Understanding how living cells respond to physical forces is one of the biggest challenges in modern biology. Cells inside the human body constantly experience pressure, stretching, fluid flow, and mechanical stress. These physical signals influence everything from blood circulation and immune responses to wound healing and disease progression.
But studying these effects in the laboratory has always been difficult, especially for cells that do not naturally stick to surfaces. Traditional methods for immobilising, or holding cells in place, often damage the cells, require chemical coatings, or fail under strong fluid flow conditions.
Now, researchers led by Soffe and team have developed a new technique that could solve many of these problems. Their method uses a phenomenon called dielectrophoresis to quickly and safely immobilise cells inside tiny microfluidic devices. Unlike older methods, the technique is label-free, fast, stable, and minimizes harm to the cells.
Most importantly, the researchers successfully exposed immobilised cells to very high levels of shear stress — forces similar to those experienced in real blood vessels — while continuously monitoring cellular responses in real time.
This breakthrough could open entirely new possibilities for studying mechanobiology, drug testing, vascular diseases, and cellular signalling.
Why Immobilising Cells Matters
In many biological experiments, scientists need cells to remain fixed in one location while they observe how the cells react to chemical or physical stimulation.
For example, researchers may want to:
Observe how cells react to flowing blood-like fluids
Study calcium signalling inside cells
Monitor ion channels responding to pressure
Test how drugs influence cellular behaviour
Capture microscopic images during experiments
If cells move around or detach during testing, accurate measurements become extremely difficult.
This is especially challenging for non-adherent cells — cells that naturally float instead of attaching firmly to surfaces.
Traditional immobilisation methods typically rely on modifying surfaces with special coatings such as:
Poly-L-lysine
Laminin
Fibronectin
Adhesive antibodies
These coatings help cells stick to glass or plastic surfaces.
However, these methods come with serious drawbacks.
The Problems With Traditional Techniques
Surface modification techniques can unintentionally alter cell behaviour. The interaction between cells and coated surfaces depends on several factors, including:
Surface charge
Roughness
Thickness
Chemical composition
As a result, cells may behave differently than they would inside the human body.
Another major problem is instability. Under strong fluid flow, cells can detach or rearrange themselves. This becomes a serious issue when scientists want to study high shear stress conditions similar to those inside arteries and veins.
Researchers have explored several alternative technologies, including:
Hydrodynamic Traps
These physically trap cells using microstructures. But they can clog easily and often need redesigning for different cell types.
Optical Tweezers
These use focused laser beams to hold cells in place. While precise, lasers may damage cells or affect cellular proteins.
Acoustophoresis
This technique uses sound waves to move and position cells. However, controlling cell placement precisely can be difficult.
Magnetic Tweezers
These require cells to be labelled with magnetic particles, making experiments more complicated.
Each method solves some problems while introducing others.
Enter Dielectrophoresis
The new approach relies on dielectrophoresis, often shortened to DEP.
This process uses non-uniform electric fields to manipulate polarizable particles like cells. When exposed to these electric fields, cells move toward specific regions within the microfluidic device.
DEP offers several advantages:
Label-free operation
Rapid cell immobilisation
Selective control
Compatibility with microfluidic systems
However, conventional DEP methods also have limitations.
Long exposure to electric fields can:
Damage cells
Reduce viability
Alter cellular function
Cause heating due to electrical currents
Trigger unwanted chemical reactions
Additionally, many DEP systems require low electrical conductivity buffers instead of normal cell culture media, which may stress cells during long experiments.
The Key Innovation: Short Exposure DEP
Soffe and team solved these problems using what they describe as a “discontinuous dielectrophoresis” approach.
Instead of keeping the electric field active throughout the experiment, they used it for only 120 seconds — just long enough to immobilise the cells.
After the cells were fixed in place:
The electric field was turned off
Normal cell culture media called HEPES was flushed through the system
Experiments continued under healthy conditions
This simple but powerful strategy dramatically reduced harmful exposure to electric fields and low-conductivity solutions.
The result was impressive.
Under optimal conditions, around 90% of cells remained stably immobilised even when exposed to extremely high shear stress of 63 dyn/cm².
That level of force covers the full physiological range found in human blood vessels.
Why High Shear Stress Matters
Inside the body, cells constantly experience fluid forces from moving blood.
In arteries and veins, shear stress typically ranges from 10 to 60 dyn/cm².
Studying how cells react to these forces is extremely important because mechanical stress influences:
Blood vessel function
Immune signalling
Inflammation
Tissue repair
Cardiovascular diseases
But until now, most experiments were limited to relatively low shear stress because cells detached too easily.
The new technique finally allows researchers to examine cellular behaviour under realistic physiological conditions.
Investigating the TRPV4 Ion Channel
To demonstrate the power of their system, the researchers studied a mechanosensitive ion channel called TRPV4.
Transient Receptor Potential Vanilloid 4 is part of the transient receptor potential family of ion channels and plays an important role in sensing mechanical forces.
TRPV4 is involved in:
Blood vessel regulation
Cellular calcium signalling
Vascular homeostasis
Response to mechanical stress
The team used HEK-293 cells engineered to express TRPV4 channels.
HEK-293 Cells are widely used in biological research because they are easy to manipulate genetically and naturally express very few interfering ion channels.
However, these cells normally do not stick well to surfaces, making them difficult to study under strong fluid flow.
Using the new DEP-based immobilisation technique, researchers successfully exposed these cells to the full physiological range of shear stress while monitoring calcium signalling in real time.
What the Scientists Discovered
The researchers observed clear, dose-dependent calcium responses when TRPV4-expressing cells experienced increasing shear stress.
In simple terms:
Higher shear stress produced stronger calcium signalling
More cells responded as stress levels increased
The results were far clearer than previous studies
This is important because earlier experiments struggled to produce consistent evidence for TRPV4’s response to shear stress.
The ability to apply stronger and more realistic mechanical forces finally revealed clearer cellular behaviour.
This suggests that some mechanosensitive ion channels may only activate under higher stress thresholds that older experimental systems could not reach.
A Major Step Forward for Mechanobiology
The study represents an important advancement in mechanotransduction research.
Mechanotransduction is the process by which cells sense physical forces and convert them into biological responses.
This process influences many critical cellular functions, including:
Cell growth
Migration
Differentiation
Tissue maintenance
Disease progression
Despite its importance, mechanotransduction remains poorly understood because scientists lack tools capable of applying realistic physical forces to fragile non-adherent cells.
The new immobilisation platform could help solve this problem.
Beyond This Study
Although the researchers focused on calcium signalling and TRPV4 channels, the technique has far broader applications.
Potential future uses include:
Drug screening
Cancer cell analysis
Immune cell research
Blood flow studies
Stem cell biology
Real-time microscopy experiments
Organ-on-chip technologies
Because the system is label-free and does not require surface coatings, it may also simplify many laboratory workflows.
The ability to immobilise cells quickly without significantly affecting their health makes the approach especially attractive for long-term biological studies.
The Bigger Picture
This research highlights how engineering and biology are increasingly merging together.
Microfluidic systems combined with advanced cell manipulation techniques are allowing scientists to recreate realistic biological environments inside tiny laboratory chips.
The work by Soffe and team demonstrates that even small improvements in experimental methods can unlock entirely new areas of discovery.
By safely immobilising fragile cells under extreme mechanical conditions, researchers now have a powerful new tool for exploring how living systems sense and respond to physical forces.
And that could ultimately improve our understanding of cardiovascular diseases, inflammation, cellular communication, and many other processes that shape human health.
Reference: Soffe, R., Baratchi, S., Tang, SY. et al. Analysing calcium signalling of cells under high shear flows using discontinuous dielectrophoresis. Sci Rep 5, 11973 (2015). https://doi.org/10.1038/srep11973
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