KAIST

Some bacteria form endospores on cell walls to protect their DNA in case of nutrient deficiency. When an endospore meets a suitable environment for survival, the cell can revert to the original state from which it can reproduce.  

The technique that can artificially control such phenomenon was developed by an international team of researchers. At first, a cell is wrapped and preserved like an egg. When the cell is needed, the technique allows the endospore to decompose while it is alive. Future applications for this technique include cell-based biosensor, cell therapy, and biocatalyst processes.

Professors Insung Choi and Younghoon Lee from the Department of Chemistry at KAIST as well as and Professor Frank Caruso from the University of Melbourne developed this technique which permits a cell to stay alive by coating it with film on a nanometer scale and then to be decomposed while it is alive.

The research finding was published in the November 10th issue of Angewandte Chemie International Edition as the lead article.

Cell encapsulation allows researchers to capture a cell in a tight capsule while it is alive. It is highly recognized in cell-based applications where the control of cell stability and cell-division is the biggest issue.

Traditional cell encapsulation methods utilized organic film or inorganic capsules that are made of organic film moldings. Although these films tightly closed around the cell, because they were not easily decomposable, it was difficult to apply the method.
The research team succeeded in encapsulating each cell in a metal-polyphenol film by mixing tannic acid and iron ion solution with yeast cells.

Usually extracted from oak barks or grape peels, tannic acid is a natural substance. It forms a metal-polyphenol film within ten seconds when it meets iron ions due to its high affinity with cells. Cells encapsulated with this film presented high survival rates. Since the film forms quickly in a simple manner, it was possible to obtain large amount of encapsulated cells.

The research team also found that the metal-polyphenol film was stable in neutral pH, but is easily degradable under a weak acidic condition. Using this property, they were able to control cell division by restoring the cell to its pre-encapsulated state at a desired moment.

Protecting the cell from the external environment like an egg shell, the metal-polyphenol film protected the cell against foreign conditions such as lytic enzymes, extended exposure to UV radiation, and silver nanoparticles. The research indicated that the encapsulated cells had a high survival rate even under extreme environments.

Professor Lee said that “not only the cells remain alive during the encapsulation stage, but also they can be protected under extreme environment.” He added, “This is an advanced cell encapsulation technology that allows controlling cell-division of those cells through responsive shell degradation on-demand.”

Professor Choi commented, “Although the cell encapsulation technology is still in its infancy, as the technology matures the application of cell-manipulation technology will be actualized.” He highlighted that “it will serve as a breakthrough to problems faced by cell-based applications.”

Sponsored by the Ministry of Science, ICT and Future Planning and the National Research Foundation of Korea, the research was led by two Master’s candidates, Ji Hun Park and Kyung Hwan Kim, under the joint guidance of research professors from KAIST and the University of Melbourne. 

Figure 1: Lead article of Angewandte Chemie 

Background: Shows a live native yeast (in green) encapsulated in a metal-polyphenol film (in red) illustrating the vitality of the yeast

Front: A native yeast at each encapsulation stage

Pictured on the bottom left is a cell prior to encapsulation. Following the red arrow, the native yeast is in purple to show metal-polyphenol film formed around the cell. The cell after the green arrow is a visualization of the degradation of the film in weak acidic condition. 

Figure 2: A mimetic diagram of cell encapsulation with a metal-polyphenol film

Top: A native yeast before encapsulation

Middle: A native yeast encapsulated with Tannic Acid-Fe (III) Nanoshell – cell-division of the encapsulated cell is controlled by pH and the shell is protected against silver nanoparticle, lytic enzyme, and UV-C
Bottom: Shell degradation on-demand depending on pH