Material Characterization of Insect Tracheal Tubes
The insect respiratory system serves as a model for both robust microfluidic transport and mate- rial design. In the system, the convective flow of gas is driven through local deformations of the tracheal network, a phenomenon that is dependent on the unique structure and material properties of the tracheal tissue. To understand the underlying mechanics of this method of gas transport, we studied the microstructure and material properties of the primary thoracic tracheal tubes of the American cockroach (Periplaneta americana). We performed quasi-static uniaxial tests on the tissue which revealed a nonlinear stress-strain response even under small deformations. A detailed analysis of the tissue's microstructural arrangement using both light and electron mi- croscopy revealed the primary sources of reinforcement for the tissue as well as heterogeneity on the meso-scale that may contribute to the physiological function of the tracheae during respi- ration. Finally, a custom mechanical testing system was developed with which inflation-extension tests on the tracheae were used to gather data on the biaxial elastic response of the tissue over a wide range of physiologically relevant loading conditions. From information gathered about the material microstructure, a robust constitutive model was chosen to quantify the biaxial response of the tracheae. This model will provide a basis from which to simulate the behavior of tracheal net- works in future computational studies. This study gives the first description of the elastic response of the tracheae which is essential for understanding the mechanics of respiration in insects. Thus it brings us closer to the realization of novel bio-inspired microfluidic systems and materials that utilize mechanical principles from the insect respiratory system.