Rewritable and shape-memory soft matter with dynamically tunable microchannel geometry in a biological temperature range

Abstract

Here we present on-demand switchable microchip materials that display potent rewritable and shape-memory properties which are shown to contribute to fluidic control as pumps and valves. Semi-crystalline poly(e-caprolactone) (PCL) was chemically crosslinked to show shape-memory effects over its melting temperature (Tm) because the crosslinking points set the permanent shape and the crystalline domains serve as thermally reversible mobile phase. The Tm was adjusted to nearly biologically relevant temperatures by crosslinking two and four branched PCL macromonomers with different ratios. The Tm decreased proportionally with increasing four branched PCL content because an increase in crosslinking density imposes restrictions on chain mobility and reduces the crystallization. The sample with 50/50 wt% mixing ratio of two- and four-PCL had a Tm around 33 °C. Permanent surface patterns were first generated by crosslinking the macromonomers in a mold, and temporary surface patterns were then embossed onto the permanent patterns. From the cross-sectional profiles, almost 100% recovery of the permanent pattern was successfully achieved after shape-memory transition. The effects of dynamic geometric changes of the shape-memory channels on the microfluidic flow were also investigated and shape-memory channel closing was achieved by the application of heat. The proposed system can be potentially applied as a new class of microfluidic control techniques, which enables portable microfluidic based diagnostic tools for biomedical applications and environmental monitoring allowing on-site analysis.