Materials shape human progress – think stone age or bronze age. The 21st century has been referred to as the molecular age, a time when scientists are beginning to manipulate materials at the atomic level to create new substances with astounding properties.
Taking a step in that direction, Jens Bauer at the Karlsruher Institute of Technology (KIT) and his colleagues have developed a bone-like material that is less dense than water, but as strong as some forms of steel. "This is the first experimental proof that such materials can exist," Bauer said.
Since the Industrial Revolution our demand for new materials has outstripped supply. We want these materials to do many different things, from improving the speed of computers to withstanding the heat when entering Mars' atmosphere. However, a key feature of most new materials still remains in their strength and stiffness – that is, how much load can they carry without bending or buckling.
All known materials can be represented quite neatly in one chart where each line means the strength or density of the material goes up ten times: The line in the middle at 1000 kg/m3 is the density of water – all materials to its left are lighter than water and those on the right are heavier. No solid material is lighter than water unless it is porous. Porous materials like wood and bone exhibit exquisite structures when observed under a microscope, and they served as inspiration for Bauer's work.
For many years, material scientists have thought that some empty areas on the compressive strength-density chart should be filled by materials that theory predicts. Computer simulations could be used to indicate an optimum microstructure that would give a material the right properties. However, nobody had tools to build materials with defined patterns at the scale of a human hair.
With recent developments in lasers and 3D printing, however, a German company called Nanoscribe started offering lasers that could do just what Bauer wanted. Nanoscribe's system involves the use of a polymer that reacts when exposed to light and a laser that can be neatly focused on a tiny spot with the help of lenses.