Joined: 16 Mar 2004
|Posted: Fri May 08, 2009 9:45 am Post subject: Enzyme Coat Kills Germs, Digests Stains
|A way to attach a coating of 'live' enzymes onto plastic and other materials could lead to clothes that digest stains as soon as they occur, or kitchen surfaces able to kill bacteria.
US researchers have shown they can make plastic films containing active enzymes like those in biological clothes detergents. The process used is based on one typically used to produce thin, flat plastic products such as CDs, DVDs and flat-screen displays.
Known as "spin coating", it involves placing a large dollop of a liquid onto a flat surface which is then rotated at great speed. This generates powerful centrifugal forces that push the solution towards the surface edges and cause some liquid to evaporate, leaving behind a thin, solid film over the entire surface.
The thickness of the film depends on the properties of the original solution, such as its viscosity, and the spinning speed.
In a spin
Using 10-cm plastic discs as their flat surface, the team led by Ping Wang at the University of Minnesota, St. Paul, US, used spin coating to layer four films on top of each other.
First came a thin film of polystyrene modified to chemically bind to enzymes. Then Wang and his team covered this with a solution containing a protein-digesting enzyme known as subtilisin Carlsberg, commonly used in biological washing powders to remove stains.
The enzymes in the solution naturally bound to the chemical groups displayed on the polystyrene film.
Protein-digesting enzyme subtilisin Carlsberg forms layers in the coating
The team next added a layer of a chemical called glutaraldehyde that creates links between enzymes to ensure they are firmly attached to the plastic. Finally, another layer of subtilisin Carlsberg topped off the film.
Tests showed that nothing short of burning or harsh chemical treatments could now dislodge the enzymes, Wang says. "The bonding between the enzyme and the polymer coating is as strong as the chemical bonds that are responsible for the integrity of plastics."
Despite this strong bond, the attached enzymes still retained much of their activity, able to digest the protein albumin when it was sloshed on in solution, or deposited on the film using spin coating.
Building such a film into fabric could allow it to start digesting stains as soon as they occurred. The mothod could also provide an alternative to using silver nanoparticles to make fabrics anti-bacterial, which were recently found to easily wash out, potentially causing environmental damage. The enzymes could take on bacteria by attacking proteins on the outside of the cells.
"Our preliminary results showed that enzymes can be spin-coated onto any pre-prepared plastic structures and, beyond that, probably inorganic structures such as metals and ceramics," Wang says.
The underlying chemistry is flexible enough to spin coat directly onto fabric, alternatively a plastic-enzyme film could be made first and later incorporated into material.
Wang says such enzyme-coated materials could have a wide range of uses, including self-healing materials or protective suits able to digest chemical or biological hazards. One surface could be given multiple functions by simply coating it with a variety of enzymes.
Suwan Jayasinghe, a biophysicist at University College London, UK, agrees that there are a wide range of potential uses for such enzyme-coated inorganic materials.
"Functional structures such as these are going mainstream, and are continuously elucidating their great promise to the biomedical sciences," he says.