Proteins Indicate Microcracks
By adding fluorescent proteins, researchers at the University of Basel have been able to produce a polymer material in which microscopic cracks and similar damage becomes visible. In the future, the proteins could help to indicate material damage at an early point in time and prevent component failure. A visualization of the material damage is based on fluorescence resonance energy transfer (FRET). This involves transfer of energy between two fluorescent proteins separated by only a few nanometers. If the spacing between the molecules changes, the fluorescence characteristics of the protein pair change. For this reason, FRET has established itself in biochemistry in particular as an optical analytical tool for measuring distances in the nanometer range.
In the experiments, a protein complex with an intentional breaking point located exactly between the two fluorescent proteins was employed. As long as the two proteins remain at the specified distance, they emit a yellowish light. If the protein complex is incorporated into a polymer matrix, extremely small mechanical stresses are generated. These change the distance between the two fluorescent proteins, causing the fluorescence to assume a blue color. As soon as the plastic is damaged and cracks appear, the protein complexes resume their original shape in this region. In the damaged region, the color of the fluorescence changes from blue back to yellow. In the experiments, it was possible to observe this visual effect at a protein content in the polymer as low as 0.2%.
Since the stability limit of the proteins is about 70°C, they are not very well suited for processing of thermoplastics. As an alternative, it might be possible in the future to incorporate the proteins into monomer mixtures and then produce molded parts via subsequent polymerization. Other possible applications include paints and surface coatings.