MicroCT-Based Degradation-Induced Sub-Voxel Porosity Mapping: A Case Study of a PHBV/PLGA/TCP Composite Scaffold

Microcomputed tomography (microCT) enables non-destructive 3D imaging, but conventional segmentation cannot resolve objects smaller than a voxel. This study presents a microCT-based method that maps degradation-induced sub-voxel porosity by converting voxel-specific X-ray attenuation changes between registered pre- and post-degradation datasets into porosity estimates. The method also accounts for other degradation-induced physical and chemical changes that affect X-ray attenuation; however, their contributions cannot be directly separated from the estimated change in porosity. The method was demonstrated on poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), Poly(lactic-co-glycolic acid) (PLGA) and tricalcium phosphate (TCP) scaffolds. Specimens were scanned before and after degradation using identical acquisition and reconstruction settings, and datasets were 3D-registered. The estimated effective sub-voxel porosity increase was 8.33 ± 0.63%, versus a gravimetric mass loss of 7.89 ± 0.82%. SEM showed a pore area fraction of 7.64 ± 0.23% and a mean equivalent pore diameter of 1.79 ± 1.15 μm, below the 5.5 μm voxel size. Maps revealed spatially heterogeneous degradation-related changes. The consistency between the microCT-derived estimate and the complementary evidence from gravimetry and SEM provides indirect validation of the interpretation of the measured X-ray attenuation changes in terms of effective sub-voxel porosity.