A Mild Bioinspiration Route to Bacillus-Shaped Silica with Enhanced Immune Responses

Rod-shaped mesoporous silica nanoparticles exhibit huge potential in biomedical research and even show an improvement in drug delivery efficacy compared to spherical silica. However, their usage may be restricted by the complex chemical process and high energy consumption. Here, inspired by sponge, a mild biomineralization method is developed to fabricate Bacillus-shaped mesoporous silica nanoparticles (B-MSs) that can be used as vaccine adjuvants. Escherichia coli displaying protein silicatein (Sα) on its surface serves as a biological template to induce mineralization of silica and maintain the appearance of the adjuvants. B-MSs show large surface area and hierarchical porous structures, allowing a high adsorption capacity of the model proteins. By introducing electrostatic attraction, amino-modified B-MSs (B-MSH-NH2) show the slowest sustained release behavior in vitro compared with control groups. Moreover, B-MSs exhibit low cytotoxicity and visible biodegradation behavior, promoting its biological safety in the biomedicine area. In vivo studies show that Bacillus-shaped B-MSH-NH2 can significantly enhance immune responses including the secretion levels of both IgG and CD8+ T cells, even higher than that of complete Freund’s adjuvant. This work offers a good opportunity to gain deep insight into biomineralization and to design vaccine adjuvants with a new strategy.