Hongwei Zhou

Self-regulated intelligent systems: where adaptive entities meet chemical oscillators

In a world where adaptive entities meet chemical oscillators, materials are in autonomic motion and assembly systems are completely self-regulated! We review herein the key challenges and new trends at the interface of the fields of adaptive entities and chemical oscillators, where the adaptive entities exhibit autonomous, reversible and periodical variation without any external stimuli. Particular attention is paid to the design philosophy of the recently reported autonomic actuators and self-regulated assembly systems.

A modular approach to self-oscillating polymer systems driven by the Belousov–Zhabotinsky reaction

Inspired by the self-oscillating phenomena in nature, such as heartbeat, brain waves, pulsatile secretion of hormones, cell cycles and biorhythms, a new kind of responsive polymers, so-called the self-oscillating polymers (SOPs) are developed. Different from the traditional responsive polymers, SOPs are driven by chemical oscillating reactions and exhibit autonomous response without “ON/OFF” switching of external stimuli. From the perspective of modular design, we explore the principle, construction and integral control of SOP systems based on the recent developments. Attention is also paid to the emergent techniques for on-line study of self-oscillating behaviors and engineering approaches to novel SOP systems with unique functions and high oscillating performances.

Self-tunable thermosensitive behavior by reorganizable architecture variation in the Belousov–Zhabotinsky reaction

This work presents an approach to self-tunable thermosensitive behavior by reorganizable architecture variation in the Belousov–Zhabotinsky (BZ) reaction. By utilizing a terpyridine–ruthenium complex as the reversible conjunction point, it is demonstrated that the thermosensitive behavior can be autonomously tuned through the dynamic complex formation.

Preparation and self-healing behaviors of poly(acrylic acid)/cerium ions double network hydrogels

This work aims at developing an approach to poly(acrylic acid)/cerium ions (PAA/cerium ions) double network hydrogels and exploring the self-healing properties of the hydrogels, with expectation to provide some clues for constructing new healable gel actuators and enrich the family of self-healable hydrogels. The hydrogel is covalently crosslinked by a traditional crosslinking agent N,N’-methylene bis-acrylamide to form the first network and further physically crosslinked by the ionic interaction between cerium ions and the carboxyl groups in the hydrogel network. The preparation method and self-healing behaviors of the hydrogels are investigated.

Dually Synergetic Network Hydrogels with Integrated Mechanical Stretchability, Thermal Responsiveness, and Electrical Conductivity for Strain Sensors and Temperature Alertors

The first example of dually synergetic network hydrogel, which has integrated mechanical stretchability, thermal responsiveness, and electrical conductivity, has been constructed by a versatile and topological co-cross-linking approach. Poly( N-isopropylacrylamide) (PNIPAAm) is introduced as the thermally responsive ingredient, and polyaniline (PANI) is selected as the electrically conductive ingredient. PNIPAAm network is cross-linked by double-bond end-capped Pluronic F127 (F127DA). PANI network is doped and cross-linked by phytic acid. These two ingredients are further mechanically interlocked. Due to the integrated multiple functionalities, the topologically co-cross-linked hydrogels, as will be mentioned as F-PNIPAAm/PANI hydrogels, can be fabricated into resistive-type strain sensors. The strain sensors can achieve a gauge factor of 3.92, a response time of 0.4 s, and a sensing stability for at least 350 cycles and can be further applied for monitoring human motions, including motion of two hands, bending of joints, and even swallowing and pulse rate. Moreover, F-PNIPAAm/PANI hydrogels are utilized to construct efficient temperature alertors based on the disconnection of circuits induced by volume shrinkage at high temperature.

A Selective, Colorimetric and Ratiometric Chemosensor for Hg2+ and Its Application as Test Papers

Chemosensors provide an efficient and low-cost approach to the detection of various metal ions and small molecules. In the present work, we present a detailed investigation of a simple, easily-prepared, yet efficient, coumarin-based sensor for Hg(2+). The sensor is based on a fluorescent group of coumarin. When exposed to Hg(2+), the sensor solution shows a significant color change from yellow to red, and a fluorescence change from green to orange. Further study revealed that the sensor responds solely to Hg(2+), and shows excellent selectivity even in the presence of other potential competition metal ions, including Na(+), K(+), Co(2+), Fe(2+), Cd(2+), Cu(2+), Ni(2+), Ag(+), Zn(2+), Mg(2+), Mn(2+), Pb(2+), Fe(3+). Furthermore, the sensor has been successfully applied to detect Hg(2+) in a form of test paper, which may promote easy and effective application of the sensor.

Dual-functional probe based on rhodamine for sequential Cu 2+ and ATP detection in vivo

A rhodamine-based fluorescent probe for Cu2+ and ATP has been designed. The fluorescence intensity/absorbance was significantly enhanced upon the addition of Cu2+ owning to the opening of the spiro-ring of rhodamine, which quickly returned to the original level due to the reconstruction of the probe by the reacting with ATP. Cu2+/ATP-induced fluorescent intensity/aborbance changes showed a good linear relationship with the concentration of Cu2+/ATP in the range of 2-20 μM/0-10 μM with a detection limit of 0.1 μM/1.0 μM. The proposed method is simple in design and fast in operation, and is suitable for the reversible monitoring of Cu2+ and ATP in bioanalytical applications.

Poly(NIPAAm-co-Ru(bpy) 3 2+ ) hydrogels crosslinked by double-bond end-capped Pluronic F127: preparation, properties and coupling with the BZ reaction

Topological network design is an effective way to obtain new functionalities and regulate the properties of stimuli responsive hydrogels. In this work, poly(NIPAAm-co-Ru(bpy)32+) hydrogels (NIPAAm: N-isopropylacrylamide, Ru(bpy)32+: Ruthenium bipyridine complex monomer) crosslinked by amphiphilic triblock copolymers were designed and constructed by a photo-induced gelation method, utilizing double-bond end-capped Pluronic F127 (F127DA) as the crosslinking agent, NIPAAm and Ru(bpy)32+ as the monomers, α-ketoglutaric acid as the photoinitiator and H2O as the solvent. The resulting F127DA crosslinked hydrogels exhibit unique swelling behaviors, mechanical properties, fluorescent behaviors and thermosensitive properties and can be coupled with the BZ reaction. The present example may enrich the family of metal-containing polymer materials and provide clues to develop other functional hydrogels by designing topologically crosslinked network.

Extremely stretchable and electrically conductive hydrogels with dually synergistic networks for wearable strain sensors

Flexible strain sensors are highly used in soft robotics, human–machine interfaces and health monitoring devices. However, it is still a big challenge to construct strain sensors with excellent mechanical properties and broad sensing ranges. In this study, a class of extremely stretchable and electrically conductive hydrogels with dually synergistic networks are fabricated for wearable resistive-type strain sensors. Dually synergistic networks are composed of a soft poly(acrylic acid) (PAA) network and a rigid conductive polyaniline (PANI) network. The PAA network is crosslinked by amphiphilic block copolymers, and the PANI network is chemically doped and ionically crosslinked by phytic acid and these two networks are further interlocked by physical entanglements, hydrogen bonds and ionic interactions. The resulting hydrogels have high tensile strength, controllable conductivity and large tensile deformation (1160%). Moreover, these hydrogels are utilized for fabricating strain sensors with good sensitivity and a wide sensing range (0–1130%). The high performances of hydrogels make such strain sensors suitable for wearable devices monitoring both subtle and large strains induced by human motions, including moving of two hands, bending of joints, conducting of gestures and swallowing.

Reaction-based fluorescent probes for rapid detection of hydrogen sulfide in vivo

In this work, a series of novel fluorescent probes based on the fluorophores 3-benzothiazolyl-7-hydroxycoumarin/7-hydroxycoumarin were developed for detection of H2S. The probes exhibited excellent specific responses to H2S over other related competing species, including reactive sulfur, nitrogen and oxygen species. Moreover, the further successful imaging of the targetable fluorescent probe for sensing H2S in vivo was exciting and revealed that this targetable probe could serve as an efficient tool to study H2S-related chemical biology in physiological and pathological events.