Research
Active Matter
Active matter systems, whose constituents possess the ability to convert internal energy or energy from the local environment into their own motion, their behavior is thus intrinsically out-of-equilibrium. Active systems exhibit a plethora of exotic phenomena, such as clustering, segregation, swarming, vortex formation, and anomalous density fluctuations. Many systems with such behavior can be found across many length scales in nature, such as crowds of humans, schools of fish, flocks of birds, and colonies of bacteria. The majority of natural active suspensions often contain high concentrations of micro-organisms and can display intriguing collective behavior such as bio-convection, formation of biofilms, bacterial turbulence, and swarming, where cells 'self-organize' into partially coherent swimming structures. Understanding and controlling such collective phenomena is a major challenge and is relevant across many disciplines, ranging from microbiology to chemistry to material science to physics to engineering.
1. Synthetic Biological Systems:
Biological cells are remarkable soft microsystems that possess the ability to process chemical and mechanical information and dynamically respond to internal and external stimuli. Despite decades of research, unraveling the mysteries of cellular self-organization and function remains a fundamental challenge in modern science, and understanding the basic principles of life is crucial to advancing our knowledge of the world around us. However, by engineering simple cell-mimicking systems, we can not only gain insights into the workings of natural cells but also derive design principles for creating soft functional micro-robots capable of performing cell-like tasks and beyond.
Active Vesicles
Biological cells generate intricate structures by sculpting their membrane from within to actively sense and respond to external stimuli or explore their environment. Several pathogenic bacteria provide examples of how localized forces can strongly deform cell membranes from the inside, leading to the invasion of neighboring healthy mammalian cells. Although giant unilamellar vesicles have been successfully used as a minimal model system to mimic biological cells, realizing a minimal system with localized active internal forces that can strongly deform lipid membranes from within and lead to dramatic shape changes remains a challenge. We address this challenging task by developing a unique synthetic system where active particles are confined within giant vesicles.
Ref. H. R. Vutukuri, et al., Active particles induce large shape deformations in giant lipid vesicles, Nature, 586, 52-56 (2020). https://www.nature.com/articles/s41586-020-2730-x
2. Self-propelled particles (SPPs) or Artificial Mircroswimmers:
Locomotion is the hallmark feature of living systems. This has fueled an emerging new research field, namely active matter, focused on designing synthetic active building blocks with unique capabilities such as autonomous transport, self-assembly, and adaptation to local environments. In recent years, there has been an increasing interest in developing new micron-sized self-propelled particles (SPPs) or artificial microswimmers.
a. Two-engines with one body:
By exploiting different photocatalytic activities on each side of half-gold-coated anatase Titania particles, we can reverse the propulsion direction on demand. Control over the surface chemistry enables a rapid reversal of propulsion direction using distinct wavelengths of light. Now the direction of motion entirely depends on the wavelength of the incident light. Strikingly, the trajectories of our direction reversible particles resemble the motion of run-and-reverse behavior of several marine microorganisms, e.g., Myxococcus xanthus, Pseudoalteromonas holoplankton, and Vibrio alginolyticus.
Ref. H. R. Vutukuri, et al., Light-switchable propulsion of active particles with reversible interactions, Nature Communi. 11, 2628(2020). https://www.nature.com/articles/s41467-020-15764-1
b. Micropumps: active and passive mixtures
Here, we demonstrate that our propulsion-direction switchable particles can be used to stir or pump the fluid locally with light.
Ref. H. R. Vutukuri, et al., Light-switchable propulsion of active particles with reversible interactions, Nature Communi. 11, 2628(2020).
https://www.nature.com/articles/s41467-020-15764-1
Check out the highlight of our paper Nature Chemistry Bolg, (2020).
c. Active colloidal polymers
We have developed an effective, yet simple method for the fabrication of internally powered active colloidal polymers or colloidal bead chains with tunable stiffness. Our active bead chains are the first experimental realization of a new type of self-propelled particles that spontaneously rotate or spin when the spherical swimmers are rigidly connected, while they show flagellum-like propulsion when the connections between the spherical swimmers are semiflexible.
Ref. H. R. Vutukuri, et al., Rational design and dynamics of self-propelled colloidal bead chains: from rotators to flagella, Scientific Reports, 7, 16758 (2017). https://www.nature.com/articles/s41598-017-16731-5
Rotators
