Research

Soft matter physics is the study of soft, squishy, and deformable objects. Examples of soft matter are all around us. Most parts of our body (e.g. skin, tendon, blood) and many engineered materials (e.g. plastics, rubbers, foams, gels) fall under the category of soft matter. More precisely, the field of soft matter physics encompasses systems where room temperature thermal energy is comparable to that of applied mechanical or thermal stresses. Soft matter often includes structure on mesoscopic size scales (sizes anywhere from roughly 10 nm up to about 100 µm — between that of a single atom but smaller than we can easily see with the naked eye).

The Physics of Soft Matter Lab (PoSMLab) at Harvey Mudd College is broadly interested in the physical principles that govern the behavior of soft materials. Our recent work has focused on understanding the physical principles of latch-mediated spring actuated (LaMSA) systems, in which springs primarily drive motion. An archer’s bow and arrow provides a great example of how a LaMSA system works: first a motor (the archer’s muscles) loads elastic energy into a spring-like element (the bow), which is held in place by a latch (the archer’s fingers). Upon releasing the latch, the stored elastic energy is rapidly converted into kinetic energy of motion.

In the next few years PoSMLab is focused primarily on two guiding questions: 1) What properties determine the maximum kinematic performance of elastic materials? 2) What principles govern the mechanics of biological LaMSA systems?

Earlier work from the group examined polymer thin films and fluid dynamics at the nanoscale.

Latch-mediated spring actuation (LaMSA)

Some organisms have a loading motor, spring, and latch built into their anatomy, and use this combination to perform ultra-fast movement. Mantis shrimp use elastic energy to drive their hammer-like appendages at speeds greater than 60 mph, fast enough to break open snail and crab shells. What’s perhaps even more impressive is that the performance of some of these biological LaMSA systems exceeds that of current engineering capabilities for repeatable kinematic performance at small sizes. By understanding the physical principles that govern these systems, our aim is to contribute to a better understanding of the evolutionary dynamics of these organisms and to inform future engineering design.

Key papers:

Ilton et al., Science 2018 — The principles of cascading power limits in small, fast biological and engineered systems
Longo et al., J. Exp. Biol. 2019 — Beyond power amplification: latch-mediated spring actuation is an emerging framework for the study of diverse elastic systems
Ilton et al., Soft Matter 2019 — The effect of size-scale on the kinematics of elastic energy release
Sutton et al., Integr. Comp. Biol. 2019 — Why do large animals never actuate their jumps with latch-mediated springs? Because they can jump higher without them
Divi et al., J. R. Soc. Interface 2020 — Latch-based control of energy output in spring actuated systems
Acharya et al., J. R. Soc. Interface 2021 — The ultrafast snap of a finger is mediated by skin friction
Cook et al., Integr. Organismal Biol. 2022 — A Tunable, Simplified Model for Biological Latch Mediated Spring Actuated Systems
Tsai et al., J. R. Soc. Interface 2024 — Viscoelastic materials are most energy efficient when loaded and unloaded at equal rates
Anderson et al., bioRxiv (preprint) 2024 — Tuning a mechanical model to biological reality: A case study in the LaMSA system of the trap-jaw ant Strumigenys
Zheng et al., Soft Matter 2026 — Elastodynamic mechanical analyzer for high strain-rate mechanical characterization

Polymer thin films and fluid dynamics

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Before turning to biomechanics, our group’s work examined hydrodynamic slip and flow at the nanoscale, using capillary leveling of thin polymer films to probe how polymer chains interact with a solid interface.

Key papers:

Ilton et al., Nat. Commun. 2018 — Adsorption-induced slip inhibition for polymer melts on ideal substrates