Women and tropical diseases. Introduction

Conversion of chemical signals into mechanical force is very important for implementation of stimuli-responsive hydrogels. We design a core–shell hydrogel capsule that can translate the variations of alcohol concentration into mechanical force. Oil-in-water-in-oil (O/W/O) emulsions are prepared with microfluidic technique and serve as templates for the synthesis of the core–shell capsules. The oil core is ejected from the capsule by the mechanical force generated from the deswelling of the capsule membrane upon increasing the alcohol concentration at a certain temperature below the lower critical solution temperature. The influences of alcohol concentration and temperature on the deswelling process of capsule membranes are investigated systematically. The deswelling rate also plays an important role in the ejection of the oil core. These demonstrations of conversion of alcohol concentration variations into mechanical force provide proof that these core–shell capsules can function as both sensors and actuators of alcohols

Conversion of Alcoholic Concentration Variations into Mechanical Force via Core–Shell Capsules

Conversion of chemical signals into mechanical force is very important for implementation of stimuli-responsive hydrogels. We design a core–shell hydrogel capsule that can translate the variations of alcohol concentration into mechanical force. Oil-in-water-in-oil (O/W/O) emulsions are prepared with microfluidic technique and serve as templates for the synthesis of the core–shell capsules. The oil core is ejected from the capsule by the mechanical force generated from the deswelling of the capsule membrane upon increasing the alcohol concentration at a certain temperature below the lower critical solution temperature. The influences of alcohol concentration and temperature on the deswelling process of capsule membranes are investigated systematically. The deswelling rate also plays an important role in the ejection of the oil core. These demonstrations of conversion of alcohol concentration variations into mechanical force provide proof that these core–shell capsules can function as both sensors and actuators of alcohols

Comprehensive Effects of Metal Ions on Responsive Characteristics of P(NIPAM-<i>co</i>-B18C6Am)

Comprehensive investigations of the effects of species and concentrations of metal ions on the ion-responsive behaviors of poly­(<i>N</i>-isopropylacrylamide-<i>co</i>-benzo-18-crown-6-acrylamide) (P­(NIPAM-<i>co</i>-B18C6Am)) are systematically carried out with a series of P­(NIPAM-<i>co</i>-B18C6Am) linear copolymers and cross-linked hydrogels containing different crown ether contents. The results show that when the B18C6Am receptors form stable B18C6Am/M^<i>n</i>+ host–guest complexes with special ions (M^<i>n</i>+), such as K⁺, Sr²⁺, Ba²⁺, Hg²⁺, and Pb²⁺, the LCST of P­(NIPAM-<i>co</i>-B18C6Am) increases due to the repulsion among charged B18C6Am/M^<i>n</i>+ complex groups and the enhancement of hydrophilicity, and the order of the shift degree of LCST of P­(NIPAM-<i>co</i>-B18C6Am) is Pb²⁺ > Ba²⁺ > Sr²⁺ > Hg²⁺ > K⁺. With increasing the content of pendent crown ether groups, the LCST shift degree increases first and then stays unchanged when the B18C6Am content is higher than 20 mol %. Remarkably, it is found for the first time that there exists an optimal ion-responsive concentration for the P­(NIPAM-<i>co</i>-B18C6Am) linear copolymer and cross-linked hydrogel in response to special metal ions, at which concentration the P­(NIPAM-<i>co</i>-B18C6Am) exhibits the most significant ion-responsivity either in the form of linear copolymers or cross-linked hydrogels. With an increase of the content of crown ether groups, the value of corresponding optimal ion-responsive concentration increases. Interestingly, there exists an optimal molar ratio of metal ion to crown ether for the P­(NIPAM-<i>co</i>-B18C6Am) copolymer in response to Pb²⁺, which is around 4.5 (mol/mol). If the ion concentration is too high, the ion-responsive behaviors of P­(NIPAM-<i>co</i>-B18C6Am) may even become surprisingly unobvious. Therefore, to achieve satisfactory ion-responsive characteristics of P­(NIPAM-<i>co</i>-B18C6Am)-based materials, both the operation temperature and the ion concentration should be optimized for the specific ion species. The results in this study provide valuable guidance for designing and applying P­(NIPAM-<i>co</i>-B18C6Am)-based ion-responsive materials in various applications

Wetting-Induced Coalescence of Nanoliter Drops as Microreactors in Microfluidics

Controllable one-to-one coalescence of surfactant-stabilized nanoliter water drops is successfully achieved from wetting-induced drop engulfing in microfluidics by surrounding one of the drops with a thin layer of immiscible wetting fluid. This wetting layer can spread over the other drop to drain away the liquid film between the two drops, thereby inducing coalescence. This innovative approach is totally spontaneous and highly potential in a myriad of fields, such as quantitative analysis, microreaction, and high-throughput injection. To demonstrate this potential, we successfully perform the drop-coalescence-triggered microreaction in microchannels for pH indicator and syntheses of functional materials including micro- and nanoparticles

Core–Shell Chitosan Microcapsules for Programmed Sequential Drug Release

A novel type of core–shell chitosan microcapsule with programmed sequential drug release is developed by the microfluidic technique for acute gastrosis therapy. The microcapsule is composed of a cross-linked chitosan hydrogel shell and an oily core containing both free drug molecules and drug-loaded poly­(lactic-<i>co</i>-glycolic acid) (PLGA) nanoparticles. Before exposure to acid stimulus, the resultant microcapsules can keep their structural integrity without leakage of the encapsulated substances. Upon acid-triggering, the microcapsules first achieve burst release due to the acid-induced decomposition of the chitosan shell. The encapsulated free drug molecules and drug-loaded PLGA nanoparticles are rapidly released within 60 s. Next, the drugs loaded in the PLGA nanoparticles are slowly released for several days to achieve sustained release based on the synergistic effect of drug diffusion and PLGA degradation. Such core–shell chitosan microcapsules with programmed sequential drug release are promising for rational drug delivery and controlled-release for the treatment of acute gastritis. In addition, the microcapsule systems with programmed sequential release provide more versatility for controlled release in biomedical applications

Portable Diagnosis Method of Hyperkalemia Using Potassium-Recognizable Poly(<i>N</i>‑isopropylacrylamide-<i>co</i>-benzo-15-crown-5-acrylamide) Copolymers

A novel, simple, portable, and low-cost method for diagnosis of hyperkalemia by using K⁺-recognizable poly­(<i>N</i>-isopropylacrylamide-<i>co</i>-benzo-15-crown-5-acrylamide) [poly­(NIPAM-<i>co</i>-B15C5Am)] linear copolymer as indicator is presented in this work. The pendent 15-crown-5 units in the linear copolymers can selectively and specifically recognize K⁺ to form stable 2:1 “sandwich” host–guest complexes, which cause the copolymer chains to change from the hydrophilic state to the hydrophobic state isothermally, whereas other tested metal ions (e.g., Li⁺, Na⁺, Cs⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Cu²⁺, Fe³⁺, Pb²⁺, Cd²⁺, Cr³⁺) cannot be recognized. With increasing the 15-crown-5 content or the K⁺ concentration, the poly­(NIPAM-<i>co</i>-B15C5Am) linear copolymers exhibit higher sensitivity to K⁺. The hyperkalemia can be simply diagnosed by observing the K⁺-induced optical transmittance change of human blood samples with poly­(NIPAM-<i>co</i>-B15C5Am) linear copolymer as an indicator. Normal blood samples with low potassium level containing the poly­(NIPAM-<i>co</i>-B15C5Am) linear copolymer are almost transparent since the copolymer is hydrophilic and soluble at the operating temperature. However, severe hyperkalemia samples with high potassium level become completely cloudy since the copolymer is hydrophobic and insoluble at this temperature. The presented diagnosis method with poly­(NIPAM-<i>co</i>-B15C5Am) linear copolymer as indicator is quite simple and low-cost, and it would bring a new candidate material to design simple and portable tools for diagnosis of hyperkalemia in the general population. Moreover, the results in this work provide valuable guidance for building novel poly­(NIPAM-<i>co</i>-B15C5Am)-based artificial K⁺-recognizable “smart” or “intelligent” systems in various application fields

Smart Hydrogels with Inhomogeneous Structures Assembled Using Nanoclay-Cross-Linked Hydrogel Subunits as Building Blocks

A novel and facile assembly strategy has been successfully developed to construct smart nanocomposite (NC) hydrogels with inhomogeneous structures using nanoclay-cross-linked stimuli-responsive hydrogel subunits as building blocks via rearranged hydrogen bonding between polymers and clay nanosheets. The assembled thermoresponsive poly­(<i>N</i>-isopropylacrylamide-<i>co</i>-acrylamide) (poly­(NIPAM-<i>co</i>-AM)) hydrogels with various inhomogeneous structures exhibit excellent mechanical properties due to plenty of new hydrogen bonding interactions created at the interface for locking the NC hydrogel subunits, which are strong enough to tolerate external forces such as high levels of elongations and multicycles of swelling/deswelling operations. The proposed approach is featured with flexibility and designability to build assembled hydrogels with diverse architectures for achieving various responsive deformations, which are highly promising for stimuli-responsive manipulation such as actuation, encapsulation, and cargo transportation. Our assembly strategy creates new opportunities for further developing mechanically strong hydrogel systems with complex architectures that composed of diverse internal structures, multistimuli-responsive properties, and controllable shape deformation behaviors in the soft robots and actuators fields

Smart Hydrogels with Inhomogeneous Structures Assembled Using Nanoclay-Cross-Linked Hydrogel Subunits as Building Blocks

A novel and facile assembly strategy has been successfully developed to construct smart nanocomposite (NC) hydrogels with inhomogeneous structures using nanoclay-cross-linked stimuli-responsive hydrogel subunits as building blocks via rearranged hydrogen bonding between polymers and clay nanosheets. The assembled thermoresponsive poly­(<i>N</i>-isopropylacrylamide-<i>co</i>-acrylamide) (poly­(NIPAM-<i>co</i>-AM)) hydrogels with various inhomogeneous structures exhibit excellent mechanical properties due to plenty of new hydrogen bonding interactions created at the interface for locking the NC hydrogel subunits, which are strong enough to tolerate external forces such as high levels of elongations and multicycles of swelling/deswelling operations. The proposed approach is featured with flexibility and designability to build assembled hydrogels with diverse architectures for achieving various responsive deformations, which are highly promising for stimuli-responsive manipulation such as actuation, encapsulation, and cargo transportation. Our assembly strategy creates new opportunities for further developing mechanically strong hydrogel systems with complex architectures that composed of diverse internal structures, multistimuli-responsive properties, and controllable shape deformation behaviors in the soft robots and actuators fields

Near-Infrared Light-Responsive Poly(<i>N</i>‑isopropylacrylamide)/Graphene Oxide Nanocomposite Hydrogels with Ultrahigh Tensibility

Novel near-infrared (NIR) light-responsive poly­(<i>N</i>-isopropylacrylamide)/graphene oxide (PNIPAM-GO) nanocomposite hydrogels with ultrahigh tensibility are prepared by incorporating sparse chemical cross-linking of small molecules with physical cross-linking of graphene oxide (GO) nanosheets. Combination of the GO nanosheets and thermoresponsive poly­(<i>N</i>-isopropylacrylamide) (PNIPAM) polymeric networks provides the hydrogels with an excellent NIR light-responsive property. The ultrahigh tensibility of PNIPAM-GO nanocomposite hydrogels is achieved by simply using a very low concentration of <i>N</i>,<i>N</i>′-methylenebis­(acrylamide) (BIS) molecules as chemical cross-linkers to generate a relatively homogeneous structure with flexible long polymer chains and rare chemically cross-linked dense clusters. Moreover, the oxidized groups of GO nanosheets enable the formation of a hydrogen bond interaction with the amide groups of PNIPAM chains, which could physically cross-link the PNIPAM chains to increase the toughness of the hydrogel networks. The prepared PNIPAM-GO nanocomposite hydrogels with ultrahigh tensibility exhibit rapid, reversible, and repeatable NIR light-responsive properties, which are highly promising for fabricating remote light-controlled devices, smart actuators, artificial muscles, and so on

Insights into the Effects of 2:1 “Sandwich-Type” Crown-Ether/Metal-Ion Complexes in Responsive Host–Guest Systems

In-depth investigations of the specific ion-responsive characteristics based on 2:1 “sandwich” structures and effects of crown ether cavity sizes on the metal-ion/crown-ether complexation are systematically performed with a series of PNIPAM-based responsive copolymers containing similar contents of crown ether units with different cavity dimensions (12-crown-4 (12C4), 15-crown-5 (15C5), 18-crown-6 (18C6)). The lower critical solution temperature (LCST) values of copolymers in deionized water shift to lower temperatures gradually when the crown ether contents increase or the ring sizes decrease from 18C6 to 12C4. With increasing the concentrations of alkali metal ions (Na⁺, K⁺, Cs⁺) or the contents of pendent crown ether groups, the copolymers with different crown ether cavity sizes exhibit higher selectivity and sensitivity to corresponding cations. Importantly, the ion sensitivities of the copolymers in response to corresponding alkali metal ions increase dramatically with an increase in the crown ether cavity size. Interestingly, a linear relationship between the crown ether cavity size and the diameter of corresponding cation for the formation of stable 2:1 “sandwich” complexes is found for the first time, from which the size of metal ions or other guests that able to form 2:1 “sandwich” complexes with crown ethers can be deduced. The results in this work are valuable and useful for further developments and practical applications of various crown-ether-based smart materials