HEMISPHERESMAGAZINE.COM
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OCTOBER2015
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ILLUSTRATIONBYJAMESONSIMPSON
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INNOVATION
BUSINESS
GADGETRY
BRIGHT IDEAS
T
hefirst steam enginewas patentedmore than three
centuries ago, paving the way for the Industrial
Revolution.Now, researchers atColumbiaUniver-
sity are once again harnessing the power of water—this
time with a twist.The new innovation? Scrapping the
need for a heat source and instead using a simple puddle
of room-temperature water to generate electricity.To
achieve this seemingly impossiblegoal,bioengineershave
turned to an unlikely (and decidedly low-tech) ally: the
common grass bacteria,
Bacillus subtilis
.This microbe’s
sporeboasts theuniquepropertyofdramaticallychanging
size when exposed to even themost minuscule shift in
humidity.LedbybioengineerOzgur Sahin, the teamhas
put these spores towork inwhat they’recallingHYDRAs,
orhygroscopy-drivenartificialmuscles,which functionby
contracting and expanding—a process that has already
been used to power a primitive piston engine and run a
miniaturemodel car.Best of all, thedevice costs less than
$5 toconstruct.Here’show scientistshope toexercise their
bacterialmight andmuscle their way into the renewable
energy game.
—
NICHOLASDERENZO
TheFirstEvaporation-PoweredEngine
how it’s done
To createHYDRAs, bacterial spores areglued toboth sidesof
thin strips of plastic tape, resulting in something that looks like
kinky ramennoodles.When theair surrounding theHYDRAgets
even slightlymorehumid, the stripsabsorb thewatermolecules
andnearlyquadrupleinsize,much likeaSlinkybeingstretchedout.
HYDRAsareattachedtoshuttersandplaced insideanenclosure,
over a puddle of water. As thewater evaporates, the HYDRA
expandsandforcesopentheshutters,allowingmoisturetoescape.
As humiditydecreases, theHYDRAs dryout, contract and close
theshutters.TheHYDRAsareconnectedtoatinyelectromagnetic
generator thatyieldsabout50microwattsofenergypercycle (a
microwatt isamillionthofawatt). That’snota lotofenergy, but
ithasalreadybeenshown to turnonanLED light inearly trials.
The inventorshavealsocreateda “moisturemill,”whichuses
HYDRAs inarotaryengine.Stripsareaffixedtoapaddleboat-like
wheel,halfofwhich istucked intoasemicircularcavity,andthen
placedonatwo-axlecar.Water is introduced,andhumiditybuilds
up in theprotectedhalf, which spins thewheels and scoots the
caralong. Itmaybeyearsbeforeweactuallyfill upour tankson
tapwater, but the concept isproving that evaporation-powered
enginesmightbea littlemorescienceanda little lessfiction.
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