High‐throughput formation of miniaturized cocultures of 2D cell monolayers and 3D cell spheroids using droplet microarray

Most of the biological processes,including cell signaling,cancer invasion,embryogenesis,or neural development,are dependent on and guided by the complex architecture and composition of cellular microenvironments.Mimicking such microenvironments in cell coculture models is crucial for fundamental and applied biology investigations.The ability to combine different cell types grown as both two‐dimensional(2D)monolayers and three‐dimensional(3D)spheroids in specific defined location inside a microculture environments is a key towards in vitro tissue modeling and towards mimicking complex in vivo cellular processes.In this study,we introduce and investigate a method to create in vitro models of 2D cell monolayers cocultured with 3D spheroids in defined preorganization.We demonstrate the possibility of creating such complex cellular microenvironments in a high‐throughput and automated manner by creating arrays of such droplets containing prearranged 2D and 3D cellular microcolonies.Furthermore,we demonstrate an application of this approach to study paracrine propagation of Wnt signaling between 2D and 3D cellular colonies.This method provides a general approach for the miniaturized,high‐throughput,and automated formation of complex coculture cellular microarchitectures that will be useful for mimicking various in vivo complex cellular structures and for studying complex biological processes in vitro.

Opto-fluidically multiplexed assembly and micro-robotics

Techniques for high-definition micromanipulations,such as optical tweezers,hold substantial interest across a wide range of disciplines.However,their applicability remains constrained by material properties and laser exposure.And while microfluidic manipulations have been suggested as an alternative,their inherent capabilities are limited and further hindered by practical challenges of implementation and control.Here we show that the iterative application of laser-induced,localized flow fields can be used for the relative positioning of multiple micro-particles,irrespectively of their material properties.Compared to the standing theoretical proposal,our method keeps particles mobile,and we show that their precision manipulation is non-linearly accelerated via the multiplexing of temperature stimuli below the heat diffusion limit.The resulting flow fields are topologically rich and mathematically predictable.They represent unprecedented microfluidic control capabilities that are illustrated by the actuation of humanoid micro-robots with up to 30 degrees of freedom,whose motions are sufficiently well-defined to reliably communicate personal characteristics such as gender,happiness and nervousness.Our results constitute high-definition micro-fluidic manipulations with transformative potential for assembly,micro-manufacturing,the life sciences,robotics and optohydraulically actuated micro-factories.

Two-beam phase correlation spectroscopy:a label-free holographic method to quantify particle flow in biofluids

We introduce two-beam phase correlation spectroscopy(2B-ΦCS)as a label-free technique to measure the dynamics of flowing particles;e.g.,in vitro or in vivo blood flow.2B-ΦCS combines phase imaging with correlation spectroscopy,using the intrinsic refractive index contrast of particles against the fluid background in correlation analysis.This method starts with the acquisition of a time series of phase images of flowing particles using partially coherent point-diffraction digital holographic microscopy.Then,phase fluctuations from two selected circular regions in the image series are correlated to determine the concentration and flow velocity of the particles by fitting pair correlation curves with a physical model.2B-ΦCS is a facile procedure when using a microfluidic channel,as shown by the measurements on flowing yeast microparticles,polymethyl methacrylate microparticles,and diluted rat blood.In the latter experiment,the concentration and average diameter of rat blood cells were determined to be(4.7±1.9)×10^(6)μL^(-1)and 4.6±0.4μm,respectively.We further analyzed the flow of mainly red blood cells in the tail vessels of live zebrafish embryos.Arterial and venous flow velocities were measured as290±110μm s^(-1)and 120±50μm s^(-1),respectively.We envision that our technique will find applications in imaging transparent organisms and other areas of the life sciences and biomedicine.