A DURABLE, NON-POWER-CONSUMPTIVE, AND SIMPLE SEAL FOR ROTARY BLOOD PUMPS

Abstract

One the key technologies required for rotary blood pumps is the sealing of the motor shaft. A mechanical seal, a journal bearing, magnetic coupling and magnetic suspension have been developed, but they have drawbacks such as wear, thrombus formation, and power consumption. A ferrfluidic seal was developed for an axial flow pump. A ferrofluidic seals is durable, simple and non-power-consumptive. Long-term experiments and finite element modeling (FEM) analyses confirmed these advantages. The seal body was composed of a Ned-Fe magnet (Hc:-114kA/m, 8 mm in diameter and 1 mm in thickness) and two pole pieces (8 mm in diameter and 0.5 mm in thickness). This seal was formed by injecting ferrofluid into the gap (50 μm) between the pole pieces and the motor shaft (3 mm in diameter). To contain the ferrofluid in the seal and to minimize the possibility of ferrofluid making contact with blood, a shield with a small cavity was provided on the pole piece. Vibration of the motor shaft was maintained within 5 μm. The sealing pressure of the seal was measured while in blood. The sealing pressure was 188 mmHg with the ferrofluid LS-40 (Saturated magnetization: 24.3 kA/m) at a motor speed of 10,000 rpm and 225 mmHg in a static condition. The ferrofluidic seals have been perfect against pressure of 100 mmHg for 440+ days in static condition, and 51,39+ and 34+ days at a motor speed of 8,000 rpm. The FEM analyses indicated a theoretical sealing pressure of 260 mmHg. Leakage of the ferrofluid into water was measured with spectrophotometer. Leakage was not detected (less than the resolution). The specially designed ferrofluidic seal for sealing out liquids is useful for axial flow blood pumps. The ferrofluidic seal is incorporated into an intra-cardiac axial flow pump.