Introduction

Compared to suture and stapled anastomoses, magnetic compression anastomosis (MCA) is a simple and safe non-suture anastomosis method1,2. MCA can be used for esophageal anastomosis3,4, esophagogastric anastomosis5, gastrointestinal anastomosis6,7, colorectal anastomosis8,9, and rectovaginal fistula repair10. Outside the digestive system, MCA can be used for vascular anastomosis11,12and ureterovesical anastomosis13. In addition, it can be used to perform digestive tract fistula14and cystostomy15. MCA can also be used to create pathological fistula for establishing animal models of various diseases, such as those of tracheoesophageal fistula16. Therefore, MCA has great clinical application potential.

MCA typically involves the placement of a daughter magnet and a parent magnet on the opposite sides of the organ site where the anastomosis is to be established to ensure that both the daughter and parent magnets are attracted to each other. MCA can be easily conducted in open or laparoscopic surgery. MCA, along with endoscopy, can be employed as a novel minimally invasive treatment model for gastrointestinal stenosis. In a patient with gastrostomy or enterostomy, the daughter and parent magnets can be placed at the predetermined site through the natural cavity and the ostomy channel17,18. However, the existing cylindrical or circular magnetic anastomosis devices are incapable of meeting the clinical needs of patients with digestive tract stenosis without an ostomy channel.

The design scheme of Smart Self-Assembling MagnetS for ENdoscopy (SAMSEN)19 inspired us to propose a novel design idea of Y-Z deformable self-assembled magnetic anastomosis rings (Y-Z DSAMARs). We here introduce the design scheme and magnetic properties of Y-Z DSAMARs. We also evaluate the reliability of the self-assembly deformation of Y-Z DSAMARs through an in vitro simulation and an in vitro deformation.

Materials and methods

Materials

The study protocol and all experimental procedures were carried out strictly in accordance with the Guidelines for Care and Use of Experimental Animals issued by the Xi’an Jiaotong University Medical Center. This experimental study was approved by the Experimental Ethics Committee of Xi’an Jiaotong University (Permit number: 2022 − 1451). The isolated pig esophagi were taken from other experimental animals euthanized (intravenous overdose of pentobarbital sodium, 90 mg/kg) after the end of the experiment in our research group.

Design of Y-Z DSAMARs

We designed and developed our own Y-Z DSAMAR (designed by Xiaopeng Yan and Miaomiao Zhang), which comprises 10 trapezoidal magnetic units (Fig. 1A). The Y-Z DSAMAR was in a straight linear state when the 10 magnetic units were placed in a particular order and the hard guide wire was passed through the central hole of the magnetic unit (Fig. 1B). When the hard guide wire was slowly removed, the adjacent magnetic units lose the constraints of the wire and automatically attract each other on the side face (Fig. 1C). When the guide wire was completely removed, all magnetic units self-assembled into a ring (Fig. 1D). Each magnetic unit comprised an N50-sintered neodymium-iron-boron (NdFeB) permanent magnet with a titanium nitride surface coating. These units exhibited trapezoidal surface saturation magnetization. A Gaussian meter was employed to determine the magnetic field intensity of the magnetic units. A magnetic pole display card was used to show the magnetic field distribution of the magnetic unit. An electronic material testing machine was used to test the magnetic unit and generate the Y-Z DSAMAR magnetic curve.

Fig. 1
figure 1

Y-Z DSAMAR design schematic. (A) A single magnetic unit. (B) Arrangement of magnetic units in a straight line under the constraint of the guide wire. (C) State of the magnetic unit in deformation self-assembly. (D) Magnetic unit deforms and self-assembles into a ring.

Study design

We examined the deformation performance of Y-Z DSAMARs by conducting an in vitro deformation test and an in vitro organ deformation test.

In vitro deformation test

We arranged the 10 magnetic units in a straight line. We then passed the hard guide wire through the resulting central hole. Next, we slowly withdrew the hard guide wire while pushing the catheter, which allowed the magnetic units to self-assemble into a ring. We carried out this process 100 times, and then we statistically analyzed the success rate of the self-assembly deformation of the magnetic unit. The self-assembly deformation was deemed successful when the gradual withdrawal of the hard guide wire transformed the 10 magnetic units into a ring without requiring any other external force.

In vitro internal deformation test for isolated organs

We procured esophagi from 10 pigs. Each esophagus was approximately 40 cm long. We inserted a 14 Fr nasogastric tube into the esophagus through the oral channel. We then conducted double ligation on the nasogastric tube using a 7 − 0 silk thread in the middle of the esophagus, followed by the removal of the tube. The internal diameter of the esophageal cavity at the ligation site was approximately 4 mm. The distal end of the esophagus was clamped using a vascular clamp. We next inserted a plastic tube into the proximal end of the esophagus and slowly and continuously injected air to inflate and expand the esophagus. X-ray observation showed the successful formation of a simple isolated esophageal stenosis model.

The linear Y-Z DSAMARs were gradually inserted into the esophagus through the oral channel under constant X-ray monitoring. As the last magnetic unit passed the stenosis, the hard guide wire was slowly withdrawn using a push catheter. The self-assembly deformation process of the magnetic unit was observed under X-ray until the magnetic unit was completely self-assembled into a ring. The linear Y-Z DSAMARs were placed at the proximal end of esophageal stenosis using the same method. We conducted X-ray monitoring of the deformation process until we observed the formation of a ring. Then, the magnetic rings at the ends of the narrow esophagus were adjusted to ensure that they attracted each other. Next, we examined the magnet attraction state under X-ray and observed the state of the serous membrane under magnetic ring attraction from outside the esophagus. We performed each of the 10 esophageal operations three times, totaling 30 operations. We then noted the success rates of attraction and Y-Z DSAMAR deformation in the esophagus.

Statistical analysis

SPSS 20.0 software was used for statistical analysis. Measurement data with a normal distribution were expressed as the mean ± SD, while those with a skewed distribution were expressed as the median. The normality of the study variables was assessed by Shapiro-Wilk test.

Results

Successful production and procession of Y-Z DSAMARs

We successfully produced a trapezoidal magnet with a mass of 1.25 g. The magnetic field intensity at its surface was 480 mT. Figure 2 shows the physical structure of the magnet and the distribution of magnetic fields in each plane of the magnet. Figure 3 shows the magnetic field distribution during the deformation of Y-Z DSAMARs. A universal material testing machine was used to show that the magnetic force of the working faces of two magnetic units at zero distance is 15.59 N. The magnetic curve is shown in Fig. 4A. The magnetic force on the side of neighboring magnetic units at zero distance is 6.24 N. The magnetic curve is shown in Fig. 4B. The magnetic curve of two self-assembled rings of Y-Z DSAMARs is shown in Fig. 4C. The maximum magnetic force of 183.57 N is obtained at zero distance.

Fig. 2
figure 2

Magnetic unit and the magnetic field distribution on each surface of the magnetic unit.

Fig. 3
figure 3

Magnetic field distribution during the deformation of Y-Z DSAMARs. (A) Magnetic field distribution in a linear arrangement of magnetic units. (B) Magnetic field distribution of the magnetic unit during deformation. (C) Magnetic field distribution when the magnetic units deform and self-assemble into a ring.

Fig. 4
figure 4

Magnetic force curve. (A) Magnetic force curve of the working faces of the magnetic unit. (B) Magnetic force curve on the side face of adjacent magnetic units. (C) Magnetic force curve of the circular ring formed by Y-Z DSAMARs.

Test parameters

We performed 100 in vitro deformation tests using Y-Z DSAMARs and obtained a 100% success rate (100/100) (Fig. 5 and Video 1). We successfully prepared the esophageal stenosis model through silk ligation (Fig. 6) and conducted the deformation and anastomosis of the magnetic unit in the esophagus (Fig. 7). We carried out 30 isolated organ simulations, with an operation time of 181–242 s and an average operation time of 212.13 ± 18.78 s. The success rates for both self-assembly deformation and esophageal stenosis anastomosis were 93.33% (28/30), while that for esophageal stenosis anastomosis with successful deformation was 100% (28/28). In two cases, the magnetic units failed to position themselves according to the established pattern during the deformation of the magnetic ring at the distal end of the narrow esophagus, leading to deformation failure (Fig. 8).

Fig. 5
figure 5

Y-Z DSAMARs in vitro deformation test. (A) Magnetic units arranged in a straight line. (B) Magnetic unit during deformation. (C) Magnetic unit deforms successfully into a ring.

Fig. 6
figure 6

Esophageal stenosis model prepared by silk ligation. (A) External view of the esophageal stenosis model. (B) X-ray image of esophageal stenosis.

Fig. 7
figure 7

Deformation self-assembly and anastomosis of Y-Z DSAMARs in the esophagus. (A) Linear magnetic units passing through esophageal stenosis. (B) All magnetic units passed through esophageal stenosis. (C) Y-Z DSAMAR deformational process of the distal end of esophageal stenosis. (D) Magnetic unit at the distal end of esophageal stenosis self-assembles into a ring. (E) A linear magnetic unit enters the proximal end of esophageal stenosis. (F) Y-Z DSAMAR deformational process of the proximal end of esophageal stenosis. (G) Magnetic unit at the proximal end of esophageal stenosis self-assembles into a ring. (H) Y-Z DSAMAR rings on both sides of stenosis esophagus attract each other. (I) External view of the esophagus after the magnetic rings attract each other.

Fig. 8
figure 8

Two cases of deformation failure of the esophageal magnetic unit. (A) Case 1: Magnetic units in the middle section of the esophagus fail to attract each other, resulting in a “3” shape. (B) Case 2: Deformation self-assembly process and the attracting process failed.

Discussion

We designed a Y-Z DSAMAR for placing a magnetic anastomotic ring at the narrow distal end of the digestive system through a transoral or transanal passage. Therefore, the ability of the magnetic units to self-assemble and deform is the most important criterion to evaluate the performance of Y-Z DSAMARs. The success rates of Y-Z DSAMARs were as high as 100% in vitro and 93.33% (28/30) in vitro in isolated organs.

Unlike previously reported deformable magnetic anastomosing devices, Y-Z DSAMARs have the following characteristics. First, the previously reported deformation magnets depend on multiple wires to assist the magnet transforming into a ring20,21. However, Y-Z DSAMARs employ the lateral magnetic force of the magnetic unit itself to complete the deformation process, immensely simplifying the deformation process as well as the auxiliary structure and device involved. Second, the guide wire of our Y-Z DSAMARs has a dual role of guiding as well as controlling the magnetic unit. It guides the magnetic unit to the target position and ensures that each magnetic unit is arranged in a straight line as the Y-Z DSAMAR traverses the digestive system. Third, the previously reported deformable magnetic anastomosis device can be delivered only through an endoscopic biopsy hole20or a specially made catheter21, which limits its applicability. In contrast, the magnetic unit of our Y-Z DSAMARs easily reaches the target position with the help of the guide wire and the catheter, which significantly increases the flexibility and extent of the potential applications of Y-Z DSAMARs. Fourthly, the magnetic unit can pass through even very narrow stenoses, where it self-assembles to a large magnetic anastomosis ring. The ratio of the cross-sectional areas before and after deformation can reach 1:15, a critical performance indicator of the device. Hence, the device can be used to successfully manage digestive tract stenoses. Fifth, because of the unique arrangement of magnetic units in Y-Z DSAMARs, the magnetic force between the two rings of the device at zero distance can be as high as 183 N. Hence, the device has remarkable magnetic properties. Sixth, because the N- and S-poles of the magnetic units of Y-Z DSAMARs are arranged alternately, the torus of one device can automatically attract that of the other when both devices are circular. To attract the complete magnetic ring, the N- and S-poles of the magnetic ring must be close to each other. This is another important characteristic of Y-Z DSAMARs.

Our study showed two cases when Y-Z DSAMARs failed to deform in the isolated organ. In one case, the adjacent magnetic rings present in the middle of the device failed to attract each other according to the established requirements, resulting in a “3”-shaped magnetic ring (Fig. 8A). In the second case, the last magnetic unit of the distal Y-Z DSAMAR displaced during deformation. Instead of correcting it, we inserted another Y-Z DSAMAR at the proximal end in the hope that the displaced magnetic unit could be reset. However, the results showed that the two magnetic rings attract each other side by side under the influence of the shifted magnetic unit (Fig. 8B). Our analysis demonstrated that the Y-Z DSAMAR deformation failure occurred because of the uneven force exerted by the guide wire during the withdrawal process or poor lubrication of the guide wire, which caused the magnetic unit to “hold.” As this failure was not due to any flaw in the design principle of the device, we remain confident in our Y-Z DSAMARs.

In conclusion, Y-Z DSAMARs exhibit remarkable deformation-controllable characteristics. They can be inserted in the body from both ends of esophageal stenosis through a single channel with a high success rate of deformation. As Y-Z DSAMARs have a remarkable ability for self-assembly deformation, they can be employed for furthering both experimental research and potential clinical applications. Further optimization of the operational procedure and its verification through animal experiments would make Y-Z DSAMARs clinically applicable. In future studies, we plan to conduct in vivo experiments to further test the feasibility of Y-Z DSAMARs.