  Driven or self-propelling particles moving in viscoelastic fluids recently
emerge as novel class of active systems showing a complex yet rich set of
phenomena due to the non-Newtonian nature of the dispersing medium. Here we
investigate the one-dimensional growth of clusters made of active colloidal
shakers, which are realized by oscillating magnetic rotors dispersed within a
viscoelastic fluid and at different concentration of the dissolved polymer.
These magnetic particles when actuated by an oscillating field display a flow
profile similar to that of a shaker force dipole, i.e. without any net
propulsion. We design a protocol to assemble clusters of colloidal shakers and
induce their controlled expansion into elongated zigzag structures. We observe
a power law growth of the mean chain length and use theoretical arguments to
explain the measured $1/3$ exponent. These arguments agree well with both
experiments and particle based numerical simulations.
