Steph Höhn

The mechanics of cell sheet folding

The folding of cellular monolayers is an essential process during animal and human embryo development, examples including gastrulation, neurulation, and organogenesis. We use the so-called inversion process in the multicellular micro-alga Volvox as a relatively simple example of cell sheet folding. Volvox embryos resemble a spherical shell, consisting of a single layer of cells. During inversion one hemisphere folds inwards and the embryo turns itself inside-out through an opening. We use a morphoelastic continuum model, time-lapse imaging, and mechanical perturbations to test hypotheses on the interplay between dynamic geometry and mechanical tissue properties. We showed how the mechanical constraints due to initial spherical vs. hemi-spherical embryo geometry drives the evolution of differences in local stretching and bending in different species [1-3]. The results of laser ablation experiments and model-based analyses indicate that changes in mechanical tissue properties are required to facilitate tissue folding [4]. A newly developed, tissue-scale micro-aspiration approach shows that local differences in bending modulus determine the site of tissue folding [in preparation]. Spatial differences in bending modulus likewise occur in a wide range of animal species, pointing towards a general biomechanical principle of tissue folding.

[1] BMC Biol 9, 89 (2011). https://doi.org/10.1186/1741-7007-9-89
[2] BMC Dev Biol, 16, (2016). https://doi.org/10.1186/s12861-016-0134-9
[3] PLOS Biol 16, e2005536 (2018). https://doi.org/10.1371/journal.pbio.2005536
[4] Phys Rev E 111, 014420 (2025). https://doi.org/10.1103/PhysRevE.111.014420