Engineers at the Massachusetts Institute of Technology (MIT) have shown that ultraviolet light can be used to sculpt three-dimensional microparticles, which may have many applications in medical diagnostics and tissue engineering.
The researchers say that their technique may give microparticles a design that is useful for probes to identify DNA and other molecules, or to release medicines or nutrients.
They say that the new technique offers unprecedented control over the size, shape and texture of the particles, and allows the designing of 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.
The research team started with a method called continuous flow lithography, which Doyle and his students reported in a 2006 issue of Nature Materials to create two-dimensional particles. 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.
The researchers have now modified the method to add three-dimensionality. The new 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.
Such particles range in size from about a millionth of a meter to a millimetre, say the researchers.
The new process works 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's work in multi-beam lithography, adds three-dimensional texture and other physical traits, such as porosity.
"It's very easy to integrate the (second) phase mask into the microfluidic apparatus. Professor Doyle was controlling the overall shape, and now what we're doing is controlling these inner labyrinth networks," said Prof. Edwin Thomas, Morris Cohen Professor of Materials Science and Engineering and head of the Department of Materials Science and Engineering.
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.
The study has been published in the journal Angewandte Chemie, published by the German Chemical Society.