Development of carboxymethyl cellulose-based hydrogel and nanosilver composite as antimicrobial agents for UTI pathogens.

Silver nanoparticles (AgNPs) containing hydrogel composite were first synthesized by preparing a new hydrogel from carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), and the cross-linker ethylene glycol diglycidyl ether (EGDE), followed by the incorporation of AgNPs by microwave radiation. The resulting neat hydrogels and AgNPs-hydrogel composites were characterized using spectral, thermal, microscopic analysis and X-ray diffraction (XRD) analyses. The SEM and TEM results demonstrated that the synthesized AgNPs were spherical with diameters ranging from 8 to 14nm. In addition, the XRD analysis confirmed the nanocrystalline phase of silver with face-centered cubic (FCC) crystal structure. Energy dispersive spectroscopy (EDS) analysis of the AgNPs confirmed the presence of an elemental silver signal, and no peaks of any other impurities were detected. Additionally, the antibacterial activities of the neat hydrogel and AgNPs-hydrogel composites were measured by Kirby-Bauer method against urinary tract infection (UTI) pathogens. The rheology measurement revealed that the values of storage modulus (G') were higher than that of loss modulus (G″). The AgNPs-hydrogel composites exhibited higher antibacterial activity against Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Proteus vulgaris, Staphylococcus aureus and Proteus mirabilis compared to the corresponding neat hydrogel.

Robust biopolymer based ionic-covalent entanglement hydrogels with reversible mechanical behaviour.

Emerging applications of hydrogels such as soft robotics and cartilage tissue scaffolds require hydrogels with enhanced mechanical performance. We report the development of a robust biopolymer based ionic-covalent entanglement network hydrogel made from calcium cross-linked gellan gum and genipin cross-linked gelatin. The ratio of the two polymers and the cross-linker concentrations significantly affected the mechanical characteristics of the hydrogels. Hydrogels with optimized composition exhibited compressive fracture stress and work of extension values of up to 1.1 ± 0.2 MPa and 230 ± 40 kJ m-3 for swelling ratios of 37.4 ± 0.6 and 19 ± 1, respectively. The compressive and tensile mechanical properties, swelling behavior (including leachage), pH sensitivity and homogeneity are discussed in detail. Fully swollen hydrogels (swelling ratio of 37.4 ± 0.6) were able to recover 95 ± 2% and 82 ± 7% of their energy dissipation (hysteresis) at 37 °C after reloading to either constant stress (150 kPa) or constant strain (50%), respectively.

Extrusion printing of ionic-covalent entanglement hydrogels with high toughness.

Three-dimensional (3D) printing of hydrogels has recently been investigated for use in tissue engineering applications. One major limitation in the use of synthetic hydrogels is their poor mechanical robustness but the development of 'tough hydrogels' in conjunction with additive fabrication techniques will accelerate the advancement of many technologies including soft robotics, bionic implants, sensors and controlled release systems. This article demonstrates that ionic-covalent entanglement (ICE) gels can be fabricated through a modified extrusion printing process that facilitates in situ photopolymerisation. The rheological properties of alginate-acrylamide hydrogel precursor solutions were characterised to develop formulations suitable for extrusion printing. A range of these printed hydrogels were prepared and their mechanical performance and swelling behaviour evaluated. ICE gels exhibit a remarkable mechanical performance because ionic cross links in the biopolymer network act as sacrificial bonds that dissipate energy under stress. The printed ICE gels have a work of extension 260 ± 3 kJ m-3. Swelling the hydrogels in water has a detrimental effect upon their mechanical properties, however swelling the hydrogels in a calcium chloride solution as a post-processing technique reduces the effects of swelling the hydrogels in water. The integration of the modified extrusion printing process with existing plastic 3D printing technologies will allow for the fabrication of functional devices.

Films, Buckypapers and Fibers from Clay, Chitosan and Carbon Nanotubes.

The mechanical and electrical characteristics of films, buckypapers and fiber materials from combinations of clay, carbon nanotubes (CNTs) and chitosan are described. The rheological time-dependent characteristics of clay are maintained in clay-carbon nanotube-chitosan composite dispersions. It is demonstrated that the addition of chitosan improves their mechanical characteristics, but decreases electrical conductivity by three-orders of magnitude compared to clay-CNT materials. We show that the electrical response upon exposure to humid atmosphere is influenced by clay-chitosan interactions, i.e., the resistance of clay-CNT materials decreases, whereas that of clay-CNT-chitosan increases.

Nanofibrilar-polyaniline/Carbon nanotube composites: aqueous dispersions and films.

Entirely nanostructured nanofibrilar-polyaniline/multi-walled carbon nanotube (NF-PANI/MWNT) composites with nanotube loadings as high as 50 wt% were synthesized via a facile in-situ chemical polymerization process. These are composed of a nanofibrilar polyaniline (NF-PANI) matrix in which multi-walled carbon nanotubes (MWNTs) are homogeneously embedded and partially covered by polyaniline. Stable and homogeneous aqueous dispersions in concentrations up to 10 mg/ml in water easily were prepared. For the first time, dispersions and casted films of this novel type of NF-PANI/MWNTs composites are characterized. Both, dispersions and films reveal the typical behavior of PANI with slightly changed redox values and with fast reaction kinetics due to the presence of MWNTs. Conductivity of drop cast films reveal values of 20 to 50 S/m. Local SPM measurements confirm the intrinsic fibril structure. Individual fibrils show both semiconducting and metallic behavior with values up to 100 S/m. This new class of nanostructured NF-PANI/MWNT composites with its water-based processing possibilities as well as with its conducting and electrochromic effects will contribute to further progress in the field of smart plastic electronics.