Biomechanics of Biogenic Termite Structures

Cellulose-based composites possess notable properties such as high-strength to weight ratio, non-toxicity and biodegradability which make them suitable for applications ranging from aerospace to construction. Due to challenges with manufacturability, synthetic production of cellulose-based composites has failed to achieve comparable outcomes to their natural counterparts. One solution is to look to nature for insights and apply biomimetic principles of design to the development of novel fabrication techniques. Here we focused on the cellulose-based structures created by termites to explore the rules and design principles.<br/><br/>Subterranean Termites produce a cellulose-based composite called Carton that is used as a construction material during nest formation. Carton is a sponge-like material that consists of biocemented fecal matter, soil, and saliva. Despite relatively weak microconstituents, Carton is light, resistant to weathering, and multi-functional, adapting macroscopic composition and architecture according to function. Although the macroscopic features of nests have been evaluated in existing literature, there are few studies on material structure, and those that exist are limited by specie, variable and test type. Elucidating the compositional properties of cartons at the microscale may yield learning about interfacial interactions between cellulose polymer and its matrix and solvents for solubilizing cellulose.<br/><br/>Samples of carton from Coptotermes Gestroi were obtained from 4 yr-old laboratory reared colonies. After termite extraction and drying, carton was cut and sectioned according to distinct morphological characteristics, correlated with functional architectural features. These features are referred to in this study as nursery, high-cellulose and high-soil regions. Duplicates of samples were taken from each region and embedded in resin. The embedded media was sanded then polished to prepare for material characterization.<br/><br/>Here we perform imaging, Raman Spectroscopy, and Nanoindentation to determine the underlying structure-function-compositional characteristics of the carton and use that to elucidate design principles for cellulose-based structural composite design. The above-proposed research area remains largely unexplored, and this study represents the first of its kind for biogenic structures produced by subterranean termites.