Development of implantable electrode based on bioresorbable Mg alloy for tissue welding application

Abstract

An implantable electrode based on bioresorbable Mg-Nd-Zn-Zr alloy was developed for next-generation radiofrequency (RF) tissue welding application, aiming to reduce thermal damage and enhance anastomotic strength. The Mg alloy electrode was designed with different structural features of cylindrical surface (CS) and continuous long ring (LR) in the welding area, and the electrothermal simulations were studied by finite element analysis (FEA). Meanwhile, the temperature variation during tissue welding was monitored and the anastomotic strength of welded tissue was assessed by measuring the avulsion force and burst pressure. FEA results showed that the mean temperature in the welding area and the proportion of necrotic tissue were significantly reduced when applying an alternating current of 110 V for 10 s to the LR electrode. In the experiment of tissue welding ex vivo, the maximum and mean temperatures of tissues welded by the LR electrode were also significantly reduced and the anastomotic strength of welded tissue could be obviously improved. Overall, an ideal welding temperature and anastomotic strength which meet the clinical requirement can be obtained after applying the LR electrode, suggesting that Mg-Nd-Zn-Zr alloy with optimal structure design shows great potential to develop implantable electrode for next-generation RF tissue welding application.

Keywords: Anastomotic strength; Electrothermal simulation; Implantable electrode; Mg alloy; Radiofrequency tissue welding; Structural design.

Figure 1

Different functions of Mg-based implantable electrode during the processes of RF tissue welding, tissue support and tissue recovery.

Figure 2

Electrode designs and models of tissue welding. (a,b) Physical drawings of the two Mg-based electrodes: the top one is the CS electrode and the bottom one is the LR electrode; (c,d) Tissue welding models established based on the CS and LR electrodes, respectively.

Figure 3

Experiment of tissue welding ex vivo. (a) The picture of tissues in RF welding experiment under the proper compressive pressure; (b) images of the two Mg-based electrodes; (c) typical anastomotic anastomotic stoma welded by the LR electrode; (d,e) schematic diagrams of the avulsion force and burst pressure measurements.

Figure 4

Temperature distributions and proportions of necrotic tissues in electrothermal simulations. Temperature distributions of the models for the CS (a) and LR (b) electrodes. (c) Mean temperatures of welded tissues and (d) necrotic tissue proportions obtained by the CS and LR electrodes.

Figure 5

Temperature variations of domain points. (a) Domain points on the CS (A-D) and LR (A1-D1) electrodes. Temperature variations of the corresponding positions on the central points of tissues (b), the interfaces between the tissue and the outer copper electrodes (c) and the interfaces between the tissue and the inner Mg-based electrodes (d).

Figure 6

Temperature variations of different positions corresponding to domain points of (a) A-A1, (b) B-B1, (c) C-C1, (d) D-D1.

Figure 7

Biomechanical properties of welded tissues under different welding parameters. Anastomotic avulsion force of different welding times on tissues when the applied RF energy was (a) 120 W, (b) 140 W and (c) 160 W, respectively. (d) Burst pressures of welded tissues after applying an energy power of 120 W and a compression pressure of 176 kPa for 8 s.

Figure 8

Real-time temperature variations monitored by an infrared imager. 3D thermographs of temperatures for the tissues welded by the CS (a) and LR (b) electrodes; The maximum (c) and mean (d) temperature variations of tissues welded by CS and LR electrodes.

Figure 9

H&E images of tissues. (a) Normal intestinal tissue. Anastomotic stoma welded by the CS (b) and LR (c) electrodes.