University of Göttingen studies details of cell interior

07 Aug 2024

Optical trap-based process tests mechanical properties of cell components.

A project at the University of Göttingen has developed a new technique for assessing the mechanical behavior of constituent components within living cells.

Reported in Nature Materials, the findings could offer a route to improved understanding of cell dynamics, as well as producing valuable parameters related to the health of organic matter and commercial produce.

"Despite more than 100 years of intensive research, many cell properties remain hidden inside the cell," said the project.

"A new approach can determine the particularly difficult-to-detect mechanical properties of the cell interior, by taking a closer look."

Assessing the mechanical properties of cell components, rather than parameters relating strictly to biochemistry, is known to give researchers data about living organic systems that can otherwise remain elusive.

A 2019 project at the French CNRS research labs developed an optical technique to assess the physical properties of cancer tumors using Brillouin light scattering microscopy, creating a map of where the tumor was most rigid. This data could help in the design of new anticancer molecules and the personalization of treatments.

However, many approaches to mechanical testing of interior cell components end up damaging the delicate organic structures involved, commented the Göttingen team. A different method was required.

The project started with an analysis of the random fluctuating movement that all microscopic particles perform. It first simulated the expected fluctuations, and then checked those predictions using optical laser traps to capture and release cell components and precisely control those movements.

A new fingerprint of cell behavior

Using this approach, the research team was able to analyze the movement of microscopic particles with precision in the nanometer range and a time resolution of around 50 microseconds. The analysis also took into account the past movements of the microparticles, and revealed that many objects always want to return to a certain place after having moved away randomly.

This tendency of cell contents to return to a previous position allowed the project to define a new parameter termed the mean back relaxation (MBR), representing the average trajectory of a particle after a recent motion, calculated from three-point probabilities. MBR let the project assess the viscoelastic material properties of cell components in a non-invasive manner and from passive measurements, a new way to quantifying the active mechanics of living cells.

According to the project, MBR data described the complex behavior of components inside cells precisely, despite being based on principles initially worked out for much simpler systems.

"With MBR, we can obtain more information from the object movements than is possible with the usual approaches," commented Matthias Krüger from the Institute of Theoretical Physics at the University of Göttingen. "This new variable now serves as a kind of fingerprint: it contains information about the causes of the observed movements. This makes it possible for the first time to distinguish active processes from purely temperature-dependent processes."