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Light-activated hydrogel might one day repair degraded cartilage in arthritic joints

Researchers reinforce cow cartilage with polymeric system

by Stu Borman
March 14, 2016 | A version of this story appeared in Volume 94, Issue 11

Set of three drawings show cartilage with normal glycosaminoglycan levels and normal hydration, compressibility, and wear resistance; osteoarthritic cartilage with depleted glycosaminoglycan levels; and treated cartilage in which cross-linked hydrogel forms double network that restores normal hydration, compressibility, and wear resistance.
Credit: Angew. Chem. Int. Ed. 2016
In this cartoon, normal cartilage (left) contains glycosaminoglycans (leaflike structures) that retain water and resist compression and wear. Osteoarthritic cartilage (center) has depleted glycosaminoglycan levels. In treated cartilage (right), a cross-linked hydrogel (blue strands) forms a double network that restores cartilage’s normal hydration, compressibility, and wear resistance.

A collaborative chemistry and orthopedics team has developed a technique that, if verified in animal and human tests, might one day be a therapy for osteoarthritis.

In osteoarthritis, joint cartilage loses some of its glycosaminoglycans, highly charged polysaccharides that enable the tissue to retain water, giving it load-bearing capacity and an ability to resist compression and wear. The result is joint pain, for which no direct treatment is currently available.

Now, chemist and biomedical engineer Mark W. Grinstaff and coworkers at Boston University, in collaboration with orthopedists at Beth Israel Deaconess Medical Center, have devised a method for polymerizing a restorative charged hydrogel network inside damaged cartilage (Angew. Chem. Int. Ed. 2016, DOI: 10.1002/anie.201511767). Researchers have used hydrogels and polymers to strengthen tissues before, but only at surfaces, not throughout tissues, as in this study.

Grinstaff and coworkers soaked cow cartilage with a mixture of 2-methacryloyl­oxyethyl phosphorylcholine, which absorbs water and resists compression; ethylene glycol dimethacrylate, a cross-linking agent; and photoinitiating reagents. They then used an optical fiber to irradiate the tissue with green laser light. The light triggered the photoinitiating reagent to jump-start a cross-linking polymerization reaction throughout the tissue.

The resulting double network of synthetic and natural components attracts water and improves compressive strength and wear resistance to levels similar to those of healthy cartilage, the team found.

Andrew P. Dove of the University of Warwick, a specialist in degradable biomaterials and sustainable polymers, comments that the use of a biological matrix in a double network is “an exciting new approach that has huge potential.” Initiation by green light, which doesn’t penetrate tissue well, might not be ideal for real-world use, he says, but the team should be able to modify its system to work with other types of light or other types of initiators.


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