Hope for Back Pain

This sounds extremely promising and provides a new departure for gelapplications. Replacing cartilage is an obvious starting point. Italso is likely to be a great starting point for a helmet that moldsitself to the skull and able to provide a cushion against sharpacceleration. Since it is tough, the amount used could be minimizedeasily also to handle weight demands.
It is even tougher than cartilage. Thus joint replacement doesbecome possible while retaining original function. This isparticularly welcome for those facing the prospect of joint surgeryover the next decade and thereafter. It will still take time toimplement, but that was the one thing missing.
Of course, the big job for artificial cartilage is spine repair whichhas been utterly unsatisfactory up to this point. It is really verygood news and real hope for back pain.

Tough gel stretches to 21 times its length, recoils, and healsitself
September 05, 2012
Biocompatible material created at Harvard is much tougher thancartilage
CONTACT: CarolinePerry, (617) 496-1351
http://www.seas.harvard.edu/news-events/press-releases/tough-gel-stretches-to-21-times-its-length
Cambridge, Mass. -September 5, 2012 - A team of experts in mechanics, materialsscience, and tissue engineering at Harvard have created an extremelystretchy and tough gel that may pave the way to replacing damagedcartilage in human joints.
Called a hydrogel,because its main ingredient is water, the new material is a hybrid oftwo weak gels that combine to create something much stronger. Notonly can this new gel stretch to 21 times its original length, but itis also exceptionally tough, self-healing, and biocompatible—avaluable collection of attributes that opens up new opportunities inmedicine and tissue engineering.
The material, itsproperties, and a simple method of synthesis are described in theSeptember 6 issue of Nature.
The researchers pinnedboth ends of the new gel in clamps and stretched it to 21 times itsinitial length before it broke. (Photo courtesy of Jeong-Yun Sun.)
"Conventionalhydrogels are very weak and brittle—imagine a spoon breakingthrough jelly," explains lead author Jeong-Yun Sun, apostdoctoral fellow at the Harvard School of Engineering and AppliedSciences (SEAS). "But because they are water-based andbiocompatible, people would like to use them for some verychallenging applications like artificial cartilage or spinal disks.For a gel to work in those settings, it has to be able to stretch andexpand under compression and tension without breaking."
Sun and his coauthorswere led by three faculty members: Zhigang Suo, Allen E. andMarilyn M. Puckett Professor of Mechanics and Materials at SEAS and aKavli Scholar at the Kavli Institute for Bionano Science andTechnology at Harvard; Joost J. Vlassak, Gordon McKay Professorof Materials Engineering and an Area Dean at SEAS; and David J.Mooney, Robert P. Pinkas Family Professor of Bioengineering at SEASand a Core Faculty Member at the Wyss Institute for BiologicallyInspired Engineering at Harvard.
To create the toughnew hydrogel, they combined two common polymers. The primarycomponent is polyacrylamide, known for its use in soft contact lensesand as the electrophoresis gel that separates DNA fragments inbiology labs; the second component is alginate, a seaweedextract that is frequently used to thicken food.
Separately, these gelsare both quite weak—alginate, for instance, can stretch to only 1.2times its length before it breaks. Combined in an 8:1 ratio,however, the two polymers form a complex network of crosslinkedchains that reinforce one another. The chemical structure of thisnetwork allows the molecules to pull apart very slightly over a largearea instead of allowing the gel to crack.
By themselves,polyacrylamide gels (a) and alginate gels (b) are brittle. The newhydrogel (c), however, has a more complex molecular structure thathelps to dissipate stress across a wide area. The red circlesrepresent calcium ions, and the blue triangles and green squaresrepresent covalent crosslinks between chains. (Image courtesy ofJeong-Yun Sun and Widusha R. K. Illeperuma.)
The alginate portionof the gel consists of polymer chains that form weak ionic bonds withone another, capturing calcium ions (added to the water) in theprocess. When the gel is stretched, some of these bonds betweenchains break—or "unzip," as the researchers putit—releasing the calcium. As a result, the gel expands slightly,but the polymer chains themselves remain intact. Meanwhile, thepolyacrylamide chains form a grid-like structure that bondscovalently (very tightly) with the alginate chains.
Therefore, if the gelacquires a tiny crack as it stretches, the polyacrylamide grid helpsto spread the pulling force over a large area, tugging on thealginate's ionic bonds and unzipping them here and there. Theresearch team showed that even with a huge crack, a critically largehole, the hybrid gel can still stretch to 17 times its initiallength.
The researchers used arazor blade to cut a 2-cm notch across the gel. In the image above(left), the gel has been stretched very slightly so that the notch isvisible. This damaged gel was still able to stretch to 17 times itsinitial length without breaking. (Photo courtesy of Jeong-Yun Sun.)
Importantly, the newhydrogel is capable of maintaining its elasticity and toughness overmultiple stretches. Provided the gel has some time to relax betweenstretches, the ionic bonds between the alginate and the calcium can"re-zip," and the researchers have shown that this processcan be accelerated by raising the ambient temperature.
The group's combinedexpertise in mechanics, materials science, and bioengineering enabledthe group to apply two concepts from mechanics—crack bridging andenergy dissipation—to a new problem.
"The unusuallyhigh stretchability and toughness of this gel, along with recovery,are exciting," says Suo. "Now that we've demonstrated thatthis is possible, we can use it as a model system for studying themechanics of hydrogels further, and explore various applications.""It's verypromising," Suo adds.
Beyond artificialcartilage, the researchers suggest that the new hydrogel could beused in soft robotics, optics, artificial muscle, as a toughprotective covering for wounds, or "any other place where weneed hydrogels of high stretchability and high toughness."


Coauthorsincluded Xuanhe Zhao, a former Ph.D. student and postdoc atSEAS, now a faculty member at Duke University; Widusha R. K.Illeperuma, a graduate student at SEAS; Ovijit Chaudhuri, a postdocin Mooney's lab; and Kyu Hwan Oh, Sun's former adviser and afaculty member at Seoul National University in Korea.
This work wassupported by the U.S. Army Research Office, the National ScienceFoundation (NSF), the Defense Advanced Research Projects Agency, theNational Institutes of Health, and the NSF-funded Materials ResearchScience and Engineering Center (MRSEC) at Harvard. The researchersalso individually received support from the NSF Research TriangleMRSEC, a Haythornthwaite Research Initiation grant, the NationalResearch Foundation of Korea, an Alexander von Humboldt Award, andHarvard University.