Cell separation Cells with different densities and compression strengths can theoretically be separated with<unk>  force. It has been suggested that<unk>  could be used to separate lipid particles from red blood cells. This is a problem during cardiac surgery supported by a heart-lung machine, for which current technologies are insufficient. According to the proposal,<unk>  force applied to blood plasma passing through a channel will cause red blood cells to gather in the pressure node in the center and the lipid particles to gather in antinodes at the sides (see Figure 4). At the end of the channel, the separated cells and particles exit through separate outlets. The<unk>  method might also be used to separate particles of different sizes. According to the equation of primary<unk>  radiation force, larger particles experience larger forces than smaller particles. Shi et al. reported using interdigital transducers (IDTs) to generate a standing surface<unk>  wave (SSAW) field with pressure nodes in the middle of a microfluidic channel, separating microparticles with different diameters. When introducing a mixture of particles with different sizes from the edge of the channel, larger particles will migrate toward the middle more quickly and be collected at the center outlet. Smaller particles will not be able to migrate to the center outlet before they are collected from the side outlets. This experimental setup has also been used to separate blood components, bacteria, and hydrogel particles. 3D cell focusing Fluorescence-activated cell sorters (FACS) can sort cells by focusing a fluid stream containing the cells, detecting fluorescence from individual cells, and separating the cells of interest from other cells. They have high throughput but are expensive to purchase and maintain, and are bulky with a complex configuration. They also affect cell physiology with high shear pressure, impact forces and electromagnetic forces, which may result in cellular and genetic damage.<unk>  forces are not dangerous to cells, and there has been progress integrating<unk>  with optical/electrical modules for simultaneous cell analysis and sorting, in a smaller and less-expensive machine.<unk>  have been developed to achieve 3D focusing of cells/particles in microfluidics. A pair of interdigital transducers (IDTs) are deposited on a piezoelectric substrate, and a microfluidic channel is bonded with the substrate and positioned between the two IDTs. Microparticle solutions are infused into the microfluidic channel by a pressure-driven flow. Once an RF signal is applied to both IDTs, two series of surface<unk>  waves (SAW) propagate in opposite directions toward the particle suspension solution inside the microchannel. The constructive interference of the two SAWs results in the formation of a SSAW. Leakage waves in the longitudinal mode are generated inside the channel, causing pressure fluctuations that act laterally on the particles. As a result, the suspended particles inside the channel will be forced toward either the pressure nodes or antinodes, depending on the density and compressibility of the particles and the medium. When the channel width covers only one pressure node (or antinode), the particles will be focused in that node. In addition to focusing in a horizontal direction, cells/particles can also be focused in the vertical direction. After SSAW is on, the randomly distributed particles are focused into a single file stream (Fig. 10c) in the vertical direction. By integrating a standing surface<unk>  wave (SSAW)-based microdevice capable of 3D particle/cell focusing with laser-induced fluorescence (LIF) detection system,<unk>  are developed into a microflow cytometer for high-throughput single cell analysis. The tunability offered by chirped interdigital transducers renders it capable of precisely sorting cells into a number (e.g., five) of outlet channels in a single step. This is a major advantage over most existing sorting methods, which typically only sort cells into two outlet channels. Noninvasive cell trapping and patterning A glass reflector with etched fluidic channels is clamped to the PCB holding the transducer. Cells infused into the chip are trapped in the ultrasonic standing wave formed in the channel. The<unk>  forces focus the cells into clusters in the center of the channel as illustrated in the inset. Since the trapping occurs close to the transducer surface, the actual trapping sites are given by the near-field pressure distribution as shown in the 3D image. Cells will be trapped in clusters around the local pressure minima creating different patterns depending on the number of cells trapped. The peaks in the graph correspond to the pressure minima. Manipulation of single cell, particle, or organism Fig. 4: Traces of single cell manipulation Manipulating single cells is important to many biological studies, such as in controlling the cellular microenvironment and isolating specific cells of interest.<unk>  have been demonstrated to manipulate each individual cell with micrometer-level resolution. Cells generally have a diameter of 10–20 μm. To meet the resolution requirements of manipulating single cells, short-wavelength<unk>  waves should be employed. In this case, a surface<unk>  wave (SAW) is preferred to a bulk<unk>  wave (BAW), because it allows using shorter-wavelength<unk>  waves (normally less than 200 μm). Ding et al. reported a SSAW microdevice that is able to manipulate single cells with prescribed paths. Figure 6 records a demonstration that the movement of single cells can be finely controlled with<unk> . The working principle of the device lies in the controlled movement of pressure nodes in an SSAW field. Ding et al. employed chirped interdigital transducers (IDTs) that are able to generate SSAWs with adjustable positions of pressure nodes by changing the input frequency. They also showed that the millimeter-sized microorganism C. elegan can be manipulated in the same manner. They also examined cell metabolism and proliferation after<unk>  treatment, and found no significant differences compared to the control group, indicating the non-invasive nature of<unk>  base manipulation. In addition to using chirped IDTs, phaseshift-based single particle/cell manipulation has also been reported. Manipulation of single biomolecules Sitters et al. have shown that<unk> s can be used to manipulate single biomolecules such as DNA and proteins. This method, which the inventors call<unk>  force spectroscopy, allows measuring the force response of single molecules. This is achieved by attaching small microspheres to the molecules at one side and attaching them to a surface at the other. By pushing the microspheres away from the surface with a standing<unk>  wave the molecules are effectively stretched out. Manipulation of organic nano-materials Polymer-dispersed liquid crystal (PDLC) displays can be switched from opaque to transparent using<unk> . A SAW-driven PDLC light shutter has been demonstrated by integrating a cured PDLC film and a pair of interdigital transducers (IDTs) onto a piezoelectric substrate. Manipulation of inorganic nano-materials<unk>  provide a simple approach for tuneable nanowire patterning. In this approach, SSAWs are generated by interdigital transducers, which induced a periodic alternating current (AC) electric field on the piezoelectric substrate and consequently patterned metallic nanowires in suspension. The patterns could be deposited onto the substrate after the liquid evaporated. By controlling the distribution of the SSAW field, metallic nanowires are assembled into different patterns including parallel and perpendicular arrays. The spacing of the nanowire arrays could be tuned by controlling the frequency of the surface<unk>  waves. Selective manipulation While most<unk>  are able to manipulate a large number of objects collectively, a complementary function is to be able to manipulate a single particle within a cluster without moving adjacent objects. To achieve this goal, the<unk>  trap must be localized spacially. A first approach consists in using highly focused<unk>  beams. Since many particles of interest are attracted to the nodes of an<unk>  field and thus expelled from the focus point, some specific wave structures combining strong focalization but with a minimum of the pressure amplitude at the focal point (surrounded by a ring of intensity to create the trap) are required to trap this type of particle. These specific conditions are met by Bessel beams of topological order larger than zero, also called<unk> al vortices". With this kind of wave structures, the 2D and 3D selective manipulation of particles has been demonstrated with an array of transducers driven by programmable electronics. Alternatively, another approach to localize the<unk>  energy relies on the use of nanosecond-scale pulsed fields to generate localized<unk>  standing waves. High frequency<unk>  and holographic InterDigitated Transducers (IDTs) The individual selective manipulation of micro-objects requires to synthesize complex<unk>  fields such as<unk>  vortices (see previous section) at sufficiently high frequency to reach the necessary spatial resolution (typically the wavelength must be comparable to the size of the manipulated object to be selective). Many holographic methods have been developed to synthesize complex wavefields including transducer arrays, 3D printed holograms, metamaterials or diffraction gratings. Nevertheless all these methods are limited to relatively low frequencies with an insufficient resolution to address micrometric particles, cells or microorganisms individually. On the other hand, InterDigitated Transducers (IDTs) were known as a reliable technique to synthesize<unk>  wavefields up to GHz frequency.
Acoustic tweezers
Magill forceps
Metzenbaum scissors
Tenotomy scissors
Debakey forceps
Mayo scissors
Surgical mask
Surgical elevator