Titanium dioxide nanoparticles alter mesenchymal stem cell function and exosome signalling: Possible implications in periprosthetic osteolysis.

Periprosthetic osteolysis (PPO) remains the leading cause of late orthopaedic implant failure and is primarily driven by the biological response to wear particles released at the implant interface. Among these, titanium dioxide nanoparticles (TiO2 NPs) generated from titanium-based prosthetic components have emerged as potent modulators of early inflammatory signalling and bone regeneration. Human mesenchymal stem cells (hMSCs) are central to osteogenesis and periprosthetic tissue repair; however, the direct effects of TiO2 NPs on their function and exosome-mediated communication remain insufficiently understood. In this study, hMSCs were exposed to TiO2 NPs for 3 and 21 days under control and osteogenic conditions to assess NPs-induced cellular responses and exosome (Exos) biogenesis. TiO2 NPs increased intracellular reactive oxygen species without compromising viability or cytoskeletal integrity over prolonged exposure. Despite preserved proliferation, osteogenic differentiation was significantly impaired, as evidenced by reduced alkaline phosphatase activity and early osteogenic markers. Notably, NP-treated cells exhibited enhanced calcium phosphate deposition, reflecting the strong adsorption properties of TiO2 NPs and indicating pathological calcification rather than functional mineralisation. TiO2 NPs also altered Exos release and cargo composition in a time-dependent manner: early exposure enriched extracellular matrix-related proteins, whereas prolonged exposure favoured inflammatory and immune-associated mediators. Overall, our findings demonstrate that TiO2 NPs disrupt hMSC osteogenic capacity and reshape Exos molecular cargo, potentially propagating NPs-induced dysfunction within the periprosthetic niche. These early cellular and exosomal alterations provide mechanistic insight into PPO onset and highlight hMSC-derived Exos as promising biomarkers for particle-induced osteolysis and implant failure. STATEMENT OF SIGNIFICANCE: Orthopaedic implants can fail over time due to bone loss around the implant, a condition partly driven by titanium wear particles. While previous studies have focused mainly on immune cells and osteoblasts, this study is the first to systematically investigate how titanium dioxide nanoparticles affect human mesenchymal stem cells and their exosomes, which are key regulators of bone repair and cell communication. We show that nanoparticles impair osteogenic differentiation and alter exosome release and molecular cargo without causing overt cell death, shifting cell signalling toward inflammatory and immune-related pathways. These findings provide new mechanistic insight into the early events of implant failure and identify exosome-associated signatures as promising biomarkers and therapeutic targets for periprosthetic osteolysis.