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Artificial seashell shapes: Learning from nature's underwater architects

Nature has inspired modern structural engineering in many ways, from Michael Phelps' shark-skin inspired swimsuit to birdlike airplanes. However, until now, engineers have mainly been restricted to the simpler natural architectural shapes that millennia of evolution have produced. Studying and mimicking natural structures allows us to profit from millennia of evolution and natural selection to create optimal designs. A research team led by Chandra Sekhar Tiwary and Professors Kamanio Chattopadhyay and Debiprosad Roy Mahapatra from the Indian Institute of Science (IISc), has shed light on fascinating details of seashell design that pushes the boundaries of nature-inspired architecture.

Seashells are a beautiful example of the extremely intricate designs found in nature, while also serving the important structural purpose of protecting their mollusc inhabitants. The motivation of the research was to discover how seashells remain stable and redirect the stress that is inevitable at the immense depths experienced at the bottom of oceans. By studying their mechanical properties and reproducing 3D printed replicas, the research team has shown that seashell structures have evolved to distribute high pressures away from the soft tissues of the animals inside them, and to protect themselves from damage.

The two types of seashells studied, a fan-shaped and a corkscrew-shaped shell, were modelled using software, and a virtual stress test was performed by numerical simulation. The shell structures were also compared to their closest geometric shapes, a hemisphere and a cone. Owing to a non-uniform distribution of stress in the shells, the two shell shapes could survive approximately double the mechanical load which could be withstood by a simple sphere or cone.

The researchers explain that the distributions of stresses seen ensure that the soft tissues of the organisms inside the cavity of the shells do not feel the majority of the water pressure in the mollusc's deep underwater habitat. “Nature keeps on making things that look beautiful, but we don’t really pay attention to why the shapes are what they are,” said Chandra Sekhar Tiwary. This apparent optimisation of the shells' structures for the benefit of the organism indicates that the shapes of the shells have been rigorously selected through a gradual evolution over the ages and are not dependent merely on environmental factors.

The software models of the shells were converted to 3D printed models, which were then subjected to real physical stress tests to compare them with the natural shells. The researchers find that their artificial 3D printed models could withstand much better mechanical loads than even the natural shells. Chandra Sekhar Tiwary adds, “The understanding of such efficient shapes and the ability to make them using 3D printing opens up the possibility of designing a whole new range of protective structures”. Given that the natural shells evolved to their optimal shape but in restricted material environments, synthetic structures using these designs, combined with sturdier materials, might be much more resilient. In the near future, this may become a whole new arena for automobile engineers and architects to explore.

About the authors

Kamanio Chattopadhyay is a Professor at the Department of Materials Engineering, Indian Institute of Science, Bangalore. Chandra Sekhar Tiwary, Sharan Kishore and Suman Sarkar are research scholars at his lab. Debiprosad Roy Mahapatra is an Associate Professor at the Department of Aerospace Engineering, IISc. Pulickel M. Ajayan is at the Department of Materials Science and Nanoengineering, Rice University, USA.

Contact:

Kamanio Chattopadhyay: http://materials.iisc.ernet.in/~kamanio/

kamanio@materials.iisc.ernet.in; 080 22932262 (office), 080 22932678 (lab)

Roy Mahapatra: http://www.aero.iisc.ernet.in/users/droymahapatra

About the paper

The paper appeared in the journal Science Advances on 15th May 2015. http://advances.sciencemag.org/content/1/4/e1400052