Cytotoxicity and in vitro immersion study in Hanks’ Balanced Salt Solution (HBSS) of electrospun MgO@nesquehonite (MgCO3·3H2O) core–shell fibers

In this work, we report the fabrication and characterization of bioactive MgO@nesquehonite (MgCO 3 ·3H 2 O) core–shell nanofibers for potential applications in bone tissue regeneration. The composite fibers were produced by needle-free electrospinning of a polyvinyl alcohol (PVA) and magnesium acetate precursor, followed by calcination at 450 °C. Structural and chemical characterization (TGA, XRD, FTIR, Raman, and TEM) confirmed the formation of a stable reactive architecture consisting of an MgO-rich core with a carbonated surface layer. In vitro bioactivity was evaluated by immersion in Hanks’ Balanced Salt Solution (HBSS), revealing behavior consistent with a dissolution–precipitation mechanism. The MgO phase was associated with the early presence of Mg species in the immersion medium and transient pH modulation, while the nesquehonite may have contributed to the progressive surface mineralization observed during immersion. This process involved the transient formation of monetite as an intermediate phase, which progressively transformed into a dense, homogeneous layer of carbonated apatite within 21–28 days, as supported by SEM-EDS, XRD, FTIR, Raman, and pH-monitoring results. The cytocompatibility of the material was assessed using L929 fibroblasts exposed to extracts obtained from fibers after the bioactivity assay. Cell viability, determined by the MTT assay, ranged from 89% to 98% for both undiluted (100%) and diluted (50%) extracts, with no significant differences among the evaluated groups (ANOVA, p > 0.05). According to ISO 10993-5 criteria, all samples exhibited viability values well above the cytotoxicity threshold, confirming the non-cytotoxic behavior of the material. The synergistic combination of MgCO 3 ·3H 2 O and MgO within an electrospun, fibrous system exhibited early ion-exchange behavior, pH modulation, progressive apatite nucleation, and cytocompatibility. These findings position the material as a promising candidate for bone-related applications at the in vitro level, warranting further investigation through advanced biological assays and in vivo studies to validate its performance under physiological conditions.