Development of smart, multifunction materials is challenging but important for many fundamental and industrial applications. Here, we synthesized and characterized zwitterionic poly(3-(1-(4-vinylbenzyl)-1H-imidazol-3-ium-3-yl)propane-1-sulfonate) (polyVBIPS) brushes as ion-responsive smart surfaces via the surface-initiated atom transfer radical polymerization. PolyVBIPS brushes were carefully characterized for their surface morphologies, compositions, wettability, and film thicknesses by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), contact angle, and ellipsometer, respectively. Salt-responsive, switching properties of polyVBIPS brushes on surface hydration, friction, and antifouling properties were further examined and compared both in water and in salt solutions with different salt concentrations and counterion types. Collective data showed that polyVBIPS brushes exhibited reversible surface wettability switching between in water and saturated NaCl solution. PolyVBIPS brushes in water induced the larger protein absorption, higher surface friction, and lower surface hydration than those in salt solutions, exhibiting "anti-polyelectrolyte effect" salt responsive behaviors. At appropriate ionic conditions, polyVBIPs brushes were able to switch to superlow fouling surfaces (<0.3 ng/cm(2) protein adsorption) and superlow friction surfaces (u ∼ 10(-3)). The relationship between brush structure and its salt-responsive performance was also discussed. This work provides new zwitterionic surface-responsive materials with controllable antifouling and friction capabilities for multifunctional applications.

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.

Some polyzwitterionic brushes exhibit a strong "anti-polyelectrolyte effect" and ionic specificity that make them versatile platforms to build smart surfaces for many applications. However, the structure-property relationship of zwitterionic polymer brushes still remains to be elucidated. Herein, we aim to study the structure-dependent relationship between different zwitterionic polymers and the anti-polyelectrolyte effect. To this end, a series of polyzwitterionic brushes with different cationic moieties (e.g., imidazolium, ammonium, and pyridinium) in their monomeric units and with different carbon spacer lengths (e.g., CSL = 1, 3, and 4) between the cation and anion were designed and synthesized to form polymer brushes via the surface-initiated atom transfer radical polymerization. All zwitterionic brushes were carefully characterized for their surface morphologies, compositions, wettability, and film thicknesses by atomic force microscopy, contact angle measurement, and ellipsometry, respectively. The salt-responsiveness of all zwitterionic brushes to surface hydration and friction was further examined and compared both in water and in salt solutions with different salt concentrations and counterion types. The collective data showed that zwitterionic brushes with different cationic moieties and shorter CSLs in salt solution induced higher surface friction and lower surface hydration than those in water, exhibiting strong anti-polyelectrolyte effect salt-responsive behaviors. By tuning the CSLs, cationic moieties, and salt concentrations and types, the surface wettability can be changed from a highly hydrophobic surface (∼60°) to a highly hydrophilic surface (∼9°), while interfacial friction can be changed from ultrahigh friction (μ ≈ 4.5) to superior lubrication (μ ≈ 10). This work provides important structural insights into how subtle structural changes in zwitterionic polymers can yield great changes in the salt-responsive properties at the interface, which could be used for the development of smart surfaces for different 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.

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Bilayer poly(N-isopropylacrylamide)/graphene oxide hydrogels with dual thermo- and near-infrared-responsive properties were prepared by a simple, in situ polymerization centrifugation method.

Background. Several studies have shown a possible involvement of Helicobacter pylori (H. pylori) infection in individuals with hyperemesis gravidarum (HG), but the relationship remains controversial. This meta-analysis was performed to validate and strengthen the association between HG and H. pylori infection. Methods. PubMed, Embase, and Web of Science databases up to March 20, 2014, were searched to select studies on the prevalence of H. pylori infection between pregnant women with HG and the normal pregnant control subjects. Results. Of the HG cases, 1289 (69.6%) were H. pylori-positive; however, 1045 (46.2%) were H. pylori-positive in control group. Compared to the non-HG normal pregnant controls, infection rate of H. pylori was significantly higher in pregnant women with HG (OR = 3.34, 95% CI: 2.32–4.81, P < 0.001). Subgroup analysis indicated that H. pylori infection was a risk factor of HG in Asia, Africa, and Oceania, especially in Africa (OR = 12.38, 95% CI: 7.12–21.54, P < 0.001). Conclusions. H. pylori should be considered one of the risk factors of HG, especially in the developing countries. H. pylori eradication could be considered to relieve the symptoms of HG in some intractable cases.

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