Quantification of a novel h‐shaped ultrasonic resonator for separation of biomaterials under terrestrial gravity and microgravity conditions

A novel, h‐shaped ultrasonic resonator was used to separate biological particulates. The effectiveness of the resonator was demonstrated using suspensions of the cyanobacterium, Spirulina platensis . The key advantages of this approach were improved acoustic field homogeneity, flow characteristics, and overall separation efficiency (σ = 1 − ratio of concentration in cleared phase to input), monitored using a turbidity sensor. The novel separation concept was also effective under microgravity conditions; gravitational forces influenced overall efficiency. Separation of Spirulina at cleared flow rates of 14 to 58 L/day, as assessed by remote video recording, was evaluated under both microgravity (≤0.05 g ) and terrestrial gravity conditions. The latter involved a comparison with 5‐ and 24‐μm‐diameter polystyrene microspheres. Influences of gravity on σ were evaluated by varying the relative inclination angle (within a range of 120°) between the resonator and the gravitational vector. Cells of Spirulina behaved in a manner comparable to that of the 5‐μm‐diameter polystyrene microspheres, with a significant decrease in mean (±SE, n = 3) σ from 0.97 ± 0.03 and 0.91 ± 0.02 at a flow rate of 14 L/day, to corresponding values of 0.53 ± 0.05 and 0.57 ± 0.03 ( P < 0.05) at 58 L/day, respectively. During a typical microgravity period of ca. 22 s, achieved during the 29th ESA Parabolic Flight Campaign, σ was unchanged at a flow rate of 14 L/day, compared with terrestrial gravity conditions; with increased flow rates, σ was significantly reduced. Overall, these results demonstrate that, for optimum resonator performance under the relatively short microgravity period utilized in this study, flow rates of ca. 14 L/day were preferred. These data provide a baseline for exploiting noninvasive, compact, ultrasonic separation systems for manipulating biological particulates under microgravity conditions. © 2003 Wiley Periodicals, Inc. Biotechnol Bioeng 82: 74–85, 2003.