Zhuang Liu

Microfluidic Fabrication of Bio-Inspired Microfibers with Controllable Magnetic Spindle-Knots for 3D Assembly and Water Collection.

A simple and flexible approach is developed for controllable fabrication of spider-silk-like microfibers with tunable magnetic spindle-knots from biocompatible calcium alginate for controlled 3D assembly and water collection. Liquid jet templates with volatile oil drops containing magnetic Fe3O4 nanoparticles are generated from microfluidics for fabricating spider-silk-like microfibers. The structure of jet templates can be precisely adjusted by simply changing the flow rates to tailor the structures of the resultant spider-silk-like microfibers. The microfibers can be well manipulated by external magnetic fields for controllably moving, and patterning and assembling into different 2D and 3D structures. Moreover, the dehydrated spider-silk-like microfibers, with magnetic spindle-knots for collecting water drops, can be controllably assembled into spider-web-like structures for excellent water collection. These spider-silk-like microfibers are promising as functional building blocks for engineering complex 3D scaffolds for water collection, cell culture, and tissue engineering.

Gating membranes for water treatment: detection and removal of trace Pb2+ ions based on molecular recognition and polymer phase transition

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.

Hydrogel Walkers with Electro-Driven Motility for Cargo Transport

In this study, soft hydrogel walkers with electro-driven motility for cargo transport have been developed via a facile mould-assisted strategy. The hydrogel walkers consisting of polyanionic poly(2-acrylamido-2-methylpropanesulfonic acid-co-acrylamide) exhibit an arc looper-like shape with two “legs” for walking. The hydrogel walkers can reversibly bend and stretch via repeated “on/off” electro-triggers in electrolyte solution. Based on such bending/stretching behaviors, the hydrogel walkers can move their two “legs” to achieve one-directional walking motion on a rough surface via repeated “on/off” electro-triggering cycles. Moreover, the hydrogel walkers loaded with very heavy cargo also exhibit excellent walking motion for cargo transport. Such hydrogel systems create new opportunities for developing electro-controlled soft systems with simple design/fabrication strategies in the soft robotic field for remote manipulation and transportation.

Microfluidic fabrication of chitosan microfibers with controllable internals from tubular to peapod-like structures

Here we report on a simple and flexible approach for continuous in situ fabrication of chitosan microfibers with controllable internals from tubular to peapod-like structures in microfluidics. Tubular and peapod-like jet templates can be generated at stable operation regions for template synthesis of chitosan microfibers with controllable tubular and peapod-like internals. The structure of each jet template can be precisely adjusted by simply changing the flow rates to tailor the structures of the resultant tubular and peapod-like chitosan microfibers. Both the tubular and peapod-like microfibers possess sufficient mechanical properties for further handling for biomedical applications. The tubular microfibers are used as biocompatible artificial vessels for transporting fluid, which is promising for delivering nutrition and blood for tissue engineering and cell culture. The peapod-like microfibers with controllable and separate oil cores can serve as multi-compartment systems for synergistic encapsulation of multiple drugs, showing great potential for developing drug-loaded medical patches for wound healing. The approach proposed in this study provides a facile and efficient strategy for controllable fabrication of microfibers with complex and well-tailored internals for biomedical applications.

Comprehensive Effects of Metal Ions on Responsive Characteristics of P(NIPAM-co-B18C6Am)

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/M(n+) host-guest complexes with special ions (M(n+)), such as K(+), Sr(2+), Ba(2+), Hg(2+), and Pb(2+), the LCST of P(NIPAM-co-B18C6Am) increases due to the repulsion among charged B18C6Am/M(n+) complex groups and the enhancement of hydrophilicity, and the order of the shift degree of LCST of P(NIPAM-co-B18C6Am) is Pb(2+) > Ba(2+) > Sr(2+) > Hg(2+) > 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 Pb(2+), 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.

Graphene Oxide Membranes with Strong Stability in Aqueous Solutions and Controllable Lamellar Spacing

Graphene oxide (GO) membranes become emerging efficient filters for molecular or ionic separation due to their well-defined two-dimensional nanochannels formed by closely spaced GO sheets and tunable physicochemical properties. The stability of GO membranes in aqueous solutions is a prerequisite for their applications. Here we show a novel and easy strategy for fabricating GO membranes with strong stability in aqueous solutions and controllable lamellar spacing by simply doping with partially reduced graphene oxide (prGO) sheets. With our prGO-doping strategy, the interlayer stabilizing force in GO membranes is enhanced due to the weakened repulsive hydration and enhanced π-π attraction between GO sheets; as a result, the fabricated GO membranes are featured with controllable lamellar spacing and extraordinary stability in water or even strong acid and base solutions as well as strong mechanical properties, which will expand the application scope of GO membranes and provide ever better performances in their applications with aqueous solution environments.

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(N-isopropylacrylamide-co-acrylamide) (poly(NIPAM-co-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.

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-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.

Smart gating membranes with in situ self-assembled responsive nanogels as functional gates

Smart gating membranes, inspired by the gating function of ion channels across cell membranes, are artificial membranes composed of non-responsive porous membrane substrates and responsive gates in the membrane pores that are able to dramatically regulate the trans-membrane transport of substances in response to environmental stimuli. Easy fabrication, high flux, significant response and strong mechanical strength are critical for the versatility of such smart gating membranes. Here we show a novel and simple strategy for one-step fabrication of smart gating membranes with three-dimensionally interconnected networks of functional gates, by self-assembling responsive nanogels on membrane pore surfaces in situ during a vapor-induced phase separation process for membrane formation. The smart gating membranes with in situ self-assembled responsive nanogels as functional gates show large flux, significant response and excellent mechanical property simultaneously. Because of the easy fabrication method as well as the concurrent enhancement of flux, response and mechanical property, the proposed smart gating membranes will expand the scope of membrane applications, and provide ever better performances in their applications.

Fabrication of glass-based microfluidic devices with dry film photoresists as pattern transfer masks for wet etching

A simple, cheap and rapid method is developed to fabricate glass-based microfluidic devices with dry film photoresists (DFR) as pattern transfer masks for wet etching. In this method, the DFR mask for wet etching can be easily achieved by a one-step lamination, and no expensive facilities and materials are used; therefore, both the difficulty and the cost of fabrication of glass microchips with etched microchannels are reduced greatly compared with those in conventional methods. With the DFR mask, mass-production of glass microchips can be achieved efficiently and controllably in general laboratories. The fabricated glass microfluidic devices feature very flexible design of microchannels, good chemical compatibility and optical properties, easy modification of channel surface wettability, mass producibility and satisfactory reproducibility. We demonstrate the utilities of fabricated glass microchips in the preparation of monodisperse water-in-oil (W/O) and oil-in-water (O/W) emulsions, and the formation of a stable laminar flow interface and concentration gradient in microchannels.