Low Polymer Concentrations Research Articles

Enhanced Retention and Synergistic Plugging Effect of Multi-Complexed Gel on Water-Swellable Rubber

For the management of fractured large pores in high-water-bearing reservoirs, the general approach is to use transfer dissection and sealing. Conventional regulators have a limited regulating radius and can only produce blocking in the near-well zone, which is not ideal. Deep dissection technology can expand the radius of action and substantially improve the blocking effect. The existing deep-dissection agent system has problems such as high cost and poor effect, which affect its large-scale application. In this paper, to address these problems, a gel-type dissection modifier cross-linking agent was synthesized and optimized in the laboratory using low-concentration polymer, and the factors affecting the final gel formation effect were experimentally studied. The final polymer concentration was chosen to be 1500 mg/L~3000 mg/L, the poly-crossing ratio was 30:1, the pH was controlled at 7–9, and the temperature was controlled at 30–60 °C; the rubber was formed with good shear resistance and thermal stability, and had good adaptability to the high-mineralization environment. The optimal injection concentration of water-expanded rubber particles for this system was confirmed to be 3000 mg/L. Cryo-electron microscopy was used to observe the morphology of polymer gel formation and the adhesion of nucleated water-expanded particles to the gel, to clarify the mechanism of enhanced retention and sealing of nucleated water-expanded rubber particles by the multiple complex gel system, and finally to verify the sealing performance of the composite sealing system and determine the use effect by indoor simulation experiments with a two-dimensional flat plate model. This study is of great significance for the efficient development of high-water-bearing late reservoirs and further improvement of crude oil recovery.

Influence of temperature on the compression behavior of pharmaceutical excipients

Tableting on an industrial scale is characterized by an increase in temperature, which is dependent on numerous factors. The aim of this study was to examine the glass transition temperature of frequently used polymers as a critical parameter on tablet properties. Tablets were produced in a tablet press equipped with a temperature-controlled die at four different temperatures ranging from 22 to 70 °C. While pure polymers were characterized for their temperature-dependent compressibility behavior using Heckel analysis, tableting was performed from binary blends containing lactose as a filler and the polymer to be examined (ratio 9:1). Tablets were characterized in terms of tabletability, compactibility and their correlation with the glass transition temperature. The decrease in mean yield pressure upon temperature rise could clearly be correlated to the glass transition temperature of a given polymer, whereby polymers with low glass transition temperatures proved to be more responsive to temperature changes. Tablet properties were equally affected by the applied temperature despite the low polymer content. Thus, polymers with higher glass transition temperatures should be preferred in a full-production scale to avoid an alteration of tablet characteristics, whereas polymers with lower glass transition temperatures could be advantageous if a change of material properties is desired.

Experimental study on compatibility of reservoir and polymer gel profile control agent

The coupling relationship between polymer gel system and reservoir pores is an important basis for scientific formulation of tertiary oil recovery programs. The polymer gel profile control agent can significantly modify the fluid migration path inside the reservoir. In this study, artificial cores were used to carry out indoor water flooding experiments after polymer gel injection that considering formation permeability, polymer concentration and polymer injection rates. Based on the accurate records of the breakthrough pressure and injection volume during water flooding, as well as a large number of observations of the microscopic morphology of the cores after the polymer gel profile control and displacement, a set of criteria for determining reservoir-matched polymer gel profile control agents is proposed. The experimental results show that a complex spatial network structure is formed after the gelation of the polymer gel system. As the polymer concentration increases, the network structure of the gel system becomes denser. At the same time, the unit network structure is becoming smaller, and the order of the grid chain structure becomes clearer. Under the condition of low polymer concentrations, the backbone structures of the gel are obvious, but there are a lot of fine pores. When the polymer concentration is greater than 1,500 mg/L and the injection rate is less than 0.15 ml/min, the water flooding breakthrough pressure is greater than 0.2 MPa, the plugging rate is greater than 95%, and a good plugging effect is obtained.

Investigation of the Impact of Hydrolytically Cleavable Groups on the Stability of Poly(ethylene glycol) Based Hydrogels Cross-Linked via the Inverse Electron Demand Diels-Alder (iEDDA) Reaction.

Eight-armed poly(ethylene glycol) (PEG) hydrogels cross-linked via inverse electron demand Diels-Alder reaction between norbornene and tetrazine groups are promising materials for long-term protein delivery. While a controlled release over 265 days is achieved for 15% w/v hydrogels in the previous study, the material shows high stability over 500 days despite having cleavable ester linkages between the PEG macromonomers and their functionalities. In this study, the hydrolyzable ester linkers in the PEG-norbornene precursor structure are exchanged to reduce the degradation time. To this end, 3,6-epoxy-1,2,3,6-tetrahydrophthalimide, phenyl carbamate, carbonate ester, and phenyl carbonate ester are introduced as degradable functional groups. Oscillatory shear experiments reveal that they are not affected the in situ gelation. All hydrogel types have gel points of less than 20 s even at a low polymer concentration of 5% w/v. Hydrogels with varying polymer concentrations have similar mesh sizes, all of which fell in the range of 4-12nm. The inclusion of phenyl carbonate ester accelerates degradation considerably, with complete dissolution of 15% w/v hydrogels after 302 days of incubation in phosphate buffer (pH 7.4). Controlled release of 150kDa fluorescein isothiocyanate-dextran over a period of at least 150 days is achieved with 15% w/v hydrogels.

One-Dimensional Assemblies of Co3O4 Nanoparticles Formed from Cobalt Hydroxide Carbonate Prepared by Bio-Inspired Precipitation within Confined Space

Nanostructured spinel-type cobalt(II,III) oxide (Co3O4) finds applications in a wide range of technological fields including clean energy conversion systems and electrochemical devices. Low-dimensional morphologies have been identified as particularly promising for the optimization of transport characteristics and the design of anisometric building blocks for the controlled assembly into higher order superstructures. We here introduce a facile bio-inspired room-temperature approach to direct precipitation of one-dimensional basic cobalt carbonate as a precursor to Co3O4 by combining confined submicrometer reaction environments with a carboxylated structure-directing polyelectrolyte. Variation of the polymer concentration and molecular weight then affords control over the mode of infiltration into cylindrical track-etch membrane pores. While a high concentration of the polyelectrolyte additive induces the formation of high aspect ratio smooth fibers with a length resembling the entire pore volume, shorter porous rods with a needle-like substructure are deposited at low polymer concentrations or higher molecular weights. The generality of the infiltration mechanism is demonstrated by gradual substitution of Co2+ ions by Mn2+. Calcination pseudomorphically transforms the resulting intramembrane basic cobalt and manganese carbonate rods and fibers into hierarchical one-dimensional oxides with a porous nanoparticle-based mesostructure.

Tuning the rheological properties of kaolin suspensions using biopolymers

Kaolin based suspensions have wide range of applications such as slurry wall, drilling fluids, adhesives, cosmetics, refractories and pharmaceuticals, due to their abundance in nature, low cost and non-swelling nature. On the other hand, the unique properties (i.e., biodegradability) of biopolymers make them suitable candidate for variety of applications including modification of clay suspensions. In this study, the rheological properties of kaolin suspensions modified with different biopolymers (xanthan gum (XG), sodium carboxymethyl cellulose (CMC), potato starch (PS), chitosan (Ch) and apple fibre (AF)) have been investigated by varying the biopolymer type, content and clay content. The main objective of the present study is to propose a substitute for the natural mud sample. Frequency sweep tests, stress ramp-up tests and time-dependent tests were performed by using the Couette geometry (coaxial cylinders) for the prepared suspensions. The rheological results showed that both viscosity and moduli were significantly influenced by adding different biopolymers into the kaolin suspensions. For instance, an increase in viscosity of modified suspensions was observed: 3 – 4 orders of magnitude by adding xanthan gum (1 wt%) or sodium carboxymethyl cellulose (5 wt%) and 6 orders of magnitude by adding apple fibre (5 wt%). Likewise, the incorporation of different biopolymers significantly affected the complex modulus of modified clay suspensions. For example, similar or higher values of complex modulus than the pure kaolin suspension were observed at low xanthan gum or sodium carboxymethyl cellulose content (0.1 wt%). In case of chitosan, the complex modulus of the modified suspensions was higher than the complex modulus of pure kaolin suspension, even at very low polymer content (1 wt%). In the case of potato starch, a decrease in complex modulus by increasing polymer content till 10 wt% was observed followed by an increase in complex modulus with polymer content. The shear rate ramp-up and ramp-down experiments showed that the time-dependent behaviour of kaolin suspensions was not strongly influenced by adding different biopolymers. This knowledge will provide a base to choose a suitable substitute for the natural mud sample.

Considerations in the Development of Physically Stable High Drug Load API- Polymer Amorphous Solid Dispersions in the Glassy State

In this Commentary, the authors expand on their earlier studies of the solid-state long-term isothermal crystallization of amorphous API from the glassy state in amorphous solid dispersions, and focus on the effects of polymer concentration, and its implications for producing high load API doses with minimum polymer concentration. After presenting an overview of the various mechanistic factors which influence the ability of polymers to inhibit API crystallization, including the chemical structure of the polymer relative to the API, the nature and strength of API-polymer noncovalent interactions, polymer molecular weight, impact on primary diffusive molecular mobility, as well as on secondary motions in the bulk and surface phases of the glass, we consider in more detail, the effects of polymer concentration. Here, we examine the factors that appear to allow relatively low polymer concentrations, i.e., less than 10%w/w polymer, to greatly reduce crystallization, including a focus on the heterogeneous structure of the glassy state, and the possible spatial distribution and concentration of polymer in certain key regions of the glass. This is followed by a review and analysis of examples in the recent literature focused on determining the minimum polymer concentration in an amorphous solid dispersion, capable of producing optimally stable high drug load amorphous dispersions.

Matrix free polymer nanocomposites from amphiphilic hairy nanoparticles: Solvent selectivity and mechanical properties

Matrix free polymer nanocomposite of spherical nanoparticles with shells made of amphiphilic homopolymer was studied in molecular dynamics experiments. The amphiphilic homopolymer was presented as sequence of identical monomer units, each containing two beads having different affinity to solvent. The self-assembly in solution of such hairy nanoparticles was studied depending on solvent quality and selectivity for different polymer concentrations. Two of the most characteristic morphologies were identified and described. The first one is a structure resembling a mixture of sea hedgehogs. There is a nanoparticle in the core of a hedgehog, and the spines consist of several grafted chains. Hedgehogs float freely, do not aggregate with other nanoparticles, their solutions have a low moduli of elasticity and viscosity up to a fairly high polymer concentration. The second morphology is thin membrane lamellae assembled from amphiphilic homopolymers. In this case, the nanoparticles are joined into a single network-like aggregate at very low polymer concentrations. Such networks possess a unique porous structure and demonstrate high elasticity and viscosity moduli. These findings could be useful for molecular design of smart materials, that are able to reversibly assemble, disintegrate on request and repair damage by self-healing mechanism. • Nanoparticles, coated with amphiphilic homopolymers, are studied. • Such nanoparticles can self-assemble either into gels or into “hedgehogs” mixture. • Gels have membrane-like, porous structure, and demonstrate elastic and viscous response. • Core-shell filaments preserve aggregation and favor uniform distribution of “hedgehogs”. • Structure type is determined by solvent quality and selectivity.

Binding and stability properties of PEG2000 to globular proteins: The case of lysozyme

• Lysozyme-PEG interaction was studied using calorimetry and spectroscopic techniques. • A PEG/lysozyme interaction in the low polymer concentration regime occurs. • The interaction process is weak, and it is entropically driven. • At low concentration, PEG induces an increase of the denaturation temperature. Poly(ethylene glycol) is a linear polymer widely used in many biotechnological and industrial applications. It is thought that PEG is an inert polymer and its effect on protein stability and dynamics is essentially due to the excluded volume effect which depends on its concentration. However, increasing evidence suggests that direct interactions can be established between PEG and proteins. With the aim to shed more light on PEG-protein interactions, this work evaluated the enthalpy pair interaction coefficient and the enthalpy cross-interaction coefficient for the system PEG2000-lysozyme. In addition, using calorimetry and spectroscopy, the binding, the stability and the conformational behaviour of lysozyme were evaluated in the low polymer concentration regime. We found that a weak interaction between lysozyme and PEG occurs with a binding constant of 1600 ± 230 M −1 . The interaction process is mainly entropically driven: the release of water molecules associated to protein surface and polymer chains may account for this phenomenon. In addition, we found that the general lysozyme structure was only marginally affected by PEG interaction. A small but significant increase in the denaturation temperature was observed most likely due to weak interactions with the polymer and to the dehydration of protein surface.

Experimental Study on Profile Control of Polymer and Weak Gel Molecules in Porous Media.

Weak gel is a gel system formed by the mixing and crosslinking of a low-concentration polymer and a slow-release crosslinker. It can be used for profile control in deep reservoir, but its effect is greatly affected by mechanical shearing. Currently, the shearing effect on weak gel is mainly studied by way of mechanical stirring, while the effect of porous media shear on weak gel molecules and properties has been rarely discussed. In this paper, polymer solution, aluminum gel and phenolic gel were prepared. The molecular coil size, viscoelastic modulus and microscopic aggregation morphology in water solution of three systems before and after core shearing were investigated, and the injection performance of the three systems in cores with different permeabilities was tested by physical simulation experiments. The study results show that at equivalent permeability, the system with a larger equivalent sphere diameter of molecular coil is more seriously sheared and suffers greater viscosity loss. In the core with permeability of 1.0 D, polymer solution remains as the aggregation, while phenolic gel and aluminum gel cannot form network aggregations and they are inferior to polymer solution in migration capacity in the mid-deep part of the core. In the core with permeability of 1–5.8 D, the polymer solution remains as a Newtonian fluid, while phenolic gel and aluminum gel become purely viscous non-Newtonian fluids. The elastic modulus of aluminum gel and phenolic gel is four times more than that of a polymer. In the core with permeability higher than 8.5 D, aluminum gel and phenolic gel migrate with less effect by core shearing, and their profile control capacity in deep reservoir is higher than that of the polymer. In the core with permeability lower than 8.5 D, because the monomolecular activity of weak gels becomes poor, they migrate in porous media with more effect by core shearing, and their profile control and oil displacement capacity in deep reservoir is lower than that of the polymer.

Proton-conducting membranes based on CsH2PO4 and copolymer of tetrafluoroethylene with vinylidene fluoride

In this work, proton conductivity, morphology and mechanical properties of (1–x)CsH2PO4–xF-42 (x=0.05–0.3, weight ratio) membranes were investigated for the first time. Thin flexible membranes for x≥0.15 with the uniform distribution of the components were obtained by a tape casting method. Mechanical properties of the membranes were measured by Vickers microhardness tests for a low polymer content (x˂0.15), also the tensile strength for membranes with high polymer content x=0.2–0.3 were evaluated. Proton conductivity of the (1–x)CsH2PO4–xpF-42 composite polymer electrolytes decreases monotonically with increasing x due to the effect of a «conductor-insulator» percolation. The combination of conductivity, mechanical strength and hydrophobic properties of (1–x)CsH2PO4–xF-42 makes certain compositions of proton-conducting membranes (x~0.2–0.25) promising for their use in intermediate-temperature fuel cells, despite decreased conductivity.

Effect of silicones and polymers on the wetting and foaming properties of anionic and nonionic hydrocarbon surfactants.

To better understand the effects of nonionic silicones and polymers on the wetting and foaming properties of anionic and nonionic hydrocarbon surfactants and different forces between molecules, nonionic silicone surfactant (GT-248), polymer (HPMC), anionic surfactant (AES), and nonionic surfactants (APG0810) were selected. The CMC ratio is used as a reference to determine the concentration ratio of the APG0810/GT-248 and AES/GT-248 compound solutions, after which HPMC was added to form a compound solution to test the wetting and foaming properties of the compound solution. The results showed that GT-248 obtained a high density of methyl groups on the surface of the solution due to its excellent spreadability and good flexibility of the siloxane chain, effectively reduces the surface tension and wetting time of AES and APG0810 solutions. But in terms of foam performance, after adding GT-248 to solution, the foam stability of AES solution is enhanced, the foam height of AES solution was reduced by 33.7%, the foam stability of APG0810 solution is weakened a lot, and the foam height of APG0810 solution was reduced by 85.4%. Mainly because of the difference in electronegativity between the AES and APG0810 head groups, the strong electronegativity between the AES head groups resulted in a smaller number of GT-248 insertions in the liquid film, which weakened the defoaming effect of GT-248. The weak interaction between the head groups of APG0810 resulted in a higher amount of GT-248 in the liquid film, and thus, the foam performance was greatly reduced. After the AES/GT-248 compound solution was preferred, by comparing the viscosity, surface tension, and the half-life of the foam, it was found that the addition of low concentration of polymer effectively improved the half-life of the foam without affecting the foaming properties, and the final choice of 4:1(AES/GT-248) + 1mgHPMC and 2:1(AES/GT-248) + 1mgHPMC composite solutions can be used as a superior dust suppression material.

Transport and targeted binding of Pluronic-coated nanoparticles in unsaturated porous media

The effectiveness of most in situ remedial technologies, including nanoremediation, lies on successful delivery of reagents to a subsurface target treatment zone. Targeted delivery of engineered nanoparticles (NPs) to treat petroleum hydrocarbons present in the unsaturated zone requires an understanding of their transport behaviour in these systems. A series of column experiments explored the effect of initial water saturation, flowrate, input dosage, and porous medium texture on the transport of iron oxide or cobalt ferrite NPs coated with an amphiphilic co-polymer, as well as their targeted attachment to a crude oil zone. As the initial water content increased with a concomitant reduction in air saturation, the degree of tailing present in the NP breakthrough curves (BTCs) reduced, and the mass of NPs recovered increased. Air saturation is positively correlated with the magnitude of air-water interfaces, which provide additional NP retention sites. At a lower injection flow rate, NP retention increased due to a longer residence time and comparatively high air saturation. NP transport behaviour was not sensitive to NP injection dose over the range tested. Increased retention and retardation of the NP BTC was observed in sediments with a higher clay and silt content. NPs coated with a lower concentration of a Pluronic block co-polymer to promote binding were preferentially retained within the crude oil zone. To simulate the asymmetrical NP breakthrough curves observed from the unsaturated systems required the use of a model that accounted for both mobile and immobile flow regions as well as NP attachment and detachment with nonlinear Langmuirian blocking. This model allowed examination of attachment and detachment rate coefficients which captured NP interaction with the porous medium and/or crude oil. It was found that the initial water saturation and flow rate did not have an appreciable impact on the NP attachment rate coefficient, while it increased by ~10× with increasing clay and silt content, and by ~100× in the presence of crude oil, indicating preferential NP attachment within the crude oil zone. As a result of the lower NP polymer concentration coating used to promote increased attachment to crude oil, higher retention was observed near the column inlet and was captured quantitatively by adding a depth-dependent straining term to the model. This retention behaviour represents a combination of irreversible attachment at the air-water interfaces and straining near the column inlet enhanced by the formation of NP aggregates. The detachment rate coefficient decreased with a lower initial water saturation and flowrate, but increased with higher clay and silt content. The findings from this study contribute to our understanding of the transport and binding behaviour of Pluronic-coated NPs in unsaturated conditions and, in particular, the role of initial water content, flowrate and porous medium texture. Demonstrated delivery of NPs to a target zone is an important step towards expanding the utility of NPs as treatment reagents.

Imaging of the microstructure of Carbopol dispersions and correlation with their macroelasticity: A micro- and macrorheological study

We developed a new data analysis strategy, the so-called micro-rheo-mapping technique, based on multiparticle tracking experiments to obtain an accurate and direct visualization of the microstructure of commercial acrylate thickeners of Carbopol-type with high (Ultrez 10), intermediate (ETD 2020), and low (ETD 2050) degree of crosslinking. At low polymer concentration, aggregates made of several primary Carbopol particles are formed with an average diameter of 43 ± 11, 56 ± 14, and 10 ± 2.5 μm for Ultrez 10, ETD 2020, and ETD 2050, respectively. For ETD 2050, the least crosslinked thickener, the shell of dangling polymer chains covering the aggregate surface is thicker than for ETD 2020 and Ultrez 10. At technically relevant polymer concentrations, our results indicate, for all three thickeners, that the microstructure is highly heterogeneous with regions of different crosslink densities. One region inaccessible for tracer particles corresponding to a mixture of polydisperse aggregates and individual primary particles with a core mesh size less than 200 nm and a second, diluted enough to be accessible and which exhibits both elastic and viscous characteristics. The study of the impact of pH, polymer concentration, and crosslink density on these local structural and viscoelastic heterogeneities as well as macrorheological properties allowed us to establish a correlation between microstructure and macroelasticity. In particular, we found that the bulk shear modulus strongly depends on the fraction of inaccessible areas, making this microscopic parameter most relevant for describing the macroelasticity of Carbopol gels, whereas the local elasticity of the interstitial regions is of minor importance.

Systematic Exploration of a Catalytic Metal–Organic Framework/Polyurethane Composite for Medical Device Applications: Effects of MOF Particle Size, MOF Loading, and Polymer Concentration on Composite Material Activity

The metal–organic framework (MOF) CuBTTri, H3[(Cu4Cl)3(BTTri)8] (where H3BTTri = 1,3,5-tris(1H-1,2,3-triazol-5-yl)benzene), is a promising catalyst for the development of antithrombotic medical device materials via localized nitric oxide (NO) generation from endogenous S-nitrosothiols. This work evaluates the effects of three key parameters of CuBTTri-embedded polyurethane composite materials—MOF preparation/particle size, MOF loading, and polymer concentration—on the rate of NO generation. We discovered that CuBTTri preparation and particle size have a significant impact on NO generation. Specifically, hand-ground MOF particles (0.3 ± 0.1 µm diameter) generate NO at greater rates compared to larger as-prepared, raw MOF particles (0.4 ± 0.2 µm diameter) and smaller, filtered MOF particles (0.2 ± 0.1 µm diameter) for composite materials. This finding contradicts previous research for CuBTTri powder which found that the smaller the particles, the greater the catalytic rate. In examining the effects of MOF loading and polymer concentration, our data show that increasing these parameters generally results in increased rates of NO generation; though thresholds appear to exist in which increasing these parameters results in diminishing returns and impedes NO generation capacity for certain composite formulations. We found that polymer concentration is the key determinant of water absorptivity and statistically significant decreases in water uptake accompany statistically significant increases in NO generation. It was also found that formulations with relatively high MOF loadings and low polymer concentrations or low MOF loadings and high polymer concentrations inhibit the rate of NO generation. In summary, this research provides a framework for more strategic selections of key parameters when fabricating composite materials for medical device applications.

3D bioprinting of gellan gum-based hydrogels tethered with laminin-derived peptides for improved cellular behavior.

The treatment of skeletal muscle defects is still a topic of noteworthy concern since surgical intervention is not capable of recovering muscle function. Herein, we propose myoblasts laden in laminin-inspired biofunctionalized gellan gum hydrogels as promising tissue-engineered skeletal muscle surrogates. Gellan gum-based hydrogels were developed by combining native gellan gum (GG) and GG tethered with laminin-derived peptides (CIKVAVS (V), KNRLTIELEVRTC (T) or RKRLQVQLSIRTC (Q)), using different polymer content (0.75%-1.875%). Hydrogels were characterized in terms of compressive modulus, molecules trafficking, and C2C12 adhesion. Hydrogels with higher polymeric content (1.125%-1.875%) showed higher stiffness whereas hydrogels with lower polymer content (0.75%-1.125%) showed higher fluorescein isothiocyanate-dextran molecules diffusion. Cell spreading was achieved regardless of the laminin-derived peptide but preferred in hydrogels with higher polymer content (1.125%-1.875%). Taken together, hydrogels with 1.125% of polymer content were selected for printability analysis. GG-based inks showed a non-newtonian, shear-thinning, and thixotropic behavior suitable for printing. Accordingly, all inks were printable, but inks tethered with T and Q peptides presented some signs of clogging. Cell viability was affected after printing but increased after 7 days of culture. After 7 days, cells were spreading but not showing significant signs of cell-cell communications. Therefore, cell density was increased, thus, myocytes loaded in V-tethered GG-based inks showed higher cell-cell communication, spreading morphology, and alignment 7, 14 days post-printing. Overall, myoblasts laden in laminin-inspired biofunctionalized GG-based hydrogels are a promising skeletal muscle surrogate with the potential to be used as in vitro model or explored for further in vivo applications.

Sol-gel transition programmed self-propulsion of chitosan hydrogel.

Active soft materials exhibit various dynamics ranging from boat pulsation to thin membrane deformation. In the present work, in situ prepared ethanol-containing chitosan gels propel in continuous and intermittent motion. The active life of the organic material loaded to the constant fuel level follows a linear scaling, and its maximal velocity and projection area decrease steeply with chitosan concentration. A thin propelling platelet forms at low polymer content, leading to the suppression of intermittent motion. Moreover, the fast accelerating thin gels can split into a crescent and circular-like shape or fission into multiple asymmetric fragments.

Enzymatic co-crosslinking of star-shaped poly(ethylene glycol) tyramine and hyaluronic acid tyramine conjugates provides elastic biocompatible and biodegradable hydrogels.

A combination of the viscoelastic properties of hyaluronic acid (HA) and the elastic properties of star shaped 8-arm poly(ethylene glycol) (8-arm PEG) was used to design in-situ forming hydrogels. Hydrogels were prepared by the enzymatic crosslinking of a partially tyramine modified 8-arm PEG and a tyramine conjugated HA using horseradish peroxidase in the presence of hydrogen peroxide. Hydrogels of the homopolymer conjugates and mixtures thereof were rapidly formed within seconds under physiological conditions at low polymer and enzyme concentrations. Elastic hydrogels with high gel content (≥95%) and high storage moduli (up to 22.4 kPa) were obtained. An in vitro study in the presence of hyaluronidase (100 U/mL) revealed that with increasing PEG content the degradation time of the hybrid hydrogels increased up to several weeks, whereas hydrogels composed of only hyaluronic acid degraded within 2 weeks. Human mesenchymal stem cells (hMSCs) incorporated in the hybrid hydrogels remained viable as shown by a PrestoBlue and a live-dead assay, confirming the biocompatibility of the constructs. The production of an extracellular matrix by re-differentiation of encapsulated human chondrocytes was followed over a period of 28 days. Gene expression indicated that these highly elastic hydrogels induced an enhanced production of collagen type II. At low PEG-TA/HA-TA ratios a higher expression of SOX 9 and ACAN was observed. These results indicate that by modulating the ratio of PEG/HA, injectable hydrogels can be prepared applicable as scaffolds for tissue regeneration applications.

Enhancing the mechanical behaviour of concretes through polymer modification of the aggregate-cement paste interface

A critical obstacle to the design of polymer-cement composites is its relatively large contents required for a significant improvement on concrete performances, which increased materials cost and decreased compressive strength. In this study, an asphalt emulsion, waterborne epoxy resin, and waterborne epoxy resin modified asphalt emulsion were used to pretreat aggregates for improving the toughness of concrete at relatively low polymer contents. The results showed that, for the model aggregate concrete, the partial replacement of polymer-coated aggregates could induce cracks and yielded better improvement in concrete toughness as compared to full replacement. However, the three-point bending tests showed the opposite results, compared with partial replacement, complete replacement of polymer coated aggregate increases the fracture energy which can be attributed to the interlocking effect of the gravel aggregate. The addition of water-based epoxy resin-asphalt emulsion composite emulsion showed the best improvement on concrete toughness. With 30% composite emulsion coated aggregate, concrete showed almost the same strength with 33% increase in concrete fracture energy. With 100% composite emulsion coated aggregate, concrete showed about 11.5% decrease in compressive strength, but 73.4% increase in concrete fracture energy. Increasing the polymer film thickness on the aggregate surface could significantly increase the energy consumption during the fracture process of concrete and improve its toughness.

High‐performance atactic polypropylene modified bitumen blends fabricated via conventional, hot, and in‐situ blending techniques

AbstractThis research presents an investigation on the incorporation of atactic polypropylene (APP) as a modifier in bitumen at weight concentrations from 0 to 30 wt%. An APP‐modified bitumen (APPMB) was prepared by conventional, hot, and in situ blending and characterized for mechanical, morphological, thermal, structural, and physical properties. APPMB specimens using maleic anhydride (MA) functionalized polymer at its optimized concentration of 20 weight percentage (wt%), along at several other concentrations, were prepared using in situ and hot blending methods using an overhead stirrer mixer at a blending temperature of 160°C for 2 h. Fourier transform infrared revealed a strong interaction of APP or APP‐g‐MA with bitumen. The ultimate compressive strength, acquired in Mega Pascal (MPa) units, was increased from 0.24 MPa at 5 wt% APP to 0.70 MPa at 20 wt% APP loading. Scanning electron microscopy micrographs manifested dispersed phases of APP in bitumen due to the high temperature and shearing application with overhead stirring. In situ and hot blended specimens exhibited better mechanical, thermal, and structure–property relations. This research highlights the novelty in terms of property optimization and advancements at a high‐weight percentage of the modifier (i.e., 20 wt%) along with emphasizing the comparison of three different fabrication techniques; however, the previous research manifested the advancements in the properties of polymer and bitumen blends at low concentrations of polymers.