Graphene Nanoplatelet-Modified Portland Cement: Surface Microhardness and In Vitro Fibroblast Metabolic Activity

Background: White Portland cement (PC) is compositionally related to mineral trioxide aggregate (MTA) and provides an experimental platform for evaluating targeted modification of calcium silicate materials. This study investigated the effects of graphene nanoplatelet (GNP) incorporation on surface microhardness, cellular metabolic activity and mineral-related characteristics of PC. Methods: White PC was modified with 1%, 2% or 3 wt.% GNP. Surface microhardness was assessed on independently prepared discs, with three indentations averaged to obtain one specimen-level value. Day-14 MTT metabolic activity of WPS9 human periradicular fibroblasts was evaluated using direct-contact (n = 4 per group), filtered-eluate (n = 6 per group) and insert-based assays (n = 3 per group, except MTA, n = 2). Endpoint pH, cell morphology and association, vimentin-associated fluorescence, surface deposits and X-ray diffraction (XRD) profiles were assessed descriptively. Results: Surface microhardness differed significantly among the formulations (Welch's F(3,14.15) = 190.36, p < 0.001), increasing from 44.9 ± 4.9 HV for PC to 142.2 ± 33.0, 177.5 ± 43.4 and 299.3 ± 33.1 HV for 1%, 2% and 3% GNP-PC, respectively. All GNP-containing formulations had significantly greater hardness than PC, while 3% GNP-PC was significantly harder than the 1% and 2% formulations. No significant group differences in day-14 MTT metabolic activity were detected in the direct-contact or insert-based assays. In the filtered-eluate assay, all GNP-containing formulations produced significantly higher metabolic activity than PC eluate (p < 0.001). Endpoint pH values were 13 for PC and 1% GNP-PC and 8 for the 2% and 3% formulations. Representative microscopy showed fibroblast-like morphology, cell association with the tested surfaces and vimentin-associated fluorescence. Descriptive XRD analysis of one specimen per formulation showed numerical differences in calcium phosphate-related signals, with 3% GNP-PC having the highest apatite-family classification. Conclusions: Under the tested conditions, GNP incorporation significantly increased PC surface microhardness, while filtered eluates from GNP-containing formulations produced higher day-14 MTT metabolic activity than PC eluate. The remaining outcomes provided descriptive formulation-related observations, and no formulation consistently outperformed the others across all measures. Further replicated mechanical, physicochemical and cellular evaluation is warranted.