Internal Architecture of a 3D-Printed Ti-6Al-4V Capsule and Preliminary FEM Simulation of Diffusion: CAD-Informed Modeling with Qualitative Micro-CT Characterization.

A central challenge in implantable local-delivery systems is to determine how internal device architecture shapes solute transport before drug-specific loading, release, and biological validation are available. This study examines the reservoir-channel architecture of the previously characterized KTD/KTM Ti-6Al-4V capsule platform and evaluates its effect on diffusion-dominated concentration redistribution in a preliminary finite-element model. Micro-computed tomography (micro-CT) was used for qualitative characterization of the as-fabricated internal architecture, whereas the representative computational geometry was defined from the capsule computer-aided design (CAD) concept and previously reported dimensions. Transport of a nominal, fully dissolved species was modeled in COMSOL Multiphysics 5.2 using Fickian diffusion with a prescribed effective diffusion coefficient (Deff = 1 × 10-9 m2/s) and a nominal peak initial concentration scale of 1.0 mol/m3. Under the closed no-flux condition, the internal control-point concentration decreased to near zero within approximately 4 h, while the remote outer control point reached approximately 0.002-0.003 mol/m3 by 6 h. A one-sided Dirichlet sink produced a more directional concentration field, demonstrating the sensitivity of the simulated distribution to geometry and boundary conditions. These results describe an idealized, CAD-informed diffusion problem and do not represent experimentally validated drug-release kinetics, therapeutic concentrations, or biological performance. The model is therefore intended as a design-phase framework for guiding subsequent drug-specific transport and experimental validation studies.