Cells migrate in response to environmental gradients as part of development, immune response, wound healing, and disease progression. For decades, the prevailing understanding has been that cell migration towards stiffer substrates (a process called durotaxis) depends critically on focal adhesions. These molecular anchors sense substrate stiffness and transmit forces that guide directed cell motion. However, recent research reveals a fundamentally different migration mechanism that operates without focal adhesions entirely.
A new study published in Nature Communications by Shellard et al. demonstrates that cells confined within microfluidic channels can perform directed migration up stiffness gradients even in the complete absence of focal adhesions. The mechanism underlying this focal adhesion-independent durotaxis is frictiotaxis, a physical process in which cells migrate towards regions of higher friction. Importantly, the research relied on silicon wafer substrate preparation using the Henniker Plasma HPT-100 to clean wafers before photolithography, enabling the fabrication of the precise microfluidic devices used throughout the study.
This article summarises the research challenge, how plasma surface preparation supported the work, and the key findings that broaden our understanding of cell migration mechanisms.
The Challenge: How Do Cells Migrate Without Focal Adhesions?
Durotaxis — directed cell migration along stiffness gradients has been observed across multiple cell types in vitro and in vivo. The prevailing model explains this behaviour through focal adhesions, which act as mechanical sensors. These adhesion complexes, such as integrins and focal adhesion proteins, bind to the extracellular matrix (ECM) and transmit forces that bias cell motion towards stiffer regions.
However, this focal adhesion-dependent model has a significant limitation. It cannot explain how certain cells perform durotaxis in confined environments where focal adhesions either cannot form or are severely restricted. Understanding whether, and how, cells can sense and respond to stiffness gradients without focal adhesions remained an open question — one with profound implications for development, immune cell migration, and cancer progression in confined tissue spaces.
The research team designed a series of carefully controlled experiments using microfluidic devices. To create these devices with precision, they needed to prepare silicon wafer substrates using reliable, contamination-free methods. Plasma surface treatment was essential to this process.
How Plasma Surface Preparation Supported the Research
Plasma surface treatment played an important role in preparing the gold nanoparticle substrates for electrochemical investigation. The Henniker Plasma HPT-100 was used for oxygen plasma cleaning of the freshly prepared MLagg substrates.
Ensured Reproducible Substrate Preparation
Organic molecules, including residual citrate ligands from the nanoparticle synthesis, must be completely removed before electrochemical experiments can begin. The HPT-100 provided a controlled oxygen plasma environment that oxidatively stripped these contaminants from the gold surface, exposing a clean, well-defined substrate ready for rescaffolding and electrochemical cycling.
Enabled the Electrochemical Rescaffolding Protocol
The cleaned MLagg substrates were subsequently treated with hydrochloric acid to reintroduce the cucurbit[n]uril scaffolding molecules. Without thorough plasma-based cleaning, these scaffolds would not rebind effectively, and the precisely defined sub-1 nm nanogaps essential to the SERS measurements would not form reliably. The plasma preparation step therefore underpinned the entire experimental workflow.
Supported Chemical Rescaffolding (Ch-ReSERS)
Beyond electrochemical regeneration, the researchers extended their plasma-cleaned substrates to a chemically driven rescaffolding protocol (Ch-ReSERS). Here, the MLagg was first oxidised with oxygen plasma using the HPT-100 and then treated with hydrochloric acid and the scaffolding molecule. This demonstrates the versatility of plasma treatment — serving both as a cleaning step and as an active surface modification tool within the research methodology.
The Results: Key Findings on Gold Nanoparticle Surface Chemistry
1. Cells Perform Durotaxis Despite Lacking Focal Adhesions
When Walker cells (a model amoeboid cell line) were cultured in microfluidic channels coated with polyethylene glycol (PEG) a non-adhesive coating that prevents focal adhesion formation — they nevertheless migrated persistently towards stiffer regions of the channel. Remarkably:
- Cells exhibited a directional migration bias towards stiffer substrate
- Migration was ~2.5–3 times more persistent on stiffness gradients than on uniform stiffness
- Neither integrin-blocking antibodies nor focal adhesion inhibitors affected durotaxis, confirming the mechanism was truly adhesion-independent
2. Frictiotaxis: A Friction-Gradient Mechanism
The researchers proposed and validated a new mechanism: frictiotaxis. In this model, stiffer substrates offer higher friction to the migrating cell. Because friction and stiffness are correlated, cells moving along such surfaces naturally accumulate more myosin activity on the high-friction (stiff) side, breaking symmetry in their contractile forces.
- Cells spontaneously polarise due to asymmetric myosin concentration
- Higher myosin intensity accumulates at the stiffer, higher-friction side
- This asymmetric force distribution drives directed cell motion towards higher friction
- The mechanism works even when stiffness is uniform, provided a friction gradient exists
3. Broad Applicability Across Multiple Cell Types
The frictiotaxis mechanism was not limited to Walker cells. The researchers demonstrated that multiple cell types can perform friction-guided migration in confined environments:
- HL60 neutrophil-like cells exhibited frictiotaxis
- Lifeact-GFP cells (actin-labeled) showed clear myosin polarisation driving motion
- Results are broadly relevant to development, immune migration, and cancer cell behaviour in confined tissue spaces
Conclusion
This study, published in Nature Communications, fundamentally expands our understanding of how cells sense and respond to their mechanical environment. The discovery of frictiotaxis — a friction-driven mechanism of directed migration — reveals that cells can navigate confined spaces without relying on focal adhesions. This has profound implications for understanding cell migration during development, immune surveillance, and cancer progression in tissue environments that naturally constrain cell behaviour.
The precise microfluidic devices central to this work were fabricated using silicon wafers cleaned with the Henniker Plasma HPT-100. Without reliable, contamination-free surface preparation, the consistent fabrication of channels with precisely controlled stiffness gradients would not have been possible. Plasma surface treatment therefore played an important enabling role in this research discovery.
For biomedical researchers designing microfluidic platforms, cell culture substrates, and tissue-engineered scaffolds, plasma surface treatment of silicon wafers and other materials offers a proven method for achieving the surface cleanliness and reproducibility essential to advanced experimental systems.
Henniker plasma systems remain trusted tools in biomedical research laboratories worldwide, delivering the reliable surface preparation that rigorous experimental programmes require.
References
Readers are referred to the original publication, available through the provided DOI link, or click the links below for further details on the Henniker Plasma HPT-100.
Adam Shellard, Kai Weißenbruch, Peter A. E. Hampshire, Namid R. Stillman, Christina L. Dix, Richard Thorogate, Albane Imbert, Guillaume Charras, Ricard Alert & Roberto Mayor
Nature Communications, Volume 16, Article 5887, April 2025
DOI: https://doi.org/10.1038/s41467-025-58912-1
