Tzu-Chieh (ZiJay) Tang

Zijay: Hi everyone. My name is Zijay and I’m a grad student at Department of Biological Engineering here. I work with professor Timothy Lu at the synthetic biology center as well as Neri here. I would like to thank the organizers, this is amazing opportunity for us to brainstorm the future of biological wearables. Zijay: So today I’m going to talk about how we can actually grow these materials from kombucha cultures. I’m really happy I’m not the first speaker.

00:28 - Rachel did amazing job laying all the foundations, because oftentimes you need to convince people why you need bugs in your materials. That’s a face. Since we are now all on board. Zijay: Living materials, they are very cool, they can sense and respond to environment and this is due to the huge advancement in the past two decades on synthetic biology. We can actually program cells to sense computer recording accurate, just like how you program computers. Zijay: There are a lot of living materials work that was proposed in the past 10 years. There are different design space you can operate in them from.

01:09 - These are the three most important dimensions I think, personally. You can have micro scale materials like biofilms, and you can have macro scale materials like bricks and mycelium, like mushroom walls. Also, you can use different design approaches. You can do a top-down. You predefine the forms, use 3D printed, you do casting hydrogels devices, or you can do bottom-up. You encode that information in the genome of the microbes, so they can do morphogenesis.

01:39 - And of course, you can have artificial scaffold like what we have seen before, or you can have the microbes produce the material, like in The Matrix, by themselves. Zijay: The work I’m going to talk about is at this corner, where we use a bottom-up approach, everything’s encoded in the DNA. Then, it’s at macro scale, and it’s a biologically fabricated matrix. This work is in collaboration with the Ellis Lab and Imperial College, London. Because one day they came to us they say, “Hey, we found this really cool kombucha material, and we isolated one bacteria from Czech Republic that’s really amazing in producing a lot of cellulose. So we’re looking to kombucha culture. We know this is like a hipster drink. It’s very healthy for you, as they say.

02:30 - Me personally, I’m not going to make any scientific claims about that, but you can grow this in your kitchen, and the kombucha mother is a very strong material. Potentially they can live forever as long as you transfer the mother into new batch of tea and sugar. Zijay: Of course a lot of artists, they have done amazing work using this kind of materials. Apparently you can make clothes. You can make one dressing and you can make a lot of different devices out of this kind of bacteria cell of those materials. Zijay: Were looking at different kinds of naturally occurring living materials. The most obvious example is plants.

03:11 - You see they can respond to light, they can have different functionalization on different surfaces on a tree leaves, and they can react and to stimulate. So chemicals or some molecules in the gas. And also, they have this symbiotic division of labor. Most of the plants they actually co-exist with microbes, and they perform different tasks. We were thinking, in this kombucha thing there are usually two members. You have bacteria that produces cellulose, and you have yeast there. You have yeast that produce basically alcohol and provide food for the bacteria. Zijay: We were thinking this is like a pretty good analogy. In a leaf you can see different kinds of specialist cells. They are in charge of different tasks. But in this cold culture we engineer, we can actually have the bacteria and produce the material, and have the yeast to be the computer that do the sensing, and then compute, and then provide an output. Zijay: This is the schematic.

04:16 - We are now going to engineer the bacterium. For the first reason, biologic is messy and slow. We thought if we want to achieve a level of have enough toolbox to engineer the bacterium and you will take about 10 years, so we look at the yeast. Luckily, yeast has been a major workforce in synthetic biology for decades. There are a lot of things you can do with yeast. Zijay: So to start with, you just mix the two microbes in the magical ratio, so they can coexist. After three to five days, you can have this pretty thick material. Zijay: This is a four day culture. You can just pull it up from the air liquid interface, and then you have yeast cells embedded in it. Zijay: The first thing we were wondering, if we can actually make this like a catalytic material. So we can have the yeast, which is commonly used to produce a lot of different enzymes.

05:12 - So we use an enzyme that can convert a yellow substrate into a red product. And we fuse this enzyme, like anchor it, onto the cellulose matrix. Then we found this material, when it’s wet, they can convert the chemical into the red product. Even when they are dried out, they can still do this because you don’t really need the cells to be alive once the enzymes are secreted. So there’s a use scenario where you can kill the cell, and still make a functional material.

05:44 - Zijay: You can actually pretty much do all the enzymes you can think of and functionalize this the cellulose matrix. In this case you can actually produce enzymes that can do blue pigments, or basically this is to show we can actually degrade contaminants and other hazardous chemicals in the environment. Zijay: Then we come into an issue, because I don’t know if you guys have seen kombucha culture, but there’s a sediment at the bottom. Basically the yeast, they are very heavy and dense. They tend to sink. We thought this is not really ideal because we want the computer to be in the material.

06:26 - So then, we started to play with the density of the growth medium. We increase the density and try to push the yeast up to the pellicle. On the left, you can see before the engineering of the solution, you have all the yeast loosely attached to the surface. But on the right, you can have the entire yeast colony embedded in the cellulose matrix. Zijay: This is what it looks like on the surface. You have a lot of yeast cells in there.

06:59 - Zijay: Once you bring the cell closer to the material, you can do more things. For example, in this case we secrete enzymes that can break down different positions along the cellulose fibers. You can actually tune the mechanical property of that material. Zijay: This is before producing the enzyme. Zijay: This is after. You can see these just become very loose, and you can see all the cells still get trapped into matrix. Zijay: By using different enzymes.

07:27 - You can have pellicles, like this material with different stiffness. Zijay: These are just to show you can do different characterization to see there is a difference. Zijay: One funny thing about this, we tried to make it stronger, but this is naturally super strong. So the only demonstration is to try to make it weaker, and we try to convince people sometimes it’s better to make it weaker. You can still make different functional materials out of it.

07:55 - Zijay: And of course, we want to do sensing and in this case we just use the preexisting sensors that yeast have. So in this case, they can sense an environmental hormone, estrogen, and turn on the expression of green fluorescent protein. What’s interesting about this is like they are functional when they are alive and wet. You can actually store this up to four months. The yeast cell are still alive in the matrix. You just have to reactivate it in a growth medium. And also you can swap out output from the GFP, which is not very useful, into some enzymes that can actually do bioremediation. So they can sense contaminants, they can remove the contaminant. Zijay: Then the final demonstration, we thought it would be really cool if we can actually do optogenetics that is use light as an input, and use the yeast to produce an output. So we engineer a optical circuit so they can actually sense blue light, and then produce an enzyme that produce bioluminescence.

09:00 - Zijay: This is a mandatory school logo photo, which is very common outside media lab. You can see, by using different engineering, like we have different yeast strings, we can have different resolutions. And we can tune the resolution by control the growth rate of the yeast. Or like on the right, you can let it grow for a longer time. You have a better resolution. Zijay: So those are the things we have done. So what we are thinking is, this is a 2D material thing, what we want is volume. We want a lot of volume. So we turned to YouTube for inspirations. This is a small scale one I believe a lot of people seem like they can actually do this in a much larger scale. So some of them in this YouTube videos, they actually use yeast as the catalyst. There’s an enzyme called catalase in yeast that can convert peroxide into oxygen, and it’s a miracle in nature. This is like the best, most efficient enzyme you can use.

10:02 - In this video they use a chemical as a catalyst, but if you use yeast, you can kind of have the same effect. So we were thinking this is what we’ve been trying to do right now. If you can actually start with very little volume of liquid, and then you can just add peroxide and you can have about 100 times increasing volume. Zijay: We are also doing Derika evolution. So what we think will be really useful is now you can have a living material that’s actually you can do evolution on the material properties.

10:36 - For example, here you have the density of the cell, you can make it magnetic, you can make it more adhesive. Zijay: This is another demonstration. They can actually take up the metal ions. So if you engineer a metal binding protein into the yeast, it’s basically like a plug and play system, because there are just so many things you can do with the lab strain of yeast. So you see this environmental [Essien] image. The black dots mean they’ve taken metal ions. Zijay: Also, you can produce a lot of different kinds of antimicrobials to kill pathogens, because we know bacteria cellulose is actually one of the most popular one tracing materials.

11:22 - So if you can actually incorporate active ingredients into it, that’ll be pretty cool. Besides killing microbes, what we are trying to do now is, they can actually provide a lot of growth factors to direct the differentiation of STEM cells or immune cells. Zijay: What would be really cool to me, we seen a problem before is about yeast cells being really dense. This would not be the problem in this space. So, if we can actually provide them like a low gravity environment, they can form a solid phase, very homogeneous distribution, kind of like living material.

12:00 - Zijay: Yeast has been used for devices for point of care, like point of detection, because they can actually provide a lot of medical relevant molecules that are human use. So we’re thinking maybe this is an opportunity. We should really look into that. Zijay: With that, I would like to thank a lot of the people I work together, in this work specifically. People at Imperial, and also Brandon here, and George Sun at Belcher Lab. Thank you. .