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.
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.
There may be a study out there somewhere that could answer your question, Rob, although it would depend on the specific topic. Most of what I've seen in robotics is defense-funded, for example.
From what you're saying, Ann, it sounds like more dollars are getting spent on research these days. Do you have any sense of whether that's the case? If so, is it coming from government? Business?
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.
We're several years aay from knee replacements. I'm not sure if even Baby Boomers will benefit from this on a large scale. I haven't read anything about computer trails or even animal testing yet.
The fact that two relatively weak hydrogels were combined to create something amazing and strong is another lesson for many. Finding the right combination in the right scale is, very often, the key to innovation.
Ann, I'll ask a question that I've asked before, but in a slightly broader way. All of this surprising new technology -- are these developments accelerating, or does it just seem that way because you're shining a light in a lot of disparate corners? It sure seems there's a flood of shocking advancements in medical and robotics.
Inspired by the hooks a parasitic worm uses to penetrate its host's intestines, the Karp Lab has invented a flexible adhesive patch covered with microneedles that adheres well to wet, soft tissues, but doesn't cause damage when removed.
Engineers at the University of California, San Diego are designing a robotic arm that takes inspiration from the loose, flexible, yet very strong structure of the armored plates on a seahorse's tail.
Researchers at the Missouri University of Science & Technology have designed a new nanoscale material that can transmit light faster than the 186,000 miles per second it usually takes to travel through air.
It has often been said that as California goes, so goes the nation. This spring, the state's wind power is setting energy generation records and solar energy generation is expected to rise sharply during the second half of 2013.
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