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Recent and ongoing projects

Environmental pressure and sufficient time can lead to clever manipulation of abiotic materials, geometry, and external forces toward crucial function. We are interested in principles underlying natural solutions and how they may be directed toward pressing human problems, especially those of sustainability.

Emergent mechanics of a bird nest

A cardinal will use its own body as template in building its cup-nest. Found, filamentous material are added and randomly packed against the bird-defined boundaries. The resulting structure will not be very stiff, but it will reliably hold its shape, enough to protect its valuable contents against various disturbances. This seemingly simple, naturally-selected engineering solution for keeping one’s offspring safe, is instead the result of a subtle interplay between geometry, topology, elasticity, and friction. Using experimental approaches adapted from granular physics, and in close collaboration with simulators at UIUC, we are characterizing the emergent quasi-static and dynamic mechanical behavior of “nest” materials, and their dependence on constituent fiber properties and the distribution of their disordered, impermanent contacts.

Fluid dynamics of fog collection

In coastal deserts, moist air can frequently blow over dry land, without ever coalescing or precipitating down on the surface. These regions often also suffer economic hardship and lack of infrastructure, such that harnessing airborne moisture can be a basis for life. Humans have spent some decades developing meshes to intercept and collect fog. The living world has spent eons whimsically mixing physical and chemical mechanisms. A Namib desert beetle, which collects fog from the morning wind atop sand dunes near the coast, has raised the prospect of transformative biomimetic solutions, but nearly all research has focused on the surface transport mechanism, particularly with respect to wettability. We are investigating the fluid dynamics of the other crucial step: droplet interception before coalescence and collection, focusing on the role of surface morphology (ie. bumps like those of beetle elytra) and non-trivial flow geometries, to find new angles on improved collection efficiency, and insight into the antithetical problem of icing in flight and wind power.

Soft contact dynamics underwater

Many biological systems, such as the gecko in engaging adhesive pads and mussel foot in depositing byssus, face the challenge of acheiving intimate contact with hard, rough systems in the presence of water. While understanding the chemistry and adhesive forces involved can provide valuable insight, the dynamics by which entrapped fluid is evacuated can enhance or undermine ultimate performance. The dynamics just before contact depend on surfaces’ softness, approach speed, and fluid viscosity. Upon touching, interfacial energies are found to play a direct role in the evacuation: counterintuitively, the same attractive interactions that energetically prefer better contact lead to inhibition of fluid evacuation, entrapping puddles that take orders of magnitude longer to drain. We investigate these dynamics during development of contact with varying surface chemistry with a custom, frustrated total internal reflection (FTIR) apparatus.

Physics of termite mound respiration and moisture conservation

Many termite species live in large colonies and harvest fungus to supplement nutrition. Living underground keeps them cool and protected, but creates a serious issue for respiration. The tall mounds that protrude above the nests are effectively lungs, which harness oscillations of ambient temperature to drive bulk flow between the nest and mound, while gases exchange via diffusion through the porous walls. Mound architecture amplifies transient thermal gradients along connected conduits to facilitate the internal convection, in an inspirational example of emergent engineering.

Understanding the physical mechanisms by which their design manages to respire metabolic gases while conserving moisture is our present focus.

Thermoregulation in an ant-plant house

The ant Philidris nagasau sows and maintains its plant-hosts (Squamellaria) in the trees of Fiji. In return, squamellaria offer both food and ready-made housing in an obligate mutualist relationship: the ants cannot build their own nests, and the plants do not propagate on their own. The strategy involves conflicting goals: squamellaria planted high in the canopy give more sugar, but exposure to high temperatures can harm ant broods. The morphologically distinct, farmed (specialized) Squamellaria appear to be cooler than their non-ant-farmed (generalist) counterparts when exposed to the same conditions. In order to extract the evolved, architectural design principle(s) responsible for this passive thermoregulation, we are developing and deploying custom sensor modules to thoroughly document, in-situ, relevant heat transfer parameters and exploring minimal models for leading-order mechanisms.

Wrinkling and crumpling of thin sheets

When a thin sheet is compressed in one thin direction, it readily buckles outward, demonstrating the relative ease in storing energy in bending rather than in-plane stresses. If the sheet is adhered to a soft (or liquid) substrate, the same Euler instability leads to a pattern of smooth wrinkles, caused by competition between the bending modulus of the sheet and the stiffness (or weight) of the substrate. This buckling motif fundamentally differs from that observed when one crumples a piece of paper: pointy cusps connected by ridges. The sharpness in the crumpled shape illustrate the phenomenon of stress focusing, in which the sheet chooses to concentrate elastic energy in small regions in response to confinement from the boundaries. By confining a flat sheet to a slightly, variably curved, liquid meniscus and optically measuring its deformation, we tested predictions for wrinkle extent in the simplest case of non-uniform confinement, and discovered a generic route by which a featureless sheet assumes a crumpled shape.


  1. A. Shahrokhian*, F. K. Chan*, J. Feng, M. Gazzola and H. King. (2024) Geometry for low-inertia aerosol capture: Lessons from fog-basking beetles. PNAS Nexus
  2. T. Houette, M. Dibia, N. Mahabadi, and H. King. (2023) Pull-out resistance of biomimetic root-inspired foundation systems. Acta Geotechnica
  3. S. Nepal, A. Shahrokhian, and H. King. (2023) Microwave driven atmospheric water harvesting with common sorbents. Journal of Applied Physics
  4. N. Weiner*, Y. Bhosale*, A. Butler, S. H. Kim, M. Gazzola and H. King. (2022) Micromechanical origin of elastoplasticity in disordered packings of filaments. Physical Review Letters  (Cover, Editor’s choice)
  5. M. Tello-Ramos, S. Sugasawa, M. Dibia, and H. King. (2022) Tools, behavior, and materials: What should we learn from animal nest construction? in Biomimicry for Materials, Design and Habitats Elsevier
  6. J. Feng, B. Khakipoor, J. May, M. Mulford, J. Davis, K Siman, G. Russell, A. W. Smith and H. King. (2021) An open-source dual-beam spectrophotometer for citizen-science-based water quality monitoring HardwareX
  7. M. Sun*, N. Kumar*, A. Dhinojwala and H. King. (2021) Attractive forces slow contact formation between deformable bodies underwater PNAS
  8. A. Shahrokhian*, J. Feng* and H. King. (2020) Surface morphology enhances deposition efficiency in biomimetic, wind-driven fog collection Journal of the Royal Society Interface
  9. N. Weiner, Y. Bhosale, M. Gazzola and H. King. (2019) Perspective: Mechanics of randomly packed filaments – the ’bird nest’ as a metamaterial Journal of Applied Physics (featured article)
  10. R. Bogucki, M. Greggila, P. Mallory, J. Feng, K. Siman, B. Khakipoor, H. King, and A. W. Smith. (2019) A 3D-Printable Dual Beam Spectrophotometer with Multiplatform Smartphone Adaptor J. Chem. Ed.
  11. S. Ocko*, H. King* D. Andreen, P. Bardunias, R. Soar, J. S. Turner and L. Mahadevan. (2017) Solar-powered ventilation of African termite mounds. Journal of Experimental Biology (Featured in Inside JEB)
  12. H. King. (2016) The superorganism behind nature’s skyscraper. Laboratory News (Invited feature)
  13. J. D. Paulsen, E. Hohlfeld, H. King, J. Huang, Z. Qui, T. P. Russell, N. Menon, D. Vella and B. Davidovitch. (2016) Curvature-induced stiffness and the spatial variation of wavelength in wrinkled sheets PNAS
  14. H. King*, S. Ocko* and L. Mahadevan. (2015). Termite mounds harness diurnal temperature oscillations for ventilation PNAS (Publicity: Harvard MagazineScience NewsCBC’s As It Happens interviewBoston Globe)
  15. J. Chung, H. King, and L. Mahadevan. (2014). Evaporative microclimate driven hygrometers and hygromotors EPL (U.S. Patent Application No.: 15/358,025)
  16. H. King*, R. Schroll*, B. Davidovitch and N. Menon. (2012). A sheet on a drop reveals wrinkling and crumpling as distinct symmetry-breaking instabilitiesPNAS (cover) (Publicity: New England Public Radio interviewsciencedaily)
  17. H. King, R. White, I. Maxwell, and N. Menon. (2011). Inelastic impact of a sphere on a massive plane: Nonmonotonic velocity-dependence of the restitution coefficientEPL
  18. J. A. Hanna and H. King. (2011). An Instability in a Straightening Chain DFD Gallery of Fluid Motion


Referenced elsewhere

  1. P. Ball, Explaining the Mechanics of a Birds Nest, Physics May 13, 2022
  2. Abby Tang, How this tiny beetle could help solve our water crisis Business Insider August 21, 2020
  3. Siobhan Roberts, Why birds are the world’s best engineers New York Times March 17, 2020
  4. Eva Frederick, Could this desert beetle help humans harvest water from thin air? Science November 27, 2019
  5. Malia Wollan, How to build a bird’s nest New York Times April 16, 2019
  6. Claude Christensen, UA-based business wants you to help tackle harmful algae blooms in Lake Erie Devil Strip December 19th, 2018
  7. Saalman Craig, Can termites teach us to build environmentally friendly communities? Massive Science December 4, 2017