Animal development consists of a cascade of tissue differentiation and shape change. Associated mechanical signals regulate tissue differentiation. Here we demonstrate that endogenous mechanical cues also trigger biochemical pathways, generating the active morphogenetic movements shaping animal development through a mechanotransductive cascade of Myo-II medio-apical stabilization. To mimic physiological tissue deformation with a cell scale resolution, liposomes containing magnetic nanoparticles are injected into embryonic epithelia and submitted to time-variable forces generated by a linear array of micrometric soft magnets. Periodic magnetically induced deformations quantitatively phenocopy the soft mechanical endogenous snail-dependent apex pulsations, rescue the medio-apical accumulation of Rok, Myo-II and subsequent mesoderm invagination lacking in sna mutants, in a Fog-dependent mechanotransductive process. Mesoderm invagination then activates Myo-II apical accumulation, in a similar Fog-dependent mechanotransductive process, which in turn initiates endoderm invagination. This reveals the existence of a highly dynamic self-inductive cascade of mesoderm and endoderm invaginations, regulated by mechano-induced medio-apical stabilization of Myo-II.
Local polarization of a magnetic layer, a well-known method for storing information, has found its place in numerous applications such as the popular magnetic drawing board toy or the widespread credit cards and computer hard drives. Here we experimentally show that a similar principle can be applied for imprinting the trajectory of quantum units of flux (vortices), travelling in a superconducting film (Nb), into a soft magnetic layer of permalloy (Py). In full analogy with the magnetic drawing board, vortices act as tiny magnetic scribers leaving a wake of polarized magnetic media in the Py board. The mutual interaction between superconducting vortices and ferromagnetic domains has been investigated by the magneto-optical imaging technique. For thick Py layers, the stripe magnetic domain pattern guides both the smooth magnetic flux penetration as well as the abrupt vortex avalanches in the Nb film. It is however in thin Py layers without stripe domains where superconducting vortices leave the clearest imprints of locally polarized magnetic moment along their paths. In all cases, we observe that the flux is delayed at the border of the magnetic layer. Our findings open the quest for optimizing magnetic recording of superconducting vortex trajectories.Quantum magnetic flux units in type-II superconductors can be regarded as small solenoids, producing localized magnetic field variations extending over distances of 2λ perpendicularly to the applied field, where λ is the magnetic penetration depth. These flux lines interact with inhomogeneities inside the superconducting material, leading to a plethora of well-known pinning mechanisms. Furthermore, the static and dynamic response of individual vortices can also be modified if their stray field outside the superconducting volume is altered. This is precisely the reason why multilayered hybrid systems combining superconducting and non-superconducting materials have been an active field of research in the last decade.It has been shown, for instance, that the stray field of an isolated moving vortex can induce eddy currents in a nearby metallic layer, leading to a velocity dependent damping force 1,2 . This effect can be exploited to provide better stability and quench protection in superconducting cables by reducing the speed of flux jumps 3,4 . More spectacular is the possible use of the monopolar magnetic field emanating from a vortex as a submicron-sized magnetic tweezers to locally polarize spin carriers in a diluted magnetic semiconductor 5 . Among these hybrid devices, the heterostructures combining superconductivity and magnetism, two antagonistic quantum macroscopic states, arguably represent the most investigated systems so far [6][7][8][9] . A simple attempt to classify the superconductor (S-layer) -ferromagnet (F-layer) hybrids, where the F-layer and the S-layer are in close proximity and interact only through their stray fields, consists of comparing the relative field strength scales of each subsystem. Indeed, if the coercive field, H coe , of the ferromag...
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