Mechanics of filamentous growth in soft materials*

Candida albicans is a yeast that grows in the shape of a filament with a tip continuously moving forward in the nutritious medium. The forces at the tip are driven by the internal pressure of the cell and are strong enough to induce indentation and penetration in materials such as the human tissues. This allows C. albicans to invade a host, with possibly lethal consequences, especially in immunodeficient individuals.
How the growth rate and direction depend on the material properties provide indications of the internal behaviour and response of the organism to its environment. These can be better understood by growing filaments in controlled substrates, and even reducing experiments to observing the penetration of thin solids in soft materials. We present here experiments of both the indentation of PDMS by a micrometric-sized sphere, and the observation of C. albicans growing in PDMS substrates containing fluorescent particles where the deformations of the material can be monitored. We expect with such experiments to improve and develop models of the mechanics of penetration in brittle and elastic materials depending on their mechanical properties such as the Young modulus, the viscosity and the adhesive properties.