Figure 4. Sequential recovery of dormant shapes.

(a) Programming protocol: a sample is deformed and held in air to allow partial evaporation of water. An outer skin with low water concentration and high H-bonding strength forms upon drying and fastens the deformed shape. (b) Three angles programmed in air for different times (1:10 min; 2:30 min; 3:45 min) undergo spontaneous unfolding with different delay times (pH 3, 22 °C) (Supplementary Movie 2). The error bars indicate the standard deviation for the average of three separate experiments. (c) Upper panel: three petal-shape sheets of different sizes are cut from 50:50 MAAc-co-DMAA gel (70 wt% water) and coloured for easy distinction. The petals are then assembled and folded in air for different times (1:1 min; 2:10 min; 3:30 min) to create a dormant ‘bud'. Lower panel: sequential ‘blooming' after immersing the programmed ‘bud' in pH 3 buffer at 22 °C (Supplementary Movie 4).