Separation of microspheres via travelling surface acoustic waves

Acoustofluidic particle separator with submicron separation resolution based on their acoustofluidic parameters such as size, density, compressibility and shapeTSAWs of different frequencies used to realize continuous separation of particles as low as 200 nm.Separation of submicron microspheres via TSAWDestgeer et.al - Lab on Chip 2014

Previous seprations involved SSAW with trapping particles at the PNs.Precise controlling PNs is necessary. The use of chirped and slanted IDTs has resolved this issue to some extent as the position of the PN can be manipulated easily but the microchannel still needs to be parallel with the IDTsTilted-angle SSAW device was used which does not require to be tightly aligned with the microchannel

TSAW is easy to integrate and flexibleA single IDT is used to generate the TSAW and no significant reflection of waves from walls was ensured so that no SSAW is formedSeparation based on ARF dimensionless parameter = ka is defined, such that k = 2f/c The magnitude of the ARF is determined by the size of the particle relative to the wavelength ofthe TSAW and the density difference between the fluid and the particle

Separation tested using PS microspheres with mean diameters of 0.71, 3.0, 3.2, 3.4, 4.2, 4.5 and 5.0 m.Frequencies of 129, 155 and 192 MHz were usedThe power input was switched on from 0 mW to 19.2 mW, producing a shift in the particles streamlines aiding in separationAnother device with a normal section was introduced where the vortices seem stronger and affects the trajectories of the particles but still separation was possibleFurther Work: The separation diseased cells from a blood sample May be useful for isolation of target cells that are insignificantly different in size than others, eg. diabetic fat cells from healthy fat cells

Microscale anechoic architecture: acoustic diffusers for ultra low power microparticle separation via traveling surface acoustic wavesA very low-power traveling SAW microfluidic sorting device able to displace and separate particles of different diameter in aqueous suspensionNo need on amplifiers The travelling wave propagates through the fluid bulk and diffuses via a Schrder diffuser eliminated SSAWSSAW devices have a plane of symmetry down the middle of the microfluidic channel reducing by half the effective length of actuation across the channelPrevious studies - SAW for particle deflection, but also was responsible for acoustic streaming - disturbing particle trajectories by vortices.Unfortunately, standing waves are generated by confinement using material with a nearly identical acoustic impedance, for example, water as bounded by PDMSIf pure traveling waves could be generated, particle positioning could be controlled based upon the time of exposure because the force upon a particleSchrder diffuser used to generate TSAW through diffusion of reflections from the wall of the microfluidics.Doing so, the power required to separate microparticles is two orders of magnitude lower than SSAWA Schrder diffuser was fabricated in Si opposite to an IDT.Si is used as it has different acoustic impedance than waterFluorescent polystyrene particles 4.5, 25, and 45 m were separated in the said deviceThe 2 mW power and 30 MHz was used45 m was deflected amidst 4.5 m particles Both 25 m and 45 m particles were translated upon exposure to 2 mW SAWBelow 0.5 mW the particles were displaced but did not separate & above 2.75 mW the diffused acoustic radiation interfere forming a weak standing wave

By using a higher frequency of 50 MHz, it was possible to move the 25 m particle over distances similar to what was achieved with 45 m By increasing the frequency further the transport of even smaller particles should be possible.By fabrication limitations - UVL size @ 1 m

Standing Surface Acoustic Wave Based Cell CoculturePrecise reconstruction of heterotypic cellcell interactions in vitro requires the coculture of different cell typesStanding surface acoustic wave (SSAW)-based cell coculture platform. Different types of cells are patterned sequentially in the SSAW field to form an organized cell coculture. A coculture of epithelial cancer cells and endothelial cells was doneThe differences in intercellular adhesiveness between different cell types can drive the movement and assortment of cells. However, the organization of cell coculture arising from DAH is governed by spontaneous rearrangement of cells with little control on the final cell pattern. Micropatterning, DEP, cell printing commonly used for organized cell cocultures Problems with passive process & low controllability, mechanical stimuli, use of ionic liquids SSAW-based technique can position multiple cell types using noninvasive, contactless acoustic forces with high precision and high tunability. With flexibility to operate in literally any medium and with different types of adherent cells

when the RF signal is on, cells will be aligned in parallel lines in the established SSAW field. (12.78 MHz; RF signal V = 20 Vpp)When the RF signal is off, cells eventually settle down inside the microchannel & maintain their original pattern attaching to the surface forming a patterned cell culture ~ 1hr.Growth of the cells during this time did not affect the patterning much For an organized cell coculture, different types of cells need to be patterned in different positions, which requires changing the distribution of pressure nodes and antinodesThe interactions between epithelial cancer cells and endothelial cells was studied. HeLa cells and HMVEC-d cells as the biological modelHeLa cells pattern determined first after 24 h, the pattern of alternate lines was not disrupted, indicating that low HeLa cell mobility in monocultureThen our coculture experiment, HMVEC-d cells were introduced after 1 h. At 2 h time point of coculture - HMVEC-d cells and HeLa cells grew in alternate line regions. However, at 24 h time point the organized HeLa cell pattern was clearly disrupted indicating high HeLa cell mobility when cocultured with HMVEC-d cellsHeLa cells with HMVEC-d cells had higher mobility than those cultured alone. This mobility in is due to the cross-talk initiated by endothelial cells, which enhances cancer cell survival and mobility through STAT3/Akt/ERK, 51 integrin, and GTPases signaling pathwayIndicates that the presence of endothelial cells increases the mobility of cancer cells either in a random coculture or in an organized cocultureGreater organization in the chip causes a better mobility in HeLa cells compared to different culture methodsAcoustic Purication of ExtracellularMicrovesiclesKyungheon Lee ACS Nano 2014The small size of MVs and their presence in complex biological environment pose technical challenges in sample preparation esp. in small sample volumes. Developed an acoustic nanofilter system that size-specifically separates MVs in a continuous and contact-free manner.Ultrasound standing waves exert differential acoustic force on MVs based on size and densityMVs are membrane-bound phospholipid vesicles and are actively secreted by cells into the circulation. The vesicles carry molecular constituents of their originating cellsAn acoustic nanofilter system developed to separate MVs from other contents of biological samples. hypothesized that acoustic forces could be used to fractionate MVs according to their size, thereby enabling size-selective MV isolation on chipParticles in an acoustic field experience radiation forces and migrate toward the pressure nodes. Larger particle thus move faster to the pressure nodes, and can be transferred into sheath streams to exit. Signal frequency for SSAW generation was 38.5 MHz

System evaluated with Polystyrene beads, MVs from RBCs & exosomes The separation efficiency was determined from the fluorescence intensity of the collected particles and showed >90% for both small and large particles (190nm, 1000nm)The recovery rates, estimated from fluorescence intensity measurements, were >80% for exosomes RBC-MVs were seperated & enriched and the size of the collected RBC-MVs was