The particles are made of two distinctly
different materials: polymers called polyNIPAAm and sodium alginate,
used in drug delivery. The two are combined to manufacture so-called
Janus particles – named for the Roman god with two distinctly different
faces. Like the Roman deity, the particles have two distinctly different
sections, a design trait that makes them potentially useful for a host
of medical and research applications, said Arezoo Ardekani, an assistant professor of mechanical engineering at Purdue University.
A mixture of sodium alginate and polyNIPAAm is
formed into uniform droplets using microfluidics, a technology for
controlling minute micro-quantities of fluids with tiny tubes and
channels. The droplets are injected into a "collecting solution"
containing glycerol and barium acetate. Barium ions diffuse into the
resulting droplets, causing them to "crosslink," or reinforce with
chemical bonds, and jellify into squishy mushroom-shaped microgel
particles. The particles can be induced to deform into different shapes
by varying the concentration of glycerol in the collecting solution;
microgels also can "phase separate," producing Janus particles.
"The novelty of this work is that it is very
simple to generate different shapes just by changing the concentration
of glycerol," Ardekani said.
Findings are detailed in a research paper
published in January in the journal Langmuir. The paper was authored by
Ardekani, her postdoctoral research associate Yuandu Hu, graduate
student Shibo Wang and Harvard University postdoctoral research
associate Alireza Abbaspourrad.
The researchers found that varying the
concentration of glycerol in the collecting solution alters the shape,
surface roughness and physical characteristics of the particles,
including color and optical properties, making them potentially useful
for technologies such as optical switches.
Having the ability to control the shapes of
particles could enable researchers to create a variety of drug-delivery
vehicles, while Janus particles hold promise for a number of potential
applications. For example, one part might be hydrophobic and the other
hydrophilic, allowing them to be positioned and manipulated for tissue
engineering or co-delivery of hydrophobic and hydrophilic drugs.
Magnetic nanoparticles might be embedded into Janus particles during the
fabrication process, making it possible to control them with magnetic
fields as delivery vehicles and also for magnetically controlled optical
switches. Cells also might be reversibly encapsulated into the
microgels for tissue engineering purposes - the cells can be cultured
within microgels and easily manipulated into different tissue
structures, after which it is possible to dissolve the gels and release
the cells; these gels also might be designed to respond to external
stimuli such as temperature or pH.
The work was supported by the National Science Foundation. Scanning electron microscopy was performed at the University of Notre Dame's Integrated Imaging Facility.
Writer: Emil Venere, 765-494-4709, venere@purdue.edu
Source: Arezoo Ardekani, ardekani@purdue.edu