Autore: ExtremeTech

Paul Kouwer/Nature

Nature tends to try to leave herself as many outs as possible. The neurotic completism of natural selection has furnished our cells with a molecular contingency plan for virtually every possible crisis. From heat to physical trauma, viral invasion to old age, our cells use an arsenal of yes-no reactions to try to feel their way blindly through a jungle of metabolic dangers. As such, biological systems tend to be open-ended, both versatile and specific. The classic example is DNA, organized by a principle so simple and powerful that we’re now using it to store huge amounts of data. A paper published this week in Nature shows researchers replicating the effects of another basic molecule, using it to create a gel with some truly astonishing possibilities.

The gel (which has, in a glaring PR oversight, not been given a catchy sci-fi name) is normally just a clear and colorless liquid, seemingly quite normal in biotech labs filled with dozens of different clear, colorless liquids. Its invention was quite accidental — part of an effort to create polymers for electronics — but researchers soon noticed that the gel thickened under heat, rather than liquefying, and that it became stiffer when stretched. When subjected to both heat and sheer force, the gel became downright rubbery, stiff and remarkably strong. This “low molar-mass gel” is the first ever to show stress stiffening without being unwieldy and toxic.

Soon enough the team reverse-engineered the reason for these odd capabilities: they had created a synthetic molecule that mimicked the structure and function of intermediate filaments in the cell. These are the the support proteins that give the cell its shape, anchor its compartments in place, and help move cells throughout the body. Heat releases long, water resistant chains from polyethylene glycol, which form bundles in attempting to escape the water. A second molecule mediates the binding of these bundles into a strong, flexible matrix. If heated to the necessary temperature, these molecules can stiffen a solution of 99.994% water until it can support its own weight.

This gives us the ability to quickly and cheaply create so-called semi-flexible polymers; gels that become stiffer as they are subjected to strain. At the extreme of their ability to hold together, the strength increases dramatically. This is a difficult property to achieve synthetically, but many biological tissues exhibit it to some extent — partly because of intermediate filaments. This gives it some immediate application in medicine, as both molecules involved here are non-toxic, and because the body works best with its own systems. A strong but flexible film of gel, applied cold as a liquid then thickened by body heat, could form wash-off bandages of exceptional resiliency. A gunshot wound might be filled entirely by a quick-gelling liquid laced with antibiotics. A cushion of soft gel injected into a worn down joint might still be able to stretch and strongly hold the bones together.

As with DNA, these synthetic filament molecules can be intentionally tuned to affect their behavior. Already researchers have used similar molecules to build scaffolds for brain repair and neuron regeneration, or even drugs that form gel matrices to resist the immune system. Inducing mechanical changes is one of the body’s oldest tricks, used to get molecules in and out of tight spots all the time, but there are a wealth of possibilities associated with this basic technique. Rather than temperature, an acid-activated gel, however, might be used to ferry drugs to certain sections of the digestive system.

In the last 30 years we’ve at least attempted to mimic nature’s creativity with DNA, but essentially no other molecule has received that sort of attention. DNA is the library of the cell, and we’re now using it to wedge open arteries and stitch together micro-lacerations. With a similarly elegant organizational principle, it remains to be seen just what uses we might find for the pillars that hold the library up.

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Research paper: doi:10.1038/nature11855 – “Materials science: Synthetic polymers with biological rigidity”