3D printing with Synthetic Biology

In this blog post, I'm just going to toy around with an idea that's been bouncing around my head. This is more just to get it on paper, because it will probably never get built. (I'm still free this summer if anyone wants to take me on in a lab though...) Also, the biology only begins in the fourth paragraph.

I've been thinking about rocket engines a bunch recently, having looked at Rocket Team's liquid fuelled rocket (I'm not on Rocket Team, I just think it's cool). Rocket engines are really hard to build (it is rocket science!) for a few reasons: the materials are really exotic (I think they mentioned Zirconium Oxide?), the engine needs to be cooled so it doesn't melt (sophisticated rockets use unburnt fuel as coolant, but this requires tubing in the engine, which adds more complexity), and the surfaces need to be really smooth. Rocket Team uses a milling machine, which creates smooth surfaces, but requires that the engine be built in many parts so the cutter can actually reach what it needs to cut.

Personally, I think 3D printing is much better suited to the challenge. It could build the entire part in one piece, which would reduce weight and allow for built-in tubes for cooling. However, current 3D printers either (a) can't create a good surface finish, or (b) are very, very expensive. Can synthetic biology help?

Synthetic biology might actually be able to help with 3D printing. The size of a cell is definitely comparable, if not smaller, than the tolerances that can be achieved with a milling machine. Maybe we can do something like stereolithography with cells?

Here's the plan:

1. Build a cell that lives near the surface of some sort of opaque, water-based broth
1. When it absorbs light (which can only happen at the surface because of the opacity), it secretes Carnauba wax
1. Wax is insoluble in water, so the wax remains solid until the end of the print.
2. Then, grab an empty vat, put one of those 4K projectors on top (about $4000-$10000 right now)
3. Slowly fill the vat with more solution while the projector projects cross sections of the rocket engine onto the surface.

Why Carnauba wax? I chose wax because it is commonly used in manufacturing metals. It's common practice to build something with wax, bury it in casting sand, then burn off the wax and pour molten metal into the cavity. Usually paraffin wax is used, but that is a petroleum product, so we need to use either a plant wax or an animal wax (beeswax). I chose plant wax because beeswax probably has some complicated relationship with the honey. Carnuaba wax is produced by Copernicia Prunifera, and has a great surface finish, so that seems ideal.

So how might we design that cell?

1. First, what kind of chassis do we want to use?
1. I think algae are best suited, because they have already evolved to float and thrive on the surface of water.
2. Second, how do we detect light?
1. Let's not reinvent the wheel here. The easiest solution is usually the best, so we can just steal from (be inspired by) the Coliroid iGem team.
2. We'll use their Cph8, and their promoter.
3. Third, how do we secrete wax?
1. It turns out that one pathway to wax has only a single enzyme.
2. So, we can extract that enzyme from C. Prunifera, and stick that right after the promoter
3. We probably should also just constitutively express a bunch of related enzymes from C. Prunifera, because may be need membrane pores or other machinery. Who knows?

Would this work? Probably not. I'm guessing putting eukaryotic genes from C. Prunifera into algae (another eukaryote) probably has a lot of complications. But who knows?

Some other random thoughts:

• There should be some kind of surfactant in the solution, so that it spreads evenly over the existing layers
• Will the enzyme keep working when the light turns off? Maybe we should tag it for destruction after a short time.