Patterning of microspheres and microbubbles in an acoustic tweezers

Abstract

We describe the construction of an ultrasonic device capable of micro-patterning a range of microscopic particles for bioengineering applications such as targeted drug delivery. The device is formed from seven ultrasonic transducers positioned around a heptagonal cavity. By exciting two or three transducers simultaneously, lines or hexagonal shapes can be formed with microspheres, emulsions and microbubbles. Furthermore, phase control of the transducers allows patterning at any desired position in a controlled manner. The paper discusses in detail direct positioning of functionalised microspheres, emulsions and microbubbles. With the advantages of miniaturization, rapid and simple fabrication, ultrasonic tweezers is a potentially useful tool in many biomedical applications.

Microfluidic bio-particle manipulation for biotechnology

“…ACT methods have been implemented for bio-particle wash [95,47,96,84,125,92], trapping [125,92,[126][127][128][129][130][131][132][133][134] and separation [69,108,85,91,9,81,135,94,136,137]. Bio-particle washing relies on focusing the particles to the center of the channel, and out flowing the bio-particles collected at the center into another suspension medium.…”

“…Moreover, using trapping force, patterning of bio-particles at certain locations may also be utilized for the collection of bio-particles for bio-assaying applications [92,127]. In order to generate the acoustic waves for trapping the bio-particles, confocal piezoelectric materials which are able to focus ultrasonic waves [128], as well as configurations of piezoelectric transducer in transversal and layered configurations [129] may be used. The piezoelectric material may be placed directly in contact with the fluid where particles were suspended, and particles can consequently be trapped under the generated acoustic radiation force [130].…”

Ultrasound assisted particle and cell manipulation on-chip

“…Bernassau et al [96] used bulk acoustic waves generated by a heptagonal arrangement of transducers to act as an ultrasonic stencil, to deposit predefined patterns of cells on a glass cover slip and also demonstrated the ability to place different batches of cells at predefined relative positions. The group has also demonstrated the ability to pattern functionalised microspheres and microbubbles with the same technology [97]. Finally, the use of ultrasound transducer arrays holds significant promise for adaptive systems in which cell positions are monitored, allowing the electronic signals driving the array to be adjusted as the cell cultures develop.…”

“…This provides significant potential for building and investigating tissue constructs on-chip and provides a useful tool in exploring cell-cell interaction [101]. Devices with more dexterous manipulation abilities [46,97] should be able to extend this capability, for example by allowing different cell types to be brought together in a highly controlled environment. There is also potential to use acoustic manipulation in conjunction with other force fields such as optical tweezers or dielectrophoresis that have a more local scale of action [136], taking advantage of the strengths of both approaches.…”

Acoustic tweezing for patterning and discriminating particles

“…When two opposing transducers are excited, a linear interference pattern of nodes and antinodes is formed in the interstitial media. The micro-particles are trapped at the minima of the potential acoustic energy density [9]. Electronically shifting the excitation phase of one of the transducers, with respect to the other, proportionally translates the linear interference pattern in the direction of the added phase delay.…”