Structure of tracheae and the functional implications for collapse in the American cockroach.

The tracheal tubes of insects are complex and heterogeneous composites with a microstructural organization that affects their function as pumps, valves, or static conduits within the respiratory system. In this study, we examined the microstructure of the primary thoracic tracheae of the American cockroach (Periplaneta americana) using a combination of scanning electron microscopy and light microscopy. The organization of the taenidia, which represents the primary source of structural reinforcement of the tracheae, was analyzed. We found that the taenidia were more disorganized in the regions of highest curvature of the tracheal tube. We also used a simple finite element model to explore the effect of cross-sectional shape and distribution of taenidia on the collapsibility of the tracheae. The eccentricity of the tracheal cross-section had a stronger effect on the collapse properties than did the distribution of taenidia. The combination of the macro-scale geometry, meso-scale heterogeneity, and microscale organization likely enables rhythmic tracheal compression during respiration, ultimately driving oxygen-rich air to cells and tissues throughout the insect body. The material design principles of these natural composites could potentially aid in the development of new bio-inspired microfluidic systems based on the differential collapse of tracheae-like networks.