Strontium substitution in hydroxyapatite enables tunable properties in electrospun PCL/Gel scaffolds for bone tissue regeneration

Electrospun polymer/ceramic composites have attracted considerable attention for bone tissue engineering, yet the influence of strontium (Sr) substitution in hydroxyapatite (HA) on the properties of fibrous composite systems remains insufficiently understood. In this study, electrospun poly(ε-caprolactone)/gelatin (PCL/Gel) scaffolds incorporating HA with controlled Sr substitution levels (HA, Sr50-HA, and Sr100-HA) were fabricated to elucidate composition–structure–property relationships under identical processing conditions. Morphological characterization confirmed the formation of continuous, bead-free fibers, with a progressive reduction in fiber diameter upon ceramic incorporation and increasing Sr content. The presence of the inorganic crystals influenced ion release behaviour, as Sr50-HA-PCL/Gel showed enhanced Ca 2+ and Sr 2+ release. All composite scaffolds displayed improved acellular in vitro bioactivity, promoting apatite formation in simulated body fluid compared with the polymeric control. Despite measurable ion release, Indirect cytocompatibility assays indicated no cytotoxic effects, with all samples maintaining MG-63 cell viability above 80%. Direct cell culture confirmed good cytocompatibility, with Sr-containing scaffolds exhibiting enhanced early metabolic activity. Mechanical testing revealed composition-dependent behaviour: HA-PCL/Gel and Sr100-HA-PCL/Gel exhibited higher stiffness, whereas Sr50-HA-PCL/Gel showed a reduced modulus, consistent with its distinct structural attributes. Overall, this work demonstrates that the degree of Sr substitution governs the interplay between crystallinity, ion release, mechanical performance, and cellular response, highlighting compositional tuning as an effective strategy for optimizing electrospun scaffolds for bone tissue engineering applications.