Magneto-Mechanical Ball-Bearing Milling Induces Frequency-Dependent Structural Reorganization in Hybrid Multiphase Liposomes.

Hybrid multiphase liposomes containing coexisting aqueous and oil-rich internal compartments were used as a model system to investigate how lipid assemblies respond to externally applied mechanical stress. A magneto-mechanical system was developed in which a miniature ball-bearing, driven by a rotating magnetic field, generated localized rolling-contact shear and confinement conditions within an enclosed fluid chamber, providing a mechanically distinct actuation environment compared with conventional bulk shear methods. Under these conditions, the liposomes underwent frequency-dependent optical and structural changes associated with mechanically induced membrane perturbation. Tetramethylrhodamine ethyl ester (TMRE), used as a remotely loaded, self-quenching dye probe, exhibited progressively greater deaggregation and dequenching with increasing ball-bearing rotational frequency, as monitored using a ratiometric absorbance metric. Minimal spectroscopic change was observed at 100 Hz, whereas pronounced TMRE dequenching occurred at higher rotational frequencies (1000-1500 Hz). Frequency-dependent spectroscopic changes were observed and interpreted phenomenologically in the context of heterogeneous membrane remodeling processes. Cryogenic transmission electron microscopy (cryo-TEM) revealed progressive frequency-dependent structural remodeling, including fusion-like intermediate morphologies and subsequent reorganization into larger vesicular assemblies following high-frequency actuation. Together, these observations suggest that confined shear generated by magnetically actuated ball-bearing milling can induce extensive membrane restructuring in multiphase liposomal systems. This work presents a mechanically driven framework for studying shear- and confinement-induced restructuring of lipid assemblies.