Extended Data Fig. 4: Cross-linked actin networks promote contraction integrity.
From: 3D printed protein-based robotic structures actuated by molecular motor assemblies
a.) Schematic designs of pillar rings with different number of pillars. b.) Z projection of pillar rings without actin and myosin network. Scale bar, 10 µm. c.) Contraction of pillar rings coated with actin filaments. Scale bar, 10 µm. Pillar contraction started to differentiate on the ring with 10 pillars. d.) Contractions of pillar rings coated with actin network that was cross-linked by neutravidin (2.25 nM). Scale bar, 10 µm. Compared with the pillar rings coated with the actin filaments, the neutravidin cross-linked actin network could enhance the contraction integrity of pillar rings. e-g.) Neutravidin concentrations influence f.) the actin network density and g.) the contractions of pillar rings. Plot in f. demonstrates the relative fluorescence intensity of Alexa Fluor 647 phalloidin labeled actin networks (inner ring areas) that are crosslinked with different concentration of neutravidin. Data points are shown as mean ± s.d. (n = 6). The concentrations of the cross-linker neutravidin were titrated from 1.12 nM (1:40), 2.25 nM (1:20), to 4.5 nM (1:10) in order to optimize the contractility of actomyosin on the printed microstructures. The densities of actin networks on pillar rings were increased when increasing cross-linker concentrations. However, a reverse trend of pillar displacements was noticed in g. when the neutravidin concentration was increased to 4.5 nM, meaning the contraction was inhibited by the high cross-linking degree (neutravidin: biotin-actin ratio of 1:10 in our system). As such, we chose the 2.25 nM neutravidin concentration for further experiments, as this cross-linking condition best contractility was observed. Box plot in g: lines are median, box limits are quartiles 1 and 3, whiskers are 1.5×interquartile range and points are outliers.
