Imagine the force you’d need to blow up a balloon whose surface area nearly matched that of a tennis court. To make things challenging, imagine further that the balloon is made of exquisitely delicate material. That balloon is your lungs, and every breath you take is a miracle. What makes it possible is a thin coating of a soap-like film, or surfactant, that lowers the tension of the lung’s inner surface, radically reducing the amount of force required to inhale. Without this surfactant, you couldn’t breathe.
“Lung surfactant is endowed with amazing biological properties,” said Annelise Barron, Foundry user, UEC member, and associate professor of bioengineering at Stanford University. “The key to this is the presence, in the surfactant, of two special proteins whose structures uniquely enable them to cut surface tension.” But those same amazing structural properties, she said, also make these proteins difficult to synthesize and purify, and relatively unstable in solution, limiting shelf-life and increasing price.
Barron, who’s been working on stable, synthetic substitutes for these special proteins for two decades, appears to be nearing success. The paper was published this week in Scientific Reports.
Barron’s designer polymers, called peptoids, have specific sequences and helical structures that mimic key bioactive portions of the two important proteins, surfactant proteins B and C, found in the lungs. The mimics, which she calls pB and pC, resemble the proteins. But their component building blocks differ subtly from those of proteins in a way that makes them extremely resistant to breakdown by heat or naturally occurring bodily enzymes called proteases. In addition, they are much less inclined to aggregate into clumps and lose their bioactivity than their natural counterparts. They can be synthesized at one-quarter to one-third of the cost of obtaining the surfactant from animals or of the available synthetic version.