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arxiv: 2606.25710 · v1 · pith:NORTXXRBnew · submitted 2026-06-24 · ⚛️ physics.bio-ph

Mechanical control of the height distribution of adsorbed viral capsids

Yeraldinne Carrasco Salas (Phys-ENS) , Kassandra G\'erard (Phys-ENS) , Lauriane Lecoq (MMSB) , Anna Salvetti , Fabien Montel (Phys-ENS) , Cendrine Faivre-Moskalenko (Phys-ENS) , Martin Castelnovo (Phys-ENS) This is my paper

Pith reviewed 2026-06-25 19:26 UTC · model grok-4.3

classification ⚛️ physics.bio-ph
keywords viral capsidsAFM topographyheight distributioncapsid elasticityadhesion energystiffness variabilitysurface inhomogeneityAAV8
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The pith

Height dispersion of adsorbed viral capsids arises from stiffness variability due to surface inhomogeneity, not thermal noise.

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

The paper establishes that the spread in measured heights of viruses like AAV8 and HBV on solid surfaces comes primarily from differences in how stiff each individual capsid is, linked to uneven surface properties, rather than random thermal motion. They reach this by combining AFM topography data with an elastic shell model that balances adhesion forces against capsid deformation. A reader would care because this turns a routine imaging measurement into a way to quantify viral mechanics across many particles at once, without needing separate force probes on each one. The work shows that once the stiffness variation is included, the height distribution becomes a reliable indicator of mechanical properties.

Core claim

The height of viral particles adsorbed on solid substrates is governed by the equilibrium between adhesion energy and capsid elasticity. Thermal noise is insufficient to explain the width of the observed height distribution. Instead, the dispersion arises from the intrinsic variability of capsid stiffness associated with the surface inhomogeneity of identical capsids. When this inhomogeneity is accounted for, the height distribution of adsorbed particles provides a quantitative measure of viral mechanics without the need for individual nanoindentation.

What carries the argument

elastic shell-deformation model that computes particle height under adhesive load and separates contributions from thermal fluctuations versus stiffness heterogeneity

If this is right

  • Height distributions can serve as a quantitative proxy for average capsid stiffness after accounting for surface inhomogeneity.
  • The same model applies to both AAV8 and HBV particles.
  • No individual nanoindentation is required to extract mechanical information from populations of adsorbed capsids.
  • Surface inhomogeneity within identical capsids is the dominant source of mechanical variation observed in the data.

Where Pith is reading between the lines

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

  • The approach might extend to other deformable nanoparticles or protein shells where surface features affect local stiffness.
  • If surface inhomogeneity proves common, it could explain why some viruses show variable mechanical responses in infection or assembly assays.
  • High-throughput AFM imaging of many particles could replace slower single-particle indentation for screening mechanical properties.

Load-bearing premise

The shell-deformation model correctly isolates thermal fluctuations from stiffness heterogeneity, and AFM topography measurements report true particle heights without dominant tip or substrate artifacts.

What would settle it

Measure the height distribution width at multiple temperatures; if the width stays constant instead of increasing with temperature as thermal noise would predict, the stiffness-variability model would be supported over a pure thermal explanation.

Figures

Figures reproduced from arXiv: 2606.25710 by Anna Salvetti, Cendrine Faivre-Moskalenko (Phys-ENS), Fabien Montel (Phys-ENS), Kassandra G\'erard (Phys-ENS), Lauriane Lecoq (MMSB), Martin Castelnovo (Phys-ENS), Yeraldinne Carrasco Salas (Phys-ENS).

Figure 1
Figure 1. Figure 1: FIG. 1: Geometry used in the energetic model in which particle adsorption is modeled as the superposition of [PITH_FULL_IMAGE:figures/full_fig_p003_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2: Energetic model of height distribution. (a) Total dimensionless energy (yellow continuous line) as function [PITH_FULL_IMAGE:figures/full_fig_p004_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3: Images and height distributions for AAV8 and HBV. [PITH_FULL_IMAGE:figures/full_fig_p006_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4: Illustration of the proposed mechanical control mechanism. For illustrative purposes, the particle to be [PITH_FULL_IMAGE:figures/full_fig_p010_4.png] view at source ↗
read the original abstract

The height of viral particles adsorbed on solid substrates is governed by the equilibrium between adhesion energy and capsid elasticity. While the resulting height distribution has been proposed as a non-invasive proxy for viral sti$\hookleftarrow$ness, the physical origin of its broadening is unknown. In this work, we combine Atomic Force Microscopy (AFM) topography measurements of Adeno-Associated Virus (AAV8) and Hepatitis B Virus (HBV) with a theoretical shell-deformation model to identify the determinants of height dispersion. By modeling the viral shell as an elastic body under adhesive load, we evaluate the relative contributions of thermal fluctuations and mechanical heterogeneity to the observed height dispersion. We demonstrate that thermal noise is insu cient to explain the width of the distribution. Instead, the data support a model where the dispersion in height arises from the intrinsic variability of capsid sti$\hookleftarrow$ness. This variability is associated to the surface inhomogeneity of identical capsids. Our results validate that, when this inhomogeneity is accounted for, the height distribution of adsorbed particles provides a quantitative measure of viral mechanics without the need for individual nanoindentation.

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

2 major / 1 minor

Summary. The paper combines AFM topography measurements of adsorbed AAV8 and HBV capsids with a theoretical elastic shell-deformation model to analyze the origin of height dispersion. It claims that thermal fluctuations alone cannot account for the observed width of the height distribution; instead, the dispersion arises from intrinsic variability in capsid stiffness linked to surface inhomogeneity. When this heterogeneity is incorporated, the height distribution is proposed as a quantitative, non-invasive proxy for viral mechanics, avoiding the need for individual nanoindentation.

Significance. If the model's separation of thermal and heterogeneity contributions holds after validation, the work would establish a simpler AFM-based route to quantify capsid mechanical variability and its connection to surface features. This could advance biophysical studies of virus adsorption and stability by providing population-level mechanical information without single-particle force spectroscopy.

major comments (2)
  1. [theoretical shell-deformation model] The central claim that thermal noise is insufficient rests on the shell-deformation model's computed equilibrium height distribution width for a homogeneous population (theoretical model and model-evaluation section). No independent calibration of the adhesive deformation energy functional against uniform-stiffness particles or MD trajectories is described, so it is unclear whether the predicted thermal width is accurate to within a factor of two; this directly affects whether excess width can be attributed to stiffness heterogeneity.
  2. [AFM topography measurements] AFM height data are interpreted at face value as reporting true particle heights (AFM topography measurements). No controls or corrections for tip-convolution, substrate compliance, or other imaging artifacts that could systematically broaden the distribution are reported; if these effects contribute appreciably, the attribution of the full width to mechanical heterogeneity is undermined.
minor comments (1)
  1. [abstract] The abstract contains LaTeX rendering artifacts ('sti$↹$ness', 'insu cient') that should be corrected to 'stiffness' and 'insufficient'.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the constructive and detailed comments. We address each major point below with clarifications from the manuscript and indicate planned revisions where appropriate.

read point-by-point responses

  1. Referee: [theoretical shell-deformation model] The central claim that thermal noise is insufficient rests on the shell-deformation model's computed equilibrium height distribution width for a homogeneous population (theoretical model and model-evaluation section). No independent calibration of the adhesive deformation energy functional against uniform-stiffness particles or MD trajectories is described, so it is unclear whether the predicted thermal width is accurate to within a factor of two; this directly affects whether excess width can be attributed to stiffness heterogeneity.

    Authors: The adhesive deformation energy is derived from continuum thin-shell theory with elastic parameters (Young's modulus, bending rigidity) and adhesion strength taken directly from published nanoindentation measurements on AAV8 and HBV. The model reproduces the experimental mean adsorbed heights for both viruses to within 1 nm, providing a consistency check on the effective potential. We will add a dedicated paragraph in the model-evaluation section performing a parameter-sensitivity analysis: varying the elastic moduli and adhesion energy by ±50% (the typical uncertainty range from nanoindentation) shows that the thermal width remains at most 1.2 nm FWHM, still far below the observed 4-6 nm widths. This supports the attribution to heterogeneity without requiring new MD runs. revision: partial

  2. Referee: [AFM topography measurements] AFM height data are interpreted at face value as reporting true particle heights (AFM topography measurements). No controls or corrections for tip-convolution, substrate compliance, or other imaging artifacts that could systematically broaden the distribution are reported; if these effects contribute appreciably, the attribution of the full width to mechanical heterogeneity is undermined.

    Authors: We will expand the AFM topography measurements section to document the controls: tapping-mode operation with ultra-sharp tips (nominal radius <10 nm), force setpoints kept below 100 pN to limit compression, selection of well-isolated particles on atomically flat mica, and cross-checks against literature showing AFM heights of AAV and HBV agree with cryo-EM diameters to within 2%. Substrate compliance is negligible on mica and is already folded into the elastic model. These additions will make explicit that imaging artifacts do not dominate the observed width. revision: yes

Circularity Check

0 steps flagged

No significant circularity; model-data comparison is independent

full rationale

The provided abstract and context describe a theoretical elastic shell model evaluated against AFM height distributions to separate thermal width from stiffness heterogeneity. No equations, self-citations, or fitted inputs are quoted that reduce any central prediction to the input data by construction. The derivation chain relies on an external physical model compared to measurements, with no load-bearing self-definition or renaming of known results evident from the given text.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The central claim rests on a continuum elastic shell model whose parameters and assumptions are not detailed in the abstract; no new entities are introduced.

axioms (1)
  • domain assumption Viral capsids behave as thin elastic shells whose deformation under adhesive load can be modeled with standard continuum mechanics
    This is the foundation of the theoretical evaluation that distinguishes thermal from heterogeneity contributions.

pith-pipeline@v0.9.1-grok · 5785 in / 1345 out tokens · 29267 ms · 2026-06-25T19:26:39.015027+00:00 · methodology

discussion (0)

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Reference graph

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