Purdue researchers have created a magnetic ferropaper that might be used to make low-cost micromotors for surgical instruments, tiny tweezers to study cells and miniature speakers. Babak Ziaie, a professor of electrical and computer engineering and biomedical engineering, holds a miniature birdlike shape made from the material. The wings move slowly, but the structure is not capable of flight. (Purdue University photo/Andrew Hancock)

The material is made by impregnating ordinary paper – even newsprint – with a mixture of mineral oil and “magnetic nanoparticles” of iron oxide. The nanoparticle-laden paper can then be moved using a magnetic field.

“Paper is a porous matrix, so you can load a lot of this material into it,” said Babak Ziaie, a professor of electrical and computer engineering and biomedical engineering.

The new technique represents a low-cost way to make small stereo speakers, miniature robots or motors for a variety of potential applications, including tweezers to manipulate cells and flexible fingers for minimally invasive surgery.

“Because paper is very soft it won’t damage cells or tissue,” Ziaie said. “It is very inexpensive to make. You put a droplet on a piece of paper, and that is your actuator, or motor.”

Once saturated with this “ferrofluid” mixture, the paper is coated with a biocompatible plastic film, which makes it water resistant, prevents the fluid from evaporating and improves mechanical properties such as strength, stiffness and elasticity.

Findings will be detailed in a research paper being presented during the 23rd IEEE International Conference on Micro Electro Mechanical Systems on Jan. 24-28 in Hong Kong. The paper was written by Ziaie, electrical engineering doctoral student Pinghung Wei and physics doctoral student Zhenwen Ding.

Because the technique is inexpensive and doesn’t require specialized laboratory facilities, it could be used in community colleges and high schools to teach about micro robots and other engineering and scientific principles, Ziaie said.

The magnetic particles, which are commercially available, have a diameter of about 10 nanometers, or billionths of a meter, which is roughly 1/10,000th the width of a human hair. Ferro is short for ferrous, or related to iron.

“You wouldn’t have to use nanoparticles, but they are easier and cheaper to manufacture than larger-size particles,” Ziaie said. “They are commercially available at very low cost.”

The researchers used an instrument called a field-emission scanning electron microscope to study how well the nanoparticle mixture impregnates certain types of paper.

“All types of paper can be used, but newspaper and soft tissue paper are especially suitable because they have good porosity,” Ziaie said.

The researchers fashioned the material into a small cantilever, a structure resembling a diving board that can be moved or caused to vibrate by applying a magnetic field.

“Cantilever actuators are very common, but usually they are made from silicon, which is expensive and requires special cleanroom facilities to manufacture,” Ziaie said. “So using the ferropaper could be a very inexpensive, simple alternative. This is like 100 times cheaper than the silicon devices now available.”

The researchers also have experimented with other shapes and structures resembling Origami to study more complicated movements.

The research is based at the Birck Nanotechnology Center in Purdue’s Discovery Park.

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‘Ferropaper’ is new technology for small motors, robots

Researchers have created the tiniest laser since its invention nearly 50 years ago. Because the new device, called a 'spaser', is the first of its kind to emit visible light, it represents a critical component for possible future technologies based on 'nanophotonic' circuitry. The color diagram (a) shows the nanolaser's design: a gold core surrounded by a glasslike shell filled with green dye. Scanning electron microscope images (b and c) show that the gold core and the thickness of the silica shell were about 14 nanometers and 15 nanometers, respectively. A simulation of the SPASER (d) shows the device emitting visible light with a wavelength of 525 nanometers. (Birck Nanotechnology Center, Purdue University)

Because the new device, called a “spaser,” is the first of its kind to emit visible light, it represents a critical component for possible future technologies based on “nanophotonic” circuitry, said Vladimir Shalaev, the Robert and Anne Burnett Professor of Electrical and Computer Engineering at Purdue University.

Such circuits will require a laser-light source, but current lasers can’t be made small enough to integrate them into electronic chips. Now researchers have overcome this obstacle, harnessing clouds of electrons called “surface plasmons,” instead of the photons that make up light, to create the tiny spasers.

Findings are detailed in a paper appearing online in the journal Nature that reports on work conducted by researchers at Purdue, Norfolk State University and Cornell University.

Nanophotonics may usher in a host of radical advances, including powerful “hyperlenses” resulting in sensors and microscopes 10 times more powerful than today’s and able to see objects as small as DNA; computers and consumer electronics that use light instead of electronic signals to process information; and more efficient solar collectors.

“Here, we have demonstrated the feasibility of the most critical component – the nanolaser – essential for nanophotonics to become a practical technology,” Shalaev said.

The “spaser-based nanolasers” created in the research were spheres 44 nanometers, or billionths of a meter, in diameter – more than 1 million could fit inside a red blood cell. The spheres were fabricated at Cornell, with Norfolk State and Purdue performing the optical characterization needed to determine whether the devices behave as lasers.

The findings confirm work by physicists David Bergman at Tel Aviv University and Mark Stockman at Georgia State University, who first proposed the spaser concept in 2003.

“This work represents an important milestone that may prove to be the start of a revolution in nanophotonics, with applications in imaging and sensing at a scale that is much smaller than the wavelength of visible light,” said Timothy D. Sands, the Mary Jo and Robert L. Kirk Director of the Birck Nanotechnology Center in Purdue’s Discovery Park.

The spasers contain a gold core surrounded by a glasslike shell filled with green dye. When a light was shined on the spheres, plasmons generated by the gold core were amplified by the dye. The plasmons were then converted to photons of visible light, which was emitted as a laser.

Spaser stands for surface plasmon amplification by stimulated emission of radiation. To act like lasers, they require a “feedback system” that causes the surface plasmons to oscillate back and forth so that they gain power and can be emitted as light. Conventional lasers are limited in how small they can be made because this feedback component for photons, called an optical resonator, must be at least half the size of the wavelength of laser light.

The researchers, however, have overcome this hurdle by using not photons but surface plasmons, which enabled them to create a resonator 44 nanometers in diameter, or less than one-tenth the size of the 530-nanometer wavelength emitted by the spaser.

“It’s fitting that we have realized a breakthrough in laser technology as we are getting ready to celebrate the 50th anniversary of the invention of the laser,” Shalaev said.

The first working laser was demonstrated in 1960.

The research was conducted by Norfolk State researchers Mikhail A. Noginov, Guohua Zhu and Akeisha M. Belgrave; Purdue researchers Reuben M. Bakker, Shalaev and Evgenii E. Narimanov; and Cornell researchers Samantha Stout, Erik Herz, Teeraporn Suteewong and Ulrich B. Wiesner.

Future work may involve creating a spaser-based nanolaser that uses an electrical source instead of a light source, which would make them more practical for computer and electronics applications.

The work was funded by the National Science Foundation and U.S. Army Research Office and is affiliated with the Birck Nanotechnology Center, the Center for Materials Research at Norfolk State, and Cornell’s Materials Science and Engineering Department.

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Nanovis Inc., a Columbia City, Ind.-based company with offices at the Purdue Research Park in West Lafayette, will work with Birck researchers and the center’s facilities to improve the interactive process between medical implants and human tissues for reducing rejection or infection.

Ganesh Balasundaram, principal scientist at Nanovis LLC (from left), Monica M.C. Allain, managing director for Purdue's Birck Nanotechnology Center in Discovery Park, and Matt Hedrick, president and chief operating officer at Nanovis, discuss research related to spine repair using nanostructured biomaterials in a laboratory at Birck. Nanovis, which is based at the Purdue Research Park and collaborating with Birck, has begun initial testing of a bone regeneration technology with the help of a $2 million grant from the state's 21st Century Research and Technology Fund. The technology was jointly discovered by Nanovis and researchers at Purdue and Brown University. (Purdue University photo/Mark Simons)

“This industry partnership opens the door at the Birck Nanotechnology Center for enhanced opportunities for joint research with industry partners,” said Timothy Sands, the Mary Jo and Robert L. Kirk Director of the Birck Nanotechnology Center.

Nanovis, which was launched in 2006 in the Purdue Research Park from technology developed at Purdue, is commercializing a portfolio of nanostructured surfaces, materials and proprietary medical devices that better manage the interface with bone, soft tissue, nerves and cardiovascular cells. Thomas Webster, who was an associate professor of biomedical engineering at Purdue and is now a researcher at Brown University, discovered the technique.

“Through this collaboration, Nanovis will have access to some of the most advanced nanotechnology research facilities on a university campus in the world, with access to the expertise of the university’s research community,” said Matt Hedrick, Nanovis’ president and chief operating officer. “Nanovis also will get to know many of Purdue’s high-caliber graduate students who work with nanotechnology.”

Nanovis is using nanotechnology facilities at Purdue to create products that can assist in procedures from knee and hip implants to improved stents and treatments to help prevent spinal fractures, Hedrick said. The company is developing and marketing nanotechnology that, when added to a knee or other implant surface, will help the body grow around the device instead of fighting it.

Hedrick, who previously worked with a startup company in Maryland, said Indiana is creating an environment to launch such life-sciences ventures.

“I think a lot of the pieces are in place, even during the current tough economic climate, to advance Indiana’s storied strength in the life sciences,” said Hedrick, crediting the state’s agencies, lawmakers, organizations and universities with supporting new life-sciences ventures.

Assisting in the agreement were Joseph B. Hornett, senior vice president, treasurer and chief operating officer of the Purdue Research Foundation, which manages the Purdue Research Park; and Monica M.C. Allain, managing director of the Birck Nanotechnology Center.

The 187,000-square-foot Birck Nanotechnology Center, a cornerstone facility in Discovery Park that became fully operational in October 2005, involves more than 300 Purdue faculty members, researchers, staff and graduate students from 27 schools and departments. Birck opened its $10 million cleanroom, the Scifres Nanofabrication Laboratory, to researchers in June 2006.

The facility is named for Michael and Katherine (Kay) Birck of Hinsdale, Ill., who contributed $30 million for the building. Michael Birck is a Purdue alumnus, member of the Purdue board of trustees and chairman of Naperville, Ill.-based Tellabs Inc.

Alumni William B. and Mary Jane Elmore provided $2 million toward the center’s William and Mary Jane Elmore Advanced Concept Validation Laboratory.

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