Patient-specific design of concentric tube robots [electronic resource]
Keywords: Mechanical Engineering.

Robot-assisted minimally invasive surgical systems enable procedures with reduced pain, recovery time, and scarring compared to traditional open surgery. While these improvements benefit a large number of patients, safe access to diseased sites is not always possible for specialized patient groups, including pediatric and obese patients, due to their anatomical differences. To address the unmet needs of specialized patient groups, a patient- and procedure-specific (i.e., personalized) surgical robot design paradigm is proposed. This paradigm leverages the surgeon's expertise to design and fabricate robots based on preoperative medical images. We ground this work in clinical applications related to nonlinear renal access in pediatric patients, to access diseased sites such as kidney stones and tumors. Because of the small body surface area of children, accessing diseased sites with a straight needle and catheter risks damaging nearby tissue, in particular puncturing the pleural cavity. The design of a tool that can safely navigate through the compact anatomy of a pediatric patient in order to access hard-to-reach sites could improve outcomes in this specialized patient group. The type of robot used for this personalized design process is a dexterous continuum robot known as a concentric tube robot (CTR). Concentric tube robots consist of a set of hollow, pre-curved elastic tubes that fit concentrically, each one inside the next. As the tubes are rotated and inserted relative to each other, the interaction between overlapping tubes enables the entire robot to change shape in free space and when inserted through tissue. Concentric tube robots are highly customizable and lend themselves well to personalized design. The proposed patient- and procedure-specific design process includes three main steps: design, fabrication, and deployment. To design a set of patient- and procedure-specific concentric tubes, a virtual reality-based design interface, that leverages a surgeon's expertise, is presented. The interface immerses the surgeon in a virtual environment where he or she can view a 3D model of the specific patient, enabling iterative design of patient-specific tools and simulation of the tool being used in a procedure. 3D printing, or additive manufacturing, is then proposed for fabrication of these personalized tools, and a thorough investigation of 3D printing methods and materials is presented. A biodegradable polyester was selected and further testing was performed to validate its ability to withstand forces required to drive through tissue. A novel, compact, lightweight, modular actuation and control system for driving these patient-specific concentric tube robots is then presented. In addition to evaluating the precision and accuracy of the actuation modules, an integrated set of three modules was used to demonstrate the ability to drive a three-tube concentric tube robot to reach a tip position that was on average less than 2 mm from a desired target. Finally, the overall patient-specific paradigm was demonstrated, which combines the creation of a 3D model from preoperative images, design and fabrication of patient-specific tools, and deployment into a phantom patient model.