Abstract

Biologically evolved materials are often used as inspiration in the design and development of new materials as well as examinations into the underlying physical principles governing their behavior. For instance, the biopolymer constituents of the highly dynamic cellular cytoskeleton, including actin filaments and the associated set of crosslinkers and molecular motors, have inspired a deep understanding of soft polymer-based materials on both the experimental and theoretical levels. However, the molecular toolbox provided by biological systems has been evolutionarily optimized to carry out the necessary functions of cells. The resulting inability to systematically modify basic properties such as biopolymer stiffness or crosslink affinity in experimentally available model systems hinders a meticulous examination of parameter space. Using the actin cytoskeleton as inspiration, we circumvent these limitations using model systems assembled from programmable materials such as DNA . Filaments with comparable, but controllable dimensions and mechanical properties as actin can be constructed from small sets of specially designed DNA strands. In entangled networks at low density, these allow us to experimentally determine the dependence of macroscopic mechanical properties on previously inaccessible parameters such as filament stiffness. While bulk characterization of stress-strain response and microscopic single-filament analysis of snake-like reptation are consistent with established models for entangled networks of semiflexible polymers, deviating mechanical behavior with respect to the systematic variation of filament stiffness points towards a possible breakdown of fundamental assumptions. At higher concentrations in the presence of local attractive forces, we see a transition to highly-ordered bundled and “aster” phases with microscale patterning similar to those previously characterized in systems of actin or microtubules. In addition to providing a methodology for the more comprehensive characterization of soft polymer-based materials on both the micro- and macroscale, we expect this to potentially be a powerful tool for the design of mechanically tunable and switchable biomaterials.