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Highly stretchable and tough hydrogels

Jeong-Yun Sun's picture

Hydrogels are pervasive in nature and technology, but the scope of applications is often severely limited by the mechanical behavior of hydrogels.  Most synthetic hydrogels are much more brittle than natural hydrogels such as cartilage.  Despite intense efforts to synthesize hydrogels of enhanced mechanical behavior, much of the property space of hydrogels remains uncharted.  Here we report extremely stretchable and tough hydrogels made of polymers forming networks via ionic and covalent crosslinks.  Although the gel contains ~ 90% water, it can be stretched beyond 20 times its initial length, and has fracture energy of ~9000 J/m2.  We envision that gels of much improved mechanical behavior will open up applications such as artificial tissues and soft machines.


 a, A strip of the undeformed gel was glued to two rigid clamps. b, The gel was stretched to 21 times its initial length in a tensile machine (Instron model 3342). The stretch, λ, is defined by the distance between the two clamps when the gel is deformed, divided by the distance when the gel is undeformed. c, A notch was cut into the gel, using a razor blade; a small stretch of 1.15 was used to make the notch clearly visible. d, The gel containing the notch was stretched to 17 times its initial length.



zhan-sheng guo's picture

great work.

Zhigang Suo's picture

A science writer asks us to say a few words about possible impact of this paper.  Here are some thoughts.

This paper demonstrates a type of hydrogel of uncommonly large stretchability and toughness.  The numbers are summarized in the first paragraph of the paper.  You may also wish to watch a viedo  to get a feel for the material.  A piece by Ken Shull  in the section of Nature News and Views places the work into perspective.  

Tofu, contact lens and cartilage are all hydrogels.  Tofu is brittle.  We will not use tofu as a contact lens.  Contact lens is tough, but much less so than cartilage.  We will not use contact lens to replace cartilage.  Indeed, damaged cartilage cannot be replaced today:  one has to replace the entire knee with metal.  There has been a strong motivation to develop tough hydrogels for tissue engineering and tissue replacement.  However, the science of fracture of hydrogels is at a nascent stage, insufficient to design hydrogels of desired fracture behavior on demand.  

This paper is a basic study of the particular hydrogel we have synthesized.  Its toughness is the highest ever reported for hydrogels.  Besides, the method of synthesis is simple--many groups around world can do it within days and weeks.  They can use the hydrogels to study the science of fracture of tissue-like matter.  They can also develop the hydrogels for applications, including tissue engineering, soft robots and drug delivery.  

We would be gratified if this paper motivates many people to study the fascinating science of fracture of hydrogels, where mechanics meets chemistry.  We would also be delighted if this demonstration of hydrogels of exceptional toughness prompts people to give this class of materials a fresh look.  May their imagination create new applications of tough hydrogels.

Cai Shengqiang's picture

It is indeed a nice work with interesting demonstration. Congratulations to all the authors.

Xuanhe Zhao's picture

Crack bridging and plasticity-induced toughening are two basic concepts we learnt from Zhigang's class Fracture Mechanics. At that time, we were also fascinated by the pioneer work from Prof. Jianping Gong on tough double-network gels, which use bridging and damage-induced toughening and thus do not show good fatigue properties. Meanwhile, we found that the reversible crosslinkings in physical gel, such as alginate, can lead to significant plasticity without fracturing polymer chains. So why not try alginate as a toughening network? It turned out alginate works extremely well. Once again, basic knowledge from mechanics and materials leads to technological innovation. Congratulations, Jeong-Yun, Zhigang and every co-author of the paper!

Qiming Wang's picture

Sincere congratulations to Jeong-Yun, Xuanhe, Zhigang, and all other authors! One questions is that other than the mechanisms proposed in this paper, is there any other traditional or modern approaches to enhance fracture toughness. Then I suddenly find couples of answers in Wei's new post: .  

ChangyongCao's picture

Great work, good progress!

Congratulations to all the authors!

Konstantin Volokh's picture

Congratulations guys! I could not believe in the numbers for toughness
and stretch... It looks like you found the material of which Hell is built.
This monster cannot be peacefully called Hydrogel – it should be called Hellgel.


Kejie Zhao's picture

Yuhang Hu's picture

It is also highlighted in Harvard Gazette.

Truely an inspiring work. Congratulations to all the authors. 

Zhigang Suo's picture

I have collected some of online reports and comments on this paper.  Some of the comments are perceptive.  They may set new goals for future research. 

Kejie Zhao's picture

it might be a good idea to link the highlights on the group page with the paper,  will be interesting to see the perspective feedbacks.

Zhigang Suo's picture

Dear Kejie:  Many thanks for the suggestion.  I have made a link to some online reports from our group web site

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