Dynamics of Living Matter

Stefano Villa

Research interests

Cilia driven flow of the Cerebrospinal fluid

In collaboration with Dr. Shoba Kapoor and her group “Developmental Biodynamics”, we study the cilia driven flow of the cerebrospinal fluid (CSF) in the ventral third ventricle of the mammalian brain [1]. Ventral third ventricle (v3V) is a thin cavity located in the central part of the brain containing CSF. There, CSF flows following a complex pattern (Fig.1.1) which results from the dynamics of ciliated cells covering the inside of the ventricle. The function of such a complex pattern remains largely unknow.

In particular, we analyze image data of murine brain explants and in-vitro cell cultures provided by the group Developmental Biodynamics.

We indagate how the flow pattern arises from the cilia motion by quantifying and correlating different dynamic and static properties of the tissues:

cell polarity obtained from fluorescent microscopy of stained tissues (Fig.1.2)
cilia bundle dynamics accessed from DIC microscopy (Mov.1.1)
particle and fluorescent liposomes tracking in bright field microscopy (Fig.1.1).

We are mainly interested in deepening the interplay between biochemical signaling and hydrodynamics during cell development in order to understand the pattern function and its formation process.

Figure 1.1. Flow map measured with particle tracking and scheme of the flow modules near the v3V wall.

Figure 1.1. Flow map measured with particle tracking and scheme of the flow modules near the v3V wall.

Figure 1.2. Ependymal cells immunostained for beta catenin and gamma tubulin. From image analysis, cell polarity (white arrows) can be accessed.

Figure 1.2. Ependymal cells immunostained for beta catenin and gamma tubulin. From image analysis, cell polarity (white arrows) can be accessed.

Movie 1.1. DIC microscopy video of beating cilia in v3V explant.

https://www.youtube.com/watch?v=B_YNPTFXB3E

Collective dynamics and phase transitions in cell monolayers

Current collaboration with University of Milan and IFOM institute on the characterization of confluent cell monolayers undergoing a jamming phase transition, characterized by the rising of collective migration (Mov.2.1) and a transition from a solid-like to a fluid-like state. Flocking cell monolayers are interesting models for the study of phenotypes associated to cancer evolution towards metastasis.

In particular, we currently study the shape deformations cells nuclei undergo in jammed and flocking monolayers (Mov.2.2) correlating them with the local dynamic state of the tissue (Fig.2.1) [2].

Figure 2.1. Divergence (colormap) of the velocity field (black arrows) obtained from PIV analysis of nuclei dynamics. The colormap map is overlayed on the corresponding fluorescent microscopy frame. Blue shades higlights two segmented nuclei subjected to a negative (a) and to a positive (b) divergence.

Figure 2.1. Divergence (colormap) of the velocity field (black arrows) obtained from PIV analysis of nuclei dynamics. The colormap map is overlayed on the corresponding fluorescent microscopy frame. Blue shades higlights two segmented nuclei subjected to a negative (a) and to a positive (b) divergence.

Rheomicroscopy of soft materials

Current collaboration with University of Milan on the characterization of mechanical properties of viscoelastic soft materials. We work on the development and characterization of a microscope adapted stress controlled shear cell, assembled at the Biometra department of University of Milan. Sample strain associated to an imposed stress is assessed trough an optical measurement, thus enabling the recovering of mean mechanical properties of the sample. The simultaneous imaging of the sample (Fig.3.1, Mov.3.1, Mov.3.2) allows to correlate macrorheological properties with local dynamics of the sample at the micrometric scale, thus opening the way to a deeper comprehension of the microscale structural origin of macroscopic mechanical properties of soft materials.

Figure 3.1. Sketch of the stress-controlled shear cell operating principle: the sample is enclosed between two glass plates separated by a gap distance h. When a shearing force is exerted on the upper glass, the latter translates by x, resulting in a strain x/h of the sample. The whole system is placed on the stage of a microscope which enables the imaging of tracers dispersed within the sample. — Figure 3.1. Sketch of the stress-controlled shear cell operating principle: the sample is enclosed between two glass plates separated by a gap distance h. When a shearing force is exerted on the upper glass, the latter translates by x, resulting in a strain *x/h* of the sample. The whole system is placed on the stage of a microscope which enables the imaging of tracers dispersed within the sample.

Figure 3.1. Sketch of the stress-controlled shear cell operating principle: the sample is enclosed between two glass plates separated by a gap distance h. When a shearing force is exerted on the upper glass, the latter translates by x, resulting in a strain *x/h* of the sample. The whole system is placed on the stage of a microscope which enables the imaging of tracers dispersed within the sample.

Dynamics of colloids in the vicinity of gas-liquid interface

Project in collaboration with University of Montpellier, as a prosecution of Stefano Villa PhD work, on the description of the dynamics of micrometric particles of different shapes in the vicinity of air-water interface. Measurements are made with a Dual Wave Reflection Interference Microscopy [4] – developed at Charles Coulomb laboratory (Montpellier) - enabling 3D tracking of colloidal dynamics (Fig.4.1). The study is devoted to the understanding of the physics underlying the dynamics of bacteria and biofilms in the vicinity of water surface and, in the waste water treatment framework, the approach and trapping of micrometric pollutants at the surface of water.

Figure 4.1. Top: sequence of interference microscopy frames of a spherical bead moving near an air-water interface. All three translational degrees of freedom are accessible from the image analysis. On the bottom, a typical time evolution of the particle-interface gap distance is reported as the bead sediments towards the interface.

Figure 4.1. Top: sequence of interference microscopy frames of a spherical bead moving near an air-water interface. All three translational degrees of freedom are accessible from the image analysis. On the bottom, a typical time evolution of the particle-interface gap distance is reported as the bead sediments towards the interface.

[1] Faubel, Regina, et al. "Cilia-based flow network in the brain ventricles." Science 353.6295 (2016): 176-178.

[2] Villa, Stefano, et al. "Non-invasive measurement of nuclear relative stiffness from quantitative analysis of microscopy data." arXiv preprint arXiv:2203.06226 (2022).

[3] Edera, Paolo, et al. "Deformation profiles and microscopic dynamics of complex fluids during oscillatory shear experiments.", Soft Matter 17 (2021): 8553-8566.

[4] S. Villa, A. Stocco, C. Blanc and M. Nobili, “Multistable interaction between a spherical Brownian particle and an air–water interface.”, Soft Matter, 16 (2020): 960-969.