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.

We introduce a facile approach for the production of gas-filled microcapsules designed to withstand high pressures. We exploit microfluidics to fabricate water-filled microcapsules that are then externally triggered to become gasfilled, thus making them more echogenic. In addition, the gas-filled microcapsules have a solid polymer shell making them resistant to pressure-induced buckling, which makes them more mechanically robust than traditional prestabilized microbubbles; this should increase the potential of their utility for acoustic imaging of porous media with high hydrostatic pressures such as oil reservoirs.

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This paper describes the synthesis, swelling behavior, and applications of well-defined narrowly dispersed zwitterionic (ZW) microgels prepared by dispersion polymerization in aqueous media. Microgel stability was achieved through precise control of the dispersant composition, timely addition of a cross-linker after the nucleation stage, and the utilization of ionic initiators. Dispersion polymerization allowed for incorporation of both hydrophilic and hydrophobic comonomers, including acrylamide (AAm) and dopamine methacrylamide (Dopa-MA). The broad variety of compositions created many opportunities for practical applications such as encapsulation of mineral acids and synthesis of metal nanoparticles. The swelling behavior of ZW-co-AAm microgels in 6 M HCl was particularly interesting: whereas ZW moieties remained stable in contact with the strong acid, the amide groups underwent hydrolysis to carboxylic acid, resulting in microgel contraction and acid release. Zw-co-Dopa-MA microgels were employed as particulate microreactors, where the ZW moieties played a role of an osmotic pump delivering Ag ions to the DOPA moieties for conversion to silver nanoparticles uniformly dispersed inside the microgel particles.

Stable microbubbles can be prepared by evaporation of a liquid core inside an expandable polymeric shell. To control the expansion temperature and the size of resulting microbubbles, we prepared polymeric microcapsules that contain multiple liquids in their core. One-step suspension polymerization allowed for encapsulation of at least two different liquids with near quantitative yield. The liquids may be miscible or immiscible, which directly affects the vapor pressure inside the capsule according to either Raoult's or Dalton's law, respectively. In the case of miscible liquids, e.g., perfluorohexane and perfluoropentane, both the vapor pressure and the expansion temperature vary within a range bounded by the properties of the neat liquids. For immiscible liquids, e.g. perfluoropentane and isopentane, the total vapor pressure is above this range as it equals to a sum of the individual pressures. Due to increased vapor pressure, encapsulation of two immiscible liquids significantly lowers the expansion temperature below the corresponding temperatures observed during expansion of microcapsules with neat perfluoropentane and isopentane cores. The microbubble diameter and shell thickness were controlled within ca. 10-50 μm and 0.1-3 μm, respectively, by varying the fractions and vapor pressure of the core fluids. We also showed that the effect of core composition on the expansion temperature was more significant than the effect of the shell thickness. Furthermore, one of the encapsulated materials may carry additional functions including imaging contrast, catalysis, and density compensation. To that end, these designer microcapsules may find applications in the fields of drug delivery, acoustic imaging, drilling, and self-healing materials.