eqin Yu

Synthesis and Swelling Behavior of Superabsorbents Cross-Linked with N-Maleyl Chitosan

A kind of superabsorbent based on the monomers maleic anhydride (MA) and acrylic acid (AA) was prepared by solution polymerization using ammonium peroxodisulfate (AP) and sodium bisulfite (NaHSO3) as initiator, and N-maleyl chitosan (N-MACH) as cross-linker. Effects of process parameters such as the amount of cross-linker, mass ratio of MA to AA, and neutralization degree of AA on the water absorbency of superabsorbents are discussed. The results indicated the water absorbency of superabsorbents increased and then decreased with the increase of MA content, the amount of the N-MACH cross-linker, and the neutralization degree of AA. Under the optimal conditions, the water absorbency of superabsorbents could reach l560.42 g/g and 83.7 g/g in distilled water and in 0.9% NaCl solution, respectively. In addition, to enhance the water absorbency of superabsorbents in 0.9% NaCl solution, polyvinyl alcohol (PVA) was introduced as interpenetrating polymer in the network and 2-acrylamido-2-methyl propane sulfonic acid (AMPS) was introduced as comonomer. It was proved that PVA and AMPS could effectively improve the water absorbency of superabsorbents both in distilled water and 0.9% NaCl solution.

Controllable preparation and characterization of the thermosensitive block polymers

Two kinds of triblock copolymers based on N-isopropylacrylamide (NIPAAm) and ethyl acrylate(EA), PEAn-PNIPAAmm-PEAn (BAB type) and PNIPAAmm-PEAn-PNIPAAmm (ABA type) were prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization. Thermosensitive block polymer of PEAn-PNIPAAmm-PEAn (BAB type) and PNIPAAmm-PEAn-PNIPAAmm (ABA type) self-assembly form flower coronal and dendritic micelles in water solution with hydrophobic PEA as the core and hydrophilic PNIPAAm as the shell, respectively. Critical micelle concentration (CMC) can be obtained by measuring the surface tension of the copolymer. The study reveals that CMC of micelles are significantly affected by the monomer weight ratios of EA/NIPAAM in block copolymer and block in the order. The higher the content of the hydrophilic block, the smaller the copolymer CMC, and ABA-type with respect to the BAB-type has a smaller CMC value. Particle size of self-assembled micelles decreased first and then rapidly increased with the temperature increasing, surfactant SDS significantly affects the particle size of the polymer. By measuring the light transmission ratio of the copolymer solution, the effect of the lower critical solution temperature (LCST) in the salt solution was investigated, and it was also found that the higher content of the hydrophilic block, the higher LCST of copolymer.

Synthesis and characterization of biodegradable thermoresponsive N-maleyl gelatin-co-P(N-isopropylacrylamide) hydrogel cross-linked with Bis-acrylamide for control release

Biodegradable N-maleyl gelatin (N-MAGEL) was synthesized with gelatin (GEL) and maleic anhydride (MAH) by acylation. With Bis-acrylamide (Bis) cross-linker, a series of cross-linked poly (N-isopropylacrylamide-co-N-maleyl gelatin) [P(NIPAAm-co-N-MAGEL)] hydrogels were prepared, and their lower critical solution temperature (LCST), water content, swelling/deswelling kinetics, drug delivery behaviors, and enzymatic degradation properties were investigated. As weight ratios of N-MAGEL/NIPAAm in hydrogel were increasing, water content increased, and it had no significant influence on LCST of hydrogel in spite of the weight ratios reaching 30:70. In the swelling/deswelling kinetics, hydrogels with higher weight ratios of N-MAGEL/NIPAAm exhibited faster swelling rate and slower deswelling rate. Drug delivery for bovine serum albumin (BSA) research indicated that increasing weight ratios of N-MAGEL/NIPAAm in hydrogels contribute to raising release time and cumulative release ratios. Lastly, hydrogels with higher weight ratios of N-MAGEL/NIPAAm degraded rapidly in phosphate-buffered saline (PBS) containing papain.

Amphiphilic alginate as a drug release vehicle for water-insoluble drugs

A preliminary study on the hydrophobic modified alginate (HM-alginate) as the drug delivery system for the model water-insoluble drugs, clofazimine and Amphotericin B was performed. It was found that HM-alginate can significantly increase the solubilities of these two drugs. The apparent water solubilities of clofazimine and Amphotericin B increased up to 1100 and 160 times, respectively, in aqueous solutions containing HM-alginate. The presence of sodium chloride in polymer solution decreased the solubilities of the drugs, compared to the salt-free solutions. HM-alginate also exhibited excellent sustained release effect, which increased with concentration. The type of HM-alginate, which we used herein, might have potential applications as water-insoluble drug delivery carrier.

Synthesis and characterization of temperature-sensitive and biodegradable hydrogel based on N-isopropylacrylamide

Based on a biodegradable cross-linker, N-maleyl chitosan (N-MACH), a series of Poly(N-isopropylacrylamide) (PNIPAAm) and Poly(N-isopropylacrylamide-co-acrylamide) [P(NIPAAm-co-Am)] hydrogels were prepared, and their lower critical solution temperature (LCST), swelling kinetics, equilibrium swelling ratio in NaCl solution, and enzymatic degradation behavior in simulated gastric fluids (SGF) were discussed. The LCST did not change with different cross-linker contents. By altering the NIPAAm/Am molar ratio of P(NIPAAm-co-Am) hydrogels, the LCST could be increased to 39°C. The LCST of the hydrogel was significantly influenced by the monomer ratio of the NIPAAm/Am but not by the cross-linker content. In the swelling kinetics, all the dry hydrogels exhibited fast swelling behavior, and the swelling ratios were influenced by the cross-linker content and NIPAAm/Am molar ratios. Equilibrium swelling ratio of all the hydrogels decreased with increasing NaCl solution concentration. In enzymatic degradation tests, the weight loss of hydrogels was dependent on the cross-linker contents and the enzyme concentration.

Preparation and characterization of biosurfactant based on hydrophobically modified alginate

Hydrophobic modified alginate (HM-alginate) was synthesized using a low-energy, environment-friendly process in aqueous solution, with sodium alginate and dodecyl glycidyl ether as starting materials. The HM-alginate was characterized using 1H NMR, and the reaction efficiency was about 40%. The HM-alginate aggregated in solution; the critical micelle concentration (CMC) was determined using surface tension and dynamic light scattering methods. We observed reasonable agreement between the CMC values obtained by the different techniques, and the CMC was 4.0 × 10−4 g/mL. The zeta-potential of the HM-alginate in aqueous solution was about −82 mV, which is higher than −51 mV of the sodium alginate. Rheology measurements showed that the HM-alginate solution exhibits a Newtonian behavior at all shear rates, whereas the apparent viscosity is very low. The solubility of the liposoluble substance Sudan IV increased significantly with HM-alginate concentration. This result is promising for potential applications of HM-alginate as an ecology-safe material to encapsulate lipophilic substances.

Synthesis and characterization of thermoresponsive hydrogels cross-linked with chitosan

Hydrogels composed of N-isopropylacrylamide (NIPAAm) and acrylic acid (AAc) were prepared by redox polymerization with degradable chitosan cross-linkers. Chitosan degradable cross-linkers were synthesized by the acrylation of the amine groups of glucosamine units within chitosan and characterized with 1H NMR. With the chitosan cross-linkers, loosely cross-linked poly(N-isopropylacryamideco-acrylic acid) [P(NIPAAm-co-AAc)] hydrogels were prepared, and their phase transition behavior, lower critical solution temperature (LCST), water content and degradation properties were investigated. The chitosan cross-linked P(NIPAAm-co-AAc) hydrogels were pliable and transparent at room temperature. The LCST could be adjusted at 32∼39°C by alternating the feed ratio. Swelling was influenced by NIPAAm/AAc monomer ratio, cross-linking density, swelling media, and temperature. All hydrogels with different feeding ratios contained more than 95% water at 25°C in the ultra pure water and phosphate-buffered saline (PBS, pH = 7.4 ± 0.1), and had a prospective swelling in the simulated gastric fluids (SGF, pH = 1.2) > 72.54%. In degradation studies, breakdown of the chitosan cross-linked P(NIPAAm-co-AAc) hydrogels was dependent on the cross-linking density. The chitosan cross-linked P(NIPAAm-co-AAc) hydrogels which can be tailored to create environmentally-responsive artificial extracellular materials have great potential for future use.

Colloid properties of hydrophobic modified alginate: Surface tension, ζ-potential, viscosity and emulsification

Micelle properties of hydrophobic modified alginate (HM-alginate) in various dispersion media have been studied by surface tension, ζ-potential, and viscosity measurements. Effect of salt on micelle properties showed that the presence of counter ion weakened the repulsive interaction between surfactant ions, decreased the critical micelle concentration (CMC) value of the HM-alginate, reduced the effective volume dimensions of HM-alginate and hence viscosity, which coincide with the corresponding ζ-potential values. Soy oil-in-water emulsions, stabilized solely by HM-alginate, were produced in high speed homogenization conditions and their stability properties were studied by visual inspection, optical microscopy and droplet size measurements. The results showed that emulsions (oil-water ratio was 1:7) containing 15mg/mL HM-alginate presented better stability during 15days storage, which stating clearly that HM-alginate is an effective emulsifier to stabilize oil-in-water emulsions. The herein presented homogeneous method for preparation of emulsion has the potential to be used in food industry.

Synthesis and micelle properties of the hydrophobic modified alginate

ABSTRACT Hydrophobic modified alginate (HM-alginate) has been synthesized by derivatization of sodium alginate (SA) with dodecyl glycidyl ether (DGE) in an aqueous solution. Using orthogonal optimization methods, the optimum combined parameters were explored as follows: 75°C, 70 mL H2O, 0.20 mmol sodium dodecyl sulfate and 2.0 mL DGE (mole ratio of SA to DGE, 2.2:1), the maximum yield was 112.62%. Their micellar properties and rheological properties were investigated, respectively. In addition, their drug delivery behaviors were evaluated with Sudan IV as a hydrophobic model drug. GRAPHICAL ABSTRACT

Synthesis and properties of sodium alginate/poly(acrylic acid) double-network superabsorbent

Abstract A tough double-network (DN) superabsorbent was synthesized by a two-step method using N,N-methylenebisacrylamide as a covalent cross-linker for one monomer [acrylic acid (AA)], Ca2+ (CaCl2) as an ionic cross-linker for the other monomer (sodium alginate [SA]) and ammonium peroxodisulfate as the redox initiator. The optimized experimental conditions for the absorbency in deionized water were determined according to orthogonal experiments. Unlike conventional chemical cross-linked single-network superabsorbents, SA/poly(acrylic acid) (PAA) DN superabsorbents exhibit superb mechanical properties. Compared with the tensile strength of PAA-only superabsorbents, that of SA/PAA DN superabsorbents showed an approximately 371.9% increase with increasing amount of 6 wt.% SA. We also investigated the capacity of SA/PAA DN superabsorbents to remove heavy metal ions. It was found that the addition of SA can truly increase the metal ion removal capacity of the PAA superabsorbents and that the affinity order was Pb2+>Zn2+.