Magnetic soft micromachines made of linked microactuator networks

Soft untethered micromachines with overall sizes less than 100 μm enable diverse programmed shape transformations and functions for future biomedical and organ-on-a-chip applications. However, fabrication of such machines has been hampered by the lack of control of microactuator’s programmability. To address such challenge, we use two-photon polymerization to selectively link Janus microparticle-based magnetic microactuators by three-dimensional (3D) printing of soft or rigid polymer microstructures or links. Sequentially, we position each microactuator at a desired location by surface rolling and rotation to a desired position and orientation by applying magnetic field–based torques, and then 3D printing soft or rigid links to connect with other temporarily fixed microactuators. The linked 2D microactuator networks exhibit programmed 2D and 3D shape transformations, and untethered limbless and limbed micromachine prototypes exhibit various robotic gaits for surface locomotion. The fabrication strategy presented here can enable soft micromachine designs and applications at the cellular scales.

Polarization-resolved single-molecule tracking reveals strange dynamics of individual fluorescent tracers through a plasticized (rubbery) polymer network

<div>Tracking the movement of fluorescent single-molecule (SM) tracers has provided several new insights on the local structure and dynamics in complex environments such as soft materials and biological systems. However, SM tracking (SMT) remains unreliable at molecular length scales, as the localization-error (LE) of SM trajectories (~30-50 nm) is considerably larger than size of molecular tracers (~1-3 nm). Thus, instances of tracer (im)mobility in heterogeneous media, which provide indicator for underlying anomalous-transport mechanisms, remains obscured within the realms of SMT. Since translation of passive tracers in an isotropic network is associated with fast dipolar rotation, we propose authentic pauses within LE can be revealed upon probing SM reorientational dynamics. Here, we demonstrate how polarization-resolved SMT (PR-SMT) can provide emission-anisotropy at each super-localized position, thereby revealing tumbling propensity of SMs during random walk. For Rhodamine 6G tracers undergoing heterogeneous transport in a hydrated polyvinylpyrrolidone (PVP) network, analyses of PR-SMT trajectories enabled us to discern instances of genuine immobility and localized motion within the LE. Our investigations on 100 SMs in hydrated (plasticized) PVP films reveal a wide distribution of dwell-times and pause-frequencies, which demonstrate that majority of probes intermittently experience complete translational and rotational immobilization. This indicates tracers serendipitously encounter compact, rigid polymer cavities during transport, implying the existence of nanoscale glass-like domains sparsely distributed in a redominantly deep-rubbery polymer network far above the glass transition. PR-SMT is simple to implement and opens up alternate avenues to interrogate transient (bio)molecular interactions leading to anomalous transport in inhomogeneous media.</div>

Polarization-resolved single-molecule tracking reveals strange dynamics of individual fluorescent tracers through a plasticized (rubbery) polymer network

<div>Tracking the movement of fluorescent single-molecule (SM) tracers has provided several new insights on the local structure and dynamics in complex environments such as soft materials and biological systems. However, SM tracking (SMT) remains unreliable at molecular length scales, as the localization-error (LE) of SM trajectories (~30-50 nm) is considerably larger than size of molecular tracers (~1-3 nm). Thus, instances of tracer (im)mobility in heterogeneous media, which provide indicator for underlying anomalous-transport mechanisms, remains obscured within the realms of SMT. Since translation of passive tracers in an isotropic network is associated with fast dipolar rotation, we propose authentic pauses within LE can be revealed upon probing SM reorientational dynamics. Here, we demonstrate how polarization-resolved SMT (PR-SMT) can provide emission-anisotropy at each super-localized position, thereby revealing tumbling propensity of SMs during random walk. For Rhodamine 6G tracers undergoing heterogeneous transport in a hydrated polyvinylpyrrolidone (PVP) network, analyses of PR-SMT trajectories enabled us to discern instances of genuine immobility and localized motion within the LE. Our investigations on 100 SMs in hydrated (plasticized) PVP films reveal a wide distribution of dwell-times and pause-frequencies, which demonstrate that majority of probes intermittently experience complete translational and rotational immobilization. This indicates tracers serendipitously encounter compact, rigid polymer cavities during transport, implying the existence of nanoscale glass-like domains sparsely distributed in a redominantly deep-rubbery polymer network far above the glass transition. PR-SMT is simple to implement and opens up alternate avenues to interrogate transient (bio)molecular interactions leading to anomalous transport in inhomogeneous media.</div>

Investigation on guar gum and chitosan based polymer composite for oilfield water shut off fluid

The present study highlights the performance of guar gum and chitosan based polymer composite (GG-CH-g-PAN/AA) as water shut off polymer solution for oilfield application. Study on salinity percentage, type of salts, pH and temperature for the salt present in formulation and salts contact with the polymer were investigated. The results of physical-chemicals parameters show that the composite polymer gave positive feedback as water shut off fluid at 60◦C and strength of fully developed polymer was obtained at 0.68 bar. The alteration in the appearance of GG-CH-g-PAN/AA from liquid gel to rigid polymer was achieved at the time difference between 120 minutes and 720 minutes, respectively. Expansion of polymer was noticed at high temperature due to excessive imbibition, meanwhile at low temperature for the same polymer showed shrinking behavior due to syneresis. Polymer GG-CH-g-PAN/AA exhibited 99.98% water permeability reduction and resulting to a significant characteristic as polymeric water shut off fluid.