Surface Rheological Properties Research Articles

Enhanced rare earth element recovery with cross-linked glutaraldehyde-lanthanide binding peptides in foam-based separations

HypothesisLanthanide Binding Tag (LBT) peptides that coordinate selectively with lanthanide ions can be used to replace the energy intensive processes used for the separation of rare earth elements (REEs). These surface-active biomolecules, once selectively complexed with the trivalent REE cations, can adsorb to air/aqueous interfaces of bubbles for foam-based REEs recovery. Glutaraldehyde, an organic compound that is a homobifunctional crosslinker for proteins and peptides, can be used to enhance the adsorption and interfacial stabilization of lanthanide-bound peptides films. ExperimentsThe stability of the interfacial cross-linked films was tested by measuring their dilational and shear surface rheological properties. Surface activity of the adsorbed species was analyzed using pendant drop tensiometry, while surface density and molecular arrangement were determined using x-ray reflectivity and x-ray fluorescence near total reflection. FindingsGlutaraldehyde cross-linked REE-peptide complexes enhance the adsorption of lanthanides to air-water interfaces, resulting in thicker interfacial structures. Subsequently, these thicker layers enhance the dilational and shear interfacial rheological properties. The interfacial film stabilization and REEs extraction promoted by the cross-linker presented in this work provides an approach to integrate glutaraldehyde as a substitute of common foam stabilizers such as polymers, surfactants, and particles to optimize the recovery of REEs when using biomolecules as extractants.

Preparation of bacterial cellulose/acrylic acid-based pH-responsive smart dressings by graft copolymerization method

Conventional wound dressings used in trauma treatment have a single function and insufficient adaptability to the wound environment, making it difficult to meet the complex demands of the healing process. Stimuli-responsive hydrogels can respond specifically to the particular environment of the wound area and realize on-demand responsive release by loading active substances, which can effectively promote wound healing. In this paper, BC/PAA-pH responsive hydrogels (BPPRHs) were prepared by graft copolymerization of acrylic acid (AA) to the end of the molecular chain of bacterial cellulose (BC) network structure. Antibacterial pH-responsive ‘smart’ dressings were prepared by loading curcumin (Cur) onto the hydrogels. Surface morphology, chemical groups, crystallinity, rheological, and mechanical properties of BPPRHs were analyzed by different characterization methods. The drug release behavior under different physiological conditions and bacteriostatic properties of BPPRH-Cur dressings were also investigated. The results of structural characterization and performance studies show that the hydrogel has a three-dimensional mesh structure and can respond to wound pH in a ‘smart’ drug release capacity. The drug release behavior of the BPPRH-Cur dressings under different environmental conditions conformed to the logistic and Weibull kinetic models. BPPRH-Cur displayed good antimicrobial activity against common pathogens of wound infections such as E. coli, S. aureus, and P. aeruginosa by destroying the cell membrane and lysing the bacterial cells. This study lays the foundation for the development of new pharmaceutical dressings with positive health, economic and social benefits.

Role of cyclodextrin inclusion complexes assembled in the fast-dissolving structures of electrospun gelatin mats to extend the release of menthol

In this study, inclusion complexes (ICs) of menthol with various cyclodextrins (CDs) [α-CD, β-CD, γ-CD, (2-hydroxypropyl)-β-cyclodextrin (HP-β-CD), and methyl-β-cyclodextrin (M-β-CD)] were prepared, and the ICs with the highest encapsulation efficiency were applied in the electrospun gelatin mats to extend the release of menthol. Electrospinning feed solutions were evaluated based on surface tension, zeta potential, electrical conductivity, and rheological properties. The diameter and morphology of the pure gelatin and the CDs-loaded gelatin mats were analyzed using microscopy (FESEM and AFM). The results confirmed that CD loading leads to a decrease in the diameter of the nanofibers. The longest disintegration time belonged to the gelatin mat containing the β-CD complex. Comparison of the FTIR spectrum and XRD patterns of gelatin mats containing menthol-loaded CD complexes with the pure compounds confirmed the successful encapsulation of menthol inside the cavity of the CD, and the disappearance of the crystalline state of electrospun gelatin mats. Applying the electrospun gelatin mats as a fast-dissolving structure for the menthol-loaded inclusion complexes increased its thermal stability. In the bioadhesive test, the lowest force required to separate the gelatin mat from the skin model was obtained in the menthol-containing β-CD gelatin mat (6.21 ± 1.01 g). The menthol release from the pure gelatin mats was much faster than the electrospun mats containing CD complexes. Peppas-Sahlin and Fickian diffusion (Case-I) were the best-fitted model and menthol release mechanism, respectively.

Human mesenchymal stromal cells-laden crosslinked hyaluronic acid-alginate bioink for 3D bioprinting applications in tissue engineering

Three-dimensional (3D) bioprinting is considered one of the most advanced tools to build up materials for tissue engineering. The aim of this work was the design, development and characterization of a bioink composed of human mesenchymal stromal cells (hMSC) for extrusion through nozzles to create these 3D structures that might potentially be apply to replace the function of damaged natural tissue. In this study, we focused on the advantages and the wide potential of biocompatible biomaterials, such as hyaluronic acid and alginate for the inclusion of hMSC. The bioink was characterized for its physical (pH, osmolality, degradation, swelling, porosity, surface electrical properties, conductivity, and surface structure), mechanical (rheology and printability) and biological (viability and proliferation) properties. The developed bioink showed high porosity and high swelling capacity, while the degradation rate was dependent on the temperature. The bioink also showed negative electrical surface and appropriate rheological properties required for bioprinting. Moreover, stress-stability studies did not show any sign of physical instability. The developed bioink provided an excellent environment for the promotion of the viability and growth of hMSC cells. Our work reports the first-time study of the effect of storage temperature on the cell viability of bioinks, besides showing that our bioink promoted a high cell viability after being extruded by the bioprinter. These results support the suggestion that the developed hMSC-composed bioink fulfills all the requirements for tissue engineering and can be proposed as a biological tool with potential applications in regenerative medicine and tissue engineering.Graphical abstract

Chemical structure elucidation and functional activities comparison of two polysaccharides purified from Citrus reticulata Blanco peels

BackgroundThe Citrus reticulata Blanco peels have been widely adopted as functional food or nutraceuticals for thousands of years. In our study, two polysaccharides from the C. reticulata Blanco peels were obtained and named as CRP-WA and CRP-02A, respectively. After characterization by monosaccharide composition, methylation and NMR, chemical structures of CRP-WA and CRP-02A were elucidated.ResultsAs a result, CRP-WA with Mw of 32.8 kDa was an arabinogalactan polysaccharide composed of (β1 → 3) (β1 → 3,6)-D-Galp, (β1 → 4)-D-Manp and (β1 → 4)-D-Glcp units in the backbone. The CRP-02A with Mw of 70.5 kDa was an arabinogalacturonan type pectin formed by (α1 → 4) (α1 → 3,4)-D-GalpA units in the backbone. Moreover, the surface morphologies and rheological properties of CRP-WA and CRP-02A were quite different from each other. Both of these two polysaccharides possessed good antioxidant activities and immunoregulatory effects on RAW 264.7 cells, in which CRP-02A behaved remarkable antioxidant feature, whereas CRP-WA showed relatively high immunoregulatory activity.ConclusionOur study will provide fundamental information for C. reticulata Blanco-based nutritional foods development.Graphical

Self‐Healing, Biocompatible Injectable Hydrogel Based on Multialdehyde Moringa oleifera Gum and Carboxymethyl Chitosan: A Suitable Platform for Drug Delivery in Wound Healing Application

AbstractThis study focuses on synthesizing an injectable hydrogel (IH) using Moringa oleifera gum (MOG) with multi‐aldehyde groups (MOG‐CHO) and carboxymethyl chitosan (CMCh) through a Schiff base reaction at 37 °C. The study includes the optimal concentration of the oxidizing agent to achieve the best content of aldehydes in Moringa oleifera gum. Furthermore, the best oxidized Moringa oleifera gum decides the least gelation time. The physical properties of the optimized IH (IH‐3‐7) are assessed, including color, gel content, porosity, load‐bearing capacity, syringeability, and self‐healing capability. Structural characterization is performed using Fourier transform Infrared spectroscopy (FT‐IR) and nuclear magnetic spectroscopy (1H NMR), while scanning electron microscope (SEM) and rheometer are used to analyze surface morphology and rheological properties. IH‐3‐7 exhibits a porous structure with 35 % porosity and interconnected holes of 1.45 to 4 μm diameter. Higher swelling at pH 5.5 is shown by swelling ratio test conducted in phosphate buffer saline (PBS) at pH 7.4 and pH 5.5. Ciprofloxacin HCl (Cipro) is loaded into IH for release assays, revealing pH‐dependent drug release. In vitro, cytotoxicity assessments on L‐929 fibroblast cell lines show IH′s biocompatibility. Hydrolytic degradation of IH in PBS at pH 7.4 is also evaluated.

Formation by high power ultrasound of mimicking human fat emulsions stabilized with milk fat globule membrane

Ultrasound (US) is an innovative food processing technique that has gained significant interest for its role in modifying proteins. Our study focused on how different US time exposure influence the stability, interfacial structure, and rheological characteristics of whey protein infused with milk fat globule membrane (MFGM). Results indicated that a 9-min ultrasound treatment (US-9) of protein, yielding an emulsion with particle size of 338.3 nm and ζ-potential of −48 mV, was optimal for enhancing functional properties of the emulsion. The US-9 emulsion exhibited different surface rheological properties compared to other emulsions, revealing a heterogeneous MFGM stabilization interface predominantly made of MFGM fragments, free phospholipids, and proteins. The US-9 emulsion surface covered more phospholipids, indicating improved emulsion persistence, based on interfacial protein and phospholipid content calculations and microstructure observation. While the US-9 emulsion did not affect fat digestion, the US-6 min treatment resulted in an optimal fatty acid release rate. Further experimentation may be necessary to elucidate the intricate relationship between ultrasound duration and fat digestion. These findings have leaded to a better understanding of the emulsification capabilities of MFGM materials, as well as a foundation to improve infant formula quality.

Development of halochromic electrospun labels for non-invasive shelf life assessment of rainbow trout (Oncorhynchus mykiss): Incorporation of barberry anthocyanin extract in protein-based smart packaging.

Using barberry (Berberis vulgaris L.) as a natural dye in combination with electrospinning technology represents a promising approach for the development of intelligent packaging systems. In this study, the influence of different concentrations of zein (16, 18, and 20%) and barberry anthocyanin-rich powder (BARP) (16, 18, and 20%) on the surface tension and rheological properties of the solution were evaluated. The most favorable nanofibers (NFs) were obtained from a solution containing 18% (w/w) zein under constant voltage. The surface morphology, size, and color-changing properties of electrospun NFs derived from zein polymers containing different concentrations of BARP (16, 18, and 20%) under various electrical fields (20, 22, and 24 kV) were evaluated. The Fourier-transform infrared spectroscopy analysis confirmed the interaction of BARP within the zein-based NFs. The results indicated that the concentration of BARP had a noticeable impact on the physicochemical properties of the NFs. Furthermore, efficacy of the appropriately fabricated halochromic label was evaluated for monitoring the packed rainbow trout fillet during refrigerated storage. On the 10th day, a noticeable visual color turned from pink to pale yellow was observed in response to pH variations. Additionally, the TVN value confirmed the effectiveness of halochromic electrospun labels for non-invasive assessment of fish fillet quality.

A novel eco-friendly strategy for removing phenanthrene from groundwater: Synergism of nanobubbles and rhamnolipid

Nanobubbles (NBs), given their unique properties, could theoretically be paired with rhamnolipids (RL) to tackle polycyclic aromatic hydrocarbon contamination in groundwater. This approach may overcome the limitations of traditional surfactants, such as high toxicity and low efficiency. In this study, the remediation efficiency of RL, with or without NBs, was assessed through soil column experiments (soil contaminated with phenanthrene). Through the analysis of the two-site non-equilibrium diffusion model, there was a synergistic effect between NBs and RL. The introduction of NBs led to a reduction of up to 24.3 % in the total removal time of phenanthrene. The direct reason for this was that with NBs, the retardation factor of RL was reduced by 1.9 % to 15.4 %, which accelerated the solute replacement of RL. The reasons for this synergy were multifaceted. Detailed analysis reveals that NBs improve RL's colloidal stability, increase its absolute zeta potential, and reduce its soil adsorption capacity by 13.3 %–19.9 %. Furthermore, NBs and their interaction with RL substantially diminish the surface tension, contact angle, and dynamic viscosity of the leaching solution. These changes in surface thermodynamic and rheological properties significantly enhance the migration efficiency of the eluent. The research outcomes facilitate a thorough comprehension of NBs' attributes and their relevant applications, and propose an eco-friendly method to improve the efficiency of surfactant remediation.

Development of a 3D-printable matrix using cellulose microfibrils/guar gum-based hydrogels and its post-printing antioxidant activity

A biomaterial ink suitable for three-dimensional (3D) printing was developed using cellulose microfibrils (CMFs, 1% w/v) and guar gum (1–7 g/100 mL CMFs), and the post-printing stability and antioxidant functionality of the borax-treated construct were investigated. Rheological analysis, Fourier transform infrared spectrometry, X-ray diffractometry, and scanning electron microscopy revealed the suitability of the two polymers to form an interpenetrating composite hydrogel that would facilitate printability. The produced composite hydrogel showed good structural, morphological, thermal, and textural properties. CMFs with 5% guar gum showing optimal surface properties and rheological properties were printed with the least dimensional errors at 50% infill density, 10 mm/s printing speed, 0.8 mm nozzle diameter, and 0.5 mm layer height. The treatment with borax showed good shape fidelity during 12 h storage. The treated construct also showed considerably increased mechanical properties and antioxidant activities in comparison with the untreated construct. A stable 3D construct suitable for a variety of applications could be produced using CMFs and guar gum-based ink.

Effects of Heating Treatment on Functional and Structural Properties of Liquid Whole Egg

Liquid whole egg (LWE) products have many advantages such as convenient transportation, easy production and are safe. However, LWE has a short shelf life and high thermal sensitivity, so suitable heating treatment is the key to the production of LWE products. The aim of this study is to investigate the effects of heating treatments conditions (at 55-67 °C for 0-10 min) on the emulsification, foaming activity and rheological properties of LWE. The results indicated that the emulsifying activity of LWE had no significant change after 55-64 °C heating treatment, while it decreased significantly after heating treatment at 67 °C. The foaming property of LWE increased significantly after 55 °C to the 64 °C heating treatment; while the foaming property showed a downward trend with the increase in heat treatment temperature, it can significantly improve the foam stability of LWE. The heating treatment thoroughly changed the molecular weight distribution of LWE protein, thus promoted the protein surface hydrophobicity, hydrophobicity activity and rheological properties. The heating treatment at 61 °C for 6 min had a better effect on the functional properties than that of the other heating groups. In addition, the results of this study provide the change in rules of LWE under different heating treatment conditions and provide theoretical guidance for the production and processing of LWE.

Stabilization of Olive Oil in Water Emulsion with Dairy Ingredients by Pulsed and Continuous High Intensity Ultrasound.

Application of high intensity ultrasound (HIUS) for stabilization of olive oil in water emulsion with different dairy ingredients including sodium caseinate (NaCS) and whey protein isolate (WPI) was investigated. The emulsions were prepared by homogenization with a probe and then treated with either a second homogenization or HIUS at a different power level (20 and 50%) in pulsed or continuous mode for 2 min. The emulsion activity index (EAI), creaming index (CI), specific surface area (SSA), rheological properties, and droplet size of the samples were determined. The temperature of the sample rose when HIUS was applied in continuous mode and at increasing power level. HIUS treatment increased EAI and SSA of the emulsion and decreased droplet size and CI compared with those of the double-homogenized sample. Among the HIUS treatments, the highest EAI was found in the emulsion with NaCS that was treated at a power level of 50% in continuous mode, and the lowest one was obtained by HIUS applied at a power level of 20% in pulsed mode. SSA, droplet size, and span of the emulsion were not affected by HIUS parameters. Rheological properties of HIUS-treated emulsions were not different from those of the double-homogenized control sample. Continuous HIUS at 20% power level and pulsed HIUS at 50% power level reduced creaming in the emulsion after storage at a similar level. HIUS at a low power level or in pulsed mode can be preferred for heat sensitive materials.

Biophysical profiling of synthetic ultra-long tear film lipids

The tear film lipid layer (TFLL) is a unique biological membrane of importance to the maintenance of ocular surface health. The underlying factors at play, e.g. the ability to retard evaporation and offer protection from the environment, are all closely connected to the properties of individual lipid components and their interplay. The TFLL contains unique ultra-long polar lipid species such as O-acyl-ω-hydroxy fatty acids, type I-St diesters and type II diesters, which are considered important for its proper function. Herein, we have synthesized model compounds from these categories and studied their biophysical and surface rheological properties at the aqueous interface. Altogether, we provide insights on the distinct biophysical profiles of these lipid classes and discuss how their interplay may affect the structure and function of the TFLL.

Recent Advances in the Interfacial Shear and Dilational Rheology of Polymer Systems: From Fundamentals to Applications.

The study of the viscoelastic properties of polymer systems containing huge internal two-dimensional interfacial areas, such as blends, foams and multilayer films, is of growing interest and plays a significant role in a variety of industrial fields. Hence, interfacial rheology can represent a powerful tool to directly investigate these complex polymer–polymer interfaces. First, the current review summarizes the theoretical basics and fundamentals of interfacial shear rheology. Particular attention has been devoted to the double-wall ring (DWR), bicone, Du Noüy ring and oscillating needle (ISR) systems. The measurement of surface and interfacial rheological properties requires a consideration of the relative contributions of the surface stress arising from the bulk sub-phases. Here, the experimental procedures and methodologies used to correct the numerical data are described considering the viscoelastic nature of the interface. Second, the interfacial dilational rheology is discussed, starting with the theory and underlying principles. In particular, the Langmuir trough method, the oscillating spinning drop technique and the oscillating pendant drop technique are investigated. The major pioneering studies and latest innovations dedicated to interfacial rheology in both shear and dilatation–compression are highlighted. Finally, the major challenges and limits related to the development of high-temperature interfacial rheology at the molten state are presented. The latter shows great potential for assessing the interfaces of polymer systems encountered in many high-value applications.

The Effect of Electrolytes and Urea on the Ethyl Lauroyl Arginate and Cellulose Nanocrystals Foam Stability

Carboxylated cellulose nanocrystals (cCNC) are highly dispersible particles useful in many industries. In particular, they can be applied to form Pickering emulsions and foams for “green” applications in the cosmetics, pharmaceutical industry or food processing. We demonstrated that carboxylated cellulose nanocrystals enhance foamability and foam stability when mixed with cationic surfactant ethyl lauroyl arginate (LAE), having superior properties over sulfated cellulose nanocrystals (sCNC) concerning surfactant concentration range and foam volume. Mixtures of LAE and cCNC were characterized for their hydrodynamic diameter, zeta potential, surface tension and surface rheological properties. The influence of electrolytes, namely, sodium chloride, guanidine hydrochloride and sodium salicylate, and the addition of concentrated urea to LAE-cCNC mixtures on foamability and foam stability were investigated. Electrolytes in the concentration of 5 mM showed a moderate effect on foam stability. In contrast, spectacular foam collapse was detected after adding concentrated urea. The preliminary rheological data from the pendant drop oscillations revealed low elastic modulus upon urea addition and the loss modulus that increased with the frequency, which suggested a viscous interfacial layer.

Relation between adhesiveness and surface leachate rheological properties of cooked noodles: From the view of starch fine molecular structure

Adhesiveness is one of the important sensory properties of noodles. A better understanding of the molecular basis of the sensory property would allow for a more reasonable selection of wheat ingredients. In this study, the adhesiveness of cooked noodles made from reconstituted wheat flour was evaluated using a texture profile analyzer. The rheological properties of dissolved solids from the noodle surface were measured. The composition and structure of leachate, as well as multi-structure of native starch were analyzed. The correlation analysis showed that adhesiveness positively correlates with the loss modulus parameters [log K' (consistency coefficient) and Ea (activation energy)]. Increased content of leached starch can ascend the rheological parameters (log K' and Ea). In addition, more short amylose chains with 100–500 degree of polymerization (DP) in leached starch also induced the increase of log K' (p < 0.01) and Ea (p < 0.01). The fraction of short amylose chains in leached starch was negatively correlated with the content of long amylopectin chains ranged from 37 to 100 DP in native starch (p < 0.05), as well as the median diameter of particles (p < 0.01). Multi-level structures of native starch granules largely determine the composition and molecular structure of noodle leachate, consequently contributing to surface rheological properties. It is thus proposed that wheat starch with more long amylopectin chains and large granules could be used to reduce noodle adhesiveness. Moreover, the rheological approach using noodle surface materials proposed here is useful to predict the noodle adhesiveness as an important sensory characteristic.

Effects of accumulated cyanobacterial bloom biomass contents on the characteristics of surface fluid sediments in a eutrophic shallow lake

In eutrophic shallow lakes, cyanobacterial blooms will occur frequently and then accumulate on sediments, leading to the variation in the surface sediment properties. In this study, the influence of accumulated cyanobacterial blooms biomass (CBB) content on surface sediment properties was determined in microcosm experiments through monitoring surface sediment physicochemical and rheological properties. During one-month incubation, it was found that surface sediment volume increased, and the density decreased from 1.36 g cm−3 to 1.13 g cm−3 with increase in accumulated CBB contents. The results of particle size distribution indicated that CBB accumulation in sediments led to sediment flocculation and agglomeration. In the meantime, there were high ratios polysaccharide/protein in extracellular polymeric substances (EPS) with a decrease in bound EPS/colloid EPS under high CBB contents, which enhanced the sediment particle agglomeration and reduced fluid sediment stability. Further, the critical shear stress in rheological test for sediments on day 30 presented an exponential decay (R2 = 0.97) with increase in accumulated CBB contents. And a threshold value at 0.15% accumulated CBB content indicated sediments could be resuspended easier when accumulated CBB content was higher than 0.15%. Altogether, this study showed that the accumulated CBB content had a strong influence on surface fluid sediment properties. The results were important in sediment management since CBB affects sediment suspension for eutrophication shallow lakes.

Chemical modification of alginate via the oxidation-reductive amination reaction for the development of alginate derivative electrospun composite nanofibers

To examine if the improvement of the molecular flexibility for the reductive-amination of oxidized alginate derivative (RAOA) through chemical modification could be conducive to the enhancement of alginate electrospinnability, we attempted to use the electrospinning technology to develop the alginate derivative electrospun composite nanofibers that can load the hydrophobic anti-inflammatory drug, ibuprofen, with the aid of polyvinyl alcohol (PVA). The synthesized RAOA was examined by FT-IR spectrometer, 1H NMR spectrometer and fluorescence spectrophotometer. Furthermore, the effects of surface tension, electrical conductivity and rheological properties of the RAOA/PVA blend solution on the electrospinning property and fiber morphology of the resultant RAOA/PVA electrospun composite nanofibers were explored by surface tension meter, conductivity meter, rheometer and SEM. Subsequently, the drug loading and release mechanism of ibuprofen from the RAOA/PVA electrospun composite nanofibers were analyzed through the simulated drug release test. In addition, the cytotoxicity of the RAOA/PVA electrospun composite nanofibers was also evaluated with L929 cells by Cell Counting Kit-8 (CCK-8) assay. Experimental results showed that the hydrophobic side groups were successfully grafted onto the alginate backbone by the oxidation-reductive amination reaction, which destroyed the intramolecular hydrogen bond of the raw sodium alginate (SA), thus enhancing the molecular flexibility and colloidal interface activity of RAOA. So the RAOA could exhibit good amphiphilic property with the critical aggregation concentration (CAC) of 0.42 g/L in NaCl solution, and form the self-assembled micelle with the average hydrodynamic diameter of 615 nm (PDI = 0.24) and zeta potential at about −66.5 mV. Although the oxidation-reductive amination reaction for the modification of RAOA could not fundamentally achieve the generation of bead-free nanofibers by electrospinning of single RAOA aqueous solution, it could improve the electrospinning performance of RAOA/PVA blend solution and increase its content in the RAOA/PVA electrospun composite nanofibers. Furthermore, the fabricated RAOA/PVA electrospun composite nanofibers exhibited the high encapsulation efficiency (EE) and sustained-release property in comparison with the 50/50 SA/PVA electrospun composite nanofibers, due to the good affinity of RAOA to hydrophobic ibuprofen that achieve the loading and controlled release of the hydrophobic drug. Besides, the RAOA/PVA electrospun composite nanofibers exhibited low cytotoxicity to L929 cells. Therefore, the resultant RAOA/PVA electrospun composite nanofibers, combining the structural characteristics of the electrospun nanofibers and the properties of RAOA including the good self-assembly performance, colloidal interface activity, sustained release performance and good cytocompatibility, may possess great potentials as the functional wound dressings for biomedical applications.

Charge‐Induced Structural Changes of Confined Copolymer Hydrogels for Controlled Surface Morphology, Rheological Response, Adhesion, and Friction

AbstractThe ability to modulate polyacrylamide hydrogel surface morphology, rheological properties, adhesion and frictional response is demonstrated by combining acrylic acid copolymerization and network confinement via grafting to a surface. Specifically, atomic force microscopy imaging reveals both micellar and lamellar microphase separations in grafted copolymer hydrogels. Bulk characterization is conducted to reveal the mechanisms underlying microstructural changes and ordering of the polymer network, supporting that they stem from the balance between hydrogen bonding in the substrate‐grafted hydrogels, electrostatic interactions, and a decrease in osmotically active charges. The morphological modulation has direct impacts on the spatial distribution of surface stiffness and adhesion. Furthermore, lateral force measurements show that the microphase separations lead to speed and load‐dependent lubrication regimes as well as spatial variation of friction. A proof of concept via salt screening demonstrates the dynamic control of surface morphology and adhesion. This work advances the knowledge necessary to design complex hydrogel interfaces that enable spatial and dynamic control of surface morphology and thereby of friction and adhesion through modulation of hydrogel composition and surface confinement, which is of significance for applications in biomedical devices, soft tissue design, soft robotics, and other engineered tribosystems.

High-performance sulphate-free cleansers: Surface activity, foaming and rheology.

The main objective of this paper is to analyse the composition of a sulphate-free binary or ternary surfactant system with alkyl olefin sulfonate (AOS), alkyl polyglucoside (APG) and lauryl hydroxysultaine (Sultaine). The composition was optimized by observing critical parameters such as surface activity and rheological properties while varying the concentration of APG in a ternary system, varying the ratio of AOS and Sultaine in a binary system and studying the effect of sodium chloride addition. The experimental results can provide an alternative, sulphate-free surfactant system to replace the common system containing sodium laureth sulfate (SLES) and cocamidopropyl betaine (CapB), without compromising on the parameters previously mentioned. A DuNouy Ring was utilized on a tensiometer to measure the surface tension of the samples. To observe foaming abilities of samples, a visual foaming study was conducted and recorded by taking pictures. A TA instruments mechanical rheometer was used to measure the viscosity. Studying the effect of APG concentration on surface tension illustrated that as APG concentration decreases, surface tension decreases as well. The minimum surface tension was found to be 26.587 for 7.5wt.% AOS and 7.5wt.% Sultaine. When the ratio between AOS and Sultaine changed, the 1:1system produced the lowest surface tension value again. As the concentration of AOS decreased in the ratio, the surface tension increased. When the ratio was held constant, and APG was introduced into the system, the systems containing APG had higher surface tension values compared with the systems with the same ratios but did not have APG added. As the concentration of salt increased, the surface tension decreased for AOS, increased for the binary mixture and had no effect on Sultaine. Foaming has a direct correlation with surface tension so a decrease in surface tension led to better foaming abilities; therefore, the 1:1 ratio of AOS:Sultaine had the best foaming qualities. The AOS/Sultaine system exhibited Maxwellian behaviour, suggesting the presence of worm-like micellar structures. As the concentration of APG increased, the viscosity decreased and at a concentration of 2.5wt.% AOS, 5wt.% APG and 7.5wt.% Sultaine, the system changed from shear thinning non-Newtonian fluid to Newtonian. Varying the ratio of AOS:Sultaine in the binary system, showed as the ratio changed, the viscosity decreased, and at a ratio of 1:3 AOS:Sultaine, the system was primarily Newtonian. As the ratio remained constant and APG was added, the viscosity continued to decrease and the 1:3 ratio was completely Newtonian. The addition of salt had no effect on the viscosity of Sultaine, but the viscosity of AOS increased at a salt concentration of 2wt.%. The binary mixture saw as the concentration of salt increased, the viscosity profile decreased, even though the system remained non-Newtonian and shear thinning. The surface activity and rheological study of the sulfate-free surfactant systems unveil a strong synergistic interaction between AOS and Sultaine specifically at a ratio of 1:1 resulting in high surface activity and corresponding good foaming and formation of entangled wormlike micelles resulting in excellent viscosity build in the system. If introducing a biobased surfactant into this system is desired without completely compromising the performance properties, the ternary surfactant system 4.5wt.% AOS, 3wt.% APG and 7.5wt.% Sultaine should be considered optimal. Any further addition of APG or changing the ratio results in detrimental reductions of all performance controlling physio-chemical parameters.