Magnetic concentration of drug-laden magnetic nanoparticles has been proven to increase the delivery efficiency of treatment by 2-fold. In these techniques, particles are concentrated by the presence of a magnetic source that delivers a very high magnetic field and a strong magnetic field gradient. We have found that such magnetic conditions cause even 150 nm particles to aggregate significantly into assemblies that exceed several micrometers in length within minutes. Such assembly sizes exceed the effective intercellular pore size of tumor tissues preventing these drug-laden magnetic nanoparticles from reaching their target sites. We demonstrate that by using dynamic magnetic fields instead, we can break up these magnetic nanoparticles while simultaneously concentrating them at target sites. The dynamic fields we investigate involve precessing the field direction while maintaining a field gradient. Manipulating the field direction drives the particles into attractive and repulsive configurations that can be tuned to assemble or disassemble these particle clusters. Here, we develop a simple analytic model to describe the kinetic thresholds of disassembly and we compare both experimental and numerical results of magnetic particle suspensions subjected to dynamic fields. Finally we apply these methods to demonstrate penetration in a porous scaffold with a similar pore size to that expected of a tumor tissue.
We have created a multifunctional dry adhesive film with transferred vertically aligned carbon nanotubes (VA-CNTs). This unique VA-CNT film was fabricated by a multistep transfer process, converting the flat and uniform bottom of VA-CNTs grown on atomically flat silicon wafer substrates into the top surface of an adhesive layer. Unlike as-grown VA-CNTs, which have a nonuniform surface, randomly entangled CNT arrays, and a weak interface between the CNTs and substrates, this transferred VA-CNT film shows an extremely high coefficient of static friction (COF) of up to 60 and a shear adhesion force 30 times higher (12 N/cm) than that of the as-grown VA-CNTs under a very small preloading of 0.2 N/cm. Moreover, a near-zero normal adhesion force was observed with 20 mN/cm preloading and a maximum 100-μm displacement in a piezo scanner, demonstrating ideal properties for an artificial gecko foot. Using this unique structural feature and anisotropic adhesion properties, we also demonstrate effective removal and assembly of nanoparticles into organized micrometer-scale circular and line patterns by a single brushing of this flat and uniform VA-CNT film.
Propylene/propane separation by an
adsorption process based on
pure-silica zeolites (such as Si-CHA) is an energy-efficient alternative
for cryogenic distillation. High-pressure adsorption isotherms of
propylene were obtained on large crystals of Si-CHA zeolite (11 μm)
at 303–423 K up to 1000 kPa. As propane adsorption was very
slow, equilibrium was not achieved on large crystals of Si-CHA and
even on small crystals (1 μm) after 2.5 days at 303 K. Finally,
real equilibrium isotherms of propane were measured on fine Si-CHA
particles at 373–473 K and up to 500 kPa. This is the first
time that the experimental isotherms of propane are reported. Kinetic
adsorption data of propylene and propane were evaluated at different
pressures and temperatures. The results showed that both temperature
and pressure have positive effects on diffusivities. The results showed
that Si-CHA zeolite is an excellent kinetic selective adsorbent having
propylene diffusivity 3 orders of magnitude higher than propane.
We present computer simulations and experiments on dilute suspensions of superparamagnetic particles subject to rotating magnetic fields. We focus on chains of four particles and their decay routes to stable structures. At low rates, the chains track the external field. At intermediate rates, the chains break up but perform a periodic (albeit complex) motion. At sufficiently high rates, the chains generally undergo chaotic motion at short times and decay to either closely packed clusters or more dispersed, colloidal molecules at long times. We show that the transition out of the chaotic states can be described as a Poisson process in both simulation and experiment.
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