Micrometre-Scale Surface Partitioning and Morphological Anisotropy in Reacted Bioactive Glass Quantified by SEM-EDS

Reacted bioactive-glass surfaces often contain Ca-P-rich deposits beside Si-rich regions, but qualitative overlap in SEM-EDS maps cannot establish whether Ca and P are spatially associated or merely co-occur because clustered maps occupy finite areas. Here, one archived EDS field and one separate SEM field from each of two glasses of the same nominal composition, prepared with geothermal water (77S-G) or distilled/deionised water (77S-R) and reacted for 216 h in simulated body fluid, were analysed computationally. The EDS inputs were RGB JPEG occurrence maps rather than raw-count maps. Binary elemental supports were evaluated over 16 segmentation settings, and observed overlap was compared with 47,879 non-zero toroidal translations. Ca and P remained associated throughout the sweep (median zAB = 3.31 for 77S-G and 2.48 for 77S-R) and sensitivity checks. In 77S-R, Ca-Si separation was stable, while P-Si remained negative. A local Ca-P-rich volume in 77S-G had Ca/P = 0.93 and was not assigned to hydroxyapatite. Effective lateral correlation scales were 0.40-4.56 µm, and the analysed 77S-G SEM field showed greater directional coherence over 0.2-1.2 µm. These are image-derived field-level descriptors; they do not identify a crystalline phase, establish a causal effect of synthesis water, or estimate specimen-wide properties.