Insects are fascinating creatures. Their bodies can handle great stress and survive extreme environmental conditions, not to mention many insects have evolved into very skilled predators. It is not surprising they are subject to curiosity in the world of Biomimicry. Browsing articles on AskNature.org the cockroach caught my attention. Despised by most and classified as a pest there is still one thing that cannot be denied – when cockroaches have decided to stay, it is almost impossible to get rid of them. Cockroaches survive climates that range from arctic cold to tropical heat and have existed for millions of years; they obviously adapt fairly well to current conditions. What can they teach us about life in the desert? (CSIRO, 2016)
In his article Transpiration Through the Cuticle of Insects (1945), Wigglesworth is presenting an interesting discovery. For cockroaches and other insects, the transpiration through the cuticle is constrained by a thin, lipid layer with a waxy texture. This layer is usually impermeable to water, but when the temperature surrounding the cockroach exceeds 30 degrees Celsius, Wigglesworth found that the properties of the lipid layer suddenly changes and water is allowed to traverse. The epicuticle, the uttermost layer of the cuticle, is basically a variable moisture barrier that helps the cockroach regulate its body temperature and stay hydrated in warm and arid regions. These qualities are of course very interesting to the building industry. Imagine finding a recipe for self-regulating, passive cooling and hydration, variable moisture barriers, temperature sensors and active transport of water within materials. In order to mimic the fascinating function of the epicuticle we need to know how it works.
“WATER IS LIKELY TO TRAVERSE THE MONOLAYER THROUGH HOLES TEMPORARILY OCCURING BECAUSE OF KINETIC ACTIVITY.”
The epicuticle of the cockroach is covered by a lipid substance that consists of tightly packed grease molecules. When the temperature is below 30 degrees Celsius the grease molecules are organized in a way that minimizes the size of the pore canals in the cuticle, preventing water from passing through. Being so tightly packed there is a strong van der Waals force (link) working between the molecules as well, also stopping water from permeating. When the temperature exceeds the critical temperature 30 degrees Celsius the van der Waals force is thermally destroyed and the grease molecules shift to a slightly looser organization. This small movement results in the pore canals becoming wide enough for water molecules to pass through – the water can now pass freely through the cuticle of the cockroach. As this was not interesting enough the cuticle also seem to be what researchers call asymmetric – the permeability to water is greater in one direction than the other. The cockroach can absorb more water than what disappears in transpiration. The reason behind this mind bogging fact is not completely understood, but it explains why cockroaches can survive in such hot and dry environments and will continue to motivate scientists in hope of discovering the recipe for this natural, self-regulating valve. (Beament, 1964)
TRANSLATING TO ARCHITECTURE…
So far this post has discussed things known to us, I am now leaving facts for imagination and speculation. The reactions happening in the cuticle of the cockroach is of course extremely intricate chemistry and probably too complex to copy. How can we translate the properties of the cuticle to architecture? In a building scale, a force like the van der Waals force between molecules is of course hard to accomplish without actively adding energy to a system, but features like porosity and a phase changing material is perhaps something that can fit an architectural scale. I instantly came to think of ceramics and wax. Can a porous material coated with wax be optimized to perform similar to the cuticle of the cockroach?
Since temperature and contact angle of the water is directly linked to the pore size of the material and permeability of water, a climate analysis software can be used to collect data. The data will be used to determine the exact content of the wax and to optimize the pore structure of the material. Perhaps the data will result in a sort of building block, like Cool Bricks (link), coated with wax?
To create the intricate pore system, I think the manufacturing of the ceramic building block can be done by 3D printing. It would be interesting to see what level of detail can be accomplished with today’s 3D printers and a ceramic material. The wax mostly used for commercial purposes today is paraffin wax. (link) Since paraffin is extracted from oil through crystallization one might question its environmental (if not political) impact. It would be interesting to know more about natural wax and if there is a possibility of producing such wax in vast quantities.
THE WHOLE BUILDING AS A POROUS SYSTEM?
The reason why cuticles of cockroaches work in this specific way is an interplay of chemical reactions and forces on a microscopic scale. To copy the structure of the cuticle would make no sense in a building scale since there are completely other forces in play. But for the fun of it, let us imagine it is possible to create a building block with similar properties. Can these properties be strengthened by the shape of the building? Perhaps the building with all its spaces is a porous system in itself, made up with these technical, porous building blocks? Can modern digital tools help us optimize the structure of the building material as well as the shape of the space to accomplish a building that cools and regulate hydration by itself?
Cool Brick | Emerging Objects. 2016. Cool Brick | Emerging Objects. [ONLINE] Available at:http://www.emergingobjects.com/2015/03/07/cool-brick/. [Accessed 18 September 2016].
CSIRO, 2016. Australian Insect Families, viewed 15 September 2016, <http://anic.ento.csiro.au/insectfamilies>.
Wikipedia. 2016. Paraffin wax – Wikipedia, the free encyclopedia. [ONLINE] Available at:https://en.wikipedia.org/wiki/Paraffin_wax. [Accessed 18 September 2016].
Wikipedia. 2016. Van der Waals force – Wikipedia, the free encyclopedia. [ONLINE] Available at:https://en.wikipedia.org/wiki/Van_der_Waals_force. [Accessed 18 September 2016].
Beament, J. W. L. , 1964. The Active Transport and Passive Movement of Water in Insects. Advances in Insect Physiology, Volume 2, 1964, 67–129.
Wigglesworth, V. B. , 1945. Transpiration Through the Cuticle of Insects. Journal of Experimental Biology, 1945 21, 97-114.
Cuticle of insect: http://www.earthlife.net/insects/images/anatomy/cuticle.gif
Porous ceramics: https://www.researchgate.net/profile/Yan_Zhang119/publication/257107282/figure/fig1/AS:297437370568719@1447926003639/Fig-1-SEM-micrographs-of-sintered-alumina-porous-ceramics-prepared-using-8-wt.png
Printing clay: https://i.ytimg.com/vi/vixPA7GGQpM/maxresdefault.jpg