Objective To investigate the biocompatibil ity of sil ica gel embedded permanent magnets of themicturition alert device dedicated to neurogenic bladder. Methods According to the national standards of biologicalevaluation of medical equipment (GB/T 16886), Shanghai Biomaterial Research and Test Center was confided to evaluate the biocompatibil ity of sil ica gel embedded permanent magnets both in vitro and in vivo, including cytotoxicity test, sensitization test, primary skin irritant test and acute general toxicity test. The cytotoxicity test was performed according to the agar diffusion method. The L929 cell discoloration index and cell lysis index were counted at 24 hours after the action of the specimen. The sensitization test was performed according to the maximal dose method. The skin response was evaluated in 30 male albino guinea-pigs at 24 and 48 hours after the routine induction and provocation of leaching l iquors of the specimen. The primary skin irritant test was evaluated in 2 male healthy New Zealand rabbits according to the local tissue response at 24, 48 and 72 hours after intradermal injection of leaching l iquors of the specimen. The acute general toxicity test was evaluated in 10 male Kumming mice musculus albus according to animal condition at 4, 24, 48 and 72 hours after injection of leaching l iquors of the specimen through the caudal vein. Both the general reaction of canines and the pathology of the local bladder walls were observed at 2, 4 and 8 weeks after a permanent magnet was fixed on the anterior wall of urinary bladder in three canines. Results No sensitization, no stimulation and no acute general toxicity were observed except sl ight cytotoxicity to sil ica gel embeddedpermanent magnets. After implantation of a permanent magnet, the canines showed excellent tolerace, which manifested as no abnormal ity in spirit, appetite, urine and stool, healed wounds and no infection. Adhesions occurred between the epiploon and the bladder wall around the permanent magnet in two canines at 2 and 4 weeks, and between the lower abdominal wall and the bladder wall around the permanent magnet in the other canine at 8 weeks. The local bladder wall below permanent magnet was thickened, the fibrous capsule around the permanent magnet was thin, but the bladder mucosa was normal. Inflammatory reaction such as congestion, edema and inflammatory cells lessened from the serosa layer to the mucosa layer microscopically. Conclusion Sil ica gel embedded permanent magnets used in the micturition alert device dedicated to neurogenic bladde has excellent biocompatibil ity and meet the criteria for cl inical appl ication．
To introduce a micturition alert device dedicated to neurogenic bladders. Methods The design and mechanism of the micturition alert device were explained, the effectiveness was tested in a cranine experiment. Results The micturition alert device consisted of a permanent magnet sutured on the anterior bladder wall and a warning unit sutured on theinferior abdominal wall. The warning unit was assembled with a compass-l ike switch, a power supply, a buzzer and a power switch. Bladder volume determined the position of the magnet which determined the magnetic field at the point of the warning unit. The change of magnetic field was read by the warning unit. With increasing bladder volume from initial state to 200 mL in 8 dogs, the magnet moved cranially 32.8 mm averagely (from 31.3 mm to 34.1 mm) and the hand of warning unit turned 52° (from 47° to 57°). The value of the warning unit was correlated positively to the bladder volume (r =1.0, P lt; 0.01）. If the desired bladder volume was determined as 150 mL to activate the warning unit to alarm in advance, the fullness of bladder was 147.6 mL averagely from135 mL to 160 mL, with an error less than 15 mL (10%). Conclusion The micturition alert device including a warning unit and permanent magnet could monitor bladder volume continuously and alarm in time for the patients with loss of micturition desire. It is simple, easily-made, cheap and conveniently used. It is worth of further study.
Objective To study major influential factors of the micturition alert device dedicated to neurogenic bladders for the product design and cl inical appl ication of the device. Methods One ferrite permanent magnet with thickness and diameter of 3 mm and 10 mm, respectively, and three NdFeB permanent magnets with the thickness of 3 mm and diameter of 10, 15 and 20 mm, respectively, were used. The effects of thickness of the abdominal wall as well as the position and type of permanent magnets on the micturition alert device dedicated to neurogenic bladders were measured in vitro simulated test, when the abdominal wall was set to 2, 3, 4, 5, 6, 7, 8 and 9 cm, respectively, and the position of permanent magnets was 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 and 12 cm, respectively. The effect of the geomagnetic field on the device was measured under the condition that the thickness of the simulated abdominal wall was set to 2, 3, 4 and 5 cm, respectively,and the position of permanent magnets was 2, 3, 4, 5, 6, 7, 8, 9 and 10 cm, respectively. Results The value showed inthe warning unit was positively correlated with the position of the ferrite permanent magnet only when the thickness ofthe simulated abdominal wall was 2 cm (r=0.632, P lt; 0.05). The correlation between the value of the warning unit andthe position of NdFeB permanent magnets was significant (r gt; 0.622, P lt; 0.05), which was intensified with the increasingdiameter of NdFeB permanent magnets, but weakened with the increasing thickness of the simulated abdominal wall. The effect of the geomagnetic field was correlated with the exposition of the body, the position of the permanent magnet and the thickness of the abdominal wall. Conclusion The major influential factors of the micturition alert device dedicated to neurogenic bladder include the magnetism and location of the permanent magnet, the thickness of the abdominal wall and the geomagnetic field. These factors are correlated with and affect each other. Reasonable allocation of these factors may optimize the device.