Magnetic-responsive polysaccharide hydrogels as smart biomaterials: Synthesis, properties, and biomedical applications.

This review reports recent advances in polysaccharide-based magnetic hydrogels as smart platforms for different biomedical applications. These hydrogels have proved to be excellent, viable, eco-friendly alternative materials for the biomedical field due to their biocompatibility, biodegradability, and possibility of controlling delivery processes via modulation of the remote magnetic field. We first present their main synthesis methods and compare their advantages and disadvantages. Next, the synergic properties of hydrogels prepared with polysaccharides and magnetic nanoparticles (MNPs) are discussed. Finally, we describe the main contributions of polysaccharide-based magnetic hydrogels in the targeted drug delivery, tissue regeneration, and hyperthermia therapy fields. Overall, this review aims to motivate the synthesis of novel composite biomaterials, based on the combination of magnetic nanoparticles and natural polysaccharides, to overcome challenges that still exist in the treatment of several diseases.

Methylene Blue Release from Chitosan/Pectin and Chitosan/DNA Blend Hydrogels.

Chitosan/DNA blend hydrogel (CDB) and chitosan/pectin blend hydrogel (CPB) were synthesized using an emulsion (oil-in-water) technique for the release of methylene blue (model molecule). Both hydrogels were characterized by swelling assays, Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA) and scanning electron microscopy (SEM), before and after the methylene blue (MB) loading. Higher swelling degrees were determined for both hydrogels in simulated gastric fluid. FT-IR spectra inferred absorption peak changes and shifts after MB loading. The TGA results confirmed changes in the polymer network degradation. The SEM images indicated low porosities on the hydrogel surfaces, with deformed structure of the CPB. Smoother and more uniform surfaces were noticed on the CDB chain after MB loading. Higher MB adsorption capacities were determined at lower initial hydrogel masses and higher initial dye concentrations. The MB adsorption mechanisms on the hydrogel networks were described by the monolayer and multilayer formation. The MB release from hydrogels was studied in simulated gastric and intestinal fluids, at 25 °C and 37 °C, with each process taking place at roughly 6 h. Higher release rates were determined in simulated gastric fluid at 25 °C. The release kinetics of MB in chitosan/DNA and chitosan/pectin matrices follows a pseudo-second-order kinetic mechanism.

Arabic gum-based composite hydrogels reinforced with eucalyptus and pinus residues for controlled phosphorus release.

Arabic gum-based composite hydrogels reinforced with eucalyptus and pinus residues were synthesized via free-radical reaction aiming to controlled phosphorus release. All hydrogels were characterized by swelling kinetics (SK), Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), X-Ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and mechanical assays (MA). The water and solute transports through the hydrophilic three-dimensional networks of the hydrogels occur preferably by diffusion processes and macromolecular relaxation. Hemicellulose, lignin and cellulose fibers contained in eucalyptus and pinus residues affected the crosslinking density, crystalline structure, and water/solute diffusion due to reduction of free hydroxyl and amine groups in the hydrogel networks. Hence, the eucalyptus and pinus residues improved the mechanical and thermal resistances of the composite hydrogels. Finally, the Arabic gum-based hydrogel and Arabic gum-based composite hydrogels reinforced with eucalyptus and pinus residues demonstrated to be excellent alternatives for the controlled phosphorus release in agricultural nutrient-poor soils.

Polysaccharide-based hydrogels for the immobilization and controlled release of bovine serum albumin.

Arabic gum-based and chitosan-based hydrogels were synthesized through chemical crosslinking for the immobilization and controlled release of bovine serum albumin (BSA) and characterized by Fourier-transform infrared spectrometry, scanning electron microscopy and swelling assays. The degrees of swelling of the Arabic gum-based hydrogel were 13.22 and 22.95 g water per g dried hydrogel at pH 4.5 and 7.0, respectively, whereas the degrees of swelling of the chitosan-based hydrogel were 15.32 and 36.10 g water per g dried hydrogel, respectively. The water absorption mechanism in both hydrogels was non-Fickian, which involves diffusion through pores and macromolecular relaxation of the hydrophilic three-dimensional polymer network. BSA immobilization capacities of the Arabic gum-based and chitosan-based hydrogels after 240 min at pH 4.5 were 71.0 and 175.6 mg protein per g dried hydrogel, respectively. BSA immobilization capacities after 240 min at pH 7.0 were 62.5 and 154.2 mg protein per g dried hydrogel, respectively. The controlled release of BSA from the Arabic gum-based hydrogel was slightly more efficient than that of the chitosan-based hydrogel due to its more porous structure and weaker physiochemical interactions between the polymer network and protein molecule. Both hydrogels could be employed as carriers of proteins and as capsules for food supplements.

Adsorption and controlled release of potassium, phosphate and ammonia from modified Arabic gum-based hydrogel.

In this work, a modified Arabic gum-based hydrogel copolymerized with acrylamide was synthesized and characterized for application in adsorption and controlled release of potassium, phosphate and ammonia. From FT-IR results, it would be reasonable to assume that the hydrogel was effectively synthesized. The degree of swelling at pure water with pH 6.0 was 21.0g water per g dried hydrogel whereas the degrees of swelling at buffer solutions with pH 4.5 and 7.0 were 7.2 and 9.2g water per g dried hydrogel, respectively. The water diffusion mechanism was governed by Fickian transport with tendency to occur macromolecular relaxation. The adsorption capacities of potassium, phosphate and ammonia were higher by increasing the initial concentrations due to availability of active sites in the hydrogel network, nutrient size and ionic charge. Potassium, phosphate and ammonia concentrations released from the modified Arabic gum-based hydrogel increased by increasing the release time from 0 to 1440min. Release profiles indicated that this hydrogel could be applied for the enrichment and hydration of deserted soil, avoiding losses of nutrients by leaching and percolation, with an advantage of being constituted by an eco-friendly polysaccharide.

Treatment of wastewater from the dairy industry using electroflocculation and solid whey recovery.

The aim of this study was to investigate the efficiency of electroflocculation for the treatment of wastewater from the dairy industry and the recovery of solid whey. An electrochemical apparatus containing two aluminum or iron electrodes, a power source, an electroflocculation cell and magnetic stirring was employed. The following experimental conditions were monitored: electroflocculation time, initial pH of wastewater and applied potential intensity. Chemical oxygen demand, turbidity and final pH were the response variables. The chemical oxygen demand and turbidity decreased by employing aluminum or iron electrodes, applied potential intensity of 5 V, distance between two electrodes of 2 cm, 60 min electroflocculation time and initial wastewater pH of 5.0. The removal rates of organic matter based on the measure of chemical oxygen demand and turbidity when employing aluminum electrodes were 97.0 ± 0.02% and 99.6 ± 3.00 × 10(-4)%, respectively, with a final pH of 6.72. The removal rates of organic matter when employing iron electrodes were 97.4 ± 0.01% and 99.1 ± 1.00 × 10(-4)%, respectively, with a final pH of 7.38. In conclusion, electroflocculation is an excellent alternative for the dairy wastewater treatment in comparison to conventional treatment methods. The water used in food production and equipment washing is recovered with this method, resulting in a liquid that can be properly disposed. It is also possible to recover solid whey after electroflotation, which can then be used in the production of food supplements for humans and animals. Therefore, the dairy wastewater treatment process employing electroflocculation leads to sustainable food production.

Immobilization and controlled release of ß-galactosidase from chitosan-grafted hydrogels.

Chitosan-grafted hydrogels were employed for immobilization and controlled released of ß-galactosidase. These hydrogels containing immobilized enzymes were employed to simulate the production of lactose-free food and controlled release of ß-galactosidase into lactose-intolerant individuals. The degree of swelling, efficiency of immobilization (i.e., fractional uptake of enzyme), and controlled release were studied as a function of pH and temperature. The degrees of swelling decreased in acidic media: 49.4 g absorbed water per g hydrogel at pH 7.0, and 8.4 g absorbed water per g hydrogel at pH 3.5. The immobilization efficiency was 19%, indicating that chitosan-grafted hydrogels are promising matrices for enzyme adsorption and immobilization. Cyclic experiments reveal that chitosan-grafted hydrogels containing immobilized enzymes can be reused several times without introducing additional enzyme prior to each cycle. There is no significant decrease in the activity of the immobilized enzyme during reutilization studies. All results were conducted in triplicate by considering t-tests at a 95% significance level. Analysis of ß-galactosidase activity and controlled release reveals that chitosan-grafted hydrogels containing immobilized enzymes are useful for the production of lactose-free food and controlled enzyme release with high performance.

Natural polymer-based magnetic hydrogels: Potential vectors for remote-controlled drug release.

The preparation and characterization of natural polymer-based hydrogels that contain 50-nm diameter magnetite (i.e., FeO:Fe(2)O(3)) nanoparticles are described herein. Fourier-transform infrared spectroscopy (FTIR) analysis confirmed the efficiency of the polysaccharide-modifying process. Thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and compressive moduli demostrate that the presence of magnetite improves thermal and mechanical resistance. Transient diffusion of water in magnetic hydrogels was analyzed via boundary layer mass transfer across an expaning interface, and the degree of swelling of these polysaccharide hydrogels decreases in the presence of magnetite, with no variation in the binary diffusion mechanism. The absence of hysteresis loops and coercivity observed via magnetometry suggests that magnetic hydrogels are useful for remote-controlled drug release, as demonstrated by magnetic-field-induced release of curcumin. Experiments reveal that magnetic hydrogels with greater magnetic susceptibility have the potential to release larger concentrations of drugs from the hydrogel network.

Stress-sensitive tissue regeneration in viscoelastic biomaterials subjected to modulated tensile strain.

This research contribution addresses the mechanochemistry of intra-tissue mass transfer for nutrients, oxygen, growth factors, and other essential ingredients that anchorage-dependent cells require for successful proliferation on biocompatible surfaces. The unsteady state reaction-diffusion equation (i.e., modified diffusion equation) is solved according to the von Kármán-Pohlhausen integral method of boundary layer analysis when nutrient consumption and tissue regeneration are stimulated by harmonically imposed stress. The mass balance with diffusion and stress-sensitive kinetics represents a rare example where the Damköhler and Deborah numbers appear together in an effort to simulate the development of mass transfer boundary layers in porous viscoelastic biomaterials. The Boltzmann superposition integral is employed to calculate time-dependent strain in terms of the real and imaginary components of dynamic compliance for viscoelastic solids that transmit harmonic excitation to anchorage-dependent cells. Rates of nutrient consumption under stress-free conditions are described by third-order kinetics which include local mass densities of nutrients, oxygen, and attached cells that maintain dynamic equilibrium with active protein sites in the porous matrix. Thinner nutrient mass transfer boundary layers are stabilized at shorter dimensionless diffusion times when the stress-free intra-tissue Damköhler number increases above its initial-condition-sensitive critical value. The critical stress-sensitive intra-tissue Damköhler number, above which it is necessary to consider the effect of harmonic strain on nutrient consumption and tissue regeneration, is proportional to the Deborah number and corresponds to a larger fraction of the stress-free intra-tissue Damköhler number in rigid biomaterials.

Nutrient diffusion and simple nth-order consumption in regenerative tissue and biocatalytic sensors.

This contribution addresses intra-tissue molar density profiles for nutrients, oxygen, growth factors, and other essential ingredients that anchorage-dependent cells require for successful proliferation on biocompatible surfaces. One-dimensional transient and steady state models of the reaction-diffusion equation are solved to correct a few deficiencies in the first illustrative example of diffusion and zeroth-order rates of consumption in tissues with rectangular geometry, as discussed in Ref. [(Griffith and Swartz, 2006) 1]. The functional form of the molar density profile for each species depends on geometry and the magnitude of the species-specific intra-tissue Damköhler number. The tissue's central core is reactant starved at high consumption rates and low rates of intra-tissue diffusion when the Damköhler number exceeds its geometry-sensitive critical value. Ideal tissue engineering designs avoid the diffusion-limited regime such that attached cells are exposed to all of the ingredients required for proliferation everywhere within a regenerative matrix. Analytical and numerical molar density profiles that satisfy the unsteady state modified diffusion equation with pseudo-homogeneous n(th)-order rates of intra-tissue consumption (i.e., n=0,1,2) allow one to (i) predict von Kármán-Pohlhausen mass transfer boundary layer thicknesses, measured inward from the external biomaterial surface toward its central core, and, most importantly, (ii) estimate the time required to achieve steady state conditions for regenerative tissue growth and biocatalytic sensing.

Synthesis and water absorption transport mechanism of a pH-sensitive polymer network structured on vinyl-functionalized pectin.

Polysaccharide-structured copolymer hydrogel having excellent pH-sensitivity was developed from N,N-dimethylacrylamide (DMAc) and vinyl-functionalized Pectin (Pec). The Pec was vinyl-functionalized by way of chemical reaction with glycidyl metacrylate (GMA) in water under acidic and thermal stimuli. 13C NMR, 1H NMR, and FT-IR spectra revealed that the vinyl groups coming from the GMA were attached onto backbone of the polysaccharide. The hydrogels were obtained by polymerization of the Pec-vinyl with the DMAc. 13C-CP/MAS NMR and FTIR spectra confirmed that the gelling process occurred by way of the vinyl groups attached on Pec-vinyl backbone. The values of apparent swelling rate constant (k) decreased appreciably for pH greater than 6, demonstrating the swelling process of the hydrogel becomes slower at more alkaline conditions. There was an increase of diffusional exponent (n) with increasing pH of the surrounding liquid. This means the water absorption profile becomes more dependent on the polymer relaxation in basified swelling media. In this condition, a longer water absorption half-time (t1/2) was verified, suggesting the polymer relaxation mechanism of the hydrogel would have a considerable effect on the t1/2.

Synthesis of hollow-structured nano- and microspheres from pectin in a nanodroplet emulsion.

Hollow-structured nano- and microspheres with diameters ranging from 24 microm to 160 nm were successfully produced from chemically modified pectin (Ma-Pec) through a two-step synthesis. In a first step, the Pec was modified with glycidyl methacrylate (GMA) in a heterogeneous phase system, indeed consisting of water-soluble Pec and water-insoluble GMA, via an interfacial reaction at the interface of the GMA-water phase system after 12 h under continuous stirring of 1000 rpm at 60 degrees C. In a second step, the spheres were prepared in a water-in-benzyl alcohol nanodroplet emulsion at 12000 rpm under a bubbling stream of nitrogen in the presence of sodium persulfate, as initiator, and TEMED, as catalytic agent. FT-IR spectra revealed that the vinyl groups (CC) coming from the GMA were attached onto backbone of the polysaccharide. 13C-CP/MAS NMR spectra demonstrated that the spheres were formed via carbon-carbon pi-bonds on Ma-Pec in the water phase, for the duration of the dispersion stage. The dark center (an empty core) and edge of the hollow spheres could be easily identified by SEM micrographs. This type of polymer structure represents a class of unique material with particular importance in terms of state-of the-art applications in both nano- and microencapsulation of drugs, for example, protection shields of biologically active agents.

Square wave voltammetry in the determination of Ni2+ and Al3+ in biological sample.

In this contribution, the amounts of Ni (nickel) and Al (aluminum) in tilapias (Oreochromis niloticus) were determined using square wave voltammetry (SWV) with glassy carbon working microelectrode with a mercury thin film, platinum counter electrode, and Ag/AgCl reference electrode. Ni was studied through the formation of the dimethylglyoxime-Ni (Ni-DMG) complex, while Al was studied through the formation of the Alizarin R-Al complex. The detection limit found for Ni-DMG and Alizarin R-Al complexes were 1.70 x 10(-7) and 1.0 x 10(-8) mol L(-1), respectively. The voltammetric anodic curves for the Alizarin R-Al complex were recorded over the potential range from -0.8 to -0.05 V while the voltammetric cathodic curve for the Ni-DMG complex was recorded over the potential range from -0.7 to -1.2 V. These methods detected low concentrations of Ni and Al in biological samples efficiently.

Capacity of adsorption of Pb2+ and Ni2+ from aqueous solutions by chitosan produced from silkworm chrysalides in different degrees of deacetylation.

The binding capacities of chitin (CT) and chitosan (CS) produced from silkworm chrysalides were investigated aiming at their future application in the removal of Pb2+ and Ni2+ from wastewaters. CS with 75% deacetylation degree (DD) exhibited good binding performance for Pb(2+), but bad efficiency for Ni2+. The maximum binding capacity obtained from isotherms for CS-Pb was 141.10 mg g(-1) and 52.81 mg g(-1) for CS-Ni. The binding capacities for CT were 32.01 mg g(-1) for Pb2+ and 61.24 mg g(-1) for Ni2+. The authors attribute these behaviors to two main factors: (i) the large ionic size of Pb2+ and (ii) the steric hindrance due to CT acetyl groups. Metal binding onto CS was evaluated by the Freundlich and Langmuir isotherm models. The parameter values obtained from the isotherm analysis confirmed that Pb2+ and Ni2+ interact differently with CS and that various factors influence their adsorption. Thermogravimetric analysis (TGA) showed that the thermal behavior of CS with 75% deacetylation degree was in the same profile of standard CS; however, the binding of the metals onto its structure affects the curve profile.

Novel adsorbent based on silkworm chrysalides for removal of heavy metals from wastewaters.

In this contribution, maximum capacity for adsorption of Pb(2+), Ni(2+), and Cu(2+) by silkworm chrysalides (SC) was determined. The raw silkworm chrysalides (SC(r)) and chrysalides after acidic washing (SC(w)) were used. Chitin (CT), extracted from SC, and chitosan (CS), with 85% deacetylation, were employed as reference samples. Adsorption tests showed that all the studied adsorbents exhibited excellent performance in removal of metals. The choice of a more appropriate adsorbent is related to its efficiency for removal of a specific metal. The studied materials presented different intensities for metal adsorption as follows: (i) Ni(2+)>Cu(2+)>Pb(2+) for SC(r); (ii) Pb(2+)>Cu(2+)>Ni(2+) for SC(w); (iii) Ni(2+)>Cu(2+)>Pb(2+) for CT; and (iv) Cu(2+)>Pb(2+)>Ni(2+) for CS. Metal adsorption onto SC(r) and CS was analyzed by Freundlich and Langmuir isotherm equations. Adsorption values for CS-Pb and SC(r)-Ni were provided by the Freundlich model, while the adsorption values for CS-Cu, CS-Ni, SC(r)-Pb, and SC(r)-Cu were provided by the Langmuir model. The studied adsorbents are suitable for use in treatment of wastewater. From the economic point of view, the use of SC(r) as an adsorbent of heavy metals (mainly Ni(2+)) on the large industrial scale would be more appropriate.

Removal of methylene blue dye from an aqueous media using superabsorbent hydrogel supported on modified polysaccharide.

The removal of methylene blue (MB) in water with the superabsorbent hydrogel (SH) formed by modified gum arabic, polyacrylate, and polyacrylamide was investigated. The SH exhibited excellent performance in MB absorption. The maximum absorption capacity was 48 mg of the dye per g of SH, representing 98% of the MB removed. Experimental parameters were used as follows: pH 8, hydrogel mass 50 mg, and initial concentration of MB 50 mg L(-1). In a procedure with an individual solution of orange II, an opposite effect related to the MB was observed: the hydrogel only absorbed water, resulting in an orange II-richer solution. The orange II concentration in solution increased about 50 times (relative to the initial concentration). In another experiment using an aqueous mixture of orange II and MB, the SH absorbed the MB exclusively. Compared to the MB, the orange II is separated from water by SH selectivity-absorption through an inverse process. This effect was attributed to the formation of a ionic complex between the imine groups of MB and the ionized carboxylic groups of SH.