Investigation of In-vivo Integument Mechanics for Device Design at the Bio-mechanical Interface

Abstract

The term "bio-mechanical interface" refers to the point where living organisms interact with mechanical devices. This connection often leads to varying degrees of discomfort due to force interactions and impedance differences between the two entities. Two primary strategies to alleviate this discomfort involve modifying contact conditions or adapting behaviors. Wearable sensors, a subset of bio-mechanical interfaces, have gained significant attention as technology advances. These embedded systems, affixed directly to the body, are becoming smaller, more efficient, and increasingly integrated into our daily lives. Bio-logging tags, a specific type of wearable sensor, have proven invaluable for tracking and studying animals across diverse habitats. Particularly useful for observing cetacean behavior, these tags have illuminated the activities of animals spending most of their lives underwater and traversing vast ocean expanses. Over the past two decades, suction cups have emerged as a widely employed method for temporarily attaching bio-logging tags to marine creatures such as whales, dolphins, and turtles. Suction attachment is especially beneficial when long-term invasive tagging is inappropriate due to factors like tag longevity, animal size, health condition, or tag recovery requirements. These suction cup tags are affixed to free-swimming animals using poles or ballistic delivery methods, with the smooth skin of marine mammals facilitating secure attachment. Their non-penetrative attachment and versatility across various species make suction cup tags indispensable tools for minimally invasive research. Despite their advantages, field studies and data collection have revealed issues with these tags, including early detachment, sliding from the intended position, and animals actively attempting to dislodge them. These challenges not only undermine data reliability but also prompt inquiries into the extent of disruption caused by the tags and ways to enhance suction cup design. This dissertation centers on addressing the following research questions: Q1: How does cetacean integument respond to vacuum loading? Q2: What factors contribute to suction cup failure? Q3: How can suction cup design be improved to achieve prolonged attachment, minimal motion, and reduced discomfort? The process commences with the development of a specialized optical measurement system known as the PDIC (Portable Digital Image Correlation) system. This innovation facilitates the direct examination of live cetacean integument, enabling the extraction of viscoelastic properties and vital parameters for an accurate skin deformation model during vacuum loading. Subsequently, I established a comprehensive kinetic model for suction cups, encompassing thorough characterization of attributes like linear stiffness and area composition. This step involves exploring various suction cup designs and assessing their loading capacities prior to failure thresholds. Leveraging insights from lab investigations, I integrate pressure transducers into bio-logging tags, resulting in a cutting-edge pressure-logging tag. This advanced tag excels in real-world suction cup condition monitoring, enriching our understanding of their performance dynamics. The culmination of these efforts results in a proposed suction cup design framework. This framework incorporates pivotal decision variables, environmental factors, and performance metrics, serving as a foundational guide for future advancements in suction cup design.