Bacterial Spore-Based Hygromorphs: A Novel Active Material with Potential for Architectural Applications

Emily Birch,Martyn Dade-Robertson,Ben Bridgens,Meng Zhang

doi:10.3390/su13074030

Emily Birch, Martyn Dade-Robertson + Show 2 more

Open Access

https://doi.org/10.3390/su13074030

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Journal: Sustainability	Publication Date: Apr 5, 2021
Citations: 8	License type: CC BY 4.0

Affiliation: Newcastle University, Northumbria University

Abstract

This paper introduces a new active material which responds to changes in environmental humidity. There has been growing interest in active materials which are able to respond to their environment, creating dynamic architectural systems without the need for energy input or complex systems of sensors and actuators. A subset of these materials are hygromorphs, which respond to changes in relative humidity (RH) and wetting through shape change. Here, we introduce a novel hygromorphic material in the context of architectural design, composed of multiple monolayers of microbial spores of Bacillus subtilis and latex sheets. Methods of fabrication and testing for this new material are described, showing that small actuators made from this material demonstrate rapid, reversible and repeatable deflection in response to changes in RH. It is demonstrated that the hygromorphic actuators are able to lift at least 150% of their own mass. Investigations are also extended to understanding this new biomaterial in terms of meaningful work.

Highlights

In this paper, we present a novel, responsive hygromorphic material for potential use in architectural applications
We present a new class of hygromorphic materials for architecture based on bacterial spores
Sunde et al [31] investigated the response from fully dehydrated to fully hydrated spores, whereas the current study investigated the time taken for response for spores in an environment from 42% to 95% relative humidity (RH), i.e., approximately half of the range—if hydration was linear across these RHs, it would be expected to take half the time, i.e., 4.1 min

Summary

Introduction

We present a novel, responsive hygromorphic material for potential use in architectural applications. Materials which change shape in response to environmental relative humidity (RH) or wetting are termed “hygromorphic” [4] These materials will swell in response to water, when, for example, RH is high, and shrink when RH is low as water evaporates. The moisture evaporates from the spines and the outermost layers of the bilayered structure (Figure 2) shrink, causing them to bend away from the central cone, causing the seeds to be released [14] This hygromorphic response occurs even if the tissues are dead and the cone has fallen from the tree, so it requires no cellular energy (ATP) input [4] but instead relies on natural evaporation as a reliable renewable energy resource [15]

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