I am interested in multi-components media in active matter and biophysics, spanning from tissues to cellular liquid condensates.

Those media can form mixtures, such as in multicellular aggregates composed by cells, intersticial fluids and extracellular matrix. In this case, significant variations of the physical properties can nonetheless vary inside the aggregate, between the bulk and the surface: for instance the orientation of the cells, their velocity, the exact densities of the different components, and the concentrations of different chemicals.

Phase separation may also be observed when the mixture is unstable, and for instance different cell types seggregate due notably to differential adhesion. In this case, interesting patterns, more or less transient, can emerge.

Specific active or passive interplays in the mixture may trigger or inhibit other phase transitions, like order-disorder, or flocking transitions.

Examples of systems involving this physics include notably tumor microenvironment, where the complex interactions between cancer cells, fibroblasts, macrophages, and other cells determine the fate of the tumor.

The studies involve continuous modeling, where equations are either derived from the symmetries of the system or by coarse-graining of the microscopic dynamics of discrete agents.

Theoretical work is then combined to numerical resolution of continuous equations and discrete simulations, in the frame of experimental collaboration.

Publications

2021

• Ackermann, Joseph, Martine Ben Amar, and Jean-François Joanny. "Multi-cellular aggregates, a model for living matter." Physics Reports 927 (2021): 1-29. 

2022 

• Ackermann, Joseph, et al. "Modeling the mechanics of growing epithelia with a bilayer plate theory." The European Physical Journal Plus 137 (2022): 1-29.
• Ackermann, Joseph, et al. "Morpho-elasticity of human pluripotent stem cell cysts." Journal of the Mechanics and Physics of Solids 160 (2022): 104778. 

2023

• Ackermann, Joseph, and Martine Ben Amar. "Onsager’s variational principle in proliferating biological tissues, in the presence of activity and anisotropy." The European Physical Journal Plus 138.12 (2023): 1103.

2025

• Bell, Samuel, et al. "Ordering, spontaneous flows and aging in active fluids depositing tracks." arXiv preprint arXiv:2409.05195 (2024). ACCEPTED PRE-LETTERS
• Ackermann, Joseph, et al. "How cancer-associated fibroblasts promote T cell exclusion in human lung tumors: a physical perspective." bioRxiv (2024): 2024-01. ACCEPTED ELIFE

Preprints

• Jacques, Cécile, et al. "Aging and freezing of active nematic dynamics of cancer-associated fibroblasts by fibronectin matrix remodeling." bioRxiv (2023): 2023-11. 
• Benaroch, Philippe, et al. "Tissue-resident macrophages favor early lung cancer development via direct physical interactions with cancer cells." (2024).