Hydrogel Beads of Amidoximated Starch and Chitosan as Efficient Sorbents for Inorganic and Organic Compounds.

The synthesis of hydrogel beads involving natural polymers is, nowadays, a leading research area. Among natural polymers, starch and chitosan represent two biomolecules with proof of efficiency and low economic impact in various utilization fields. Therefore, herein, the features of hydrogel beads obtained from chitosan and three sorts of starch (potato, wheat and rise starches), grafted with acrylonitrile and then amidoximated, were deeply investigated for their use as sorbents for heavy metal ions and dyes. The hydrogel beads were prepared by ionotropic gelation/covalent cross-linking of chitosan and functionalized starches. The chemical structure of the hydrogel beads was analyzed by FT-IR spectroscopy; their morphology was revealed by optical and scanning electron microscopies, while the influence of the starch functionalization strategies on the crystallinity changes was evaluated by X-ray diffraction. Molecular dynamics simulations were used to reveal the influence of the grafting reactions and grafted structure on the starch conformation in solution and their interactions with chitosan. The sorption capacity of the hydrogel beads was tested in batch experiments, as a function of the beads' features (synthesis protocol, starch sort) and simulated polluted water, which included heavy metal ions (Cu2+, Co2+, Ni2+ and Zn2+) and small organic molecules (Direct Blue 15 and Congo red).

Polybetaines in Biomedical Applications.

Polybetaines, that have moieties bearing both cationic (quaternary ammonium group) and anionic groups (carboxylate, sulfonate, phosphate/phosphinate/phosphonate groups) situated in the same structural unit represent an important class of smart polymers with unique and specific properties, belonging to the family of zwitterionic materials. According to the anionic groups, polybetaines can be divided into three major classes: poly(carboxybetaines), poly(sulfobetaines) and poly(phosphobetaines). The structural diversity of polybetaines and their special properties such as, antifouling, antimicrobial, strong hydration properties and good biocompatibility lead to their use in nanotechnology, biological and medical fields, water remediation, hydrometallurgy and the oil industry. In this review we aimed to highlight the recent developments achieved in the field of biomedical applications of polybetaines such as: antifouling, antimicrobial and implant coatings, wound healing and drug delivery systems.

Fabrication and characterization of composite cryobeads based on chitosan and starches-g-PAN as efficient and reusable biosorbents for removal of Cu2+, Ni2+, and Co2+ ions.

Novel composite biosorbents were developed in this work as cryobeads by dual cross-linking of a mixture of chitosan (CS) and starch coming from different botanical sources, such as potato, wheat, and rice, grafted with poly(acrylonitrile) (PAN). Glutaraldehyde and poly(ethylene glycol diglycidyl ether) were used as cross-linkers. Composite cryobeads were characterized by FTIR, SEM-EDX, and swelling kinetics. Sorption of Cu2+, Ni2+, and Co2+ onto the novel biosorbents was investigated as a function of time and the concentration of the metal ion, at the optimum pH and sorbent dose. Pseudo-second-order kinetic model and Elovich model well fitted the kinetic results, indicating chemisorption as the most probable mechanism of sorption, while the Langmuir, and Sips isotherm models described the sorption at equilibrium for all metal ions. The values of the maximum sorption capacity of Cu2+, Ni2+, and Co2+ onto the composite sorbent based on CS and rice starch-g-PAN were as follows: 100.6 mg/g, 83.25 mg/g, and 74.01 mg/g, respectively. The nitrile groups present in the biocomposites CS/starch-g-PAN constitute a source to further increase the sorption capacity by their hydrolysis. A remarkable level of reusability was found for the composite cryobeads, no decrease of the sorption capacity being observed after five consecutive sorption/desorption cycles.

Preparation and characterization of oxidized starch/poly(N,N-dimethylaminoethyl methacrylate) semi-IPN cryogels and in vitro controlled release evaluation of indomethacin.

Fabrication of novel semi-interpenetrating polymer network (semi-IPN) cryogels by cross-linking polymerization of N,N-dimethylaminoethyl methacrylate (DMAEM) in the presence of either oxidized potato starch (OPS) or oxidized wheat starch (OWS) and their characterization are presented in the paper. The influence of the nature of entrapped polymer on the properties of the composite cryogels was evaluated by the swelling kinetics, FT-IR spectroscopy, scanning electron microscopy, and response at external stimuli such as temperature, pH, and ionic strength. Indomethacin (IDM), taken as a model anti-inflammatory drug, was easily loaded into the composite cryogels by the solvent sorption-evaporation strategy. The in vitro release of IDM from the semi-IPN cryogels was low in simulated gastric fluid at pH 1.3, irrespective of the nature of the entrapped oxidized starch, and consistent in simulated intestinal fluid (SIF) at pH 7.4, the influence of the entrapped polysaccharide being evident. The release mechanism of IDM from the composite cryogels was discussed based on two kinetic models, finding that the drug release at 37°C was pseudo-Fickian diffusion, regardless the cryogel composition.

Efficient sorption of Cu(2+) by composite chelating sorbents based on potato starch-graft-polyamidoxime embedded in chitosan beads.

Ionic composites based on cross-linked chitosan (CS) as matrix and poly(amidoxime) grafted on potato starch (AOX) as entrapped chelating resin were prepared as beads, for the first time in this work, by two strategies: (1) thorough mixing of previously prepared AOX in the CS solution followed by the bead formation and (2) thorough mixing of the potato starch-g-poly(acrylonitrile) (PS-g-PAN) copolymer in the initial CS solution, followed by bead formation, the amidoximation of the nitrile groups taking place inside the beads. Ionotropic gelation in tripolyphosphate was used to obtain the composite beads, and in situ covalent cross-linking by epichlorohydrin was carried out to stabilize the beads in the acidic pH range. Fourier transform infrared spectroscopy and the swelling ratio values in the acidic pH range confirmed the influence of the synthesis strategy on the structure of the CS/AOX composites. Scanning electron microscopy was employed to reveal the morphology of the novel composites, both before and after their loading with Cu(2+). The binding capacity of Cu(2+) ions as a function of sorbent composition, synthesis strategy, pH, sorbent dose, contact time, initial concentration of Cu(2+), and temperature was examined in batch mode. The main difference between the composites prepared with the two strategies consisted of the higher sorption capacity and the much faster settlement of the equilibrium sorption for the composite prepared by the in situ amidoximation of PS-g-PAN. The Langmuir, Freundlich, Temkin, Dubinin-Radushkevich, and Sips isotherms were applied to fit the sorption equilibrium data. The maximum equilibrium sorption capacity, qm, evaluated by the Langmuir model at 25 °C was 133.15 mg Cu(2+)/g for the CS/AOX composite beads prepared with the first strategy and 238.14 mg Cu(2+)/g for the CS/AOX composite beads prepared with the second strategy, at the same AOX content. The pseudo-second order kinetic model well fitted the sorption kinetics data, supporting chemisorption as the mechanism of interaction between the chelating composites and the Cu(2+) ions. The CS/AOX composite sorbents could be reused up to five sorption/desorption cycles with no significant decrease in Cu(2+) sorption capacity.