The Table Ate My Dinner

My thoughts after reading Gerber et al (2012) situations like that may not be science fiction for ever.  Inspired by natural living surfaces, such as bark or our own skin, the authors set out to create a functional living material that was capable of self cleaning.  Using PVC, agar incapasulated fungi (Penicillium roqueforti), and a 0.4 micron polycarbonate surface membrane (Figure 1) they were able to create a living surface capaable of “eating” a food spill.  The key to the succes of this material is it’s simplicity.  With a total thickness of 300 microns and the a shelf life of at least 10 days this conseptual design shows extreame promise to the devolepment of living surfaces.  The key to this technology is the surface membrane which is porous enough to allow for macromolecule exchange while have pores small enough to prevent the fungal hyphae from escaping their contained layer.  This serves to prevent both the fungi and the outside from contamination.

Figure 1. "Design of a living surface. The simplest form of a living surface is composed of three layers. The base layer (light blue) may be an inert support foil (e.g. a PVC film), a linker, or a surface that shall be coated directly with a living surface. The second layer is the living layer hosting microorganisms. The top layer (black, wireframe) is responsible for the confinement of the fungi, for nutrient, gas, and product transportation, and mechanical, chemical, and biological stability..."

A few of the success that I found most interesting was the ability for this material to respond to a variety of realistic cleaning situations, its localized response to spills, and it’s ability to clean multiple spills.  Gerber et al used ethanol hand sanitizer and hand soap on the surface of the material to mimic typical surface cleaning procedures.  In both cases sterilizing effects were limited to the outer surface of the membrane, as the biological response of the fungi to a food spill was unaffected post cleaning.  The material also displayed localized responses to food.  By creating isolated food spill on the same surface the authors demonstrated that the fungi would only proliferate at the site of the spill while other areas of the surface remained dormant.  Finally, they were able to generate multiple cleaning cycles from the same mat.  Food was introduced at two time points over a 30 day period, both instances of the spill were met with the same fungal response and resulting self cleaning.  Fascinating.

The success of this conceptual model allows us to speculate about other applications of this novel technology.  Changing the biological portion of the membrane can allow for a variety of other uses.  By incorporating antibiotic, or toxin, producing microorganisms this technology can be used to produce site and dose specific responses to bacterial populations. Truly self-sterilizing surfaces. This application alone represents a multi-million dollar area of research.  Since the response of the biological organism could simply be a visual que, surfaces could be designed to identify contamination sites at very early stages.  Applications of living materials extend to packaging, air quality, numerous consumer products, and laboratory settings.

As with all novel technologies the grand possibilities are used to overshadow the obvious problems.  In the case of the functional surface presented here I see multiple issues that would prevent this from attaining a production level item.  First, the shelf life while seemingly manageable at 10 days is masked by the fact that the foil must remain wet for that entire time period.  Failure to keep the foil moist resulted in a null response to a food spill.  The cost of storage may outweigh the actual benefits of the use.  Second, while this foil does “eat” or “self-clean” it does so at a snails pace.  It takes 8 days for the foil to absorb 2 mL of a glucose solution.  Not a timeline my wife would approve of for cleaning up a spill.  Lastly,  the membrane which allows for macromolecule transfer and keeps the fungi “trapped” is destined to become ruptured in any consumer usage.  Before a production product could even be discussed the surface membrane would have to be replaced with something that could handle the realistic wear and tear of a consumer product.

While a fascinating and promising endeavor into functional biological surfaces many more years of R & D will be required before we have a viable consumer product.  I guess stories of dinner eating tables will remain science fiction for now.

Gerber, L., Koehler, F., Grass, R., & Stark, W. (2011). From the Cover: Incorporating microorganisms into polymer layers provides bioinspired functional living materials Proceedings of the National Academy of Sciences, 109 (1), 90-94 DOI: 10.1073/pnas.1115381109

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