MIT crafts bacteria-resistant films

Having found that whether bacteria stick to surfaces depends partly on how stiff those surfaces are, MIT engineers have created ultrathin films made of polymers that could be applied to medical devices and other surfaces to control microbe accumulation.

The inexpensive, easy-to-produce films could provide a valuable layer of protection for the health care industry by helping to reduce the spread of hospital-acquired infections, which take the lives of 100,000 people and cost the United States an estimated $4.5 billion annually.

The researchers, who describe their work in an upcoming issue of the journal Biomacromolecules, found they could control the extent of bacterial adhesion to surfaces by manipulating the mechanical stiffness of polymer films called polyelectrolyte multilayers. Thus, the films could be designed to prevent accumulation of hazardous bacteria or promote growth of desirable bacteria.

“All other factors being equal, mechanical stiffness of material surfaces increases bacterial adhesion,” said Krystyn Van Vliet, the Thomas Lord Assistant Professor of Materials Science and Engineering and the paper's anchor author.

Van Vliet and her colleagues found the same trend in experiments with three strains of bacteria: Staphylococcus epidermidis, commonly found on skin, and two types of Escherichia coli.

Stiffness has usually been overlooked in studies of how bacteria adhere to surfaces in favor of other traits such as surface charge, roughness, and attraction to or repulsion from water. The new work shows that stiffness should also be taken into account, said Van Vliet.

The new films could be combined with current methods of repelling bacteria to boost their effectiveness, said Michael Rubner, an author of the paper and director of MIT's Center for Materials Science and Engineering.

Those methods include coating surfaces with antimicrobial chemicals or embedding metal nanoparticles into the surface, which disrupt the bacterial cell walls.

“For those bacteria that readily form biofilms, we have no delusions that we can prevent bacterial films from starting to form. However, if we can limit how much growth occurs, these existing methods can become much more effective,” Rubner said.

Jenny Lichter, graduate student in materials science and engineering, and Todd Thompson, a graduate student in the Harvard-MIT Division of Health Sciences and Technology, are joint lead authors of the paper. They note that the films could also be used on medical devices that go inside the body, such as stents and other cardiac implants.

“Once a foreign object enters into the body, if you can limit the number of bacteria going in with it, this may increase the chances that the immune system can defend against that infection,” said Thompson.

Another possible application for the films is to promote growth of so-called “good bugs” by tuning the mechanical stiffness of the material on which these bacteria are cultured. These films could stimulate growth of bacteria needed for scientific study, medical testing, or industrial uses such as making ethanol.

The researchers built their films, which are about 50 nanometers (billionths of a meter) thick, with layers of polyelectrolytes (a class of charged polymer). Alternating layers are added at different pH (acidity) levels, which determines how stiff the material is when hydrated at near-neutral pH, such as water. Polymer films assembled at higher pH (up to 6) are stiffer because the polymer chains crosslink readily and the polymers do not swell too much; those added at lower, more acidic pH (down to 2.5) are more compliant.

Van Vliet says the team's results could be explained by the relationship between surfaces and tiny projections from the bacterial cell walls, known as pili. Stiffer surfaces may reinforce stronger, more stable bonds with the bacterial pili. The researchers are now working on figuring out this mechanism.

Source: Massachusetts Institute of Technology

Related stories:

Researchers band together in global battle on bacterial biofilms
The discovery that bacteria are not loners, but social creatures that congregate and chemically communicate in communities — termed biofilms — has sparked a global scientific effort to control spread of these slimy coatings that grow on hospital surfaces, inside tubing, and a multitude of other places. That's the topic of an article scheduled for the June 9 issue of Chemical & Engineering News, ACS' weekly newsmagazine.
Edible food wrap kills deadly E. coli bacteria
Researchers have improved upon an edible coating for fresh fruits and vegetables by enabling it to kill deadly E. coli bacteria while also providing a flavor-boost to food. Composed of apple puree and oregano oil, which acts as a natural antibacterial agent, the coating shows promise in laboratory studies of becoming a long-lasting, potent alternative to conventional produce washes, according to a team of scientists from the U.S. Department of Agriculture (USDA) and the University of Lleida in Spain.
Chemists make beds with soft landings
Bedsprings aren't often found in biology. Now, chemists have succeeded in making a layer of tiny protein coils attached to a surface, much like miniature bedsprings in a frame. This thin film made of stable and very pure helices can help researchers develop molecular electronics or solar cells, or to divine the biology of proteins.
'Edible optics' could make food safer
Imagine an edible optical sensor that could be placed in produce bags to detect harmful levels of bacteria and consumed right along with the veggies. Or an implantable device that would monitor glucose in your blood for a year, then dissolve.
Physicists Produce Quantum-Entangled Images
Using a convenient and flexible method for creating twin light beams, researchers from the National Institute of Standards and Technology (NIST) and the University of Maryland (UM) have produced “quantum images,” pairs of information-rich visual patterns whose features are “entangled,” or inextricably linked by the laws of quantum physics.
University of Pennsylvania engineers reveal what makes diamonds slippery at the nanoscale
They call diamonds "ice," and not just because they sparkle. Engineers and physicists have long studied diamond because even though the material is as hard as an ice ball to the head, diamond slips and slides with remarkably low friction, making it an ideal material or coating for seals, high performance tools and high-tech moving parts.
Physicists produce quantum-entangled images
Using a convenient and flexible method for creating twin light beams, researchers at the Joint Quantum Institute of the Commerce Department's National Institute of Standards and Technology and the University of Maryland have produced "quantum images," pairs of information-rich visual patterns whose features are "entangled," or inextricably linked by the laws of quantum physics. In addition to promising better detection of faint objects and improved amplification and positioning of light beams, the researchers' technique for producing quantum images—unprecedented in its simplicity, versatility, and efficiency—may someday be useful for storing patterns of data in quantum computers and transmitting large amounts of highly secure encrypted information. The research team, led by JQI's Paul Lett, describes the work in the June 12 edition of Science Express.
University of Florida professor designs plasma-propelled flying saucer
Flying saucers may soon be more fact than mere science fiction. University of Florida mechanical and aerospace engineering associate professor Subrata Roy has submitted a patent application for a circular, spinning aircraft design reminiscent of the spaceships seen in countless Hollywood films. Roy, however, calls his design a "wingless electromagnetic air vehicle," or WEAV.

News discussion:

General Science news