The role of dimensionality is a growing field in cell biology, but many labs cannot afford new tools that let cells grow in three dimensions—which could, in theory, better represent what happens in vivo. As a member of F1000’s Faculty of Cell Biology, Ken Yamada at the National Institute of Dental and Craniofacial Research flagged a recent PNAS study that described an easy alternative for scientists who want to explore 3D cell culture: paper (106:18457–62, 2009).
TS: Cells are normally grown in a single layer on a plastic surface or in suspension. What’s wrong with this approach?
KY: It’s obviously spatially artificial. You lose normal three-dimensional architecture and...
The other thing about cells grown on a plastic surface is that there’s a major difference in stiffness. The substrate cannot be deformed, whereas in vivo you have elasticity of the matrix.
TS: If looking at three-dimensionality is so important, why has it taken so long to come up with a workable method for studying it?
KY: There are a number of good 3D model systems already—collagen gels, fibrin gels, other types of matrix components, nanofibers—they all have their own advantages and disadvantages, just like this one. And in vivo you might expect that you would have considerably different 3D environments; some would be stiff, some would be dense.
TS: In this paper, George Whitesides’ lab soaked chromatography paper in hydrogel and cells, and layered the paper on the bottom of tissue culture dishes so that cells would grow with other cells above and below them, creating a three-dimensional support. To analyze cells on one layer of paper, they simply peel it off from the stack.
KY: Yes, and it’s very clever and innovative in solving some of the problems with other 3D systems.
TS: What is the most important advantage of this paper-based system?
KY: It’s particularly useful in allowing the user to sample very rapidly within a living tissue by splitting apart the layers of paper without having to fix or make histological sections. That’s a real beauty; you just rip it open and you’re right there at the heart of the tissue.
TS: How important do you think this method is going to be? Are labs going to move over to a 3D system, this or another one?
KY: Yes, I think that checking findings from 2D culture in a three-dimensional system is going to be quite important. For this particular method, the jury is really still out. People need to try it and compare it with other systems. I suspect that this is going to be one of several popular 3D models.
TS: How could you improve the method?
KY: No system’s perfect. It does not have vasculature but it also doesn’t have local fluid flow. The most important thing that’s needed is some kind of micropunch method to get at the central or lateral region. Let’s say you want to see what’s happening at the center. When you peel apart the paper and try to do proteomics or metabolomics—which I think this would be great for—you’re actually sampling the whole cross-section of the tissue. What you really need to do is get, say, 200 microns from the center so you can get rid of the lateral contamination.
TS: Does your lab have plans to try it out?
KY: Not at the moment. Our focus is on high-resolution microscopy, so we have to use very thin 3D models and the paper would interfere.
TS: Could we eventually replace animal testing?
KY: I don’t think so. It could help with reducing the need for animal testing but you could never replace it. There’s vasculature, time-dependent physiological and pathological remodeling, waves of inflammatory and immune cells.
Yamada is a cell and developmental biologist whose lab studies the two-way interaction of cells with extracellular matrix. You can access his review of the paper at http://f1000biology.com/article/id/1166491.