In order to test the influence of various substances on the organism one shall first insert them into the cell, which is protected by the cell membrane. It does not only limit the space of the cell, but also protects it from the external threats. In general that is a highly beneficial role and a guarantee of proper functioning. However, it also poses quite a challenge to the scientists who want to transfer various substances into the cell for the purposes of their research.

One of the notable impediments is the nature of the membrane, which is built in a way that lets only particular substances inside, for instance ions, water or other small particles. Such transport is the main task of the canals located in the membrane. It shall be noted that each of them is designed in order to let in only the specific substance, simply due to its size. Once again, generally speaking it shall be deemed as beneficial. One could compare this to a cat doors installed by the entrance to a house, which are made specifically to let in the cats, but not necessarily bears or deer. However sometimes, solely due to scientific reasons, one must let the deer into the house. And that is the point when researchers from Instytut Chemii Fizycznej Polskiej Akademii Nauk walk in.

Putting aside quaint comparisons, we shall underscore certain issue. Scientists have already discovered quite a few methods of getting through the cell membrane, for instance using microinjections. Nonetheless this solution has certain significant disadvantages, such as the amount of time it consumes. On the other hand, CELL-IN method created by professor Robert Hołyst and his colleagues is meant to overcome those impediments.

In order to understand this invention, we shall first understand what osmosis, hyper- and hypotonic solution is. Sounds scary? Worry not, as for the purposes of this article it can be quite easily explained.

Osmosis, which some of you may remember from biology lessons, is what happens when there are two solutions divided by a membrane and the solvent of the solution of lower density moves into the solution of higher density in order to level concentration on both sides.

Bearing that in mind, hypotonic solution is a practical use of osmosis. One may use such term to call a solution with the smaller concentration of osmotically active ingredients in comparison with the inside of a cell. The hypertonic solution is the opposite. In such case the solution outside of the cell has a higher concentration than the one inside it.

That would be all when it comes to definitions. So what is the use of all that in the presented method? In the first phase, the cells are confronted with a hypertonic solution. That is why the water leaves the cell, evening out the osmotic pressure. At the same time it makes the solution inside the cell (cytoplasmic solution, to be precise) turn into a hypotonic one. As it happens, the cell membrane “untightens”. That allows the scientist to insert a substance mixed with the solutions containing polymers into the cell, as such solution is being sucked in at the moment (provided that the pressure is sufficiently high). What is highly important in this case is that this method allows the scientists to deliver particles as big as 200 nm, which  is quite a surge in the efficiency.

So far we have been roaming around the biological aspects of the issue, yet scientists underscore the importance of the physics behind their invention. They underline that the efficiency of transferring is linked closely to the size and concentration of the polymers inside the solution and not necessarily as much to the osmotic pressure. The right choice of polymers also enables the researchers to get rid of the sucrose, which has been the indispensable part of such insertions so far. In other words, the profound understanding of the physical aspects directly affects the biological outcome.

All of the aforementioned traits connected with the reduced invasiveness were so promising, that the scientists from IChF PAN decided to commercialize the CELL-IN solution and introduce it to the market.

Bibliography:

1. Jak wniknąć do komórki?, Nauka w Polsce, online access on 06/10/2022, https://naukawpolsce.pl/aktualnosci/news%2C93915%2Cjak-wniknac-do-komorki-szokujacy-pomysl-polskich-naukowcow.html?fbclid=IwAR3rpB76EN_vNt6Qd_xbzumByRr6HeUpQAKRzIFLtQhsLsEw1rgm4Ur7X8o
2. Karpińska et al. Entanglement of polymer chains in hypertonic medium enhances the delivery of DNA and other biomacromolecules into cells, Journal of Colloid and Interface Science 2022, Vol. 627, Pages 270-282 https://doi.org/10.1016/j.jcis.2022.07.040
3. Nowa Encyklopedia Powszechna PWN, Warszawa 1995, tom 2, str. 758, 760, tom 4 str. 696