Dermal mod­i­fi­ca­tion is a sig­nif­i­cant part of evo­lu­tion, says Ranajay Ghosh, an asso­ciate research sci­en­tist in the Col­lege of Engi­neering. Almost every organism has some­thing on its skin that pro­vides impor­tant sur­vival prop­er­ties such as pro­tec­tion from preda­tors, cam­ou­flaging, thermal reg­u­la­tion, and sen­so­rial func­tions. In many ani­mals, this evo­lu­tion has led to the for­ma­tion of scales.

This is why Ghosh and his col­leagues in North­eastern University’s High Per­for­mance Mate­rials and Struc­tures Lab­o­ra­tory are looking to the prop­er­ties of animal scales to help them develop the next gen­er­a­tion of armor sys­tems. The lab studies the mechan­ical behavior and per­for­mance of mate­rials and struc­tures, at var­ious scales from nanowires and living cells to ships and buildings.

Led by asso­ciate pro­fessor Ashkan Vaziri, the lab’s find­ings were recently pub­lished in the journal Applied Physics Let­ters, being fea­tured on the cover of one of December’s issues. Hamid Ebrahimi, PhD’17, who is pur­suing her doc­torate in mechan­ical engi­neering, was also a co-​​author.

Ranajay Ghosh

Ranajay Ghosh holds a 3-​​D printed model of a fish scale he used in his armor system research. Photo by Matthew Modoono

The next gen­er­a­tion of armor sys­tems are light, per­form a lot of func­tions, and at the same time do not com­pro­mise on pro­tec­tion,” Ghosh said, “and nature pro­vides very impor­tant infor­ma­tion in terms of armor development.”

The research, which is sup­ported by the National Sci­ence Foun­da­tion and Qatar Foun­da­tion, involved exam­ining dif­ferent strate­gies for gen­eral pro­tec­tive sys­tems that are light­weight and multi-​​use across industries.

The researchers chose to mimic the prop­er­ties of fish scales because fish, like a person wearing armor, need a fine bal­ance between mobility and pro­tec­tion, Ghosh explained. Using 3-​​D printing, the researchers cre­ated models of fish scales that were embedded in a soft sub­strate. Adding these scales caused the soft sub­strate to stiffen up, a response the researchers found could be achieved rather quickly because of the scales’ size and place­ment within the substrate.

This is very dif­ferent from what people have been working on before, which is focusing on the very nature of the scales them­selves, how they will behave, and whether they break easily or not,” he added. “Here, our focus is simply the effect of simple scales and their mutual con­tact and inter­ac­tion with the soft substrate.”

Ghosh said the research also iden­ti­fies that even with pedes­trian mechan­ical prop­er­ties, nature has devel­oped very com­plex systems.

In this project, the researchers’ work focused on exam­ining the impact that adding scales would have on the substrate’s elas­ticity. Having found this makes the sub­strate stiffer and less pen­e­trable, the next step is deter­mining how this work can help create tougher armor. The lab plans to con­tinue with more advanced testing on fish scales’ pro­tec­tive prop­er­ties, with the ulti­mate goal of com­bining the prop­er­ties of sev­eral dif­ferent ani­mals’ scales into one armor system. The mobility of snake scales and the optics of but­terfly wings are among these intriguing prop­er­ties the lab hopes to inves­ti­gate, he said.

We can syn­the­size what nature could not do because we have more flex­i­bility with the mate­rials we use,” Ghosh said.