miércoles, 31 de julio de 2013

Making Wires For Drug-Releasing Circuits

ORIGINAL: ACS - Chemical and Engineering News
By Katherine Bourzac
July 31, 2013

Bioengineering: Nanowires loaded with biochemicals can release their cargo in response to an electrical signal
Department: Science & Technology | Collection: Life Sciences
News Channels: Nano SCENE, Materials SCENE, Biological SCENE
Keywords: nanowires, controlled drug release

Glowing Nanowires A flexible nanostorage device (left) consists of a polyimide film coated with gold and chemical-storing nanowires. When a voltage is applied to the film, the nanowires release adenosine triphosphate (right). The area around the wires glows because the released ATP triggers enzymes to produce a bioluminescent molecule. If the researchers turn off the voltage, the wires no longer glow (center). Credit: ACS Nano

Bioengineers have designed chips that release precise doses of drugs when activated by electrical signals. Although these devices promise drug delivery to diseased tissue on cue, they are rigid, which isn’t ideal for an implant. There are more flexible materials that deliver bioactive compounds, but they do so constantly as the material slowly dissolves. Now, researchers at Seoul National University have combined flexibility and controlled release in multifunctional nanowires that discharge stored chemicals in response to an electrical signal (ACS Nano 2013, DOI: 10.1021/nn402082v).

Seunghun Hong, a nanotechnologist at Seoul National University, thinks his team’s nanowires could one day be integrated into implants like hip replacements to release an antibiotic to cure an infection. Or they could be integrated into diagnostic chips to release chemicals without need for pumps.

The researchers made the nanowires to act as electrically controlled chemical storage units. The nanowires have three segments: an electrically active polymer mixed with the chemical to be stored; a nickel segment that allows the researchers to move the wires with a magnet; and a gold or silver section that acts as an electrical contact, so that the wires can be integrated on a chip. When a voltage is applied to the polymer, it expands, releasing the chemicals trapped inside its matrix.

To make the nanowires, Hong and his group used an existing method that relies on an anodized aluminum oxide template. The template has holes 200 nm in diameter and 60 µm deep. The researchers sequentially electroplate the template with the three different materials, first filling the holes with some gold, then some nickel, then some polypyrrole mixed with the chemical of choice. Once filled, the scientists dissolve away the template, freeing the nanowires.

In one test of the wires, Hong’s group chose to store and release adenosine triphosphate (ATP), a chemical that stores energy in biological systems. They dispersed the nanowires into a solution and used magnetic fields to pull the nanowires down to precise locations on a conductive nickel surface. The solution also contained a collection of enzymes that could turn the compound luciferin into a fluorescent molecule in the presence of ATP. When the researchers applied voltage to the nanowires, the area around the wires lit up, indicating the release of ATP.

In another experiment, the researchers placed the nanowires on a conductive gold surface along with the biological motor protein kinesin, which runs on ATP. When they applied a voltage to the surface, the motors moved in response to the released ATP.

Reginald M. Penner, a chemist at the University of California, Irvine, says other groups have made tiny storage tubes out of electrically conductive polymers before, but Hong’s is the first to demonstrate that they can be integrated with electronics to control them. This electronic integration and control, he says, “is absolutely enabling for an implantable drug delivery system.

Chemical & Engineering NewsISSN 0009-2347Copyright © 2013 American Chemical Society

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