Motorized implants: the EC-13 motor

Some patients with ascites need to undergo regular draining with a needle to remove the excessive amounts of fluid that accumulate in their abdomen. The Swiss company Sequana Medical has found a solution by developing an active implant designed to regulate the accumulation of fluid in the peritoneal cavity. maxon’s EC motors, embedded in the devices, ensure the perfect and regular motion of the pump.

No more fluid aspiration with needles, thanks to the ALFApump system

Ascites, also called peritoneal fluid buildup, is the accumulation of a large amount of fluid in the peritoneal cavity. Usually treatment with medication and a special diet is enough to eliminate the fluid. However, this treatment does not always work: as much as two liters of fluid a day can build up in some patients, requiring them to undergo regular aspiration (draining with a needle).

But there is good news: Swiss company Sequana Medical has developed the ALFApump, an active implant that simplifies the lives of these patients. The system monitors the volume of fluid in the peritoneal cavity and pumps the fluid into the bladder, where it is then discharged with the urine. The system is centered around the ALFApump implant and two catheters going to the abdominal cavity and the bladder. It is accompanied by an external charger, which both charges the battery of the ALFApump implant and communicates with it.

Continuous monitoring with a laptop

The energy demand of the pump makes regular charging essential. But there is no need to plug anything in: It is simply done through the patient’s skin. Continuous monitoring is performed by a laptop computer, which the physician can use to program the implant for each patient and precisely specify how much fluid should be pumped into the bladder.

The ALFApump implant is placed between the abdominal fat layer and the peritoneum, and is made of biocompatible PEEK plastic (polyether ether ketone). The conditions prevailing in the human body require special motors and adapted electronics, because hermetically sealed encapsulation is not possible when the material used is plastic.

Permanent exposure to moisture and a high salt concentration must therefore be taken into account when selecting the materials. Additionally, a constant temperature of no more than 40 degrees has to be ensured. Therefore, the implant is sealed completely due to the ambient moisture, its electronics are protected by an additional coating, and the motor used is brushless.

High torque, even in normal operation

A complex electronic system handles low-level control of the motor, control of the pump, processing of the sensor signals, communication with the SmartCharger, and battery management. The gear pump has to pump not only the fluid, but also any air that might be enclosed (e.g., after an operation). Therefore, it is very important that very restricted tolerances are maintained; this in turn requires high torque, even during normal operation.

Operation is additionally hampered by the fact that the fluid to be removed contains high quantities of fibrin and protein from the blood plasma. These can easily clot, seriously impeding the operation of the pump. In the worst case, the pump can seize up completely. To prevent this from occurring, it is recommended to have the pump operate briefly at regular intervals without circulating any fluid.

The maxon EC 13 motor, adapted to the customer’s specific requirements, drives the pump gears of the ALFApump. The motor is equipped with Hall effect sensors that stabilize its operation and make it reliable, in particular at low speeds and high load torques.

Two processors for maximum monitoring

The stator of the sterilizable motor has a special coating, and the shaft is made from biocompatible materials. Additionally, the shaft has to be designed with special geometry. The compact design of the EC 13 motor, its excellent low-noise and low-vibration running properties, and its low heat emission make it especially suitable for use in medical technology.

To increase patient safety, a dedicated processor is used for motor control. The main processor configures the motor controller, to achieve the desired flow rate. This motor controller checks that the corresponding parameters are valid. If, for example, there is a deviation from the permissible duration of pump operation, the main processor de-energizes the motor subsystem. Thanks to this dual processor system, maximum monitoring during the pumping procedure is guaranteed, which ensures optimal operating reliability and thus also patient safety.

The motorization used

The maxon EC 13 motor drives the pump gears of the ALFApump system. The motor is equipped with Hall effect sensors that stabilize its operation and make it reliable, in particular at low speeds and high load torques.

The first two commercial operations to implant a pump system were performed in October 2011 in Vienna, Austria. According to Prof. Markus Peck-Radosavljevic, Vice-Chairman of the Division of Gastroenterology and Hepatology, both short operations were completed without complications. “I believe that the ALFApump system is a real breakthrough in the treatment of ascites. The patients can lead an easier life, as they no longer need to go to hospital for the arduous drainage procedure,” said Peck-Radosavljevic.