Background/Case Studies: Acoustophoresis is a contactless technology that uses low acoustic radiation forces to make cells and other physical objects migrate to a specific part of a fluidic channel. It is a safer and more versatile alternative to most centrifugation protocols. Aenitis uses acoustophoresis in a millifluidic channel to sort, wash or concentrate all kinds of cells and tissues, without no change in cell viability.
Study
Design/Methods: By using a channel configuration with one inlet and three outlets (see fig. 1), and a pressure node in the middle of the channel, cells migrate to the node and exit via the central outlet. With a 100% yield, the concentration will be multiplied by 3. The acoustic force is proportional to the volume of the cell. Moreover, for a given acoustic chamber, increasing the flow rate means the cells travel faster in front of the ultrasound transducer. Smaller cells will then be more difficult to concentrate at higher flow rates. This has applications in bioproduction for a vast array of biological products, such as platelet concentrates, mammalian cells, primary cells or white blood cells. In this study, high flow rates were investigated for two different cell sizes: red blood cells (6-7 µm) and Jurkat cells (10-16 µm).
Results/Findings: In microfluidics applications, flow rate is kept under 0.1 ml/min. Aenitis’ cell production device has been designed for flow rates starting at 1 ml/min. For each flow rate, the acoustic power is increased so that the cells migrate faster toward the pressure node. Results on fig. 1 show that for Jurkat cells, in average over 95 % of the cells are concentrated at flow rates up to 40 ml/min which is the physical limit of our pumps. For red blood cells, 40 ml/min was investigated and similar yields were found. It was also demonstrated that Jurkat cell viability was not affected by acoustophoresis. Experiments showed a viability above 95%, for all flow rates and powers from 5 to 30 W. Acoustic waves are usually only harmful to cells when cavitation occurs, which is not the case at the low acoustic pressures used in acoustophoresis. Conclusions: High flow rate reconcentration of Jurkat cells and red blood cells was achieved, recovering more than 90% of the cells up until flow rates of 40 ml/min, without any change of viability due to the acoustic waves. The concentration is multiplied by more than 2.7 for all cases.
With the acoustic power used in this study, concentration tests with high flow rate pumps up until 100 ml/min should be successful with similar yields and viability. Flow rates in the range 10-40 ml/min are also being explored for 3 inlet/3 outlet channels in order to wash enzymes or debris from various cell products.
Importance of research: Previous acoustophoresis technologies focused on diagnostic applications, at the microfluidic scale. A common application is to try to separate cancer cells from healthy cells. Expensive silicon and glass channels are often used for this purpose, at flow rates on the order of 10-500 µl/ml. This new technology combines plastic and stainless-steel disposable channels in order to achieve higher flow rates between 5 and 40 ml/min.
