Huiqiong Yan

Synthesis of alginate derivative via the Ugi reaction and its characterization

In this research, the systematic evaluation of fundamental properties of the alginate derivative (Ugi-Alg) synthesized by the Ugi reaction is presented. The structure of Ugi-Alg with the degree of substitution of 23.24% was confirmed by FT-IR and (1)H NMR spectrometers. The X-ray diffraction (XRD) results indicate the amorphous structure and the crystal structure change of Ugi-Alg, which is possibly ascribed to the destruction of inter- and intra-molecular hydrogen bonding interactions during the Ugi reaction. From thermal gravimetric analysis (TGA) and fluorescence spectrophotometer, Ugi-Alg shows high thermal stability and good amphiphilic functionality with the critical aggregation concentration of 0.07 g/L in 0.15 mol/L aqueous NaCl solution. Transmission electron microscope (TEM) image and dynamic light scattering (DLS) reveal that stable Ugi-Alg self-aggregated micelle with the average size of 162.3 nm and ζ potential at about -31.7 mV could form in the aqueous media, which presents tremendous potential in pharmacology and tissue engineering.

Modification of montmorillonite by ball-milling method for immobilization and delivery of acetamiprid based on alginate/exfoliated montmorillonite nanocomposite

The objective of this study was to develop a sustained drug release system based on alginate/exfoliated montmorillonite nanocomposite for acetamiprid, a neonicotinoid insecticide, to improve its sustained release performance. Montmorillonite (MMT) was modified with cetyl trimethyl ammonium bromide (CTAB) using a ball-milling method. Then, acetamiprid was immobilized into the modified MMT layers through freeze-drying technology. Subsequently, the drug-loaded alginate-exfoliated MMT composite beads were prepared by dropwise addition of the mixture of the drug-loaded modified MMT and the alginate solution into the calcium chloride and chitosan blended solutions. The structure and surface morphology of the modified MMT and composite materials were determined by the means of Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM), dynamic light scattering (DLS), BET-specific surface area measurements, thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) analysis. The experiments on immobilization and release of acetamiprid were performed to examine the effect of the modified MMT on the properties of the composite beads. Experimental results showed the intercalation of CTAB into MMT has been successfully achieved during the ball-milling process, which was beneficial to the formation of exfoliated MMT nanocomposites in alginate matrix. The intensive force supplied during the superfine pulverization of the ball-milling process was effective to increase the modified MMT’s specific surface areas and decrease its particle size, consequently improving the drug-loading rate (DL) and encapsulation efficiency (EE) of the composite beads. The alginate/exfoliated MMT nanocomposite formulation exhibited a slow and sustained release property, which was demonstrated as a promising carrier material to promote the efficient use of organic pesticide, and thereby reduce environmental pollution.

A novel and homogeneous scaffold material: preparation and evaluation of alginate/bacterial cellulose nanocrystals/collagen composite hydrogel for tissue engineering

Alginate is a well-known biomaterial which has been widely used in tissue engineering due to its excellent property. However, there are still several drawbacks, such as weak mechanical strength, the lack of cell recognition sites for cell adhesion, extensive swelling and uncontrolled degradation that limit its practical application. Therefore, the internal gelation using CaCO3–GDL complex and the incorporation of bacterial cellulose nanocrystals (BCNs) and type I collagen (COL) as the reinforcing component into alginate matrix were proposed to prepare the novel and homogeneous alginate/bacterial cellulose nanocrystals/collagen composite scaffold (ALG/BCNs/COL). The morphology, porosity, mechanical property, swelling and degradation behavior, and cytotoxicity of the resultant scaffold were investigated. The experimental results showed that ALG/BCNs/COL revealed good three-dimensional (3D) architecture as well as lamellar and porous morphologies. The incorporation of BCNs into alginate matrix obviously decreased the pore size and maintained the porosity of ALG/BCNs/COL, which was in favour of mechanical integrity. FT-IR spectra and XRD analysis revealed that the components of ALG/BCNs/COL, such as SA, BCNs and COL were combined together by intermolecular hydrogen bonds, which could effectively inhibit large swelling and retard the biodegradation of the composite scaffold. Finally, cell studies results indicated that both MC3T3-E1 and h-AMS cells were viable and proliferate well on the composite scaffold.

Investigation of modified sodium alginate-Alkyl glycoside interactions in aqueous solutions and at the oil–water interface

The interaction of cholesteryl-grafted sodium alginate derivative (CSAD) and decyl-β-D-glucopyranoside (DGP) in solution was studied through the surface tension method, fluorescence spectroscopy, electron paramagnetic resonance (EPR), and dynamic light scattering. Results showed that DGP and CSAD exhibit competitive adsorption behaviour at the water–gas interface and that this competitive behaviour can be intensified by NaCl. EPR revealed that the cholesterol groups of CSAD participate in the formation of micellar structures. The steric effect of the cholesterol groups reduces the microviscosity of the micellar structure, but high-concentration NaCl can weaken the polarity and increase the microviscosity of the formed micellar structure. In addition, at a high DGP concentration, high-concentration NaCl can facilitate DGP precipitation; this condition causes abnormal phenomena of surface tension, fluorescence spectroscopy, and EPR. For the emulsion system, analysis of particle size and rheology indicated that DGP and CSAD form a network structure between oil and water interfaces through interaction and thus enhance the non-Newtonian fluid properties of the emulsion. Owing to the competitive adsorption between CSAD and DGP at the oil–water interface, DGP gradually replaces CSAD with the increase in DGP concentration. With a further increase in DGP concentration, the stable steric effect of polymers between oil drops may disappear, and oil drops may aggregate mutually.

Fabrication and evaluation of chitosan/NaYF4:Yb3+/Tm3+ upconversion nanoparticles composite beads based on the gelling of Pickering emulsion droplets

The rare earth ion doped upconversion nanoparticles (UCNPs) synthesized by hydrophobic organic ligands possess poor solubility and low fluorescence quantum yield in aqueous media. To conquer this issue, NaYF4:Yb3+/Tm3+ UCNPs, synthesized by a hydrothermal method, were coated with F127 and then assembled with chitosan to fabricate the chitosan/NaYF4:Yb3+/Tm3+ composite beads (CS/NaYF4:Yb3+/Tm3+ CBs) by Pickering emulsion system. The characterization results revealed that the as-synthesized NaYF4:Yb3+/Tm3+ UCNPs with an average size of 20nm exhibited spherical morphology, high crystallinity and characteristic emission upconversion fluorescence with an overall blue color output. The NaYF4:Yb3+/Tm3+ UCNPs were successfully conjugated on the surface of chitosan beads by the gelling of emulsion droplets. The resultant CS/NaYF4:Yb3+/Tm3+ CBs showed good upconversion luminescent property, drug-loading capacity, release performance and excellent biocompatibility, exhibiting great potentials in targeted drug delivery and tissue engineering with potential tracking capability and lasting release performance.

Synthesis of a benzyl-grafted alginate derivative and its effect on the colloidal stability of nanosized titanium dioxide aqueous suspensions for Pickering emulsions

TiO2 nanoparticles (nano-TiO2) as one of the most extensively used nanoscale materials easily undergo spontaneous aggregation and gravity sedimentation ascribed to their high adsorption energy, which significantly restricts their actual applications. For this reason, a benzyl-grafted alginate derivative (BAD) with good colloidal interface activity, prepared by a bimolecular nucleophilic substitution (SN2) reaction, was used as the dispersant to stabilize nano-TiO2. The structure and colloidal properties of BAD was evaluated by FT-IR spectroscopy, 1H NMR spectroscopy, thermal gravimetric analysis (TGA) and dynamic light scattering (DLS). The effects of pH and ionic strength on the dispersion stability of BAD/nano-TiO2 suspensions were also examined by DLS. To further probe its feasibility as a drug delivery system, the BAD/nano-TiO2 complex was applied as particulate emulsifiers to fabricate drug-loaded Pickering emulsions. Meanwhile, the morphology properties and the sustained release performance of the drug-loaded Pickering emulsions were also investigated. Experimental results showed that the adsorption of BAD on nano-TiO2 was achieved by an intermolecular hydrogen bond between the carboxylic functional groups of BAD and the Ti–OH of TiO2. The adsorption of BAD enhanced the electrostatic repulsion and steric hindrance between nano-TiO2 improving the dispersion stability of nano-TiO2 at different pH and ionic strength. Additionally, the obtained Pickering emulsions displayed good drug-loading capacity and sustained release performance with the release mechanism of non-Fickian transport, which exhibited great potential in the pharmaceutical field.

Synthesis of Zn–Fe double metal cyanide complexes with imidazolium-based ionic liquid cocatalysts via ball milling for copolymerization of CO2 and propylene oxide

In this work, Zn–Fe double metal cyanide (DMC) catalysts were successfully synthesized via clean and efficient ball milling. Imidazolium-based ionic liquids as cocatalysts were incorporated into the structure of the DMC catalysts during the grinding process. The modified Zn–Fe DMC catalysts were effective for the alternating copolymerization of carbon dioxide and propylene oxide under controlled reaction conditions. The properties and structures of the Zn–Fe DMC catalysts and the resulting polymers were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction, elemental analysis, 1H and 13C NMR spectroscopy, gel permeation chromatography, and thermogravimetric analysis. The results indicate that the Zn–Fe DMC catalysts exhibit higher thermal stability compared to the DMC catalysts without imidazolium-based ionic liquids (DMC-Blank). We determined that the introduction of a small amount of imidazolium-based ionic liquids can increase the carbonate content of the poly(propylene carbonate) (PPC) copolymer in the range of 18.48–29.00%. The turnover numbers of PPC were ∼4.40. In addition, the measured number-average relative molecular mass was in the range of 2.96 × 103–4.98 × 103 with a narrow polydispersity index of 1.00–1.08.