Large Amplitude Oscillatory Shear Flow: Microstructural Assessment of Polymeric Systems

Nano-enabled smart and functional materials toward human well-being and sustainable developments

Fabrication and operation on increasingly smaller dimensions have been highly integrated with the development of smart and functional materials, which are key to many technological innovations to meet economic and societal needs. Along with researchers worldwide, the Waterloo Institute for Nanotechnology (WIN) has long realized the synergetic interplays between nanotechnology and functional materials and designated 'Smart & Functional Materials' as one of its four major research themes. Thus far, WIN researchers have utilized the properties of smart polymers, nanoparticles, and nanocomposites to develop active materials, membranes, films, adhesives, coatings, and devices with novel and improved properties and capabilities. In this review article, we aim to highlight some of the recent developments on the subject, including our own research and key research literature, in the context of the UN Sustainability development goals.

Large and small amplitude oscillatory shear techniques evaluate the nonlinear rheological properties of Ficus pumila polysaccharide -wheat starch gel

Polysaccharides are used in starch-based product formulations to enhance the final quality of food products. This study examined the interaction mechanisms in Ficus pumila polysaccharide (FPP) and wheat starch (WS) gel systems with varying FPP concentrations using linear and nonlinear rheological analysis. Physicochemical structural analyses showed non-covalent FPP-WS interactions, strengthening hydrogen bonding between molecules and promoting water binding and ordered structure generation during WS gel aging. Small amplitude oscillatory shear analyses revealed that elevated FPP concentrations led to increased storage modulus (G'), loss modulus (G"), critical strains (From 29.02 % to 53.32 %) and yield stresses (From 0.94 Pa to 30.97 Pa) in the WS gel system, along with improved resistance to deformation and short-term regeneration. In the nonlinear viscoelastic region, FPP-WS gels shifted from elastic to viscous behavior. Higher FPP concentrations displayed increased energy dissipation, strain hardening (S>0, e3/e1 > 0) and shear thinning (T<0, v3/v1<0). FPP contributes more nonlinearity in the dynamic flow field as showed by the high harmonic ratio, with a larger I3/I1 values overall. This study highlights FPP's potential in starch gel food processing, and offers a theoretical basis for understanding hydrocolloid-starch interactions.

Tailoring 3D-printed high internal phase emulsion-rice starch gels: Role of amylose in rheology and bioactive stability

This study investigated the properties of 3D-printed high internal phase emulsion (HIPE)-rice starch gels, specially tailored for personalized nutrition by co-encapsulating resveratrol and β-carotene. We examined the influence of amylose content on various parameters, including functional groups, linear and nonlinear rheology, printed precision and microstructural stability. Additionally, we assessed the protective efficacy and release in vitro digestion of these gels on the encapsulated bioactive components. Compared to HIPE, HIPE-starch gels differently impacted by amylose content in starches. Low-level amylose weakened the network structure, attributed to amylose mainly responsible for gel formation and weak hydrogen bond interaction between the surface-active molecules and amylose due to gelatinized starch granules rupturing the protein network. Oppositely, high-level amylose led to denser, more gel-like structures with enhanced mechanical strength and reversible deformation resistance, making them suitable for 3D printing. Furthermore, 3D-printed gels with high-level amylose demonstrated well-defined structures, smooth surfaces, stable printing and less dimension deviation. They were also regarded as effective entrapping and delivery systems for resveratrol and β-carotene, protecting them against degradation from environment and damage under the erosion of digestive fluid. Overall, this research offers a straightforward strategy for creating reduced-fat HIPE gels that serve as the carrier for personalized nutraceutical foods.

A novel edible solid fat substitute: Preparation of biphasic stabilized bigels based on glyceryl monolaurate and gellan gum

Solid fats contribute to a delicate and pleasant flavor for food, but its excessive intake increases the risk of cardiovascular disease. Bigel is considered a promising solid fat substitute as it significantly reduces fat content while meeting consumer demands for food flavor and a balanced diet. In this study, bigels were prepared by mixing glyceryl monolaurate-based oleogel (10 wt%) and gellan gum-based hydrogel (0.8 wt%) at ratios of 1:3, 1:1, and 3:1. The microscopic results indicated that the oleogel/hydrogel ratios influenced the structure of bigels, forming oil-in-water, bi-continuous, and water-in-oil bigels with the increase of oleogel proportion, respectively. All bigels presented a semi-solid structure dominated by elasticity, and their hardness, gumminess, chewiness, and cohesiveness increased with the enhancement of hydrogel proportion. Among them, the bigels (S25:L75 and S25:H75) prepared with an oleogel/hydrogel ratio of 1:3 showed excellent freeze-thaw stability, maintaining an oil holding capacity of >95 % after three freeze-thaw cycles. Meanwhile, they also presented good oxidative stabilities, where the peroxide values and malondialdehyde contents were below 0.07 g/100 g and 1.5 mg MDA/kg at 12 d, respectively. Therefore, S25:L75 and S25:H75 are expected to be green, low-cost, healthy, and sustainable alternatives to solid fats.

Structural characterization of solvent-based food preparation of jellyfish

Jellyfish as a potential sustainable food material has recently gained increasing interest. However, with their soft gel-like texture and easy spoilage, it remains challenging to achieve desirable edible structures from jellyfish. The culinary preparation of jellyfish is a complex process and extends beyond conventional cooking methods. In this study, we investigate the transformation of jellyfish into crispy-like structures by manipulating their microstructural and mechanical properties through a solvent-based preparation. The study focuses on the use of "poor solvents", namely ethanol and acetone, and employs rheology measurements and quantitative microscopy techniques to analyze the effects of these solvents on the mechanical properties and microstructure of jellyfish. Our findings reveal that both ethanol and acetone lead to a significant increase in jellyfish hardness and deswelling. Notably, a micro-scale network is formed within the jellyfish matrix, and this network is then mechanically reinforced before a crispy-like texture can be obtained. Our study points to solvent polarity as also being a crucial factor for creating these effects and determines an upper polarity limit in the range of 12.2-12.9 MPa1/2 for added solvents, corresponding to approximately 60% of added ethanol or 70% of added acetone. Our study highlights that solvent-based preparation serves as a "reverse cooking" technique, where mechanical modification rather than traditional softening mechanisms are employed to stabilize and strengthen the microstructures and fibers of jellyfish. By elucidating the underlying mechanisms of solvent-induced stabilization, our findings may facilitate the development of innovative and sustainable culinary practices, paving the way for broader applications of jellyfish and other soft edible materials in the gastronomic landscape.

Improvement in the Thermomechanical Properties and Adhesion of Wood Fibers to the Polyamide 6 Matrix by Sequential Ball Milling Technique

The engineering thermoplastics industry has largely limited the use of natural fiber reinforcements due to their susceptibility to low-onset thermal degradation and water absorption. Therefore, in order to utilize these economically viable and environmentally friendly materials effectively through common composite fabrication methods such as hot pressing, safeguarding them from thermal degradation becomes essential. This work presents a viable industrially technique called sequential ball milling for processing unbleached softwood kraft pulp fibers (PF) with an engineering thermoplastics polyamide 6 (PA6) with high melting temperatures (>220 °C). An additional eco-friendly modification step that employs ball milling and cellulose nanocrystal (CNC) has been implemented in this study to enhance the mechanical properties of the composites. Special attention is given to fine-tuning key variables, such as milling duration and PF particle size, to produce optimal composites. Leveraging the ability of sequential ball milling to evenly distribute pulp fibers into PA6, a 160% increase in Young's modulus was achieved with the incorporation of 30 wt % PF. Importantly, the introduction of a 5 wt % CNC modifying agent elevated Young's modulus to 4.3 GPa, marking a 187% improvement over unmodified PA6. Diverse techniques, including rheological analyses, thermomechanical evaluations, morphological examinations, and assessments of moisture absorption, were utilized to validate the efficiency of the suggested processing approach and the modification phase.

A critical study of the nonlinear rheological properties in major classes of foods using the Sequence of Physical Processes (SPP) method and the Fourier Transform Coupled with Chebyshev Decomposition (FTC) method

The nonlinear rheological behaviors of three different classes of foods (emulsion, suspension, and elastic network) were studied and analyzed using the Rogers Sequence of Physical Processes (SPP) method and the Ewoldt-McKinley method of coupling Fourier Transform with Chebyshev Decomposition (FTC). SPP analysis led to instantaneous rheological parameters G't and G″t at any point in time, providing a more accurate picture of the linear viscoelastic region and crossover points by the 3D amplitude sweep. When G't is plotted against G″t, the resulting graph is a deltoid which offers a detailed and distinctive intracycle behavior of each class of food. Analyzing the revolution of deltoids with increasing strain allows for the determination of a critical strain, beyond which irreversible network breakdown occurs. The strain range between the linear viscoelastic limit and the critical strain found in SPP is comparable to the MAOS region as determined with FTC. Under increasing amplitude, predominantly elastic networks showed a gradual structural rearrangement, while more erratic and abrupt changes were observed in the suspension and emulsion we studied. Under increasing frequency, elastic responses dominate viscous responses in all samples due to the shorter experimental time, allowing less relaxation.

Surfactant-Mediated Highly Conductive Cellulosic Inks for High-Resolution 3D Printing of Robust and Structured Electromagnetic Interference Shielding Aerogels

Technological fusion of emerging three-dimensional (3D) printing of aerogels with gel processing enables the fabrication of lightweight and functional materials for diverse applications. However, 3D-printed constructs via direct ink writing for fabricating electrically conductive structured biobased aerogels suffer several limitations, including poor electrical conductivity, inferior mechanical strength, and low printing resolution. This work addresses these limitations via molecular engineering of conductive hydrogels. The hydrogel inks, namely, CNC/PEDOT-DBSA, featured a unique formulation containing well-dispersed cellulose nanocrystal decorated by a poly(3,4-ethylene dioxythiophene) (PEDOT) domain combined with dodecylbenzene sulfonic acid (DBSA). The rheological properties were precisely engineered by manipulating the solid content and the intermolecular interactions among the constituents, resulting in 3D-printed structures with excellent resolution. More importantly, the resultant aerogels following freeze-drying exhibited a high electrical conductivity (110 ± 12 S m-1), outstanding mechanical properties (Young's modulus of 6.98 MPa), and fire-resistance properties. These robust aerogels were employed to address pressing global concerns about electromagnetic pollution with a specific shielding effectiveness of 4983.4 dB cm2 g-1. Importantly, it was shown that the shielding mechanism of the 3D printed aerogels could be manipulated by their geometrical features, unraveling the undeniable role of additive manufacturing in materials design.

Chitosan-based emulgel and xerogel film containing Thymus pubescens essential oil as a potential wound dressing

Controlling the wound exudates accompanied by microbial wound infections has still remained as one the most challenging clinical issues. Herein, a chitosan/gelatin/polyvinyl alcohol xerogel film containing Thymus pubescens essential oil is fabricated for antimicrobial wound dressing application. The chemical and physical characteristics of the devised formulation is characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, atomic force microscope, and tensile tests. Moreover, swelling capability, water vapour transmission rate, water contact angle, solubility, moisture content, and release properties are also studied. The antimicrobial and antibiofilm tests are performed using the broth microdilution and XTT assay, respectively. The produced formulation shows excellent antimicrobial efficacy against Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa and Candida species. It is also demonstrated that the obtained film can reduce (∼80 %) Candida albicans biofilm formation, and its biocompatibility is confirmed with MTT (∼100 %) and hemolysis tests. The antimicrobial activity can be correlated to the microbial membrane attraction for Candida albicans cells, illustrated by flow cytometry. This proposed film with appropriate mechanical strength, high swelling capacity in different pH values (∼200-700 %), controlled release property, and antimicrobial and antioxidant activities as well as biocompatibility can be used as a promising candidate for antimicrobial wound dressing applications.

Super-Macroporous Lightweight Materials Templated from Bicontinuous Intra-Phase Jammed Emulsion Gels Based on Nanochitin

Non-equilibrium multiphase systems are formed by mixing two immiscible nanoparticle dispersions, leading to bicontinuous emulsions that template cryogels with interconnected, tortuous channels. Herein, a renewable, rod-like biocolloid (chitin nanocrystals, ChNC) is used to kinetically arrest bicontinuous morphologies. Specifically, it is found that ChNC stabilizes intra-phase jammed bicontinuous systems at an ultra-low particle concentration (as low as 0.6 wt.%), leading to tailorable morphologies. The synergistic effects of ChNC high aspect ratio, intrinsic stiffness, and interparticle interactions produce hydrogelation and, upon drying, lead to open channels bearing dual characteristic sizes, suitably integrated into robust bicontinuous ultra-lightweight solids. Overall, it demonstrates the successful formation of ChNC-jammed bicontinuous emulsions and a facile emulsion templating route to synthesize chitin cryogels that form unique super-macroporous networks.

Encapsulation of Zataria multiflora essential oil in polyvinyl alcohol/chitosan/gelatin thermo-responsive hydrogel: Synthesis, physico-chemical properties, and biological investigations

Zataria multiflora essential oil is a natural volatile plant product whose therapeutic applications require a delivery platform. Biomaterial-based hydrogels have been extensively used in biomedical applications, and they are promising platforms to encapsulate essential oils. Among different hydrogels, intelligent hydrogels have recently attracted many interests because of their response to environmental stimuli such as temperature. Herein, Zataria multiflora essential oil is encapsulated in a polyvinyl alcohol/chitosan/gelatin hydrogel as a positive thermo-responsive and antifungal platform. According to the optical microscopic image, the encapsulated spherical essential oil droplets reveal a mean size of 1.10 ± 0.64 μm, which are in consistent with the SEM imaging results. Encapsulation efficacy and loading capacity are 98.66 % and 12.98 %, respectively. These results confirm the successful efficient encapsulation of the Zataria multiflora essential oil within the hydrogel. The chemical compositions of the Zataria multiflora essential oil and the fabricated hydrogel are analyzed by gas chromatography-mass spectroscopy (GC-MS) and Fourier transform infrared (FTIR) techniques. It is found that thymol (44.30 %) and γ-terpinene (22.62 %) are the main constituents of the Zataria multiflora essential oil. The produced hydrogel inhibits the metabolic activity of Candida albicans biofilms (~60-80 %), which can be related to the antifungal activity of the essential oil constituents and chitosan. Based on the rheological results, the produced thermo-responsive hydrogel shows a gel-sol viscoelastic transition at a temperature of 24.5 °C. This transition leads to a facile release of the loaded essential oil. The release test depicts that about 30 % of Zataria multiflora essential oil is released during the first 16 min. In addition, 2, 5-diphenyl-2H-tetrazolium bromide (MTT) assay demonstrates that the designed thermo-sensitive formulation is biocompatible with high cell viability (over 96 %). The fabricated hydrogel can be deemed as a potential intelligent drug delivery platform for controlling cutaneous candidiasis due to antifungal effectiveness and less toxicity, which can be a promising alternative to traditional drug delivery systems.

Comparative Large Amplitude Oscillatory Shear (LAOS) Study of Ionically and Physically Crosslinked Hydrogels

Hydrogels are highly versatile and widely applicable materials within various scientific, technological, and food sectors. Alginate and gelatin hydrogels, along with their crafted variations, are possibly the most common ones. However, the ionic crosslinking of alginate-Ca⁺⁺ is a different gelation mechanism than the physical crosslinking of gelatin. In this work, we prepare alginate-Ca⁺⁺ hydrogels using individual layer gelation and experimentally evaluate LAOS rheological behavior. We apply shear-stress decomposition using the MITlaos software and obtain the elastic and viscous contributions within the nonlinear response of the individual alginate-Ca⁺⁺ layer. We compare these results with the nonlinear responses of the gelatin-alginate ex situ individual layer. The strain-sweep patterns are similar, with loss modulus overshoot. The applied shear can destroy the larger-scale structural units (agglomerate/aggregates), resulting in analogous patterns. However, the critical strain points are different. Based on the shear-thickening ratio T of the LAOS analysis, it can be assumed that the common feature of ex situ preparation, i.e., gelation as individual layers, provides a matching bulk microstructure, as the hydrogels differ significantly at a molecular-binding level.