The coffee ring phenomenon has long been known for its ability to concentrate particles at the rim of a dried liquid droplet, yet little is known about its particle separation capability. Here, we elucidate the physics of particle separation during coffee ring formation, which is based on a particle-size selection mechanism near the contact line of an evaporating droplet. On the basis of this mechanism, we demonstrate nanochromatography of three relevant biological entities (proteins, micro-organisms, and mammalian cells) in a liquid droplet, with a separation resolution on the order of ∼100 nm and a dynamic range from ∼10 nm to a few tens of micrometers. These findings have direct implications for developing low-cost technologies for disease diagnostics in resource-poor environments.

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Rationale Left-right (LR) asymmetry is ubiquitous in animal development. Cytoskeletal chirality was recently reported to specify LR asymmetry in embryogenesis, suggesting that LR asymmetry in tissue morphogenesis is coordinated by single- or multi-cell organizers. Thus, to organize LR asymmetry at multiscale levels of morphogenesis, cells with chirality must also be present in adequate numbers. However, observation of LR asymmetry is rarely reported in cultured cells. Objectives Using cultured vascular mesenchymal cells, we tested whether LR asymmetry occurs at the single cell level and in self-organized multicellular structures. Methods and Results Using micropatterning, immunofluorescence revealed that adult vascular cells polarized rightward and accumulated stress fibers at an unbiased mechanical interface between adhesive and non-adhesive substrates. Green fluorescent protein transfection revealed that the cells each turned rightward at the interface, aligning into a coherent orientation at 20° relative to the interface axis at confluence. During the subsequent aggregation stage, time-lapse videomicroscopy showed that cells migrated along the same 20° angle into neighboring aggregates, resulting in a macroscale structure with LR asymmetry as parallel, diagonal stripes evenly-spaced throughout the culture. Removal of substrate interface by shadow mask-plating, or inhibition of Rho kinase or non-muscle myosin attenuated stress fiber accumulation and abrogated LR asymmetry of both single cell polarity and multicellular coherence, suggesting that the interface triggers asymmetry via cytoskeletal mechanics. Examination of other cell-types suggests that LR asymmetry is cell-type specific. Conclusions Our results show that adult stem cells retain inherent LR asymmetry that elicits de novo macroscale tissue morphogenesis, indicating that mechanical induction is required for cellular LR specification.

Cellular force regulates many types of cell mechanics and the associated physiological behaviors. Recent evidence suggested that cell motion with left-right (LR) bias may be the origin of LR asymmetry in tissue architecture. As actomyosin activity was found essential in the process, it predicts a type of cellular force that coordinates the development of LR asymmetry in tissue formation. However, due to the lack of appropriate platform, cellular force with LR bias has not yet been found. Here we report a nanowire magnetoscope that reveals a rotating force-torque-exerted by cells. Ferromagnetic nanowires were deposited and internalized by micropatterned cells. Within a uniform, horizontal magnetic field, the nanowires that initially aligned with the magnetic field were subsequently rotated due to the cellular torque. We found that the torque is LR-biased depending on cell types. While NIH 3T3 fibroblasts and human vascular endothelial cells exhibited counterclockwise torque, C2C12 myoblasts showed torque with slight clockwise bias. Moreover, an actin ring composed of transverse arcs and radial fibers was identified as a major factor determining the LR bias of cellular torque, since the disruption of actin ring by biochemical inhibitors or elongated cell shape abrogated the counterclockwise bias of NIH 3T3 fibroblasts. Our finding reveals a LR-biased torque of single cells and a fundamental origin of cytoskeletal chirality. More broadly, we anticipate that our method will provide a different perspective on mechanics-related cell physiology and force transmission necessary for LR propagation in tissue formation.

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Key pointsr The development of the lung is a highly stereotypical process, including the structured deployment of three distinct modes of branching: first side branching and then tip splitting with and without 90°rotation of the branching plane.r These modes are supposedly under genetic control, but it is not clear how genes could act to produce these spatial patterns.r Here, we show that cascades of branching events emerge naturally; the branching cascade can be explained by a relatively simple mathematical model, whose equations model the reaction and diffusion of chemical morphogens.r Our low-dimensional model gives a qualitative understanding of how generic physiological mechanisms can produce branching phenomena, and how the system can switch from one branching pattern to another using low-dimensional 'control knobs' .r The model makes a number of experimental predictions, and explains several phenomena that have been observed but whose mechanisms were unknown.Abstract Recent experimental work has described an elegant pattern of branching in the development of the lung. Multiple forms of branching have been identified, including side branching and tip bifurcation. A particularly interesting feature is the phenomenon of 'orthogonal rotation of the branching plane' . The lung must fill 3D space with the essentially 2D phenomenon of branching. It accomplishes this by rotating the branching plane by 90°with each generation. The mechanisms underlying this rotation are not understood. In general, the programmes that underlie branching have been hypothetically attributed to genetic 'subroutines' under the control of a 'global master routine' to invoke particular subroutines at the proper time and location, but the mechanisms of these routines are not known. Here, we demonstrate that fundamental mechanisms, the reaction and diffusion of biochemical morphogens, can create these patterns. We used a partial differential equation model that postulates three morphogens, which we identify with specific molecules in lung development. We found that cascades of branching events, including side branching, tip splitting and orthogonal rotation of the branching plane, all emerge immediately from the model, without further assumptions. In addition, we found that one branching Y. Guo and T.-H. Chen contributed equally to this work. mode can be easily switched to another, by increasing or decreasing the values of key parameters. This shows how a 'global master routine' could work by the alteration of a single parameter. Being able to simulate cascades of branching events is necessary to understand the critical features of branching, such as orthogonal rotation of the branching plane between successive generations, and branching mode switch during lung development. Thus, our model provides a paradigm for how genes could possibly act to produce these spatial structures. Our low-dimensional model gives a qualitative understanding of how generic physiological mechanisms can produce branching phenomena, and how the system can switch f...

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Rebuilding injured tissue for regenerative medicine requires technologies to reproduce tissue/biomaterials mimicking the natural morphology. To reconstitute the tissue pattern, current approaches include using scaffold with specific structure to plate cells, guiding cell spreading, or directly moving cells to desired locations. However, the structural complexity is limited. Also, the artificially-defined patterns are usually disorganized by cellular self-organization in the subsequent tissue development, such as cell migration and cell-cell communication. Here, by working in concert with cellular self-organization rather than against it, we experimentally and mathematically demonstrate a method which directs self-organizing vascular mesenchymal cells (VMCs) to assemble into desired multicellular patterns. Incorporating the inherent chirality of VMCs revealed by interfacing with micro-engineered substrates and VMCs’ spontaneous aggregation, difference in distribution of initial cell plating can be amplified into the formation of exquisite radial structures or concentric rings mimicking the cross-sectional structure of liver lobules or osteons, respectively. Furthermore, when co-cultured with VMCs, non-pattern-forming endothelial cells tracked along the VMCs and formed a coherent radial or ring pattern in a coordinated manner, indicating the applicability to heterotypical cell organization.