When we see the gleam of stainless steel, most of us don't suspect that it is a material on which bacteria thrive. Despite this fact, hospitals, restaurants and other places that prize cleanliness choose stainless steel, as it's easy to clean. But a lapse in environmental hygiene can spell disaster.

When Harry Brearley accidentally discovered stainless steel over a century ago, he found that mixing the correct amount of chromium with steel prevents the cooled material from tarnishing when exposed to air. Stainless steel features an invisible layer of chromium oxide that does not allow iron oxide (corrosion) to form when the steel reacts with water and air.

To solve the problem of bacteria, scientists have used bioengineering to find two new ways of processing stainless steel so that it disinfects itself and keeps its anti-corrosion qualities. These bio-inspired adhesives are materials engineered to mimic substances found in nature that have adhesive qualities, but are harmless to the environment.

The first discovery in 2012 by Christophe Detrembleur and colleagues occurred while they sought a process for making stainless steel that was friendlier to the environment and also had antibacterial properties. Existing techniques were difficult and expensive, and they used chemicals that are potentially poisonous to those making it and the environment.

The researchers invented a 10-minute, water-based process with no toxic solutions that creates an antibacterial coating that killed E. coli bacteria in two hours, according to laboratory tests. The process uses an application of a bio-inspired adhesive to the finished steel and then alternating layers of the negatively charged polymer and positively charged polymer micelles containing silver-based particles to create a four-layer bacterial barrier.

Another great example of bio-inspired discoveries is one made public recently by the European Space Agency.

Engineers specify stainless steel for use in rockets and satellites. In the aerospace industry, companies use stainless steel for stowing and management of fuel, waste, parts of thermal protection systems and for high-strength fasteners and bolts.

Before its use, stainless steel material must be free of all faults. To get it free from defects, stainless steel undergoes a process known as "passivation." When stainless steel is passivated, removal of the top layer of the material happens. By stripping off the top layer, remnants of contamination and imperfections that are left over from the machining process come off with the surface layer. If not passivated, the material could rust.

The usual method for passivation calls for immersing the stainless steel parts in a nitric acid bath. However, nitric acid requires handling of a hazardous material that produces nitrogen oxides, which are greenhouse gases that damage the environment and could also harm workers.

Looking for a more economical and less hazardous way to process stainless steel, industry scientists are now promoting citric acid. It is found in diluted form in lemon juice and is a better alternative to nitric acid for passivation. It is quickly finding favor with the automotive, medical and aerospace industries.

Now, the European Space Agency has undertaken testing citric acid for stainless steel passivation. The study involves passivating stainless steel alloys and parts used in space with citric acid and then putting them through a rigorous round of tests that include atmospheric and laboratory corrosion testing, stress corrosion cracking, mechanical fatigue and adhesion testing. After testing, the ESA plans to run a complete metallurgical analysis.

These two examples show how bioengineering leads to environmentally friendly methods of production that are not dangerous for our planet, plants and animals.