Microfluidic Flow Creation in the Insect Respiratory System

• Main Author: Garrett, Joel Frederick
• Other Authors: Department of Biomedical Engineering and Mechanics
• Format: Others
• Published: Virginia Tech 2021
• Subjects: microfluidics; entomology; engineering; simulation
• Online Access: http://hdl.handle.net/10919/101784

In this dissertation, we examine how advective and diffusive flows are created in the insect respiratory system, using a combination of direct biological studies and computational fluid dynamics simulations. The insect respiratory system differs significantly from the vertebrate respiratory system. While mammals use oxygen-carrying molecules such as hemoglobin, insects do not, favoring the direct delivery of oxygen to the tissues. An insect must balance advective flow with diffusive flux in order to sustain the appropriate oxygen concentrations at the tissue level. To better understand flow creation mechanisms, we studied the Madagascar hissing cockroach. In Chapter One, we used x-ray imaging to identify how tracheal tube compression, spiracular valving, and abdominal pumping coordinate to produce unidirectional flow during active respiration. In Chapter Two, we altered the environmental conditions by exposing the animals to various levels of hypoxia and hyperoxia, then examined how they changed their respiratory behaviors. In Chapter Three, we used our previous findings to construct a simulated insect respiratory system to parametrically study the effects of network geometry and valve timing on the creation of unidirectional advective flow and diffusive flux. These results can be used to inform future studies of the insect respiratory system, as well as act as the basis for bio-inspired microfluidic devices. === Doctor of Philosophy === The insect respiratory system works through the direct delivery of oxygen to the tissues. This occurs via a complex network of pumps, tubes, valves, and other structures that facilitate flow. These mechanisms allow insects to survive and prosper under a wide range of environmental and physiological conditions. While these structures have been studied extensively in a wide range of insect species, there are still many aspects of the respiratory system that remain unexplored. Here, we use the Madagascar hissing cockroach to examine how both bulk flow and diffusion are created in some types of insect respiratory systems. First, in Chapter One, we studied the animal under normal environmental conditions in order to determine how abdominal pumping, tracheal tube collapse, and spiracular valving are coordinated. Then, in Chapter Two, we exposed the animals to a range of oxygen concentrations to identify how the animals respond to varying environmental conditions. Finally, in Chapter Three, we constructed a simulated insect respiratory system to parametrically study the effects of network geometry and valve timing on the creation of advective and diffusive flow. By combining these three studies, we were able to improve our understanding of flow creation in the insect respiratory system.