Unraveling the Web of Mystery Surrounding Spider Silk

Until recently, there was so little we knew about the physical properties of a spider web. Spider silk is one of the most unique fibers in the world, being able to endure all kinds of abuse like stretching and soaking, and still being able to function as normal afterwards. It is stronger than steel and stronger than Kevlar, the stuff that makes up bulletproof vests, when you compare it ounce for ounce.

Now, we know a lot more about spider silk, after a team of scientists was able to measure the elastic properties of an intact spider web and this increased knowledge should help with further innovations about silk that we previously mentioned in our blog here and here.

The Stanford researchers utilized a technique known as Billouin spectroscopy, which shines a laser at the spider web and then records the scattering of light to measure the mechanical properties of spider silk. In short, it is a much more complicated form of the spectrophotometry done in freshman and sophomore labs to measure absorbance values, except Billouin spectroscopy measure the mechanical properties of a material.

Measuring mechanical properties of spider silk using Billouin spectroscopy

The researchers learned that although spider webs are made of uniform spider silk, the stiffness and elasticity of the silk varies between individual strands. They also discovered that the silk stiffens in conditions of 100% humidity to produce a tighter web, a behavior known as supercontraction. The second discovery that adjusting water content to alter the mechanical properties of spider silk is especially interesting and Kristie Koski, the lead researcher, say could lead to new and exciting advancements.

A Closer Look at Cellulose

A few weeks ago, we mentioned the promise of cellulose in medical devices due it being both biocompatible and a relatively accessible material. However, in this post we will take a closer look at the properties of cellulose that make it an ideal nanomaterial to consider, in particular how hydrogen bonding makes cellulose a very special molecule.

The orientation of glucose molecules in the chain causes the difference in strength between cellulose and starch, a strength that results from hydrogen bonding between adjacent strands of cellulose. Hydrogen bonds are very strong, which is why cellulose is an excellent fiber that is used from paper to hemp rope. The next time, you have a sheet of paper, try to pull it apart from the sides and you will notice how hard it is to do so.

Hydrogen bonding between cellulose chains also means that cellulose will not dissolve in water. Such a property both practical and useful. What this means in terms of using a medical device made of cellulose is that the medical device will not spontaneously dissolve after coming in contact with the water present in the human body. To explain the dissolving of cellulose in water in terms of free energy, the change in free energy of the reaction would be positive as the reaction is never spontaneous.  This also tells us that the enthalpy change of the reaction is positive and the entropy change of the reaction is negative. If you do not understand how one would arrive at the previous conclusion, consider the Free Energy equation:

where G is Gibbs Free Energy, H is enthalpy, S is entropy, and T is temperature.

Hopefully this post gave you greater insight about how cellulose serves as such a great nanomaterial.