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We explore the rheology during a startup flow of well-characterized polyelectrolyte microgel suspensions, which form soft glasses above the jamming concentration. We present and discuss results measured using different mechanical histories focusing on the variations of the static yield stress and yield strain. The behavior of the shear stress growth function is affected by long-lived residual stresses and strains that imprint a slowly decaying mechanical memory inside the materials. The startup flow response is not reversible upon flow reversal and the amplitude of the static yield stress increases with the time elapsed after rejuvenation. We propose an experimental protocol that minimizes the directional memory and we analyze the effect of aging. The static yield strain γ p and the reduced static yield stress σ p / σ y , where σ y is the dynamic yield stress measured from steady flow measurements, are in good agreement with our previous simulations [Khabaz et al., “Transient dynamics of soft particle glasses in startup shear flow. Part I: Microstructure and time scales,” J. Rheol. 65, 241 (2021)]. Our results demonstrate the need to consider memory and aging effects in transient measurements on soft particle glasses.
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This content will become publicly available on July 17, 2027
Stress-Induced Mechanical Memory in Respiratory Mucus: Anisotropy, Network Reorganization, and Directional Transport
Mucus transport is essential for lung health, as ciliated cells constantly propel mucus outward to clear bacteria, viruses, and particles. This defense relies on a material that must be elastic enough to maintain ciliary traction, but capable of reorganizing under sustained directional loading. How the mucin network reconciles these demands, and whether it retains a memory of the stresses it experiences, remains poorly understood. Here we show that lung mucus develops a persistent, direction-dependent mechanical asymmetry under physiologically relevant stress—a mechanical memory encoded in the slow scaffold of the network. Using bulk rheology, we find that directional pre-stress produces a residual anisotropy that grows with stress magnitude and persists long after the load is removed. A transient network model attributes this memory to a separation of timescales between transient bonds and a long-lived crosslink scaffold, and particle-tracking microrheology confirms that the memory reorganizes the network geometry at the scale of biological particles, biasing tracer diffusion along the axis of applied stress. The stresses required to induce memory are within the range generated by ciliary beating and remain below the mucus yield threshold, suggesting that mucociliary clearance operates in a regime where directional alignment accumulates without compromising the coherence of the mucus layer. This proximity to yield may not be coincidental, it allows mucus to accumulate mechanical memory under physiological forcing while remaining poised to flow during clearance events such as coughing.
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- Award ID(s):
- 2527013
- PAR ID:
- 10712134
- Publisher / Repository:
- bioRxiv
- Date Published:
- Subject(s) / Keyword(s):
- Respiratory mucus, Mechanical memory, Mucociliary clearance, Shear-induced anisotropy, Microrheology, Transient network theory
- Format(s):
- Medium: X
- Institution:
- bioRxiv
- Sponsoring Org:
- National Science Foundation
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