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Foams made of immiscible polymer blends have attracted great interest in both academia and industry, because of the integration of desirable properties of different polymers in a hybrid foam. However, the foamability and end-use properties are hampered because of the poor interfacial strength within the immiscible blends. Furthermore, few investigations have been carried out on the mechanisms by which interfacial strength and structure affect the foamability of polymer blends. In this work, two different reactive interfacial compatibilizers, i.e., poly(styrene

Bilayer hydrogels are attracting tremendous attention for their capability to integrate several different functions on the two sides of the gel, that is, imparting the gel with Janus characteristics, which is highly desired in many engineering and biomedical applications including soft actuators, hydrogel patches, and wearable electronics. However, the preparation process of the bilayer materials usually involves several complicated steps and is time-consuming, while the interfacial bonding is another main concern. Here, a simple and versatile method is proposed to obtain bilayer hydrogels within just one step based on the method of introducing viscosity contrast of the precursors for different layers. The bilayer structure can be well maintained during the whole preparation process with a constrained interfacial molecular exchange to ensure the strong bonding strength. The key requirements for forming distinct bilayer structures in situ are studied and discussed in detail. Bilayer hydrogels with different chemical designs are prepared via this strategy to tailor the good distribution of desired functions for soft actuators, wound healing patches, and wearable electronics. We believe that the strategy illustrated here will provide new insights into the preparation and application of bilayer materials.

Development of smart switchable surfaces to solve the inevitable bacteria attachment and colonization has attracted much attention; however, it proves very challenging to achieve on-demand regeneration for noncontaminated surfaces. We herein report a smart, host-guest interaction-mediated photo/temperature dual-controlled antibacterial surface, topologically combining stimuli-responsive polymers with nanobactericide. From the point of view of long-chain polymer design, the peculiar hydration layer generated by hydrophilic poly(2-hydroxyethyl methacrylate) (polyHEMA) segments severs the route of initial bacterial attachment and subsequent proliferation, while the synergistic effect on chain conformation transformation poly(N-isopropylacrylamide) (polyNIPAM) and guest complex dissociation azobenzene/cyclodextrin (Azo/CD) complex greatly promotes the on-demand bacterial release in response to the switch of temperature and UV light. Therefore, the resulting surface exhibits triple successive antimicrobial functions simultaneously: (i) resists ∼84.9% of initial bacterial attachment, (ii) kills ∼93.2% of inevitable bacteria attack, and (iii) releases over 94.9% of killed bacteria even after three cycles. The detailed results not only present a potential and promising strategy to develop renewable antibacterial surfaces with successive antimicrobial functions but also contribute a new antimicrobial platform to biomedical or surgical applications.

Numerous efforts to fabricate antimicrobial surfaces by simple yet universal protocols with high efficiency have attracted considerable interest but proved to be particularly challenging. Herein, we designed and fabricated a series of antimicrobial polymeric coatings with different functions from single to multiple mechanisms by selectively utilizing diethylene glycol diglycidyl ether (PEGDGE), polylysine, and poly[glycidylmethacrylate-co-3-(dimethyl(4-vinylbenzyl)ammonium)propyl sulfonate] (poly(GMA-co-DVBAPS)) via straightforward mussel-inspired codeposition techniques. Bactericidal polylysine endowed the modified surfaces with a high ability (∼90%) to kill attached bacteria, while PEGDGE components with unique surface hydration prevented bacterial adhesion, avoiding the initial biofilm formation. Moreover, excellent salt-responsive poly(GMA-co-DVBAPS) enabled reactant polymeric coatings to change chain conformations from shrinkable to stretchable state and subsequently release >90% attached bacteria when treated with NaCl solution, even after repeated cycles. Therefore, the obtained polymeric coatings, polydopamine/poly(GMA-co-DVBAPS) (PDA/PDV), polydopamine/polylysine/poly(GMA-co-DVBAPS) (PDA/l-PDV), and polydopamine/polylysine/poly(GMA-co-DVBAPS)/diethylene glycol diglycidyl ether (PDA/l-PDV-PEGDGE), controllably realized functions from single and dual to multiple antimicrobial mechanisms, as evidenced by long-term antifouling activity to bacteria, high bactericidal efficiency, and salt-responsive bacterial regeneration performance with several bacterial killing-release cycles. This study not only contributes to mussel-inspired chemistry for polymeric coatings with controllable functions but also provides a series of reliable and highly efficient antimicrobial surfaces for potential biomedical applications.

DNA nanotechnology is powerful in constructing programmable nanostructures with distinct dimensions, sizes, and shapes. However, natural DNA molecules are prone to nuclease degradation, thus limiting the in vivo applications of such DNA nanostructures. 2'-Fluoroarabinonucleic acid (FANA) is a chemically modified oligonucleotide with similar base pairing properties to DNA and exhibits superior physical and chemical stabilities. In this work, FANA molecules were used to construct double crossover nanostructures, and it was demonstrated that incorporation of FANA conferred nucleic acid nanostructures with increased thermal stability and stronger nuclease resistance. More importantly, FANA nanostructures were able to maintain the structural integrity in the strongly acidic environment (pH 1.2). Last, such FANA nanostructures functioned well in acting as stable carriers of small-molecule cargoes for cellular delivery in simulated gastric fluid, while the DNA counterparts were mostly degraded. Collectively, these results demonstrated that FANA self-assembly was not only a substantial complement to the structural DNA nanotechnology but also an appealing molecular tool for in vivo biomedical applications.

Recently, the antisoiling performances of superhydrophobic (SH) surfaces have received much attention due to their potential applications in self-cleaning photovoltaic glass and other surfaces without the need to be rinsed with water. In this work, we systematically compared the antisoiling performances of lotus leaf and other plant leaves by first drying them in the shade and then placing them outdoors in a slight breeze for 1-2 months. The results show that after being dried in the shade, the lotus leaf and the canna leaf retain their SH properties, comparable with their fresh states. The firmiana leaf is still hydrophilic. However, when the leaves are exposed to rain, no rain drops adhere to the surface of the lotus leaf but many droplets adhere to the canna leaf. Furthermore, after being incubated outdoors in the absence of rain for 1 month, the lotus leaf retained its SH properties, the canna leaf was no longer SH, and the firmiana leaf became more hydrophilic. SEM imaging with EDS and elemental mapping all confirmed that after outdoor exposure for 1-2 months, only a small amount of dust was found on the lotus leaf but a significant amount of dust was present on the canna leaf, with even more on the firmiana leaf. These results confirm that the lotus leaf has excellent antisoiling performance. The low interactions between the lotus leaf surface and the dust particles are most likely responsible for this unique property. On the contrary, the canna leaf, and especially the firmiana leaf, do not possess this property because neither their surface microstructures nor their surface free energies are favorable to reduce interactions between the leaf surface and dust particles. This study will be helpful in designing and preparing a surface with antisoiling performance.

Continuously growing interest in the controlled and tunable transport or separation of target molecules has attracted more attention recently. However, traditional “on–off” stimuli-responsive membr...

Bilayer hydrogels are one of the most promising materials for use as soft actuators, artificial muscles, and soft robotic elements. Therefore, the development of new and simple methods for the fabrication of such hydrogels is of particular importance for both academic research and industrial applications. Herein, a facile, one-pot, and one-step methodology was used to prepare bilayer hydrogels. Specifically, several common monomers, including N-isopropyl acrylamide, acrylamide, and N-(2-hydroxyethyl)acrylamide, as well as two salt-responsive zwitterionic monomers, 3-(1-(4-vinylbenzyl)-1H-imidazol-3-ium-3-yl)propane-1-sulfonate (VBIPS) and dimethyl-(4-vinylphenyl)ammonium propane sulfonate (DVBAPS), were chosen and employed with different combinations and ratios to understand the formation and structural tunability of the bilayer hydrogels. The results indicated that a salt-responsive zwitterionic-enriched copolymer, which could precipitate from water, plays a dominant role in the formation of the bilayer structure and that the ratio between the common monomer and the zwitterionic monomer had a significant effect on the structure. Due to the salt-responsive properties of polyVBIPS and polyDVBAPS, the resultant bilayer hydrogels exhibited excellent bidirectional bending properties in response to the salt solution. With the optimal monomer pair and ratio determined, the bend of the hydrogel could be reversed from ∼-360 to ∼266° in response to a switch between water and a 1.0 M NaCl solution. Additionally, this method was further used to fabricate small-scaled patterns with structural and compositional distinction in two-dimensional hydrogel sheets. These two-dimensional hydrogel sheets exhibited complex and reversible three-dimensional shape transformations due to the different bending behaviors of the patterned hydrogel stripes under the action of an external stimulus. This work provides greater insight into the mechanism of the one-step, one-pot method fabrication of bilayer hydrogels, demonstrates the ability of this method for the preparation of small-scale patterns in hydrogel sheets to endow the complex with a three-dimensional shape transformation capability, and hopefully opens up a new pathway for the design and fabrication of smart hydrogels.

Development of smart soft actuators is highly important for fundamental research and industrial applications but has proved to be extremely challenging. In this work, we present a facile, one-pot, one-step method to prepare dual-responsive bilayer hydrogels, consisting of a thermoresponsive poly( N-isopropylacrylamide) (polyNIPAM) layer and a salt-responsive poly(3-(1-(4-vinylbenzyl)-1 H-imidazol-3-ium-3-yl)propane-1-sulfonate) (polyVBIPS) layer. Both polyNIPAM and polyVBIPS layers exhibit a completely opposite swelling/shrinking behavior, where polyNIPAM shrinks (swells) but polyVBIPS swells (shrinks) in salt solution (water) or at high (low) temperatures. By tuning NIPAM:VBIPS ratios, the resulting polyNIPAM/polyVBIPS bilayer hydrogels enable us to achieve fast and large-amplitude bidirectional bending in response to temperatures, salt concentrations, and salt types. Such bidirectional bending, bending orientation, and degree can be reversibly, repeatedly, and precisely controlled by salt- or temperature-induced cooperative swelling-shrinking properties from both layers. Based on their fast, reversible, and bidirectional bending behavior, we further design two conceptual hybrid hydrogel actuators, serving as a six-arm gripper to capture, transport, and release an object and an electrical circuit switch to turn on-and-off a lamp. Different from the conventional two- or multistep methods for preparation of bilayer hydrogels, our simple, one-pot, one-step method and a new bilayer hydrogel system provide an innovative concept to explore new hydrogel-based actuators through combining different responsive materials that allow us to program different stimuli for soft and intelligent materials applications.

Development of stimuli-responsive, shape-transformable materials is fundamentally and practically important for smart actuators. Herein, we design and synthesize a bilayer hydrogel by assembling a polycationic (polyMETAC/HEAA) layer with polyelectrolyte effect and a polyzwitterionic (polyVBIPS) layer with antipolyelectrolyte effect together. The bilayer hydrogels adopt a pseudo-double-network structure, and both polyelectrolyte and polyzwitterionic layers have salt-responsive swelling and shrinkage properties, but in a completely opposite way. The resulting polyMETAC/HEAA-polyVBIPS bilayer hydrogels exhibit bidirectional bending in response to salt solutions, salt concentrations, and counterion types. Such bidirectional bending of this bilayer hydrogel is fully reversible and triggered between salt solution and pure water multiple times. The bending orientation and degree of the bilayer hydrogel is driven by the opposite volume changes between the volume shrinking (swelling) of polyMETAC/HEAA layer and the volume swelling (shrinking) of polyVBIPS layer. Such cooperative, not competitive, salt-responsive swelling-shrinking properties of the two layers are contributed to by the polyelectrolyte and antipolyelectrolyte effects from the respective layers. Moreover, an eight-arm gripper made of this bilayer hydrogel is fabricated and demonstrates its ability to grasp an object in salt solution and release the object in water. This work provides a new shape-regulated, stimuli-responsive asymmetric hydrogel for actuator-based applications.