Controlled assembly of microscale objects can be achieved by exploiting interactions that dominate at that length scale. Capillary interactions are an excellent candidate for this purpose; microparticles trapped at fluid interfaces disturb the interface shape, migrate, and assemble to minimize the interfacial area. These interactions are independent of microparticle material properties and so can be used to assemble objects of arbitrary materials. By using a magnetic robot as a mobile distortion source, additional control over assembly can be achieved. For example, millimeter-scale magnetic robots that are heavy enough to distort the interface have been used to generate long range capillary attractions and collect passive particles that are hundreds of micrometers in diameter. However, for smaller robots and particles, gravity is less important, and capillary interactions rely on interface distortions from undulated contact lines. We use a magnetic microrobot to manipulate passive microparticles at the water/hexadecane interface via an interplay of hydrodynamic and capillary interactions. Furthermore, we demonstrate preferred docking at corners of a square microrobot without the need for high resolution position control. We modulate the strength of docking interactions, allowing structure assembly and release. Finally, we design undulated docking stations with multiple stable sites for cargo delivery. The ability to dynamically manipulate microparticles and their structures at fluid interfaces creates new possibilities for manufacturing of complex microstructures.
Even though there is a clear link between Alzheimer’s Disease (AD) related neuropathology and cognitive decline, numerous studies have observed that healthy cognition can exist in the presence of extensive AD pathology, a phenomenon sometimes called Cognitive Resilience (CR). To better understand and study CR, we develop the Alzheimer’s Disease Cognitive Resilience Score (AD-CR Score), which we define as the difference between the observed and expected cognition given the observed level of AD pathology. Unlike other definitions of CR, our AD-CR Score is a fully non-parametric, stand-alone, individual-level quantification of CR that is derived independently of other factors or proxy variables. Using data from two ongoing, longitudinal cohort studies of aging, the Religious Orders Study (ROS) and the Rush Memory and Aging Project (MAP), we validate our AD-CR Score by showing strong associations with known factors related to CR such as baseline and longitudinal cognition, non AD-related pathology, education, personality, APOE, parkinsonism, depression, and life activities. Even though the proposed AD-CR Score cannot be directly calculated during an individual’s lifetime because it uses postmortem pathology, we also develop a machine learning framework that achieves promising results in terms of predicting whether an individual will have an extremely high or low AD-CR Score using only measures available during the lifetime. Given this, our AD-CR Score can be used for further investigations into mechanisms of CR, and potentially for subject stratification prior to clinical trials of personalized therapies.
Topological defects on colloids rotating in nematic liquid crystals form far-from-equilibrium structures that perform complex swim strokes in which the defects periodically extend, depin, and contract. These defect dynamics propel the colloid, generating translation from rotation. The swimmer’s speed and direction are determined by the topological defect’s polarity and extent of elongation. Defect elongation is controlled by a rotating external magnetic field, allowing control over particle trajectories. The swimmers’ translational motion relies on broken symmetries associated with lubrication forces between the colloid and the bounding surfaces, line tensions associated with the elongated defect, and anisotropic viscosities associated with the defect elongation adjacent to the colloid. The scattering or effective pair interaction of these swimmers is highly anisotropic, with polarization-dependent dimer stability and motion that depend strongly on entanglement and sharing of their extended defect structures. This research introduces transient, far-from-equilibrium topological defects as a class of virtual functional structures that generate modalities of motion and interaction.
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