Yuhong Feng

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.

A pH-responsive emulsion stabilized by alginate-grafted anisotropic silica and its application in the controlled release of λ-cyhalothrin

Alginate (Alg) was grafted on the surface of anisotropic silica (SiO2-x) via the Ugi reaction (Alg-SiO2-1, Alg-SiO2-2, and Alg-SiO2-4). Compared with pristine SiO2-x, modified SiO2-x is more sensitive to pH. Three stable liquid paraffin-in-water emulsions were prepared with Alg-SiO2-1, Alg-SiO2-2, and Alg-SiO2-4. Alg-SiO2-2 exhibited satisfactory emulsification ability. The emulsions became more stable as emulsion pH varied from 2.0 to 6.2 because of polymer chain interactions that led to the formation of a three-dimensional network. When the emulsion pH varied from 6.2 to 8.0, the particle charge increased, in turn increasing interparticle the electrostatic interactions that increased emulsion stability. When the emulsion pH was 9.0, the subsequent decrease in particle charge, decreased the emulsion stability. The model drug λ-cyhalothrin was embedded in the emulsions. A sustained-release assay demonstrated that increasing emulsion pH from 3.0 to 8.0 decreased cumulative drug release from the emulsion from 99.7% to 13.5%. This result indicated that the emulsion is a pH triggered drug delivery system. The sustained-release curves of λ-cyhalothrin are describable by the Weibull model.

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.

Structural and rheological characterizations of nanoparticles of environment-sensitive hydrophobic alginate in aqueous solution

Amphiphilic polymers that form self-assembled structures in aqueous media have been investigated and used for the diagnosis and therapy of various diseases, including cancer. In our work, a series of environment-sensitive hydrophobic alginates (Ugi-Alg) with various weight-average molecular mass values (Mw~6.7×105-6.7×104g/mol) were synthesized via Ugi reaction. The structure of Ugi-Alg was characterized by 1HNMR spectrometer. The electrostatic self-assembly of different molecular weight (Mw) and composition (M/G ratio) of Ugi-Alg chain under various Na+ concentrations, was investigated by dynamic light scattering, electron spin resonance experiments, and transmission electron microscopy. Result showed that by comparing to other Ugi-Alg, the mid-Mw Ugi-Alg (Mw~2.8×105g/mol) could form stable and homogeneous nanoparticles in low Na+ concentration solution. However, G/M values exerted no obvious effect on nanoparticles structure. Additionally, steady-shear flow, thixotropy and dynamical viscoelasticity tests were performed to characterize the rheological behavior of Ugi-Alg aqueous solutions as influenced by Mw and M/G ratio. All of the samples exhibited a non-Newtonian shear-thinning behavior above a critical shear rate (γ̇c2). The greater the Mw, the more sensitive the temperature-dependent behavior will be. The upward-downward rheograms showed that all of the systems evaluated in this study displayed a hysteresis loop, indicating a strong thixotropic behavior, and the thixotropic of mid-Mw Ugi-Alg was the strongest. The dynamical viscoelastic properties were characterized by oscillatory frequency sweep, revealing the gel-like viscoelastic behavior of mid-low Ugi-Alg and the fluid-like viscoelastic behavior of high-Mw Ugi-Alg.

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.

Self-aggregation behavior of hydrophobic sodium alginate derivatives in aqueous solution and their application in the nanoencapsulation of acetamiprid

In this study, cholesteryl-grafted sodium alginate derivatives (CSAD) with different molecular weights were synthesized by esterification. The structure of CSAD was confirmed by FT-IR and 1H NMR spectrometers. The effects of pH and CSAD polymer concentration on the self-assembled behavior and particle size of CSAD were investigated by fluorescence measurement (FM) and dynamic light scattering (DLS). In the presence of Ca2+, the cholesteryl-grafted sodium alginate derivative was used for fabricating self-assembled nanoparticles that can effectively encapsulate the drug acetamiprid. The drug-loaded nanoparticles were characterized by transmission electron microscopy (TEM). The encapsulation efficiency (EE) and acetamiprid drug release behavior from the nanoparticles were also studied. The results reveal that CSAD self-assembled nanoparticles had a diameter of 100nm and were nonaggregated in aqueous media; Moreover, the encapsulation efficiency and the release behavior of nanoparticles were influenced by the MW of CSAD. The mechanism of acetamiprid release was found to vary from non-Fickian (anomalous) to Fickian transport with a decrease in the molecular weight of CSAD.

Highly dispersed Ag nanoparticles embedded in alumina nanobelts as excellent surface-enhanced Raman scattering substrates

Nearly monodispersed Ag nanoparticles embedded in alumina nanobelts were fabricated with a template method by integrating facile coordination polymerization with an atomic layer deposition (ALD) technique. The composite nanobelts with specific hierarchical micro/nano-structure showed superior SERS properties for the R6G probe molecule.

Electrolyte and pH-sensitive amphiphilic alginate: synthesis, self-assembly and controlled release of acetamiprid

In this study, a pH-responsive amphiphilic alginate (Ugi-Alg) was synthesized via Ugi reaction without using a catalyst. The structure of Ugi-Alg was confirmed by FT-IR and 1H NMR spectroscopy. Amphiphilic alginate can form micelles in an aqueous medium due to its amphiphilic nature.. The impacts of Na+ concentration and pH on the micelle size were characterized by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The dynamic light scattering observations showed that micelle size increases with the decrease in Na+ concentration in aqueous solution. However, the micelle size decreases first and then increases as the pH value decreases from 5.3 to 2.0. Transmission electron microscopy confirmed that the mean size of micelles is 30–200 nm. In addition, a model hydrophobic pesticide (acetamiprid) was loaded in the micelles. The encapsulation efficiency and release behavior of micelles were studied, which could be controlled by Na+ concentration and pH. The results indicated that encapsulation efficiency of acetamiprid increases from 55% to 96% due to the increase in Na+ concentration from 0.01 M to 0.3 M. Moreover, with the decrease in pH from 5.3 to 2.0, encapsulation efficiency increases from 55% to 80%. Furthermore, the data of acetamiprid release kinetics could be well-fitted by the Weibull model.

Effect of an eco-friendly o/w emulsion stabilized with amphiphilic sodium alginate derivatives on lambda-cyhalothrin adsorption–desorption on natural soil minerals

The effects of amphiphilic O/W emulsions, stabilized by the alkyl polyglycoside (APG) or cholesterol-grafted sodium alginate (CSAD)/APG systems, on lambda-cyhalothrin adsorption/desorption mechanisms on natural soil minerals (i.e., illite and kaolinite) were investigated. Sorption and desorption of lambda-cyhalothrin onto soil minerals was studied via batch equilibration to give insight into the adsorption equilibrium, kinetics, and thermodynamics of lambda-cyhalothrin adsorption onto minerals. The results indicate the following: (i) The adsorption processes for the APG system and CSAD/APG system include: rapid adsorption, slow adsorption, and adsorption equilibrium. The adsorption kinetics of pesticide on illite and kaolinite are in accordance with the Ho and McKay model, and the adsorption isotherm conforms to the Freundlich model. In addition, the adsorption processes of pesticide for the two systems on minerals were spontaneous and feasible (ΔG0 < 0), endothermic (ΔH0 > 0), and mainly involved chemical bonding (ΔH0 > 60). (ii) The equilibrium adsorption percentages of the pesticide on illite for the APG system and CSAD/APG system were 42.4% and 64.8%, and the corresponding equilibrium adsorption percentages on kaolinite were 40.8% and 61.8%, respectively. Moreover, the pesticide adsorption rate K2-CSAD/APG was faster than K2-APG, and its adsorption capacity Kf-CSAD/APG was greater than Kf-APG. Meanwhile, the pesticide desorption Kfd in the CSAD/APG system was smaller than that in the APG system. As a result, this eco-friendly O/W emulsion based on amphiphilic sodium alginate derivatives might provide a green pesticide formulation, since it could reduce the amount of lambda-cyhalothrin entering aquatic systems to threaten non-target fish and invertebrate species.