The research protocol and all experimental procedures were strictly in accordance with the Guidelines for the 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 the Xi'an Jiaotong University (Permit number: 2021-1536).
Twelve female New Zealand rabbits, weighing 2.0–3.0 kg, were obtained from the Experimental Animal Center, College of Medicine, Xi'an Jiaotong University (Xi’an, China). The animal protocol was designed to minimize pain or discomfort to the animals. The animals were acclimatized to laboratory conditions (23°C, 12h/12h light/dark, 50% humidity, ad libitum access to food and water) for one week prior to commencing the experiments. This was an exploratory study; therefore, all animals were included in the experimental investigations, and there was no control group. Intramuscular injection of pethidine hydrochloride (1 mg/kg) was administered every 12 hours for analgesia for three days after surgery. At the end of the study, all animals were euthanized by a barbiturate overdose (intravenous injection, 150 mg/kg pentobarbital sodium) for tissue collection.
According to the anatomical characteristics of rabbit lower urinary tract, the parent and daughter magnets for cystostomy were designed and manufactured. The daughter magnet was a cylinder (diameter: 5 mm; height: 7 mm) with a 1-mm hole in the center, and magnetic field intensity of 4260 GS. The parent magnet was a cylinder (diameter: 10 mm; length: 5 mm) with magnetic field intensity of 3680 GS (Fig. 1). The weight of parent magnet and daughter magnet was 2.470 g and 0.975 g, respectively. The parent and daughter magnets were made of neodymium-iron-boron (N45).
Before the surgery, rabbits were reared in single cage for 1 week and provided ad libitum access to standard rabbit chow and water. The rabbits were anesthetized by intravenous injection of 3% pentobarbital sodium (1 mL/kg) via ear vein after weighing. When the loss of paw retraction reflex was confirmed, the animal was placed in the supine position on the operating table and the limbs were immobilized. The lower abdomen and perineum were shaved. The interventional guide wire (0.035 in; TERUMO, Japan) was inserted through the urethra into the bladder and confirmed by x-ray (Fig. 2A). The end of the guide wire was inserted into the central hole of the daughter magnet and the scalp needle tube (Fig. 2B). By pushing the scalp needle tube, the daughter magnet was pushed along the guide wire into the bladder (Fig. 2C). Subsequently, the guide wire was removed and the daughter magnet was left in the bladder (Fig. 2D). The parent magnet was placed over the abdominal wall above the pubis so that the daughter magnet in the bladder was attracted to it (Fig. 2E). The attachment of the magnets was monitored under x-ray, and the position of the magnets was confirmed by cystography.
Calculation of operating time
The duration of operation was calculated as time elapsed from the beginning of insertion of the guide wire to the time when the parent and the daughter magnets were attracted together. The operation time of each rabbit was recorded.
After surgery, rabbits were housed individually in cages. The state of magnets was monitored daily, and the time of magnets falling off was recorded.
After the magnets fell, the rabbits were euthanized with an overdose of anesthetic. Urethra, bladder, and part of the abdominal wall around the site of cystostomy were taken as gross specimens to examine the fistula.
The cystostomy specimen was soaked overnight in 10% formalin. After fixation, the specimen was paraffin-embedded, and 4-mm thick sections were prepared from the anastomotic site. The sections were stained with hematoxylin and eosin and Masson trichromatic staining, and examined under a bright field microscope.
SPSS statistical 18.0 software was used for data analysis. The quantitative data were described using mean ± standard deviation.