Chitosan-silica Hybrid Research Articles

Process development for hydrometallurgical recovery of valuable metals from sulfide-rich residue generated in a secondary lead smelter

Two routes were investigated to selectively recover lead and minor metals (Cu, Ni, Zn) from a sulfide-rich lead smelter residue, matte. The first route comprises a two-step leaching process that combines Fe(III)-HNO3 leaching with roasting, followed by water leaching. In the first step, the efficiency of Pb leaching was 90% at the optimum condition (L/S ratio 8, 0.5mol⋅L−1 HNO3, 0.15mol⋅L−1 Fe(III), 25°C). In the second step, roasting at 600°C followed by water leaching at 50°C selectively leached Ni, Cu, and Zn while fully converting iron sulfides to oxides. One-step oxidative pressure leaching in HNO3 was investigated as an alternative to simultaneously leach Pb, Cu, Ni and Zn. At the optimal conditions (130°C, 60min, 0.3mol⋅L−1 HNO3, 0.07mol⋅L−1 Fe(III), L/S ratio 20), Pb, Cu, Zn and Ni leaching were 92, 60, 70 and 66%, respectively, while Fe leaching remained low (2%). The leachates obtained from both leaching routes were treated by ion-exchange adsorption with diethylenetriaminepentaacetic acid (DTPA) functionalized chitosan-silica hybrid materials to investigate the selective recovery of Cu, Zn and Ni. The adsorption order appeared to be in the same order as the corresponding stability constants for complexes between the respective metal ions and free DTPA: Ca(II)<Zn(II)<Pb(II)≈Ni(II)<Cu(II). This allows not only to selectively recover Cu, Zn and Ni from the leachates, but also to mutually separate them by using the functionalized resin as a stationary phase in column chromatography. To avoid adsorbent contamination, Fe(III) and Pb(II) may be removed from the leachates in a pre-treatment step. Based on these results, the investigated methods can be combined as process steps of two possible routes for the selective recovery of valuable metals from the studied secondary lead smelting residue. The two-step leaching process seems to be superior since a more concentrated solution of Cu, Ni, and Zn is produced in the 2nd leaching step with low capital cost.

The accelerating effect of chitosan-silica hybrid dressing materials on the early phase of wound healing.

Commercialized dressing materials with or without silver have played a passive role in early-phase wound healing, protecting the skin defects from infections, absorbing exudate, and preventing dehydration. Chitosan (CTS)-based sponges have been developed in pure or hybrid forms for accelerating wound healing, but their wound-healing capabilities have not been extensively compared with widely used commercial dressing materials, providing limited information in a practical aspect. In this study, we have developed CTS-silica (CTS-Si) hybrid sponges with water absorption, flexibility, and mechanical behavior similar to those of CTS sponges. In vitro and in vivo tests were performed to compare the CTS-Si sponges with three commercial dressing materials [gauze, polyurethane (PU), and silver-containing hydrofiber (HF-Ag)] in addition to CTS sponges. Both in vitro and in vivo tests showed that CTS-Si sponges promoted fibroblast proliferation, leading to accelerated collagen synthesis, whereas the CTS sponges did not exhibit significant differences in fibroblast proliferation and collagen synthesis from gauze, PU, and HF-Ag sponges. In case of CTS-Si, the inflammatory cells were actively recruited to the wound by the influence of the released silicon ions from CTS-Si sponges, which, in return, led to an enhanced secretion of growth factors, particularly TGF-β during the early stage. The higher level of TGF-β likely improved the proliferation of fibroblasts, and as a result, collagen synthesis by fibroblasts became remarkably productive, thereby increasing collagen density at the wound site. Therefore, the CTS-Si hybrid sponges have considerable potential as a wound-dressing material for accelerating wound healing. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1828-1839, 2017.

Preparation and Application of Modified VEGFR-2 Cell Membrane Chromatographic Separation System

The vascular endothelial growth factor receptor-2 (VEGFR-2) in some tumor cells is a significant target for drug discovery. In this work, a modified model of VEGFR-2 cell membrane stationary phase (CMSP) was prepared by immobilizing U251 cell membrane onto the surface of chitosan-silica (CTS-SiO2) hybrid carrier. The surface and chromatographic characteristics of VEGFR-2 CMSP were studied. We have developed modified VEGFR-2 cell membrane chromatography for screening drugs and sunitinib malate was used as a positive control. The interaction between the new compounds and membrane receptor was determined by the capacity factors (kʹ). The in vitro cytotoxicity of 10 new compounds on U251 cell viability was determined by MTT test separately to verify the potential pharmacological activity. The modified VEGFR-2 cell membrane chromatographic system demonstrated fast and effective characteristics for screening leading compounds.

Recovery of scandium from leachates of Greek bauxite residue by adsorption on functionalized chitosan–silica hybrid materials

Scandium recovery from bauxite residue leachates was investigated using ion-exchange adsorption. EGTA–chitosan–silica showed exceptionally high selectivity for scandium. It was used as resin material for column chromatography to isolate pure scandium.

Organic-inorganic bonding in chitosan-silica hybrid networks: Physical properties

The research project is implemented within the framework of the Action Supporting Postdoctoral Researchers of the Operational Program Education and Lifelong Learning (Action's Beneficiary: General Secretariat for Research and Technology), and is co-financed by the European Social Fund (ESF) and the Greek State, Grant No.: NARGEL-PE5 (2551). J. L. Gomez Ribelles acknowledges the support of the Ministerio de Economia y Competitividad, MINECO, through the MAT2013-46467-C4-1-R project. CIBER-BBN is an initiative funded by the VI National R&D&I Plan 2008-2011, Iniciativa Ingenio 2010, Consolider Program, CIBER Actions and financed by the Instituto de Salud Carlos III with the assistance from the European Regional Development Fund.

Preparation of thermally stable microcapsules with a chitosan-silica hybrid.

Addition of microcapsules with a high dielectric constant and low specific heat capacity to a battered layer was designed to create a higher temperature in the crust than in the prefried fish nuggets to prevent the water vapor in the fish nuggets from migrating to the crust during microwave heating. Therefore, chitosan-silica hybrids and soybean oil were utilized to prepare the shell and core of the thermally stable microcapsules (MC(CS)), respectively. The MC(CS) were prepared by sol-gel coacervation from an oil-in-water emulsion. The sodium silicate was hydrolyzed and coacervated through polymerization for 24 h at pH 5. The zeta potential analysis indicated that chitosan with a positive charge and silica with a negative charge interacted through electrostatic attraction to form a hybrid shell. The volume mean particle size and encapsulation efficiency of the MC(CS) were 9.6 ± 0.2 μm and 75.6% ± 1.3%, respectively, when oil/chitosan = 0.2 and chitosan/silica = 0.5 (w/w). In addition to H-bonding and electrostatic attraction, Si-O-N bonds were formed between chitosan and silica. Dehydration of the bound water in the MC(CS) was observed in the range of 25 to 250 °C in the differential scanning calorimetry thermal analysis, with the lack of apparent thermal peaks indicating its high thermal stability. The decrease of force to cut the crust observed by texture analysis as well as the increase of hedonic score by consumer acceptance test revealed the addition of 1% MC(CS) significantly improved the crispness of the crust in the microwave-reheated nuggets.

Improving the crispness of microwave-reheated fish nuggets by adding chitosan-silica hybrid microcapsules to the batter

In this study, thermostable microcapsules prepared with a hybrid of chitosan and silica (MCCS) as the shell material and soybean oil with a low specific heat capacity as the nucleus were applied to maintaining the crispness of microwave-reheated battered and breaded fish nuggets. The MCCS added batter at 1 g/100 mL concentration exhibited desirable rheological properties and a 40% pick-up rate, as well as a high cutting force, low deformation and desirable number of peaks in the cutting force profile of the fish nuggets reheated in a microwave oven. After microwave reheating, the moisture content of the crust was lower, and moisture content of the fish meat was higher, in the MCCS-containing nuggets than in the MCCS-free nuggets. This phenomenon suggested that the MCCS facilitated the formation of a water barrier by high temperature and high pressure during microwave reheating, which prevented moisture molecules from migrating from the fish meat to the crust.

Adsorption performance of functionalized chitosan–silica hybrid materials toward rare earths

Functionalized chitosan–silica hybrid materials were synthesized, characterized and used for adsorption of rare-earth ions. These adsorbents can be used for the separation of mixtures of rare-earths.

A novel microfluidic approach for preparing chitosan-silica core-shell hybrid microspheres with controlled structures and their catalytic performance.

A facile microfluidic approach to prepare chitosan-silica core-shell hybrid microspheres with different pore structures has been developed. The hybrid microspheres showed good performance in mechanics and adsorption and are outstanding and green catalyst supports. Under optimum conditions, the adsorption capacity of Cu(ii) is about 1.7 times that of chitosan-silica hybrid microspheres with uniform component distribution for the effective protection of -NH2 provided by the silica shell while the mechanical intensity is about 2 times that of porous chitosan microspheres. Furthermore, when the adsorbed Cu(ii) is reduced to Cu(i), the chitosan-silica supported Cu(i) will be an outstanding catalyst for azide-alkyne cycloaddition reaction and the reaction can complete in water within 3 h at room temperature. The catalyst was easy to be recovered just through sedimentation by gravity or filtration. Further, the chitosan-silica supported catalyst can be reused many times without losing its activity and it can be reproducible when the catalytic activity decreases. The whole process is green, environmentally friendly and atom economic.

Chemical characterisation and fabrication of chitosan-silica hybrid scaffolds with 3-glycidoxypropyl trimethoxysilane.

Chitosan has been explored as a potential component of biomaterials and scaffolds for many tissue engineering applications. Hybrid materials, where organic and inorganic networks interpenetrate at the molecular level, have been a particular focus of interest using 3-glycidoxypropyl trimethoxysilane (GPTMS) as a covalent crosslinker between the networks in a sol-gel process. GPTMS contains both an epoxide ring that can undergo a ring opening reaction with the primary amine of chitosan and a trimethoxysilane group that can co-condense with silica precursors to form a silica network. While many researchers have exploited this ring-opening reaction, it is not yet fully understood and thus the final product is still a matter of some dispute. Here, a detailed study of the reaction of GPTMS with chitosan under different pH conditions was carried out using a combination of solution state and solid state MAS NMR techniques. The reaction of GPTMS with chitosan at the primary amine to form a secondary amine was confirmed and the rate was found to increase at lower pH. However, a side-reaction was identified between GPTMS and water producing a diol species. The relative amounts of diol and chitosan-GPTMS species were 80 and 20% respectively and this ratio did not vary with pH. The functionalisation pH had an effect on the mechanical properties of 65 wt% organic monoliths where the properties of the organic component became more dominant. Scaffolds were fabricated by freeze drying and had pore diameters in excess of 140 μm, and tailorable by altering freezing temperature, which were suitable for tissue engineering applications. In both monoliths and scaffolds, increasing the organic content disrupted the inorganic network, leading to an increase in silica dissolution in SBF. However, the dissolution of silica and chitosan was congruent up to 4 weeks in SBF, illustrating the true hybrid nature resulting from covalent bonding between the networks.

Synthesis of novel chitosan–silica/CpG oligodeoxynucleotide nanohybrids with enhanced delivery efficiency

Chitosan–silica/CpG oligodeoxynucleotide (ODN) nanohybrids were synthesized to stimulate Toll-like receptor 9-mediated induction of interleukin-6 (IL-6). The chitosan–silica hybrid was first synthesized from a mixture of chitosan and 3-glycidoxypropyl trimethoxysilane under acidic conditions via a sol–gel process, and then used to condense CpG ODN2006x3-PD to yield chitosan–silica/CpG ODN nanohybrids. Scanning electron microscopy and atomic force microscopy showed that the chitosan–silica/CpG ODN nanohybrids had an elliptic shape with a diameter of 100–200nm. After soaking in HAc–NaAc buffer solution (pH5.5), the nanohybrids exhibited sustained release of CpG ODN. When the nanohybrids were separately exposed to 293XL-hTLR9 cells and peripheral blood mononuclear cells, no significant toxicity was observed. An immunochemical assay for cellular uptake revealed that the nanohybrids were taken up by the cells and located in endolysosomes. An enzyme-linked immunosorbent assay for cytokines indicated that the nanohybrids effectively stimulated the induction of IL-6. Chitosan–silica/CpG ODN nanohybrids underwent cellular uptake and enhanced induction of IL-6 to a greater degree than conventional chitosan/CpG ODN nanocomplexes, indicating that they have an enhanced delivery efficiency.

Ion-imprinted carboxymethyl chitosan–silica hybrid sorbent for extraction of cadmium from water samples

A new ion-imprinted carboxymethyl chitosan-functionalized silica gel sorbent was synthesized by surface imprinting technique using Cd(II) as the template, carboxymethyl chitosan (CMCS) as the functional monomer and glutaraldehyde as the cross-linking agent for the selective adsorption of Cd(II) from aqueous solution. The optimum batch experimental conditions (pH, amount of adsorbent, contact time) and column experimental conditions (concentration and volume of elution solution) were evaluated. The maximum static adsorption capacity of the ion-imprinted sorbent for Cd(II) was 20.7mg/g. The enrichment factor of Cd(II)-imprinted polymer for Cd(II) was 257. The relative selectivity factor values of Cd(II)/Pb(II), Cd(II)/Co(II) were 5.3 and 1.5, respectively. The recoveries of water samples were about 98.0–104.0% (R.S.D.≤0.8). The proposed method was successfully applied to determination of Cd(II) in water samples with satisfactory.

A CHITOSAN TEMPLATED SYNTHESIS OF BIMODAL POROUS SILICA

Biopolymer chitosan templated bimodal porous silica materials with uniform macroporosity and narrowed mesopore size distribution were synthesized via fast precipitation of chitosan–silica hybrid composites (Chi/ SiO2 ). Clear Chi/ SiO2 solutions containing the biopolymer chitosan and siloxane-based inorganic network were prepared by hydrolysis of sodium metasilicate in the presence of biopolymer chitosan. The relative amount of chitosan in as-made Chi/ SiO2 was analyzed by thermogravimetric analysis (TGA). Chi/ SiO2 was calcined at 600°C for 5 h in the presence air to remove chitosan, and characterized by scanning electron microscope (SEM), transmission electron microscope (TEM) and N2 adsorption–desorption isotherms. These porous silica products had high specific surface area of 500–550 m2/g, narrow pore size distribution and also bicontinuous macropore structure.

Mesostructured chitosan–silica hybrid as a biodegradable carrier for a pH-responsive drug delivery system

A biodegradable mesoporous chitosan-silica hybrid has been synthesized by self-assembly of non-toxic F127 Pluronic non-ionic surfactant, biodegradable chitosan and silica source through a real liquid-crystal templating route. On the basis of these biodegradable hybrids, we developed a facile one-pot pH-responsive drug delivery system relying on the coordinate bonding of a "host-metal-guest" architecture. Here, the "host", "metal" and "guest" represent amino groups of chitosan units, metal ions and drug molecules, respectively. Here, daunorubicin (DNR) was chosen as a typical anti-cancer drug molecule, the release of which can be achieved through the cleavage of the coordination bonds that are sensitive to variations in external pH at weak acidic conditions. The successful release of DNR has been observed at pH 5-6, while negligible release has been observed under physiological conditions. The existence of chitosan in the mesoporous silica enhanced both the biodegradability and the strength of the "host-metal-guest" coordination bond.

Heavy metals adsorption by novel EDTA-modified chitosan–silica hybrid materials

Novel adsorbents were synthesized by functionalizing chitosan–silica hybrid materials with (ethylenediaminetetraacetic acid) EDTA ligands. The synthesized adsorbents were found to combine the advantages of both silica gel (high surface area, porosity, rigid structure) and chitosan (surface functionality). The Adsorption potential of hybrid materials was investigated using Co(II), Ni(II), Cd(II), and Pb(II) as target metals by varying experimental conditions such as pH, contact time, and initial metal concentration. The kinetic results revealed that the pore diffusion process played a key role in adsorption kinetics, which might be attributed to the porous structure of synthesized adsorbents. The obtained maximum adsorption capacities of the hybrid materials for the metal ions ranged from 0.25 to 0.63 mmol/g under the studied experimental conditions. The adsorbent with the highest chitosan content showed the best adsorption efficiency. Bi-Langmuir and Sips isotherm model fitting to experimental data suggested the surface heterogeneity of the prepared adsorbents. In multimetal solutions, the hybrid adsorbents showed the highest affinity toward Pb(II).

Chitosan–silica hybrid‐coated open tubular column for hydrophilic interaction capillary electrochromatography

A novel and convenient protocol for the preparation of an open-tubular column coated with chitosan-silica hybrid using chitosan and silane-coupling agent (γ-glycidoxy-propyltrimethoxysilane) was developed for CEC, in which, chitosan was covalently bonded to the inner wall of a fused-silica capillary using γ-glycidoxy-propyltrimethoxysilane as a cross-linking agent. The stationary phase was hydrophilic due to the chitosan-silica hybrid with abundant amine and hydroxyl functional groups. The chromatographic characteristics of the column were evaluated by the separation of some organic acids and inorganic anions. The column showed good selectivity for nucleotides, aromatic acids, and inorganic anions. The mechanism for the separation of these compounds was primarily based on the hydrophilic and electrostatic interactions combined with the electrophoretic mechanism. The CEC method on the column for the separation of these compounds was compared with CE method in a bare capillary.

Characterization and drug release behavior of chip-like amphiphilic chitosan–silica hybrid hydrogel for electrically modulated release of ethosuximide: an in vitro study

The hydrogel response under environmental induction often decreases with time because of the mechanical weakness of polymeric hydrogels. Therefore, to reinforce the conventional hydrogels with improved responsiveness and service performance to an external stimulus, a hybrid hydrogel consisting of an amphiphilic chitosan and inorganic silica with a minimal concentration of organic cross-linker was made in order to ascertain the biocompatibility of resulting hydrogels and improve stimulus-induced responsiveness. The hybrid hydrogels generally illustrated a rapid drug (ethosuximide, ESM) release profile over a time period of less than 60 minutes. However, after assembling the hybrid hydrogels into a chip-like device, the sandwiched hybrid showed, under a number of applied DC voltages, a variety of release profiles from a burst-like to slow-elution pattern. A release mechanism was proposed and can be successfully explained as a result of combined effects of electrophoretic and electroosmotic operations. Kinetic analysis indicated that the ESM released from the chip-like device is essentially a shuttle between the swelling-controlled pattern and the diffusion-controlled mechanism, depending on the chemical compositions that were used to prepare the hybrid hydrogels under a given DC electrical field. The hybrid hydrogel chip-like device designed in this work has experimentally proved its technical potential as an electrically responsive drug delivery system to meet various biomedical demands.

One-step synthesis of chitosan-silica hybrid microspheres in a microfluidic device

This article describes a simple microfluidic method to fabricate chitosan-silica hybrid microspheres in one step. We dissolved tetraethoxysilane (TEOS) into a chitosan/acetic acid aqueous solution to form a chitosan-silica sol, and then emulsified it in an organic phase mainly containing n-octanol and an organic base triotylamine (TOA) via a co-axial microfluidic device. The formed aqueous droplets were solidified because of the extraction of acetic acid and water to the organic phase. The simple method presented has the advantages of controllable sphere diameter, narrow size distribution and good sphericity. The porous structures of the microspheres were displayed by SEM images. It is found that the inner and surface structures can be controlled by adjusting the solidification reagent component. Furthermore, we chemically grafted bovine serum albumin (BSA) on the microspheres. The existence of silica in the chitosan spheres can enhance both of mechanical intensity and protein loading capacity of the microspheres.

Synthesis and Characterization of Silica-Chitosan Porous Hybrids for Tissue Engineering

A variety of types of organic polymers have been employed in the synthesis of hybrids with silica. In this work the sol-gel method was used for preparation of macroporous 3D hybrid scaffolds based on silica and chitosan in various compositions (10, 20 and 30% wt). The hybrids were analyzed by Scanning Electron Microscopy (SEM), X-ray Diffraction (DRX) and Infra-red Spectroscopy (FTIR) and the effect of addition of the polymer was evaluated. The foams obtained by sol-gel process were appropriate to produce hybrids based on chitosan-silica and showed large pore size distribution and porosity, except for hybrids with higher polymer content. The FTIR spectroscopy showed a band relative to Si-O-C bond that was also found to increase with the increasing the amounts of chitosan in the hybrid. This fact can suggest an interaction between the organic-inorganic phases in the material and provide new insights on the advantages of chitosansilica hybrid materials produced via sol-gel methodology.

Composite hybrid membrane of chitosan–silica in pervaporation separation of MeOH/DMC mixtures

Chitosan–silica hybrid membranes (CSHMs) were prepared by cross-linking chitosan (CS) with 3-aminopropyl-triethoxysilane (APTEOS). The dynamic behaviors of the CS membrane and the CSHM were investigated in pervaporation (PV) of methanol/dimethyl carbonate (MeOH/DMC) mixtures. The membranes were characterized by X-ray diffraction (XRD), contact angle meter, scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The transition state of PV processes were studied. During the PV processes, the amorphous region of the membranes increases and the contact angle between MeOH and the membrane decreases within a range of operating time and then remains almost constant implying a reconstruction occurred on the membrane surface. The silica is well distributed in the CSHM matrix and the thermal stability of the CSHM is enhanced. The time for a PV process to reach a steady state decreases with increasing MeOH concentration or feed temperature, and it is longer for the CSHM than the CS membrane under the same operating condition. Swelling experiments show that the degree of swelling (DS) is greatly depressed by cross-linking CS with APTEOS. Sorption data indicate that the selectivity of solubility and diffusion of the CSHM are greatly improved over the CS membrane. The CSHM presents superior separation behaviors over other membranes with a flux of 1265 g / ( h m 2 ) and separation factor of 30.1 in PV separation of 70 wt% MeOH in feed at 50 °C.