Making Complex Microparticles

Polymer microparticles could deliver drugs to specific targets within the body and could be used to build scaffolds for growing stem cells into new tissue. Researchers would like to be able to make such microparticles with complex three-dimensional shapes to improve their targeting capabilities and to control the timing of how drugs get released. It would also allow for building tissue scaffolds with different geometries. Now a team of researchers has developed an easy and efficient method for making such complex 3-D microparticles in large volumes (ACS Appl. Mater. Interfaces 2015, DOI: 10.1021/acsami.5b01955).

Existing high-volume methods of building microparticles either can build only a limited variety of 3-D shapes or offer little ability to control the particles’ shapes in the third dimension. The new method, developed by Chang-Soo Lee of South Korea’s Chungnam National University and colleagues, uses various fluids to tune the shape of microsized molds. They say the method is simpler and produces a wider variety of geometries.

The team started by etching shapes a few tens of micrometers in size into silicon using conventional lithography processes. They then poured polydimethylsiloxane (PDMS) over the silicon and cured it to create a micromold they could simply peel off. The researchers then filled the mold with polyethylene glycol diacrylate (PEG-DA), a material that would harden into a solid polymer when exposed to ultraviolet light.

To further control the particle shapes, they added one of several liquids on top of the PEG-DA before curing it with UV light. For example, to make particles with a dome-shaped top, they added paraffin oil, which seeped part of the way down the side walls of the mold, pushing the PEG-DA upward slightly. They also used PDMS-based fluids that swelled the walls of the mold, which changed the particle shapes more dramatically. Once the material reached its desired shape, the team cured it with UV light, creating solid particles.

Liang-Yin Chu, a professor of chemical engineering at Sichuan University, in China, calls this work “a clever and simple method to fabricate microparticles with versatile and complex 3-D structures and multiple compositions.” He says it should prove efficient, though it may be limited in the types of materials that can be used. For example, the PDMS molds might not be stable if the polymers require organic solvents.

Nguyen Thanh, who does microparticle research at Massachusetts Institute of Technology, says 3-D printing can make even more complex shapes, though it’s slower. But he worries that the new method could have another limitation: UV-curable polymers may not be compatible with biomedical applications because they haven’t been approved by the Food & Drug Administration.