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Nature-inspired superhydrophobic materials have attracted considerable interest in blood-contacting biomedical applications due to their remarkable water-repellent and self-cleaning properties. However, the interaction mechanism between blood components and superhydrophobic surfaces remains unclear. To explore the effect of trapped air on platelet adhesion, we designed four distinct hydrophobic titanium dioxide (TiO 2 ) nanostructures with different fractions of trapped air. Ultrasonication was used to remove trapped air, allowing for direct comparison between hydrophobic surfaces with and without observable trapped air. The results demonstrate that all four kinds of hydrophobic materials significantly reduce platelet adhesion, regardless of observable trapped air. As nanostructure size increases, the proportion of air also increases, trapped air reduces fibrinogen adsorption but increases platelet adhesion, particularly in the largest nanostructures with superhydrophobicity. Upon air removal, protein adsorption increases compared to the same sample with air, while platelet adhesion decreases. This indicates that trapped air reduces protein adsorption but unexpectedly enhances platelet adhesion, which is contrary to our intuitive expectations. Conversely, hydrophobic surfaces without trapped air minimize platelet adhesion. To gain a better understanding of this phenomenon, we propose an interpretable model. Overall, this study challenges conventional assumptions and offers new insights for the design and application of superhydrophobic materials.