Figure 1

Mechanical characterization of polyacrylamide (PAAm) beads. (a) Size distribution of Cy3 conjugated Poly-L-lysine (PLL-Cy3) functionalized PAAm beads (n = 1339) determined by a macro implemented on Fiji²⁸. Inset left: microscopic image of the bead production by microfluidic flow-focusing. Inset right: confocal microscopy section showing PAAm beads (magenta) functionalized with PLL-Cy3. Scale bar, 15 µm. (b) Young’s modulus of PAAm beads as determined by AFM-based indentation after PAAm polymerization (w/o NHS), after NHS ester modification (w NHS) and after PLL-Cy3 functionalization (n = 50, temperature = 24 °C). (c) Young’s modulus stability with increasing temperature. Identical PLL-Cy3 functionalized PAAm beads (n = 25) were measured for each condition. (d) Stress-strain relation of PLL-Cy3 functionalized PAAm beads during osmotic compression. The dotted line indicates a linear fit that is used for the determination of the bulk modulus. Results are represented as mean ± SD. Inset: confocal microscopy images of a PAAm bead (magenta) in dextran solution (FITC label, green) confirming that dextran molecules (hydrodynamic radius: 27 nm) are not able to enter the polymer network (mesh size: 21 nm²⁸). Scale bar, 20 µm. (b,c) The boxes are determined by the 25^th and 75^th percentiles. The mean is shown as filled square symbol, the median as straight line, the whiskers represent the standard deviation and the 1^st and 99^th percentiles are indicated by crosses. (b–d) Insets are a schematic representation of the applied methods. A homogeneous osmotic pressure compressing the bead and a spherical cantilever tip indenting the PAAm bead, respectively.