A roller assembly comprises a central section with a hub; a plurality of arms coupled to the central section, each arm having a radial section, an arcuate section, and a bent section; and a plurality of rollers, one roller coupled to the bent section of each arm. The arms may be flexible such that the rollers are capable of moving with respect to the central section when the arms flex. The rolling surface of the rollers is arranged to engage a polymer sheet or flexible tubing throughout travel of the arms.