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(ε-caprolactone) (PCL) was chemically crosslinked to show shape-memory effects over its melting temperature (T_m) because the crosslinking points set the permanent shape and the crystalline domains serve as thermally reversible mobile phase. The T_m was adjusted to nearly biologically relevant temperatures by crosslinking two and four branched PCL macromonomers with different ratios. The T_m 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 T_m 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.