Navigation Links
Tough gel stretches to 21 times its length, recoils, and heals itself

Cambridge, Mass. - September 5, 2012 - A team of experts in mechanics, materials science, and tissue engineering at Harvard have created an extremely stretchy and tough gel that may pave the way to replacing damaged cartilage in human joints.

Called a hydrogel, because its main ingredient is water, the new material is a hybrid of two weak gels that combine to create something much stronger. Not only can this new gel stretch to 21 times its original length, but it is also exceptionally tough, self-healing, and biocompatiblea valuable collection of attributes that opens up new opportunities in medicine and tissue engineering.

The material, its properties, and a simple method of synthesis are described in the September 6 issue of Nature.

"Conventional hydrogels are very weak and brittleimagine a spoon breaking through jelly," explains lead author Jeong-Yun Sun, a postdoctoral fellow at the Harvard School of Engineering and Applied Sciences (SEAS). "But because they are water-based and biocompatible, people would like to use them for some very challenging applications like artificial cartilage or spinal disks. For a gel to work in those settings, it has to be able to stretch and expand under compression and tension without breaking."

Sun and his coauthors were led by three faculty members: Zhigang Suo, Allen E. and Marilyn M. Puckett Professor of Mechanics and Materials at SEAS and a Kavli Scholar at the Kavli Institute for Bionano Science and Technology at Harvard; Joost J. Vlassak, Gordon McKay Professor of Materials Engineering and an Area Dean at SEAS; and David J. Mooney, Robert P. Pinkas Family Professor of Bioengineering at SEAS and a Core Faculty Member at the Wyss Institute for Biologically Inspired Engineering at Harvard.

To create the tough new hydrogel, they combined two common polymers. The primary component is polyacrylamide, known for its use in soft contact lenses and as the electrophoresis gel that separates DNA fragments in biology labs; the second component is alginate, a seaweed extract that is frequently used to thicken food.

Separately, these gels are both quite weakalginate, for instance, can stretch to only 1.2 times its length before it breaks. Combined in an 8:1 ratio, however, the two polymers form a complex network of crosslinked chains that reinforce one another. The chemical structure of this network allows the molecules to pull apart very slightly over a large area instead of allowing the gel to crack.

The alginate portion of the gel consists of polymer chains that form weak ionic bonds with one another, capturing calcium ions (added to the water) in the process. When the gel is stretched, some of these bonds between chains breakor "unzip," as the researchers put itreleasing the calcium. As a result, the gel expands slightly, but the polymer chains themselves remain intact. Meanwhile, the polyacrylamide chains form a grid-like structure that bonds covalently (very tightly) with the alginate chains.

Therefore, if the gel acquires a tiny crack as it stretches, the polyacrylamide grid helps to spread the pulling force over a large area, tugging on the alginate's ionic bonds and unzipping them here and there. The research team showed that even with a huge crack, a critically large hole, the hybrid gel can still stretch to 17 times its initial length.

Importantly, the new hydrogel is capable of maintaining its elasticity and toughness over multiple stretches. Provided the gel has some time to relax between stretches, the ionic bonds between the alginate and the calcium can "re-zip," and the researchers have shown that this process can be accelerated by raising the ambient temperature.

The group's combined expertise in mechanics, materials science, and bioengineering enabled the group to apply two concepts from mechanicscrack bridging and energy dissipationto a new problem.

"The unusually high stretchability and toughness of this gel, along with recovery, are exciting," says Suo. "Now that we've demonstrated that this is possible, we can use it as a model system for studying the mechanics of hydrogels further, and explore various applications."

"It's very promising," Suo adds.

Beyond artificial cartilage, the researchers suggest that the new hydrogel could be used in soft robotics, optics, artificial muscle, as a tough protective covering for wounds, or "any other place where we need hydrogels of high stretchability and high toughness."

Contact: Caroline Perry
Harvard University

Related biology news :

1. Toughened silicon sponges may make tenacious batteries
2. Our coral reefs: In trouble - but tougher than we thought
3. Short stretches of piRNA evaluate cells genetic history
4. Bird louse study shows how evolution sometimes repeats itself
5. Green plants reduce city street pollution up to 8 times more than previously believed
6. How to make global fisheries worth 5 times more: UBC research
7. Palladium-gold nanoparticles clean TCE a billion times faster than iron filings
8. Longer sleep times may counteract genetic factors related to weight gain
9. Pain relief with PAP injections may last 100 times longer than a traditional acupuncture treatment
Post Your Comments:
Related Image:
Tough gel stretches to 21 times its length, recoils, and heals itself
(Date:5/24/2016)... Calif. , May 24, 2016 Ampronix facilitates superior patient care by ... LMD3251MT  3D medical LCD display is the latest premium product recently added to the ... ... ... Sony 3d Imaging- LCD Medical Display- Ampronix News ...
(Date:5/16/2016)... YORK , May 16, 2016   EyeLock ... solutions, today announced the opening of an IoT Center ... to strengthen and expand the development of embedded iris ... an unprecedented level of convenience and security with unmatched ... authenticate one,s identity aside from DNA. EyeLock,s platform uses ...
(Date:5/9/2016)... , UAE, May 9, 2016 ... when it comes to expanding freedom for high net ... Even in today,s globally connected world, there is ... conferencing system could ever duplicate sealing your deal with ... obtaining second passports by taking advantage of citizenship via ...
Breaking Biology News(10 mins):
(Date:6/23/2016)... , June 23, 2016 Houston ... with the Cy-Fair Sports Association to serve as ... the agreement, Houston Methodist Willowbrook will provide sponsorship ... and connectivity with association coaches, volunteers, athletes and ... with the Cy-Fair Sports Association and to bring ...
(Date:6/23/2016)... June 23, 2016   EpiBiome , a precision ... million in debt financing from Silicon Valley Bank (SVB). ... and to advance its drug development efforts, as well ... "SVB has been an incredible strategic partner ... a traditional bank would provide," said Dr. Aeron ...
(Date:6/23/2016)... Ky. , June 23, 2016 ... two Phase 1 clinical trials of its complement ... placebo-controlled, single and multiple ascending dose studies designed ... pharmacodynamics (PD) of subcutaneous injection in healthy adult ... subcutaneously (SC) either as a single dose (ranging ...
(Date:6/23/2016)... ... 23, 2016 , ... ClinCapture, the only free validated electronic ... showcase its product’s latest features from June 26 to June 30, 2016 for ... Disrupting Clinical Trials in The Cloud during the conference. DIA (Drug Information ...
Breaking Biology Technology: