Yuehui Hou

Controllable self-growth of a hydrogel with multiple membranes

The controllable self-growth of a supramolecular hydrogel of folic acid (FA) was developed based on the conduction of transition metal ions. The growth behavior of the gel could be flexibly controlled by adjusting the ambient environmental factors such as gelator concentration, temperature and external chemical stimuli. The obtained gel was characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM) and rheological measurements. Differential scanning calorimetry (DSC) showed that the gel possessed excellent thermal stability. A mechanism for the fibrous formation of the gel was suggested based on the experimental results of Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance spectroscopy (NMR) and UV-Vis spectroscopy. The gel exhibited multiple stimuli-responsive properties to changes in ligand and pH. Furthermore, the gel can be incorporated into multi-layer hydrogels in both artificial and spontaneous ways, showing the advantages of self-growth and flexible control of the gel system. This novel hydrogel and the preparation strategy may provide a new route to rationally design advanced materials for biomedical applications.

Self-recovering β-cyclodextrin gel controlled by good/poor solvent environments

A unique β-cyclodextrin (β-CD) gel with ordered structure was fabricated. The ordered aggregation of β-CD was achieved by controlling the solubility of β-CD in good/poor solvents. Physicochemical properties of the gel were systematically investigated. Mechanical properties were tested by rheological measurements, and the fibrous morphology was observed by confocal laser scanning microscopy. The anisotropic property of gel fibers was detected under polarized optical microscopy. Well-defined tetragonal and channel packed microstructures were formed in gel fibers, which revealed hollow channels of cyclodextrins. By changing physicochemical environments, macroscopic phase transitions were aroused, and self-recovering phenomena occurred when a certain amount of NaCl was added into the gel as a stimulus or the shear rate loop test was performed (thixotropy). By adjusting the concentrations of external stimuli or volume ratios of good/poor solvents, properties of the gel including mechanical strength or thermostability can be easily altered. The ordered empty channels assembled by CDs with the self-recovering properties may shed new light on this traditional host molecule.

Multi-responsive supramolecular organogel with a crystalline-like structure

A multi-responsive cyclodextrin-based organogel with a crystalline-like structure is first reported. An amount of β-cyclodextrin (β-CD) and lithium chloride (LiCl) was added into N,N-dimethylformamide (DMF), and the system obtained could transform instantly from a transparent solution into a gel state by introducing ethylene diamine (EDA), and then the gel could turn into another precipitate-like gel by undergoing a heating-cooling process. Among a series of aliphatic amines, only EDA was found to be able to induce the gel formation. Both the gels possess crystalline-like structures in their morphology with sheet-like layers, in a highly-ordered channel-type packing mode, which were proved by OM, SEM, XRD, and FT-IR measurements. Furthermore, the gel could respond to H(+) and Cu(2+) by transforming into an amorphous precipitate. This research may pave the way for the design of novel smart materials.

Organogels based on β-cyclodextrin system with molecular recognition property

We reported a supramolecular system consisted of β-cyclodextrin, N,N-dimethylformamide and LiCl, which could exhibit different behaviors toward various alcohols. When some liquid monohydric alcohols were injected into the system at room temperature, a semitransparent organogel (the ambient temperature organogel) was formed. Compared with liquid monohydric alcohols, the addition of solid alcohols could induce the formation of a heat-set organogel, a solution, and an ice-like crystal at different temperatures. The xerogels and dried ice-like crystal were characterized by scanning electron microscope, Fourier transform infrared spectroscopy, X-ray powder diffraction, thermogravimetry and derivative thermogravimetry. The systems were also studied by 1H nuclear magnetic resonance and 2D rotating frame overhauser effect spectroscopy. The alcohol-responsive properties of this system could be further designed as molecule switches based on molecular recognition.Graphical AbstractThe mechanism of the three-dimensional network formation by self-assembly in the systems: a, LiCl and heat (or liquid monohydric alcohol); b, LiCl, solid alcohol and heat (or cool). We found a novel supramolecular system containing β-cyclodextrin. It was a clear solution at room temperature and could form a heat-set organogel by heating. It could exhibit different behaviors toward various alcohols: ambient temperature organogel, ice-like crystal, heat-set organogel or solution.

A facile method to construct dual-responsive organogels with color changes

A novel organogel that is dually responsive to pH and Li+ was facilely constructed from mixtures of β-cyclodextrin, thymolphthalein and sodium formate in N,N′-dimethylacetamide. Acidity (pH) can trigger a color change of the organogels between a transparent colorless state and a dark-blue state due to the presence of thymolphthalein. It is interesting that Li+ could decompose the gel system while Na+ and K+ do not disturb the gelatinous state. Scanning electron microscopy (SEM) images show that these organogels are composed of fibrous structures. These organogels possess relatively high viscoelasticity indicated by rheology measurements. A mechanism for the gel formation is proposed based on the results of X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). The systems could be expected to act as non-liquid materials for sensing with the naked eye.

Transformation from a heat-set organogel to a room-temperature organogel induced by alcohols

A unique transformation from a heat-set organogel to a room-temperature organogel induced by ethanol (EtOH) was reported here. When the system containing β-cyclodextrin, 4,4′-isopropylidenediphenol, N,N-dimethylacetamide and LiCl was heated to the gelling temperature (Tgel), a heat-set organogel would be formed. In contrast, a semitransparent organogel (room-temperature organogel) could be obtained by injecting EtOH into the system at ambient temperature. In this transformation process, EtOH played a role in the formation of hydrogen bonds, which was critical for the self-assembly. The influence of other guest molecules, solvents and alcohols on this transformation was also investigated. These organogels were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction, thermal gravity analysis and differential thermal gravity. Further, the formation mechanism of the organogels was proposed based on the above measurements.

Light-responsive drug carrier vesicles assembled by cinnamic acid-based peptide

A novel cinnamic acid-based dipeptide is designed and prepared from cinnamic acid and glycylglycine. In aqueous solution, the molecules can self-assemble into vesicular structures, which were characterized in detail by transmission electron microscopy, scanning electron microscopy, and dynamic light scattering. Aromatic stacking and intermolecular hydrogen bonding interactions are regarded as the driving force in the formation of the stable supramolecular structure. Subsequently, the stimuli-responsive property of the vesicles to UV irradiation was also studied. The vesicles were also found to be able to efficiently carry hydrophobic drugs. We believe that this study may provide more references in the fields of body-friendly smart materials with the hope of in vivo applications.