US scientists have developed a microfluidic method for making complex 3D microparticles they claim could be used in tissue engineering.

Patrick Doyle and colleagues at the Massachusetts Institute of Technology, Cambridge, call their method Lock Release Lithography (LRL). They shone UV light through transparent masks to polymerise monomers in a microchannel into different shapes. Structures hanging down from the channel's ceiling then locked the particles in place and made indents in the particles' structures. By applying high pressure, the team released the dish-like structures and collected them. They also made particles with pillars on their surfaces using a channel with indents in its ceiling.

Fluorescence images of microparticles with different complex shapes

Doyle demonstrated that the method can be used to make particles made of two different monomers. He polymerised the first monomer type and locked the structure in place. He then introduced the second monomer type into the channel and used light to polymerise it to the existing structure, making patterned particles with intricate shapes, interior features and borders by changing the masks.

'This is a very impressive approach towards truly complex particles. While a range of different asymmetric and multifunctional particles have been made in recent years, these particles are, without any doubt, outstanding,' says Joerg Lahann, a specialist in microparticles at the University of Michigan, Ann Arbor, US.

'We believe that LRL will provide a powerful means to mass-produce functional units in areas such as microfluidic operation, filtration and tissue engineering,' says Doyle. 'The length scales in LRL are ideally suited to generating tissue engineering mesocontructs, each containing multiple cell lines that are precisely positioned within the particle.'

Currently, the particle size is limited to the micrometre range but Doyle says he plans to extend the technique to make other particle sizes.

Michael Brown

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