The insect cuticle: (3) self-assembly

The insect cuticle: (3) self-assembly

This post is part of a series on the insect cuticle as a biological material that can inspire novel engineered materials. The characteristics of the cuticle, setting it apart from most synthetic/engineered materials, will be discussed in this series. The introduction to the series can be found here.

Self-assembly: manufacturing the future

The materials and structures that we humans create for ourselves generally involve large factory manufacturing systems where we “Heat, Beat and Treat” materials into the structure we require.

Motor Manufacturing Gardiner

Motor Manufacturing” By Clive Gardiner for the Empire Marketing Board. c1930 National Archives UK

In contrast to most engineered materials, biological materials are assembled from the bottom up, rather than from the top down. The formation of materials like chitin, which is the main component of the insect cuticle, is the result of self-assembly and well ordered biosynthesis.

In engineering the material used is relatively cheap but the shape of the structure is expensive, since it results of very energy-intensive processing (the heating, beating and treating parts).

A Blast Furnace” By Clive Gardiner for the Empire Marketing Board. c1930 National Archives UK

In biology it is actually the other way around. The instructions for manufacturing processes are stored in the genes of all living things. The information contained in an organism’s DNA determines the sequence of molecules that will be expressed by the organism’s cells. It is the characteristics of these molecules that will determine how they interact and ultimately determine the shape of the final material and resulting structure (=self-assembly). In other words, energy is replaced by information, which is cheap. In biology it is the building blocks that make the structure that are relatively expensive to obtain (through capture, consumption, assimilation, etc.) and organisms cannot afford to waste these building blocks.

The biological manufacturing process is constrained by a range of external factors, which then may result in different structures under different circumstances. These external factors are, for instance, temperature (variable on different time-scales), mechanical loading (variable at different life stages and during different seasons) and the presence or absence of water, light and appropriate nutrition (which all three vary over the lifetime of an organism).

“Kreeping It Real” (Graffiti art on boxcar). Picture by Rob Swatski. Flickr.com.

A characteristic of biological materials is that they grow relatively slowly. At first this may seem like a disadvantage, but since these materials as they grow are exposed to a range of forces they can adapt to situations that may alter over the course of the structure’s lifetime. Engineers, using traditional manufacturing techniques, do not have this luxury, they have to preempt and anticipate changing conditions – or ignore them resulting in a reduced effective lifetime.

Self-assembly happens at all scales in nature – it starts at the molecular scale at which molecules are formed into globs which are formed into fibers. Manufacturing at the nano- or micro-scale may still be in its infancy but great strides are being made. And in the meantime we can apply nature’s lessons regarding biosynthesis and self-assembly at a larger scale – creating hybrids of multiple materials with the functional variety that is required of the material.

As Carl Hastrich points out on his Bouncing Ideas blog:

[the] future is fibre. Everything in nature is a fibre. From beetle exoskeletons, to the incredible structures found in the botanical world, they are all fibres. The results are complex, malleable, repairable materials that integrate a vast array of functions. Have a look at a cross section of human muscle and you’ll see what I mean. Humans on the other hand build with large brittle mono-materials and achieve complex function by mechanically integrating multiple components.

Over the past few decades we have tried to incorporate more manufacturing techniques that are non-toxic, water-based, and do not require high-energy inputs – life-friendly chemistry. 3-D printing techniques open up such an avenue since it is by definition builds from the bottom-up, rather than top-down, thus already mimicking nature in that regard, and new non-toxic base materials for these printers are being developed.

 The future of manufacturing. (Art based on pictures by M. Alleyne,  Yogendra Joshi and MKZero)

The future of manufacturing biological materials. (Art based on pictures by M. Alleyne, Yogendra Joshi and MKZero)

Further Reading

For this post I looked at a lot of graffiti/street art since I wanted my insect images to have an “industrial” feel. I came across some great art. For examples click here and here and (my favorite) here.

Self-assembly lesson for high-school level students.

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