Search for: All records

By introducing light-activated motors, we spatiotemporally pattern nematic defect structure and flow in two-dimensional microtubule nematics. 

Here we present a new, compact magnetic tweezers design that enables precise application of a wide range of dynamic forces to soft materials without the need to raise or lower the magnet height above the sample. This is achieved through the controlled rotation of the permanent magnet array with respect to the fixed symmetry axis defined by a custom-built iron yoke. These design improvements increase the portability of the device and can be implemented within existing microscope setups without the need for extensive modification of the sample holders or light path. This device is particularly well-suited to active microrheology measurements using either creep analysis, in which a step force is applied to a micron-sized magnetic particle that is embedded in a complex fluid, or oscillatory microrheology, in which the particle is driven with a periodic waveform of controlled amplitude and frequency. In both cases, the motions of the particle are measured and analyzed to determine the local dynamic mechanical properties of the material. 

Significance Active forces sculpt the forms of living things, generating adaptable and reconfigurable dynamical materials. Creating synthetic materials that exhibit comparable control over internally generated active forces remains a challenge. We demonstrate that active composite networks, collectively driven by the force-generating molecular motors, exhibit complex spatiotemporal patterns similar to those observed in cell biology. Amongst others, we describe robust self-assembly of onion-like layered asters. A self-regulating mechanism ensures the asters’ layered structure survives coalescence-like events, while their temporal stability is encoded in the mechanical properties of the network. Our model system elucidates the essential role of passive elasticity in controlling the emergent nonequilibrium dynamics while also establishing a robust experimental platform for engineering lifelike materials. 

Microtubule-based active matter provides insight into the self-organization of motile interacting constituents. We describe several formulations of microtubule-based 3D active isotropic fluids. Dynamics of these fluids is powered by three types of kinesin motors: a processive motor, a non-processive motor, and a motor which is permanently linked to a microtubule backbone. Another modification uses a specific microtubule crosslinker to induce bundle formation instead of a non-specific polymer depletant. In comparison to the already established system, each formulation exhibits distinct properties. These developments reveal the temporal stability of microtubule-based active fluids while extending their reach and the applicability. 

An enticing feature of active materials is the possibility of controlling macroscale rheological properties through the activity of the microscopic constituents. Using a unique combination of microscopy and rheology we study three dimensional microtubule-based active materials whose autonomous flows are powered by a continually rearranging connected network. We quantify the relationship between the microscopic dynamics and the bulk mechanical properties of these nonequilibrium networks. Experiments reveal a surprising nonmonotonic viscosity that strongly depends on the relative magnitude of the rate of internally generated activity and the externally applied shear. A simple two-state mechanical model that accounts for both the solidlike and yielded fluidlike elements of the network accurately describes the rheological measurements.