Mathias Ohlin

Ultrasound-controlled cell aggregation in a multi-well chip

We demonstrate a microplate platform for parallelized manipulation of particles or cells by frequency-modulated ultrasound. The device, consisting of a silicon-glass microchip and a single ultrasonic transducer, enables aggregation, positioning and high-resolution microscopy of cells distributed in an array of 100 microwells centered on the microchip. We characterize the system in terms of temperature control, aggregation and positioning efficiency, and cell viability. We use time-lapse imaging to show that cells continuously exposed to ultrasound are able to divide and remain viable for at least 12 hours inside the device. Thus, the device can be used to induce and maintain aggregation in a parallelized fashion, facilitating long-term microscopy studies of, e.g., cell-cell interactions.

Influence of acoustic streaming on ultrasonic particle manipulation in a 100-well ring-transducer microplate

We characterize and quantify the performance of ultrasonic particle aggregation and positioning in a 100-well microplate. We analyze the result when operating a planar ultrasonic ring transducer at ...

Temperature-controlled MPa-pressure ultrasonic cell manipulation in a microfluidic chip

We study the temperature-independent impact on cell viability of relevant physical parameters during long-term, high-acoustic-pressure ultrasonic exposure in a microfluidic chip designed for ultrasonic-standing-wave trapping and aggregation of cells. We use a light-intensity method and 5 μm polymer beads for accurate acoustic pressure calibration before injecting cells into the device, and we monitor the viability of A549 lung cancer cells trapped during one hour in an ultrasonic standing wave with 1 MPa pressure amplitude. The microfluidic chip is actuated by a novel temperature-controlled ultrasonic transducer capable of keeping the temperature stable around 37 °C with an accuracy better than ±0.2 °C, independently on the ultrasonic power and heat produced by the system, thereby decoupling any temperature effect from other relevant effects on cells caused by the high-pressure acoustic field. We demonstrate that frequency-modulated ultrasonic actuation can produce acoustic pressures of equally high magnitudes as with single-frequency actuation, and we show that A549 lung cancer cells can be exposed to 1 MPa standing-wave acoustic pressure amplitudes for one hour without compromising cell viability. At this pressure level, we also measure the acoustic streaming induced around the trapped cell aggregate, and conclude that cell viability is not affected by streaming velocities of the order of 100 μm s(-1). Our results are important when implementing acoustophoresis methods in various clinical and biomedical applications.

Ultrasound-Induced Cell–Cell Interaction Studies in a Multi-Well Microplate

This review describes the use of ultrasound for inducing and retaining cell-cell contact in multi-well microplates combined with live-cell fluorescence microscopy. This platform has been used for s ...

An intra-droplet particle switch for droplet microfluidics using bulk acoustic waves

To transfer cell- and bead-assays into droplet-based platforms typically requires the use of complex microfluidic circuits, which calls for methods to switch the direction of the encapsulated particles. We present a microfluidic chip where the combination of acoustic manipulation at two different harmonics and a trident-shaped droplet-splitter enables direction-switching of microbeads and yeast cells in droplet microfluidic circuits. At the first harmonic, the encapsulated particles exit the splitter in the center daughter droplets, while at the second harmonic, the particles exit in the side daughter droplets. This method holds promises for droplet-based assays where particle-positioning needs to be selectively controlled.

Particle Manipulation Methods in Droplet Microfluidics

This Feature describes the different particle manipulation techniques available in the droplet microfluidics toolbox to handle particles encapsulated inside droplets and to manipulate whole droplets. We address the advantages and disadvantages of the different techniques to guide new users.

Chapter 13:Applications of Acoustic Streaming

In this chapter, we provide a qualitative description of acoustic streaming and review its applications in lab-on-a-chip devices. It covers boundary layer driven streaming, including Schlichting and Rayleigh streaming, Eckart streaming in the bulk fluid, cavitation microstreaming and surface-acousticwave- driven streaming.

Acoustic formation of multicellular tumor spheroids enabling on-chip functional and structural imaging

Understanding the complex 3D tumor microenvironment is important in cancer research. This microenvironment can be modelled in vitro by culturing multicellular tumor spheroids (MCTS). Key challenges when using MCTS in applications such as high-throughput drug screening are overcoming imaging and analytical issues encountered during functional and structural investigations. To address these challenges, we use an ultrasonic standing wave (USW) based MCTS culture platform for parallel formation, staining and imaging of 100 whole MCTS. A protein repellent amphiphilic polymer coating enables flexible production of high quality and unanchored MCTS. This enables high-content multimode analysis based on flow cytometry and in situ optical microscopy. We use HepG2 hepatocellular carcinoma, A498 and ACHN renal carcinoma, and LUTC-2 thyroid carcinoma cell lines to demonstrate (i) the importance of the ultrasound-coating combination, (ii) bright field image based automatic characterization of MTCS, (iii) detailed deep tissue confocal imaging of whole MCTS mounted in a refractive index matching solution, and (iv) single cell functional analysis through flow cytometry of single cell suspensions of disintegrated MTCS. The USW MCTS culture platform is customizable and holds great potential for detailed multimode MCTS analysis in a high-content manner.

On-chip acoustic sample preparation for cell studies and diagnostics

We describe a novel platform for acoustic sample preparation in microchannels and microplates. The utilized method is based on generating a multitude of acoustic resonances at a set of different frequencies in microstructures, in order to accurately control the migration and positioning of particles and cells suspended in fluid channels and chambers. The actuation frequencies range from 30 kHz to 7 MHz, which are applied simultaneously and/or in sweeps. We present two devices: A closed microfluidic chip designed for pre-alignment, size-based separation, isolation, up-concentration and lysis of cells, and an open multi-well microplate designed for parallel aggregation and positioning of cells. Both devices in the platform are compatible with high-resolution live-cell microscopy, which is used for fluorescence-based optical characterization. Two bioapplications are demonstrated for each of the devices: The first device is used for size-selective cell isolation and lysis for DNA-based diagnostics, and the second device is used for quantifying the heterogeneity in cytotoxic response of natural killer cells interacting with cancer cells.

Ultrasonic standing waves for dynamic micro-array cytometry

We describe a novel platform for dynamic micro-array cytometry (DMAC), i.e., parallel screening of individual cell-cell interactions based on ultrasonic standing wave aggregation and positioning of cells in a multi-well microplate. Upon ultrasound actuation, clusters containing one or a few cells are quickly formed and retained in a precise location synchronously in each of the 100 wells on the microplate. By combining the acoustic cell handling tool with high-resolution fluorescence microscopy, detailed time-lapse monitoring of individual cell-cell interactions in a highly parallel manner is possible. Of particular interest in our group is to study the long-term interaction between natural killer (NK) cells and different target cells at the level of single cells. In this talk we demonstrate both theoretically and experimentally how to design a microchip capable of trapping and positioning individual cells by ultrasound in a highly parallel manner, and with a spatial accuracy of the order of a cell diamet...