Enhancing Enzyme Stability and Functionality: Covalent Immobilization of Trypsin on Magnetic Gum Arabic Modified Fe3O4 Nanoparticles.

This study aimed to fabricate gum Arabic (GA)-coated Fe3O4 nanoparticles bearing numerous active aldehyde groups on their surface, followed by an assessment of their capability as a magnetic support for the covalent immobilization of the trypsin enzyme for the first time. FT-IR, XRD, TGA, and SEM results demonstrated the successful synthesis of GA-coated Fe3O4 nanoparticles, along with the covalent immobilization of the enzyme onto the support. Immobilization enhanced the relative enzymatic activity across a range of aqueous solution pH levels (ranging from 4 to 11) and temperatures (ranging from 20 to 80 °C) without altering the optimum pH and temperature for trypsin activity. Kinetic studies using Michaelis-Menten plots revealed changes in kinetic parameters, including a lower Vmax and higher Km for immobilized trypsin compared to the free enzyme. The immobilization onto magnetic gum Arabic nanoparticles resulted in an improved stability of trypsin in the presence of various solvents, maintaining a stability order comparable to that of the free enzyme due to the stabilizing effect of the support. The reusability results showed that the immobilized enzyme can retain over 93% of its activity for up to 15 cycles.

Preparation of chitosan/sodium alginate/nano cellulose composite for the efficient removal of cadmium (II) cations from wastewater and soil systems.

In this study, chitosan/sodium alginate/nano cellulose (CSA-N) nanocomposite hydrogels were prepared using a completely green route and used as sorbents to adsorb Cd2+ ions from water and soil systems of an environmental aspect. The sorbents were characterized by FTIR, SEM, and XRD. The influences of initial Cd2+ concentration, the presence of nano cellulose, type of the polluted environment, and ionic strength on adsorption and desorption isotherms were investigated. The maximum adsorption capacity of cadmium onto CSA was significantly increased from 2264.9 to 4380.97 µmol/g when the system was changed from soil to water, respectively. While, the maximum adsorption capacity of cadmium onto CSA-N was almost the same in the soil and wastewater systems, i.e., 3419.5 and 3230.3 µmol/g, respectively. The results indicated that Langmuir and Freundlich models provided the best fit for the experimental adsorption data for CSA and CSA-N, respectively. By comparing the amounts of Δq, the difference between adsorption and desorption amounts, the CSA was not economically feasible sorbent at high initial concentrations of Cd2+ in the wastewater system, while, CSA-N was demonstrated to be a more efficient adsorbent than CSA for cadmium removal from both the soil and wastewater systems.

3D porous bioadsorbents based on chitosan/alginate/cellulose nanofibers as efficient and recyclable adsorbents of anionic dye.

Natural polysaccharides are attractive materials for fabrication of eco-friendly biodsorbents for efficient water remediation. However, scarcity of adsorbents that possess features of high stability and adsorption capacity at various pH conditions, low-cost, eco-friendly, and recycleability at the same time still remains a great challenge. Herein, porous ionically crosslinked biofoams were prepared by freeze-drying of chitosan (CS)/sodium alginate (SA) complex (CSA). FTIR and XRD were used to characterize the structure of the bioadsorbents. SEM observations revealed that adsorbents have a 3D interconnected porous structure, which is a favorable morphology for dye adsorption. Accordingly, CSA and its nanocomposite containing 15 wt% cellulose nanofibers (CSAC15) exhibited a fast and efficient adsorption behavior with qm values of 2015 and 2297 mg/g for adsorption of the Eriochrome black-T (EBT) anionic dye, respectively, which are quite outstanding among the developed EBT adsorbents in the literature so far. The CSAC15 preserved its stability and high adsorption capacity at various pH solutions. The adsorption of EBT onto the bioadsorbents was well-described with the pseudo-second order kinetics and Freundlich isotherm. The proposed CSAC15 bioadsorbent featured repeated dye removal capability after five cycles of adsorption.

Magnetic κ-carrageenan/chitosan/montmorillonite nanocomposite hydrogels with controlled sunitinib release.

This work aimed to design montmorillonite-incorporated pH-responsive and magnetic κ-carrageenan/chitosan hydrogels via a completely green route for controlled release of sunitinib anticancer drug. This was accomplished by ionic cross-linking of two biopolymers, κ-carrageenan and chitosan, in the presence of magnetic montmorillonite (mMMt) nanoplatelets. Interestingly, it was observed that the amount of mMMt affected not only the microstructure of hydrogels, but also the drug loading efficiency of nanocomposite hydrogels was noticeably increased by introducing mMMt (from 69 to 96%). The in vitro sunitinib release experiments showed that a low content of loaded sunitinib was released from all hydrogels in the buffered solution with pH 7.4. In contrast, a relatively sustained release with a high content of drug release was observed in the acidic solution of pH 5.5. During 48 h, the hydrogels nanocomposite containing a high content of mMMt showed cumulative release of 64.0 and 8.6% at pH 5.5 and 7.4, respectively. During two days, while the cumulative release of sunitinib was obtained 84.3% for the magnetic-free hydrogel, the magnetic ones showed 74.4 and 64% with the low and high contents of magnetic MMt, respectively. The developed κ-carrageenan/chitosan hydrogels with a high capacity of drug loading and subsequent pH-sensitive drug release can be considered in prolonged cancer therapy with reduced side effects.

Dual drug delivery of vancomycin and imipenem/cilastatin by coaxial nanofibers for treatment of diabetic foot ulcer infections.

Diabetic foot ulcer infections are the main causes of hospitalization in diabetics. The present study aimed to develop vancomycin and imipenem/cilastatin loaded core-shell nanofibers to facilitate the treatment of diabetic foot ulcers. Therefore, novel core-shell nanofibers composed of polyethylene oxide, chitosan, and vancomycin in shell and polyvinylpyrrolidone, gelatin, and imipenem/cilastatin in core compartments were prepared using the electrospinning technique. The nanofibers were characterized using scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, tensile test, and drug release. The antibacterial activity of drug-loaded nanofibers in different drugs concentrations was evaluated against Methicillin-resistant Staphylococcus aureus (MRSA), Escherichia coli, and Pseudomonas aeruginosa by disk diffusion method. Furthermore, the cytotoxicity of fibers was investigated by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide assay. The obtained results showed that the prepared nanofibers were smooth having a core-shell structure with almost no cytotoxicity. The nanofibrous mats exhibited significant antibacterial activity against S. aureus and MRSA with the inhibition zones of 2.9 and 2.5 cm and gram-negative bacteria species of E. coli and P. aeruginosa with the inhibition zones of 1.9 and 2.8 cm, respectively. With respect to the significant antibacterial activities of these nanofibrous mats, they might be used as suitable drug delivery devices not only for diabetic foot ulcer infections but also for other chronic wounds.

Electrospun, sepiolite-loaded poly(vinyl alcohol)/soy protein isolate nanofibers: Preparation, characterization, and their drug release behavior.

Wound management and drug release are important applications for electrospun nanofibers. In this study, poly(vinyl alcohol)/soy protein isolate (PVA/SPI) nanofiber mats were produced by electrospinning and used as drug carriers. The mats were loaded with ketoprofen by dissolving the drug in the solutions for nanofiber electrospinning. To improve drug release control of the nanofiber mats, a natural tubular nanoparticle, sepiolite, was used as a secondary release control tool. Three types of nanofiber mats were fabricated by electrospinning the solutions prepared by 1) direct mixing of PVA, SPI, and ketoprofen, 2) direct mixing of PVA, SPI, sepiolite, and ketoprofen, and 3) mixing PVA, SPI, and ketoprofen-preloaded sepiolite. The drug release behavior of the mats was studied using UV-vis spectroscopy and the mechanical properties of the mats were investigated by tensile testing. The results showed that sepiolite had a high impact on the release of ketoprofen, with the drug-loaded sepiolite leading to the slowest release. The incorporation of SPI and sepiolite into the PVA nanofibers also increased the mechanical strength of the mats, making them easier to handle and potentially longer-lasting. This study demonstrated the potential of using natural biomaterials and nanomaterials as the components of controlled-release drug delivery vehicles.

pH-dependent swelling and antibiotic release from citric acid crosslinked poly(vinyl alcohol) (PVA)/nano silver hydrogels.

In this work, a pH-sensitive and antibacterial drug delivery system based on poly(vinyl alcohol) (PVA)/citric acid (CA)/Ag nanoparticles (NPs) was designed using a completely green, facile and one-step route. Interestingly, the crosslinking of PVA with CA, and in-situ formation of Ag NPs within the polymeric matrix were simultaneously and simply carried out using an annealing process without need for any toxic chemicals. The developed hydrogels were characterized by FTIR, UV-vis spectra, SEM and TEM techniques. It was found that CA not only acted as a crosslinker of PVA via esterification reaction, but also it endowed pH-responsiveness and antibacterial activity to the PVA matrix due to presence of free carboxylic acid groups on CA. Hydrogels demonstrated a pH-dependent swelling as well as drug release behavior, as the swelling ratio and the drug release at pH 7.4 were found higher than pH 1.2. Furthermore, the release of ciprofloxacin was more sustained when Ag NPs were incorporated into hydrogels. In addition, the incorporation of CA, Ag NPs and ciprofloxacin into the PVA matrix provided an effective antibacterial activity against E. coli and S. aureus microorganisms. The developed hydrogels can be considered as a promising material in the prolonged antibiotic therapy such as intestinal infection treatment.

Effective dye adsorption behavior of poly(vinyl alcohol)/chitin nanofiber/Fe(III) complex.

A novel Fe(III) crosslinked poly (vinyl alcohol) (PVA)/chitin nanofiber composites were prepared for dye adsorption from water. The adsorbents were characterized by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive X-ray (EDX) analysis. The effects of Fe(III) content and chitin nanofibers (NFs) incorporation on the dye removal efficiency of adsorbents were investigated. The adsorption influencing parameters such as solution pH, contact time and initial dye concentration were optimized for maximum methyl orange (MO) adsorption. With loading of chitin NFs, the dye removal efficiency of PVA/Fe(III) adsorbents was noticeable increased. In addition, the dye removal efficiency did not show significant decline in alkaline solution in the presence of chitin NFs. Kinetics, isotherms and thermodynamics of dye adsorption process were also thoroughly studied. The adsorption data were better fitted with the pseudo-second-order kinetics and Freundlich isotherm model. PVA-chitin NFs-Fe(III) adsorbent exhibited a high maximum adsorption capacity of 810.4 mg/g for MO adsorption. Furthermore, reuse experiments revealed that the adsorption efficiency remained almost constant during five cycles of adsorption/desorption. At last, the possible mechanism for dye adsorption-desorption was proposed. The obtained results revealed that the developed bionanocomposites could be considered as promising recyclable adsorbents for wastewater treatment.

Preparation of Polyurethane Acrylate Coated Carbon Nanotube Nanocomposites by Emulsion Polymerization.

The aim of this work was to prepare strong and conductive polyurethane acrylate nanocomposites. First, urethane prepolymers with different molecular weights and hydrophilicities were synthetized. Then, their corresponding polyurethane acrylate nanocomposites were prepared by ultrasonically-assisted emulsion polymerization in the presence of various ratios of urethane prepolymers and acrylate monomers. Thermogravimetric analysis (TGA) and tensile results showed that thermal stability and mechanical properties of polyurethane acrylate samples are significantly dependent on the molecular weight and hydrophilicity of the urethane prepolymer as well as the content of acrylate monomers. Polyurethane acrylate sample (i.e., PUAc-2B50) with optimum mechanical properties and thermal stability were chosen as matrix to prepare nanocomposites in the presence of nanotubes grafted with polymerizable acrylate groups (G-MWNTs). Transmission electron microscope (TEM) revealed that the surface of nanotubes is uniformly coated with polymer nanoparticles. The nanocomposites containing 3 wt% G-MWNTs demonstrated a great modulus up to 374 MPa and excellent strength up to 18.74 MPa. Meanwhile, they indicated remarkable high electrical and thermal conductivities; as the electrical conductivity of the nanocomposites increased by more than twelve orders of magnitude, and thermal conductivity reached to 12.5 times of the neat matrix. The developed nanocomposites hold high potential for diverse applications, such as printable electronic devices, nano-sensors, and heat/electrical induced shape memory polymers.

Model protein BSA adsorption onto novel magnetic chitosan/PVA/laponite RD hydrogel nanocomposite beads.

Chitosan-based magnetic beads were developed by solution-mixing method. Firstly, the Fe3O4 nanoparticles were in situ immobilized on laponite RD sheets. The magnetic laponite RD was then dispersed in PVA and mixed with chitosan solution. PVA was aimed to prevent the disintegration of chitosan under acidic media due to its ability to form hydrogel network through freezing-thawing method. The manufactured magnetic chitosan/PVA/laponite RD beads were utilized for adsorption study of a model protein, bovine serum albumin (BSA). The adsorption of BSA on beads was pH-dependent where smaller mass of protein was adsorbed at pH values lower than isoelectric point of BSA. Moreover, it was discovered that introduction of magnetic laponite RD can improve the adsorption capacity of magnetic beads for BSA in which hydrogel with the highest content of magnetic laponite RD demonstrated the maximum adsorption capacity for BSA (qm=240.5mg/g). Langmuir model described the isotherm data better than Freundlich model.

Self-healing and tough hydrogels with physically cross-linked triple networks based on Agar/PVA/Graphene.

The aim of this work was to prepare polyvinyl alcohol (PVA)/Agar/Graphene nanocomposite hydrogels through a one-pot and green solution mixing method using water as solvent. Herein a novel strategy for designing stiff, tough and self-healing triple network (TN) hydrogels was proposed. The prepared TN hydrogels composed of strong Agar polysaccharide as the first network, tough PVA biopolymer gel as the second network, and graphene nanoplatelets as the third network. Interestingly, similar to natural biomaterials, all of the networks of the nanocomposite hydrogel were physically cross-linked via dynamic hydrogen bonding associations, i.e. Agar helix bundles, PVA crystallites and polymer chain physisorption on graphene. Therefore, the prepared hydrogels demonstrated simultaneous high strength, toughness, and autonomous self-healing within a short time of 10min, which is rare in the literature. The developed hydrogels can be a promising material in many biomedical applications, such as scaffolds, cartilages, tendons and muscles.

Thermally and Electrically Triggered Triple-Shape Memory Behavior of Poly(vinyl acetate)/Poly(lactic acid) Due to Graphene-Induced Phase Separation.

This work aimed to develop a facile and broadly applicable method for fabricating multistimuli responsive triple-shape memory polymers (SMPs). Hence, herein the SMPs were prepared through the simple physical blending of two commercially available biopolymers, poly(lactic acid) (PLA) and poly(vinyl acetate) (PVAc), in the presence of robust and conductive graphene nanoplatelets. Interestingly, atomic force microscopy observations and thermal analyses revealed that the presence of nanofillers led to phase separation and appearance of two well-separated transition temperatures in the blend of these two miscible polymers. Consequently, shape memory results showed that the unfilled blend of PLA/PVAc with a single thermal transition can only show moderate heat triggered dual-shape memory behavior. While, PLA/PVAc/graphene nanocomposite blends demonstrated excellent thermally and electrically actuated triple-shape memory effects besides their remarkable dual-shape memory behavior. In addition, electrical conductivity of the blend was enhanced by ∼14 orders of magnitude in the presence of graphene. More interestingly, electroactive shape recovery experiments exhibited that depending on the applied voltage, temporary shapes in each region of sample can be either individually or simultaneously recovered.

Bioinspired fully physically cross-linked double network hydrogels with a robust, tough and self-healing structure.

The conventional covalently cross-linked double network (DN) hydrogels with high stiffness often show low toughness and self-healing property due to the irreversible bond breakages in their networks. Therefore, scarcity of hydrogels that possess simultaneous features of stiffness, toughness, and autonomous self-healing properties at the same time remains a great challenge and seriously limits their biomedical applications. While, many natural materials acquire these features from their dynamic sacrificial bonds. Inspired by biomaterials, herein we propose a novel strategy to design stiff, tough and self-healing DN gels by substitution of both covalently cross-linked networks with strong, dynamic hydrogen bond cross-linked networks. The prepared fully physically cross-linked DN gels composed of strong agar biopolymer gel as the first network and tough polyvinyl alcohol (PVA) biopolymer gel as the second network. The DN gels demonstrated multiple-energy dissipating mechanisms with a high modulus up to 2200kPa, toughness up to 2111kJm-3, and ability to self-heal quickly and autonomously with regaining 67% of original strength only after 10min. The developed DN gels will open a new avenue to hydrogel research and holds high potential for diverse biomedical applications, such as scaffold, cartilage, tendon and muscle.

Magnetic- and pH-responsive κ-carrageenan/chitosan complexes for controlled release of methotrexate anticancer drug.

The aim of the present work was to develop green carriers for methotrexate using κ-carrageenan/chitosan complexes. Magnetic Fe3O4 nanoparticles were first synthesized in the presence of κ-carrageenan through in situ method. Then, the obtained magnetic κ-carrageenan was crosslinked using the polycation chitosan biopolymer. The physical and structural properties of hydrogels were investigated by FTIR, XRD, SEM, TEM, TGA, and VSM techniques. The pH-dependent swelling behavior of hydrogels was examined in various buffer solutions. All of the prepared hydrogels showed a high swelling capacity in basic solutions. The introduction of magnetite nanoparticles into κ-carrageenan/chitosan complexes had a significant effect on the swelling capacity of magnetic hydrogels, as the water absorbency of hydrogels decreased with increasing magnetite content. Methotrexate as an anticancer and model drug was loaded on hydrogels and the release profiles were investigated at pH=7.4 and 5.3. The methotrexate encapsulation efficiency was increased by increasing magnetite and chitosan contents. The results demonstrated that the release of methotrexate from magnetic hydrogels is pH-dependent with a high release content at pH=7.4. The release profiles were analyzed by Peppas's empirical model and the release of drug from hydrogels followed Fickian type of diffusion mechanism at both pHs.

Magnetic hydrogel beads based on PVA/sodium alginate/laponite RD and studying their BSA adsorption.

In this study double physically crosslinked magnetic hydrogel beads were developed by a simple method including solution mixing of sodium alginate and poly(vinyl alcohol) (PVA) containing magnetic laponite RD (Rapid Dispersion). Sodium alginate and PVA were physically crosslinked by Ca(2+) and freezing-thawing cycles, respectively. Magnetic laponite RD nanoparticles were incorporated into the system to create magnetic response and strengthen the hydrogels. All hybrids double physically crosslinked hydrogel beads were stable under different pH values without any disintegration. Furthermore, adsorption of bovine serum albumin (BSA) on the hydrogel beads was investigated on the subject of pH, ion strength, initial BSA concentration, and temperature. Nanocomposite beads exhibited maximum adsorption capacity for BSA at pH=4.5. The experimental adsorption isotherm data were well followed Langmuir model and based on this model the maximum adsorption capacity was obtained 127.3mgg(-1) at 308K. Thermodynamic parameters revealed spontaneous and monolayer adsorption of BSA on magnetic nanocomposites beads.