Hydrogels consist of a porous matrix saturated with liquid. They can be highly porous, and thus have a great capacity to retain or release liquid. For these reasons, they are used in a wide range of applications, notably in the environmental sector (soil decontamination or hydratation) or in the food industry where hydrogels are mainly designed to function as a carrier system for bioactive compounds, or to adapt the texture and water retention of foods.These gels can be made of a dispersion of nano- particles that form aggregates through drying process. To design new gels with controlled structure and mechanical properties, a promising way of research concerns the addition of swimming micro-organisms in the dispersion; this ”active bath” can modulate the effective inter-particle interactions and then control the aggregation process. Thus, when swimming micro-organisms are dispersed in a fluid, there is a complex interplay with the collective dynamics of micro-organisms and the surrounding fluid; if this system is let to dry, there will have some flows due to the evaporation of solvent and then at the end of the drying process, a gel is formed: the structure of the gel and its final mechanical properties depend on how the particles have aggregated. The role of the bacteria and how they modify the fluid flows during drying and the aggregation process has to be understood.