REVIEW 2 major objections 4 minor 51 references
From shallow to full wrapping: geometry and deformability dictate lipid vesicle internalization
T0 review · 2 major / 4 minor · reviewed 2026-08-06 · deepseek-v4-flash
Pith's one-line read A small vesicle's deformability can suppress its complete engulfment by a larger membrane even when enough membrane area exists, according to experiments and continuum simulations.
desk verdict Careful experiment/simulation study with a credible geometric wrapping transition; the deformability-suppression headline is promising but rests on two points, so treat as conditional. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The central object is the bendo-capillary length $L = \sqrt{\kappa/w}$, the scale at which membrane bending and adhesion energies balance, together with the reduced volume $\nu_i$ that measures how much excess membrane area a vesicle has and hence how deformable it is. The study organizes the problem around the ratio $R_{\rm small}/L$ and derives an effective reduced volume $\nu_\gamma$ (Eq.~7) for the large vesicle once it has wrapped the small one; the condition $\nu_\gamma \le 1$ is the geometric criterion for full engulfment. Energy-minimized continuum simulations of the Helfrich free energy (Eq.~8), with constant membrane area and volume enforced by Lagrange multipliers, supply the equilibrium morphologies and phase boundaries that the experiments are compared against.
What would settle it
Take a vesicle pair with $\nu_{\rm small} \approx 0.8$ and $R_{\rm small}/L \approx 1$ that lies just below the predicted full-wrapping boundary, slowly raise the adhesion strength until it wraps, then slowly lower it again; if the pair stays fully wrapped below the predicted boundary, or if partial wrapping persists where the boundary predicts full wrapping, the observed states are kinetically trapped rather than equilibrium ones.
Extended reading notes
Core claim
The paper establishes a two-regime picture of vesicle-vesicle engulfment. When $R_{\rm small}/L \gg 1$, adhesion dominates over bending and the partial-to-full wrapping transition is governed by geometry alone: full engulfment is possible precisely when the effective reduced volume of the large vesicle after wrapping, $\nu_\gamma = (1+\phi)/(\nu_{\rm large}^{-2/3} - \phi^{2/3}\nu_{\rm small}^{-2/3})^{3/2}$, is at most 1. When $R_{\rm small}/L \approx 1$, full engulfment can be suppressed even if $\nu_\gamma < 1$, and the suppression grows as the small vesicle becomes more deformable: the transition curves require increasing adhesion strength, equivalently larger $R_{\rm small}/L$, as $\nu_{\rm small}$ drops from 0.99 to 0.80. Experiments and simulations agree on wrapping fractions and morphologies across volume ratios from 0.001 to 0.8 and size ratios from 1.6 to 19, and the measured bendo-capillary length is $L_{\rm exp} = 0.61 \pm 0.10\,\mu\rm m$. The paper therefore claims that deformability is not a minor correction but a decisive control parameter in the crossover regime, and that the same energetic balance explains both endocytic and exocytic engulfment.
Load-bearing premise
The comparison rests on the assumption that each measured vesicle pair has relaxed to the global minimum of the Helfrich free energy at fixed volume and area, so the computed equilibrium phase boundaries describe the experimental morphologies; the paper does not demonstrate that wrapping is reversible or that the states are not kinetically trapped by the narrow neck that forms near full wrapping.
Editorial extensions
If this is right
- In the geometry-dominated regime, the outcome of engulfment can be predicted from three measured quantities, the volume ratio and the two reduced volumes, without needing a precise value of the adhesion strength or bending rigidity.
- Near $R_{\rm small}/L \approx 1$, modest changes in the deformability of the cargo vesicle shift the adhesion strength required for full uptake, so softness is a practical control parameter for engulfment.
- Increasing the excess membrane area of the large vesicle, for example by light-triggered area expansion, drives a pair from shallow to deep to full wrapping and offers an external switch for the process.
- Because the same energy balance reproduces both endocytic and exocytic morphologies, the framework should transfer to uptake of soft carriers in synthetic-cell and drug-delivery contexts.
- The cargo vesicle changes from oblate to prolate as wrapping deepens, so wrapping fraction and cargo shape co-evolve instead of the cargo staying rigid.
Reading between the lines
- An untested consequence of the equilibrium picture is reversibility: if adhesion is slowly removed, a fully wrapped vesicle should unwrap along the same path. The paper only shows progressive wrapping, so a direct unwrapping experiment would show whether the phase boundaries are thermodynamic or partly kinetic.
- The single outlier near the geometric boundary suggests that bending energy can inhibit full engulfment even when Eq.~7 says it is possible; mapping the transition systematically at intermediate $R_{\rm small}/L$, roughly 2 to 10, would quantify how sharp the crossover really is.
- The geometric criterion $\nu_\gamma \le 1$ treats the small vesicle through its volume and area only, so extending the framework to non-spherical or multi-domain cargo would require an effective shape parameter beyond the reduced volume.
Signed reviews
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. This manuscript combines confocal fluorescence imaging of GUV–GUV engulfment with Surface Evolver continuum simulations to map wrapping morphologies as functions of volume ratio, reduced volumes, and the ratio of small-vesicle size to the bendo-capillary length. The authors derive an analytic geometric condition for full engulfment in the R_small/L >> 1 regime (Eq. 7), calibrate L_exp by matching peak mean curvature, and construct state diagrams for endocytic and exocytic geometries. They report a geometry-dominated regime and a deformability-dominated regime near R_small/L ~ 1, where lower small-vesicle reduced volume suppresses complete wrapping despite sufficient excess area.
Significance. If the central claim holds, this is a valuable direct experimental test of long-standing theoretical predictions that soft-object deformability inhibits full engulfment, with implications for endocytosis, viral entry, and drug delivery. The paper's strengths include quantitative 3D morphometry, the clean analytic formula in Eq. 7, treatment of both endo- and exocytic geometries, and a photo-switchable area-expansion control. The main evidential weakness is that the headline deformability-suppression result rests on two experimental points and an untested equilibrium assumption, so the definitive status of that claim depends on additional experiments and analysis.
major comments (2)
- [Modelling the vesicle-vesicle engulfment; Fig. 4B; Fig. 6] The central claim that deformability suppresses full wrapping when R_small/L ≈ 1 assumes each observed pair is at the global minimum of the Helfrich free energy in Eq. 8. Surface Evolver is a local gradient-descent minimizer from an initial guess, and the time series in Fig. 4B only shows progressive wrapping; no spontaneous unwrapping or repeated cycling is reported. A partially wrapped pair at R/L = 2.9 could be kinetically trapped behind the catenoidal-neck barrier rather than representing the equilibrium phase boundary in Fig. 6. Please test reversibility directly, for example by lowering the polymer concentration or switching azo-PC back from cis to trans and showing that partially and fully wrapped states interconvert, and/or by computing and reporting energy barriers from near-full initial configurations. Without such a test, the geometry-dominated result (Eq. 7, Fig. 5) remains secure, but the deformability-suppression claim is not fully supported.
- [Fig. 6 and the 'nearly identical parameters' comparison after Fig. 5] The experimental evidence for Fig. 6 consists of two data points at νγ = 0.93 with R/L = 7.1 (fully wrapped) and R/L = 2.9 (partially wrapped). This single comparison carries the headline claim, but the manuscript does not tabulate all four dimensionless parameters for these two pairs, does not provide replicate counts or experimental uncertainties, and does not propagate the ±0.10 µm uncertainty in L_exp to R/L. If the two pairs differ appreciably in φ, ν_small, or ν_large, or if the R/L = 2.9 point has an uncertainty reaching the phase boundary, the attribution to R/L and deformability is confounded. Please provide a table with exact values and errors for all parameters of these pairs, and ideally add more data points in the R/L ≈ 1–5 range at fixed ν_small, with error bars on wrapping fractions as well.
minor comments (4)
- [Fig. 3C] The wrapping fractions in Fig. 3C are shown without error bars or replicate counts; please state the number of independent vesicle pairs per condition and the measurement uncertainty, or acknowledge the absence of replicates in the figure caption.
- [Eq. 2] As rendered in the arXiv text, Eq. 2 appears to define ν_i as the cube root of (4πV_i/A_i^{3/2}), which is not the standard reduced volume and would be inconsistent with Eq. 7. If the intended expression is ν_i = 3√(4π) V_i / A_i^{3/2}, please typeset it unambiguously.
- [Data and materials availability] The availability statement says only that data are present in the paper and/or Supporting Information; please state whether Surface Evolver input files and analysis scripts are available, as this would strengthen reproducibility.
- [Azo-PC area expansion] The estimated ~3% membrane area increase is inferred rather than measured directly; please clarify whether this is an upper bound and how the uncertainty affects the inferred ν_large values in Fig. 5B.
Circularity Check
No significant circularity: the bendo-capillary length is calibrated on curvature, while the central phase-boundary and wrapping-fraction comparisons are independent outputs of energy minimization and geometric bookkeeping.
full rationale
The paper's only fitted quantity is L_exp, obtained by matching the peak mean curvature of five experimental vesicle pairs to Surface Evolver simulations with varying L_sim (Eq. 5). This is a standard one-parameter calibration: the observable used in the fit is M*, a local curvature feature, not the wrapping fraction f, the partial/full wrapping state, or the location of the phase boundaries. The central claims are then tested against these independent observables. Eq. 7 is a geometric volume/area-accounting condition for whether full engulfment is geometrically possible; it is derived from the definitions of phi, nu_large and nu_small and does not contain L, so it cannot be forced by the calibration. The Fig. 6 transition curves are computed from total-energy curves as a function of wrapping fraction at fixed input parameters (nu_large = 0.75, three nu_small values), and the two experimental points at nu_gamma = 0.93 are placed on the resulting diagram after the fact; they are not used to construct the curves. No load-bearing uniqueness theorem or ansatz is imported solely from the authors' prior work; the cited prior theoretical studies are corroborative, not the derivation. The remaining reader concerns, such as the untested equilibrium assumption for the R/L = 2.9 partially wrapped pair and the sparse two-point experimental support for the deformability-suppression claim, are correctness or robustness risks rather than circularity: they do not show that any prediction reduces by construction to its fitted input. Accordingly, the derivation chain is self-contained apart from normal parameter calibration, and no circular step is identified.
Assumptions & free parameters
free parameters (1)
- bendo-capillary length L_exp (effective adhesion strength w) =
0.61 +/- 0.10 um
assumptions (7)
- domain assumption Zero spontaneous curvature for both vesicle membranes.
- domain assumption Equal bending rigidity for large and small vesicle, kappa_small = kappa_large = kappa.
- standard math Constant vesicle volume and membrane area enforced by Lagrange multipliers.
- domain assumption Adhesion energy is proportional to contact area with a single effective adhesion strength w.
- domain assumption Observed experimental morphologies correspond to global energy minima of the Helfrich-type functional.
- domain assumption The catenoidal neck in fully wrapped states has zero bending energy and can be omitted.
- domain assumption Gravitational effects are negligible for most simulated shapes and are not included in the model.
Cite this review
Pith. "Pith review of From shallow to full wrapping: geometry and deformability dictate lipid vesicle internalization." pith.science (2026). https://pith.science/paper/WOKUKPVI
@misc{pith2026250717434,
author = {Pith},
title = {Pith review of: From shallow to full wrapping: geometry and deformability dictate lipid vesicle internalization},
year = {2026},
howpublished = {\url{https://pith.science/paper/WOKUKPVI}},
note = {Machine review of arXiv:2507.17434}
}
read the original abstract
The deformability of vesicles critically influences their engulfment by lipid membranes, a process central to endocytosis, viral entry, drug delivery, and intercellular transport. While theoretical models have long predicted this influence, direct experimental validation has remained elusive. Here, we combine experiments with continuum simulations to quantify how vesicle deformability affects the engulfment of small giant unilamellar vesicles (GUVs) by larger GUVs under depletion-induced adhesion. Using 3D confocal reconstructions, we extract vesicle shape, curvature, wrapping fraction, and the bendo-capillary length, a characteristic length scale that balances membrane bending and adhesion forces. We find that when vesicle size exceeds this length scale, engulfment is primarily governed by geometry. In contrast, when vesicle size is comparable to this scale, deformability strongly affects the transition between shallow, deep, and fully wrapped states, leading to suppression of full engulfment of vesicles. These findings connect theoretical predictions with direct measurements and offer a unified framework for understanding vesicle-mediated uptake across both synthetic and biological systems, including viral entry, synthetic cell design, drug delivery, and nanoparticle internalization.
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Works this paper leans on
-
[1]
B. Gy¨ orgy, T. G. Szab´ o, M. P´ aszt´ oi, Z. P´ al, P. Misj´ ak, B. Aradi, V. L´ aszl´ o, E. P´ allinger, E. Pap, A. Kittel,et al., Membrane vesicles, current state-of-the-art: emerging role of extracellular vesicles, Cellular and Molecular Life Sciences68, 2667 (2011)
work page 2011
-
[2]
S. Arandjelovic and K. S. Ravichandran, Phagocytosis of apoptotic cells in homeostasis, Nature Immunology16, 907 (2015)
work page 2015
-
[3]
F. S. Cohen, How viruses invade cells, Biophysical Jour- nal110, 1028 (2016)
work page 2016
- [4]
- [5]
- [6]
-
[7]
T. M. Allen and P. R. Cullis, Liposomal drug delivery systems: from concept to clinical applications, Advanced Drug Delivery Reviews65, 36 (2013)
work page 2013
-
[8]
D. Guimar˜ aes, A. Cavaco-Paulo, and E. Nogueira, Design of liposomes as drug delivery system for therapeutic ap- plications, International Journal of Pharmaceutics601, 120571 (2021)
work page 2021
Show all 51 references
-
[9]
L. M. Bareford and P. W. Swaan, Endocytic mechanisms for targeted drug delivery, Advanced Drug Delivery Re- views59, 748 (2007)
2007
-
[10]
B. S. Joshi, M. A. de Beer, B. N. Giepmans, and I. S. Zuhorn, Endocytosis of extracellular vesicles and release of their cargo from endosomes, ACS Nano14, 4444 (2020)
2020
-
[11]
S. D. Conner and S. L. Schmid, Regulated portals of entry into the cell, Nature422, 37 (2003)
2003
-
[12]
Lipowsky and H.-G
R. Lipowsky and H.-G. D¨ obereiner, Vesicles in contact with nanoparticles and colloids, Europhysics Letters43, 219 (1998)
1998
-
[13]
Dasgupta, T
S. Dasgupta, T. Auth, and G. Gompper, Shape and ori- entation matter for the cellular uptake of nonspherical particles, Nano Letters14, 687 (2014)
2014
-
[14]
van der Ham, J
S. van der Ham, J. Agudo-Canalejo, and H. R. Vutukuri, Role of shape in particle-lipid membrane interactions: from surfing to full engulfment, ACS Nano18, 10407 (2024)
2024
-
[15]
A. H. Bahrami, Orientational changes and impaired in- ternalization of ellipsoidal nanoparticles by vesicle mem- branes, Soft Matter9, 8642 (2013)
2013
-
[16]
Agudo-Canalejo and R
J. Agudo-Canalejo and R. Lipowsky, Critical particle sizes for the engulfment of nanoparticles by membranes and vesicles with bilayer asymmetry, ACS Nano9, 3704 (2015)
2015
-
[17]
Agudo-Canalejo, Particle engulfment by strongly asymmetric membranes with area reservoirs, Soft Mat- ter17, 298 (2021)
J. Agudo-Canalejo, Particle engulfment by strongly asymmetric membranes with area reservoirs, Soft Mat- ter17, 298 (2021)
2021
-
[18]
H. T. Spanke, R. W. Style, C. Fran¸ cois-Martin, M. Fe- ofilova, M. Eisentraut, H. Kress, J. Agudo-Canalejo, and E. R. Dufresne, Wrapping of microparticles by floppy lipid vesicles, Physical Review Letters125, 198102 (2020)
2020
-
[19]
A. H. Bahrami, M. Raatz, J. Agudo-Canalejo, R. Michel, E. M. Curtis, C. K. Hall, M. Gradzielski, R. Lipowsky, and T. R. Weikl, Wrapping of nanoparticles by mem- branes, Advances in Colloid and Interface Science208, 214 (2014)
2014
-
[20]
X. Yi, X. Shi, and H. Gao, Cellular uptake of elas- tic nanoparticles, Physical Review Letters107, 098101 (2011)
2011
-
[21]
Yi and H
X. Yi and H. Gao, Incorporation of soft particles into lipid vesicles: Effects of particle size and elasticity, Lang- muir32, 13252 (2016)
2016
-
[22]
Imoto, S
Y. Imoto, S. Raychaudhuri, Y. Ma, P. Fenske, E. San- doval, K. Itoh, E.-M. Blumrich, H. T. Matsubayashi, L. Mamer, F. Zarebidaki,et al., Dynamin is primed at en- docytic sites for ultrafast endocytosis, Neuron110, 2815 (2022)
2022
-
[23]
H. Tang, H. Zhang, H. Ye, and Y. Zheng, Wrapping of a deformable nanoparticle by the cell membrane: insights into the flexibility-regulated nanoparticle-membrane in- teraction, Journal of Applied Physics120(2016)
2016
-
[24]
Midya, T
J. Midya, T. Auth, and G. Gompper, Membrane- mediated interactions between nonspherical elastic par- ticles, ACS Nano17, 1935 (2023)
2023
-
[25]
Satarifard and R
V. Satarifard and R. Lipowsky, Mutual remodeling of interacting nanodroplets and vesicles, Communications Physics6, 6 (2023)
2023
-
[26]
Kusumaatmaja and R
H. Kusumaatmaja and R. Lipowsky, Droplet-induced budding transitions of membranes, Soft Matter7, 6914 (2011)
2011
-
[27]
A. C. Anselmo, M. Zhang, S. Kumar, D. R. Vogus, S. Menegatti, M. E. Helgeson, and S. Mitragotri, Elas- ticity of nanoparticles influences their blood circulation, phagocytosis, endocytosis, and targeting, ACS Nano9, 3169 (2015)
2015
-
[28]
J. Sun, L. Zhang, J. Wang, Q. Feng, D. Liu, Q. Yin, D. Xu, Y. Wei, B. Ding, X. Shi,et al., Tunable rigidity of (polymeric core)-(lipid shell) nanoparticles for regulated cellular uptake., Advanced Materials27, 1402 (2014)
2014
-
[29]
Dimova and C
R. Dimova and C. Marques,The giant vesicle book(CRC Press, 2019)
2019
-
[30]
Dinsmore, D
A. Dinsmore, D. Wong, P. Nelson, and A. Yodh, Hard spheres in vesicles: curvature-induced forces and particle- induced curvature, Physical Review Letters80, 409 (1998)
1998
-
[31]
Asakura and F
S. Asakura and F. Oosawa, On interaction between two bodies immersed in a solution of macromolecules, The Journal of Chemical Physics22, 1255 (1954)
1954
-
[32]
Machado, V
S. Machado, V. Mercier, and N. Chiaruttini, Limeseg: a coarse-grained lipid membrane simulation for 3d image segmentation, BMC Bioinformatics20, 1 (2019)
2019
-
[33]
Schindelin, I
J. Schindelin, I. Arganda-Carreras, E. Frise, V. Kaynig, M. Longair, T. Pietzsch, S. Preibisch, C. Rueden, S. Saalfeld, B. Schmid,et al., Fiji: an open-source plat- form for biological-image analysis, Nature Methods9, 676 (2012)
2012
-
[34]
Seifert, K
U. Seifert, K. Berndl, and R. Lipowsky, Shape trans- formations of vesicles: Phase diagram for spontaneous- curvature and bilayer-coupling models, Physical Review A44, 1182 (1991). 14
1991
-
[35]
H. A. Faizi, C. J. Reeves, V. N. Georgiev, P. M. Vla- hovska, and R. Dimova, Fluctuation spectroscopy of gi- ant unilamellar vesicles using confocal and phase contrast microscopy, Soft Matter16, 8996 (2020)
2020
-
[36]
Francois, D
J. Francois, D. Sarazin, T. Schwartz, and G. Weill, Poly- acrylamide in water: molecular weight dependence of <R2>and [η] and the problem of the excluded vol- ume exponent, Polymer20, 969 (1979)
1979
-
[37]
Tuinier and H
R. Tuinier and H. Lekkerkerker, Excluded-volume polymer-induced depletion interaction between parallel flat plates, The European Physical Journal E6, 129 (2001)
2001
-
[38]
Helfrich and R
W. Helfrich and R. M. Servuss, Undulations, steric in- teraction and cohesion of fluid membranes, Il Nuovo Ci- mento D3, 137 (1984)
1984
-
[39]
Lipowsky and E
R. Lipowsky and E. Sackmann,Structure and dynamics of membranes: I. from cells to vesicles/II. generic and specific interactions(Elsevier, 1995)
1995
-
[40]
N.-N. Deng, M. Yelleswarapu, L. Zheng, and W. T. Huck, Microfluidic assembly of monodisperse vesosomes as ar- tificial cell models, Journal of the American Chemical Society139, 587 (2017)
2017
-
[41]
Kraus, U
M. Kraus, U. Seifert, and R. Lipowsky, Gravity-induced shape transformations of vesicles, Europhysics Letters 32, 431 (1995)
1995
-
[42]
Pernpeintner, J
C. Pernpeintner, J. A. Frank, P. Urban, C. R. Roeske, S. D. Pritzl, D. Trauner, and T. Lohmu¨ uller, Light- controlled membrane mechanics and shape transitions of photoswitchable lipid vesicles, Langmuir33, 4083 (2017)
2017
-
[43]
Aleksanyan, A
M. Aleksanyan, A. Grafm¨ uller, F. Crea, V. N. Georgiev, N. Yandrapalli, S. Block, J. Heberle, and R. Dimova, Photomanipulation of minimal synthetic cells: Area in- crease, softening, and interleaflet coupling of membrane models doped with azobenzene-lipid photoswitches, Ad- v...
2023
-
[44]
Mangiarotti, M
A. Mangiarotti, M. Aleksanyan, M. Siri, T.-W. Sun, R. Lipowsky, and R. Dimova, Photoswitchable endocy- tosis of biomolecular condensates in giant vesicles, Ad- vanced Science11, 2309864 (2024)
2024
-
[45]
Agudo-Canalejo, Engulfment of ellipsoidal nanopar- ticles by membranes: full description of orientational changes, Journal of Physics: Condensed Matter32, 294001 (2020)
J. Agudo-Canalejo, Engulfment of ellipsoidal nanopar- ticles by membranes: full description of orientational changes, Journal of Physics: Condensed Matter32, 294001 (2020)
2020
-
[46]
H. R. Vutukuri, M. Hoore, C. Abaurrea-Velasco, L. van Buren, A. Dutto, T. Auth, D. A. Fedosov, G. Gompper, and J. Vermant, Active particles induce large shape de- formations in giant lipid vesicles, Nature586, 52 (2020)
2020
-
[47]
A. Moga, N. Yandrapalli, R. Dimova, and T. Robinson, Optimization of the inverted emulsion method for high- yield production of biomimetic giant unilamellar vesicles, ChemBioChem20, 2674 (2019)
2019
-
[48]
J. A. Frank, D. A. Yushchenko, D. J. Hodson, N. Lip- stein, J. Nagpal, G. A. Rutter, J.-S. Rhee, A. Gottschalk, N. Brose, C. Schultz,et al., Photoswitchable diacylglyc- erols enable optical control of protein kinase c, Nature Chemical Biology12, 755 (2016)
2016
-
[49]
H. M. Weakly, K. J. Wilson, G. J. Goetz, E. L. Pruitt, A. Li, L. Xu, and S. L. Keller, Several common meth- ods of making vesicles (except an emulsion method) cap- ture intended lipid ratios, Biophysical Journal123, 3452 (2024)
2024
-
[50]
E. E. Diel, J. W. Lichtman, and D. S. Richardson, Tu- torial: avoiding and correcting sample-induced spherical aberration artifacts in 3d fluorescence microscopy, Nature Protocols15, 2773 (2020)
2020
-
[51]
Jacobson, D
A. Jacobson, D. Panozzo,et al., libigl: A sim- ple C++ geometry processing library (2018), https://libigl.github.io/
2018
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