Wednesday, September 14, 2011

The Structure of a Spider Web

It is a well known biomimicry meme that ounce for ounce, spider silk is stronger than steel or Kevlar.  But what is it about the structure of a spider silk that makes it so strong?   Is it the nano scale makeup of the silk?  Is it the pattern?  Do the patterns indicate function?  Over the summer, I've collected a couple images of spider webs as I've seen them and tried to learn a little more about what makes them so special and how we can learn from them.
Spiral orb web in the forest

I started by taking a walk in the forest preserve near my house. Quite quickly I came upon the most ratty looking, massive spider web I'd ever seen.  It looked like something out of a haunted house movie - spiral, torn, and at the center was a huge spider.  As soon as I walked through the brush to get a closer look, the spider took off thinking it should be afraid of me (the feeling was mutual).

It's about Scale
The first thing I learned about spider web construction is that it is modular based on the size of the spider - the larger the spider, the larger the gaps between the threads for the simple fact that the spider must walk on it without getting stuck in its own web.  In fact, the scale of the space between the sticky threads that catch prey is directly proportional to the space from the tip of its back leg to its spinner.

This makes me think of the whole idea of "human scale" in architecture, which of course varies.  Frank Lloyd Wright designed homes for men of smaller stature, such as himself, so that when a taller person such as me walks through a home he designed, I feel like a giant.  The difference is mere inches, but it is noticeable.  Cathedrals were designed in direction opposition to the idea of human scale - they were designed to overwhelm the humans that entered them in order to convey the greatness of their god.  But the spaces where we feel most comfortable are the ones that have been designed down to the detail with our proportions in mind.

It's about Building from the Bottom Up 
A spider web is built in layers, building from the bottom up.  It starts spinning the web by casting a thin thread that can blow in the wind and when it catches on something, the spider begins to reinforce it with additional threads until it is strong enough to walk on.  This built-up silk becomes the major structure for the web and the silk is called Ampullate (Major). The spider then begins constructing the radials, closely spaced so that it can walk between each.  After spinning the radials, it begins to reinforce the center and then spiral from the inside out with largely spaced non-sticky circular threads, like scaffolding, called  Ampullate (Minor).  It then works outside in, to replace this scaffolding with more closely spaced, sticky adhesive threads, called Flagelliform. Another type of silk, called Piriformforms bonds between attachment points and other types of silk capture prey and protect eggs.  Each type of silk is optimized at the molecular level for its function.    

Sketch diagram of a spiral orb web outside my home - attached to my house!
Buildings are constructed in much the same way - scaffolding and structure are completed first and then the function of the building is layered on top of the structure, but the materials we make our buildings out of do not always emulate this process.  One of my instructors quoted an executive at a carpet company in saying that nature builds a leaf from the cellular level; if humans were to build a leaf we would start with a large sheet and cut smaller leaves out of it.  If we want to truly emulate nature's construction process, we need to begin constructing things from the nano scale on up instead of cutting them down from larger pieces.  

It's about Life Friendly Chemistry
Spider silk is comprised of amino acids and protein crystals that are made from a mixture of water and chopped up gnats and flies and from this soup, it is the combination of these two types of materials that produces a material that is stretchy, but still stiff and strong.  Additionally, the properties of the silk change based on how they are spun through the spinnerette while using the same chemical base.  When the spider is done with the web, it eats it so that the proteins and acids can be used again and again.  Imagine if the materials we create were as multi-functional and reusable while maintaining its function as spider silk is?

It's about Location
An orb web is a two dimensional surface constructed radially that vibrates when prey is caught to alert the visually challenged spiders to its food.  The pattern itself is a result of how it is constructed, but its location is indicitive of its function - to catch flying insects as they fly between objects.  So optimizing the location of where we build will help us maintain the function we need while minimizing energy and material use.
Huge spider web outside my house - it was gone a few days later, however, so I suppose the spider has something to learn about resilience and choosing a more appropriate location and scale for its web. 
What I take away when learning from a spider web is that location, scale, building in layers, and using multi-functional, reusable materials can help us design structures that are more in keeping with nature's Life's Principles.  


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