Designing Tough Hydrogels

Dr. Bob Weiss, Associate Dean for Research, College of Polymer Science and Engineering, University of Akron
When Oct 09, 2015
from 01:00 PM to 02:00 PM
Where Ernst Hall, Room 310
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Abstract

Hydrogels are three-dimensional networks composed of chemically and/or physically-crosslinked hydrophilic polymers that have application as biomedical materials, sensors, actuators, soft machines, battery components, separation media, food products, sealants and adhesives. Even though hydrogels may be greater than 90% water, they behave mechanically as elastic solids, but they generally exhibit poor mechanical strength (< 100 kPa) and toughness (<10 J/mc), because they lack a mechanism for energy dissipation. In the biomedical field alone, mechanical robustness can be a challenge for hydrogels used in applications such as drug delivery, ophthalmology, wound healing and tissue engineering. In 2003, Gong and coworkers1 developed a new class of hydrogel, termed a double network (DN), that was purportedly an interpenetrating network (IPN) and exhibited exceptionally high strength (~1 MPa) and toughness (> 100 J/m2). Subsequent work by other research groups have demonstrated other structures for achieving tough hydrogels that are largely based on the incorporation of physical, reversible crosslinks. Although covalent hydrogels provide the optimum ability for shape retention, physical hydrogels include an inherent mechanism for energy dissipation, namely supramolecular crosslink. Toughness values of > 1000 J/m2, which is the inherent toughness of naturally occurring cartilage, have been achieved with physical hydrogels. Alternatively, hybrid hydrogels, incorporating both covalent and physical crosslinks, provide a mechanism for both shape-retention and energy dissipation, and have been employed in some cases to achieve robust hydrogels with good shape reversibility and improved mechanical properties.

This talk will discuss the design of tough hydrogels using primarily our own research on DN hydrogelsii, physical hydrogels and hybrid hydrogelsiii-v. Among the topics we plan to discuss are the actual microstructure of DN hydrogels, which are not IPNs as originally proposed, and the advantages of physical and hybrid hydrogels with regard to shaping hydrogels by melt extrusion or injection molding, injectability of physical gels for biomedical applications, electrospinning hydrogel nanofibers and shape memory behavior.

1 Gong, J. P., Katsuyama, Y., Kurokawa, T. & Osada, Y. Double-Network Hydrogels with Extremely High Mechanical Strength. Advanced Materials 15, 1155–1158 (2003).
ii Es-Haghi, S. S., A. I. Leonov and R. A. Weiss. On The Necking Phenomenon in Pseudo-Semi-Interpenetrating Double-Network Hydrogels, Macromolecules, 2013, 46, 6203–6208.
iii Hao, J.; Weiss, R. A. Viscoelastic and Mechanical Behavior of Hydrophobically Modified Hydrogels, Macromolecules, 2011, 44, 9390-9398.
iv Hao, J.; Weiss, R. A. Mechanical behavior of hybrid hydrogels composed of a physical and a chemical network. Polymer, 2011, 54, 2174–2182.
v Hao, J.; Weiss, R. A. Mechanically Tough, Thermally Activated Shape Memory Hydrogels. ACS Macro Lett. 2013, 2, 86–89.

Speaker's Biography

Bob Weiss is the Hezzleton E. Simmons Professor of Polymer Engineering and Associate Dean for Research at the University of Akron. Prior to that appointment in 2009, he was a Board of Trustees Distinguished Professor and the United Technologies Corp. Professor of Advanced Materials and Processing at the University of Connecticut. He received a B.S. in chemical engineering from Northwestern University in 1972 and a PhD in chemical engineering from the University of Massachusetts in 1976. He spent 5 years in the Plastics Technology Division of Exxon Chemical and the Corporate Research Laboratories of Exxon Research and Engineering Co. before joining the Chemical Engineering Dept. at the University of Connecticut in 1981. He is a Fellow of the American Physical Society, the American Chemical Society, the Society of Plastics Engineers, the North American Thermal Analysis Society and the Polymer Materials: Science and Engineering Division of the American Chemical Society. He was the recipient of the Society of Plastics Engineers’s International Award in 2008. Prof. Weiss's research interests include structure-property relationships of multiphase polymers, notably ionomers, block copolymers, liquid crystalline polymers, polymer blends and gels. He has published nearly 250 journal papers and over 300 conference proceedings and he has 20 U.S. patents. He served 25 years as associate editor and editor-in-chief of the journals Polymer Engineering and Science and Polymer Composites.