Research News
[Prof. Yong-Lae Park] Soft Miniaturized Actuation and Sensing Units for Dynamic Force Control of Cardiac Ablation Catheters
Author
mina7789
Date
2024-04-12
Views
159
Authors
Nitish Kumar, Jackson Wirekoh, Samir Saba, Cameron N. Riviere, and Yong-Lae Park
Abstract
Recently, there has been active research in finding robotized solutions for the treatment of atrial fibrillation (AF) by augmenting catheter systems through the integration of force sensors at the tip. However, limited research has been aimed at providing automatic force control by also integrating actuation of the catheter tip, which can significantly enhance safety in such procedures. This article solves the demanding challenge of miniaturizing both actuation and sensing for integration into flexible catheters. Fabrication strategies are presented for a series of novel soft thick-walled cylindrical actuators, with embedded sensing using eutectic gallium–indium. The functional catheter tips have a diameter in the range of 2.6–3.6 mm and can both generate and detect forces in the range of < 0.4 N, with a bandwidth of 1–2 Hz. The deformation modeling of thick-walled cylinders with fiber reinforcement is presented in the article. An experimental setup developed for static and dynamic characterization of these units is presented. The prototyped units were validated with respect to the design specifications. The preliminary force control results indicate that these units can be used in tracking and control of contact force, which has the potential to make AF procedures much safer and more accurate.
Discussion and Conclusion
In this work, we designed a series of soft miniaturized actuation and sensing units varying in size and material, which met the challenging requirement specifications for the cardiac ablation procedures with respect to compactness and integration. The embedded microfluidic sensor system was fabricated using eGaIn. Although eGaIn has low toxicity, future designs will focus on identifying optimal nontoxic biocompatible alternatives, such as sensing based on optical fiber19,45 or sensing based on ionic liquid.46–48 During contact force control, proper contact between the heart wall and the catheter tip was assumed, allowing for a one-DOF force measurement system.
In this proposed design, the catheter control from outside still lies with the cardiac physiologist. The advantage of this lies in the fact that the physician can adjust the orientation of the catheter tip using an adjustable sheath to minimize off-axis errors in placement, before fixing the system in place. However, the overall system design and workflow can be improved through the introduction of multimodal sensing (i.e., displacement and three-axis force). In addition, an anchoring mechanism can help secure the tip close to the heart wall.
An experimental setup, using hydraulic actuation for safety as opposed to pneumatic actuation typical of PAMs, was developed and used to characterize and control the prototyped units. However, a few issues must be addressed before the proposed system can be used in clinical settings.
The inlet tubing must have a smaller diameter to allow for the passage of electrode and sensing wires. Depending upon the length and the inner diameter of the tubing used for the hydraulic transmission, frictional losses might not be negligible. These losses would need to be calculated and the corresponding pressure loss would then need to be estimated for more accurate force control at the soft catheter tip.
Before clinical use, future work required includes the design of a modified catheter and the corresponding integration of the soft catheter tips. The modified catheter design would need to keep the same form and factor as traditional catheters, so as to be compatible with the current AF techniques. The inclusion of the wiring for the RF ablation electrodes and the microchannels for dispersing the X-ray contrast agent also would need to be considered. One possible modified catheter design could be along the lines of multisegment cardiac catheter steering mechanism presented in this work.49
Through experimental characterization, we have demonstrated that the soft miniaturized units met the static and dynamic performance requirements for the cardiac ablation procedures. Moreover, a theoretical model of soft thick-walled cylindrical actuators was developed, which could be used for prediction of static and dynamic performance for a parametric design evaluation.
We used an inexpensive linear stepper motor (LP25–35; Nanotec) which drives the syringe and is responsible for generating the hydraulic pressure driving the soft catheter actuator against the external load. It would be recommended to use a high-quality linear direct current (DC) motor with a much higher bandwidth, especially for force control experiments.
The effect of the low bandwidth of the stepper motor was clearly visible in the preliminary force control experimental results. While the contact force tracking worked well, as shown in Figure 9a and b, when the level of external force was low (0.1 − 0.25 N), the linear stepper motor was not fast enough to keep up at higher load levels of 0.4 − 0.7 N. Therefore, even with the force controller on, the level of interaction forces decreased enough (from ∼0.7 to 0.45 N) but not close to 0.25 N, as shown in Figure 9c and d. The contact force kept decreasing to the effect of almost no contact before recovering contact around 3 s; this observation also supports the finding that the linear stepper motor should be replaced by a DC motor with much higher bandwidth for better force control results.
Even though these actuation and sensing units were developed for targeted requirements of cardiac ablation procedures, a parametric design approach with different materials and sizes was presented, which could be tailored for other applications as well with requirement specification having similar orders of magnitude. The future work consists of developing force control strategies with these miniaturized units and demonstration of the same under various user case scenarios and cadaver studies using a modified overall catheter design. Another area of future work includes the development of multiaxis force sensing units in the limited space of the catheter tip, which will enable detection of the orientation of the tip to the wall.
More Information : Soft Miniaturized Actuation and Sensing Units for Dynamic Force Control of Cardiac Ablation Catheters | Soft Robotics (liebertpub.com)
