From the Labs: Nanotechnology

Nano Lube for NEMS
A new way to reduce friction could make nanomachines practical

Source: “Atomic-Scale Control of Friction by Actuation of Nanometer-Sized Contacts”
Anisoara Socoliuc et al.
Science 313: 207-210

Results: Researchers at the University of Basel, Switzerland, have created a practical form of lubrication for nanoscale electromechanical systems (NEMS) that reduces friction between the devices’ tiny moving parts 100-fold. The new method is needed because liquid lubricants do not work at the nanoscale, and other dry approaches to reducing friction have been too difficult to use in experimental nano­mechanical devices.

Why it matters: Some of the most promising nanotechnologies involve micro- and nanoelectromechanical devices, including microscopic mirrors for communications routers and ultradense computer memory that uses the tip of an atomic force microscope (AFM) to write data bits. But friction can cause the mechanical parts in these devices to wear out too quickly, limiting their commercial use.

Methods: When researchers move a microscopic tip across a surface to make nano features, friction causes the tip to alternately stick and slip. The Swiss team eliminated this problem by vibrating the tip of a silicon AFM probe, reducing the friction between it and test surfaces of sodium chloride and potassium bromide. The application of this technique would be straightforward in AFM-based memory; other NEMS devices could incorporate small oscillators to vibrate parts that might stick.

Next steps: The researchers recently tested their method on oxidized silicon in air, and initial results suggest that it works. But they still need to apply the technique to existing devices.

Source: “Controlling Interlayer Diffusion to Achieve Sustained, Multiagent Delivery from Layer-by-Layer Thin Films”
Kris C. Wood et al.
Proceedings of the National Academy of Sciences 103(27): 10207-10212

Results: By developing a way to segregate components in ultrathin surface coatings, MIT researchers have made a new class of materials that can release drugs, and even genes, in an exact sequence and at a predetermined rate.

Why it matters: Coated with the new materials, medical implants such as artificial hips could prove safer and more effective than their predecessors, releasing first antibiotics and then growth factors and other drugs exactly where and when they are needed. Efforts to engineer complex tissues such as bones, blood vessels, muscles, and livers could also benefit from scaffolds coated with the new materials, which could encourage the growth of specific cell types.

Methods: The researchers dip a surface to be coated into a series of solutions alternately containing polymers of one charge and drugs or drug carriers of the opposite charge. These layered coatings will break down in water, freeing their contents. To prevent all the layers from breaking down at once, the researchers separate them with boundary layers of covalently linked molecules. The scientists believe that a given boundary layer will peel off after it has been exposed to water; but that doesn’t happen until the layer above it has completely dissolved. The result is an ordered, sequential release of drugs, its timing dependent on the number of layers.

Next steps: The researchers are now developing coatings that incorporate a specific sequence of therapeutics for orthopedic applications, such as hip implants, which will then be tested for safety and efficacy.