Fig. 4: Humanoid robots capable of expressing emotional body language, facilitated by context-aware dynamic alignment strategies to minimize hydrodynamic coupling.

a In close proximity of particles (separation in the range of the particles’ size), hydrodynamic coupling may occur and impact the assembly. This can be resolved via context-aware decisions to switch from pushing to pulling. We observe approach and separation to be stable via pushing and pulling fields respectively, while both the separation via pushing flow fields, and the approach via pulling fields yield unstable repulsive and unstable attractive convergence dynamics, respectively (see also Supplementary Video 6). Scale bars: 10 µm. b Statistics of convergence dynamics showing context-aware decisions (‘push or pull’) to be most efficient and reliable. Time of arrival is defined as the time from the start of the alignment until the average distance of both particles to their targets is decreased to 2 µm. In the bar plot the time of arrival is averaged over 10 or 11 repetitions each, error bars show the standard deviation. c, d Context-aware decisions might also prevent oscillatory stalling behaviors in confined spaces (see Supplementary Video 7). Scale bar: 15 µm. e Humanoid micro-robots can be assembled and animated sufficiently accurate to express emotional body language (see Supplementary Videos 8 and 9). Differences in perceived gender or emotion are caused by changes in the body anatomy (female vs. male) and by subtle changes of the dynamic motion patterns of the figures²⁸ (e.g., stiffer body movement for nervous vs sad, compare video). Scale bars: 15 µm