  We explore the self-assembly process of colloidal structures immersed in
active baths. By considering low-valence particles we numerically investigate
the irreversible aggregation dynamics originated by the presence of
run-and-tumble swimmers. We observe the formation of long closed chains --
vesicles -- densely filled by active swimmers. On the one hand the active bath
drives the self-assembly of closed colloidal structures, and on the other hand
the vesicles formation fosters the self-trapping of swimmers, suggesting new
ways both to build structured nanomaterials and to trap microorganisms.
