Porous materials: Less is more

Many components in simple or complex devices contain some degree of designed porosity, which specifically equips them to deliver a set of required performances. In porous polymers, the length scale for the cells has traditionally been of the order of millimeters, and the foam materials are typically of very low density, consisting of 95% or more voids and only a few percent of solid material. There is currently much research directed toward micro-cellular metals based on alloy systems different from aluminum, in particular higher-melting iron, copper and nickel-based alloys, for which powder metallurgy is often used, allowing for the creation of smaller pores in the range of 10-100 μm. Porous titanium has been under particularly vigorous study because its biocompatibility makes it an ideal permanent bone implant. The combination of ceramic and polymers in a same component or cell-seeded titanium foams have also been recently proposed.