Abstract : Several biological mechanisms use polymerization of actin filaments as mechanical motor. The chemical energy released with the addition of a monomer in the filament is converted into mechanical work thereby generating a force. Filaments are regulated by actin binding proteins, and form structures that possess different mechanical and elastical properties, and also different functions in the biological processes. Our experimental setup permits to study the link between the mechanical properties and the mechanisms that produce a force. The polymerization of actin filaments is directly initiated on the surface of magnetic particles. Within a magnetic field, particles organize themselves in a chain due to dipole-dipole interactions, and a compressive force is induced on the polymerizing filaments. Polymerization pushes the particles apart over time and as a function of the applied force, the velocity of the particles gap slows down. While following the evolution of the distance between particles, we obtain information on the force-velocity profile and the mechanical properties of the filaments.