Active Brownian motion in a narrow channel

We review recent advances in rectification control of artificial microswimmers, also known as Janus particles, diffusing along narrow, periodically corrugated channels. The swimmer self-propulsion mechanism is modeled so as to incorporate a nonzero torque (propulsion chirality). We first summarize the effects of chirality on the autonomous current of microswimmers freely diffusing in channels of different geometries. In particular, left-right and upside-down asymmetric channels are shown to exhibit different transport properties. We then report new results on the dependence of the diffusivity of chiral microswimmers on the channel geometry and their own self-propulsion mechanism. The self-propulsion torque turns out to play a key role as a transport control parameter.Comment: to be published in Eur. Phys. J Special Topic

Activity induced delocalization and freezing in self-propelled systems

We study a system of interacting active particles, propelled by colored noises, characterized by an activity time {\tau}, and confined by a single-well anharmonic potential. We assume pair-wise repulsive forces among particles, modelling the steric interactions among microswimmers. This system has been experimentally studied in the case of a dilute suspension of Janus particles confined through acoustic traps. We observe that already in the dilute regime - when inter-particle interactions are negligible - increasing the persistent time pushes the particles away from the potential minimum, until a saturation distance is reached. We compute the phase diagram (activity versus interaction length), showing that the interaction does not suppress this delocalization phenomenon but induces a liquid- or solid-like structure in the densest regions. Interestingly a reentrant behavior is observed: a first increase of {\tau} from small values acts as an effective warming, favouring fluidization; at higher values, when the delocalization occurs, a further increase of {\tau} induces freezing inside the densest regions. An approximate analytical scheme gives fair predictions for the density profiles in the weakly interacting case. The analysis of non-equilibrium heat fluxes reveals that in the region of largest particle concentration equilibrium is restored in several aspects

Cooperative Switching in Large‐Area Assemblies of Magnetic Janus Particles

Magnetic Janus particles (MJPs) have received considerable attention for their rich assembly behavior and their potential technological role in applications ranging from simple magnetophoretic displays to smart cloaking devices. However, further progress is hampered by the lack of predictive understanding of the cooperative self‐assembly behavior of MJPs and appropriate dynamic control mechanisms. In this paper, a detailed experimental and theoretical investigation into the magnetically directed spatiotemporal self‐assembly and switching of MJPs is presented. For this purpose, a novel type of MJPs with defined hemispherical compartments carrying superparamagnetic iron oxide nanoparticles as well as a novel simulation model to describe their cooperative switching behavior is established. Combination of the theoretical and experimental work culminates in a simple method to direct assemblies of MJPs, even at high particle concentrations. In addition, a magnetophoretic display with switchable MJPs is developed on the basis of the theoretical findings to demonstrate the potential usefulness of controlled large‐area assemblies of magnetic Janus particles.Anisotropic particles that have one hemisphere selectively loaded with magnetite nanoparticles rotate in response to magnetic fields as indicated by visually observable color changes.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/155896/1/adfm201907865-sup-0001-SuppMat.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/155896/2/adfm201907865.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/155896/3/adfm201907865_am.pd

Structure and mechanics of active colloids

11 pages Acknowledgments MCM thanks Xingbo Yang and Lisa Manning for their contribution to some aspects of the work reviewed here and for fruitful discussions. MCM was supported by NSF-DMR-305184. MCM and AP acknowledge support by the NSF IGERT program through award NSF-DGE-1068780. MCM, AP and DY were additionally supported by the Soft Matter Program at Syracuse University. AP acknowledges use of the Syracuse University HTC Campus Grid which is supported by NSF award ACI-1341006. YF was supported by NSF grant DMR-1149266 and the Brandeis Center for Bioinspired Soft Materials, an NSF MRSEC, DMR-1420382.Peer reviewedPreprin

NanoJanus and Nanosatellite Assembly for Biomolecular Delivery and Cancer Therapeutics

Nanotechnology has been utilized widely in medical fields to improve the treatment and diagnosis of several diseases. One of the key players to drive medical nanotechnology forward is nanoparticles, which have been intensively studied and used as a tool for imaging, drug delivery, and disease treatments. Gold and iron oxide, undoubtedly, are on the short list of the nanoparticles used in medical nanotechnology due to their biocompatibility, tunable surface, and unique physico-chemical properties. In this dissertation, we developed novel nanostructures using gold, iron oxide nanoparticles and polymers for various applications including Janus motors, vaccine delivery, and controlled drug release. We generated an asymmetrical Janus nanostructure using thermo-cleavable polymer, gold, and iron oxide nanoparticles for photothermal enhancement and nano motors through an active rotational motion. Gold/iron oxide Janus nanoparticles (JNS) are developed by a seed-mediated self-assembly using a thermo-cleavable polymer facilitating the process. The formed JNS strongly displays an asymmetrical photothermal effect to activate a rotational motion and enhances photothermia resulting in significant cell killing effects under weak near-infrared (NIR) light exposure. In addition, the JNS displays distinct active rotational motion under NIR laser light due to the temperature gradient at its surface, which can be used potentially as Janus motors for drug delivery in the future. We next harnessed the same thermo-cleavable polymer used in JNS formation for controlled drug release under NIR laser light irradiation. The iron oxide nanoparticles (IONP) were first encapsulated in the thermo-cleavable polymeric micelles with doxorubicin (Dox), a chemotherapeutic drug. After NIR trigger, the polymer is cleaved due to heat transfer from the IONP resulting in the release of doxorubicin from the micelles. This study demonstrated that the thermo-cleavable polymer could be used as a smart material for controlled drug release. We also generated another type of secondary structure, a “gold/iron oxide nanosatellite”, using poly (- methacryloxypropyl trimethoxysilane) -b- poly (ethylene oxide) polymer (MPS-b-PEO). This nanosatellite structure, in which IONP is a central core and surrounded by multiple gold nanoparticles as satellites, is used for delivering antigens and an adjuvant for HPV+ head and neck cancer treatment. These nanosatellites deliver high surface density of E7/E6 oncogenic peptides and cyclic- guanosine-adenosine monophosphate (cGAMP) adjuvant to antigen presenting cells (APC) and further activate type I interferon (IFN-I) response. The nanosatellite vaccine also promotes antigen specific CD8+ T cells to infiltrate the tumors and inhibits tumor growth in an HPV+ head and neck tumor model when used as a single therapy or in combination therapy with an anti PD-L1 antibody. Nanosatellites offer many advantages for antigenic peptide and adjuvant delivery such as having a larger surface area, higher antigenic peptide density, higher cell uptake, and lower systemic elimination. This thesis presents the versatile developments and applications of gold/iron oxide nanostructures (Janus and Nanosatellite) which have advantages for drug and vaccine delivery in the future.PHDPharmaceutical SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/140893/1/kanokwas_1.pd