Nano Biomaterials

Detergent manufacturers have long used enzymes in their formulations for fighting really tough dirt. Jonathan Dordick, a chemical engineer at Rensselaer Polytechnic Institute in Troy, NY, is taking the battle against dirt a step further, using nanotechnology to design a self-cleaning plastic in which the enzyme molecules are an integral part of the material. When the plastic comes into contact with bacteria or other pathogens, the enzymes attack the microbes and destroy their ability to bind to its surface.

Dordick’s innovation is far more than a boon for those challenged by a sponge and disinfectant. It reflects a growing opportunity for materials scientists to form novel combinations of biological and nonbiological molecules. Indeed, one implication of the rapidly developing field of nanotechnology is that at such small scales, the distinction between biological and nonbiological materials often blurs. As a result, researchers around the world are beginning to fabricate hybrid materials that combine nonbiological elements with biological ones such as DNA and proteins.

Such combinations could give researchers the best of both worlds. Many inorganic materials and plastics excel at conducting electricity or emitting light. Biological materials, on the other hand, are excellent at recognizing other molecules with exquisite sensitivity and can spontaneously assemble themselves into numerous complex structures. “Putting the two together will lead to some unique applications,” says Dordick.

To fabricate the self-cleaning material, Dordick and his Rensselaer colleagues attach enzymes to the surface of large carbon-based molecules called nanotubes. The nanotubes, which stabilize the enzymes, are then incorporated into a polymer. The technique could work for any number of enzymes, opening the door to an array of applications, including materials that kill specific microbes or even degrade oil sludge on contact. Coatings of the enzyme-polymer material could protect implantable medical devices from scar tissue formation.

Hybrid Highlights
INVESTIGATOR	FOCUS
Center for Biological and Environmental Nanotechnology/Rice University	Investigating the interface of biological and nonbiological materials
Angela Belcher/MIT	Using viruses to produce nanomaterials for optical, electronic, and magnetic devices
Yet-Ming Chiang/MIT and Anand Jagota/DuPont	Identifying biological molecules to organize carbon nanotubes for new sensors and electronic devices
Jonathan Dordick/Rensselaer Polytechnic Institute	Fabricating new materials out of biological and nonbiological components
Nadrian Seeman/New York University	Using DNA to assemble inorganic particles

Outside the body, biological molecules can have some surprising properties. For example, Dordick has found superstrong and lightweight proteins, and he is trying to stuff them into carbon nanotubes to create “self-healing” materials. Computer simulations show that when the nanotubes break under stress, they release the proteins, which aggregate and form an adhesive. If his simulations prove correct, these hybrid materials could become components in structures such as airplane wings. As cracks propagate over time, fractured nanotubes would release the adhesive, making repairs that would prolong the wing’s useful life.

Many biological molecules such as DNA can spontaneously form complex structures in a process chemists call self-assembly. Researchers are hoping to take advantage of this natural process, using it to help construct complex nanostructures. New York University chemist Nadrian Seeman, for example, is using DNA as a scaffold for assembling nanoparticles of conducting materials.

Strands of DNA with attached nano-size particles could be “coded” to assemble spontaneously into a specific structure, for instance, the configuration of a circuit. “DNA is good for doing this because the molecule is so well understood, and it’s easy to control and predict what its final structure will be,” says Seeman. He and his colleagues have had success making two-dimensional structures out of DNA, and they are now working on making three-dimensional crystals. One of the ultimate goals is to use DNA’s knack for self-assembly as an easy and cheap way to fabricate nanoscale electronic materials or devices that could be used in ultrafast or ultrasmall computers.

Although it may be more than a decade before such bioelectronic materials are available, Dordick believes that relatively simple materials such as his self-cleaning or self-healing plastics could emerge in the next few years. “Things are moving quickly, and the number of people getting into this is increasing dramatically,” says Dordick. Still, researchers readily acknowledge that they are just beginning to explore the possibilities of new hybrid materials and that eventual applications remain uncertain. “We will all go in different directions because it’s such a rich field and because there are so many possibilities,” predicts Seeman.

But one thing seems certain. As material scientists continue to discover novel and interesting combinations of biological and nonbiological materials, it is a field that is coming alive.