Robotic artificial muscles are a subset of artificial muscles that are capable of producing biologically inspired motions useful for robot systems, i.e., large power-to-weight ratios, inherent compliance, and large range of motions. These actuators, ranging from shape memory alloys to dielectric elastomers, are increasingly popular for biomimetic robots as they may operate without using complex linkage designs or other cumbersome mechanisms. Recent achievements in fabrication, modeling, and control methods have significantly contributed to their potential utilization in a wide range of applications. However, no survey paper has gone into depth regarding considerations pertaining to their selection, design, and usage in generating biomimetic motions. In this paper, we discuss important characteristics and considerations in the selection, design, and implementation of various prominent and unique robotic artificial muscles for biomimetic robots, and provide perspectives on next-generation muscle-powered robots.

We present a modular sensing system to measure the deflection of a minimally invasive neurosurgical intracranial robot (MINIR): MINIR-II. The MINIR-II robot is a tendon-driven continuum robot comprised of multiple spring backbone segments, which has been developed in our prior work. Due to the flexibility of the spring backbone and unique tendon routing configuration, each segment of MINIR-II can bend up to a large curvature ( $\geq$ 100 m ^$-$1 ) in multiple directions. However, the shape measurement of the robot based on tendon displacement is not precise due to friction and unknown external load/disturbance. In this regard, we propose a bending sensor module comprised of a fiber Bragg grating (FBG) fiber, a Polydimethylsiloxane (PDMS) cylinder, and a superelastic spring. The grating segment of the FBG fiber is enclosed inside a PDMS cylinder (1 mm in diameter), and the PDMS cylinder is bonded with the superelastic spring in series. The deflection or bending of the robot backbone segment is translated into an axial loading in the superelastic spring, which applies tension to the FBG; therefore, by measuring the peak wavelength shift of the FBG, the bending angle can be estimated. This letter describes the design, fabrication, and kinematic aspects of the sensor module in detail. To evaluate the proposed concept, one such sensor module has been tested and evaluated on the MINIR-II robot.

To treat atrial fibrillation (AFib), radiofrequency ablation is usually implemented with a cardiac catheter to block abnormal electrical signals from pulmonary veins. However, it is challenging to manipulate a passive catheter. In addition, the radiation exposure to patients under fluoroscopic guidance has been a concern. To address these two major issues, this work presents the development of a steerable and magnetic resonance imaging (MRI) compatible cardiac catheter by using shape memory alloy (SMA) as an alternative interventional tool for AFib. The developed cardiac catheter is comprised of a passive and flexible tubing, and a steerable tip. The tip is composed of multiple bending modules and each module is actuated by a pair of antagonistic SMA wires. To improve the MRI-compatibility of SMA actuators, the electric current required for SMA actuation is significantly reduced by developing a technique of conductive heating actuation. In this letter, the design and fabrication of the cardiac catheter are presented, followed by modeling the SMA bending module. The working performance of the SMA bending module is experimentally studied. In the end, a proof-of-concept demonstration of the cardiac catheter is performed in an explanted heart.

This paper presents the design, modeling, and control of a meso-scale torsion actuator based on shape memory alloy (SMA) for image-guided surgical procedures. Developing a miniature torsion actuator is challenging, but it opens the possibility of significantly enhancing the robot agility and maneuverability. The proposed torsion actuator is bidirectionally actuated by a pair of antagonistic SMA torsion springs through alternate Joule heating and natural cooling. The torsion actuator is integrated into a surgical robot prototype to demonstrate its working performance in the humid environment under C-Arm CT image guidance.

Surgical robots have been extensively researched for a wide range of surgical procedures due to the advantages of improved precision, sensing capabilities, motion scaling, and tremor reduction, to name a few. Though the underlying disease condition or pathology may be the same across patients, the intervention approach to treat the condition can vary significantly across patients. This is especially true for endovascular interventions, where each case brings forth its own challenges. Hence, it is critical to develop patient-specific surgical robotic systems to maximize the benefits of robot-assisted surgery. Manufacturing patient-specific robots can be challenging for complex procedures and, furthermore, the time required to build them can be a challenge. To overcome this challenge, additive manufacturing, namely, 3D-printing, is a promising solution. 3D-printing enables fabrication of complex parts precisely and efficiently. Although 3D-printing techniques have been researched for general medical applications, patient-specific surgical robots are currently in their infancy. After reviewing the state-of-the-art in 3D-printed surgical robots, this article discusses 3D-printing techniques that could potentially satisfy the stringent requirements for surgical interventions. We also present the accomplishments in our group in developing 3D-printed surgical robots for neurosurgical and cardiovascular interventions. Finally, we discuss the challenges in developing 3D-printed surgical robots and provide our perspectives on future research directions.

Atrial fibrillation (AFib) is a significant healthcare problem caused by the uneven and rapid discharge of electrical signals from pulmonary veins (PVs). The technique of radiofrequency (RF) ablation can block these abnormal electrical signals by ablating myocardial sleeves inside PVs. Catheter contact force measurement during RF ablation can reduce the rate of AFib recurrence, since it helps to determine the effective contact of the catheter with the tissue, thereby resulting in effective power delivery for ablation. This paper presents the development of a 3-D force sensor to provide the real-time measurement of triaxial catheter contact force. The 3-D force sensor consists of a plastic cubic bead and five flexible force sensors. Each flexible force sensor was made of a PEDOT:PSS strain gauge and a polydimethylsiloxsane (PDMS) bump on a flexible PDMS substrate. Calibration results show that the fabricated sensor has a linear response in the force range required for RF ablation. To evaluate its working performance, the fabricated sensor was pressed against gelatin tissue by a micromanipulator and also integrated on a catheter tip to test it within deionized water flow. Both experiments simulated the ventricular environment and proved the validity of applying the 3-D force sensor in RF ablation.