 Okay, so can you hear me? So thank you very much for the introduction. This is official title of my talk, but I should probably change it to, it's a wrong presentation, one second please. But I should probably change it to collective behavior in biomechanical hybrid system. So, you must ask me what is my biomechanical hybrid systems and why we are so interested in studying it. And if you go to department of energy website, you will find a few grand challenges. And one of the grand challenge is to discover general principles describing the systems far from equilibrium to enable efficient and robust by biologically inspired machines. So in other words, the government wants us to create something which combines the properties of engineered mechanical materials and living organisms. I don't know if we can see it, but this is like a Robocop. And one of the, so these systems, they can adapt to environmental changes. They can respond to stimuli. And more importantly, they can, since they're alive, they can self heal damages. And before playing with the humans hybrids biomechanical hybrids, so we decided to start with something a little bit simpler with swimming bacteria. So I'm sure that many of you have seen these movies or similar movies many times, but yeah, bacillus subtlos and many other bacteria like E. coli, they're pretty good swimmers, but at 18 helical filaments, flagella, they can swim pretty fast. And what is interesting that if you increase the concentration of bacteria, they start to swim collectively like here, which is manifested by the formation of large-scale vortices, jets, flows, and the correlation length of velocity field is much larger than an individual size of a single bacterium. And you might think that since they swim collectively, probably bacteria should be aligned parallel to each other and it should look like enigmatic material. But in reality, this is not the case. It turns out if you zoom in on a fraction of this collective behavior, bacteria are not very well aligned. So the orientation is pretty much random. So while there is like a long range of orientational order for velocities, there is no long range orientation for bacterial orientation. But we can fix it by putting bacteria inside synthetic material, liquid crystal. So fortunately, there is liquid crystal, which is not toxic for bacteria. It's a leotropic liquid crystal. Basically, it's a mixture of salt and water and a certain range of salt concentration and certain range of temperature. This material goes to the enigmatic phase and by mixing bacteria with the liquid crystal, we create what we call living liquid crystal. So it's a synthetic material combining the properties of life matter, such as bacteria, cell self-propulsion, with the properties of liquid crystal, such as long range orientational order, anisotropic viscosity and anisotropic elasticity. So before talking about the results of our work, I just want to quickly describe the technique we used. It's called cross polarized microscopy. So like long story short, basically, this is a standard technique to study liquid crystal. So by transmitting the polarized light through the liquid crystal and blocking it with the second polarizer perpendicular to the first one, you get the image and intensity allows you estimate the orientation of molecules of liquid crystal. So what we did, we put this liquid crystal inside, we sandwiched it basically between two glass plates, treat it in a special way. I don't know if you can see them, but these are bacteria. So the director field, which is parallel to the orientation of molecules of liquid crystal is uniform everywhere. And as you can see, the bacteria swim parallel to this director field. That happens because of the tourism. So first, since the viscosity of liquid crystals highly isotropic, the drag in this direction is much less than drag and perpendicular direction. That's why bacteria prefer to swim this way. But also if you immerse any even immatial object, elongated object in the liquid crystal, it will align parallel to the director field just to minimize the free energy. But you can also see that swimming bacteria flagella creates a wave, which is visible using the optical microscope. And that's quite interesting because flagella is only 24 nanometers wide, and it's not possible to see it in optical microscope without like fluorescent tricks, for example. But if we use liquid crystal, we can visualize the dynamic of flagella. We can measure pitch. We can measure frequency of the rotation. And that's quite useful tool because, for example, in this experiment, two bacteria swimming next to each other, like they swim parallel to each other. And while they are approaching, the difference in their swimming speed is reducing. But what is even more interesting that the difference in the frequencies of flagella rotation is also reducing. So this is dashed line frequency of flagella rotation. And this is an evidence of hydrodynamic synchronization between flagella and different bacteria. And this may be quite important because the synchronization of flagella may be one of the reason why at high concentration, bacteria swim much more efficiently and much faster than at low concentration. What is also was quite puzzling that in spite of the fact that liquid crystal is very viscous medium, the viscosity is by 100 or 1,000 times larger than viscosity of water, bacteria swim still pretty fast. So the blue line represents the velocity distribution. And as you can see, the average swimming speed is about 15 microns per second, which is only 25% less than the swimming speed of the bacteria in water, 20 microns per second. The rotation rate of the flagella in water is about 100 Hertz. The rotation rate in liquid crystal is 15 Hertz. So it's seven times less. But the swimming speed is only by 25% less, which means that while in water, single bacterium travels 0.15 microns per each rotation of flagella, somehow in liquid crystal the same bacterium travels one micron per each rotation of flagella. So it's like a corkscrew motion, much more efficient. And the reason why it happens is that in liquid crystal the flow created, the bacteria virtually swim inside a channel, inside a tube. So since the viscosity is very isotropic, the flow created by a single bacterium is allocated along the line parallel to the bacterial body. So the flow decays very slowly in this direction and very fast in the perpendicular direction. That's a very important result because if we have many bacteria or a few bacteria, the interaction range is highly isotropic. So they interact at very large distance if they're on the same line, on the same trajectory, and they don't interact if they're on the different lines even if they're very close to each other. And in this movie, for example, you can see that this fluorescent tracer, this white spot will be transferred by the bacteria while the bacteria is quite far, 100 microns from this particle. I don't know if you will be able to see it, but we will try it. So yeah, sorry, it's not visible. But this particle is moved by the bacteria while the bacteria is quite far from this particle, but at the same line. And before talking about the collective behavior, I just want to quickly show you a few quite interesting tricks how we can guide bacteria. For example, we can create such a configuration of liquid orientation of liquid crystal, like I don't know, star configuration. Then all bacteria, since they're swimming parallel to the director field, they will swim towards the center and away from the center. So they will concentrate in the center of this star. But if we create like a vortex configuration like here, it's even more interesting. Bacteria will think that they are fish now and they will school. And take a note that there is certain type of instability. So you can see the formation of wave like this. And the mechanism why you see this instability, well, basically you can see like three wave lengths, three periods here, or four, sorry, four periods here. So there, the mechanism is the collective interaction between bacteria. So basically this is the collective behavior. Of course, we can create a system of vortices, interacting vortices or non-interacting vortices. So here you can see like basically four different schools of bacteria. So the reason why you saw these waves is following. So remember, I told you that the bacteria, the range, the interact range of bacteria is quite large if they're on the single trajectory on the same line. So if you have one bacteria, the velocity field decays very slowly in this direction. And, but still decays. And if there isn't another bacteria here, the hydrodynamic forces created by the first bacteria acting on the head and the tail of another bacteria are different. And because of this, the first bacteria introduces a torque. And this torque hydrodynamic interaction between bacteria tends to misalign bacteria. While elastic forces and liquid crystals and hydroelastic material tends to align them back. And the interplay between elastic forces and hydrodynamic interaction defines the wavelength of this instability you saw. And in this experiment, for example, the first, we make bacteria immatial temporarily by cutting off the oxygen. So we reduce the oxygen concentration to zero, they become non-matel, and they align parallel to the director field uniformly everywhere. So their orientation is like this everywhere. And then if you use a cross polarized microscopy, you don't see anything, you'll see like a black color. But then we introduce oxygen to the system from the left side and bacteria start to swim. They start to interact and they create a bending instability. And this bending instability can be observed using again cross-parallel microscopy as stripes. And these stripes propagate to the right with the diffusion of oxygen. So if you continue to increase the activity of the bacteria or concentration of bacteria, you can create like a turbulent motion like in this movie. So it's very similar to what I showed you on the first slide, but now it's a little bit slower. But what is more important that now bacteria very well align with each other. So it's turbulence in the pneumatic material, pneumatic medium. And you can see the formation of defects here. I'm not gonna talk about it, but that's very rich system and we continue to study it now. And at the very last few minutes, I want, so you saw that bacteria may behave like a fish and now I'll show you that they can behave like ants. So before I talked to you about, so in the previous experiment, the orientation of liquid crystal was parallel to the glass plates. So it's called a planar orientation. We can also create a hematropic orientation. Then the liquid crystal is perpendicular to the glass plates. And then if the bacteria is relatively short and not very fast, it will become, it will be aligned parallel to the liquid crystal molecules perpendicular to the glass plates. It will spin the flat shell, but it will remain vertical. And this bacteria is seen from the top as dots here. But some bacteria, if they're relatively long and more importantly, if they're powerful enough, they can escape this vertically trapped state and become swimming, horizontally swimming. For example, in this video, you see that now most of the bacteria are vertical, but then we introduce oxygen to the system. They start to swim and they escape this vertical state and start to swim horizontally. What you can also notice that each bacteria will create a wide trace. And this trace is basically, you'll see in the other movie. So this trace is a disturbance of vertically, initially vertically oriented director field. So swimming bacteria creates such configuration like, I don't know, the final configuration and attracts other bacteria to the trace. And you can see in this movie that, for example, there is a few bacteria traveling next to each other free bacteria. So the first bacteria create a trace and other bacteria follow this trace. So, and you may find another example, then the bacteria, for example, here, find like a trace from the previous bacteria start to follow because swimming along this trajectory is easier than swimming somewhere else. And I think this is the end of my talk. I just want to thank my collaborators and ready to answer your questions.