Ultrasonic manipulation of particles in microgravity

Abstract

The manipulation of yeast cells and latex particles of diameters 1.3, 12 and in aqueous suspension in 1 and 3 MHz ultrasonic standing waves has been examined and compared in microgravity (0 g), 1 g and 1.8 g. The experiments were carried out during the 23rd ESA parabolic flight campaign. The suspended particles concentrated to form bands at half wavelength separation in the axial direction of a vertical tubular sample holder with a Bessel pressure amplitude distribution profile. At 1 g small ( latex) particles formed bands but these broke up within a few seconds. In contrast throughout 0 g bands of these particles formed and remained stable. The transition from 0 to 1.8 g during flight induced streaming which broke up the bands of latex. Bands formed with yeast cells were more stable at 1 g but, during transitions from 0 to 1.8 g, some bands broke up. Bands of the larger (12 and ) particles were stable at 0, 1 and 1.8 g and during all transitions between the fields. Thermal gradient convective flow rather than acoustic streaming was identified as the main source of flow in the sample holder at 1 g. The absence of thermal streaming at 0 g allowed manipulation of smaller particles in that situation. A frequency ramping technique appropriate for removal of particles from suspension in 1 g had a better performance in 0 g.

Microstreaming effects on particle concentration in an ultrasonic standing wave

“…be expected to terminate so quickly. Hawkes et al 1998 showed that thermal streaming was essentially eliminated in a 5-cm path length multiwavelength standing-wave system in the environment. More recent work with a chamber as described here showed that streaming patterns that have been observed at 1 g continued during the 20-s duration of expo-Ž sure to microgravity J. J. Hawkes, personal communication,…”

Analysis of Gene Transfer Rate with Immobilized Retroviral Vectors

“…During acoustic exposure, microparticles (i.e., suspended cells) are driven to the pressure nodal planes by the primary radiation force, which then coalesce to form cell bands separated by half‐wavelength intervals 8 . Theoretically, suspension cells can arrive to the pressure nodal planes in a time scale of seconds, whereas the nanoparticles (i.e., viruses for this study) proceed over a time scale of minutes 9 . However, it is difficult for viruses to stay on pressure nodal planes because acoustic microstreaming‐induced drag force ( f ) imposed on viral nanoparticles is comparable to the primary radiation force Here, μ is fluid viscosity, R is particle radius, v is particle velocity, and U is microstreaming velocity 10 …”

“…8 Theoretically, suspension cells can arrive to the pressure nodal planes in a time scale of seconds, whereas the nanoparticles (i.e., viruses for this study) proceed over a time scale of minutes. 9 However, it is difficult for viruses to stay on pressure nodal planes because acoustic microstreaming-induced drag force (f ) imposed on viral nanoparticles is comparable to the primary radiation force…”

Scaling-up ultrasound standing wave enhanced sedimentation filters

“…However, cross-flow as low as 200 lm s À1 will move yeast cells away from the nodal regions and destroy the bands [11,49,50]. Since most bands of yeast cells form parallel to the duct wall it is important to minimise crossflow within the duct.…”