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arxiv: 2509.05110 · v1 · submitted 2025-09-05 · ❄️ cond-mat.soft · physics.bio-ph· q-bio.TO

Elasticity and plasticity of epithelial gap closure

Pith reviewed 2026-05-18 18:46 UTC · model grok-4.3

classification ❄️ cond-mat.soft physics.bio-phq-bio.TO
keywords epithelial gap closurecell intercalationactomyosin cabletissue fluidisationepibolywound healingcontinuum modelplasticity
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The pith

A minimal continuum model reveals that epithelial gap closure switches between cell intercalation into the gap and deintercalation from the boundary depending on the relative size of the intercalation energy barrier and released energy.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper builds a minimal continuum model of a circular epithelial gap bounded by a contractile actomyosin cable to examine how plastic cell intercalations interact with tissue elasticity during closure. When the energy barrier to intercalation greatly exceeds the energy released, cells move into the gap and close it. In fluidised tissues where the barrier is low, cells instead move from the boundary into the tissue bulk, with inhomogeneities in the actomyosin cable gaining an emergent mechanical function. This accounts for the observed role of tissue fluidisation in beetle serosa closure and related processes such as epiboly and wound healing.

Core claim

In the minimal continuum model of the closure of a circular gap bounded by a contractile actomyosin cable, the interplay between elasticity and plasticity is governed by the energy barrier Eb to cell intercalation and the energy ΔE released by it: if Eb ≫ ΔE, cells intercalate into the gap to close it, whereas for a fluidised tissue with Eb ≪ ΔE, cells deintercalate from the boundary into the bulk and inhomogeneities of the actomyosin cable acquire an emergent mechanical role.

What carries the argument

The single energy barrier Eb and released energy ΔE for cell intercalation in the minimal continuum description, which sets whether the tissue closes by adding cells at the edge or by ejecting them from the boundary.

If this is right

  • When Eb greatly exceeds ΔE, cells intercalate into the gap and close it through addition at the edge.
  • When Eb is much smaller than ΔE in a fluidised tissue, cells deintercalate from the boundary into the bulk.
  • In the fluidised regime, inhomogeneities in the actomyosin cable play an emergent mechanical role in closure.
  • The model explains the mechanical contribution of tissue fluidisation to serosa closure in Tribolium and to epiboly and wound healing more generally.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Modulating tissue fluidity might offer a way to steer gap closure outcomes in wound-healing contexts.
  • The same energy-barrier logic could apply to gap closure in other epithelial systems beyond the circular geometry studied here.
  • Testing the model on tissues with controlled actomyosin cable tension variations would check whether inhomogeneities indeed dominate only in the low-barrier regime.

Load-bearing premise

A minimal continuum model that uses only one energy barrier Eb and one released energy ΔE for intercalation is enough to capture the main mechanical competition between elasticity and plasticity in real epithelial tissues.

What would settle it

Live imaging of cell trajectories at the gap boundary in an epithelial tissue whose fluidity (and thus Eb relative to ΔE) can be tuned, checking whether cells move into the gap or outward into the bulk during closure.

Figures

Figures reproduced from arXiv: 2509.05110 by Maryam Setoudeh, Pierre A. Haas.

Figure 1
Figure 1. Figure 1: FIG. 1. Mechanics of epiboly. (a) Schematic of epiboly: a [PITH_FULL_IMAGE:figures/full_fig_p001_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2. Intercalation dynamics. (a) Discrete model of cell [PITH_FULL_IMAGE:figures/full_fig_p002_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3. Intercalation energetics. (a) Sketch of the energy [PITH_FULL_IMAGE:figures/full_fig_p003_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4. Dynamics of epithelial gap closure. Top row: dynamics for [PITH_FULL_IMAGE:figures/full_fig_p004_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: FIG. 5. Dynamics of epiboly for ∆ [PITH_FULL_IMAGE:figures/full_fig_p004_5.png] view at source ↗
read the original abstract

Epiboly, during which a tissue closes around the surface of the egg, pervades animal development. This epithelial gap closure involves cell intercalations at the edge of the gap. Here, inspired by serosa closure in the beetle Tribolium, we study the interplay between these plastic cell rearrangements and the elasticity of the tissue in a minimal continuum model of the closure of a circular gap bounded by a contractile actomyosin cable. We discover two different closure mechanisms at the tissue scale depending on the energy barrier $E_\text{b}$ to and the energy $\Delta E$ released by intercalation: If $E_\text{b}\gg\Delta E$, cells intercalate into the gap to close it. For a fluidised tissue in which $E_\text{b}\ll\Delta E$, however, cells deintercalate from the boundary into the bulk of the tissue, and we reveal an emergent mechanical role of inhomogeneities of the actomyosin cable. Our work thus explains the mechanical role of tissue fluidisation in Tribolium serosa closure and processes of epiboly and wound healing more generally.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

1 major / 1 minor

Summary. The manuscript develops a minimal continuum model of circular epithelial gap closure bounded by a contractile actomyosin cable, motivated by serosa closure in Tribolium. Plasticity is encoded via a single energy barrier Eb to cell intercalation and an energy release ΔE upon intercalation. The central result is a bifurcation in closure mechanism: when Eb ≫ ΔE cells intercalate into the gap, whereas when Eb ≪ ΔE (fluidised regime) cells deintercalate from the boundary into the tissue bulk, with inhomogeneities in the actomyosin cable acquiring an emergent mechanical role.

Significance. If the two-regime distinction and the emergent role of cable inhomogeneities survive scrutiny, the work supplies a compact mechanical explanation for how tissue fluidisation modulates gap closure in epiboly and wound healing, linking a simple energy-barrier model to observable cell behaviours at the tissue scale.

major comments (1)
  1. [Model setup] Model setup / continuum limit: the claim that cells deintercalate from the gap boundary when Eb ≪ ΔE is generated inside a coarse-grained description that ties the plastic strain rate to an effective potential whose minimum shifts with the Eb/ΔE ratio. Because the continuum smoothing erases discrete cell–cell and cell–cable contacts that set the local force balance at the free edge, it is unclear whether the predicted direction of plastic flow is robust or an artefact of the coarse-graining. This issue is load-bearing for the fluidised-regime mechanism.
minor comments (1)
  1. [Abstract] The abstract states the qualitative outcomes clearly but does not indicate the explicit form of the energy functional or the constitutive relation for the plastic strain rate; adding one sentence on these points would improve accessibility without lengthening the abstract.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for their detailed reading of our manuscript and for identifying a key point concerning the robustness of the continuum description in the fluidised regime. We address this comment below and have revised the manuscript accordingly to strengthen the justification of our approach.

read point-by-point responses
  1. Referee: [Model setup] Model setup / continuum limit: the claim that cells deintercalate from the gap boundary when Eb ≪ ΔE is generated inside a coarse-grained description that ties the plastic strain rate to an effective potential whose minimum shifts with the Eb/ΔE ratio. Because the continuum smoothing erases discrete cell–cell and cell–cable contacts that set the local force balance at the free edge, it is unclear whether the predicted direction of plastic flow is robust or an artefact of the coarse-graining. This issue is load-bearing for the fluidised-regime mechanism.

    Authors: We agree that the continuum limit requires careful justification, as averaging necessarily smooths discrete cell–cell and cell–cable interactions. In our model the plastic strain rate is obtained from the derivative of an effective potential whose minima are set by the ratio Eb/ΔE; this potential is constructed by coarse-graining the microscopic energy landscape of intercalation events. When Eb ≪ ΔE the minimum shifts to favour negative plastic strain (deintercalation), reflecting a thermodynamic preference for reducing the number of boundary cells. The contractile cable enters through the boundary stress condition, which remains well-defined after averaging. While local force fluctuations at individual contacts are lost, the net direction of plastic flow is preserved because it is dictated by the global energy balance rather than by any single contact geometry. To make this explicit we have added a paragraph in the Model section together with a supplementary derivation that starts from a discrete energy functional and shows that the sign of the coarse-grained flow is unchanged under spatial averaging. We have also included a brief discussion of the regime of validity of the continuum approximation. revision: partial

Circularity Check

0 steps flagged

No significant circularity; outcomes follow from independent model parameters

full rationale

The paper presents a minimal continuum model in which Eb and ΔE are introduced as independent parameters whose ratio determines the direction of plastic flow (intercalation into the gap when Eb ≫ ΔE versus deintercalation when Eb ≪ ΔE). These regimes and the emergent role of actomyosin inhomogeneities are obtained by solving the model's equations rather than by fitting to data or by any self-referential definition. No load-bearing self-citations, uniqueness theorems, or ansatzes imported from prior work are invoked to force the central claims; the derivation chain remains self-contained against the stated modeling assumptions.

Axiom & Free-Parameter Ledger

2 free parameters · 1 axioms · 0 invented entities

The model treats Eb and ΔE as independent control parameters whose ratio determines the closure mode; the circular gap geometry and the contractile cable are modelling choices taken from the biological system. No new particles or forces are postulated.

free parameters (2)
  • Eb
    Energy barrier to intercalation, introduced as a tunable parameter that controls whether cells intercalate inward or deintercalate outward.
  • ΔE
    Energy released upon intercalation, introduced as a second tunable parameter whose magnitude relative to Eb selects the closure mechanism.
axioms (1)
  • domain assumption The tissue can be described by a minimal continuum model that couples elasticity to discrete plastic rearrangements via an energy barrier.
    Invoked in the model setup to justify the continuum approach to cell intercalations.

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