We’ve all made Jell-O, right? If it’s been too long since you have and you can’t remember how, here’s a refresher: You mix the Jell-O powder into a pot of
water. Then you heat it. Then when it cools, it hardens up.
Jell-O is a polymer. The key ingredient in the gelatin in the Jell-O is collagen. When the water is heated, the bonds that hold the collagen protein chains together break. Each chain is a triple helix that float around in the mixture until the water cools, and new bonds then form between the amino acids in the protein, according to About.com. Water fills the spaces between the polymer chains. If you heated the Jell-O again, the bonds would break and the desert would tern to liquid again.
But what if the opposite happened? What if when you heated the solution for the first time, it formed a strong gelatin solid, but then liquefied when it cooled?
Then you’d have something developed by Alan Rowan, a materials chemist at Radboud University in the Netherlands. His polymer could be used to fill a wound, for example. The cold polymer solution would form a gel barrier when it solidified by body heat and protect the wound, reports Nature. When the gel was no longer needed, an ice pack could be applied to liquefy the solution.
Rowan’s innovation is a synthetic polymer — traditionally thought of as being relatively floppy — that can match the rigidity found in many biological polymers, such as DNA or collagen. Nature explains the polymer’s structure:
Rowan’s polymer strands have a helical backbone with thousands of short peptides jutting out from the sides, each carrying long tails made of repeating carbon and oxygen chains. Nitrogen and hydrogen atoms in neighboring peptides bond to each other to give the backbone rigidity, and the carbon and oxygen tails readily grab water molecules, making the polymer extremely soluble.
Once dissolved, the polymer, when warmed, pushes water molecules away and links to neighboring polymer strands. At a certain temperature, the solution turns into a gel in seconds as the strands self-assemble into bundles about 10 nm wide that, like fibers in a rope, stiffen the whole structure.
The bundling is what is important for strong biopolymers. Rowan’s research team has measured the relationship between the stiffness of individual strands and their concentration in bundles. “Now that we understand the principles, we can start making gels at even lower concentrations,” he says.
Source: “How Jell-O Works,” About.com
Source: “Polymer can turn swimming pool to jelly,” Nature, 1/23/13
Image by Naib.
Dale McGeehon has been a journalist and editor for more than 25 years, covering chemical regulation and testing for Pesticides and Toxic Chemical News and innovations in material sciences for the National Technology Transfer Center. His writing credits include Omni and College Park magazines and The New York Times.
