Syntheses and biomedical applications of hollow micro-/nano-spheres with large-through-holes

Hollow micro-/nano-spheres with large-through-holes in shells (denoted as HMLS) have demonstrated great potential in biomedical applications owing to the combination of hollow structure and their porous shells. In this review, we provide a comprehensive overview of synthesis methods of HMLS obtained from the template-directed approach, shell-breaking method, Ostwald ripening and galvanic replacement primarily based on the formation mechanism of the large-through-holes in the shell. We further discuss the biomedical applications of HMLS including guest adsorption and encapsulation of proteins, drug/gene delivery, biomedical imaging, and theranostics. We conclude this review with some perspectives on the future research and development of the HMLS with desired morphologies and properties.