<p>Biological systems dynamically grow high-aspect-ratio architectures from a site, enabling traversal of phase boundaries and functional execution. Emulating this growth strategy in synthetic systems could yield functional microsystems for operation across interfaces. However, engineering such bio-inspired growth to proceed out of plane from a substrate in synthetic colloidal assemblies remains challenging, as it requires overcoming gravitational collapse while maintaining structural coherence during extension. Here, we present a field-driven particle system that achieves gravity-resisting growth of high-aspect-ratio structures via frequency-modulated magnetic and hydrodynamic interactions. This growth is enabled by combining static and oscillating magnetic fields, which guide the assembly of magnetic particles into dynamic structures exhibiting a distinct segmented, seaweed-like morphology. These architectures are reconfigurable, stabilizable, programmably actuatable, and capable of penetrating a perfluorohexane–water interface. When functionalized with enzymes, the growing structures act as micro-transporters, delivering catalytic activity across the interface and triggering detectable reactions in both bulk two-phase and microfluidic chip systems. This work establishes a field-driven assembly-to-function approach that integrates structural growth, phase-boundary penetration, and triggered functionality, enabling active microsystems capable of interfacial transport and functional execution.</p>