Magnetic drug targeting is a drug delivery approach in which therapeutic magnetizable particles are injected, generally into blood vessels, and magnets are then used to guide and concentrate them in the diseased target organ. Although many analytical, simulation, and experimental studies on capturing schemes for drug targeting have been conducted, there are few studies on delivering the nanoparticles to the target region. Furthermore, the sticking phenomenon of particles to vessels walls near the injection point, and far from the target region, has not been addressed sufficiently. In this paper, the sticking issue and its relationship to nanoparticle steering are investigated in detail using numerical simulations. For wide ranges of blood vessel size, blood velocity, particle size, and applied magnetic field, three coefficient numbers are uniquely generalized: vessel elongation, normal exit time, and force rate. With respect these new parameters, we investigated particle distribution trends for a Y-shaped channel and computed ratios of correctly guided particles and particles remaining in the vessel. We found that the sticking of particles to vessels occurred because of low blood flow velocity near the vessel walls, which is the main reason for low targeting efficiency when using a constant magnetic gradient. To reduce the sticking ratio of nanoparticles, we propose a novel field function scheme that uses a simple time-varying function to separate the particles from the walls and guide them to the target point. The capabilities of the proposed scheme were examined by several simulations of both Y-shaped channels and realistic three-dimensional (3-D) model channels extracted from brain vessels. The results showed a significant decrease in particle adherence to walls during the delivery stage and confirmed the effectiveness of the proposed magnetic field function method for steering nanoparticles for targeted drug delivery.

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A stereoscopic particle image velocimetry velocity field measurement technique was used to investigate the flow structure and entrainment rate of a turbulent elliptic jet of aspect ratio AR = 2. A 3D calibration procedure was established to compensate for the distortion and refraction effects embedded in the captured particle images; the results of this procedure were used to calculate three orthogonal velocity components. The instantaneous velocity fields of three orthogonal components in several cross sections perpendicular to the jet axis were measured and the spatial distributions of the turbulent statistics were obtained by ensemble averaging 500 instantaneous velocity fields. The variation of the entrainment rate along the jet axis was evaluated from the mean velocity fields and compared with that of the round jet of the same equivalent diameter. At x/De = 2, the jet widths along the major and minor axes are almost identical and axis-switching occurs. As the flow goes further downstream, the jet width grows much faster along the minor axis than along the major axis. After axis-switching, the flow structure of the elliptic jet shows two critical points on the minor axis, which are not observed in the round jet. The total entrainment rate of the elliptic jet is about 1.5% larger than that of the round jet. In addition, entrainment of the surrounding fluid is more active on the minor axis as a result of the fast expansion of the jet along this axis due to the self-induction of the elliptic vortical structure in the near field.

A stereoscopic particle image velocimetry (PIV) measurement system based on the translation configuration was developed and applied to the flow behind a forward-swept axial-fan with five blades in a water tank. The 3D calibration procedure was employed to compensate the distortion and refraction of particle images. The perspective error caused by the out-of-plane motion was estimated by direct comparison of the 2D PIV and stereoscopic PIV (SPIV) results. The SPIV and 2D PIV comparison was carried out for the particle images captured simultaneously. The difference of mean velocity data measured by 2D PIV and SPIV techniques is nearly proportional to the mean out-of-plane velocity component. The difference appears to be relatively large in the region near the fan blade having higher out-of-plane motion. The perspective error estimated from the calibration data and mean out-of-plane velocity data agrees with the mean velocity difference between the 2D PIV and SPIV results. The turbulence intensity measured by the 2D PIV method is overestimated in comparison to that of the SPIV method due to the projected velocity fluctuations of the out-of-plane velocity component. The turbulent fluctuations caused by the out-of-plane velocity component were estimated by multiplication of the incident angle obtained in the calibration procedure and out-of-plane velocity fluctuations. The estimated perspective fluctuation of the out-of-plane velocity component was compared with the difference measured by the two methods. In SPIV measurements of turbulent statistics, therefore, the ratio of out-of-plane to in-plane RMS error determined from the system set-up should be considered in order to obtain reliable results.

We demonstrate an efficient approach for quantifying frictional forces (sub-piconewton) at nano-bio interfaces by controlled magnetic forces, which is based on simultaneous measurements of critical frequencies for streptavidin-coupled magnetic particles. The maximum phase angle, being corresponded with the critical frequency, is formulated in terms of magnetic, frictional, and viscous forces of the particles on DNA- and SiO-functionalized micromagnet arrays. The streptavidin/DNA interface shows lower friction as an enhanced lubrication than the streptavidin/SiO interface, which is indicated by the lower transition field of quasi-static motion, the larger ratio of dynamic particles, and also the higher velocity of the particles. The friction coefficients at the streptavidin/DNA and streptavidin/SiO interfaces are evaluated numerically as 0.07 and 0.11, respectively, regardless of the vertical force and the velocity. The proposed method would open up new possibilities to study mechanical interactions at biological surfaces.