Cell-cell communication is a crucial component of many biological functions. For example, understanding how immune cells and cancer cells interact, both at the immunological synapse and through cytokine secretion, can help us understand and improve cancer immunotherapy. The study of how cells communicate and form synaptic connections is important in neuroscience, ophthalmology, and cancer. But in order to increase our understanding of these cellular phenomena, better tools need to be developed that allow us to study cell-cell communication in a highly controlled manner. Some technical requirements for better communication studies include manipulating cells spatiotemporally, high resolution imaging, and integrating sensors. Microfluidics is a powerful platform that has the ability to address these requirements and other current limitations. In this review, we describe some new advances in microfluidic technologies that have provided researchers with novel methods to study intercellular communication. The advantages of microfluidics have allowed for new capabilities in both single cell-cell communication and population-based communication. This review highlights microfluidic communication devices categorized as “short distance,” or primarily at the single cell level, and “long distance,” which mostly encompasses population level studies. Future directions and translation/commercialization will also be discussed.

Targeted vesicle fusion is a promising approach to selectively control interactions between vesicle compartments and would enable the initiation of biological reactions in complex aqueous environments. Here, we explore how two features of vesicle membranes, DNA tethers and phase‐segregated membranes, promote fusion between specific vesicle populations. Membrane phase‐segregation provides an energetic driver for membrane fusion that increases the efficiency of DNA‐mediated fusion events. The orthogonality provided by DNA tethers allows us to direct fusion and delivery of DNA cargo to specific vesicle populations. Vesicle fusion between DNA‐tethered vesicles can be used to initiate in vitro protein expression to produce model soluble and membrane proteins. Engineering orthogonal fusion events between DNA‐tethered vesicles provides a new strategy to control the spatiotemporal dynamics of cell‐free reactions, expanding opportunities to engineer artificial cellular systems.

Ligand spatial presentation and density play important roles in signaling pathways mediated by cell receptors and are critical parameters when designing protein-conjugated therapeutic nanoparticles. Here, we harness lipid phase separation to spatially control the protein presentation on lipid vesicles. We use this system to improve the cytotoxicity of TNF-related apoptosis inducing ligand (TRAIL), a therapeutic anticancer protein. Vesicles with phase-separated TRAIL presentation induce more cell death in Jurkat cancer cells than vesicles with uniformly presented TRAIL, and cytotoxicity is dependent on TRAIL density. We assess this relationship in other cancer cell lines and demonstrate that phase-separated vesicles with TRAIL only enhance cytotoxicity through one TRAIL receptor, DR5, while another TRAIL receptor, DR4, is less sensitive to TRAIL density. This work demonstrates a rapid and accessible method to control protein conjugation and density on vesicles that can be adopted to other nanoparticle systems to improve receptor signaling by nanoparticles.

It remains a great challenge to establish a high‐throughput platform that can explore the interactions among multiple lymphocytes (>2 cells) and retrieve the interested cells for downstream analysis. This study demonstrates a microfluidics cell loading‐dock system (Cell‐Dock) to enclose multiple cells in 1D, 2D, and 3D chambers with high throughput and efficiency and single‐cell accuracy. The loading efficiencies of 95%, 85%, and 74% for one‐, three‐, and five‐cell systems are achieved, respectively. The Cell‐Dock system provides precise and dynamic cell packing models to facilitate lymphocyte‐interaction studies. The results demonstrate that individual natural killer (NK) cells may function independently rather than cooperate to lyse target cells in the defined microenvironment. Furthermore, the strong/weak NK cells are retrieved based on their on‐chip cytotoxicity and mRNA sequencing is conducted to find the possible mechanisms for “serial killing,” an important but unsolved issue. This study finds that the stronger NK cells overexpress multiple genes involved in cytotoxicity and adhesion molecules (including the well‐known ICAM1 and seldom reported B4GALT1) might play important roles in the regulation of NK cytolysis.

Targeted vesicle fusion is a promising approach to selectively control interactions between vesicle compartments and would enable the initiation of biological reactions in complex aqueous environments. Here, we explore how two features of vesicle membranes, DNA tethers and phase‐segregated membranes, promote fusion between specific vesicle populations. Membrane phase‐segregation provides an energetic driver for membrane fusion that increases the efficiency of DNA‐mediated fusion events. The orthogonality provided by DNA tethers allows us to direct fusion and delivery of DNA cargo to specific vesicle populations. Vesicle fusion between DNA‐tethered vesicles can be used to initiate in vitro protein expression to produce model soluble and membrane proteins. Engineering orthogonal fusion events between DNA‐tethered vesicles provides a new strategy to control the spatiotemporal dynamics of cell‐free reactions, expanding opportunities to engineer artificial cellular systems.

The extent to which membrane biophysical properties, such as hydrophobic thickness, can drive membrane protein organization remains unknown. Inspired by this question, we used de novo protein design, molecular dynamic simulations, and cell-free systems to elucidate how membrane-protein hydrophobic mismatch affects protein integration and organization in synthetic lipid membranes. We found that membranes must deform to accommodate membrane-protein hydrophobic mismatch, which reduces the expression and co-translational insertion of membrane proteins into synthetic membranes. We used this principle to sort proteins both between and within membranes, thereby achieving one-pot assembly of vesicles with distinct functions and controlled split-protein assembly, respectively. Our results shed light on protein organization in biological membranes and provide a framework to self-organizing membrane-based materials with new functions.

Targeted vesicle fusion is ap romising approach to selectively control interactions between vesicle compartments and would enable the initiation of biological reactions in complex aqueous environments.H ere,w ee xplore how two features of vesicle membranes,D NA tethers and phasesegregated membranes,promote fusion between specific vesicle populations.M embrane phase-segregation provides an energetic driver for membrane fusion that increases the efficiency of DNA-mediated fusion events.T he orthogonality provided by DNAt ethers allows us to direct fusion and delivery of DNA cargo to specific vesicle populations.V esicle fusion between DNA-tethered vesicles can be used to initiate in vitro protein expression to produce model soluble and membrane proteins. Engineering orthogonal fusion events between DNA-tethered vesicles provides an ew strategy to control the spatiotemporal dynamics of cell-free reactions,e xpanding opportunities to engineer artificial cellular systems.

As the primary structural protein of our bodies, fibrillar collagen and its organizational patterns determine the biomechanics and shape of tissues. While the molecular assembly of individual fibrils is well understood, the mechanisms determining the arrangement of fibers and thus the shape and form of tissues remain largely unknown. We have developed a cell culture model that successfully recapitulates early tissue development and the de novo deposition of collagen fibers to investigate the role of mechanical cues on collagen fiber alignment. The devices used a thin, collagen-coated deformable PDMS membrane inside a tissue culture well built on microscope-grade coverslips. Deformations and strains in the PDMS membrane were quantified by tracking fluorescent bead displacement and through the use of a COMSOL model. Cyclical strains were applied to serum-cultured rabbit corneal cells at 0.5 Hz for 24–48 h and showed a preferred alignment after 36 h of cyclical loading. Cells cultured with ascorbic acid under methylcellulose serum-free conditions deposited a collagenous matrix that was visible under live second harmonic generation microscopy at week 4. Our microfabricated tissue culture system allows for the controllable application of a wide range of stress profiles to cells, and for the observation and quantification of cells and de novo collagen formation in vitro. Future studies will involve the fabrication of models to study the formation and organization of collagen in ocular diseases.