In our previous work we introduced the inverted MiniMag, a magnetic manipulation system capable of 5 degree-of-freedom (5-DOF) wireless control of micro- and nano structures. In this work, we implement a depth tracking algorithm to provide feedback on the z-position of manipulated particles in the absence of a side camera. We demonstrate 3D closed-loop servoing of magnetic microbeads along predefined trajectories. We successfully position magnetic microbeads functionalized with antibodies in close proximity to macrophages with sub-cellular resolution and record the phagocytosis of the beads. We also show that the system can be used for 3D targeted microtissue manipulation inside microfabricated devices.

Upon cell adhesion, talin physically couples the cytoskeleton via integrins to the extracellular matrix, and subsequent vinculin recruitment is enhanced by locally applied tensile force. Since the vinculin binding (VB) sites are buried in the talin rod under equilibrium conditions, the structural mechanism of how vinculin binding to talin is force-activated remains unknown. Taken together with experimental data, a biphasic vinculin binding model, as derived from steered molecular dynamics, provides high resolution structural insights how tensile mechanical force applied to the talin rod fragment (residues 486-889 constituting helices H1-H12) might activate the VB sites. Fragmentation of the rod into three helix subbundles is prerequisite to the sequential exposure of VB helices to water. Finally, unfolding of a VB helix into a completely stretched polypeptide might inhibit further binding of vinculin. The first events in fracturing the H1-H12 rods of talin1 and talin2 in subbundles are similar. The proposed force-activated alpha-helix swapping mechanism by which vinculin binding sites in talin rods are exposed works distinctly different from that of other force-activated bonds, including catch bonds.