Bi Research group - Metamaterials

Metamaterials

Our research on metamaterials focuses on creating innovative materials inspired by the complexity and functionality found in biological systems. We explore tunable hyperuniformity in cellular structures, revealing how these materials can suppress density fluctuations to exhibit exceptional optical, mechanical, and acoustic properties. Additionally, we develop synthetic biomimetic systems that mimic the collective behavior of cell monolayers, uncovering shape-driven transitions that inform the design of advanced materials. By leveraging nature-inspired designs, we engineer disordered acoustic and photonic materials with tunable, isotropic bandgaps, robust against defects and adaptable to real-time environmental changes. These breakthroughs open new possibilities for designing next-generation materials with customizable properties for a wide range of applications.

Tunable Hyperuniformity in Cellular Structures

Our recent work explores the fascinating world of hyperuniform materials, which lie at the intersection of order and randomness. These materials are distinguished by their ability to suppress density fluctuations and exhibit vanishing structure factors as the wave number approaches zero. Such unique properties impart hyperuniform materials with exceptional optical, mechanical, and acoustic characteristics, making them highly valuable in various fields of materials science and engineering.

Traditional approaches to creating hyperuniform structures, such as collective-coordinate optimization and centroidal Voronoi tessellations, have largely been computational and often struggle to replicate the complexity found in naturally occurring systems. In our work, we introduce a novel theoretical framework inspired by the collective organization of biological cells within epithelial tissue layers. By adjusting key parameters, including cell elasticity and interfacial tension, we have identified a range of hyperuniform states, spanning from fluid-like to rigid, each with distinct mechanical properties and characteristic density fluctuations.

This research not only deepens our understanding of hyperuniformity in biological tissues but also opens new avenues for designing advanced materials with customizable properties. By drawing inspiration from the natural world, we aim to bridge the gap between theoretical models and practical applications, paving the way for the development of next-generation materials with tailored functionalities.

Related Publication(s):

Tang, Yiwen, Xinzhi Li, and Dapeng Bi. "Tunable Hyperuniformity in Cellular Structures." arXiv preprint arXiv:2408.08976 (2024). https://arxiv.org/abs/2408.08976

A synthetic biomimetic system for cell monolayers

Many critical biological processes, such as wound healing, rely on the ability of densely packed cell monolayers or tissues to transition from a jammed, solid-like state to a fluid-like one. While numerical studies suggest that changes in cell shape alone can drive this unjamming process, experimental evidence has been inconclusive, as fluidization due to density changes in living systems cannot be excluded. The challenge is further complicated by the fact that cells can modulate their motility, and even in assemblies of rigid active particles, changes in self-propulsion dynamics can have complex effects. In this study, we designed and assembled a monolayer of synthetic cell mimics to examine their collective behavior. By systematically increasing the persistence time of self-propulsion, we discovered a shape-driven, density-independent re-entrant jamming transition. Remarkably, we found that cell shape and shape variability were mutually constrained in the confluent limit, following the same universal scaling observed in confluent epithelia. However, dynamical heterogeneities did not adhere to this scaling, with faster cells exhibiting suppressed shape variability—a phenomenon our simulations attribute to transient confinement by slower neighbors. Our experiments clearly establish a morphodynamic link, showing that geometric constraints alone can dictate epithelial jamming and unjamming.

Related Publication(s):

Arora, Pragya, et al. "A shape-driven reentrant jamming transition in confluent monolayers of synthetic cell-mimics." Nature Communications 15.1 (2024): 5645. https://doi.org/10.1038/s41467-024-49044-z (Collaboration with the group of Prof. Rajesh Ganapathy at JNCASR )

Nature-inspired designs for disordered acoustic bandgap materials

We have developed an innovative amorphous mechanical metamaterial, inspired by the way cells pack in biological tissues. Recent studies have shown that spatial heterogeneity in the local stiffness of these materials significantly influences the mechanics of confluent biological tissues and cancer invasion. Leveraging this bio-inspired structure, we design mechanical metamaterials with large, tunable acoustic bandgaps. Unlike periodic acoustic crystals, our metamaterials feature directionally isotropic bandgaps that are robust to defects due to their lack of positional order. We explore ways to manipulate these bandgaps through a combination of tissue-level elastic modulus and local stiffness heterogeneity of cells. By dynamically perturbing the system with external sinusoidal waves, we demonstrate the existence of these bandgaps, as evidenced by valleys in the calculated transmission coefficients. This design opens the door to engineering self-assembled rigid acoustic structures with tunable, full bandgaps, enabling applications ranging from vibration isolation to mechanical waveguides.

Related Publication(s):

Li, Xinzhi, and Dapeng Bi. "Nature-inspired designs for disordered acoustic bandgap materials." Soft Matter 19.42 (2023): 8221-8227. https://doi.org/10.1039/D3SM00419H

Disordered Photonic Materials

We have designed an amorphous material with a full photonic bandgap, inspired by the way cells pack in biological tissues. The size of this photonic bandgap can be precisely manipulated through thermal and mechanical tuning. Unlike traditional photonic crystals, these directionally isotropic photonic bandgaps persist in both solid and fluid phases, resulting in a robust photonic fluid-like state that remains stable under fluid flow, rearrangements, and thermal fluctuations. This innovative design paves the way for the engineering of self-assembled, nonrigid photonic structures with real-time, tunable photonic bandgaps controlled through mechanical and thermal adjustments.

Related Publication(s):

Li, Xinzhi, Amit Das, and Dapeng Bi. "Biological tissue-inspired tunable photonic fluid." Proceedings of the National Academy of Sciences 115.26 (2018): 6650-6655. https://doi.org/10.1039/D3SM00419H