Self-organized gels in DNA/F-actin mixtures without crosslinkers: Networks of induced nematic domains with tunable density

We examine mixtures of DNA and filamentous actin (F-actin) as a model system of like-charged rigid rods and flexible chains. Confocal microscopy reveals the formation of elongated nematic F-actin domains reticulated via defect-free vertices into a network embedded in a mesh of random DNA. Synchrotron x-ray scattering results indicate that the DNA mesh squeezes the F-actin domains into a nematic state with an interactin spacing that decreases with increasing DNA concentration as dactin ρDNA-1/2. Interestingly, the system changes from a counterion-controlled regime to a depletion-controlled regime with added salt, with drastic consequences for the osmotic pressure induced phase behavior. © 2008 The American Physical Society