A species-specific protein corona determines osteogenic fate of multi-walled carbon nanotubes by modulating macrophage polarization.

Multi-walled carbon nanotubes (MWCNTs) have emerged as promising candidates for bone tissue engineering due to their excellent biocompatibility, mechanical strength, and chemical stability. However, disparities often exist between their osteogenic performance in vitro and in vivo. The formation of protein corona on biomaterials is a key factor that may govern these biological outcomes. This study investigated how the distinct protein corona compositions in mouse serum (MS) and fetal bovine serum (FBS) modulate the immune recognition and osteogenic capacity of MWCNTs, thereby mimicking in vitro and in vivo environments, respectively. It was demonstrated that the MS-derived corona complexes, enriched with immunoreactive proteins such as complement 3, potently induced a pro-inflammatory M1 response via recognizable immune signals in both Raw264.7 cells and a mouse calvarial defect model. In contrast, FBS-derived corona complexes lacked murine-specific "alarm signals", thereby attenuating reactive oxygen species generation and polarizing macrophages toward M2 phenotype both in vitro and in vivo. Consequently, the MS-derived corona conferred no significant osteogenic effect, whereas the FBS-derived corona markedly enhanced osteogenic differentiation. We propose that the FBS corona acts as a physical barrier, preventing subsequent adsorption of host alarm signals onto MWCNTs, thereby suppressing immunogenicity and enhancing osteogenesis. These findings highlight a critical limitation of using FBS in conventional in vitro models for predicting in vivo immune responses, and underscore the decisive role of species-specific immune recognition in determining the osteogenic fate of biomaterials.