Joshua B. Gafford

Force-sensing surgical grasper enabled by pop-up book MEMS

The small scale of minimally-invasive surgery (MIS) presents significant challenges to developing robust, smart, and dexterous tools for manipulating millimeter and sub-millimeter anatomical structures (vessels, nerves) and surgical equipment (sutures, staples). Robotic MIS systems offer the potential to transform this medical field by enabling precise repair of these miniature tissue structures through the use of teleoperation and haptic feedback. However, this effort is currently limited by the inability to make robust and accurate MIS end effectors with integrated force and contact sensing. In this paper, we demonstrate the use of the novel Pop-Up Book MEMS manufacturing method to fabricate the mechanical and sensing elements of an instrumented MIS grasper. A custom thin-foil strain gage was manufactured in parallel with the mechanical components of the grasper to realize a fully-integrated electromechanical system in a single manufacturing step, removing the need for manual assembly, bonding and alignment. In preliminary experiments, the integrated grasper is capable of resolving forces as low as 30 mN, with a sensitivity of approximately 408 mV/N. This level of performance will enable robotic surgical systems that can handle delicate tissue structures and perform dexterous procedures through the use of haptic feedback guidance.

A monolithic approach to fabricating low-cost, millimeter-scale multi-axis force sensors for minimally-invasive surgery

In this paper we have rapidly prototyped customized, highly-sensitive, mm-scale multi-axis force sensors for medical applications. Using a composite laminate batch fabrication process with biocompatible constituent materials, we have fabricated a fully-integrated, 10×10 mm three-axis force sensor with up to 5 V/N sensitivity and RMS noise on the order of ~1.6 mN, operational over a range of -500 to 500 mN in the x- and y-axes, and -2.5 to 2.5 N in the z-axis. Custom foil-based strain sensors were fabricated in parallel with the mechanical structure, obviating the need for post-manufacturing alignment and assembly. The sensor and its custom-fabricated signal conditioning circuitry fit within a 1×1×2 cm volume to realize a fully-integrated force transduction platform with potential haptics and control applications in minimally-invasive surgical tools. The form factor, biocompatibility, and cost of the sensor and signal conditioning makes this method ideal for rapid-prototyping low-cost, mm-scale distal force sensors. Sensor performance is validated in a simulated tissue palpation task using a robotic master-slave platform.

Shape Deposition Manufacturing of a Soft, Atraumatic, Deployable Surgical Grasper

Laparoscopic pancreaticoduodenectomy (also known as the Whipple procedure) is a highly-complex minimallyinvasive surgical (MIS) procedure used to remove cancer from the head of the pancreas. While mortality rates of the MIS approach are comparable with those of open procedures, morbidity rates remain high due to the delicate nature of the pancreatic tissue, proximity of high-pressure vasculature, and the number of complex anastomoses required [1]. The sharp, rigid nature of the tools and forceps used to manipulate these structures, coupled with lack of haptic feedback, can result in leakage or hemorrhage, which can obfuscate the surgeon’s view and force the surgeon to convert to an open procedure. We present a deployable atraumatic grasper with onboard pressure sensing, allowing a surgeon to grasp and manipulate soft tissue during laparoscopic pancreatic surgery. Created using shape deposition manufacturing, with pressure sensors embedded in each finger enabling real-time grip force monitoring, the device offers the potential to reduce the risk of intraoperative hemorrhage by providing the surgeon with a soft, compliant interface between delicate pancreatic tissue structures and metal laparoscopic forceps that are currently used to manipulate and retract these structures on an ad-hoc basis. Initial manipulation tasks in a simulated environment have demonstrated that the device can be deployed though a 15mm trocar and develop a stable grasp on a pancreas analog using Intuitive Surgical’s daVinci robotic end-effectors.

Microsurgical Devices by Pop-Up Book MEMS

The small scale of microsurgery poses significant challenges for developing robust and dexterous tools to grip, cut, and join sub-millimeter structures such as vessels and nerves. The main limitation is that traditional manufacturing techniques are not optimized to create smart, articulating structures in the 0.1–10 mm scale. Pop-up book MEMS is a new fabrication technology that promises to overcome this challenge and enable the monolithic fabrication of complex, articulated structures with an extensive catalog of materials, embedded electrical components, and automated assembly with feature sizes down to 20 microns. In this paper, we demonstrate a proof-of-concept microsurgical gripper and evaluate its performance at the component and device level to characterize its strength and robustness. 1-DOF Flexible hinge joints that constrain motion and allow for out-of-plane actuation were found to resist torsional loads of 22.8±2.15 N·mm per mm of hinge width. Adhesive lap joints that join individual layers in the laminate structure demonstrated a shear strength of 26.8±0.53 N/mm2. The laminate structures were also shown to resist peel loads of 0.72±0.10 N/mm2. Various flexible hinge and adhesive lap components were then designed into an 11-layered structure which ‘pops up’ to realize an articulating microsurgical gripper that includes a cable-driven mechanism for gripping actuation and a flexural return spring to passively open the gripper. The gripper prototype, with final weight of 200 mg, overall footprint of 18 mm by 7.5 mm, and features as small as 200 microns, is able to deftly manipulate objects 100 times is own weight at the required scale, thus demonstrating its potential for use in microsurgery.Copyright

Self-Assembling, Low-Cost, and Modular mm-Scale Force Sensor

The innovation in surgical robotics has seen a shift toward flexible systems that can access remote locations inside the body. However, a general reliance on the conventional fabrication techniques ultimately limits the complexity and the sophistication of the distal implementations of such systems, and poses a barrier to further innovation and widespread adoption. In this paper, we present a novel, self-assembling force sensor manufactured using a composite lamination fabrication process, wherein linkages pre-machined in the laminate provide the required degrees-of-freedom and fold patterns to facilitate self-assembly. Using the purely 2-D fabrication techniques, the energy contained within a planar elastic biasing element directly integrated into the laminate is released post-fabrication, allowing the sensor to self-assemble into its final 3-D shape. The sensors are batch-fabricated, further driving down the production costs. The transduction mechanism relies on the principle of light intensity modulation, which allows the sensor to detect axial forces with millinewton-level resolution. The geometry of the sensor was selected based on the size constraints inherent in minimally invasive surgery, as well as with a specific focus on optimizing the sensors linearity. The sensor is unique from the fiber-based force sensors in that the emitter and the detector are encapsulated within the sensor itself. The bare sensor operates over a force range of 0-200 mN, with a sensitivity of 5 V/N and a resolution of 0.8 mN. The experimental results show that the sensors stiffness can be tuned using a thicker material for the spring layer and/or encapsulation/integration with soft materials. The empirical validation shows that the sensor has the sensitivity and the resolution necessary to discern the biologically relevant forces in a simulated cannulation task.

Soft pop-up mechanisms for micro surgical tools: Design and characterization of compliant millimeter-scale articulated structures

This paper introduces a manufacturing technique which enables the integration of soft materials and soft fluidic micro-actuators in the Pop-up book MEMS paradigm. Such a technique represents a promising approach to the design and fabrication of low cost and scalable articulated mechanisms provided with sensing capabilities and on-board actuation with potential applications in the field of minimally invasive surgery. Design and integration of soft components in the rigid-flex laminates is described along with the resulting soft pop-up mechanisms realized at different scales. Prototype characterization is presented, demonstrating forces and dexterity in a range suitable for surgical applications, as well as the possibility to integrate sensing capabilities. Based on these results, a multi-articulated robotic arm is fabricated and mounted on top of an endoscope model to provide a proof of concept of simple robotic mechanisms that could be useful in a surgical scenario.

Soft Wearable Orthotic Device for Assisting Kicking Motion in Developmentally Delayed Infants

Cerebral palsy is diagnosed in 1 out of 3000 people in the U.S. Nearly half of affected children have a limited ability to crawl and walk and a majority of them rely on the use of assistive devices for mobility [1]. Exploratory kicking motion in infants is essential for developing the coordination between the knee and hip joints, which leads to crawling and eventually the development of a coordinated gait [2]. Because infants with cerebral palsy tend to exhibit very little independent motion during the kicking stage, they often have gait deficiencies that limit their ability to walk when they reach adulthood [3]. Cerebral palsy is typically not diagnosed until the age of two, when a child starts walking and abnormal gait patterns become apparent. At that point, the abnormalities are difficult if not impossible to correct without costly and invasive treatment methods. On the other hand, several well-known factors are associated with an increased probability of developing cerebral palsy, most notably premature birth [1]. In these cases, early intervention treatment can be administered during the infant stage and has the potential to stimulate the formation of neuromuscular connections that would otherwise not develop due to the onset of the impairment [3]. However, the high cost and scarcity of such methods limit their current utility as potential therapies. There is a need for early intervention treatment methods that can improve infants’ motor coordination before they begin walking; such treatments would likely reduce gait deficiencies and dependence on assistive devices later in life. The soft, wearable kicking device presented in this paper actively assists kicking in infants at the hip and knee joints in all relevant planes of motion. By stimulating kicking motion, the device may help build nerve connections in the infants’ legs, thereby improving the development of motor control and proper gait.

Toward Medical Devices With Integrated Mechanisms, Sensors, and Actuators Via Printed-Circuit MEMS

Recent advances in medical robotics have initiated a transition from rigid serial manipulators to flexible or continuum robots capable of navigating to confined anatomy within the body. A desire for further procedure minimization is a key accelerator for the development of these flexible systems where the end goal is to provide access to previously inaccessible anatomical workspaces and enable new minimallyinvasive surgical (MIS) procedures. While sophisticated navigation and control capabilities have been demonstrated for such systems, existing manufacturing approaches have limited the capabilities of mm-scale end-effectors for these flexible systems to date and, to achieve next generation highlyfunctional end-effectors for surgical robots, advanced manufacturing approaches are required. We address this challenge by utilizing a disruptive 2D layer-by-layer precision fabrication process (inspired by printed circuit board manufacturing) that can create functional 3D mechanisms by folding 2D layers of materials which may be structural, flexible, adhesive, or conductive. Such an approach enables actuation, sensing and circuitry to be directly integrated with the articulating features by selecting the appropriate materials during the layer-by-layer manufacturing process. To demonstrate the efficacy of this technology, we use it to fabricate three modular robotic components at the millimeter-scale: (1) sensors, (2) mechanisms, and (3) actuators. These modules could potentially be implemented into transendoscopic systems, enabling bilateral grasping, retraction and cutting, and could potentially mitigate challenging MIS interventions performed via endoscopy or flexible means. This research lays the ground work for new mechanism, sensor and actuation technologies that can be readily integrated via new mm-scale layer-by-layer manufacturing approaches.

A high-force, high-stroke distal robotic add-on for endoscopy

‘Snap-On’ robotic modules that can integrate distally with existing commercially-available endoscopic equipment have the potential to provide new capabilities such as enhanced dexterity, bilateral manipulation and feedback sensing with minimal disruption of the current clinical workflow. However, the desire for fully-distal integration of sensors and actuators and the resulting form factor requirements preclude the use of many off-the-shelf actuators capable of generating the relevant strokes and forces required to interact with tools and tissue. In this work, we investigate the use of millimeter-scale, optimally-packed helical shape memory alloy (SMA) actuators in an antagonistic configuration to provide distal actuation without the need for a continuous mechanical coupling to proximal, off-board actuation packages to realize a truly plug-and-play solution. Using phenomenological modeling, we design and fabricate antagonistic helical SMA pairs and implement them in an at-scale roboendoscopic module to generate strokes and forces necessary for deflecting tools passed through the endoscope working port, thereby providing a controllable robotic ‘wrist’ inside the body to otherwise passive flexible tools. Bandwidth is drastically improved through the integration of targeted fluid cooling. The integrated system can generate maximum lateral forces of 10N and demonstrates an additional 96 degrees of distal angulation, expanding the reachable workspace of tools passed through a standard endoscope.

Design and control of a parallel linkage wrist for robotic microsurgery

This paper presents the design and control of a teleoperated robotic system for dexterous micromanipulation tasks at the meso-scale, specifically open microsurgery. Robotic open microsurgery is an unexplored yet potentially a high impact area of surgical robotics. Microsurgical operations, such as microanastomosis of blood vessels and reattachment of nerve fibers, require high levels of manual dexterity and accuracy that surpass human capabilities. A 3-DoF robotic wrist is designed and built based on a spherical five-bar mechanism. The wrist is attached to a 3-axis commercial off-the-shelf linear stage, achieving a fully dexterous system. Design requirements are determined using motion data collected during a simulated microanastomosis operation. The wrist design is optimized to maximize workspace and manipulability. The system is teleoperated using a haptic device, and has the required bandwidth to replicate microsurgical motions. The system was successfully used in a micromanipulation task to stack 1 mm-diameter metal spheres. The micromanipulation system presented here may improve surgical outcomes during open microsurgery by offering better accuracy and dexterity to surgeons.