**3.1 Magnetic endoluminal artificial urinary sphincter**

Urinary incontinence is not considered an illness but a symptom and is only treated when it becomes a social problem. Urinary incontinence is defined by the complaint of any involuntary leakage of urine (Abrams et al., 2002) or unintentional loss of urine that occurs with such frequency and in such quantities as to cause physical and/or emotional distress in the person experiencing it. Moreover, the number of people suffering from this is estimated to be around a million people among the adult population in western countries (Irwin et al., 2006).

Depending on the origin and the severity of the affection, it is treated with absorbent pads, pharmacological or surgical methods. For more than 30 years physicians have implanted inflatable artificial sphincters that simulate the sphincter function and permit the voluntary control of the micturition (American Medical System). However this device requires highly invasive surgery since it is necessary to implant a cuff around the urethra, in addition to a balloon, that regulates the cuff pressure and a bulb that controls the inflation and deflation of the cuff.

The objective of developing a magnetic artificial urinary sphincter is to look for a minimally invasive device that permits voluntary micturition control, making use of the potential of the magnetic field to exert a force without physical contact.

The preliminary specifications for the device are the following:


The device consists of a magnetic valve placed in the urethra. The urine is evacuated by bringing a permanent magnet near the body of the patient. The magnetic valve consists on (Figure 9) a hollow cylindrical body valve with a toroidal magnet fixed at one of their ends and a soft magnetic material piston that is attracted by the magnet, closing the evacuation hole. As a sealing gasket a medical grade silicone O-ring is used.

If a more powerful external magnet is brought near the valve, the magnetization of the piston (made of a soft magnetic material) is reversed and a repulsion force between the internal magnet and the piston appears, causing the evacuation hole to open. When the external magnet is moved away, the interaction between the internal magnet and the piston turns attractive again and the valve closes automatically. Furthermore, the system is provided with a safety system preventing overpressure in the bladder. By adjusting the distance between the piston and the internal magnet, a pressure level can be fixed in such a way that if the pressure inside the bladder reaches that value, then the valve opens automatically.

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Fig. 11. Sketch of the magnetic valve operation. A) Closed position. B) Open position.

From the point of view of the biocompatibility of the system the ferromagnetic elements are the most critical ones. For the piston, a Fe based alloy is used, PM2000, that previous studies have proved, has a good biocompatibility (Flores et al., 2004) together with a good magnetization for the fields that the magnet produces at millimetres distances. Moreover, the NdFeB magnet has been coated with gold in order to isolate it from the biological medium. For the body valve, a medical grade polyurethane with biomedical grade has been chosen. The problem regarding the fixation to the urethra has been solved by adapting the valve to a urinary ball-probe. Trials on experimental animals have shown good preliminary results.

Fig. 9. Sketch of the magnetic valve.

Figure 10 shows the sphincter prototype for the trials performed on animal models, in the Service of Experimental Surgery of Puerta de Hierro Hospital.

Fig. 10. Sphincter prototype for trials on animal models.

Fig 11 shows the operating system of the valve and its relative position concerning the bladder. Without any external action, the valve is in its closed position thanks to the action of the magnetic force exerted by the internal magnet (Fig11, A).

Figure 10 shows the sphincter prototype for the trials performed on animal models, in the

Fig 11 shows the operating system of the valve and its relative position concerning the bladder. Without any external action, the valve is in its closed position thanks to the action

Fig. 9. Sketch of the magnetic valve.

Service of Experimental Surgery of Puerta de Hierro Hospital.

Fig. 10. Sphincter prototype for trials on animal models.

of the magnetic force exerted by the internal magnet (Fig11, A).

Fig. 11. Sketch of the magnetic valve operation. A) Closed position. B) Open position.

From the point of view of the biocompatibility of the system the ferromagnetic elements are the most critical ones. For the piston, a Fe based alloy is used, PM2000, that previous studies have proved, has a good biocompatibility (Flores et al., 2004) together with a good magnetization for the fields that the magnet produces at millimetres distances. Moreover, the NdFeB magnet has been coated with gold in order to isolate it from the biological medium. For the body valve, a medical grade polyurethane with biomedical grade has been chosen. The problem regarding the fixation to the urethra has been solved by adapting the valve to a urinary ball-probe. Trials on experimental animals have shown good preliminary results.

Magnetic Sensors for Biomedical Applications 143

The manganese oxides perovskite La1-x(SrCa)xMnO3 have a Curie temperature that, depending on the cation ratio, can range from 300 K to 350 K (so 42-44 ºC is within the

The preparation of the particles is as follows. First the particles are created by the ceramic method from compounds of La2O3, CaCO3, SrCO3, and MnO2. These particles obtained by the ball milling method form agglomerates due to the dipolar magnetic interaction and the lack of surfactants. The agglomerates also have a large size distribution, with sizes greater than 1 m. Since the magnetic interaction decreases with temperature, the particles are dispersed in ethanol and heated over the Tc in order to disaggregate them and to select the smaller ones, thus obtaining an average size of 100 nm. These NPs are not biocompatible so

The magnetic properties are not significantly affected by the size selection. Since the size is around 100 nm, the selected NPs still behave quite like the as-prepared ceramic. However, the magnetic properties are affected by the coating: the total magnetization is reduced by the presence of diamagnetic silica and the Curie Temperature decreases when the nanoparticles are coated. For example, for the composition La0.56(CaSr)0.22MnO3, at low temperature the magnetization at 1 kOe decreases from 31 to 21 emu/g (about 32%) while the Tc decreases

Another problem that must be faced is if it is necessary to increase the temperature up to 42 – 44 ºC in the whole tumour (so needing magnetic nanoparticles with very high magnetic moment or a very high concentration of nanoparticles) (Lacroix et al., 2009) in order to induce tumour damage or if it is enough to raise the temperature locally in the cells to induce apoptotic tumour death. The study of intracellular hyperthermia can shed light on

Biological tests with perovskites were performed in order to prove their validity as a heating source for tumour hyperthermia. They were put inside a culture of HeLa cells. HeLa cells are a family of tumour cells widely used by biologists. HeLa cells were incubated with a concentration of 0.5 mg/ml of perovskites for 3 h. After incubation, cells were washed 3 times with PBS and then exposed for 30 min to a 100 KHz alternating magnetic field

The cells incubated with the perovskites but without being submitted to an alternating magnetic field do not show any change, thus, demonstrating that the coating of the nanoparticles makes them biocompatible as expected. For the cells submitted to an alternating field the cell morphology was not affected immediately after the incubation and exposition to AMF. However, the perovskite + AMF treatment provoked deep morphological alterations, 24 h after the combined treatment, which corresponds to different stages of cell death by an apoptotic process. It is known that apoptosis is a regulated process which requires the active participation of specific molecules and is a characteristic mechanism of cell death for temperature around 42 ºC. The temperature increase of the culture during the application of the AMF (controlled by an infrared thermometer) was lower than 0.5 K for the PER incubated HeLa cells. This means that the small size of the perovskites cannot heat the cell culture. However, perovskites can induce local hot spots that damage irreversibly the structure and functionality of the cell proteins triggering the

they have to be coated with silica following the Stöber method (Stöber et al., 1968).

from 68 ºC to 44 ºC for the uncoated and the coated nanoparticles respectively.

this question.

of 15 mT.

cell apoptosis (Fig 12).

range) and they have large magnetization values of about 30 – 35 emu/g.
