Building 3-D particles with light
Engineers at the Massachusetts Institute of Technology (MIT) have used ultraviolet light to create mass-producing 3-D microparticles that could be used for 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.' This new technique allows an excellent control over the size, shape and texture of the particles and also allows researchers to design particles with specific chemical properties, such as porosity. But read more...
You can see above differential interference contrast (DIC) images of the particles created by the researchers after they have been suspended in ethanol. "The phase-mask-induced pattern is clearly visible in the close-up DIC and SEM [Scanning Electron Microscope] images. These monodisperse, 60-mm particles were synthesized at a rate of 10000 per hour.(Credit: Patrick Doyle research group at MIT).
This project has been led by Patrick Doyle, an MIT associate professor of chemical engineering, and several members of his research group. Interestingly, Doyle is associated with the Institute For Soldier Nanotechnologies at the MIT. MIT materials scientist Ned Thomas, head of the department of materials co-led the project with the collaboration of the members of his research group.
All these researchers started with a method that Doyle and his students used in 2006 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."
In an article in Technology Review, "Mass-Producing 3-D Particles," Peter Fairley gives additional details, focusing on Thomas's views. "Thomas says that the 3-D-structured particles have potential to become ultrafast, ultrasensitive biosensors. They're sensitive because they have plenty of surface area to which DNA or other biotags can attach. With conventional solid microarrays and particles, biotags only adorn the probe's surface. In contrast, biotags can attach inside the latticework particles, increasing the number of target molecules that bind to a particle, and therefore producing a more intense fluorescent signal. "The particle, of course, is transparent, so if the fluorescence is occurring in the center of the particle, it's still visible outside," says Thomas. He adds that he and his team have demonstrated about a 10-fold signal boost so far, and he predicts that they will optimize the lattice to yield at least a 10,000-fold signal boost."
According to the MIT news release, many applications for these 3-D particles are possible, including 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."
But once again, Technology Review provides more details. "Looking beyond biosensors, Thomas envisions applications that dynamically exploit the particles' mechanical properties. Particles with narrow scaffolding, for example, should be capable of squashing down to squeeze into tight spaces, much as fresh red blood cells squeeze into the tightest capillaries. He also imagines that the latticework particles could beget tunable sieves for handling and sorting much smaller nanoparticles by using polymers that swell and seal up the lattice in response to external conditions such as acidity. 'If you were trying to choke off transport of virus particles, for example, this would work nicely,' says Thomas. 'That's one of our dreams.'"
For more information, this research work has been published online on October 8, 2007 in the Angewandte Chemie International Edition journal under the title "A Route to Three-Dimensional Structures in a Microfluidic Device: Stop-Flow Interference Lithography" (Volume 46, Issue 47, Pages 9027-9031) Here are two links to the abstract and to the full text of this article (PDF format, 6 pages, 705 KB) from which the above image has been extracted.
Sources: MIT news release, December 3, 2007; Peter Fairley, Technology Review, December 3, 2007; and various websites
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