3D Analysis of Film Structures Using FIB-SEM Tomography

To understand the properties of these films, detailed imaging and characterization are essential. Phase-separated films typically feature interconnected pores ranging from tens of nanometers to a few micrometers. Focused ion beam scanning electron microscopy (FIB-SEM) enables 3D visualization by sequentially milling and imaging thin cross-sections, producing high-resolution slices that reveal the film’s internal structure (Fager et al., 2020).

Segmenting these structures is challenging due to visible subsurface features within the pores. Traditional thresholding often misclassifies pores as solid material. However, machine learning techniques like random forest classifiers have proven effective for segmenting FIB-SEM data of porous materials (Röding et al., 2020). These segmented models support mass transport simulations (Fager et al., 2021) and pore structure analysis (Fager et al., 2020).

Structure Evolution of Phase-Separated Films

Porous phase-separated ethylcellulose/hydroxypropylcellulose (EC/HPC) films are commonly used to regulate drug release from pharmaceutical pellets. As the water-soluble HPC leaches out, a porous structure forms, controlling drug diffusion. In industrial settings, these films are applied via fluidized bed spraying, resulting in layered structures with varying porosity. However, the mechanisms behind this multilayer formation remain poorly understood.

To investigate, EC/HPC films were produced via spin coating, a reproducible method that mimics industrial processes. Their structural evolution was tracked in 2D using confocal laser scanning microscopy (CLSM), while the final 3D architecture was characterized using both CLSM and FIB-SEM (Carmona et al.).