Spontaneous Formation of Uniform Cell-Sized Microgels through Water/Water Phase Separation.

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.

Periodic Alignment of Binary Droplets via a Microphase Separation of a Tripolymer Solution under Tubular Confinement.

We report the spontaneous formation of a characteristic periodic pattern through the phase separation of a tripolymer solution comprising polyethylene-glycol (PEG)/dextran (DEX)/gelatin. When this tripolymer solution is introduced into a glass capillary with a PEG-coated inner surface, we observe the time-dependent growth of microphase separation. Remarkably, a self-organized, periodic alignment of DEX- and gelatin-rich microdroplets ensues, surrounded by a PEG-rich phase. This pattern demonstrates considerable stability, enduring for at least 8 h. The fundamental characteristics of the experimentally observed periodic alignment are successfully replicated via numerical simulations using a Cahn-Hilliard model underpinned by a set of simple, theoretically derived equations. We propose that this type of kinetically stabilized periodic patterning can be produced across a broad range of phase-separation systems by selecting appropriate boundary conditions such as at the surface within a narrow channel.

Emergence of uniform linearly-arranged micro-droplets entrapping DNA and living cells through water/water phase-separation.

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.