Publications

2025

Controlling Moving Interfaces in Solid-State Batteries

Salem Mosleh, Emil Annevelink, Venkatasubramanian Viswanathan, L. Mahadevan
Proc. R. Soc. A, 2025
https://doi.org/10.1098/rspa.2024.0785

AI Summary

This work models the electrochemical and mechanical instabilities at lithium–solid electrolyte interfaces and proposes feedback mechanisms to stabilize them—drawing inspiration from biological growth regulation.

Abstract

All-solid-state lithium metal batteries enable high-energy-density applications, such as electric aviation, but suffer from instabilities during operation that lead to rough interfaces between the metal and electrolyte. These cause void formation and dendrite growth that degrades performance and safety. Inspired by the morphogenetic control of thin lamina such as tree leaves that robustly grow into flat shapes, we propose a range of approaches to control lithium metal stripping and plating via a range of feedback mechanisms. A minimal model that captures the coupling between interface motion, thermodynamics, electrochemistry and mechanics shows that local feedback cannot stop the formation of rough interfaces, while long-range feedback allows us to stabilize the interface and keep it flat. Our theoretical study suggests various approaches to achieve this, and provides the beginning of a practical framework for analysing and designing stable electrochemical interfaces in terms of their mechanical properties and the physical chemistry that underlie their dynamics.

Data-driven quasi-conformal morphodynamic flows
Salem Al Mosleh, Gary P. T. Choi, L. Mahadevan
Proc. R. Soc. A, 2025
https://doi.org/10.1098/rspa.2024.0527

AI Summary

This paper introduces a framework for modeling shape changes in biological tissues using quasiconformal flows, enabling the analysis of complex morphodynamic processes from sparse data.

Abstract

We develop a data-driven method for reconstructing smooth, invertible morphodynamic flows from sparse growth observations using quasiconformal mapping techniques. This approach offers robust recovery of tissue deformation in biological contexts, enabling quantification of anisotropy, directionality, and time-dependent shape changes. We demonstrate the method on both synthetic and experimental biological datasets and show that it generalizes well across varying spatial resolutions and growth patterns.

2024

The Sex of Organ Geometry
Laura Blackie, Pedro Gaspar, Salem Mosleh, ..., Marta Varela, L. Mahadevan, Irene Miguel-Aliaga
Nature, 2024
https://doi.org/10.1038/s41586-024-07463-4

AI Summary

This study explores how organ shape is maintained and varies between sexes. It reveals that while size often overlaps, the three-dimensional geometry of organs consistently differs between male and female flies and humans. These shape differences are developmentally regulated and affect interorgan relationships and function.

Abstract

Organs have a distinctive yet often overlooked spatial arrangement in the body. We propose that there is a logic to the shape of an organ and its proximity to its neighbours. Here, by using volumetric scans of many Drosophila melanogaster flies, we develop methods to quantify three-dimensional features of organ shape, position and interindividual variability. We find that both the shapes of organs and their relative arrangement are consistent yet differ between the sexes, and identify unexpected interorgan adjacencies and left–right organ asymmetries. Focusing on the intestine, which traverses the entire body, we investigate how sex differences in three-dimensional organ geometry arise. The configuration of the adult intestine is only partially determined by physical constraints imposed by adjacent organs; its sex-specific shape is actively maintained by mechanochemical crosstalk between gut muscles and vascular-like trachea. Indeed, sex-biased expression of a muscle-derived fibroblast growth factor-like ligand renders trachea sexually dimorphic. In turn, tracheal branches hold gut loops together into a male or female shape, with physiological consequences. Interorgan geometry represents a previously unrecognized level of biological complexity which might enable or confine communication across organs and could help explain sex or species differences in organ function.

Integrating Evolutionary Biology into Physics Classroom: Scaling, Dimension, Form and Function
Kausik S. Das, Larry Gonick, Salem Al Mosleh
arXiv, 2024
https://doi.org/10.48550/arXiv.2408.04070

AI Summary

This paper presents a framework for integrating concepts of form, function, and evolution into physics education using examples like body size, animal movement, and dimensional analysis.

Abstract

We present a framework for integrating evolution and development with introductory physics, focusing on how physical laws constrain the shape and function of living systems. Using examples such as body size, limb shape, and animal movement, we demonstrate how physics can enhance understanding of evolution and how evolution can enrich physics pedagogy. We outline teaching modules and concepts that highlight the deep connections between mechanics and biology and show how they may be used to bridge disciplinary boundaries in STEM education.

2023

Beak Morphometry and Morphogenesis Across Avian Radiations

Salem Al Mosleh, Gary P. T. Choi, Grace M. Musser, Helen F. James, Arhat Abzhanov, L. Mahadevan

Proceedings of the Royal Society B, 2023
https://doi.org/10.1098/rspb.2023.0420

AI Summary

Analyzing beak shapes across bird species, the study identifies geometric growth laws that govern morphogenesis, shedding light on evolutionary diversification.

Abstract

Adaptive avian radiations associated with the diversification of bird beaks into a multitude of forms enabling different functions are exemplified by Darwin’s finches and Hawaiian honeycreepers. To elucidate the nature of these radiations, we quantified beak shape and skull shape using a variety of geometric measures that allowed us to collapse the morphological variation of beak orientation, aspect ratios, and curvatures into a low-dimensional morphospace. We then used this morphospace to analyze the evolutionary trajectories of beak shapes and to propose a mechanistic model of beak morphogenesis based on curvature-driven growth.

Combined Measures of Mimetic Fidelity Explain Imperfect Mimicry in a Brood Parasite–Host System

Tanmay Dixit, Gary P. T. Choi, Salem Al Mosleh, Jess Lund, Jolyon Troscianko, Collins Moya, L. Mahadevan, Claire N. Spottiswoode

Biology Letters, 2023

https://doi.org/10.1098/rsbl.2022.0538

AI Summary

This research quantifies egg mimicry by brood parasites using both visual and behavioral measures, showing that seemingly imperfect mimicry can still deceive hosts effectively.

Abstract

The persistence of imperfect mimicry in nature presents a challenge to mimicry theory. Some hypotheses for the existence of imperfect mimicry make differing predictions depending on how mimetic fidelity is measured. Here, we measure mimetic fidelity in a brood parasite–host system using both trait-based and response-based measures of mimetic fidelity. We find that while trait-based measures suggest imperfect mimicry, response-based measures indicate high levels of host acceptance, suggesting that the apparent imperfection may be sufficient to deceive the host.

How to Grow a Flat Leaf

Salem Al Mosleh, L. Mahadevan

Physical Review Letters, 2023

https://doi.org/10.1103/PhysRevLett.131.098401

AI Summary

This paper explains how leaves achieve and maintain flatness during growth through mechanical feedback between curvature and tissue growth rate.

Abstract

Leaves are generally flat, and this shape is maintained during growth. We present a mechanical feedback model that ensures flatness through coupling between curvature and growth. The model predicts robust flatness across varying boundary conditions and explains the observed morphology of leaves as a stable result of dynamic regulation.

2022

Feedback Linking Cell Envelope Stiffness, Curvature, and Synthesis Enables Robust Rod-Shaped Bacterial Growth
Salem Al Mosleh, Ajay Gopinathan, Christian D. Santangelo, Kerwyn Casey Huang, Enrique R. Rojas
PNAS, 2022
https://doi.org/10.1073/pnas.2200728119

AI Summary

This study reveals how bacteria regulate rod-shaped growth by using feedback between local curvature and synthesis of the cell envelope. The model shows how mechanical forces coordinate with biochemical processes to ensure shape homeostasis.

Abstract

Bacterial growth is remarkably robust to environmental fluctuations, yet the mechanisms of growth-rate homeostasis are poorly understood. Here, we combine theory and experiment to infer mechanisms by which Escherichia coli adapts its growth rate in response to changes in osmolarity, a fundamental physicochemical property of the environment. Our analysis suggests that feedback between curvature and synthesis of the cell wall is key to preserving rod-shaped growth in bacteria. This feedback loop compensates for physical perturbations and maintains cellular integrity by coordinating envelope synthesis with geometric cues.

Optimal Policies for Mitigating Pandemic Costs: A Tutorial Model
Mattia Serra, Salem Al Mosleh, S. Ganga Prasath, V. Raju, S. Mantena, J. Chandra, S. Iams, L. Mahadevan
Physical Biology, 2022
https://doi.org/10.1088/1478-3975/ac7e9e

AI Summary

This paper provides a simple optimal control framework for designing intervention strategies that balance economic and health costs during a pandemic. It serves both as a research model and a pedagogical tool.

Abstract

We present a minimal model for analyzing intervention strategies during pandemics, balancing health outcomes and economic impacts. Using optimal control, we derive time-dependent intervention policies under various cost functions and epidemiological constraints. Our results demonstrate how a wide range of behavioral and policy-based responses can be understood in a unified mathematical framework, making the paper a useful entry point for students and researchers in mathematical biology and public health planning.

2021

Geometry and Dynamics Link Form, Function, and Evolution of Finch Beaks
Salem Al Mosleh, Gary P. T. Choi, Arhat Abzhanov, L. Mahadevan
PNAS, 2021
https://doi.org/10.1073/pnas.2105957118

AI Summary

This paper combines 3D morphometric analysis and mechanical modeling to relate finch beak geometry to biting performance and ecological function. It shows that a small set of geometric parameters captures variation across species and links development to evolutionary adaptation.

Abstract

Darwin's finches are a classic example of adaptive radiation, exemplified by their adaptive and functional beak morphologies. To quantify their form, we carry out a morphometric analysis of the three-dimensional beak shapes of all of Darwin's finches and find that they can be fit by a transverse parabolic shape with a curvature that increases linearly from the base toward the tip of the beak. The morphological variation of beak orientation, aspect ratios, and curvatures allows us to quantify beak function in terms of the elementary theory of machines, consistent with the dietary variations across finches. Finally, to explain the origin of the evolutionary morphometry and the developmental morphogenesis of the finch beak, we propose an experimentally motivated growth law at the cellular level that simplifies to a variant of curvature-driven flow at the tissue level and captures the range of observed beak shapes in terms of a simple morphospace. Altogether, our study illuminates how a minimal combination of geometry and dynamics allows for functional form to develop and evolve.

Instabilities and Patterns in a Submerged Jelling Jet
Aditi Chakrabarti, Salem Al Mosleh, L. Mahadevan
Soft Matter, 2021
https://doi.org/10.1039/D1SM00517K

AI Summary

This study examines how a sodium alginate jet undergoes various coiling and buckling instabilities as it gels in a calcium chloride bath. It reveals how flow rate, viscosity, and jet composition can be tuned to sculpt 3D filaments with controllable mechanical properties.

Abstract

When a thin stream of aqueous sodium alginate is extruded into a reacting calcium chloride bath, it polymerizes into a soft elastic tube that spontaneously forms helical coils due to the ambient fluid drag. We quantify the onset of this drag-induced instability and its nonlinear evolution using experiments, and explain the results using a combination of scaling, theory, and simulations. By co-extruding a second (internal) liquid within the aqueous sodium alginate jet and varying the diameter of the jet and the rates of the co-extrusion of the two liquids, we show that we can tune the local composition of the composite filament and the nature of the ensuing instabilities to create soft filaments of variable relative buoyancy, shape, and mechanical properties. Altogether, by harnessing the fundamental varicose (jetting) and sinuous (buckling) instabilities associated with the extrusion of a submerged jelling filament, we show that it is possible to print complex three-dimensional filamentous structures in an ambient fluid.

2017 - 2018

Growth of Form in Thin Elastic Structures
Salem Al Mosleh, Ajay Gopinathan, Christian D. Santangelo
Soft Matter, 2018
https://doi.org/10.1039/C8SM01136B

AI Summary

This paper develops a mathematical model of how growing thin elastic structures, like petals or bacterial cell walls, evolve their shape. It uses a metric-driven growth formulation and shows how feedback between local curvature and growth laws controls morphological stability.

Abstract

Heterogeneous growth plays an important role in the shape and pattern formation of thin elastic structures ranging from the petals of blooming lilies to the cell walls of growing bacteria. Here we address the stability and regulation of such growth, which we modeled as a quasi-static time evolution of a metric, with fast elastic relaxation of the shape. We consider regulation via coupling of the growth law, defined by the time derivative of the target metric, to purely local properties of the shape, such as the local curvature and stress. For cylindrical shells, motivated by rod-like E. coli, we show that coupling to curvature alone is generically linearly unstable to small wavelength fluctuations and that additionally coupling to stress can stabilize these modes. Interestingly, within this framework, the longest wavelength fluctuations can only be stabilized with the mean curvature flow. Our approach can readily be extended to gain insights into the general classes of stable growth laws for different target geometries.

Nonlinear Mechanics of Rigidifying Curves
Salem Al Mosleh, Christian D. Santangelo
Physical Review E, 2017
https://doi.org/10.1103/PhysRevE.96.013003

AI Summary

This theoretical work shows how certain embedded curves within a thin elastic shell can become mechanically stiff and dominate its deformation behavior. The paper develops a geometric framework for how curves interact with global shell mechanics.

Abstract

Thin shells are characterized by a high cost of stretching compared to bending. As a result, isometries of the midsurface of a shell play a crucial role in their mechanics. In turn, curves with zero normal curvature play a critical role in determining the number and behavior of isometries. In this paper, we show how the presence of these curves results in a nonlinear coupling between bending and stretching that leads to the rigidification of the shell along the curve. We develop a theoretical framework to describe this phenomenon and validate our predictions with numerical simulations.

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