R&D DIGEST

Researchers at Johns Hopkins University are working with materials that could one day play a role in repairing damaged spinal cords or creating artificial tissue. They're laying the foundation for these potential uses by investigating how to use the materials, called organic electronics, for new structures to regulate cell-to-cell communication. Being able to control this type of communication opens the door to uses in reengineering neural networks and other damaged tissue.

Organic electronic materials are carbon-based molecules or polymers with solid-state electronic properties that mimic the characteristics of typical semiconductors such as silicon or metals such as copper wire. Although they don't always perform the same as typical materials, they can be processed into devices from a solution at ambient room conditions. This attribute paves the way to developing lightweight and flexible devices, according to John Tovar, assistant professor in the department of chemistry at Johns Hopkins.

Tovar's team is working with an organic electronic unit consisting of carbon rings with highly delocalized electronics. The unit is sandwiched between two small peptide sequences, with a length of about 42 Å, similar to those found in proteins.

“Under certain conditions, the molecule is freely dissolved in water, but we can trigger the molecules to preferentially self-assemble into larger structures,” Tovar explains. “This is due to the peptide's desire to maximize intermolecular interactions.”

Such association leads to the formation of nanowires with diameters less than 6 nm and lengths of several microns. Preparing the nanomaterials from a defined molecular precursor eliminates the need to use advanced semiconductor processing techniques, such as lithography, to yield small feature sizes.

The researchers have been investigating the organic nanostructures for two years. They're currently trying to assess the types of molecular changes that must be made to achieve a self-assembly process, and their long-term goal is to explore biomedical applications. Due to intellectual property issues, Tovar isn't able to provide details about this work, but he indicated that the materials have potential use in pacemakers, among other areas.

With regard to changes to the organic materials, Tovar says his group is trying to expand the types of electronic properties that the molecules display from high electrical conductivity to unusual optical effects. They plan to develop a molecular synthesis to build new electronic structures. The researchers are also looking into the surface chemistry of the nanomaterials to encourage cell adhesion as a prelude to using these electronic conduits to regulate cell-to-cell interactions. For example, such communication could one day lead to a device that can bypass a damaged spinal cord and restore movement to paralyzed legs.

Organic electronics could also be developed for use in artificial muscles. Although Tovar's team isn't working in this area, he says the concept has potential. The plastics are insulating in their neutral state, and once the charge is chemically removed from an organic molecule, the material swells or contracts as a function of its conductive property. The swelling is controlled in a manner similar to the way a muscle contracts and relaxes. The materials could also be used as stimuli-sensitive polymers for drug delivery and artificial retinas, says Tovar.

Although these biomedical uses won't come to fruition in the immediate future, the team at Johns Hopkins is laying the foundation. Their work with organic electronics has been published in a recent issue of the Journal of the American Chemical Society.

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