Silver Foams with Hierarchical Porous Structures: From Manufacturing to Antibacterial Activity.

The development of porous materials with hierarchical porous structures is currently of great interest. These materials exhibit properties representative of different pore scales and thus open up the possibility of being used in new applications. In this paper, a method for the preparation of silver foams with hierarchical porous structures is discussed. Here, the replication method, which is typically used to produce coarse-pore foams, is merged with dealloying, which is commonly used to manufacture small-pore foams. For this purpose, packed NaCl particles (hard template) were infiltrated with 75%Al-25%Ag alloy (whose so-called soft template is the Al-rich phase). Both the hard and soft templates were removed by water dissolution and dealloying with HCl or NaOH solutions, respectively. Extensive characterization of the resulting materials revealed pores ranging from a few nanometers to hundreds of micrometers. The materials were characterized by their antibacterial performance against Gram-positive and Gram-negative bacteria and showed significantly higher activity than both silver foams prepared by sintering pure Ag particles and silver nanofoams produced by chemical dealloying. The combinations of pores of different sizes and the resulting high internal specific surface area have a decisive influence on the antibacterial capacity of these new materials.