Magnetic Micromanipulation for In Vivo Measurement of Stiffness Heterogeneity and Anisotropy in the Mouse Mandibular Arch
Mandibular arch stiffness quantification. (a) Schematic depicting magnetic bead surface functionalization. (b) Sketch describing the definition of the middle region and the distal region of the mandibular arch. (c) 3D rendering of optical projection tomography of an E9.25 WT (21 som.) mouse embryo. Zoom-in view illustrates the mandibular arch with two magnetic beads deposited in the center of the middle region and the distal region. (d) Two magnetic beads within mandibular mesenchyme. The magnetic bead in the middle region (arrow labelled) and the magnetic bead in the distal region were located at different depths in the mandibular arch because of the difference in thickness of the middle and distal regions. The zoom-in shows the magnetic bead in the sagittal view (before rotation) and the dorsal view (after rotation). (e) Higher magnification view of the magnetic bead before actuation. The zoom-in views show the displacement of the magnetic bead during one complete actuation cycle. The red dashed lines indicate the edges of the magnetic beads identified by the subpixel tracking algorithm. The white solid line indicates the original location of the magnetic bead. (f) Representative bead displacement of one actuation cycle (right inset) characterized by an immediate elastic response followed by a continuous creep which plateaus near the end of force application. The blue line shows the standard linear solid model (left inset) fitting result. (g) Effective stiffness of the middle and distal regions of E9.25 (20 som.) WT mouse mandibular arch ( embryos; two-tailed -test, ). (h) Normalized effective stiffness of the middle and distal regions measured in proximal, distal, anterior, posterior, medial, and lateral directions (paired two-tailed -test, ,). (i) Anisotropic index of measured stiffness in the middle and distal regions (paired two-tailed -test, ).