Mohammad Sabzi

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.

Synthesis and characterization of hydroxypropyl methylcellulose-g-poly(acrylamide)/LAPONITE® RD nanocomposites as novel magnetic- and pH-sensitive carriers for controlled drug release

pH-responsive magnetic nanocomposite hydrogels based on hydroxypropyl methylcellulose-g-poly(acrylamide)/LAPONITE® RD (HPMC-g-PAALap) were developed. The magnetic nanoparticles were synthesized inside HPMC-g-PAALap through an in situ method. The structure of the nanocomposite hydrogels was characterized using FTIR, XRD, SEM, TEM, and VSM techniques. The TEM micrograph revealed that the magnetite nanoparticles were immobilized onto the LAPONITE® RD surface. The FTIR of the magnetic nanocomposite showed that carboxylate groups are produced during magnetic nanoparticles formation in alkaline solution. The swelling capacities of the magnetic nanocomposites obtained were higher than that of non-magnetic hydrogel HPMC-g-PAALap, which was ascribed to the introduced carboxylate pendants. Due to the carboxylate groups, the magnetic nanocomposites indicated a pH-dependent swelling behaviour. Diclofenac sodium (DS) as a model drug was loaded in the nanocomposite hydrogels and the release of the drug was investigated with respect to pH of the media and also external alternative magnetic field. At pH 7.4, the content of the released drug was considerably increased as compared with that released at pH 1.2. The magnetic nanocomposite showed magnetic behaviour and the content of released drug was enhanced by increasing the strength of the external magnetic field.

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 Peppass empirical model and the release of drug from hydrogels followed Fickian type of diffusion mechanism at both pHs.

Incorporation of surface modified graphene nanoplatelets for development of shape memory PLA nanocomposite

In this study, a temperature sensitive shape memory polymer (SMP) system based on polylactic acid (PLA) has been developed and the effect of graphene nanoplatelets (GNPs) on the shape memory properties was evaluated. Dispersion of GNPs in PLA was improved with the aid of a zwitterionic surfactant. X-ray diffraction (XRD) and transmission electron microscopy (TEM) showed that the surface modified graphene nanoplatelets (SMGNPs) were exfoliated and homogenously dispersed in the PLA matrix due to enhancement of the polymer-graphene interaction. Mechanical properties of the samples namely stiffness and elasticity were increased upon incorporation of graphene nanoplatelets accompanied by their good dispersion in the PLA matrix. Furthermore, differential scanning calorimetry (DSC) revealed that the nucleation effect of graphene promote the crystallization and noticeably enhanced the degree of crystallinity. Finally, prominent mechanical properties along with high degree of crystallization due to fine dispersion of surface modified graphenes, resulted in drastic improvement in shape memory performance.

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.

Dispersion of Graphene Nanoplatelets in Polylactic Acid with the Aid of a Zwitterionic Surfactant: Evaluation of the Shape Memory Behavior

ABSTRACT Developments in the dispersion of graphene nanoplatelets in polylactic acid were achieved with the aid of a zwitterionic surfactant. The graphene nanoplatelet surface modification was tracked by Fourier transform infrared spectroscopy, thermogravimetric analysis, X-ray diffraction, and elemental analysis. Different amounts of graphene nanoplatelets and surface-modified graphene nanoplatelets (3 and 6 phr) were used to prepare the polylactic acid nanocomposite through a solvent-mixing method. It was found that surface-modified graphene nanoplatelets were exfoliated and homogeneously dispersed in the polylactic acid matrix. Better dispersion of surface-modified graphene nanoplatelets compared with graphene nanoplatelets was due to enhancement of the polymer–graphene interaction induced by the zwitterionic surfactant. The shape memory properties of nanocomposites were evaluated using thermomechanical analysis. The obtained results revealed that the shape memory performance of nanocomposite samples was affected by the degree of dispersion. Higher shape recovery of nanocomposite samples in comparison with that of neat polylactic acid was obtained, which originated from their higher elastic glassy modulus. Up to 91% shape recovery was determined in nanocomposite samples containing surface-modified graphene nanoplatelets, which was attributed to the good dispersion of surface-modified graphene nanoplatelets in the polylactic acid matrix. GRAPHICAL ABSTRACT

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.

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.

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.

The release of cefazolin from chitosan/polyvinyl alcohol/sepiolite nanocomposite hydrogel films

Films of chitosan/polyvinyl alcohol (PVA)/sepiolite nanocomposite were prepared by a simple and “green” route through solution mixing; followed by freezing–thawing cycles. The structures of nanocomposites were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), thermogravimetric analysis, X-ray diffractometry, and Fourier transform infrared spectroscopy. The SEM and TEM micrographs confirmed a needle-type dispersion of sepiolite nanoclay in the hydrogel nanocomposites. The effects of sepiolite and chitosan/PVA weight ratio on the swelling of nanocomposites were investigated. The water absorbency of nanocomposites was decreased by introducing sepiolite nanoclay. The nanocomposites with high content of chitosan showed high swelling capacity. The nanocomposite films showed pH-dependent swelling behavior with a maximum water absorbency under acidic pH. The cefazolin with a broad-spectrum activity toward gram-positive and gram-negative bacteria was loaded in hydrogels. The release of cefazolin from nanocomposites was evaluated at pH 7.4. The content of released drug was affected by both sepiolite amount and chitosan/PVA weight ratio. The nanocomposites films released more cefazolin than the neat hydrogel film. Cefazolin-loaded nanocomposites showed the antibacterial activity with a large zone of inhibition against gram-positive Bacillus cereus bacterium.