[Editors] MIT sculpts 3D particles with light

[Elizabeth Thomson]

MIT News Office
Massachusetts Institute of Technology
Room 11-400
77 Massachusetts Avenue
Cambridge, MA  02139-4307
Phone: 617-253-2700
http://web.mit.edu/newsoffice/www

======================================
MIT sculpts 3D particles with light

--Medical applications could include diagnostics, tissue engineering

======================================

For Immediate Release
MONDAY, DEC. 3, 2007
Contact: Elizabeth A. Thomson, MIT News Office -- Phone: 617-258-5402  
-- Email: thomson at mit.edu

PHOTO AVAILABLE

CAMBRIDGE, Mass.--MIT engineers have used ultraviolet light to sculpt  
three-dimensional microparticles that could have many applications in  
medical diagnostics and tissue engineering. For example, they could  
be designed to act as probes to detect certain molecules, such as  
DNA, or to release drugs or nutrients.

The new technique offers unprecedented control over the size, shape  
and texture of the particles. It also allows researchers to design  
particles with specific chemical properties, such as porosity (a  
measure of the void space in a material that can affect how fast  
different molecules can diffuse through the particles).

“With this method, you can rationally design particles, and precisely  
place chemical properties,” said Patrick Doyle, associate professor  
of chemical engineering. Doyle is one of the authors of a paper on  
the work that will appear in the Dec. 3 issue of the journal  
Angewandte Chemie, published by the German Chemical Society.

The research team started with a method that Doyle and his students  
reported in a 2006 issue of Nature Materials to create two- 
dimensional particles. Called continuous flow lithography, this  
approach allows shapes to be imprinted onto flowing streams of liquid  
polymers. Wherever pulses of ultraviolet light strike the flowing  
stream of small monomeric building blocks, a reaction is set off that  
forms a solid polymeric particle. They have now modified that method  
to add three-dimensionality.

This process can create particles very rapidly: Speeds range from  
1,000 to 10,000 particles per second, depending on the size and shape  
of the particles. The particles range in size from about a millionth  
of a meter to a millimeter.

The team's new process works by shining ultraviolet light through two  
transparency masks, which define and focus the light before it  
reaches the flowing monomers. The first mask, which controls the size  
and shape of the particles, is part of the technique reported last  
year by Doyle and his students. The second mask, which is based on  
MIT professor Edwin Thomas' work in multibeam lithography, adds three- 
dimensional texture and other physical traits, such as porosity.

The collaboration sprung from a conversation between Ji-Hyun Jang, a  
postdoctoral associate in Thomas' lab, and Dhananjay Dendukuri, a  
recent Ph.D. recipient in Doyle's lab, who are also authors on the  
paper.

“It's very easy to integrate the (second) phase mask into the  
microfluidic apparatus,” said Thomas, Morris Cohen Professor of  
Materials Science and Engineering and head of the Department of  
Materials Science and Engineering. “Professor Doyle was controlling  
the overall shape, and now what we're doing is controlling these  
inner labyrinth networks.”

Adding inner texture is desirable because it increases the particles'  
surface-to-volume ratio, which means if the particle is loaded with  
probes, there are more potential binding sites for target molecules.

In a paper published in Science earlier this year, Doyle and MIT  
graduate student Daniel Pregibon showed that the particles can be  
used as probes to identify DNA and other molecules.

Other applications for the particles include tissue engineering. For  
example, they could form a scaffold that would both provide  
structural support for growing cells and release growth factors and  
other nutrients. The particles can be designed so diffusion occurs in  
a particular direction, allowing researchers to control the direction  
of nutrient flow.

Alan Hatton, the Ralph Landau Professor of Chemical Engineering  
Practice, is also an author on the paper.

This research was funded by the U.S. Army Research Office through the  
MIT Institute for Soldier Nanotechnologies.

--END--

Written by Anne Trafton, MIT News Office