Numerical modelling for coupled flow, transport, pharmacokinetic and pharmacodynamic of tablet-loaded hollow microneedle patch for transdermal drug delivery

In this study, we report the development of a numerical simulation framework for controlled transdermal delivery of ibuprofen (IBU) using a tablet-loaded hollow microneedle (HMN) patch. The model integrates pressure-driven, coupled laminar flow through the MN lumen and skin tissue, employing the Beavers-Joseph interfacial condition at the HMN tip and skin interface to represent the transition between free flow (lumen) and porous regions (tissue). For modelling purposes, IBU is loaded into a porous tablet within the HMN reservoir, which, in practice, can increase the shelf life of the drug formulation and provide greater ease of handling. Drug transport in the system is modelled using the convection-diffusion equation for diluted species (i.e., ignoring any inter-species interactions) coupled with a pharmacokinetic component to predict systemic absorption of the drug. Parametric analyses have revealed that MN geometry, drug loading, and skin permeability significantly influence delivery efficiency. Notably, an increase in the drug-loaded tablet diameter leads to higher fluid velocity within the tablet, enhancing drug release. Among the key design parameters, the number of MNs and lumen diameter exhibit the strongest effect on the IBU (drug) permeability, with the permeability nearly doubling when the needle count increases four times from 9 to 36. In contrast, the pitch has a relatively minor impact. Inlet pressure emerges as a critical design factor: while higher pressures (e.g., 40 kPa) improve IBU permeability, they also reduce delivery control and compromise pharmacodynamic stability. The results indicate that maintaining moderate pressure levels enables a more balanced and sustained therapeutic effect, supporting the need for optimised delivery parameters tailored to specific drug characteristics and patient safety.