Joseph D. Greer

A soft robot that navigates its environment through growth

A class of soft robot can substantially and rapidly increase length from its tip and steer to navigate its environment. Across kingdoms and length scales, certain cells and organisms navigate their environments not through locomotion but through growth. This pattern of movement is found in fungal hyphae, developing neurons, and trailing plants, and is characterized by extension from the tip of the body, length change of hundreds of percent, and active control of growth direction. This results in the abilities to move through tightly constrained environments and form useful three-dimensional structures from the body. We report a class of soft pneumatic robot that is capable of a basic form of this behavior, growing substantially in length from the tip while actively controlling direction using onboard sensing of environmental stimuli; further, the peak rate of lengthening is comparable to rates of animal and robot locomotion. This is enabled by two principles: Pressurization of an inverted thin-walled vessel allows rapid and substantial lengthening of the tip of the robot body, and controlled asymmetric lengthening of the tip allows directional control. Further, we demonstrate the abilities to lengthen through constrained environments by exploiting passive deformations and form three-dimensional structures by lengthening the body of the robot along a path. Our study helps lay the foundation for engineered systems that grow to navigate the environment.

Methods for Improving the Curvature of Steerable Needles in Biological Tissue

Objective: Robotic needle steering systems have the potential to improve percutaneous interventions such as radiofrequency ablation of liver tumors, but steering techniques described to date have not achieved sufficiently small radius of curvature in biological tissue to be relevant to this application. In this study, the impact of tip geometry on steerable needle curvature was examined. Methods: Finite-element simulations and experiments with bent-tip needles in ex vivo liver tissue were performed. Motivated by the results of this analysis, a new articulated-tip steerable needle was designed, in which a distal section is actively switched by a robotic system between a straight tip (resulting in a straight path) and a bent tip (resulting in a curved path). Results: Selection of tip length and angle can greatly improve curvature, with radius of curvature below 5 cm in liver tissue possible through judicious selection of these parameters. An articulated-tip mechanism allows the tip length and angle to be increased, while the straight configuration allows the needle tip to still pass through an introducer sheath and rotate inside the body. Conclusion: Validation testing in liver tissue shows that the new articulated-tip steerable needle achieves smaller radius of curvature compared to bent-tip needles described in previous work. Significance: Steerable needles with optimized tip parameters, which can generate tight curves in liver tissue, increase the clinical relevance of needle steering to percutaneous interventions.

Surgeon design interface for patient-specific concentric tube robots

Concentric tube robots have potential for use in a wide variety of surgical procedures due to their small size, dexterity, and ability to move in highly curved paths. Unlike most existing clinical robots, the design of these robots can be developed and manufactured on a patient- and procedure-specific basis. The design of concentric tube robots typically requires significant computation and optimization, and it remains unclear how the surgeon should be involved. We propose to use a virtual reality-based design environment for surgeons to easily and intuitively visualize and design a set of concentric tube robots for a specific patient and procedure. In this paper, we describe a novel patient-specific design process in the context of the virtual reality interface. We also show a resulting concentric tube robot design, created by a pediatric urologist to access a kidney stone in a pediatric patient.

Real-Time 3D Curved Needle Segmentation Using Combined B-Mode and Power Doppler Ultrasound

This paper presents a real-time segmentation method for curved needles in biological tissue based on analysis of B-mode and power Doppler images from a tracked 2D ultrasound transducer. Mechanical vibration induced by an external voice coil results in a Doppler response along the needle shaft, which is centered around the needle section in the ultrasound image. First, B-mode image analysis is performed within regions of interest indicated by the Doppler response to create a segmentation of the needle section in the ultrasound image. Next, each needle section is decomposed into a sequence of points and transformed into a global coordinate system using the tracked transducer pose. Finally, the 3D shape is reconstructed from these points. The results of this method differ from manual segmentation by 0.71 ± 0.55 mm in needle tip location and 0.38 ± 0.27 mm along the needle shaft. This method is also fast, taking 5-10 ms to run on a standard PC, and is particularly advantageous in robotic needle steering, which involves thin, curved needles with poor echogenicity.

Series pneumatic artificial muscles (sPAMs) and application to a soft continuum robot

We describe a new series pneumatic artificial muscle (sPAM) and its application as an actuator for a soft continuum robot. The robot consists of three sPAMs arranged radially around a tubular pneumatic backbone. Analogous to tendons, the sPAMs exert a tension force on the robots pneumatic backbone, causing bending that is approximately constant curvature. Unlike a traditional tendon driven continuum robot, the robot is entirely soft and contains no hard components, making it safer for human interaction. Models of both the sPAM and soft continuum robot kinematics are presented and experimentally verified. We found a mean position accuracy of 5.5 cm for predicting the end-effector position of a 42 cm long robot with the kinematic model. Finally, closed-loop control is demonstrated using an eye-in-hand visual servo control law which provides a simple interface for operation by a human. The soft continuum robot with closed-loop control was found to have a step-response rise time and settling time of less than two seconds.

A Soft, Steerable Continuum Robot That Grows via Tip Extension

Soft continuum robots exhibit access and manipulation capabilities in constrained and cluttered environments not achievable by traditional robots. However, navigation of these robots can be difficult due to the kinematics of these devices. Here we describe the design, modeling, and control of a soft continuum robot with a tip extension degree of freedom. This design enables extremely simple navigation of the robot through decoupled steering and forward movement. To navigate to a destination, the robot is steered to point at the destination and the extension degree of freedom is used to reach it. Movement of the tip is always in the direction tangent to the end of the robots backbone, independent of the shape of the rest of the backbone. Steering occurs by inflating multiple series pneumatic artificial muscles arranged radially around the backbone and extending along the robots whole length, while extension is implemented using pneumatically driven tip eversion. We present models and experimentally verify the growing robot kinematics. Control of the growing robot is demonstrated using an eye-in-hand visual servo control law that enables growth and steering of the robot to designated locations.

Toward the Design of Personalized Continuum Surgical Robots

Robot-assisted minimally invasive surgical systems enable procedures with reduced pain, recovery time, and scarring compared to traditional 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 patients, due to their anatomical differences. We propose a patient-specific design paradigm that leverages the surgeon’s expertise to design and fabricate robots based on preoperative medical images. The components of the patient-specific robot design process are a virtual reality design interface enabling the surgeon to design patient-specific tools, 3-D printing of these tools with a biodegradable polyester, and an actuation and control system for deployment. The designed robot is a concentric tube robot, a type of continuum robot constructed from precurved, elastic, nesting tubes. We demonstrate the overall patient-specific design workflow, from preoperative images to physical implementation, for an example clinical scenario: nonlinear renal access to a pediatric kidney. We also measure the system’s behavior as it is deployed through real and artificial tissue. System integration and successful benchtop experiments in ex vivo liver and in a phantom patient model demonstrate the feasibility of using a patient-specific design workflow to plan, fabricate, and deploy personalized, flexible continuum robots.

PD42-12 DESIGN, FABRICATION, AND TESTING OF PATIENT-SPECIFIC CONCENTRIC TUBE ROBOTS FOR NONLINEAR RENAL ACCESS AND MASS ABLATION

INTRODUCTION AND OBJECTIVES: To address limitations of current commercial, mass-produced robot-assisted surgical systems widely used in urology and other surgical specialties, we propose to develop patientand procedure-specific dexterous robots. Our focus is on a class of continuum robots known as concentric tube robots, which are comprised of a series of hollow, nesting, precurved tubes that are individually inserted and rotated with respect to one another in order to change the shape of the overall robot. We aim to develop a method for designing, fabricating, and driving a patient-specific concentric tube robot as an alternative paradigm to traditional robotic surgical systems in order to improve procedures for specialized patient groups. As a test case we focus here on nonlinear renal access, for example, subcostal punctures into the upper pole calyces of the kidney to ablate an endophytic renal mass. METHODS: To enable patient-specific design of these robots, a virtual-reality based interface was developed. The interface leverages the expertise of a surgeon by immersing him or her in a 3-D virtual environment that includes a reconstructed model of the patient’s thoracoabdominal anatomy based on CT scans. Once the surgeon designs the set of concentric tubes, we generate a 3-D model and subsequently 3-D print each tube using a biocompatible polycaprolactone (PCL) filament. The printed tubes are then nested one inside the next and attached to the compact, modular actuation and control system we built for driving these robots. The surgeon controls the movement of the concentric tube robot through a teleoperation control scheme. RESULTS: A board-certified urologist performed a preliminary test of the entire system. After an explanation of the interface and its features, the surgeon was immersed in the virtual environment (using 3D reconstructions of an actual patient’s upper abdominal anatomy, including kidney and an associated upper caliceal lesion) and tasked with designing a set of tubes to access the lesion. Based on his intuition and expertise, he designed three different sets, which were then 3-D printed with PCL. The surgeon then performed mock procedures by driving each concentric tube robot into a phantom model of the patient’s thoracoabdominal anatomy in order to reach the lesion. The lesion was generated using a thermochromic dye which changes color when heated. Once the target was reached, a radiofrequency ablation (RFA) probe was passed through the concentric tube robot and successful ablation confirmed by color change of the lesion. CONCLUSIONS: This work proposes a framework for integration of the surgeon into design and fabrication of a set of patientand procedurespecific concentric tubes. Preliminary results demonstrate that a surgeon can use the interface to design a concentric tube robot to access and ablate renal lesions by RFA.

Remote electromagnetic vibration of steerable needles for imaging in power Doppler ultrasound

Robotic needle steering systems for minimally invasive medical procedures require complementary medical imaging systems to track the needles in real time. Ultrasound is a promising imaging modality because it offers relatively low-cost, real-time imaging of the needle. Previous methods applied vibration to the base of the needle using a voice coil actuator, in order to make the needle visible in power Doppler ultrasound. We propose a new method for needle tip vibration, using electromagnetic actuation of small permanent magnets placed inside the needle to improve needle tip visibility in power Doppler imaging. Robotic needle insertion experiments using artificial tissue and ex vivo porcine liver showed that the electromagnetic tip vibration method can generate a stronger Doppler response compared to the previous base vibration method, resulting in better imaging at greater needle depth in tissue. It also eliminates previous issues with vibration damping along the shaft of the needle.