Highly absorbent hydrogels, used in medical and bioengineering applications, tend to be flexible, but also brittle and not very stretchable. A team of engineering and materials science researchers from Harvard University, Seoul National University, and Duke University has invented a set of tough, synthetic hydrogels that can be stretched up to 21 times their length and still recover.
Used to make scaffolds for tissue engineering, as well as drug delivery vehicles, hydrogels absorb as much as 99.9 percent water and are made of natural or synthetic polymers. They are used in biology research and medical applications because their high water content makes them flexible, like living tissue.
A new flexible, self-healing hydrogel that could replace cartilage can be stretched it to 21 times its length before breaking. (Source: Jeong-Yun Sun/Harvard University)
In an article published in Nature (subscription or payment required), the researchers say they synthesized their new materials from polymers that form ionically and covalently crosslinked networks. The new hybrid hydrogels were formed of alginate and polacrylamide, and contain about 90 percent water. Although some elastic hydrogels have stretched to between 10 and 20 times their length, samples that contained notches or other deformations stretched much less. When containing notches, the new materials stretch up to 17 times their length, and notches remain stable. (Watch a video of the notched material stretching here.)
The new hydrogels have a fracture energy of about ~9,000 J m-2, compared to ~10 J m-2 for most hydrogels and ~1,000 J m-2 for cartilage. The researchers say:
We attribute the gels' toughness to the synergy of two mechanisms: crack bridging by the network of covalent crosslinks, and hysteresis by unzipping the network of ionic crosslinks. Furthermore, the network of covalent crosslinks preserves the memory of the initial state, so that much of the large deformation is removed on unloading. The unzipped ionic crosslinks cause internal damage, which heals by re-zipping.
(Watch a video of a large, recoverable deformation formed by a metal ball dropping on a membrane of the gel here.)
Because the new gels are tough, self-healing, biocompatible, and flexible, they could be used as replacements for human cartilage, in soft robotics, as artificial muscles, or as a protective covering for wounds. Different combinations of weak and strong molecular integration could make hybrid hydrogels with different sets of characteristics.
The research team included Jeong-Yun Sun of Harvard University and Seoul National University; Widusha R. K. Illeperuma, Ovijit Chaudhuri, David J. Mooney, Joost J. Vlassak, and Zhigang Suo of Harvard University; Kyu Hwan Oh of Seoul National University; and Xuanhe Zhao of Duke University.
bobj, glad you liked the article. I hope you were doing all that running on earth, not concrete. This technology is very much in its infancy, as are most of the discoveries I write on reported by universities, instead of commercial companies. That said, hydrogels as a class have a history as cartilage replacements already, so the timeline might be shorter than "normal," if there is such a thing. I guess growing up in Silicon Valley makes me appreciative of Heiseneberg. Anyway, I also have hip issues, although so far only in winter.
Years ago, 35 to be exact, my wife and I enjoyed running-10Ks mostly. Well, father time has put an end to that activity but the "remains of the day" linger. I have real problems with my right hip and right knee. Hip replacement surgery has been recommended but I have put it off for several months due to schedule and the fact that I'm 168 pounds of rompin stompin coward. I talked with my doctor about repairing the cartilage in the joint but he tells me the repair, if possible at all, would be considerably worse than the replacement. With that being the case, Ann do you have a time-line for commercialization of the hydrogels or is this technology in its infancy--tried but unproven? Great article also.
Mydesign, replacement knee surgery is not a sure thing re results, not at all guaranteed, can cause a lot of problems and is insanely expensive: at least half the cost of a low-end car. Otherwise I would have done it by now. Also, most replacement knee implants/structures are engineered for men, not women. But you probably know all that. Meanwhile, any claims of technologies that regrow cartilage are, AFAIK, untrue.
Ann, I had done a bit research for my mother having the same problem. She has some wear and tear in her knee cartilage and doctors advising us for a complete knee replacement. We are looking for some alternate therapy, which can regenerate the cartilages. Eventhough many are clamming that it can be regenerate, but so far nothing is medically proven.
Rob, I think it's both: I do like finding obscure but weird and potentially earth-shaking developments in technology of several kinds. It's also true that we have more researchers now than ever before in many different disciplines, countries and cultures, working on many different solutions to many different problems. Humans have been ingenious creatures for hundreds of millenia: these advances aren't nearly as earth-shattering and shocking as the first sentences, or the first tools, or the first wheels.
I wonder if anyone is working on a substance that could contract to a fraction of its original length, simulating a muscular contraction. If such a substance could be interfaced with nerves it could replace lost muscles and limbs -- and think of the possibilities for robotics without motors.
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