Portland, Ore. -- Microfluidics devices sense, search and sort through molecules by channeling them down nanoscale pipes that have been etched from polymer substrates. Unfortunately, the tiny channels can become clogged when biological materials stick to them, degrading their performance until they are disassembled for cleaning. Now researchers at the Rensselaer Polytechnic Institute believe they have a better solution--a material that optically switches from slippery to sticky.
Exposed to ultraviolet (UV) light, the polymer dislodges anything stuck to its surfaces by becoming more slippery than teflon, thereby enabling even the most clogged microfluidic channels to be flushed clean. The researchers also predict that the polymer will be useful for filtering specific proteins from biological fluids, which often clog the pores of conventional filters.
Polymer membranes are already in common use as biological filters and for microfluidic devices, but their lifetime is often short as increased usage clogs their pores. To solve the problem, RPI professor Georges Belfort began investigating polymers that can change their surface characteristics so that stuck materials can be flushed out without requiring harsh chemical solvents or complete disassembly of the device for cleaning.
Belfort was assisted by Arpan Nayak, a graduate student in chemical and biological engineering, and Hongwei Liu, a post-doctoral research associate in chemical and biological engineering at RPI (Troy, N.Y.).
The new material is based on an old standby--PES (poly ether sulfon)--but with its surface impregnated with the light-switchable molecule called spiropyran. Spiropyran is a molecular switch that can be changed from a passive, uncharged form to an active, strongly polarized molecule when exposed to UV.
When switching from its nonpolar to its polarized form, any materials previously sticking to it can be easily flushed away with water, according to the researchers. A second UV exposure switches it back to the nonpolar form, which is also transparent (compared to the reddish color of the polarized form), allowing easy visual confirmation of its state.
The Rensselaer Polytechnic Institute has patented the procedure of grafting the spiropyran molecules onto the PES polymer. Besides lab-on-a-chip applications, the researchers also expect the material to be used for biological filter membranes and for releasing drugs only after they have arrived at their target in the body.
In microfluidic devices, the material could be fabricated into nanoscale valves that either allow the passage of individual cells, or block their passage by making them stick to the valve's aperture.
Funding was provided by the U.S. Department of Energy, the National Science Foundation and Rensselaer Polytechnic Institute's Center for Biotechnology and Interdisciplinary Studies. n