Objective: Intracorporeal suturing and knot tying can complicate, prolong or preclude minimally invasive surgical procedures, reducing their advantages over conventional approaches. An automated knot-tying device has been developed to speed suture fixation during minimally invasive cardiac surgery white retaining the desirable characteristics of conventional hand-tied surgeon's knots: holding strength and visual and haptic feedback. A rotating slotted disc (at the instrument's distal end) automates overhand throws, thereby eliminating the need to manually pass one suture end through a loop in the opposing end. The electronic actuation of this disc produces left or right overhand knots as desired by the operator. Methods: To evaluate the effectiveness of this technology, seven surgeons with varying laparoscopic experience tied knots within a simulated minimally invasive setting, using both the automated knot-tying toot and conventional laparoscopic tools. Suture types were 2/0 braided and 4/0 monofilament. Results: Mean knot-tying times were 246 +/- 116 s and 102 +/- 46 s for conventional and automated methods, respectively, showing an average 56% reduction in time per surgeon (p = 0.003, paired t-test). The peak holding strength of each knot (the force required to break the suture or loosen the knot) was measured using tensile-testing equipment. These peak holding strengths were normalised by the ultimate tensile strength of each suture type (57.5 N and 22.1 N for 2/0 braided and 4/0 monofilament, respectively). Mean normalised holding strengths for all knots were 68.2% and 71.8% of ultimate tensile strength for conventional and automated methods, respectively (p = 0.914, paired t-test). Conclusions: Experimental data reveal that the automated suturing device has great potential for advancing minimally invasive surgery: it significantly reduced knot-tying times while providing equivalent or greater holding strength than conventionally tied knots. (C) 2009 European Association for Cardio-Thoracic Surgery. Published by Elsevier B.V. All rights reserved.

This paper details the development of a Neural Network (NN) controller for a Shape Memory Alloy (SMA) actuated catheter, with potential application to tele-operated cardiac ablation procedures. The robotic catheter prototype consists of a central tubular structure actuated by four SMA tendons. A dual-camera imaging system provides position feedback of the catheter tip. Open loop bending responses are obtained and associated nonlinearities are identified. A NN controller is designed using time-shifted input-output maps generated from randomized open loop measurements. The tracking performance of this NN controller is compared with PI/PID controllers for various reference trajectories.

Introduction: While catheters have proven effective in numerous cardiovascular procedures, their functionality and versatility can be greatly improved by incorporating active steering capabilities to the catheter tip. Shape memory alloy (SMA) actuation is ideally suited to this application, as these materials offer superior power density, energy density and biocompatibility. In this research, we investigate the transient behavior of an SMA-actuated active catheter to optimize its design and enable precise computer-controlled navigation. Methods: The active catheter prototype consists of a central beam actuated by a single SMA tendon, both enclosed by an outer Teflon sleeve. Joule heating is used to generate tip deflections, which are measured in real time using a dual-camera imaging system. SMA actuation is described using the Seelecke-Muller-Achenbach single-crystal model whose parameters are experimentally derived from stress-strain characteristics of the SMA tendon measured at different temperatures. These characteristics are used to optimize the design parameters of the catheter to maximize the bending response. The effects of outer sleeve thickness on the transient behavior of the catheter are also studied. Results: The catheter’s bending mechanics are described using a circular arc model, which is experimentally validated. Catheter actuation is found to be slower with increased sleeve thickness, as explained by heat transfer analysis. Dynamic simulation of the system model shows excellent correlation to experimental data for low frequency actuation.

In this paper we investigate the transient behavior of a simple active catheter: a central tube actuated by a single nitinol tendon enclosed by an outer sleeve. Dynamic models are developed to characterize the transient behavior and optimize the design of an experimental prototype. The bending mechanics are derived using a circular arc model and are experimentally validated. Nitinol actuation is described using the Seelecke-Muller-Achenbach model for single-crystal shape memory alloys using experimentally determined parameters. The dynamic characteristics of this active catheter system are simulated and compared with experimental results. Joule heating is used to generate tip deflections, which are computed in real time using a dual-camera imaging system. The effects of outer sleeve thickness on heat transfer and transient response characteristics are studied.

This research highlights the design, fabrication and experimental validation of a Shape Memory Alloy (SMA) actuated robotic catheter. The prototype consists of four SMA tendons that actuate a central tubular substructure in two orthogonal directions. The experimental shape memory characteristics are used to optimize the design. Joule heating is used to generate tip deflections and the experimental bending characteristics are obtained using a dual camera imaging system. These measurements reveal important nonlinearities and hysteretic characteristics of the system. A dynamic model of the system is developed to describe the SMA-effected bending mechanics, and simulation results are compared to experimental measurements for model validation. The applicability of this technology to cardiovascular procedures, like atrial ablation, is demonstrated through precise tracking of trajectories using PID control.