A novel type of smart polymersomes with rapid K+-triggered drug-release properties is developed in this work. Block copolymers with biocompatible poly(ethylene glycol) (PEG) as the hydrophilic block and poly(N-isopropylacrylamide-co-benzo-18-crown-6-acrylamide) (PNB) copolymer as the K+-responsive block are successfully synthesized. Because of the presence of 18-crown-6 units, the PEG-b-PNB block copolymers exhibit excellent K+-dependent phase-transition behaviors, which show a hydrophilic–hydrophobic state in simulated extracellular fluid and present a hydrophilic–hydrophilic state in simulated intracellular fluid. Polymersomes with regular spherical shape and good monodispersity are prepared by the self-assembly of the PEG-b-PNB block copolymers. Both hydrophilic fluorescein isothiocyanate–dextran and hydrophobic doxorubicin are selected as model drugs and are successfully encapsulated into the PEG-b-PNB polymersomes. After being placed in a simulated intracellular fluid with high K+ concentration, the PEG-b-PNB polymersomes immediately disassemble accompanied by the rapid and complete release of drugs. Such K+-responsive polymersomes with the desired drug-release properties provide a novel strategy for advanced intracellular drug delivery and release, which can enhance the safety and efficacy of cancer therapy.Keywords: block copolymers; drug-delivery systems; K+-triggered release; polymersomes; responsive materials;

Facile fabrication of novel functional membranes with excellent dual thermo- and pH-responsive characteristics has been achieved by simply designing dual-layer composite membranes. pH-Responsive poly(styrene)-block-poly(4-vinylpyridine) (PS-b-P4VP) block copolymers and polystyrene blended with thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) nanogels are respectively used to construct the top layer and bottom layer of composite membranes. The stretching/coiling conformation changes of the P4VP chains around the pKa (∼3.5–4.5) provide the composite membranes with extraordinary pH-responsive characteristics, and the volume phase transitions of PNIPAM nanogels at the pore/matrix interfaces in the bottom layer around the volume phase transition temperature (VPTT, ∼33 °C) provide the composite membranes with great thermoresponsive characteristics. The microstructures, permeability performances, and dual stimuli-responsive characteristics can be well tuned by adjusting the content of PNIPAM nanogels and the thickness of the PS-b-P4VP top layer. The water fluxes of the composite membranes can be changed in order of magnitude by changing the environment temperature and pH, and the dual thermo- and pH-responsive permeation performances of the composite membranes are satisfactorily reversible and reproducible. The membrane fabrication strategy in this work provides valuable guidance for further development of dual stimuli-responsive membranes or even multi stimuli-responsive membranes.Keywords: composite membranes; dual thermo-/pH-response; nanogels; responsive membranes; self-assembly;

A novel type of composite hollow microfiber with K+-responsive controlled-release characteristics based on a host–guest system is prepared by embedding K+-responsive poly(N-isopropylacrylamide-co-acryloylamidobenzo-15-crown-5) (P(NIPAM-co-AAB15C5)) microspheres in the wall of poly(lactic-co-glycolic acid) (PLGA) microfibers as “micro-valves” using a controllable microfluidic approach. By adjusting the volume change of microspheres in response to the environmental K+ concentration, the release rate of the encapsulated drug molecules from the composite hollow microfibers can be flexibly regulated owing to the change in the interspace size between the microfiber wall and microspheres. When the environmental K+ concentration is increased, due to the formation of stable 2:1 “sandwich-type” host–guest complexes of 15-crown-5 units and K+ ions, P(NIPAM-co-AAB15C5) microspheres change from a swollen state to a shrunken state. Thus, the interspace size becomes larger, resulting in a rapid increase in the release rate of encapsulated drugs. When the ambient K+ concentration is decreased, the interspace size becomes smaller due to isothermal swelling of microspheres caused by the decreased amount of host–guest complexes, resulting in a decrease in the release rate. The K+-responsive drug release behaviors are reversible. This kind of K+-responsive hollow microfiber with K+-concentration-dependent controlled-release properties provides a new mode in the design of more rational drug delivery systems, which are highly attractive for biomedical applications.

A facile and controllable microfluidic strategy is developed to fabricate synthetic microfibers of crosslinked 4-arm polyethylene glycol with maleimide end groups (PEG–4Mal) for cell encapsulation and culture with high viability. The gelling condition in this strategy is mild for cell encapsulation and the crosslinking process is rapid, thus guaranteeing the high viability of encapsulated cells. The diameters of PEG–4Mal synthetic microfibers are precisely adjustable by simply changing the flowrates of the inner and outer fluids in microfluidic devices. The prepared PEG–4Mal synthetic microfibers possess excellent permselectivity, which could not only guarantee the normal metabolism of encapsulated cells but also provide immunoisolation for encapsulated cells. MC3T3 cells and NIH3T3 cells are successfully encapsulated into the PEG–4Mal synthetic microfibers, and the formed microfibers enable high viability for cell encapsulation and culture. The proposed PEG–4Mal synthetic microfibers show great potential as efficient cell encapsulation systems for many potential biomedical applications in cell culture, cell therapy and tissue engineering.

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-co-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.Keywords: chitosan; microcapsulesc; nanoparticles; PLGA; programmed sequential drug release

•Capsule membranes are successfully prepared under different pH conditions.•pH values during preparation do not affect the microstructures of APSi capsules.•Membranes prepared at different pH values exhibit similar pH-responsive properties.•Capsule membranes exhibit pH-responsive properties for the solutes with a suitable size.•Molecular weights of solutes heavily affect the pH-responsive permeation characteristics.Ca-alginate/protamine/silica (APSi) hybrid capsule membranes with pH-responsive controlled release characteristics are successfully prepared by combining co-extrusion minifludics, adsorption and biosilicification under different pH conditions from 3 to 7. The microstructures of the prepared capsule membranes are characterized by optical photography, CLSM and SEM. The pH-responsive permeability of APSi hybrid capsule membranes is controlled by the electrostatic interactions between Ca-alginate networks and protamine molecules. Four kinds of solute molecules with different molecular weights including methylene blue, VB12, 4 kDa and 10 kDa FITC-dextran molecules are selected as solute molecules to comparatively study the diffusional permeability characteristics of solutes across APSi hybrid capsule membranes. The results show that, for the solutes with suitable molecule sizes such as VB12 and 4 kDa FITC-dextran, the diffusional permeabilities across the capsule membranes at pH 4 are lower than those at pH 5; however, for the solutes with too small molecule size such as methylene blue or too large molecule size such as 10 kDa FITC-dextran, the diffusional permeabilities across the capsule membranes at pH 4 are very close to those at pH 5. The results in this study provide valuable guidance for fabrication and application of APSi capsule membranes in the various fields including controlled release of drugs and immobilization of enzymes and so on.

Monodisperse erythrocyte-sized and acid-soluble chitosan microspheres are successfully prepared by an electrospraying method for the first time. Effects of the physical properties of the polymer solution and the condition parameters of the electrospraying process on the size and size distribution of the chitosan microspheres are systematically studied, to optimize the conditions for preparation of chitosan microspheres with our specific requirements. The microsphere size is mainly controlled by the viscosity of the spray liquid, and the microsphere monodispersity mainly depends on the electric conductivity of the spray liquid, the flow rate and the needle size. Under the optimized conditions, monodisperse chitosan microspheres with an average diameter of 6.4 μm, which is similar to the erythrocyte size, are prepared with a narrow size distribution (CV < 3%). Due to the use of terephthalaldehyde as cross-linker via formation of Schiff base bonds, the prepared chitosan microspheres can maintain structural integrity and show green fluorescence in a neutral medium, but display rapid acid-triggered decomposition. The prepared erythrocyte-sized and acid-soluble chitosan microspheres are highly attractive as promising substitutes of blood samples for calibration of hematology analyzers and flow cytometers.

•A simple method was developed to study micromechanical properties of hydrogel microspheres.•Force-deformation data of PNIPAM hydrogel microspheres fitted well with Hertz theory.•Compositions of PNIPAM microspheres significantly affected the micromechanical properties.•Microsphere with larger thermo-responsive volume change had lower modulus of elasticity.•Moduli of elasticity of PNIPAM microspheres at 37 °C was much larger than that at 25 °C.Temperature-responsive poly(N-isopropylacrylamide) (PNIPAM) hydrogel microspheres have attracted extensive attention because of their promising diverse biomedical applications. A quantitative understanding of the micromechanical properties of these microspheres is essential for their practical application. Here, we report a simple method for the characterization of the elastic properties of PNIPAM hydrogel microspheres. The results show that PNIPAM hydrogel microspheres exhibit elastic deformation and the obtained force-deformation experimental data fits the Hertz theory well. The moduli of elasticity of the PNIPAM hydrogel microspheres prepared under different conditions were systematically investigated in this work for the first time. The PNIPAM hydrogel microsphere composition significantly affects their micromechanical properties and their temperature sensitivity behavior. PNIPAM hydrogel microspheres with a larger equilibrium volume change have a lower modulus of elasticity. The modulus of elasticity of the PNIPAM hydrogel microspheres at body temperature (37 °C, above the lower critical solution temperature (LCST) of PNIPAM) is much higher than that at room temperature (25 °C, below the LCST of PNIPAM) because of thermo-induced volume shrinkage and an increase in stiffness. These results provide valuable guidance for the design of smart materials for practical biomedical applications. Moreover, the simple microcompression method presented here also provides a versatile way to investigate the micromechanical properties of microscopic biomedical materials.

Smart core–shell microspheres for selective Pb2+ adsorption and separation have been developed. Each microsphere is composed of a Pb2+ recognizable poly(N-isopropylacrylamide-co-benzo-18-crown-6-acrylamide) (PNB) shell and a magnetic Fe3O4 core. The magnetic PNB core–shell microspheres show excellent Pb2+ adsorption selectivity among the coexisting Cd2+, Co2+, Cr3+, Cu2+, Ni2+, Zn2+, K+, and Ca2+ ions by forming stable B18C6Am/Pb2+ host–guest complexes and exhibit an interesting temperature-dependent Pb2+ adsorption. The inner independent magnetic Fe3O4 cores enable the Pb2+-adsorbed microspheres with a magnetically guided aggregation to be separated from the treated solution using a remotely controlled manner. The isothermal Pb2+ adsorption result fits well with the Freundlich isotherm. The magnetic PNB core–shell microspheres show very fast adsorption of Pb2+, and the adsorption process of Pb2+ onto magnetic PNB core–shell microspheres fits well with the pseudo-second-order model. Moreover, Pb2+-adsorbed microspheres can be regenerated by simply increasing the operation temperature and washing with deionized water. The proposed magnetic PNB core–shell microspheres provide a promising candidate for Pb2+ adsorbents with selectively separable and efficiently reusable abilities.Keywords: host−guest chemistry; magnetic microspheres; Pb2+ adsorption; polymer materials; template synthesis;

A novel type of smart microspheres with K+-induced shrinking and aggregating properties is designed and developed on the basis of a K+-recognition host–guest system. The microspheres are composed of cross-linked poly(N-isopropylacrylamide-co-acryloylamidobenzo-15-crown-5) (P(NIPAM-co-AAB15C5)) networks. Due to the formation of stable 2:1 “sandwich-type” host–guest complexes between 15-crown-5 units and K+ ions, the P(NIPAM-co-AAB15C5) microspheres significantly exhibit isothermally and synchronously K+-induced shrinking and aggregating properties at a low K+ concentration, while other cations (e.g., Na+, H+, NH4+, Mg2+, or Ca2+) cannot trigger such response behaviors. Effects of chemical compositions of microspheres on the K+-induced shrinking and aggregating behaviors are investigated systematically. The K+-induced aggregating sensitivity of the P(NIPAM-co-AAB15C5) microspheres can be enhanced by increasing the content of crown ether units in the polymeric networks; however, it is nearly not influenced by varying the monomer and cross-linker concentrations in the microsphere preparation. State diagrams of the dispersed-to-aggregated transformation of P(NIPAM-co-AAB15C5) microspheres in aqueous solutions as a function of temperature and K+ concentration are constructed, which provide valuable information for tuning the dispersed/aggregated states of microspheres by varying environmental K+ concentration and temperature. The microspheres with synchronously K+-induced shrinking and aggregating properties proposed in this study provide a brand-new model for designing novel targeted drug delivery systems.Keywords: aggregation; K+-recognition; microspheres; phase transition; responsive host−guest system

A simple and efficient method is developed to fabricate monodisperse and fast-responsive poly(N-isopropylacrylamide) (PNIPAM) microgels with open-celled porous structure. First, numerous fine oil droplets are fabricated by homogeneous emulsification method and are then evenly dispersed inside monodisperse PNIPAM microgels as porogens via the combination of microfluidic emulsification and UV-initiated polymerization methods. Subsequently, the embedded fine oil droplets inside the PNIPAM microgels are squeezed out upon stimuli-induced rapid volume shrinkage of the microgels; as a result, a spongelike open-celled porous structure is formed inside the PNIPAM microgels. The open-celled porous structure provides numerous interconnected free channels for the water transferring convectively inward or outward during the volume phase transition process of PNIPAM microgels; therefore, the response rates of the PNIPAM microgels with open-celled porous structure are much faster than that of the normal ones in both thermo-responsive shrinking and swelling processes. Because of the fast-responsive characteristics, the microgels with open-celled porous structure will provide ever better performances in their myriad applications, such as microsensors, microactuators, microvalves, and so on.

Although multiple methods have been developed to detect or remove trace Pb2+ ions, performing both roles together still remains a challenging task. In this study, we present a gating membrane with poly(N-isopropylacrylamide-co-acryloylamidobenzo-18-crown-6) (poly(NIPAM-co-AAB18C6)) copolymer chains as functional gates, in which a large amount of crown ether units are introduced as Pb2+ receptors by a two-step method. This gating membrane can be used in water treatment for selective detection and removal of trace Pb2+ ions. The gating action of the synthesized membrane for detecting trace Pb2+ ions is significant and reproducible. By simply changing the operation temperature, effective removal of trace Pb2+ ions and efficient membrane regeneration are achieved. This gating membrane has high potential for various industrial and agricultural applications, such as online detection and timely treatment of trace Pb2+ ions in wastewater discharge, analysis for water quality, and remediation and protection of soil.

A novel, simple, portable, and low-cost method for diagnosis of hyperkalemia by using K+-recognizable poly(N-isopropylacrylamide-co-benzo-15-crown-5-acrylamide) [poly(NIPAM-co-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-co-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-co-B15C5Am) linear copolymer as an indicator. Normal blood samples with low potassium level containing the poly(NIPAM-co-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-co-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-co-B15C5Am)-based artificial K+-recognizable “smart” or “intelligent” systems in various application fields.

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 investigations of the effects of species and concentrations of metal ions on the ion-responsive behaviors of poly(N-isopropylacrylamide-co-benzo-18-crown-6-acrylamide) (P(NIPAM-co-B18C6Am)) are systematically carried out with a series of P(NIPAM-co-B18C6Am) linear copolymers and cross-linked hydrogels containing different crown ether contents. The results show that when the B18C6Am receptors form stable B18C6Am/Mn+ host–guest complexes with special ions (Mn+), such as K+, Sr2+, Ba2+, Hg2+, and Pb2+, the LCST of P(NIPAM-co-B18C6Am) increases due to the repulsion among charged B18C6Am/Mn+ complex groups and the enhancement of hydrophilicity, and the order of the shift degree of LCST of P(NIPAM-co-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-co-B18C6Am) linear copolymer and cross-linked hydrogel in response to special metal ions, at which concentration the P(NIPAM-co-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-co-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-co-B18C6Am) may even become surprisingly unobvious. Therefore, to achieve satisfactory ion-responsive characteristics of P(NIPAM-co-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-co-B18C6Am)-based ion-responsive materials in various applications.

K+-recognition capsules are developed to translate K+-recognition into a squirting release function. Upon recognition of K+, the capsules shrink rapidly and squirt out encapsulated oil cores due to the cooperative interaction of host–guest complexation and phase transition in capsule membranes. The capsules provide a promising model for K+-recognition smart functional systems.

Novel monodisperse cationic pH-responsive microcapsules are successfully prepared using oil-in-water-in-oil double emulsions as templates by a microfluidic technique in this study. With the use of a double photo-initiation system and the adjustment of pH value of the monomer solution, cross-linked poly(N,N-dimethylaminoethyl methacrylate) (PDM) microcapsules with good sphericity and monodispersity can be effectively fabricated. The obtained microcapsule membranes swell at low pH due to the protonation of N(CH3)2 groups in the cross-linked PDM networks. The effects of various preparation parameters, such as pH of the aqueous monomer fluid, concentration of cross-linker, concentration of monomer N,N-dimethylaminoethyl methacrylate (DM) and addition of copolymeric monomer acrylamide (AAm), on the pH-responsive swelling characteristics of PDM microcapsules are systematically studied. The results show that, when the PDM microcapsules are prepared at high pH and with low cross-linking density and low DM monomer concentration, they exhibit high pH-responsive swelling ratios. The addition of AAm in the preparation decreases the swelling ratios of PDM microcapsules. The external temperature has hardly any influence on the swelling ratios of PDM microcapsules when the external pH is less than 7.4. The prepared PDM microcapsules with both biocompatibility and cationic pH-responsive properties are of great potential as drug delivery carriers for tumor therapy. Moreover, the fabrication methodology and results in this study provide valuable guidance for preparation of core–shell microcapsules via free radical polymerization based on synergistic effects of interfacial initiation and initiation in a confined space.Graphical abstractNovel cationic pH-responsive poly(N,N-dimethylaminoethyl methacrylate) (PDM) microcapsules are successfully prepared using oil-in-water-in-oil double emulsions as templates using a microfluidic technique. The pH-responsive characteristics of these PDM microcapsules are significantly affected by the composition and pH of the monomer solutions.Research highlights► Novel cationic pH-responsive microcapsules are prepared by a microfluidic technique. ► The microcapsules swell at low pH due to the protonation of N(CH3)2 groups. ► The pH-sensitivity of the microcapsules is affected by pH of the monomer solutions.

Smart responsive microcapsules capable of recognizing heavy metal ions are successfully prepared with oil-in-water-in-oil double emulsions as templates for polymerization in this study. The microcapsules are featured with thin poly(N-isopropylacrylamide-co-benzo-18-crown-6-acrylamide) (P(NIPAM-co-BCAm)) membranes, and they can selectively recognize special heavy metal ions such as barium(II) or lead(II) ions very well due to the “host–guest” complexation between the BCAm receptors and barium(II) or lead(II) ions. The stable BCAm/Ba2+ or BCAm/Pb2+ complexes in the P(NIPAM-co-BCAm) membrane cause a positive shift of the volume phase transition temperature of the crosslinked P(NIPAM-co-BCAm) hydrogel to a higher temperature, and the repulsion among the charged BCAm/Ba2+ or BCAm/Pb2+ complexes and the osmotic pressure within the P(NIPAM-co-BCAm) membranes result in the swelling of microcapsules. Induced by recognizing barium(II) or lead(II) ions, the prepared microcapsules with P(NIPAM-co-BCAm) membranes exhibit isothermal and significant swelling not only in outer and inner diameters but also in the membrane thickness. The proposed microcapsules in this study are highly attractive for developing smart sensors and/or carriers for detection and/or elimination of heavy metal ions.Graphical abstractA novel smart responsive microcapsule has been developed for sensing heavy metal ions. The microcapsule exhibits an isothermal and significant swelling by recognizing special heavy metal ions.Research highlights► Smart responsive microcapsules are fabricated with poly(N-isopropylacrylamide-co-benzo-18-crown-6-acrylamide) membranes. ► Microcapsules can selectively recognize heavy metal ions such as Pb2+ or Ba2+ by forming host-guest complexes. ► Microcapsules exhibit isothermal and significant swelling by recognizing Pb2+ or Ba2+.

Halloysite nanotube-composited thermo-responsive hydrogel system has been successfully developed for controlled drug release by copolymerization of N-isopropylacrylamide (NIPAM) with silane-modified halloysite nanotubes (HNT) through thermally initiated free-radical polymerization. With methylene blue as a model drug, thermo-responsive drug release results demonstrate that the drug release from the nanotubes in the composited hydrogel can be well controlled by manipulating the environmental temperature. When the hydrogel network is swollen at temperature below the lower critical solution temperature (LCST), drug releases steadily from lumens of the embedded nanotubes, whereas the drug release stops when hydrogel shrinks at temperature above the LCST. The release of model drug from the HNT-composited hydrogel matches well with its thermo-responsive volume phase transition, and shows characteristics of well controlled release. The design strategy and release results of the proposed novel HNT-composited thermo-responsive hydrogel system provide valuable guidance for designing responsive nanocomposites for controlled-release of active agents.

K+-recognition capsules are developed to translate K+-recognition into a squirting release function. Upon recognition of K+, the capsules shrink rapidly and squirt out encapsulated oil cores due to the cooperative interaction of host–guest complexation and phase transition in capsule membranes. The capsules provide a promising model for K+-recognition smart functional systems.

Although multiple methods have been developed to detect or remove trace Pb2+ ions, performing both roles together still remains a challenging task. In this study, we present a gating membrane with poly(N-isopropylacrylamide-co-acryloylamidobenzo-18-crown-6) (poly(NIPAM-co-AAB18C6)) copolymer chains as functional gates, in which a large amount of crown ether units are introduced as Pb2+ receptors by a two-step method. This gating membrane can be used in water treatment for selective detection and removal of trace Pb2+ ions. The gating action of the synthesized membrane for detecting trace Pb2+ ions is significant and reproducible. By simply changing the operation temperature, effective removal of trace Pb2+ ions and efficient membrane regeneration are achieved. This gating membrane has high potential for various industrial and agricultural applications, such as online detection and timely treatment of trace Pb2+ ions in wastewater discharge, analysis for water quality, and remediation and protection of soil.

A novel type of composite hollow microfiber with K+-responsive controlled-release characteristics based on a host–guest system is prepared by embedding K+-responsive poly(N-isopropylacrylamide-co-acryloylamidobenzo-15-crown-5) (P(NIPAM-co-AAB15C5)) microspheres in the wall of poly(lactic-co-glycolic acid) (PLGA) microfibers as “micro-valves” using a controllable microfluidic approach. By adjusting the volume change of microspheres in response to the environmental K+ concentration, the release rate of the encapsulated drug molecules from the composite hollow microfibers can be flexibly regulated owing to the change in the interspace size between the microfiber wall and microspheres. When the environmental K+ concentration is increased, due to the formation of stable 2:1 “sandwich-type” host–guest complexes of 15-crown-5 units and K+ ions, P(NIPAM-co-AAB15C5) microspheres change from a swollen state to a shrunken state. Thus, the interspace size becomes larger, resulting in a rapid increase in the release rate of encapsulated drugs. When the ambient K+ concentration is decreased, the interspace size becomes smaller due to isothermal swelling of microspheres caused by the decreased amount of host–guest complexes, resulting in a decrease in the release rate. The K+-responsive drug release behaviors are reversible. This kind of K+-responsive hollow microfiber with K+-concentration-dependent controlled-release properties provides a new mode in the design of more rational drug delivery systems, which are highly attractive for biomedical applications.

A facile and controllable microfluidic strategy is developed to fabricate synthetic microfibers of crosslinked 4-arm polyethylene glycol with maleimide end groups (PEG–4Mal) for cell encapsulation and culture with high viability. The gelling condition in this strategy is mild for cell encapsulation and the crosslinking process is rapid, thus guaranteeing the high viability of encapsulated cells. The diameters of PEG–4Mal synthetic microfibers are precisely adjustable by simply changing the flowrates of the inner and outer fluids in microfluidic devices. The prepared PEG–4Mal synthetic microfibers possess excellent permselectivity, which could not only guarantee the normal metabolism of encapsulated cells but also provide immunoisolation for encapsulated cells. MC3T3 cells and NIH3T3 cells are successfully encapsulated into the PEG–4Mal synthetic microfibers, and the formed microfibers enable high viability for cell encapsulation and culture. The proposed PEG–4Mal synthetic microfibers show great potential as efficient cell encapsulation systems for many potential biomedical applications in cell culture, cell therapy and tissue engineering.