Scattering investigations of the structure and chain conformations, and the rheological properties of polyelectrolyte complexes (PECs) comprising model polyelectrolytes are presented. The use of ...charged polypeptides - (poly)-lysine and (poly)-glutamic acid with identical backbones allowed for facile tuning of the system parameters, including chain length, side-chain functionality, and chirality. Systematic studies using small-angle X-ray scattering (SAXS) of liquid PEC coacervates revealed a physical description of these materials as strongly screened semidilute polyelectrolyte solutions comprising oppositely charged chains. At the same time, solid PECs were found to be composed of hydrogen-bonding driven stiff ladder-like structures. While the coacervates behaved akin to semidilute polyelectrolyte solutions upon addition of salt, the solids were largely unaffected by it. Rheology measurements of PEC coacervates revealed a terminal relaxation regime, with an unusual plateauing of the storage modulus at low oscillation frequencies. The plateau may be ascribed to a combination of instrumental limitations and the long-range electrostatic interactions contributing to weak energy storage modes. Excellent superposition of the dynamic moduli was achieved by a time-salt superposition. The shift factors, however, varied more strongly than previously reported with added salt concentration.
Gelatin methacrylate (GelMA) and hyaluronic acid methacrylate (HAMA) are frequently used biomaterials for 3D bioprinting, with individual well-established material characteristics.
To identify an ...ideal combination of GelMA and HAMA for chondrogenesis, a novel, primary human chondrocyte COL2A1-Gaussia luciferase reporter system (HuCol2gLuc) was developed. With this non-destructive, high-throughput temporal assay, Gaussia luciferase is secreted from the cells and used as a proxy for measuring type II collagen production. GelMA:HAMA ratios were screened using the reporter system before proceeding to 3D bioprinting. This method is efficient, saving on time and materials, resulting in a streamlined process of biomaterial optimization. The screen revealed that the addition of HAMA to GelMA improved chondrogenesis over GelMA (15%) alone. Storage moduli were measured using dynamic mechanical analysis of the same GelMA:HAMA ratios and established an initial threshold for chondrogenesis of ∼30kPa. To determine if biomaterial storage moduli impact cell mobility, human primary chondrocytes transduced with green fluorescent protein (GFP) were 3D bioprinted in either 1:1 or 2:1 ratios with storage moduli of 32kPa and 57.9kPa, respectively. We found that reduced cell mobility, in the stiffer biomaterial, had higher type II collagen expression, than the softer material with more cell mobility. Finally, after 3D bioprinting with HuCol2gLuc cells we successfully identified an optimal combination (2:1) of GelMA:HAMA and photo-crosslinking time (38s) for chondrogenesis.
One challenge of 3D bioprinting is identifying ideal biomaterials that stimulate articular cartilage development. To identify an optimal combination of gelatin methacrylate and hyaluronic acid methacrylate for chondrogenesis we developed a primary human chondrocyte type II collagen Gaussia luciferase reporter cell (HuCol2gLuc). This non-destructive, high-throughput assay uses a secreted Gaussia luciferase as a proxy for temporal type II collagen production. This reporter system streamlines the biomaterial optimization process before 3D bioprinting. We also used it to determine the level of stiffness required for chondrogenesis. And for the first time, we quantified chondrocyte mobility in a 3D bioprinted construct. Together these results indicate that a biomaterial with a higher storage modulus and less cell mobility, improves chondrogenesis.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
In this study, using a solution casting process, thermoplastic polyurethane elastomer (TPU) composites containing different contents of lead zirconate titanate (PZT) ferroelectric particles were ...produced. The damping treatment of composites at high volume of fillers was investigated. SEM micrographs showed that PZT particles had a proper distribution in the PU matrix. Differential scanning calorimetry (DSC) thermograms indicates that melting enthalpy decreases by raising PZT filler content. The results of the dynamic mechanical thermal analysis (DMTA) proved that the magnitude of loss factor (tan δ) strongly depends on PZT content, and it decreased from 0.51 to 0.27 as PZT content increased. The value of E0 increases to 0.32 GPa in the composite reinforced with 50 v% of PZT. The role of PZT on the acoustic behavior of TPU was measured using the acoustic absorption coefficient (a). The results showed that as PZT content increased from 0 to 50%, the acoustic absorption coefficient reached 0.25 at 6000 Hz frequency. The composites of PZT/PU with 0–3 connectivity were poled, and the optimal poling conditions that could be applied without sample breakdown were studied. Moreover, we prepared composites containing 70 vol% PZT particles by modifying the particles. Modification of PZT particles caused a decrease in both d33 and g33 constants of the PZT/PU composites.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
We report herein the synthesis of a novel photocleavable crosslinker, 4-formylphenyl 4-((4-formylphenoxy)methyl)-3-nitrobenzoate (CHO-ONB-CHO) and its joining with amine-based polysaccharides,
viz
. ...chitosan, resulting in the formation of a dual stimuli-responsive (ONB-chitosan) hydrogel having UV- and pH-responsive sites. The detailed mechanism for the formation of CHO-ONB-CHO and ONB-chitosan hydrogel is proposed. The (CHO-ONB-CHO) crosslinker was characterized using
1
H-NMR, LCMS and UV-visible spectroscopy. The dual responsive hydrogel is characterized by FTIR, SEM, XRD, DSC and TGA. The crosslinked hydrogel displayed mechanical robustness with a storage modulus of about 1741 pa. The pH-responsiveness of the hydrogel was studied
via
equilibrium swelling studies in various pH media at 37 °C. The photocleavable behavior of the crosslinker was observed in the UV-absorption range of 310-340 nm and the hydrogel exhibited maximum swelling at pH 5.7. The higher swelling of the hydrogel in acidic conditions and its photo-responsiveness can be exploited for the controlled, temporal and spatial release of therapeutic drugs at any inflammatory areas with acidic environments. It was observed that the hydrogel exhibited higher drug release at pH 5.7 than at pH 7.4.
We report the synthesis of a novel photocleavable crosslinker and its joining with amine-based polysachharides,
viz.
chitosan, resulting in the formation of a dual stimuli-responsive hydrogel having UV- and pH-responsive sites.
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IJS, KILJ, NUK, UL, UM, UPUK
The high values of recycled acrylonitrile-butadiene-styrene plastics (rABS) have drawn wide attentions and research interests. Herein, the renovation of molecular chains and phase interface of rABS ...was successfully achieved through simple melt-blending modification, in which the in-situ chain extension reaction was conducted between rABS and pyromellitic dianhydride (PMDA). PMDA acted as a chain extender with hydroxyl units. The modified rABS were characterized by Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), mechanical properties testing, scanning electron microscopy (SEM), and dynamic mechanical analysis (DMA). The results indicated that compared with rABS, the molecular weight, impact strength, tensile strength, storage modulus and loss modulus of modified rABS were apparently improved. Especially, when PMDA content was 0.9 wt%, the notch impact strength reached 15.9 kJ/m2, which was 140% higher than that of rABS. Besides, the interface between polybutadiene (PB) phase and styrene-acrylonitril copolymer (SAN) phase was blurred and the compatibility between two phases became better. The aforementioned results revealed that rABS has been achieved with high-value recycling usage.
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•Reparation of recycled acrylonitrile-butadiene-styrene (rABS) was done by pyromellitic dianhydride (PMDA).•The reparation of rABS was carried out in a simple melt-blending process.•The PMDA reparation increased the notch impact strength and molecular weight.•The PMDA reparation enhanced the compatibility between PB phase and SAN phases.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Many food products can be categorized as emulsion gels. This is especially the case for protein-based oil-in-water emulsions which can be converted into soft-solid-like materials by common food ...processing operations such as heating, acidification, and enzyme action. This review article outlines how the rheological and structural properties of protein-stabilized emulsion gels are influenced by the dispersed oil volume fraction, the oil–water interfacial composition, and the colloidal interactions of the constituent emulsion droplets. For model systems of variable oil content and containing different food proteins, some general trends of rheological behaviour at small and large deformations are identified. Experimental rigidity data are considered in relation to: (i) material science theories of the reinforcement of solid materials by active and inactive filler particles, and (ii) Brownian dynamics simulations of aggregated particle networks containing bonded and non-bonded particles. Influences of interfacial composition and particle–matrix interactions on microstructure and rheology are explained with particular reference to the role of small-molecule surfactants. Compositional and structural factors affecting the large-deformation rheology and fracture properties are described. Finally, the practical relevance of the model system studies to the behaviour of real food products is critically assessed.
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► Food emulsions gels are mainly formed by heating, acidification and enzyme action. ► Rheology and fracture properties depend on character of particle–matrix interactions. ► Protein-coated droplets are active fillers; surfactant-coated droplets are inactive fillers. ► Models of particle-filled gels and aggregated particle gels provide mechanistic insight.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
A series of long-chain branched polyamide 6 samples (LCB PA6s) with well-defined branch length were successfully fabricated via reactive extrusion by tuning various linear PA6s as reactive materials. ...Their structure-property relationships were systematically investigated. The GPC-rheology method was performed to demonstrate the existence of LCB topological structure and quantitatively determine the relative branch length for three LCB PA6s. Rheological characterization showed that an increase in branch length resulted in the increased zero-shear viscosity and storage modulus at low frequency, reduced loss factor and high strain hardening coefficient under elongational flow, i.e., the enhanced elastic response and melt strength of PA6s. Finally, the melt foamability of the LCB PA6s were verified by batch foaming experiments with supercritical CO2 as the blowing agent. The LCB-Mb 4.5 with the longest branch length and highest melt strength appeared the biggest expansion ratio of 18.2 and broadest foaming window of 70 °C, which was expected to be in production on a large scale through continuous extrusion foaming process.
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•LCB PA6s with well-fined branch length were first fabricated via reactive extrusion.•The relative branch length was quantitatively determined using the GPC-rheology method.•The rheological properties were greatly improved with increasing branch length.•The LCB-Mb4.5 sample exhibited the biggest expansion ratio and the broadest foaming window.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Additive manufacturing (AM) techniques and so-called 2D materials have undergone an explosive growth in the past decade. The former opens multiple possibilities in the manufacturing of ...multifunctional complex structures, and the latter on a wide range of applications from energy to water purification. Extrusion-based 3D printing, also known as Direct Ink Writing (DIW), robocasting, and often simply 3D printing, provides a unique approach to introduce advanced and high-added-value materials with limited availability into lab-scale manufacturing. On the other hand, 2D colloids of graphene oxide (GO) exhibit a fascinating rheology and can aid the processing of different materials to develop 'printable' formulations. This work provides an in-depth rheological study of GO suspensions with a wide range of behaviours from Newtonian-like to viscoelastic 'printable' soft solids. The combination of extensional and shear rheology reveals the network formation process as GO concentration increases from <0.1 vol% to 3 vol%. Our results also demonstrate that the quantification of 'printability' can be based on three rheology parameters: the stiffness of the network
via
the storage modulus (
G
′), the solid-to-liquid transition or flow stress (
σ
f
), and the flow transition index, which relates the flow and yield stresses (FTI =
σ
f
/
σ
y
).
Delving into the '
printability
' of
soft matter
using bespoke rheological protocols on suspensions and gels of 2D colloids.
In this work, we demonstrate that a graphene oxide (GO) hydrogel with unique rheological properties, such as high storage modulus, shear-thinning nature and fast viscosity recovery, is highly ...suitable as an ink for three dimensional (3D) printing. The results show that the GO ink has the characteristics of both gel and viscous liquid, where the gel-liquid transition depends on the shear rate and shear strain amplitude. In the extrusion and printing process, the ink shows significant shear thinning and rapid viscosity recovery after cessation of shearing, which are desirable for 3D printing through direct ink writing (DIW). A suitable scanning speed and extrusion speed were determined to construct a precise 3D structure. After the reduction, the RGO electrode with hierarchical porous structures is stable, of higher precision, and loaded with more of the effective materials per unit area. The 3D printed micro-supercapacitors (MSCs) with interdigitated architecture exhibit a high areal specific capacitance of 101 mF cm
−2
at a current density of 0.5 mA cm
−2
and 111 mF cm
−2
at a scan rate of 10 mV s
−1
, which are superior compared with most of the reported MSCs of carbon-based materials.
This work demonstrates successful fabrication of a high areal specific capacitance micro-supercapacitor
via
direct 3D printing of a graphene oxide hydrogel.
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As an emerging bioplastic, poly(glycolic acid) (PGA) possesses excellent bio-compostability, gas barrier properties, mechanical strength and heat resistance. However, the inherent brittleness and ...inferior melt-strength of PGA severely limits its processability and application possibilities. In the present contribution, a two-step reactive melt blending of PGA and poly(butylene adipate-co-terephthalate) (PBAT) with epoxy functionalized copolymer (ethylene-methyl acrylate-glycidyl methacrylate) (EMAG) as compatibilizer was investigated to solve these shortcomings. The EMAG was first blended with PBAT and then with PGA to in-situ form PGA-g-EMAG-g-PBAT copolymers. These copolymers selectively locate at the interface between PGA and PBAT, which effectively improved the interfacial adhesion and the compatibility. Consequently, the PGA/(PBAT/EMAG) blends with 1 wt % EMAG exhibited high elongation at break (45 ± 4%) and a notched impact strength (14.4 ± 1.6 kJ/m2) respectively, which is about 1100% and 410% higher than that of PGA. Meanwhile, the viscosity and storage modulus of the PGA/(PBAT/EMAG) blends at 50.1 Hz were enhanced by 130% and 230% compared with PGA. This work provides a facile route to fabricate PGA-based blends with excellent toughness and melt strength, which could open up new possibilities for the application of PGA materials.
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•Bio-compostable poly(glycolic acid)-based blends were prepared by reactive melt blending.•Two-step blending processes was used to control the interfacial localization of in-situ grafted copolymers.•Interface-localized copolymers markedly enhance interfacial adhesion and compatibility between PGA and PBAT.•PGA/(PBAT/EMAG) blends exhibited much superior toughness and melt strength than PGA.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
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