It sounds futuristic, but today Carnegie Mellon University researchers are developing edible electronic devices that can be implanted in the body to improve patient care.

"We are creating electronically active medical devices that can be implanted in the body," said Christopher Bettinger, an assistant professor in the departments of Materials Science and Engineering and Biomedical Engineering at CMU. "The idea is for a patient to consume a pill that encapsulates the device."

Bettinger, along with Jay Whitacre, a professor of materials science and engineering, is creating edible power sources for medical devices that can be taken orally using materials found in the daily diet.

"Our design involves flexible polymer electrodes and a sodium ion electrochemical cell, which allows us to fold the mechanism into an edible pill that encapsulates the device," Bettinger said.

CMU researchers report that the edible device could be programmed and deployed in the gastrointestinal tract or the small intestine depending upon packaging. Once the battery packaging is in place, Bettinger’s team would activate the battery.

Bettinger reports that the battery could power biosensors to measure biomarkers or monitor gastric problems. The battery also could be used to stimulate damaged tissue or help in targeted drug delivery for certain types of cancer.

"There’s so much out there we can do with this novel approach to medical devices," said Bettinger, a recipient of the National Academy of Sciences Award for Initiatives in Research for his innovative work on advanced materials for next-generation implanted medical devices.  

Bettinger has worked for more than a decade at the interface of materials science and biomedical engineering. Some of his innovative technologies include new synthetic materials that mimic the natural properties of soft tissue and biodegradable electronics that could usher in a new era of electronically active implants. 

Bettinger is an assistant professor in the Departments of Materials Science and Engineering and Biomedical Engineering at Carnegie Mellon. Bettinger received an S.B. in Chemical Engineering in 2003, an M.Eng. in Biomedical Engineering in 2004, and a Ph.D. in Materials Science and Engineering in 2008 as a Charles Stark Draper Fellow, all from the Massachusetts Institute of Technology. He completed his post-doctoral fellowship at Stanford University in the Department of Chemical Engineering as an NIH Ruth Kirschstein Fellow in 2010. He has received many honors including the MIT Department of Materials Science and Engineering Award for “Outstanding PhD Thesis,” the ACS AkzoNobel Award for Polymer Chemistry, and the Tissue Engineering and Regenerative Medicine Society Young Investigator Award. Bettinger is also a co-inventor on several patents and was a finalist in the MIT $100K Entrepreneurship Competition.

Carnegie Mellon is a private research university with programs in areas ranging from science, technology and business, to public policy, the humanities and the arts. More than 12,000 students are currently in attendance across Carnegie Mellon’s multiple campuses worldwide. Carnegie Mellon’s main campus in the United States is in Pittsburgh, Pa. It has campuses in California’s Silicon Valley and Qatar, and programs in Africa, Asia, Australia, Europe and Mexico.

Controlling the shapes of nanometer-sized catalytic and electrocatalytic particles made from noble metals such as platinum and palladium may be more complicated than previously thought.

Using systematic experiments, researchers have investigated how surface diffusion – a process in which atoms move from one site to another on nanoscale surfaces – affects the final shape of the particles. The issue is important for a wide range of applications that use specific shapes to optimize the activity and selectivity of nanoparticles, including catalytic converters, fuel cell technology, chemical catalysis and plasmonics.

Results of the research could lead to a better understanding of how to manage the diffusion process by controlling the reaction temperature and deposition rate, or by introducing structural barriers designed to hinder the surface movement of atoms.

“We want to be able to design the synthesis to produce nanoparticles with the exact shape we want for each specific application,” said Younan Xia, a professor in the Wallace H. Coulter Department of Biomedical Engineering at Georgia Tech and Emory University. “Fundamentally, it is important to understand how these shapes are formed, to visualize how this happens on structures over a length scale of about 100 atoms.”

The research was reported April 8 in the early online edition of the journal Proceedings of the National Academy of Sciences (PNAS). The research was sponsored by the National Science Foundation (NSF).

Controlling the shape of nanoparticles is important in catalysis and other applications that require the use of expensive noble metals such as platinum and palladium. For example, optimizing the shape of platinum nanoparticles can substantially enhance their catalytic activity, reducing demand for the precious material, noted Xia, who is a Georgia Research Alliance (GRA) eminent scholar in nanomedicine. Xia also holds joint appointments in the School of Chemistry and Biochemistry and the School of Chemical and Biomolecular Engineering at Georgia Tech

“Controlling the shape is very important to tuning the activity of catalysts and in minimizing the loading of the catalysts,” he said. “Shape control is also very important in plasmonic applications, where the shape controls where optical absorption and scattering peaks are positioned. Shape is also important to determining where the electrical charges will be concentrated on nanoparticles.”

Though the importance of particle shape at the nanoscale has been well known, researchers hadn’t before understood the importance of surface diffusion in creating the final particle shape. Adding atoms to the corners of platinum cubes, for instance, can create particles with protruding “arms” that increase the catalytic activity. Convex surfaces on cubic particles may also provide better performance. But those advantageous shapes must be created and maintained.

Natural energetic preferences related to the arrangement of atoms on the tiny structures favor a spherical shape that is not ideal for most catalysts, fuel cells and other applications. 

In their research, Xia and his collaborators varied the temperature of the process used to deposit atoms onto metallic nanocrystals that acted as seeds for the nanoparticles. They also varied the rates at which atoms were deposited onto the surfaces, which were determined by the injection rate at which a chemical precursor material was introduced. The diffusion rate is determined by the temperature, with higher temperatures allowing the atoms to move around faster on the nanoparticle surfaces. In the research, bromide ions were used to limit the movement of the added atoms from one portion of the particle to another.

Using transmission electron microscopy, the researchers observed the structures that were formed under different conditions. Ultimately, they found that the ratio of the deposition rate to the diffusion rate determines the final shape. When the ratio is greater than one, the adsorbed atoms tend to stay where they are placed. If the ratio is less than one, they tend to move.

“Unless the atomic reaction is at absolute zero, you will always have some diffusion,” said Xia, who holds the Brock Family Chair in the Department of Biomedical Engineering. “But if you can add atoms to the surface in the places that you want them faster than they can diffuse, you can control the final destination for the atoms.”

Xia believes the research may also lead to improved techniques for preserving the unique shapes of nanoparticles even at high operating temperatures.

“Fundamentally, it is very useful for people to know how these shapes are formed,” he said. “Most of these structures had been observed before, but people did not understand why they formed under certain conditions. To do that, we need to be able to visualize what happens on these tiny structures.”

Xia’s research team also studied the impact of diffusion on bi-metallic particles composed of both palladium and platinum. The combination can enhance certain properties, and because palladium is currently less expensive than platinum, using a core of palladium covered by a thin layer of platinum provides the catalytic activity of platinum while reducing cost.

In that instance, surface diffusion can be helpful in covering the palladium surface with a single monolayer of the platinum. Only the surface platinum atoms will be able to provide the catalytic properties, while the palladium core only serves as a support.

The research is part of a long-term study of catalytic nanoparticles being conducted by Xia’s research group. Other aspects of the team’s work addresses biomedical uses of nanoparticles in such areas as cancer therapy.

“We are very excited by this result because it is generic and can apply to understand and control diffusion on the surfaces of many systems,” Xia added. “Ultimately we want to see how we can take advantage of this diffusion to improve the catalytic and optical properties of these nanoparticles.”

The research team also included Xiaohu Xia, Shuifen Xie, Maochang Liu and Hsin-Chieh Peng at Georgia Tech; and Ning Lu, Jinguo Wang and Professor Moon J. Kim at the University of Texas at Dallas.

 CITATION: Xia, Xiaoho, et al., “On the role of surface diffusion in determining the shape or morphology of noble-metal nanocrystals,” (Proceedings of the National Academy of Science, 2013). http://www.pnas.org/content/early/2013/04/05/1222109110