the dependence of diffusion rate on molecular size6,7,8,9,10,11,12,13,14,15,16. Here we report the direct experimental verification of this phenomenon. Bragg diffraction from a hydrogel containing a periodic array of monodisperse water voids confirms that polymers of different weights partition between the hydrogel matrix and the water voids according to the predictions of the entropic trapping theory. Our approach might also lead to the design of improved separation media based on entropic trapping.

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Figure 1: Fabrication of hydrogel with a cubic array of spherical water voids.
Figure 2: Bragg diffraction probes the chemical composition of HPCCA.
Figure 3: Dependence of NaPSS partitioning on molecular mass and concentration.

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Acknowledgements

We thank M. D. Morris, D. Pine, J. Holtz, J. M. Weissman and G. Pan for discussions. This work was supported by the Office of Naval Research and the US National Science Foundation.

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Author notes

  1. Lei Liu

    Present address: Praxair Service Technologies Inc., 1555 Main St, Indianapolis, Indiana, 46254, USA

  2. Pusheng Li

    Present address: Epsilon Inc., HPOS, 50 Cambridge St, Burlington, Massachusetts, 01803, USA

Authors and Affiliations

  1. Department of Chemistry, University of Pittsburgh, Pittsburgh, 15260, Pennsylvania, USA

    Lei Liu, Pusheng Li & Sanford A. Asher

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  1. Lei Liu
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Correspondence to Sanford A. Asher.

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Liu, L., Li, P. & Asher, S. Entropic trapping of macromolecules by mesoscopic periodic voids in a polymer hydrogel. Nature 397, 141–144 (1999). https://doi.org/10.1038/16426

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