Experimental Analysis and Modeling of Robot-Tissue Contact Mechanics for In Vivo Mobility

Sliker, Levin John

Graduate Thesis Or Dissertation

Experimental Analysis and Modeling of Robot-Tissue Contact Mechanics for In Vivo Mobility Público Deposited

Analytics

Citations

Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/7p88cg698

Abstract

Robotic mobility within the gastrointestinal (GI) tract is an intriguing concept, which has received wide attention from within the research community over the past ten years. Capsule endoscopes (CEs) exist commercially, but lack an active mobility system, rendering them as passive devices. These passive devices are only capable of observational procedures, and are limited by the passive speed (dependent on intestinal peristalsis), inability to control orientation, and vulnerability to retention, requiring surgical removal in severe cases. Additionally, passive capsules take photos throughout their journey, resulting in a compilation of thousands of images, which can take the attending physician hours to review. Due to these drawbacks, traditional endoscopes remain as the most popular intervention for GI related procedures. A traditional endoscope consists of a long flexible tube with a camera on the end of it. The tube usually has ports for tools, insufflation and irrigation. A user interface is located on the operator end of the scope, and can be manipulated to steer the tip of the scope. The scope is inserted through the oral or rectal orifice and is advanced by pushing the scope. As the scope is pushed, frictional forces can accumulate, resulting in advancement of the body of scope without advancement of the tip, termed looping. Looping results in distention of the bowel wall, pain for the patient and in rare cases perforation. A robotic capsule endoscope (RCE) for oral endoscopies or robotic capsule colonoscope (RCC) for rectal colonoscopies is a capsular device (tethered or non-tethered) that propels itself through the GI tract. Self-propulsion could result in less looping, less pain for the patient, more ergonomic operation for the physician, control over capsule position and orientation, and the addition of diagnostic and therapeutic tools over existing passive CEs. This work focuses on the contact mechanics of robot-tissue interaction in the GI tract with the goal of furthering the understanding of the physical problem so that more efficient and optimized mobility systems may be designed for RCEs and RCCs. This work also focuses on the design of an RCC which uses micro-patterned polydimethylsiloxane (PDMS) treads as a mobility method. The thesis is divided into nine chapters. Chapter 1 provides an overview of capsule and flexible endoscope technology as it relates to screening, diagnostics and therapy. A thorough overview of existing mobility methods (both commercial and experimental) for RCEs is also presented along with a background on micro-patterning for friction enhancement. Chapter 2 presents the qualitative analysis of micro-patterned treads through the development and in vivo testing of a series of two-wheeled robots as well as a testing apparatus for quantitatively evaluating micro-patterned robotic wheels in a static environment. Chapter 3 presents the development of a novel testing apparatus for evaluating robotic wheels in a dynamic environment, and results from data collected using the apparatus. The results from this device suggested that an automated dynamic testing environment would be necessary for deeper understanding of robot-tissue interaction. Chapter 4 presents the development of an automated traction measurement (ATM) platform for evaluation of robotic wheels on synthetic or biological tissue substrates as a function of normal force, rotational velocity and linear velocity. An empirical model for predicting traction force was also developed and validated using data collected from the ATM platform. Chapter 5 presents a study on the relationship between substrate height (i.e., stiffness), robot wheel tread pillar diameter, and the resulting generated traction force using the ATM platform for experimental collection and finite element modeling for validation. Chapter 6 presents the design and in vivo testing of an RCC which utilizes micro-patterned treads as a mobility method. The tethered prototype featured an onboard camera, and white and infrared (IR) light sources. Chapter 7 presents the development and experimental validation of an analytical model for predicting the drag force necessary to move a cylindrical capsule endoscope through the GI tract. Chapters 8 and 9 address discussion, conclusions, and future work. The work in this thesis has advanced the understanding of the contact mechanics for robot-tissue interface, especially pertaining to micro-patterned surfaces, and has resulted in several tools, both hardware and software, for measuring and modeling traction and drag force for capsule endoscope mobility methods. Additionally, this work has resulted in a novel RCC design prototype, which has the potential to evolve into a clinically viable device.

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