Calendar of MRSEC Events

Abstract: Engineers design structures to predictably resolve forces and moments through a primary load path in which deformations are small and linear. There is an enormous opportunity to design structures that rely on nonlinearities and instabilities to perform advanced functions and propagate forces in nontrivial ways. This talk will demonstrate how the complex mechanics of coupled nonlinear structures can create novel actuators, artificial muscles, soft robotic grippers, and perform rudimentary mechanical computation. I will begin by discussing the nonlinear deformations of beams bending together as they pack and compete for space. Then I will discuss how engineering defects into thin sheets provides a way to control how they deform. Typical defects include folds(origami) and cuts (kirigami), and I will describe how these defects enable the design of functional mechanical metamaterials. Lattice cuts provide a simple way to enhance the stretchability of a thin sheet. We show that certain lattice configurations are more stretchable than others, while certain configurations produce an array of bistable unit cells. The bistability provides a means to tune the stiffness of the structure in situ, while also providing a means for mechanical logic. Lattice cuts on curved sheets, i.e. kirigami shells, enable additional functionality. The natural curvature of the sheet causes the bistable lattices to curve together and close around an object, which enables the kirigami shells to act as soft robotic grippers. We will discuss the optimal kirigami geometry for a robotic gripper, and describe how the structures perform at both grasping and holding irregular objects. Finally, by coupling transmissive, multistable shells we developed universal logic gates, (NAND, NOT, XNOR), and combine them to demonstrate basic mechanical computation: binary addition via a half adder mechanical circuit.

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Abstract: The biomechanical properties of neuronal cells are critical to their development, function, and structural stability. These properties influence cytoskeletal organization, axonal growth, and the formation of functional synapses. While substantial progress has been made in understanding neuronal growth and connectivity, a complete picture of axonal dynamics—incorporating the mechanical interactions between neurons and their environment—is still lacking. In this talk, I will present an integrated experimental platform that combines three high-resolution techniques: atomic force microscopy, fluorescence imaging, and traction force microscopy. Using this experimental setup, we measure the elastic modulus of cortical neurons with high spatial resolution and correlate these measurements with the traction forces generated by axons on their substrate. We also track cytoskeletal components to connect axonal behavior with changes in cytoskeletal dynamics, cellular volume, and cell biomechanical properties. In addition, I will discuss biomechanical measurements performed on human leukemia monocytic (THP-1) cells encapsulated in silk fibroin biomaterials. These results offer valuable insights for designing advanced biomaterial interfaces aimed at enhancing cellular protection and functional integration.

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Abstract: Chemical cues mediate interactions between marine phytoplankton and bacteria, underpinning ecosystem-scale processes including nutrient cycling and carbon fixation. Specifically, viral infection alters phytoplankton metabolism, stimulating the release of chemical cues, but how this process influences ecology and biogeochemistry is poorly understood. Here, we determine the impact of viral infection on dissolved metabolites from marine cyanobacteria and the subsequent chemotactic response of heterotrophic bacteria. We developed a novel microfluidic device for high-throughput bacterial chemotaxis screening, which - together with time-resolved metabolomics - proved essential to disentangle the roles of diverse chemical compounds in this process. Our results show that metabolites released from intact, virus-infected cyanobacteria elicit strong chemoattraction from heterotrophic bacteria, especially during early infection stages prior to lysis. Ultimately, these findings establish a new mechanism for resource transfer that might impact carbon and nutrient fluxes across trophic levels.

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Abstract: Human influenza viruses, as well as SARS-CoV-2, undergo fast evolution driven by immune pressure of their hosts. Viral strains and our immune systems are a tightly coupled, fast-evolving ecosystem. Fitness models have become an important tool to predict these dynamics and to guide the selection of vaccine strains. In this talk, I present the cross-scale concepts of current predictions: changing molecular interactions of viral proteins and human antibodies affect immune protection, generate time-dependent fitness differences between strains, and shape the global evolution of the pathogen. This analysis contains building blocks of a new, computable framework for human adaptive immunity.

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Abstract: Identifying effective immunization schemes against highly mutable pathogens such as HIV and influenza viruses remains a persistent public health challenge. Our work addresses this challenge by analyzing a simplified model of affinity maturation, the Darwinian evolutionary process that B cells undergo during immunization.

In this presentation, I will introduce a minimal framework that identifies optimal selection forces exerted by time-dependent vaccination protocols. This framework aims to maximize the production of broadly neutralizing antibodies (bnAbs) that can protect against a broad spectrum of pathogen strains. The model utilizes a path integral representation within a mean-field limit to provide guiding principles for optimizing vaccine-induced selection forces. Additionally, I will discuss our ongoing research that extends this theoretical framework to more complex immunological scenarios. This extension employs regression algorithms to derive simplified dynamical equations from time series data generated by agent-based and population simulations. These equations effectively capture the evolution of B cell populations and antibody responses, providing valuable insights into antigen competition and other nonlinear effects that emerge from the complex feedback mechanisms of immunological memory.

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Abstract: Nature has developed diverse adhesion strategies, from mussel-inspired underwater glues to gecko-like dry adhesion. Silk fibroin, with its tunable structure and exceptional mechanical properties, provides a versatile foundation for bioinspired adhesives. This seminar examines key natural adhesion mechanisms and how silk fibroin can be engineered into various material formats to create functional adhesives. By leveraging its unique properties, silk-based adhesives can be tailored for applications ranging from underwater adhesion to biodegradable labeling and even superhero inspired adhesives.

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Abstract: The towering successes of twentieth century theoretical physics were marked by two guiding principles: symmetry and energy functionals (reflecting equilibrium dynamics). Yet how we can exploit these principles to develop a theory of living systems is unclear since the biological world is composed of heterogeneous, interacting components operating out of equilibrium. In this talk, I will argue that one possible strategy for taming biological complexity is to embrace the idea that many biological behaviors we observe are “typical” and can be modeled using random systems that respect biologically-inspired constraints. I will focus on high-dimensional ecology and show how we can use tools from statistical physics (cavity method, DMFT) to understand the emergence of chaos in the ecosystems with non-reciprocal interactions.

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Abstract: In this talk, we study a minimal model of a system with coexisting nematic and polar orientational orders, where one field tends to order and the other prefers isotropy. For strong coupling, the ordered field aligns the isotropic one, locking their orientations. The phase diagram reveals three distinct phases—nematopolar (aligned orders), nematic (independent orders), and isotropic (vanishing orders)—separated by continuous and discontinuous transitions, including a triple and a tricritical point. We find unique critical scaling for the nematopolar-nematic transition, distinct from standard nematic or polar universality classes. Additionally, in the locked nematopolar phase, we show nematic +1/2 topological defect pairs are connected and confined by strings with constant tension. These strings arise from frustration in locking the orientational orders and can be interpreted as elongated cores of +1 polar topological defects. When a sufficiently strong background field couples to the polar order, all topological defects are expelled from the region. Analytical predictions are quantitatively confirmed by numerical simulations. Based on joint work with Amin Doostmohammadi.

More about the Soft Condensed Matter Seminar