New method for the production of defined
microparticles with three-dimensional nanopatterns.
Many scientists are working feverishly to develop reliable but simple
methods for the production of tiny particles with defined size and shape
that are covered with special regular patterns in two or three
dimensions and at both the nano- and the microscale. These miniature
objects have countless applications in modern technology, from
diagnostic systems to the generation of artificial tissues to improved
data storage. A team headed by Edwin L. Thomas and Patrick S. Doyle at
MIT in Cambridge, Massachusetts (USA) has now developed a new method for
the large-scale synthesis of three-dimensionally patterned polymer
particles with morphological characteristics in the submicrometer range.
As described in the journal Angewandte Chemie, with the use of stop-flow
interference lithography, the team has even been able to produce Janus
particles, microparticles with two chemically different hemispheres.
�Our new method is a combination of phase mask interference
lithography and mirofluidic flow lithography, unifying the strengths
of these two methods,� explain the researchers. Liquid precursors of a
polymer whose formation is induced by light are introduced into a
microfluidic system (a system of channels that are just a few
micrometers wide). The bottom portion of the device is a phase mask
with a periodic surface structure. This arrangement is irradiated
through a transparency mask that defines the shape of the resulting
particles. In a test sample these were triangles with sides of 60 �m.
Once the parallel light rays pass through the strictly periodic
surface structure of the phase mask, the result is a complex
three-dimensional distribution of light intensity within the liquid (interference).
In regions of high intensity, the polymer precursors are cross-linked
to form three-dimensional structures in a solid hydrogel. In this way,
the researchers were able to give the triangular particles a knobby,
lattice-like structure.
Because this method works continuously, it can attain a very high
throughput: Liquid flows in and polymerizes to form particles that are
immediately rinsed away when the next portion of liquid follows�all in
less than a second. In contrast to other techniques, the liquid does
not need to be deposited in an even layer on a support and developed
stepwise.
In addition, within a microchannel, it is possible to allow two
different liquids to flow side by side without mixing. If the
transparency mask is adjusted so that the light irradiates a region
around the boundary between the two liquids, the process results in
Janus particles with two chemically different hemispheres.
Further Information and Source:
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Ji-Hyun Jang, Dr., Dhananjay Dendukuri, Dr., T. Alan Hatton, Prof.,
Edwin L. Thomas, Prof., Patrick S. Doyle, Prof.: A Route to Three-Dimensional Structures in a Microfluidic Device:
Stop-Flow Interference Lithography.
In: Angewandte Chemie International Edition 2007, 46,
9027�9031; doi:
10.1002/anie.200703525
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Homepage of
Edwin L. Thomas, Massachusetts Institute of Technology,
Cambridge (USA)
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Source:
Angewandte
Chemie International Edition, press release no 46/2007
