Engineering subcellular-patterned biointerfaces to regulate the surface wetting of multicellular spheroids
Imagine a tiny droplet of cancer cells that suddenly starts spreading like a drop of water on a surface. This behavior, which scientists call "tissue wetting," may hold the key to understanding how cancer metastasizes and how we can control it.
In laboratories around the world, researchers are now learning to direct this process by creating surfaces with nanoscale patterns—engineered landscapes so small that their features are measured in billionths of a meter.
The study of multicellular spheroid wetting represents a fascinating intersection of biology, physics, and materials science. When cell clusters transition from three-dimensional structures to spreading across a surface, they're not just moving—they're undergoing complex physical transitions that can determine whether a cancer remains contained or becomes invasive.
Recent research has revealed that we can steer this process by designing surfaces with specific subcellular patterns, potentially opening new pathways for controlling cellular behavior in tissue engineering, cancer treatment, and regenerative medicine 3 .
Spheroid wetting describes the process where three-dimensional cell aggregates transition into spreading monolayers when placed on a surface. Much like a liquid droplet wetting a surface, this process involves a complex interplay of forces, energies, and biological signals.
The concept draws from both classical wetting theory from physics and active matter principles that account for the biological activity of living cells 1 .
Cells in dense tissues can exist in different physical states—jammed (solid-like) or unjammed (fluid-like)—much like particles in condensed matter physics. When conditions change, tissues can undergo an unjamming transition, allowing cells to move freely and rearrange 1 .
The protein RAB5A has been identified as a key regulator of this transition in breast cancer. This RAB5A-mediated unjamming transforms carcinoma spheroids from rigid, solid-like structures into motile, fluid-like collectives capable of invasive spreading 1 .
While early models viewed spheroid wetting as similar to passive fluid spreading, recent research has revealed it to be a fundamentally active process. The active polar fluid model suggests that wetting emerges from the competition between traction forces (which push cells outward) and contractile intercellular stresses (which pull cells together) 8 .
In this framework, the spheroid isn't just responding to surface energies—it's actively regulating its own spreading through cellular forces 1 .
A team of researchers led by Professor Shutao Wang made a crucial discovery in 2018: they found that subcellular topography could dramatically influence how multicellular spheroids wet surfaces 3 .
They created specialized surfaces called opal films—engineered surfaces with carefully controlled patterns of colloidal particles ranging from 200 to 1,500 nanometers in diameter.
These opal films provided an ideal platform to test how surface patterns affect cell behavior. The spaces between the colloidal particles created what the researchers called "adhesion vacancies"—gaps that made it difficult for cells to form strong attachments to the surface 3 .
Data from Wang et al. 3
They created opal films with six different colloidal particle diameters (200, 300, 500, 700, 1,000, and 1,500 nanometers) alongside flat control surfaces for comparison 3 .
They used Hep G2 (hepatoma carcinoma) cells to form uniform multicellular spheroids, ensuring consistent starting points for all wetting experiments 3 .
They placed individual spheroids on each surface type and monitored their spreading over time using time-lapse microscopy 3 .
They quantified the wetting area, cell migration patterns, and molecular organization within the spreading cells, paying special attention to the "frontier cells" at the leading edge of expansion 3 .
The findings revealed a clear and striking relationship: larger colloidal particles resulted in significantly slower wetting. While spheroids spread readily on flat surfaces, their expansion was markedly impaired on opal films, with the inhibition effect strengthening as particle size increased 3 .
The most dramatic effect occurred with the largest particles (1,500 nm), where wetting was reduced by nearly half compared to flat surfaces. This demonstrated that subcellular topography alone could powerfully influence tissue-level behavior without changing surface chemistry 3 .
| Colloidal Particle Diameter (nm) | Wetting Rate Reduction |
|---|---|
| 200 | 18.5% |
| 300 | 25.5% |
| 500 | 32.5% |
| 700 | 38.5% |
| 1000 | 43.5% |
| 1500 | 48.5% |
Table 1: Effect of Colloidal Particle Size on Spheroid Wetting Rate 3
Further investigation revealed why these patterned surfaces inhibited wetting: they disrupted the function of frontier cells—those at the leading edge of the expanding spheroid. On flat surfaces, these frontier cells developed mature focal adhesions and robust stress fibers, anchoring themselves firmly to the surface and pulling the rest of the spheroid forward 3 .
On the opal films, however, the gaps between colloidal particles prevented frontier cells from forming these critical adhesion structures. The researchers observed "immature focal adhesions" and poorly developed stress fibers in these leading cells, leaving them unable to generate the strong traction forces needed for effective spreading 3 .
| Cellular Component | Flat Surfaces | Patterned Surfaces | Functional Impact |
|---|---|---|---|
| Focal Adhesions | Mature, well-developed | Immature, underdeveloped | Reduced cell-substrate adhesion |
| Stress Fibers | Robust, organized | Poorly developed | Weakened traction forces |
| Migration Behavior | Directed, persistent | Random, hesitant | Slower spreading |
Table 2: Molecular and Cellular Changes in Frontier Cells on Patterned Surfaces 3
Studying spheroid wetting requires specialized materials and methods. Here are essential tools and techniques used by researchers in this field:
Engineered surfaces with controllable colloidal particle diameters (200-1500 nm) that allow systematic study of topographic effects on cell behavior 3 .
Innovative platforms that enable spheroid formation in large media drops, preventing nutrient depletion that plagues traditional methods 6 .
Ultra-Low Attachment plates with surface-treated cultureware that prevents cell adhesion, forcing cells to aggregate and form spheroids 4 .
Materials like collagen, hyaluronic acid, and chitosan that mimic natural extracellular matrix components 4 .
Platforms made from materials like poly(lactic-co-glycolic acid) that offer precise control over mechanical and chemical properties 4 .
Techniques like Brillouin microscopy and traction force microscopy that measure mechanical properties within spreading spheroids 1 .
The ability to direct spheroid wetting through engineered biointerfaces represents a significant advancement in our quest to control cellular behavior. As we deepen our understanding of how subcellular patterns influence tissue dynamics, we move closer to practical applications that could transform medicine.
Future developments might include "smart surfaces" that dynamically change their properties in response to cellular signals.
Implants designed to promote or inhibit tissue integration based on therapeutic needs.
The research on subcellular-patterned biointerfaces reminds us that physical structure can be as influential as chemical signals in guiding biological processes. By learning to design surfaces that speak the physical language of cells, we open new possibilities for healing, repair, and understanding life's fundamental processes.
As this field advances, it continues to blur the boundaries between disciplines, showing that the most profound insights often emerge at the intersections—where biology meets physics, where medicine meets materials science, and where fundamental understanding meets practical innovation.