Microstructures Could Have Multiple Medical Applications

Originally Published MDDI May 2004

R&D DIGEST

Erik Swain

A team at the University of Illinois at Urbana-Champaign has created novel three-dimensional microstructures that could have applications in drug delivery, tissue engineering, and diagnostic-sensor technology.

The group has developed an ink that flows easily through microcapillary nozzles and then solidifies. Using a robotic deposition process called direct-write assembly, structures with three-dimensional micron-sized features are created. The team published its findings in the March 25, 2004, issue of the journal Nature. 

Extruded ink is deposited into a reservoir of deionized water and isopropyl alcohol. It is solidified by electrostatic interactions or solvent-quality effects. Dispensed from a syringe by a three-axis micropositioner, the ink leaves the nozzle as a continuous filament that is deposited on a substrate surface to create a two-dimensional pattern. Then the nozzle is raised and another layer is deposited. This continues until a three-dimensional structure is produced. The process works somewhat like a spider spinning a web. The results can be used as bioscaffolds, microfluidic networks, sensor arrays, or templates for photonic materials.

“Because this new ink is based solely on polyelectrolyte mixtures rather than colloidal particles, we are able to produce three-dimensional periodic structures with feature sizes that are 100 times smaller than before,” said lead researcher Jennifer A. Lewis, PhD, a professor of materials science and engineering and of chemical and biomolecular engineering at Illinois. “We started developing polyelectrolyte ink because we ran into issues with nozzle clogging with our colloidal inks. Polyelectrolytes are flexible and finer in size.” Also on the research team are graduate students Gregory Gratson and Mingjie Xu. 

The structures can be so small in part because the size of the ink molecules are only a few nanometers, and because their rapid solidification means wetting and spreading are suppressed, said Lewis. The implication for tissue engineering, Lewis explained, is that “our approach allows exquisite control over the minimum feature size and scaffold architectures.” For drug-delivery applications, direct-write assembly can create three-dimensional film materials “that possess an interconnected porous network that can facilitiate release of higher dosages [than two-dimensional structures can], sustained over similar periods of time,” she added. 

The next phase of research is “pursuing the use of these 3-D scaffolds to template inorganic materials for photonic band-gap and sensor applications,” she said. “Our longer-term interests include the development of bioactive inks for assembling tissue-engineering scaffolds and exploring the use of polyelectrolyte scaffolds for controlled drug release.”

The work has been funded by the U.S. Department of Energy and the U.S. Army Research Office MURI program. 

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