March 5, 2012 at 3:14 PM ET
At some point in the future, ripped contact lenses may heal themselves, thanks to a new stretchy material that behaves like Velcro at the molecular level, bioengineers reported today.
For now, the so-called self-healing hydrogel only works in highly acidic environments, such as our stomachs, where it can be used as a medical suture or a high-tech drug delivery device.
Hydrogels, such as soft contact lenses, are made of chemically cross-linked structures that contain a lot of water.
Until now, researchers have been unable to develop hydrogels that can repair themselves when cut or ripped, which can happen, for example, while fiddling with contact lenses.
"The cross-links are permanent, so you can't break and re-form them," Ameya Phadke, a graduate bioengineering student at the University of California, San Diego, explained to me Monday.
Once ripped, a hydrogel such as contact lens loses its functionality and gets tossed in the trash.
Phadke and his colleagues overcame this problem by outfitting hydrogel molecular structures with "pendant side chains" that stick out like fingers from a hand.
This makes structures that look like "the spiked balls they used in medieval times," Phadke said. "These pendant side chains can interact with pendant side chains from another hydrogel across the interface."
"It is kind of like Velcro at the molecular level," he added. "They lock across under certain conditions."
In other words, even when cross-linked structures are broken, the side chains can connect together, allowing the hydrogel to self heal.
For the pendant side chains to stick to each other, the hydrogel must be in a highly acidic solution – a pH of 3 or lower. When in a higher pH solution, above 10 or so, they become unstuck.
The process is "very, very repeatable," Phadke said. "I repeated it 12 times. After 12, I was like 'OK, this is good to go.'"
One potential use for the material is as a coating for containers used to ship acidic materials. If the container cracks, the hydrogel would seal the crack within seconds of coming into contact with the acidic material.
Hydrogels are also known to stick to the mucus lining of the stomach. As a proof-of-concept, Phadke and his team showed their hydrogel sticks to a rabbit's stomach.
The opens the possibility, he said, of using the material to deliver drugs.
"You wouldn't have to keep taking the pill, you could just load this hydrogel with the drug and then it would just slowly diffuse the drug out at that site," Phadke explained.
The team tried this approach with the antibiotic tetracycline, proving a controlled release over a four day period.
As for self-healing contact lenses, we'll have to wait until the researchers can tune the material to function in less acidic environments.
"Then you could go outside this really acidic realm and could potentially look into doing it for a much more friendly pH for the rest of the body," Phadke said.
Findings are published online today in the journal Proceedings of the National Academy of Sciences.