Figure 4: The effect of magnetic force on the endothelium in vitro.
From: Magnetic forces enable controlled drug delivery by disrupting endothelial cell-cell junctions
(a) Macroscopic view of a microfluidic device placed on an N52-grade rare-earth magnet (W × H × L=1/2″ × 1/2″ × 1″). The midline of the magnet provides the reference for positioning the microfluidic channels in the magnetic field. The arrows indicate the flow direction. (b,c) Simulated distribution of magnetic force on MNPs in z and y directions. At the midline of the magnet, fz is large and homogeneous, while fy is negligible. fy and fz increase toward the edge of the magnet. Scale bar, 5 mm. (d,e) The two-step magnetic treatment of the microfluidic channels and the corresponding force distribution. In step I, the microfluidic channel is aligned with the centre line of the magnet for 2 h, while in step II, it is aligned with one edge of the magnet for 1 h. (f) Representative confocal images of the cross-section of the endothelium following step I without or with the magnetic field. The magnetic force increased the uptake of MNPs by endothelial cells at the bottom of the channel. Dashed white lines mark the boundary of the channels. Scale bar, 20 μm. In step II, the endothelialized channels were moved to the edge of the magnet for 1 h. After that, the endothelialized channels were either directly fixed and stained for actin and VE-cadherin, or cultured overnight under flow before staining. Immunostaining indicates that the two steps of magnetic force exposure led to disorganized endothelial actin filaments (g, red) and disrupted adherens junctions (h, green. Yellow arrows indicate the disrupted adherens junctions), while step I alone did not cause any change in actin organization (Supplementary Fig. 8). In addition, the vascular endothelium became permeable to antibody molecules as visualized by collagen I staining (i, green). After overnight recovery without magnetic force, the endothelial actin filaments reorganized (j, red) and the continuous adherens junctions were restored (k, green). No collagen I staining was detectable, indicating the blockade of the endothelium to the antibody (l, green). Blue, nuclei; white, MNP. Scale bar, 20 μm.
