Laser focused 3D printing

3D printing - or additive manufacturing - has revolutionised engineering. We can make and test designs for bespoke objects quickly and cheaply. Rolls-Royce recently even began printing hard-to-manufacture parts for some of their jet engines this way. But there are limitations: you have to build up your object layer by layer, which means some structures are still tricky to make: like one object that needs to be inside another object, for instance. Now scientists have come up with a clever solution, both literally and metaphorically: they have a light-sensitive fluid that “sets” when light of a certain colour shines on it. “But, surely, wherever the light shines through you’d get a line of set material!,” I hear you cry. No, because as Stanford University’s Tracy Schloemer explains to Robert Spencer, she’s come up with a material that contains particles that convert a different, inactive, colour of light to the critical colour that sets the material. This means you can control the setting process and make objects inside objects, like the miniature boat she showed Robert…

Robert - Tracy, I'm looking at this picture and it looks like something out of The Office. There's this small item in a piece of jelly. What is it? What are we looking at?

Tracy - It is not a joke from Dwight Schrute. It is a boat that I have printed and used light to pattern on the inside of the jelly, or jello, as we would call it in the States.

Robert - This is a 3d printed boat that you've put into this solution. How did it get there?

Tracy - What I did is I used a laser, focused down, and then that's absorbed by a molecule in the jello. That allows for me to print.

Robert - Okay. It's one of these curing resins, like people might be familiar from nail gels or dental work?

Tracy - Yes. Except we made it ourselves.

Robert - So it needs light in order to set?

Tracy - Correct. And a very specific wavelength of light as well. So, when I shine the red light at it, it doesn't necessarily work right away. We have to have a certain power density to generate this blue light.

Robert - So why can't you just shine blue light into it?

Tracy - When you shine blue light at it, that blue light gets absorbed at the surface. So, I wouldn't have been able to print benchy deep within that vat of jello, I would have only been able to print benchy from the surface, and I would have had to move the resin up over time.

Robert - We should probably clarify, benchy is the little boat in there.

Tracy - Benchy is the adorable little boat. Yes.

Robert - You've managed to print this by focusing this blue light inside the resin. But, you say you can't just shine blue light because then it sort of prints at the surface. So, how did you get the blue light into the resin if you can't shine blue light onto the resin?

Tracy - We generate that blue light in situ or inside of that resin. We have some very special molecules that can convert red light into blue light. And we can do that really quite precisely.

Robert - Does that mean that you've imbued this resin with the special molecules that you've designed? How does that work?

Tracy - Yeah. What we do is we have these special molecules and we encapsulate them. If you're familiar with the drink boba, it's like we have these tiny little nanometer size boba beads, and they're so small that can't see them directly with your eyes. The resin, the jelly still looks clear, but we have those embedded in the resin. We can generate that blue light by focusing the red light really well on those boba beads and that's how we're able to do it.

Robert - So you focus this red light and then suddenly there's this flash of blue light at the point where all the focusing comes together.

Tracy - Yes, it's really cool. We can use an LED and that's much lower power than using a laser.

Robert - We've seen similar kinds of technologies before, similar light cured manufacturing. What sets this apart from the existing things that you can buy off the shelf?

Tracy - Off the shelf, if you have a spare couple million US dollars, you can buy a nanoscribe, and you're going to be able to get really, really good resolution, but you're stuck with really tiny volume. We can print a thousand times larger than that. We can print at much lower powers. We can print faster. To be fair, our technology isn't commercially available yet.

Robert - Where else is it going? This ability to take lower frequency light and upscale it to higher frequency light. Does that have any uses beyond making cute boats?

Tracy - Yes, but it is a huge challenge. How do we get high energy light precisely where we need it? Imaging optogenetics, drug delivery, where you have to use low energy light to go beyond the surface of your skin. Maybe we have a drug we want to deliver but we need yellow light to trigger it to release in the body. Well, how can we generate that high energy light beneath the surface? We can use these up conversion nano capsules that we've developed.