Morphology,rheological and crystallization behavior in non-covalently functionalized carbon nanotube reinforced poly(butylene succinate) nanocomposites with low percolation threshold

Multi-walled carbon nanotubes (CNTs) were non-covalently functionalized by surface wrapping of poly(sodium 4-styrenesulfonate) (PSS) with the aid of ultrasound. The functionalized CNTs were incorporated into poly(butylene succinate) (PBS) through solution coagulation to fabricate CNTs filled PBS nanocomposites. The morphologies of the PBS/CNT nanocomposites were studied by scanning electron microscope (SEM) and transmission electron microscope (TEM), and the effect of loading of functionalized CNT on the rheological behavior, electrical conductivity and mechanical properties of the nanocomposites was investigated systemically. SEM observation indicates that functionalized CNTs dispersed in PBS matrix without obvious aggregation and showed good interfacial adhesion with the PBS phase. TEM observation reveals that a CNT network was formed when the loading of CNTs increased from 0.1 to 0.3 wt%. Rheological investigation indicates the formation of a CNT network with a percolation threshold of only 0.3 wt%. Significant improvement in electrical conductivity occurred at CNT loading of 0.3 wt%, with the value of electrical conductivity increasing by six orders of magnitude compared to neat PBS. Differential scanning calorimetry indicates that the melt crystallization temperature of PBS was improved by ∼14 °C with addition of only 0.05 wt% functionalized CNTs. Tensile tests indicate that both the yield strength and Young's modulus of PBS were apparently reinforced by incorporation of functionalized CNTs, while the elongation at break was reduced gradually.     

Synthesis and characterization nanocomposite of polyacrylamide‐rGO‐Ag‐PEDOT/PSS hydrogels by photo polymerization method

We present a novel approach to the fabrication of advanced polymeric nanocomposite hydrogels from polyacrylamide (PAAm) by incorporation of graphene‐silver‐polyethylenedioxythiophene‐polystyrene sulfonate (rGO‐Ag‐PEDOT/PSS) by photopolymerization method. Infrared spectroscopy was employed to characterize the structure of the hydrogels. The internal network structure of nanocomposite hydrogels was investigated by scanning electron microscope. Swelling, deswelling, and mechanical properties of the hydrogels were investigated. The compressive strength of nanocomposite hydrogels reaches maximum of 1.71 MPa when the ratio of rGO‐Ag‐PEDOT/PSS to PAAm was 0.3 wt%, which is 1.57 times higher than that of PAAm hydrogels (1.09 MPa). The electrical conductivity of the PAAm‐rGO‐Ag‐PEDOT/PSS hydrogel was found to be 3.91 × 10^?5 S cm^?1. Copyright © 2015 John Wiley & Sons, Ltd.     

Graphene Oxide/Polyacrylamide/Aluminum Ion Cross‐Linked Carboxymethyl Hemicellulose Nanocomposite Hydrogels with Very Tough and Elastic Properties

Development of high‐strength hydrogels has recently attracted ever‐increasing attention. In this work, a new design strategy has been proposed to prepare graphene oxide (GO)/polyacrylamide (PAM)/aluminum ion (Al³⁺)‐cross‐linked carboxymethyl hemicellulose (Al‐CMH) nanocomposite hydrogels with very tough and elastic properties. GO/PAM/Al‐CMH hydrogels were synthesized by introducing graphene oxide (GO) into PAM/CMH hydrogel, followed by ionic cross‐linking of Al³⁺. The nanocomposite hydrogels were characterized by means of FTIR, X‐ray diffraction (XRD), and scanning electron microscopy/energy‐dispersive X‐ray analysis (SEM‐EDX) along with their swelling and mechanical properties. The maximum compressive strength and the Young's modulus of GO_3.5/PAM/Al‐CMH_0.45 hydrogel achieved values of up to 1.12 and 13.27 MPa, increased by approximately 6488 and 18330 % relative to the PAM hydrogel (0.017 and 0.072 MPa). The as‐prepared GO/PAM/Al‐CMH nanocomposite hydrogels possess high strength and great elasticity giving them potential in bioengineering and drug‐delivery system applications.     

A Two‐Step Method for Transferring Single‐Walled Carbon Nanotubes onto a Hydrogel Substrate

Carbon nanotube (CNT)‐hydrogel nanocomposites are beneficial for various biomedical applications, such as nerve regeneration, tissue engineering, sensing, or implant coatings. Still, there are impediments to developing nanocomposites, including attaining a homogeneous CNT‐polymer dispersion or patterning CNTs on hydrogels. While few approaches have been reported for patterning CNTs on polymeric substrates, these methods include high temperature, high vacuum or utilize a sacrificial layer and, hence, are incompatible with hydrogels as they lead to irreversible collapse in hydrogel structure. In this study, a novel two‐step method is designed to transfer CNTs onto hydrogels. First, dense CNTs are grown on quartz substrates. Subsequently, hydrogel solutions are deposited on the quartz‐grown CNTs. Upon gelation, the hydrogel with transferred CNTs is peeled from the quartz. Successful transfer is confirmed by scanning electron microscopy and indirectly by cell attachment. The efficient transfer is attributed to π‐interactions pregelation between the polymers in solution and the CNTs.

     

Poly(cetyl trimethylammonium 4-styrenesulfonate)-wrapped carbon nanotubes filled in polylactide nanocomposites: Fabrication and properties

Poly(cetyl trimethylammonium 4-styrenesulfonate) (PSS-CTA) was synthesized by the ionic exchange reaction of poly(sodium 4-styrenesulfonate) (PSS-Na) with cetyl trimethylammonium bromide (CTAB). It was then used as a surface modifier for carbon nanotubes (CNTs) to improve dispersion in and interfacial adhesion with a polylactide (PLA) matrix to fabricate high performance PLA/CNT nanocomposites via a solution precipitation method. The morphology, electrical conductivity, crystallization and mechanical properties of the PLA nanocomposites were investigated in detail. The results indicate that CNTs wrapped (coated) with a suitable amount of PSS-CTA dispersed in the PLA matrix homogeneously. The electrical conductivity of PLA was enhanced by up to 10 orders of magnitude with the incorporation of 1.0 wt% PSS-CTA-modified CNTs (mCNTs). The crystallization rate of PLA was improved due to the nucleation effect of mCNTs towards the crystallization of PLA, but the crystallization mechanisms and crystal structure of PLA remained unchanged with the incorporation of mCNTs. Both the tensile strength and toughness of PLA were improved by the incorporation of mCNTs, and the fracture behaviour of PLA changed from brittle e to ductile during tensile testing.     

Tough and fluorescent hydrogels composed of poly(hydroxyurethane) and poly(stearyl acrylate-co-acrylic acid) with hydrophobic associations and hydrogen bonds as the physical crosslinks

Fluorescent hydrogels have promising applications in biomedical and engineering fields. However, they are usually mechanically weak. Here, we report a fluorescent composite hydrogel with high toughness, which is facilely prepared by solution casting ethanol solution of poly(hydroxyurethane) (PHU) and poly(stearyl acrylate-co-acrylic acid) (P[SA-co-AAc]) followed by swelling the casted film in water. The composite hydrogels with water content of 62–78 wt% possess remarkable mechanical performances, with tensile breaking stress of 0.3–1.1 MPa, breaking strain of 280%–400%, Young's modulus of 0.2–0.7 MPa, and tearing fracture energy of 1250–2630 J/m². The high toughness is attributed to the effective energy dissipation of the network with hydrophobic association of SA units and hydrogen bonds between PHU and P(SA-co-AAc) as the physical crosslinks. The intense aggregation of carbamates and the formation of carbamate clusters through intra- and intermolecular hydrogen bonds endow the composite hydrogel with strong fluorescence. These hydrogels with high toughness and strong fluorescence should find applications in flexible electronics, information display, and biomedical devices.     

Kinetics studies on the accelerated curing of liquid crystalline epoxy resin/multiwalled carbon nanotube nanocomposites

A new class of nanocomposite has been fabricated from liquid crystalline (LC) epoxy resin of 4,4′‐bis(2,3‐epoxypropoxy) biphenyl (BP), 4,4′‐diamino‐diphenyl sulfone (DDS), and multiwalled carbon nanotubes (CNTs). The surface of the CNTs was functionalized by LC epoxy resin (ef‐CNT). The ef‐CNT can be blended well with the BP that is further cured with an equivalent of DDS to form nanocomposite. We have studied the curing kinetics of this nanocomposite using isothermal and nonisothermal differential scanning calorimetry (DSC). The dependence of the conversion on time can fit into the autocatalytic model before the vitrification, and then it becomes diffusion control process. The reaction rate increases and the activation energy decreases with increasing concentration of the ef‐CNT. At 10 wt % of ef‐CNT, the activation energy of nanocomposite curing is lowered by about 20% when compared with the neat BP/DDS resin. If the ef‐CNT was replaced by thermal‐insulating TiO₂ nanorods on the same weight basis, the decrease of activation energy was not observed. The result indicates the accelerating effect on the nanocomposite was raised from the high‐thermal conductivity of CNT and aligned LC epoxy resin. However, at ef‐CNT concentration higher than 2 wt %, the accelerating effect of ef‐CNTs also antedates the vitrification and turns the reaction to diffusion control driven. As the molecular motions are limited, the degree of cure is lowered. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Evaluating the effect of addition of nanodiamond on the synergistic effect of graphene-carbon nanotube hybrid on the mechanical properties of epoxy based composites

Addition of carbon nanotubes (CNT) to Graphene (Gr) is seen to have synergistic effect as reinforcement to polymer matrix. This is possible as CNTs inhibit stacking of Gr sheets, thus providing larger surface area nanophase to get bonded with polymer matrix and providing mechanical support through load sharing and crack growth inhibition. However, tube like morphology and high aspect ratio of CNT often lead to entanglement, which restricts their effect in exfoliating Gr. The aim of the present study is to investigate the potential of ND in improving the synergistic effect of Gr-CNT hybrid as a reinforcement to epoxy matrix. This study utilizes the power of ultrasonication technique, which is very simple and scalable, for dispersing and incorporating nanofillers into epoxy matrix. Addition of ND to Gr-CNT epoxy composite improved the tensile strength from ~46% with 0.5 wt% (75Gr:25ND) to ~51% with 0.8 wt% (25Gr:25CNT:50ND) as compared to neat epoxy. While the fracture toughness improved from ~140% with 0.5 wt% (25Gr:75CNT) to 165% with 0.8 wt% (25Gr:50CNT:25ND). Fractured surfaces of composites revealed improved dispersion and strong interfacial interaction with addition of ND to Gr-CNT hybrid. NDs attaches to the surface of Gr inhibit the stacking of Gr sheets by restricting π-π stabilization. NDs also help in bridging the ends of CNTs together into long chains, thereby increasing the aspect ratio of the fiber like reinforcement. This increases the total available surface area of CNTs and Gr, to interact with epoxy matrix, improves the overall efficiency of Gr-CNT hybrid as a reinforcement, resulting into improvement in mechanical properties of the composite structure.     

Impact of supramolecular interactions on swelling and release behavior of UPy functionalized HEMA‐based hydrogels

Supramolecular polymeric hydrogels based on copolymers of 2‐hydroxyethyl methacrylate (HEMA) and HEMA functionalized with ureidopyrimidinone (quadruple H‐bonding motifs and HU comonomer) were prepared at different HU comonomer ratios (PH‐Sn, n = HU mol%). For comparison, HEMA homopolymers (PH‐Cn, n = mol% of a chemical cross‐linker) were synthesized. In contrast to PH‐S0, PH‐Sn copolymers act like cross‐linked hydrogels and absorb large amounts of water while retaining shape. Viscosities of the hydrogels decreased, and elastic and loss moduli increased with increasing HU content. Compression modulus of the swollen PH‐Sn hydrogels increased with HU content and varied between 54 and 240 kPa. Study of metronidazole loading/release behaviors of PH‐S6 hydrogel against PH‐C6 revealed a negligible burst effect for the former and a sustained release that continued for about 120 hours. We conclude that modification of poly(2‐hydroxyethyl methacrylate) with HU through urethane linkages is an effective strategy to developing physical hydrogels with predictable behavior for biomedical applications.     

New silicone hydrogels based on interpenetrating polymer networks comprising polysiloxane and poly(vinyl alcohol) networks

A method for the synthesis of a new silicone hydrogel as a biphase material for soft contact lenses is considered. The method is based on the synthesis of sequential interpenetrating polymer networks (IPN) and includes the following stages: (1) cross‐linked silicone synthesis by the reaction of vinyl‐ and hydride‐containing oligosiloxanes; (2) silicone network saturation with vinyl acetate and cross‐linking monomer followed by UV‐initiated polymerization to form an IPN comprising the silicone and cross‐linked poly(vinyl acetate) (PVAc) network; (3) PVAc network alcoholysis with methanol to obtain silicone hydrogels comprising the silicone and cross‐linked poly(vinyl alcohol) (PVAl). A study of hydrophilic, optical, mechanical, and structural features of the silicone hydrogels showed that optical transparency is achieved for materials with the highest density of silicone network cross‐linking where the size of IPN structural units does not exceed 100 nm. The water content in hydrophilic networks of silicone hydrogel is found to be below the values typical of cross‐linked PVAl, leading to non‐additivity of IPN mechanical properties. Indeed, the elasticity moduli (E) of the hydrophilic and silicone networks are 0.4–0.7 and 0.7–1.8 MPa, respectively, whereas for some IPN this value reaches 3.0 MPa. The optimal parameters of synthesis providing the reduction of E to 0.8–1.6 MPa without deterioration of the required performance characteristics (optical transparency 90–92%, water content 20–39 wt%) are determined. Copyright © 2009 John Wiley & Sons, Ltd.     

Dynamic,Bioresponsive Hydrogels via Changes in DNA Aptamer Conformation

DNA aptamers are integrated into synthetic hydrogel networks with the aim of creating hydrogels that undergo volume changes when exposed to target molecules. Specifically, single‐stranded DNA aptamers in cDNA‐bound, extended state are incorporated into hydrogel networks as cross‐links, so that the nanoscale conformational change of DNA aptamers upon binding to target molecules will induce macroscopic volume decreases of hydrogels. Hydrogels incorporating adenosine triphosphate (ATP)–binding aptamers undergo controllable volume decreases of up to 40.3 ± 4.6% when exposed to ATP, depending on the concentration of DNA aptamers incorporated in the hydrogel network, temperature, and target molecule concentration. Importantly, this approach can be generalized to aptamer sequences with distinct binding targets, as demonstrated here that hydrogels incorporating an insulin‐binding aptamer undergo volume changes in response to soluble insulin. This work provides an example of bioinspired hydrogels that undergo macroscopic volume changes that stem from conformational shifts in resident DNA‐based cross‐links.     

Antibacterial Hybrid Hydrogels

Bacterial infectious diseases and bacterial‐infected environments have been threatening the health of human beings all over the world. In view of the increased bacteria resistance caused by overuse or improper use of antibiotics, antibacterial biomaterials are developed as the substitutes for antibiotics in some cases. Among them, antibacterial hydrogels are attracting more and more attention due to easy preparation process and diversity of structures by changing their chemical cross‐linkers via covalent bonds or noncovalent physical interactions, which can endow them with various specific functions such as high toughness and stretchability, injectability, self‐healing, tissue adhesiveness and rapid hemostasis, easy loading and controlled drug release, superior biocompatibility and antioxidation as well as good conductivity. In this review, the recent progress of antibacterial hydrogel including the fabrication methodologies, interior structures, performances, antibacterial mechanisms, and applications of various antibacterial hydrogels is summarized. According to the bacteria‐killing modes of hydrogels, several representative hydrogels such as silver nanoparticles‐based hydrogel, photoresponsive hydrogel including photothermal and photocatalytic, self‐bacteria‐killing hydrogel such as inherent antibacterial peptides and cationic polymers, and antibiotics‐loading hydrogel are focused on. Furthermore, current challenges of antibacterial hydrogels are discussed and future perspectives in this field are also proposed.     

Nanocomposite hydrogel consisting of Na‐montmorillonite with enhanced mechanical properties

A new kind of nanocomposite (NC) hydrogel with Na‐montmorillonite (MMT) is presented in this article. The NC hydrogels were synthesized by free radical copolymerization of acrylamide and (3‐acrylamidopropyl) trimethylammonium chloride (ATC) in the presence of MMT and N,N′‐methylene‐bis‐acrylamide used as chemical cross‐linker. Due to the cation‐exchange reaction between MMT and ATC (cationic monomer) during the synthesis of NC hydrogels, MMT platelets were considered chemical “plane” cross‐linkers, different from “point” cross‐linkers. With increasing amount of MMT, the crosslinking degree enhanced, causing a decrease of the swelling degree at equilibrium. Investigations of mechanical properties indicated that NC hydrogels exhibited enhanced strength and toughness, which resulted from chemical interaction between exfoliated MMT platelets and polymer chains in hydrogels. Dynamic shear measurements showed that both storage modulus and loss modulus increased with increasing MMT content. The idea described here provided a new route to prepare hydrogels with high mechanical properties by using alternative natural Na‐MMT. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1020–1026     

Electrical conductivity,impedance, and percolation behavior of carbon nanofiber and carbon nanotube containing gellan gum hydrogels

The electrical impedance behavior of gellan gum (GG), GG–carbon nanotube, and GG–carbon nanofiber hydrogel composites is reported. It is demonstrated that the impedance behavior of these gels can be modeled using a Warburg element in series with a resistor. Sonolysis (required to disperse the carbon fillers) does not affect GG hydrogel electrical conductivity (1.2 ± 0.1 mS/cm), but has a detrimental effect on the gel's mechanical characteristics. It was found that the electrical conductivity (evaluated using impedance analysis) increases with increasing volume fraction of the carbon fillers and decreasing water content. For example, carbon nanotube containing hydrogels exhibited a six‐ to sevenfold increase in electrical conductivity (to 7 ± 2 mS/cm) at water content of 82%. It is demonstrated that at water content of 95 ± 2% the electrical behavior of multiwalled nanotube containing hydrogels transitions (percolates) from transport dominated by ions (owing to GG) to transport dominated by electrons (owing to the carbon nanotube network). © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 864–871     

Thermally conductive cyanate ester nanocomposites filled with graphene nanosheets and multiwalled carbon nanotubes

In this work, dodecylamine‐modified graphene nanosheets (DA‐GNSs) and γ‐aminopropyl‐triethoxysilane‐treated multiwalled carbon nanotubes (f‐MWCNTs) are employed to prepare cyanate ester (CE) thermally conductive composites. By adding 5 wt% DA‐GNSs or f‐MWCNTs to the CE resin, the thermal conductivities of the composites became 3.2 and 2.5 times that of the CE resin, respectively. To further improve the thermal conductivity, a mixture of the two fillers was utilized. A remarkable synergetic effect between the DA‐GNSs and f‐MWCNTs on improving the thermal conductivity of CE resin composites was demonstrated. The composite containing 3 wt% hybrid filler exhibited a 185% increase in thermal conductivity compared with pure CE resin, whereas composites with individual DA‐GNSs and f‐MWCNTs exhibited increases of 158 and 108%, respectively. Moreover, the composite with hybrid filler retained high electrical resistivity. Scanning electron microscopy images of the composite morphologies showed that the modified graphene nanosheets (GNSs) and multiwalled carbon nanotubes (MWCNTs) were uniformly dispersed in the CE matrix, and a number of junction points among MWCNTs and between MWCNTs and GNSs formed in the composites with hybrid fillers. Generally, we can conclude that these composites filled with hybrid fillers may be promising materials of further improving the thermal conductivity of CE composites. Copyright © 2014 John Wiley & Sons, Ltd.     

The effect of a semi‐industrial masterbatch process on the carbon nanotube agglomerates and its influence in the properties of thermoplastic carbon nanotube composites

This study details an industrial process to prepare polypropylene (PP) composites reinforced with different loadings (0.5–10wt.%) of carbon nanotubes (CNTs) from a direct dilution of a masterbatch produced by an optimized extrusion compounding process. The work demonstrates how the anisotropy in the distribution of CNTs can have a positive effect on the electrical conductivity and fracture toughness of the resulting composites. The composite with the highest loading of CNTs had an electrical conductivity of 10^?2 S/m comparable with those reported in the available literature. The composites showed anisotropy in their properties that seems to be caused by the non‐homogeneous distribution of the agglomerates produced by the orientation of the flow direction during the injection process. The composites produced in this work exhibited a fracture toughness up to 55% higher than neat PP and failed by polymer ductile tearing. It was found that the CNT agglomerates distributed throughout the matrix increased the toughness of PP by promoting plastic deformation of the matrix during the fracture process and by a slight load transfer between the polymer matrix and the CNTs of the agglomerates. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55 , 189–197     

A comparative study on the effect of carbon fillers on electrical and thermal conductivity of a cyanate ester resin

Carbon fillers including multi-walled carbon nanotubes (MWCNTs), carbon black (CB) and graphite were introduced in a cyanate ester (CE) resin, respectively. The effects of the fillers on the electrical and thermal conductivity of the resin were measured and analyzed based on the microscopic observations. MWCNTs, CB and graphite exhibited percolation threshold at 0.1 wt%, 0.5 wt% and 10 wt%, respectively. The maximal electrical conductivity of the composites was 1.08 S/cm, 9.94 × 10⁻³ S/cm and 1.70 × 10⁻⁵ S/cm. MWCNTs showed the best enhancement on the electrical conductivity. The thermal behavior of the composites was analyzed by calorimetry method. Incorporation of MWCNTs, CB and graphite increased the thermal conductivity of CE resin by 90%, 15% and 92%, respectively. Theoretical models were introduced to correlate the thermal conductivity of the CE/MWCNTs composite. The interfacial thermal resistance between CE resin and MWCNTs was 8 × 10⁻⁸ m²K/W and the straightness ratio was 0.2. The MWCNTs were seriously entangled and agglomerated. Simulation results revealed that thermal conductivity of the CE/MWCNTs composites can be substantially elevated by increasing the straightness ratio and/or filler content of MWCNTs.     

Novel conductive nanocomposites from perfluoropolyether waterborne polyurethanes and carbon nanotubes

The exceptional electrical conductivity of carbon nanotubes (CNTs) has been exploited for the preparation of conductive nanocomposites based on a large variety of insulating polymers. Among these, perfluoropolyether‐polyurethanes (PFPE‐PUs) represent a class of highly performing fluorinated materials with excellent water/oil repellency, chemical resistance, and substrate adhesion. The incorporation of highly conductive fillers to this class of highly performing materials allows them to be exploited in new technological and industrial fields where their unique properties need to be combined with the electrical conductivity or the electrostatic dissipation properties of carbon nanotubes. However, no studies have been presented so far on nanocomposites based on PFPE‐PUs and CNTs. In this work, polymer nanocomposites based on waterborne PFPE‐PUs and increasing amounts of carboxylated multiwall CNTs (COOH‐CNTs) were prepared and characterized for the first time. The effect of increasing concentration of COOH‐CNTs on the physical, mechanical, and surface properties of the nanocomposites was investigated by means of rheological measurements, dynamic mechanical analysis, thermal characterization, optical contact angle measurements, and scanning electron microscopy. In addition, electrical measurements showed that the highly insulating undoped PFPE‐PU system undergoes substantial modifications upon addition of COOH‐CNTs, leading to the formation of conductive nanocomposites with electrical conductivities as high as 1 S/cm. The results of this study demonstrate that the addition of COOH‐CNTs to PFPE‐PU systems represents a promising strategy to expand their possible use to technological applications where chemical stability, water/oil repellence and electrical conductivity are simultaneously required. Copyright © 2014 John Wiley & Sons, Ltd.     

Genipin‐crosslinked gelatin hydrogel incorporated with PLLA‐nanocylinders as a bone scaffold: Synthesis,characterization, and mechanical properties evaluation

Nowadays, despite remarkable progress in developing bone tissue engineering products, the fabrication of an ideal scaffold that could meet the main criteria, such as providing mechanical properties and suitable biostability as well as mimicking the bone extracellular matrix, still seems challenging. In this regard, utilizing combinatorial approaches seems more beneficial. Here, we aim to reinforce the mechanical characteristics of gelatin hydrogel via a combination of Genipin‐based chemical cross‐linking and incorporation of the poly l ‐lactic acid (PLLA) nanocylinders for application as bone scaffolds. Amine‐functionalized nanocylinders are prepared via the aminolysis procedure and incorporated in gelatin hydrogel. The nanocylinder content (0, 1, 2, 3, and 4 wt%) and cross‐linking density (0.1, 0.5, and 1 wt/vol%) are optimized to achieve suitable morphology, swelling ratio, degradation rate, and mechanical behaviors. The results indicate that hydrogel scaffold cross‐linking by 0.5 wt% of Genipin shows optimized morphological feathers with a pore size of around 300 to 500 μm as well as an average degradation rate (40.09% ± 3.08%) during 32 days. Besides, the incorporation of 3 wt% PLLA nanocylinders into the cross‐linked gelatin scaffold provides an optimized mechanical reinforcement as compressive modulus, and compressive strength show a 4‐ and 2.6‐fold increase, respectively. 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide assay indicates that the scaffold does not have any cytotoxicity effect. In conclusion, gelatin composite reinforced with 3 wt% PLLA nanocylinders cross‐linked via 0.5 wt/vol% Genipin is suggested as a potential scaffold for bone tissue engineering applications.     

A Carbon Nanotube Layered Electrode for the Construction of the Wired Bilirubin Oxidase Oxygen Cathode

Oxidatively treated carbon nanotubes were coated on a glassy carbon surface to form a CNT‐layer. On the CNT‐layered GC surface, a redox hydrogel film of the copolymer, of polyacryamide and poly(N‐vinylimidazole) complexed with [Os(4,4′‐dichloro‐2,2′‐bipyridine)₂Cl]^+/2+ wiring bilirubin oxidase was immobilized. A good contact was achieved between the hydrogel film and the hydrophilic CNT‐layer with carboxylated CNTs. The prepared bilirubin oxidase cathode on the CNT‐layer was employed for the electrocatalytic reduction of O₂, and enhanced current and stability were observed. Electron transfers from the electrode surface O₂ molecules were analyzed. The optimal composition of the enzyme, redox polymer, and cross‐linker in the catalyst and the thickness of the CNT‐layer were determined.