Creates uniform DNA encapsulation microgels that mimic living cells

June 23, 2023

(Nanowerk News) Living cells have physiologically relevant components such as genetic material (DNA) and proteins in a ‘self-regulated’ arrangement. Understanding this process of self-assembly can reveal the mechanisms underlying the self-regulation of living matter. Water/oil (w/o) or water/water (w/w) droplets can be used as prototypes or “models” that mimic cells and can be used to study cellular self-assembly.

This model also has major implications in the field of biomedical research. Although cell mimetics can be generated using complex and expensive equipment, related methods are expensive, tedious, and challenging.

Now, researchers from Japan were recently able to develop a one-step method for producing uniform, gelatin-based cell mimetics called “microgels”. Related results are published in a journal Small (“Spontaneous Formation of Microgels of Uniform Cell Size by Water/Water Phase Separation”). By adapting the DNA-containing aqueous polymer solution, DNA-trapping droplets are generated in a self-organizing manner through microphase separation, and these droplets are converted to a gel state by lowering the temperature. Microgels are easily extruded into bulk water, retaining their size. (Image: Akihisa Shioi, Doshisha University)

Explaining the motivation behind their study, Mayu Shono and Prof. Akihisa Shioi of Doshisha University, who led the study, commented, “Currently, our research focuses on understanding the self-organization of living matter. As an extension of our research activity, we have discovered an experimental procedure that may be very useful for the preparation of microgels.” The research team also consisted of Gen Honda and Miho Yanagisawa from the University of Tokyo, and Kenichi Yoshikawa who is affiliated with Doshisha University and Kyoto University.

The mechanism of microgel formation is indeed interesting. The initial stage involves constructing a domain structure consisting of polyethylene glycol (PEG) and gelatin — two widely used synthetic crosslinkers. Lowering the temperature to 24 °C favors the selective transition of the gelatin-rich domains to the gel phase. Under a specified set of experimental conditions, the PEG-rich phase preferentially migrates to the glass surface of the capillary tube because of its higher affinity for glass and lower affinity for the gelatin-rich domains.

Consequently, the gelatin-rich droplets are engulfed by the PEG-rich phase. This finding was also validated in theoretical and numerical modeling studies using glass capillary experiments, which confirmed that the wettability of the inner surface of the glass capillary dominates the w/w phase separation.

In addition, upon addition of DNA, the gelatin-rich droplets are able to spontaneously entrap DNA molecules due to separation of the PEG and gelatin phases, giving rise to cell-mimicking microgels. The study also notes that negatively charged DNA molecules incorporated in droplets can stabilize them by preventing fusion even above the sol/gel transition temperature.

The team also used fluorescent dyes to label and track encapsulated DNA. Subsequent fluorescence microscopy experiments revealed the presence of spherical microgel structures harboring glowing DNA molecules. According to the authors, the current approach is expected to confine, store and transport large DNA molecules in small cell-sized droplets!

Excited about the scope of their future research, PhD student Mayu Shono, first author, said, “This new method for forming microgels of uniform cell size may be applicable to other biopolymers. Cell-like systems of uniform and stable cell size will also have key implications in the fields of the biological and life sciences.”

In summary, this study addresses a novel method for the preparation of gelatin-based cell mimetics, which can be modified according to the desired purpose, depending on the application area. “The method proposed in our study, which does not require special equipment, organic solvents or surfactants, can be useful for producing microgels for food, medicine, cosmetics and other materials,” concluded Prof. Shioi.

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