URV research demonstrates the mechanism by which microplastics, when in contact with cell membranes, stretch and greatly reduce their mechanical stability

It is estimated that, since the 1950s, more than 70 million tonnes of microplastics have been dumped into the oceans due to industrial manufacturing processes. These plastics are ingested by aquatic and human organisms through water, food and the air we breathe. It is estimated that their size ranges from 0.1 microns to 5 millimeters and are made mainly of polypropylene, polyethylene, polystyrene, polyamide and acrylics. Plastic particles the size of a micrometer are present literally everywhere: in the oceans, in the air, in the snow of the Himalayas, and even in human placentas. Toothpaste, sunscreens, common chemicals or packaging also contain plastics. And although studies indicate that the consumption of microplastics does not lead to death or immediate or food poisoning, there is growing evidence of its effects on cells at the molecular scale, which are difficult to identify experimentally.

In this context, Vladimir Baulin, physicist and researcher in the Department of Physical and Inorganic Chemistry at the URV, in collaboration with Jean-Baptiste Fleury, of the University of Saarland (Germany), has discovered in a recent study that microplastics can mechanically destabilize lipid membranes by adhering to and tightening them. The results of the study were published in the scientific journal PNAS.

To test how the mechanical effect of microplastics on these membranes occurs, the researchers used a theoretical model that was later confirmed with experiments on the lipid bilayer (the barrier that protects the cell) with a special microfluidic device. Through this system they discovered the mechanism that enables the mechanical stretching of membranes to occur. Once this mechanism was identified, the researchers checked the findings in red blood cells trapped in a micropipette. The results of this experiment conclude that microplastics stretch the membranes of human red blood cells and greatly reduce their mechanical stability, which can affect their proper functioning and alter, for example, their ability to transport oxygen.

The theoretical method, developed by URV physicist Vladimir Baulin, describes exactly how microplastics act on cell membranes. When tested, this model predicted that each particle would consume part of the membrane area, which induces it to contract around the plastic particles. This effect inevitably leads to a mechanical stretching of the cell membrane. “With this experiment we have shown that the theoretical model can even quantitatively predict the extent of the increase in cell membrane tension. This is an unexpected result given the model’s simplicity,” explains Baulin. To confirm the model prediction, the microfluid technique was used in a simpler model than a human cell membrane, such as red blood cells, and the tension of these membranes in contact with microplastics was measured. The researchers found that plastic particles were never kept static in cells, but were constantly moved by continuous diffusion. Given these results, the researchers consider that this diffusion is the reason why this mechanical effect is maintained and prevents the mechanical relaxation of the cell.

The researchers point out that this experimental test of the theoretical model allows conclusions to be drawn about the general validity of this mechanism, which can be transferred to a large number of human cells or organs.

“The possible toxicity of microplastics in human cells is currently being discussed,” explains Jean-Baptiste Fleury, who is conducting research as an experimental physicist at the University of Saarland. “A priori, microplastics are not fatal immediately after ingestion into living organisms. However, it is increasingly recognized that microplastics can oxidize or stress cells through biological processes. The possibility of they may also stress a cell membrane through purely physical processes, however, is completely ignored by the vast majority of studies, ”he adds.

In fact, from a physical point of view, no effect should be expected. A cell membrane is considered as having properties similar to those of a liquid. It is known that any mechanical effect on a liquid disappears over time. “Surprisingly, however, we observe that the membranes of artificial cells and red blood cells stretch in the presence of microplastics,” he continues. According to the researcher, the membrane of human red blood cells apparently deforms spontaneously, which explains the massive effect that these microplastics have on cell membranes.

This new line of research by Vladimir Baulin’s group is dedicated to the microscopic mechanisms of pollution in the marine environment. The URV has for a few months now been promoting a new spin-off, DeepSea Numerical (https://deepsea.blue/), which aims to build a network of underwater laboratories so that research staff from around the world can come and conduct underwater experiments with the aim of monitoring and safeguarding biodiversity.

Reference: Fleury, J.-B.; Baulin, V. A. Microplastics Destabilize Lipid Membranes by Mechanical Stretching. PNAS 2021, 118 (31). https://doi.org/10.1073/pnas.2104610118.