Cam­ou­flaged mem­brane in­vented that hides like an oc­to­pus

Edmonton Sun - - LIFE - BEn guarIno The Wash­ing­ton Post

No other an­i­mal has mas­tered cam­ou­flage like the oc­to­pus. The might­i­est of th­ese mor­ph­ing crea­tures, the mimic oc­to­pus, con­torts its body into a thin rib­bon and adopts the colors of a venomous sea ser­pent to scare preda­tors away. Divers have seen mimic oc­to­puses mas­quer­ade as lion fish, sea stars, shrimp and anemones. When peck­ish, the oc­to­pus takes the form of a lusty crab. Crus­taceans fooled by the dis­play end up eaten.

Ma­te­ri­als sci­en­tists and en­gi­neers also have fallen un­der the oc­to­puses' spell. A team of Cor­nell Univer­sity re­searchers, with the aid of oc­to­pus ex­pert Roger Han­lon, suc­cess­fully mim­icked the mimic us­ing sheets of rub­ber and mesh.

As they re­port in a study pub­lished Thurs­day in the jour­nal Sci­ence, the re­searchers cre­ated a thin mem­brane that con­torts into com­plex 3-D shapes - much like the shape-shift­ing skin of an oc­to­pus. The mem­branes can in­flate in sec­onds to the shapes of ev­ery­day ob­jects, such as pot­ted plants or a clus­ter of stones.

Oc­to­puses are cov­ered in mus­cly bun­dles called papil­lae, Han­lon and his col­leagues doc­u­mented in the Jour­nal of Mor­phol­ogy in 2014. The papil­lae go slack when an oc­to­pus wants to de­crease the drag of water against skin, al­low­ing it to speed away in a hurry. Con­trac­tions cause fleshy nubs to ap­pear, and the skin bulges. Oc­to­puses can match the tex­ture of sea­weed so closely they be­come al­most in­vis­i­ble.

Itai Co­hen, a ma­te­ri­als ex­pert at Cor­nell and an au­thor of the new study, said he was awed by videos of the shape-shifters.

He and fel­low Cor­nell re­searcher Robert Shep­herd as­signed James Pikul the grunt work of figuring it out.

"For a few decades, sci­en­tists and en­gi­neers have been try­ing to con­trol the shape of soft, stretch­able ma­te­ri­als," said Pikul, a grad­u­ate stu­dent at the time of this re­search and now an as­sis­tant pro­fes­sor at the Univer­sity of Penn­syl­va­nia.

But cheaply fab­ri­cat­ing th­ese ma­te­ri­als proved dif­fi­cult.

Suc­cess brought to­gether two con­cepts: the mus­cu­la­ture of the oc­to­pus with the me­chan­ics of blow­ing up a bal­loon. The trick was to cut con­cen­tric rings into a thin sur­face of sil­i­cone rub­ber and mesh. In­flat­ing the rub­ber caused the mem­brane to con­tort fol­low­ing the shape of the cuts.

Pro­gram­ming the laser cuts in just the right way en­abled the rub­ber to in­flate not only out­wardly, like a kick­ball, but as a 3-D struc­ture with con­cave re­gions. It's a bit like the sculp­tures made by twist­ing to­gether sausage­shaped bal­loons.

Ex­cept, in this case, it's all one mem­brane.

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