Non-equilibrium microrheology of topologically-active DNA solutions

DNA, which naturally occurs in linear, ring, and supercoiled topologies, frequently undergoes enzyme-driven topological conversion and fragmentation in vivo, enabling it to perform a variety of functions within the cell. In vitro, highly concentrated DNA polymers form entanglements that yield viscoelastic properties dependent on the topologies and lengths of the DNA. Enzyme-driven alterations of DNA size and shape therefore offer a means of designing active materials with programmable viscoelastic properties. Here, we incorporate enzymes into dense DNA solutions to linearize and fragment circular DNA molecules. We use optical tweezers microrheology to measure the time-dependent linear and nonlinear viscoelastic properties over the course of enzymatic digestion. We show that these 'topologically-active' fluids initially thicken after which they undergo gradual and non-monotonic thinning with enhanced athermal fluctuations. In future work, we will examine different DNA lengths, topologies, and types of enzymes to create a class of non-equilibrium reconfigurable fluids with applications from drug delivery and wound-healing to infrastructure repair.