Current surgical devices are mostly rigid and are made of stiff materials, even though their predominant use is on soft and wet tissues. With the emergence of compliant mechanisms (CMs), surgical tools can be designed to be flexible and made using soft materials. CMs offer many advantages such as monolithic fabrication, high precision, no wear, no friction, and no need for lubrication. It is therefore beneficial to consolidate the developments in this field and point to challenges ahead. With this objective, in this article, we review the application of CMs to surgical interventions. The scope of the review covers five aspects that are important in the development of surgical devices: (i) conceptual design and synthesis, (ii) analysis, (iii) materials, (iv) manufacturing, and (v) actuation. Furthermore, the surgical applications of CMs are assessed by classification into five major groups, namely, (i) grasping and cutting, (ii) reachability and steerability, (iii) transmission, (iv) sensing, and (v) implants and deployable devices. The scope and prospects of surgical devices using CMs are also discussed.
Continuum robots have the potential to form an effective interface between the patient and surgeon in minimally invasive procedures. Magnetic actuation has the potential for accurate catheter steering, reducing tissue trauma and decreasing radiation exposure. In this paper, a new design of a monolithic metallic compliant continuum manipulator is presented, with flexures for precise motion. Contactless actuation is achieved using time-varying magnetic fields generated by an array of electromagnetic coils. The motion of the manipulator under magnetic actuation for planar deflection is studied. The mean errors of the theoretical model compared to experiments over three designs are found to be 1.9 mm and 5.1 deg in estimating the in-plane position and orientation of the tip of the manipulator, respectively, and 1.2 mm for the whole shape of the manipulator. Maneuverability of the manipulator is demonstrated by steering it along a path of known curvature and also through a gelatin phantom, which is visualized in real time using ultrasound imaging, substantiating its application as a steerable surgical manipulator.
Continuum manipulators coupled with magnetic actuation have great potential as steerable instruments for diverse surgical applications. They can be maneuvered inside the human body to reach difficult-to-access surgical sites with contactless actuation. This paper presents a new design of a compliant continuum manipulator of diameter 3 mm and length 70 mm, capable of spatial bending under magnetic actuation. A quasistatic model is developed to estimate the 3D motion of the manipulator. Experiments report an overall mean error in whole shape estimation of the manipulator between the model and the ground truth of 1.7 mm and 4.8 mm, when suspended vertically and horizontally from its base, respectively. Furthermore, fiber Bragg grating (FBG) sensors are integrated with the manipulator to enable shape sensing. Closed-loop control is demonstrated to trace different trajectories with the tip of the manipulator. A square trajectory and a straight line trajectory are generated with an average error in tip position of 4.1 mm between the desired and estimated positions. The potential of the manipulator as a steerable instrument is validated by maneuvering it inside phantoms of a bifurcating arterial system and a heart with visual guidance from a miniature camera.
Soft and flexible magnetic robots have gained significant attention in the past decade. These robots are fabricated using magnetically-active elastomers, are capable of large deformations, and are actuated remotely thus allowing for small robot size. This combination of properties is appealing to the minimally invasive surgical community, potentially allowing navigation to regions of the anatomy previously deemed inaccessible. Due to the low forces involved, one particular challenge is functionalizing such magnetic devices. To address this limitation we introduce a proof-of-concept variable stiffness robot controlled by remote magnetic actuation, capable of grasping objects of varying sizes. We demonstrate a controlled and reversible high deformation coiling action induced via a transient homogeneous magnetic field and a synchronized sliding nitinol backbone. Our soft magnetic coiling grasper is visually tracked and controlled during three experimental demonstrations. We exhibit a maximum coiling deformation angle of 400 • .
Continuum manipulators have revolutionized the field of minimally invasive surgery (MIS) in the past few decades. Major advances in fiber optics, imaging technologies, teleoperation, and haptics have accelerated the development of robot-assisted surgeries. The continuum manipulators used in robot-assisted surgery are equipped with laparoscopic tools as end effectors to augment the hand movements of the surgeon with precision. With robot assistance, surgeons can perform complex procedures inside the human body with high dexterity. However, the continuum robotics research community has challenged the lack of intuitive and effective operation of the surgical tools. Much uncertainty still exists about the tool-tissue interactions which have associated risks of tissue damage caused by unreliable control and articulation of the tool. This problem is further exacerbated by the limited visualization resolution of internal organs of the human body for safe operation. There is a pressing need to develop continuum manipulators with improved maneuverability and control to reach difficult-to-access surgical sites accurately.The aforementioned challenges of MIS play a critical role in the design and development of surgical continuum manipulators. The concept of compliant mechanisms (CMs) has been central to the design of various surgical devices. CMs are flexible mechanisms that use elastic deformation to transfer or transform force, motion, or energy. Devices made of CMs are generally monolithic in nature which leads to simplified fabrication, no wear, no friction, therefore, beneficial in high precision applications. CMs and their sub-components are increasingly used to enhance the range of motion and articulation of surgical continuum manipulators. Recently, magnetic actuation has emerged as a powerful means to execute several surgical functions such as instrument positioning, navigation, grasping, resection, and retraction. Magnetic actuation coupled with CMs has considerable impact in the design of miniaturized manipulators that eliminates the need for any cables tethered for control. Furthermore, accurate modeling of the continuum manipulators and integration of embedded sensing have been effective in the localization of manipulators. Real-time three-dimensional (3D) shape sensing of manipulators in tandem with medical imaging modalities aids in iii closed-loop control strategy to trace different trajectories with the tip of the manipulator is demonstrated. Clinical feasibility of the manipulator as a steerable catheter is shown in phantoms of a bifurcating artery and a heart with the guidance of a miniature camera.Part II explores the concept of variable stiffness mechanisms for surgical applications focusing on grasping and shape locking. Chapter 5 presents a magnetically-actuated variable stiffness robot (VSR). It is made of a soft magnetic elastomer with a sliding nitinol backbone. The synchronised retraction of the backbone with magnetic actuation leads to high deformation coiling action of the VSR. The grasping of ...
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