A bumper crop
Microscopic drug needles are among the amazing new structures ‘farmed’ by engineer Sunkara
Mahendra Sunkara tends his crops with all the loving care that a 21st century farmer can.
His soil is liquid gallium metal and his “fertilizer” includes chemicals and gases. His crops are bulk quantities of nanowires and other structures one-thousandth the size of a human hair.
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Associate professor Mahendra Sunkara supervises an experiment in growing microscopic nanostructures that have potential applications in medicine, industry and more.
When he wants to see how his crops are doing, Sunkara doesn’t walk down muddy rows—he uses a scanning microscope.
While carbon nanopipettes and such have not yet replaced pork bellies on the mercantile exchange, the growing field of nanotechnology is starting to rival agriculture as a multi-billion dollar industry.
Sunkara, a chemical engineering associate professor in U of L’s J.B. Speed School of Engineering, is a pioneer in the field of growing tiny structures in bulk quantities. They promise to find vast application in everything from printer cartridges and space gear to fuel cells, chemical sensors and drug-delivery devices.
To date, one of Sunkara’s advanced-materials techniques has been patented. Another patent is pending and applications have been made for several more.
So many potential applications stem from Sunkara’s lab discoveries that he says he has a hard time focusing in on just a few.
In a recent presentation to doctors and others at
U of L’s School of Medicine, Sunkara floated the idea of using hollow carbon nanopipettes, affixed to tiny electronic devices on a skin patch, to deliver painless, timed medications to advanced Parkinson’s disease patients.
A million Americans suffer from Parkinson’s, a dopamine-deficiency disorder. Sunkara says his idea could be an improvement on the current use of Levodopa pills to treat the disease’s symptoms of stiffness, tremors, spasms and poor muscle control.
“As Parkinson’s progresses, the manner of levodopa delivery to the brain becomes more important,” Sunkara says.
Using both a tiny electronic detection device to monitor a patient’s neurotransmitter activity and a time-released nanopipette array could provide pain-free medication when needed. Sunkara says patch systems used to deliver the drugs have resulted in overmedication.
“The amount of drug needed by the patient is not high,” Sunkara says, “so regulation of small amounts when needed” is key.
Sunkara envisions a tiny electronic array, bubble-jet pump mechanism, drug tank, thin-film battery and an array of needle-sharp carbon nanopipettes all attached to a patch injecting medication into patients without them even feeling it.
He also sees similar applications for measuring inner-eye pressure and delivering drugs to glaucoma patients.
Sunkara’s research into thin-films also prompts a variety of applications. For instance, he says his novel techniques could reduce the cost of glucose-testing strips used by diabetes patients to determine their blood sugar levels.
“The biggest cost in a glucose-testing strip is the platinum it contains,” he says. “We have a patented way of reducing the platinum required to do the sensing that could reduce the cost of the strip by 50 percent.”
A Revolutionary Technique
Much of Sunkara’s research stems from discoveries he and his team of students, technical assistants and faculty colleagues have made in recent years. Sunkara directs the advanced materials research group, which includes 10 students.
“The novelty of our technique lies in the discovery of a fundamentally new phenomenon by which one-dimensional structures grow,” he says.
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Ph.D. student Hari Chandrasekaran uses a microwave plasma reactor for nanowire processes.
“Our discovery of using pools, or thin-films, of low-melting-point metals allows researchers to control the size of one-dimensional structures by manipulating the gas-phase chemistry,” he adds. “This is one big advancement.”
It also allows them to be grown in bulk.
The group’s technique overcomes previous limitations. Scientists long assumed gold or iron clusters are needed to make a pattern for one-dimensional growth of materials. Sunkara’s group proved otherwise.
They grow crops of minute structures by spreading a thin film of molten gallium on a solid substrate and exposing it to an excited gas environment such as plasma, which allows them to control the chemistry in a reactor. Sunkara says growth can be achieved through other methods, too.
“Gallium is an amazing metal,” Sunkara says. “It would melt in your hands and would not vaporize until very high temperatures. Also, it does not like to dissolve many electronically important elements such as silicon and germanium, remaining ‘clean’ and spitting out the growth material.” Sunkara adds that he has replicated the technique with other low-melting-point metals.
Sunkara’s other research includes studying how hexagonal gallium nitride crystals self-assemble to form single-crystal films, ways to improve diamond crystal development, and how metal-oxide “nanowebs” can be formed.
In the latter case, Sunkara says, “Our method allows two-dimensional arranged nanowires or nanocrystals to assemble into 2-D, web-like structures, rather than tangled 3-D clusters or forests.”
The researcher foresees applications of the resulting nanowebs in ultra-small sensors, chemical catalysis and more.
Sunkara’s research has been supported by the National Science Foundation, the U.S. Air Force and U.S. Army, Kentucky NASA, the Department of the Navy (through Knowledge Based Systems Inc.), Sud-Chemie Inc., Western Kentucky Energy Consortium, the Kentucky Science and Engineering Foundation, Optical Dynamics Inc. and others.
To see the full range of his research, visit: http://www.cvd.louisville.edu/