An ultrasonic method for filtering and separating cell suspensions

Continuous flow filtration of cell suspensions has recently become possible using ultrasound standing wave enhanced sedimentation. A filter which can be operated at either 1 or 3 MHz is described. At both 1 MHz and 3 MHz yeast cells (4.6 μm diameter) can be filtered at greater than 99% efficiency at a flow rate of 5 ml min^-1. Smaller cells such as E. coli (1.3 μm diameter) were efficiently filtered at 3 MHz. This frequency dependent filtration suggests two modes of operations as (1) a filter to remove cells from suspension, or (2) a separator to separate a mixture of large (yeast) and small (E. coli) cells