Reconfigurable Active Matter

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NONTECHNICAL SUMMARYThis award supports theoretical, computational, and data-intensive research and education and education that focuses on the design of reconfigurable active materials. When one thinks about molecules or nanoparticles in a medium, very small objects that aimlessly move and vibrate come to mind. Over the past decade, it has been discovered that it is possible to chemically alter the surface of nanoparticles so that they can utilize chemical energy in their surroundings, and they act like microscopic engines. Thus powered, they can run through a medium like bacteria at very high speeds, and in a controllable manner. This breakthrough resulted in the emergence of a new field of research that is today called active matter and includes the study of both man-made and biological microscopic systems. Because of the direct analogy with biological systems, groups of activated nanoparticles are often referred to as synthetic "living" systems, and their collective behavior is indeed reminiscent of that exhibited by swarming bacteria or flocks of birds. One of the most appealing features of these nanoparticles is that they can be made into arbitrarily complex shapes, and with a wide range of mutual interactions and speeds that can be turned on and off by exposing them to blue light. The idea of this project is to use a combination of theoretical and cutting-edge numerical and data-science strategies, including machine learning, to study the properties of assemblies of active particles. The goal is to design how these particles should be put together or linked to each other so that they can form functional microscopic objects. So, the PI aims at studying how to create microscopic “machines” that can not only quickly move through a medium, but also acquire specific shapes, and, like proteins, change their shape over time in a controllable fashion. This serves to define the term "reconfigurable active materials". If successful, this project will help enable the development of robust strategies to design the next generation of smart materials built from microscopic active machines that are put together by spontaneous assembly of active nanoparticles. The applications of reconfigurable active materials in our daily life are countless, and cover areas ranging from stimuli-responsive materials, or sensors, to tissue repair and wound healing devices. More generally, they may open new opportunities in the field of nanomedicine. This project includes educational activities, including training undergraduate and graduate students, mentoring postdoctoral research fellows, and collaboration with on-campus organizations dedicated to the advancement of women and other groups that are underrepresented in science. TECHNICAL SUMMARYThis award supports theoretical, computational, and data-intensive research, and education with the aim of designing reconfigurable active assemblies from self-propelled nanoparticles. Characteristic of active systems is the out-of-equilibrium nature of its constituent parts which results in a phenomenological complexity that is extraordinary and has no equivalent in the realm of equilibrium thermodynamics. The study of the collective behavior of self-propelled particles, one of the simplest realizations of an active system, has been at the forefront of recent theoretical efforts. Ideas, and theoretical frameworks that have been developed to study these synthetic units have found fertile ground in several biological systems which are also inherently out of equilibrium, or occur in an environment where significant active fluctuations can occur. The PI plans to use a combination of theoretical approaches and numerical simulations to develop rational design strategies to engineer reconfigurable active materials based on the controlled assembly of self-propelled particles. This will be achieved through investigating the role that hydrodynamic interactions can play in how active agents interact with each other and behave when near surfaces and colloidal cages, or in confining media, and harnessing it to design reconfigurable active clusters. Inspired by recent experiments on 4D printing, the PI will also explore an alternative path towards structure formation and active reconfigurability that does not rely on self-assembly, but on the folding dynamics of linearly connected active colloidal swimmers. The coupling between active and elastic forces developing within a linearly, or two-dimensionally, constrained set of active particles provides untapped potential towards the goal of reconfigurability without self-assembly, and leads to intriguing analogies with protein folding design and the physics of DNA origami. The PI anticipates that the outcomes of this project will help advance out-of-equilibrium statistical mechanics and provide insights into design strategies for bottom-up assembly of active reconfigurable structures. The tools and theoretical approaches that the PI will develop in this research activity should be easily applicable or extended to other active systems, and may have important implications for biological problems that rely on similar physical mechanisms, such as tissue repair and wound healing, and in nanomedicine. This project contributes to the education of undergraduate and graduate students. An outreach plan in collaboration with the on-campus organization Women in Science at Columbia, whose efforts are dedicated to the advancement of women and underrepresented populations in science, technology, engineering, and mathematics is currently underway, and will be continued and extended.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.