NEW USES FOR FEET

By Pam Eastlick

Welcome to The Deep science and technology column where we cover topics from the deep sea to deep space and beyond.

I thought I’d dip into the animal file this week and I stumbled across a couple of totally unrelated articles on, of all things, legs and feet. We all know people who “think on their feet” but new data from researchers at the Smithsonian have shown that certain species of very tiny spiders do exactly that, because their legs are full of . . . brains.

As a part of ongoing research to understand how miniaturization affects brain size and behavior, the researchers measured the central nervous systems of nine species of spiders, from rainforest giants to spiders smaller than the head of a pin. They discovered that as the spiders got smaller, their brains got proportionally bigger and filled more and more of their body cavities. The central nervous system of the smallest spiders fills up almost 80 percent of their total body cavity and (here’s the good part) about 25 percent of their legs.

Brain cells can only be so small because most cells have a nucleus that contains all of the spider’s genes, and that takes up space. The diameter of the nerve fibers or axons also can’t be made smaller because if they’re too thin, the flow of ions that carry nerve signals is disrupted, and the signals aren’t transferred properly.

Human brains only represent about 2-3 percent of our body mass. Some ant brains make up 15 percent of their biomass and these spiders have a higher brain to biomass ratio. Brain cells use a lot of energy, so these small spiders also probably convert much of the food they consume into brain power. Gives a whole new meaning to thinking on, or perhaps ‘with’ your feet!

And feet that we’re all familiar with are also making research news. For years, biologists have been amazed by the power of gecko feet, which let these small lizards produce an adhesive force roughly equivalent to carrying nine pounds up a wall without slipping.

Now, a team of polymer scientists at the University of Massachusetts Amherst have discovered exactly how the gecko does it, leading them to invent "Geckskin," a device that can hold 700 pounds on a smooth wall.

Gecko feet can be applied and removed with ease and no sticky residue remains on the surface. These properties offer a tantalizing possibility for synthetic materials that can easily attach and detach heavy everyday objects like TVs or computers to walls. Such materials would have medical and industrial applications as well.

The Geckskin device is about the size of an index card and can hold 700 pounds to a smooth surface like glass. The device can be released with negligible effort and reused many times with no loss of effectiveness. For example, it can be used to stick a 42-inch television to a wall, released with a gentle tug and restuck to another surface as many times as needed, leaving no residue.

The key innovation was to create an adhesive with a soft pad woven into a stiff fabric, which allows the pad to "drape" over a surface to maximize contact. And as in real gecko feet, the skin is woven into a synthetic "tendon," yielding a design that plays a key role in maintaining stiffness and rotational freedom at the same time.

A card-sized pad of Geckskin can this 42-inch television weighing about 40 lbs. (18 kg) to a smooth vertical surface. (Credit: Photo courtesy of UMass Amherst)

Legs full of brains and sticky feet.