Living cells maintain their lives through self-organization in an environment crowded with a rich variety of biological species. Recently, it was found that micro-droplets containing biomacromolecules, which vary widely in size, are generated accompanied by water/water phase-separation by simple mechanical mixing of an aqueous solution with binary polymers. Here, we report that cell-sized droplets of nearly the same size are generated as a linear array within a glass capillary upon the introduction of a binary polymer solution of polyethylene glycol (PEG) and dextran (DEX). Interestingly, when DNA molecules are added to the polymer solution, stable droplets entrapping DNA molecules are obtained. Similarly, living cells are entrapped spontaneously for the linearly-arranged cell-sized droplets. This simple method for generating micro-droplets entrapping DNA and also living cells is expected to stimulate further study on the self-construction of protocells and micro organoids.

In this study, a one‐step method is discussed for producing uniform cell‐sized microgels using glass capillaries filled with a binary polymer blend of polyethylene glycol (PEG) and gelatin. Upon decreasing temperature, phase separation of the PEG/gelatin blends and gelation of gelatin occur, and then the polymer blend forms linearly aligned, uniformly sized gelatin microgels in the glass capillary. When DNA is added to the polymer solution, gelatin microgels entrapping DNA are spontaneously formed, and the DNA prevents the coalescence of the microdroplets even at temperatures above the melting point. This novel method to form uniform cell‐sized microgels may be applicable to other biopolymers. This method is expected to contribute to diverse materials science via biopolymer microgels and biophysics and synthetic biology through cellular models containing biopolymer gels.

The directional movement of an aqueous solution containing gold nanoparticles under laser irradiation (532 nm) through the vicinity of an air/water interface is reported. It is shown that unidirectional flow is generated along the path of light-travel when a laser is irradiated parallel to the interface. On the contrary, liquid flow toward the light source is caused when the incident angle of the laser is tuned so as to make the total reflection at an air/water interface. Such switching of the flow direction, positive or negative to the light propagation, was applied to the movement of mm-sized floating object, revealing that repetitive back and forth motion of the solid object is generated. This directional switching of photo-induced movement is interpreted by taking into account the flow caused by the spatial gradient of the surface tension due to the thermal effect of the incident laser. A numerical model with a Navier–Stokes-type equation reproduces the essential aspects of the switching of the direction observed in the present study.

Drying of an aqueous suspension containing fine granules leads to the formation of a circular pattern, i.e., the coffee-ring effect. Here, we report the effect of mechanical rotation with drying of an aqueous suspension containing a large amount of granular particles as in the Turkish coffee. It was found that wavy fragmented stripes, or a “waggly pattern”, appear in the early stage of the drying process and a “polka-dot pattern” with many small circles is generated in the late stage. We discuss the mechanism of these patterns in terms of the kinetic effect on micro phase-segregation. We suggest that the waggly pattern is induced through a mechanism similar to spinodal decomposition, whereas polka-dot formation is accompanied by the enhanced segregation of a water-rich phase under mechanical rotation.