Directed assembly—faster, better, cheaper than 3D printing

Ahmed Bus­naina, director of the NSF (US National Science Foundation) Nanoscale Sci­ence and Engi­neering Center for High-​​rate Nanoman­u­fac­turing at North­eastern University explained current 3D printing technology and how his directed assembly method constitutes a serious upgrade in a Northeastern University Mar. 14, 2013 news release by Angela Herring,

The modern 3-​​D printer is basi­cally a spe­cial­ized ink-​​jet printer. It uses a printer head with spe­cial ink that could con­tain a polymer, par­ti­cles, or nan­otubes sus­pended in solu­tion, or really any­thing. It prints line by line, so prod­ucts requiring higher res­o­lu­tion or large areas take a very long time.

What we have devel­oped at our center is a system that’s like news­paper printing or printing money, where you have a big plate, you put ink on it, and bang: One hit, you’re done. Only here, the ink is made of very small and very sen­si­tive nanopar­ti­cles attracted to the tem­plate using elec­trophoresis, so we have to pick exact dimen­sions and materials.

We put a tem­plate with a pat­tern rep­re­sented by nanowires into a solu­tion that is sim­ilar to ink, but very dilute. Then we apply a couple of volts so that nanopar­ti­cles in the ink are drawn to the nanowires. Then we take out the tem­plate and transfer the assem­bled nanopar­ti­cles to a sur­face of either a hard or flex­ible sub­strate. That would be the first layer of a device, which takes about a minute or two. A sensor may have just a few layers, where advanced elec­tronics may have 10 layers or more.

Busnaina contrasts the speed and range of scales between the current method and his directed assembly method (from the news release),

For low-​​cost, low-​​end prod­ucts, 3-​​D printers are very good but they are slow—it can take days to print a single product. But with directed assembly, we can do low-​​cost, high-​​end prod­ucts, and we can do them very quickly. So, directed assembly will be very valu­able for high-​​value devices like sen­sors, advanced elec­tronics, energy har­vesting, or bat­teries. It might also be used for tissue engi­neering and printing bio­ma­te­rials like cells or proteins.

Directed assembly allows 3-​​D printing to be faster, cheaper, and mul­ti­scale. It can do nano, micro, and macro simul­ta­ne­ously over a large area. No 3-​​D printer can do that; this is beyond the cur­rent 3-​​D printing tech­nology. This will reduce the cost of expen­sive elec­tronics such as an iPhone for less than $10 and sensor sys­tems for a frac­tion of a dollar. These could be sen­sors for health, the envi­ron­ment, infra­struc­ture, water resources, any­thing. They will make advanced prod­ucts afford­able to people in all income classes, not just high-​​income pop­u­la­tions or countries.

What we’re trying to do is make high-​​value things, such as sen­sors, energy-​​harvesting devices, or phone dis­plays, using this tech­nology, which costs 1 per­cent of con­ven­tional man­u­fac­turing. That also means you can make all kinds of devices by design, printing things exactly to specifications—even down to the nanoscale (one thou­sand times smaller than a human hair).

For example, we devel­oped an energy-​​harvesting device that can use any heat source—even body heat—to charge a sensor or a phone. An antenna absorbs heat and con­verts it to cur­rent. We print it using carbon nan­otubes for the ink. This kind of device would not be pos­sible with tra­di­tional 3-​​D printing—it just can’t go that small.

Exciting stuff and you can read more about it at the Northeastern University website or where I first found the item at phys.org.

 

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