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  1. Anthony M. Lowman,
  2. Thomas D. Dziubla

Published Online: 15 JUL 2002

DOI: 10.1002/0471216275.esm040

Encyclopedia of Smart Materials

Encyclopedia of Smart Materials

How to Cite

Lowman, A. M. and Dziubla, T. D. 2002. Gels. Encyclopedia of Smart Materials. .

Author Information

  1. Drexel University, Philadelphia, PA

Publication History

  1. Published Online: 15 JUL 2002


Hydrogels are three-dimensional, water-swollen structures composed mainly of hydrophilic homopolymers or copolymers. They are rendered insoluble by chemical or physical cross-links. The physical cross-links can be entanglements, crystallites, or weak associations such as van der Waals forces or hydrogen bonds. Cross-links provide the network structure and physical integrity. It is possible to design hydrogels whose swelling behavior depends on the external environment. During the last thirty years, there has been significant interest in the development and analysis of environmentally or physiologically responsive hydrogels.

Hydrogels are classified in a number of ways. They can be neutral or ionic based on the nature of the side groups. They can also be classified on the basis of network morphology as amorphous, semicrystalline, hydrogen-bonded structures; supermolecular structures; and hydrocolloidal aggregates. Additionally, in terms of their network structures, hydrogels can be classified as macroporous, microporous, or nonporous. In this article, an overview of smart hydrogels and models that characterize the structure and properties of these materials are presented. Additionally, important contributions in this area and new synthetic methods that promise to lead to the development of exciting new structures for solutions to drug delivery problems are reviewed.


  • Structure;
  • Properties;
  • Hydrogels;
  • Classification;
  • Temperature-sensitive;
  • pH sensitive;
  • Complexing hydrogels