Shaoyu Lü

Environmentally Friendly Slow-Release Nitrogen Fertilizer

To sustain the further world population, more fertilizers are required, which may become an environmental hazard, unless adequate technical and socioeconomic impacts are addressed. In the current study, slow-release formulations of nitrogen fertilizer were developed on the basis of natural attapulgite (APT) clay, ethylcellulose (EC) film, and sodium carboxymethylcellulose/hydroxyethylcellulose (CMC/HEC) hydrogel. The structural and chemical characteristics of the product were examined. The release profiles of urea, ammonium sulfate, and ammonium chloride as nitrogen fertilizer substrates were determined in soil. To further compare the release profiles of nitrogen from different fertilizer substrates, a mathematical model for nutrient release from the coated fertilizer was applied to calculate the diffusion coefficient D. The influence of the product on water-holding and water-retention capacities of soil was determined. The experimental data indicated that the product can effectively reduce nutrient loss, improve use efficiency of water, and prolong irrigation cycles in drought-prone environments.

Injectable and Self-Healing Carbohydrate-Based Hydrogel for Cell Encapsulation

With the fast development of cell therapy, there has been a shift toward the development of injectable hydrogels as cell carriers that can overcome current limitations in cell therapy. However, the hydrogels are prone to damage during use, inducing cell apoptosis. Therefore, this study was carried out to develop an injectable and self-healing hydrogel based on chondroitin sulfate multiple aldehyde (CSMA) and N-succinyl-chitosan (SC). By varying the CSMA to SC ratio, the hydrogel stiffness, water content, and kinetics of gelation could be controlled. Gelation readily occurred at physiological conditions, predominantly due to a Schiff base reaction between the aldehyde groups on CSMA and amino groups on SC. Meanwhile, because of the dynamic equilibrium of Schiff base linkage, the hydrogel was found to be self-healing. Cells encapsulated in the hydrogel remained viable and metabolically active. In addition, the hydrogel produced minimal inflammatory response when injected subcutaneously in a rat model and showed biodegradability in vivo. This work establishes an injectable and self-healing hydrogel derived from carbohydrates with potential applications as a cell carrier and in tissue engineering.

Multifunctional Slow-Release Organic−Inorganic Compound Fertilizer

Multifunctional slow-release organic-inorganic compound fertilizer (MSOF) has been investigated to improve fertilizer use efficiency and reduce environmental pollution derived from fertilizer overdosage. The special fertilizer is based on natural attapulgite (APT) clay used as a matrix, sodium alginate used as an inner coating and sodium alginate-g-poly(acrylic acid-co-acrylamide)/humic acid (SA-g-P(AA-co-AM)/HA) superabsorbent polymer used as an outer coating. The coated multielement compound fertilizer granules were produced in a pan granulator, and the diameter of the prills was in the range of 2.5-3.5 mm. The structural and chemical characteristics of the product, as well as its efficiency in slowing the nutrients release, were examined. In addition, a mathematical model for nutrient release from the fertilizer was applied to calculate the diffusion coefficient D of nutrients in MSOF. The degradation of the SA-g-P(AA-co-AM)/HA coating was assessed by examining the weight loss with incubation time in soil. It is demonstrated that the product prepared by a simple route with good slow-release property may be expected to have wide potential applications in modern agriculture and horticulture.

A convenient way to synthesize comb-shaped chitosan-graft-poly (N-isopropylacrylamide) copolymer.

Comb-shaped copolymers comprised of hydrophobic and hydrophilic blocks are self-assembled in aqueous solution, which results that they are suitable for delivery of hydrophobic drug molecules. Chitosan (CS) is an important biomaterial used widely in medical applications. Herein, a comb-shaped cationic copolymer composed of long biocompatible CS main chains and short PNIPAAm side chains was prepared via atom transfer radical polymerization (ATRP) by attaching an ATRP initiating group to N-phthaloyl chitosan. By subsequent removal of the protective groups on N-phthaloyl chitosan-graft-poly(N-isopropylacrylamide) (PHCS-g-PNIPAAm) copolymer with N(2)H(4)·H(2)O lead to the polymer pendant amino groups, this study attempted to synthesize a pH/temperature multi-responsive material. This chitosan-graft-poly(N-isopropylacrylamide) (CS-g-PNIPAAm) copolymer is self-assembled in aqueous solution into stimuli-responsive core-shell micelles with hydrodynamic diameters of about 170 nm. Structural organization and solution behavior were then investigated utilizing (1)H NMR spectroscopy, transmission electron microscopy (TEM) and dynamic light scattering (DLS).

Facile preparation of pH-sensitive micelles self-assembled from amphiphilic chondroitin sulfate-histamine conjugate for triggered intracellular drug release.

Stimuli-responsive materials, enabling drugs to be released in the acidic tumor and intracellular microenvironments, draw an increasing attention in chemotherapy. Here novel pH-sensitive biodegradable micelles are fabricated using a one-step, one-medium process without organic solvent for efficient loading and rapid intracellular release of hydrophobic cargos. The amphiphilic chondroitin sulfate-histamine conjugate (CS-his) were successfully synthesized and assembled into nanoparticles in aqueous medium with desirable size (133 nm) and low critical micelle concentration (CMC) (0.05 mg/L). Owning to the pH-sensitive structure of imidazole, the nanoparticles show pH-responsive behavior upon reducing the pH value of surrounding media, accompany with formation of large aggregates and increase of ζ potential. When the nanoparticles were utilized to deliver the model drug DOX, they exhibited a specific on-off switch drug release behavior, triggering DOX release in acidic surroundings (intracellular endosomes) and sealing DOX in neutral surroundings (blood circulation or extracellular matrix). CCK-8 assays and confocal laser scanning microscopy (CLSM) against HepG2 cells indicated that the nanoparticles themselves had no associated cytotoxicity, while drug-loaded nanoparticles possessed high cytotoxicity to model cells and presented high efficiency of cellular uptake. These flexible micelles with an on-off switched drug release may offer a promising pattern to accurately deliver a wide variety of hydrophobic payloads to tumor cells for cancer therapy.

Synthesis, characterization and functional properties of low substituted acetylated corn starch

Acetylated corn starch (ACS) was synthesized by the reaction of native corn starch (NCS) with acetic anhydride (AA) in an aqueous medium in the presence of sodium hydroxide as a catalyst. The factors that could affect the degree of substitution (DS) and reaction efficiency (RE) of corn starch were investigated which included the reaction temperature and time, the mass ratio of AA to starch, the ratio of the water volume to starch mass and pH. The optimal DS of 0.071 and RE of 67.05% was obtained. FTIR spectrometry showed new bands at 1733, 1375 and 1252 cm(-1). The SEM of the ACS indicated some cavities on the granules which fused together, compared with NCS. Wide angle X-ray diffraction revealed that ACS had a similar profile as NCS (A type). However, the intensity of peaks were diminished. DSC thermograms exhibited that ACS had some lower gelatinization temperatures and enthalpies than NCS. The functional properties of ACS such as the swelling power, solubility, water absorption, clarity, freeze-thaw stability, retrogradation and viscosity were also studied. The results suggest that the ACS has much better functional properties than the NCS, and could be expected to have wide applications especially in food industry.

Thermoresponsive injectable hydrogel for three-dimensional cell culture: chondroitin sulfate bioconjugated with poly(N-isopropylacrylamide) synthesized by RAFT polymerization

A major challenge in in vitrocell delivery is to provide an optimum environment that mimics natural conditions to maintain correct cellular functions. To address this challenge, we present a biohybrid injectable hydrogel based on chondroitin sulfate (ChS) and poly(N-isopropylacrylamide) (PNIPAAm). PNIPAAm was synthesized at various molecular weights between 5 to 20 kDa by RAFT polymerization in the presence of S-1-dodecyl-S′-(α, α′-dimethyl-α′′-acetic acid) trithiocarbonate as a chain transfer agent. The molecular weight range suitable for renal clearance was an important factor in the experimental design. The phase transition behavior and the gelation time of the hydrogel were measured to evaluate its possibility for further clinical application. Furthermore, hydrogel degradation was also a concern for clinical application. Samples were incubated in PBS with 100 U/ml of hyaluronidase at 37 °C to determine their degradation behaviors and the results revealed that the hydrogel was biodegradable in physiological conditions. To evaluate the biocompatibility for potential use of the hydrogel as a cell delivery vehicle, in vitro two-dimensional (2-D) and three-dimensional (3-D) cell cultures were performed. Cells demonstrated excellent viability when cultured with the hydrogel. In addition, the arrangement of multiple cell layers in the hydrogel was achieved. These results indicate the thermoresponsive injectable hydrogel may be expected to have wide potential applications as a vehicle for the delivery of therapeutic cells.

Synthesis of linear amphiphilic tetrablock quaterpolymers with dual stimulus response through the combination of ATRP and RAFT by a click chemistry site transformation approach

Well-defined linear amphiphilic tetrablock quaterpolymers with dual stimulus response, poly(ethylene glycol)-b-poly(styrene)-b-poly(N-isopropylacrylamide)-b-poly(2-(dimethylamino)ethyl methacrylate) (PEG-b-PS-b-PNIPAM-b-PDMAEMA), were successfully synthesized through the combination of ATRP and RAFT by a click chemistry site transformation approach. Bromine-terminated diblock copolymer PEG-b-PS-Br was first prepared by ATRP of styrene initiated with macro-initiator PEG-Br, which was prepared from the esterification of PEG and 2-bromoisobutyryl bromide. PEG-b-PS-Br can then be converted into the azido-terminated diblock copolymer, PEG-b-PS-N3, by nucleophilic substitutions. Site transformation of PEG-b-PS-N3 into a macro-chain transfer agent (CTA) for RAFT polymerization was accomplished using a copper-catalyzed click chemistry approach. Afterwards, the novel linear tetrablock quaterpolymers, PEG-b-PS-b-PNIPAM-b-PDMAEMA, were synthesized by successive RAFT polymerizations of NIPAM and DMAEMA. The polymerization data indicated that both RAFT processes were well controlled. The structures of the linear amphiphilic tetrablock quaterpolymers and the corresponding precursors were characterized by 1H NMR, FTIR and GPC. Containing thermoresponsive PNIPAM and pH-responsive PDMAEMA blocks, the obtained amphiphilic PEG-b-PS-b-PNIPAM-b-PDMAEMA tetrablock quaterpolymers self-assembled into spherical micelles with hydrophobic PS cores and hydrophilic PEG/PNIPAM/PDMAEMA shells at acidic pH and room temperature but self-assembled into PS/PDMAEMA-core micelles at alkaline pH and room temperature, and PS/PNIPAM-core micelles at acidic pH and elevated temperatures.

Self-assembly behavior of pH- and thermo-responsive hydrophilic ABCBA-type pentablock copolymers synthesized by consecutive RAFT polymerization

A multi-responsive hydrophilic ABCBA-type pentablock copolymer, consisting of poly(ethylene glycol), poly(N-isopropylacrylamide), and poly(2-(diethylamino)ethyl methacrylate), PDEA-b-PNIPAM-b-PEG-b-PNIPAM-b-PDEA, was synthesized by consecutive reversible addition–fragmentation chain transfer (RAFT) polymerization. The polymerization showed all of the expected features of living radical polymerization and allowed the synthesis of copolymers with controlled lengths of the PNIPAM and PDEA blocks. Due to the multi-component and multi-functional nature of the pentablock copolymer, the solution properties can be manipulated by the changing of parameters such as temperature, pH etc. For example, the copolymer could be dissolved in acidic aqueous solution at room temperature, since the pH was below the pKa of the PDEA block, and the temperature was below the lower critical solution temperature (LCST) of the PNIPAM block. While in alkaline solution at room temperature, the copolymer self-assembled into core–shell–corona micelles, with the hydrophobic PDEA block as the core, the thermoresponsive PNIPAM block as the shell and the hydrophilic PEG block as the corona. At elevated temperatures in acidic media, the copolymer self-assembled into PNIPAM-core micelles with mixed hydrophilic PEG and pH-responsive PDEA coronas. Moreover, the self-assembly behavior of the pentablock copolymers in aqueous solution was investigated by varying the length of PDEA blocks.

Synthesis and characterization of carboxymethyl potato starch and its application in reactive dye printing

Carboxymethyl potato starch (CMPS) was synthesized with a simple dry and multi-step method as a product of the reaction of native potato starch and monochloroacetic acid in the presence of sodium hydroxide. The influence of the molar ratio of sodium hydroxide to anhydroglucose unit, the volume of 95% (v/v) ethanol, the rotation rate of motor driven stirrer and the reaction time for degree of substitution (DS) were evaluated. The product was characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and X-ray diffractometry (XRD). FTIR spectrometry showed new bonds at 1618 and 1424 cm⁻¹ when native starch underwent carboxymethylation. SEM pictures showed that the smooth surface of native starch particles was mostly ruptured. XRD revealed that starch crystallinity was reduced after carboxymethylation. The viscosity of the mixture paste of carboxymethyl starch and sodium alginate (SA) was measured using a rotational viscometer. In addition, the applied effect of mixed paste in reactive dye printing was examined by assessing the fabric stiffness, color yield and sharp edge to the printed image in comparison with SA. And the results indicated that the mixed paste could partially replace SA as thickener in reactive dye printing. The study also showed that the method was low cost and eco-friendly and the product would have an extensive application in reactive dye printing.