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a "hydrogel flower" blossoming in lab [Copy link] 中文

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Post time 2017-4-27 16:09:09 |Display all floors
(nature)--Shapeshifting enables a wide range of engineering and biomedical applications, but until now transformations have required external triggers. This prerequisite limits viability in closed or inert systems and puts forward the challenge of developing materials with intrinsically encoded shape evolution. Herein we demonstrate programmable shape-memory materials that perform a sequence of encoded actuations under constant environment conditions without using an external trigger. We employ dual network hydrogels: in the first network, covalent crosslinks are introduced for elastic energy storage, and in the second one, temporary hydrogen-bonds regulate the energy release rate. Through strain-induced and time-dependent reorganization of the reversible hydrogen-bonds, this dual network allows for encoding both the rate and pathway of shape transformations on timescales from seconds to hours. This generic mechanism for programming trigger-free shapeshifting opens new ways to design autonomous actuators, drug-release systems and active implants.


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(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). 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 .



to learn more: www.nature.com/articles/ncomms12919


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