Cocoon structure is inspiration for green architecture

A team of scientists at IIT-Kanpur are excited about the possibilities of learning from nature to build temperature regulated, green homes. Their inspiration is the cocoon. What intrigued the team is that a pupa is in a cocoon for a dormant phase of a few weeks to months and then a healthy, adult moth emerges from it. The team studied how the cocoon creates optimum temperature and living conditions within the cocoon.

They felt that the cocoon is an architectural marvel that can help design sustainable buildings for extreme temperature conditions. But what lets the pupa survive within the cocoon? The study by the IIT team revealed that the cocoon membrane is asymmetric; it allows preferential gating of CO2 from inside to outside.

This means that it allows CO2 to pass out from inside the cocoon but not the other way round. So there was no build up of CO2 inside the cocoon. The temperature within the cocoon was also regulated, irrespective of the temperature outside. The study was published recently in the Biointerphases journal. The chemistry department at IIT K in collaboration with other departments and the Defence Research Development Organisation (DRDO) in Delhi conducted the study. The team analysed the structure of dozens of cocoons from the Tassar silk worm. They also simulated a CO2 rich external environment but found that CO2 did not diffuse in to the cocoon. "But when CO2 was injected inside the cocoon it diffused out in 20 seconds indicating that the cocoon's structure did not allow the build-up of CO2 inside," says the study.

They also studied how the cocoon responds to extreme temperatures. "The cocoons were exposed to two extreme natural temperature regimes of 5 and 50 degree C, but a temperature of 25 and 34 degree C respectively were maintained inside the cocoons. Our results demonstrate, how CO2 gating and thermo-regulation helps in maintaining an ambient atmosphere inside the cocoon for the growth of pupa. Such natural architectural control of gas and temperature regulation could be helpful in developing energy saving structures and gas filters," concludes the study.