Colloidal inks form self-supporting
scaffolds through robocasting
James E. Kloeppel, Physical Sciences Editor
(217) 244-1073; kloeppel@uiuc.edu
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Photo by Bill
Wiegand
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Jennifer Lewis, professor of materials science and engineering, and
colleagues have devised a new way to assemble complex, three-dimensional
structures from specially formulated colloidal inks that could find use
in advanced ceramics, sensors, composites, catalyst supports, tissue
engineering scaffolds and photonic materials. |
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CHAMPAIGN, Ill. — A new way to assemble
complex, three-dimensional structures from specially formulated colloidal inks could find
use in advanced ceramics, sensors, composites, catalyst supports, tissue
engineering scaffolds and photonic materials.
As it was reported in the July 9 issue of the journal Langmuir, scientists have
developed colloidal, gel-based inks that form self-supporting features through a
robotic deposition process called robocasting. A computer-controlled robot
squeezes the ink out of a syringe, almost like a cake decorator, building the
desired structure layer by layer.
"Our goal is to make designer materials that can't be made by conventional
forming techniques," said Jennifer Lewis, a professor of materials science and
engineering and of chemical engineering at the University of Illinois at
Urbana-Champaign.
The work is a collaboration between Lewis, Illinois graduate student James Smay,
and Joseph Cesarano, a staff scientist at the U.S. Department of Energy’s Sandia
National Laboratories in Albuquerque, N.M.
Cesarano pioneered the concept of robocasting several years ago and implemented
it as an alternative "rapid prototyping" method for producing ceramic
components. The Illinois-Sandia group is advancing the technique to finer scales
and designing special inks that can form self-supporting features.
"The directed assembly of fine-scale, three-dimensional structures containing
spanning elements required the development of concentrated colloidal, gel-based
inks," Lewis said. "These inks must first flow through a very fine deposition
nozzle and then quickly 'set' to maintain their shape while simultaneously
bonding to the underlying layer."
The researchers have created structures with features as small as 100 microns
(about the diameter of a human hair) and have spanned gaps as large as 2
millimeters.
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| (Courtesy of Jennifer Lewis
Copyright: American Chemical Society) |
The elastic properties and the viscous response of the ink can be "tuned" by
tailoring the strength of the interparticle attractions, Lewis said. Because of
the dynamic nature of the resulting gel, the particle network forms very quickly
after the ink is pushed through the syringe, providing the desired shape
retention.
Through careful control of colloidal forces, the researchers not only can
produce complex shapes that can’t be made by conventional molding or extrusion
processes, they also can build in complexity with respect to chemical
composition.
"The robotic deposition equipment has the capability of handling multiple inks
and dispensing them simultaneously," Lewis said. "As the relative rates of
deposited ink are regulated, structures can be built that have compositional
variations in them."
Inks are housed in separate syringes mounted on the robotic deposition apparatus
and can be mixed or deposited independently. The ink exits the nozzle as a
continuous, rod-like filament that is deposited onto a moving platform, yielding
a two-dimensional pattern. After a layer is generated, the stage is raised and
another layer is deposited. This process is repeated until the desired structure
is produced.
The machine’s motion is controlled by a computer program called RoboCAD,
developed by Smay. The software allows users to rapidly design and build complex, three-dimensional structures by simply designing layers as
two-dimensional drawings.
"Ink can be made from nearly any particulate material that can be suspended in
solution, as long as the interparticle forces can be tuned to yield the desired
viscoelastic response," Lewis said. "We have made inks out of silica, alumina,
lead zirconate titanate, and hydroxyapatite (the basic inorganic constituent of
bone) colloidal particles. We also can deposit polymeric, metallic, and
semiconducting colloidal inks."
The National Science Foundation and the Department of Energy funded this work.
Original article: click
here
