When you think of surfactants, you might think of soaps, detergents and other man-made chemicals. But it turns out that some other animals utilize their own …
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No matter where you are, you likely encounter
surfactants every day.
They’re a class of chemicals that show up
practically everywhere,
from soap to sofas.
They’re a diverse group of molecules that
are super useful
for their grease-busting and foam-making properties.
But despite what you may think when you hear
the word “chemical,”
nature was using these sudsy molecules long
before
humans adopted them for handwashing.
And the properties that make surfactants so
great for us
also make them indispensable for animals that
use them.
When horses run, they work up a lathery sweat.
This soapy effect comes from a surfactant
in horse sweat called latherin.
This may seem like an incredibly odd way to
sweat,
but the soapy suds are probably just a side
effect.
The real utility of latherin most likely comes
from its ability to spread
watery sweat across the animal’s oily, water-resistant
coat.
And this ability has to do with latherin’s
chemical structure.
One end of the molecule is hydrophilic —
it easily associates with water, the main
ingredient in sweat.
The other end is hydrophobic —
it readily associates with the oily surface
of the horse’s coat.
Latherin helps the sweat spread out into an
even layer.
This way it evaporates more easily, to do
what sweat is meant to do: cool the horse.
This two-sided property — one side hydrophilic,
the other hydrophobic —
is a distinguishing feature of all surfactants.
And it’s why the surfactants in dishwashing
and laundry detergents work so well
to break up dirt and grease.
The molecules’ hydrophobic ends are attracted
to fat and dirt,
which they quickly surround.
The hydrophilic ends dissolve in water so
that whatever the other end sticks to
can be rinsed away.
And the same properties may help latherin
protect horses from bacteria.
Latherin has a lot of structural similarities
to other molecules that make it harder
for bacteria to stick to each other, and to
warm, wet surfaces.
So even though a horse’s sweaty skin seems
like an ideal place for
microorganisms to grow, latherin could help
to keep them from taking hold.
Army worm caterpillars use surfactants defensively
too —
but in a really weird and creative way.
These little caterpillars eat a range of plants.
To process their food,
they make a cocktail of digestive juices,
which includes surfactants.
One of the army worm’s main predators is
fire ants.
When an ant attacks, the caterpillar basically
throws up on it.
As you might expect, the ant immediately stops
to groom itself.
The ants can’t tell us why, but it’s probably
not because they’re grossed out.
This defense mechanism relies on another property
of surfactants —
their ability to break the surface tension
of water.
Normally, a droplet of water will bead up,
because the water molecules are more
attracted to each other than the surrounding
air, or to an ant’s exoskeleton.
Water molecules also repel the hydrophobic
ends of surfactant molecules.
So they get pushed to the surface of the droplet.
But that disrupts the connections between
water molecules at the surface.
So while pure water would normally bead up
on the ant’s waxy exoskeleton
and roll off, adding a surfactant makes the
drop spread out and stick.
The ant’s head ends up coated in a slick
of nasty liquid.
And once they’ve been hit, the ants are
unlikely to go back for another taste.
Surfactants’ ability to break surface tension
makes them useful to humans
as a wetting agent.
Wetting agents help a liquid spread out on
a solid surface,
and they come in handy for products like paint
and cosmetics.
Of course, surfactants are also great bubble
builders —
like you see with soaps and detergents.
Surfactants coat and stabilize the inner and
outer surfaces of bubbles.
With some vigorous mixing, bubbles build up
faster than they break,
and you get a foam — a whole mess of tiny
gas bubbles trapped in a liquid or solid.
Some species of frogs have become foam experts.
The túngara frog builds floating foam nests
for its eggs
on temporary water sources, like mud puddles.
The nests protect the frog eggs from all sorts
of dangers, like parasites,
predators, harsh light, and extreme temperatures.
The surfactant-filled material for making
the nest comes from the female frog.
During mating, the male frog uses its legs
to stir it into a foam,
just like you’d use running water to froth
up a bubble bath.
But, as you know if you’ve ever taken a
bubble bath, foams are unstable.
The bubbles don’t last.
In manufactured foams, like the ones in mattresses
and furniture,
you can add other chemicals to stabilize the
bubbles.
And that’s exactly what the frogs do.
The female frog’s secretions also include
foam stabilizers.
The baby frogs are usually ready to leave
after about 3 days —
but the nests can remain stable for another
week or so!
The frog surfactant, called RSN-2, is a robust
bubble builder with the same soapy,
dual-sided properties as human-made surfactants.
But it’s unusually gentle.
This is crucial for the frogs, because the
nest needs to be friendly to sperm,
eggs, embryos, and young tadpoles.
See, synthetic surfactants are really good
at disrupting cell membranes:
that thin layer that surrounds all living
cells.
That’s a useful property for soaps.
But not great for baby frogs.
So scientists are working to learn more about
gentle surfactants like RSN-2.
That information could be useful for all kinds
of applications,
like making edible foams, protecting wounds,
or building matrixes for tissue regeneration.
In other words, while we humans are proud
of our clever chemicals,
we often find that nature did it first — and
sometimes even better.
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