Numerical simulation of ultrasound-assisted microneedle drug delivery via a strongly coupled PD-IB-CLBM framework

Ultrasound-assisted transdermal drug delivery is a promising non-invasive technique, yet the underlying microscale fluid-structure interaction (FSI) mechanisms within confined skin channels remain unclear. In this work, a strongly coupled numerical framework combining Peridynamics, Immersed Boundary Method, and Cascaded Lattice Boltzmann Method (PD-IB-CLBM) is established to investigate the transport dynamics of elastic drug carriers. The model rigorously resolves the interplay between acoustic radiation forces, hydrodynamic drag, and carrier deformation. Numerical results indicate that the transport efficiency is governed by a competition between acoustic propulsion and deformation-induced wall friction. Specifically, an optimal operating window is identified, an excitation frequency of 0.5 MHz coupled with a moderate acoustic intensity (0.37 W/cm², within clinical safety limits) yields the most efficient penetration. Furthermore, the simulation predicts a critical role of particle elasticity. Carriers with intermediate stiffness (Young's modulus E ≈ 5 GPa) are found to maximize transport speed, whereas excessively soft particles suffer from stagnation due to severe deformation. Based on these findings, a generalized nondimensional map relating geometric confinement χ to the acousto-elastic number p_rms/E is constructed to provide universal design criteria. Quantitative analysis suggests potential traversal times on the order of 15 min, offering a theoretical guideline for the rational development of next-generation acoustofluidic delivery devices.