Hong Wang

Shape controllable microgel particles prepared by microfluidic combining external ionic crosslinking.

Alginate microgels with varied shapes, such as mushroom-like, hemi-spherical, red blood cell-like, and others, were generated by combining microfluidic and external ionic crosslinking methods. This novel method allows a continuous fine tuning of the microgel particles shape by simply varying the gelation conditions, e.g., viscosity of the gelation bath, collecting height, interfacial tension. The release behavior of iopamidol-loaded alginate microgel particles with varied morphologies shows significant differences. Our technique can also be extended to microgels formation from different anionic biopolymers, providing new opportunities to produce microgels with various anisotropic dimensions for the applications in drug delivery, optical devices, and in advanced materials formation.

Microfluidic Fabrication and Thermoreversible Response of Core/Shell Photonic Crystalline Microspheres Based on Deformable Nanogels

Soft photonic crystals (PC) are more appealing due to the responsiveness of the building blocking-deformable nanoparticles to the external stimuli. In this report, we demonstrate, for the first time, the generation of soft core/shell PC microspheres through a combination of a microfluidic technique, encapsulation of well-ordered temperature responsive polymer nanogels suspension, and photopolymerization of a transparent shell resin. This strategy not only ensures the monodispersity of core/shell PC microspheres, but also precisely controls their size, shell thickness, and optical properties by simply adjusting the flow rate ratio and mass fraction of the nanogels. More interestingly, the intensity of the reflection spectra of the crystalline nanogel arrays in the core can be modulated reversibly by controlling the shell thickness or the temperature. As a result of their symmetric structure, the resulting PC microspheres exhibited excellent structural colors and photonic band gaps for normal incident light independent of the position on the spherical surface. Multifunctional PC microspheres can also be generated by simply dispersing functional species together with the nanogels. This core/shell PC microsphere with tunable shell thickness and reversible thermoresponse could be significant for potential applications in the fields of chemical/biological sensors, display, encoding, and optical switching.

Janus photonic crystal microspheres: centrifugation-assisted generation and reversible optical property.

A new strategy to prepare core/shell Janus photonic crystal (PC) microspheres with reversible optical spectrum property is demonstrated. The microfluidic technique was employed to generate the uniform core/shell PC microspheres containing nanogels aqueous suspension. Under centrifugal force, the nanogel particles homogeneously dispersed in the core of microspheres would aggregate in the half of the microspheres, leading to Janus PC microspheres with varied reflection spectra at the different side of the spheres. More interestingly, such Janus structure of PC microspheres and their reflection spectrum were significantly reversible when the centrifugation was employed and removed alternatively. In addition, due to the soft and thermal-responsive nature of the building blocks (e.g., nanogels), Janus structures and optical properties of the PC microspheres are highly influenced by the temperature, centrifugal speed, and time, providing the other parameters on the manipulation of properties of the PC microspheres. This strategy provides a new concept for the preparation of Janus PC microspheres with tunable structures and optical properties, which will find potential applications in the field of sensors, optical devices, barcodes, etc.

Ion-unquenchable and thermally "on-off" reversible room temperature phosphorescence of 3-bromoquinoline induced by supramolecular gels.

Ion-unquenchable and thermally on-off reversible room temperature phosphorescence (RTP) can be induced by entrapping 3-bromoquinoline (3-BrQ) into supramolecular gels formed by the self-assembly of a sorbitol derivative (DBS). In comparison with conventional substrates inducing RTP, the gel state 3-BrQ/DBS can produce strong RTP due to the efficient restriction of the vibration of 3-BrQ. Notably, the rather inconvenient deoxygenation is no longer necessary in the preparation of 3-BrQ/DBS gels. The produced RTP was found to be very fast to reach stable, not depending on the standing time. As a reference, in the liquid state of 3-BrQ/sodium deoxycholate (NaDC), stable RTP can be observed after standing for 5 h. The investigation of RTP quenching indicates that the mechanism of RTP induced by DBS gels mainly involves the microenvironment in which 3-BrQ is located. 3-BrQ was entrapped in the hydrophobic 3D network structure of DBS gels, thereby restricting the motion and collision of 3-BrQ and avoiding RTP quenching and additionally quenching by ions. Furthermore, the RTP of 3-BrQ/DBS gels show an excellent on-off effect at 10 or 80 °C. This indicates that the solid DBS gel is beneficial for the preparation of RTP sensor devices.

Polymerized organogel particles formed and imprinted by chiral gelators and their selective adsorption for phenylalanine racemates

Novel polymerized supramolecular organogel particles were prepared by gelation and subsequent suspension polymerization. Herein, gelator was also used as a chiral template. After extraction of the gelator with ethanol, imprinted supramolecular organogel particles were obtained. SEM analysis of the particles showed porous structures after ethanol extraction. The imprinted particles were loaded as a stationary phase into a column to separate L- and D-phenylalanine racemic mixtures. The circular dichroism (CD) and optical rotation of the racemic mixtures that flowed through the column indicated that the imprinted supramolecular organogel particles exhibited distinct selective adsorption for L-phenylalanine.

Reinforcement of phenylalanine-based supramolecular hydrogels by hybridizing poly- (N-isopropylacrylamide) nanogels

In an aqueous solution of an L-phenylalanine derivative-based gelator, the addition of a suitable amount of thermosensitive poly(N-isopropylacrylamide) nanogel particles leads to the formation of hybridized supramolecular hydrogels. Due to the presence of the nanogel particles, the gelation ability of the gelator can be improved as shown by the decrease of the critical gelation concentration (CGC) of the gelator from 2.5 wt% to 0.8 wt% when 1 wt% of nanogels was employed. Meanwhile, the thermostability of the hybridized system was also improved. For instance, the phase transition temperature (TGS) increased from 48 °C to 61 °C. Rheological studies indicated that the supramolecular hydrogels can be significantly reinforced by hybridizing 0.6 wt% nanogels. When used as a drug carrier, the drug release behavior from the hybridized system can be controlled by changing the content of nanogels as well as the temperature.

Chiral Self-Assembly/Disassembly Transition of Supramolecular Aggregates Characterized by Variable Temperature Circular Dichroism Spectroscopy

Self-assembly and disassembly behavior of a series of chiral sorbitol-based derivatives in n-octanol were investigated by using the variable temperature circular dichroism (CD) technique. An attempt has been made to establish a novel strategy for the characterization of the self-assembly/disassembly transition by measuring the difference of CD signals of chiral aggregates.