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Snail’s armor could offer human protection

Jan. 19, 2010
Courtesy PNAS
and World Science staff

The robust, efficient shell of a tiny deep-sea snail could pro­vide in­spira­t­ion for ad­vanc­es in hu­man body ar­mor de­sign, re­search­ers say.

Ma­te­ri­als sci­ent­ist Chris­tine Or­tiz of the Mas­sa­chu­setts In­sti­tute of Tech­nol­o­gy and col­leagues in­ves­t­i­gated the iron-rich shell of the snail Cryso­ma­l­lon squa­m­ife­rum, re­cently dis­cov­ered near deep-sea vents in the In­di­an Ocean.

The snail Cry­so­ma­l­lon squa­m­i­fer­um. (Cour­tesy PNAS)
The shell has an un­usu­al three-lay­ered de­sign and is un­ique among an­i­mal ar­mor for in­clud­ing a lay­er based on iron sul­fide, chem­i­cal com­pounds of iron and sul­fur, re­search­ers said.

They stud­ied the me­chan­i­cal prop­er­ties of the in­di­vid­ual lay­ers in cross-sections of the shell at the mo­lec­u­lar lev­el and used the da­ta to de­vel­op a com­put­er mod­el of the snail’s out­er skel­e­ton. 

Sim­ula­t­ions of an­i­mals’ nat­u­ral pro­tec­tive sys­tems can al­low re­search­ers and en­gi­neers to ex­plore how an­i­mals de­fend them­selves while re­tain­ing free move­ment and body regula­t­ion, the sci­ent­ists not­ed. They ex­am­ined how the shell pro­tects the snail against a pred­a­tor at­tack and found that each of the shel­l’s three lay­ers seems to be re­spon­si­ble for dif­fer­ent as­pects of the ar­mor’s ef­fec­tive­ness.

The mid­dle lay­er is a “com­pli­ant” lay­er sand­wiched be­tween two stiffer “min­er­al­ized” lay­ers, they found. The in­ner, cal­cium-rich lay­er pro­vides struct­ural sup­port, while the more flex­ible mid­dle layer helps pre­vent cracks in other lay­ers from spread­ing. The outer lay­er prov­ides add­i­tional stiff­ness but also is sus­cep­tible to de­vel­op­ing “mi­cro­frac­tures” that pa­rad­ox­ic­ally head off more ser­ious cracks by dis­sip­a­ting en­ergy.

Ortiz’ at­ten­tion was drawn to the snail in 2003, when its discovery was first reported. The ani­mal lives in a harsh en­viron­ment on the sea floor, near vents that spew hot water. Thus it is exposed to fluc­tu­ations in temp­er­ature as well as high acidity, and also faces attack from pre­da­tors such as crabs and other snails. 

When a crab attacks a snail, it grasps the shell and squeezes it until it breaks—for days if ne­ces­sary.

The three-layer ar­range­ment pro­tects against pen­etra­t­ion, im­proves en­er­gy dis­sipa­t­ion, and re­sists bend­ing, the in­vest­i­gators found. This could pro­vide a mod­el for de­vel­oping pro­tec­tive ma­te­ri­als for hu­mans, they noted. Their re­port ap­pears in this week’s early on­line is­sue of the re­search jour­nal Pro­ceed­ings of the Na­tio­n­al Aca­de­my of Sci­en­ces.

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The shell of a deep-sea snail could provide inspiration for advances in human body armor design, researchers say. Materials scientist Christine Ortiz of the Massachusetts Institute of Technology and colleagues investigated the iron-rich shell of the snail Crysomallon squamiferum, recently discovered near deep-sea vents in the Indian Ocean. The snail’s shell has an unusual three-layered design and is unique among animal armor in including a layer based iron sulfide, a chemical compound of iron and sulfur, researchers said. They studied the mechanical properties of the individual layers in cross-sections of the shell at the molecular level and used the data to develop a computer model of the snail’s outer skeleton. Simulations of animals’ natural protective systems can allow researchers and engineers to explore how animals defend themselves while retaining free movement and body regulation, the scientists noted. They examined how the shell protects the snail against a predator attack and found that each of the shell’s three layers seems to be responsible for different aspects of the armor’s effectiveness. The middle of the three layers is a “compliant” layer surrounded on each side by a stiffer “mineralized” layer, they found. Their analysis indicated that this arrangement, as well as the structure of the individual layers, protects against penetration, improves energy dissipation, and resists bending. This could provide a model for developing protective materials for humans, the scientists said. Their report appears in this week’s early online issue of the research journal pnas.