Polyethylene glycol (PEG), a polymer widely employed in biomaterials for its biocompatibility and protein-repellent properties, is conventionally deemed bioinert. However, its interactions with extracellular components such as carbon dioxide (CO2), may critically influence cellular responses. The effect of PEG on cellular viability has not been properly investigated. This study investigates how PEG (2000 g/mol) at varying molar concentrations (0.5, 1.0, and 1.5 µmol/mL) alters the viability and morphology of osteoblasts and gingival fibroblasts in Dulbecco’s Modified Eagle’s Medium (DMEM), and DMEM supplemented with HEPES as a comparative buffering system. Resazurin assays, crystal violet staining, and pH measurements revealed that PEG concentration elevated medium pH, and enhanced cell viability. Notably, osteoblasts in standard DMEM exhibited the highest viability increase, 215%, 196%, and 168%, respectively, while in HEPES-buffered DMEM showed attenuated responses compared to controls (N = 5, p < 0.05). Although alkaline conditions enhanced cellular viability, concurrent morphological alterations, including membrane blebbing and cellular rounding, were observed contingent upon PEG concentration and HEPES presence. These findings underscore the capacity of PEG to modulate extracellular pH, impacting cellular behavior. Such effects challenge the perception of PEG as a passive biomaterial and highlight microenvironmental dynamics as a critical variable in biomaterial design. Thus, optimizing PEG concentration is vital to balancing biocompatibility and cell viability in tissue engineering.
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