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From discovery to technology: a mucus story.

This paper is about how mucins, a family of glycoproteins that composes our mucus, can be used as a cell-repellent coating for cell patterning. But this is also a story about how perseverance, good communication and a bit of luck are key in research.

It all started during the very first days of my postdocs at MIT. I knew that I wanted to find ways to exploit the incredible properties of the mucin biopolymers by assembling them into new materials, but I was still uncertain of what my postdoctoral work was going to look like. So I did the only thing I could do; read, develop my ideas and start with couple simple experiments. One of the first things I did in the lab was to generate and study adsorbed mucins monolayers on surfaces, most probably a reminiscence of years of surface engineering I had endured during my PhD.

At about the same time, a graduate student in the lab was studying the interactions between neutrophils and mucus gels. He was having difficulties differentiating his cells and I was helping him out troubleshooting. Imaging the cell migration within the three-dimensional mucin gel was challenging. So we thought, “why not start with a more simple system and use mucin coatings?”. The following day, I had a “quick try”, grabbing cells we had in the lab (HeLa as it happened to be) and seeding them on my mucin coatings. To my surprise the cells would not attach to the coating!

The observation was interesting, but we were not quite sure what to do with it. So the project was put in the background for a while and I started working on other interesting projects. Then, about a year later, others in the lab started using microfluidic devices to study biofilm susceptibility to antibiotics. The devices were rudimentary, with a single long channel an inlet and an outlet. And then it hit me; if I could use these microfluidic channels to spatially define where the mucin would adsorb, I could confine cell growth on the surface. I borrowed the device, and with the help of my labmate, I injected mucins through it and seeded cells on the resulting mucin coatings. And there it was, a clear band of cell-less plastic appeared in the middle of the petri dish, perfectly defined! Then, it was just a matter of asking our microfluidic collaborators to adjust the device to smaller patterns. And voila (mucin coated area is in green in the left image):


But that was not the end of it. I wanted to understand a bit more about the repulsion effect of mucin coatings and identify the parameters that were critical for the effect to occur (an engineer wanting to understand? Where is the world going?). I noticed that mucins were not forming cell-repulsive coatings on every surface; polystyrene was better than glass for example. The obvious difference was the in the hydrophobicity of the two materials. Perhaps hydrophobicity was key? Luckily, I had an ongoing collaboration with a chemical engineering group. I asked the graduate student that I was working with, “can you make thus glass slide hydrophobic for me?”, she replied “sure, easy!” A couple weeks later, we had data suggesting that a hydrophobic surface is key for cell-repulsive mucin-based coating to form.

This project took me from a simple observation to a full-blown technology. As I look back at this journey, it is obvious that this would not have been possible without the various interactions I have had with my fellow researchers. They helped create meaning out of it that eventually led to a technological innovation. So it might be obvious to say, but have a cup of coffee (or tea) with your labmates and next-door labmates from time to time. Ask them about their research and let them know what you are up to. You never know what good can come out of a cup of coffee (or tea).