Self-Alignment of Beads and Cell Trapping in Precipitate Tubes

Propagating reaction fronts allow the formation of materials in self-sustained, steep concentration gradients, which would otherwise rapidly decay. These conditions can result in macroscopic, noncrystallographic structures, such as tubes with large aspect ratios. For hollow silica/Zn(OH)2 tubes, we report the inclusion of diverse mesoscopic building blocks ranging from polymer beads to biological cells. For agarose beads, we observe spontaneous alignment along vertical tracks; the nearly periodic spacing of the beads along these tracks follows a log-normal distribution. We interpret this patterning in terms of hydrodynamic recruitment and discuss similarities to the adhesion dynamics of leukocytes in blood vessels. For diatoms and other cells, we observe novel surface textures, and yeast tagged with a green fluorescent protein shows strong fluorescence activity after trapping. The inclusion of these guest units should improve the possibilities for the application of these tubes in microfluidics and biotechnology.