As bio-sourced materials are raising interest for their sustainability, using the ability of bacteria to produce biofilms made of a protein and polysaccharide matrix has become a new strategy to make "engineered living materials" with various functionalities. This emerging field of biomaterials science mostly studies and genetically modifies the fibrous biofilm matrix to tune the properties of the final "product" [1]. In contrast, our group aims at clarifying how bacteria adapt biofilms to their environment, and at using this knowledge to tune biofilm materials properties.
For this, we culture E. coli producing curli amyloid and phosphoethanolamine-cellulose fibers [2], plate them on nutritive agar substrates with varying  physico-chemical properties, and study the growth, morphology and mechanical properties of the resulting biofilms. For example, we demonstrated that changing the surface properties of the agar with cationic polyelectrolyte coatings limits biofilm spreading but increases their surface density via extended wrinkling (i.e. growth in the third dimension) [3]. Following similar strategies, we also showed that E. coli adapt their biofilm growth, morphology and mechanical properties to the water content of their substrate [4]. Finally, we demonstrated that adding calcium and organic phosphate into the nutritive agar enables bacteria to mineralize the biofilm with hydroxyapatite crystals, thereby turning it into an hybrid organic-inorganic material.
In parallel, we also explore how post-processing biofilms, e.g. by treatment with ionic solutions, can help tuning further their properties. Finally, investigations pursued at the molecular level aim at identifying the interaction between matrix components (e.g. curli, cellulose and water) and their contribution to the ultimate materials properties.

References
[1] P.Q. Nguyen Nature communications, 2014, 5(1), p. 1-10.
[2] W. Thongsomboon, Science, 2018, 359(6373), p. 334-338.
[3] N.V. Ryzhkov, Adv. Mater. Interfaces, 2021, 8, 2001807.
[4] R. Ziege, ACS Biomater. Sci. Eng., 2021, 7(11), 5315–5325.