Kinetic study of fluid gel formation and viscoelastic response with kappa-carrageenan

Cholecalciferol- and α-tocopherol-loaded walnut oil emulsions stabilized by whey protein isolate and soy lecithin for food applications

BACKGROUND

To overcome the limitations in the use of protein as an emulsifier, soy lecithin, a natural surfactant, was used along with whey protein isolate (WPI) to produce o/w emulsions containing cholecalciferol and α-tocopherol. The physical stability of the emulsions prepared with WPI and varying concentrations of lecithin (0, 1, 2, and 3% w/w) was measured in different heat, pH, and ionic-strength food environmental conditions.

RESULTS

All emulsions were shown to be less than 250 nm in size and less than 0.3 in polydispersity index (PDI). The morphology of the emulsions was spherical, and the droplets of the emulsion containing lecithin were thicker and larger than those of the emulsion without lecithin (WPI_L0). After autoclaving, WPI_L0 increased in size from 197.8 ± 1.7 nm to 528.5 ± 28.4 nm, and the retention of cholecalciferol and α-tocopherol decreased to 40.83 ± 0.63% and 49.68 ± 1.84%, respectively. At pH 5.5, near the isoelectric point of WPI, WPI_L0 increased in size due to aggregation, but emulsions containing lecithin remained stable at a PDI under 0.3. Turbiscan stability index of the emulsion prepared with WPI and 3% lecithin was the lowest, indicating good storage stability. In addition, it was confirmed that the higher the lecithin content, the higher the viscosity, and the higher the amount of free fatty acids released in the in vitro digestion model.

CONCLUSION

This study can provide theoretical evidence for enhancing the physical stability of protein emulsions by co-stabilization with lecithin, promoting their application in various foods. © 2022 Society of Chemical Industry.

A Fast Galerkin Approach for Solving the Fractional Rayleigh–Stokes Problem via Sixth-Kind Chebyshev Polynomials

Herein, a spectral Galerkin method for solving the fractional Rayleigh–Stokes problem involving a nonlinear source term is analyzed. Two kinds of basis functions that are related to the shifted sixth-kind Chebyshev polynomials are selected and utilized in the numerical treatment of the problem. Some specific integer and fractional derivative formulas are used to introduce our proposed numerical algorithm. Moreover, the stability and convergence accuracy are derived in detail. As a final validation of our theoretical results, we present a few numerical examples.

Formulation and Cost-Effectiveness of Fluid Gels as an Age-Appropriate Dosage Form for Older Adults with Dysphagia

Dysphagia is associated with increased dependency and treatment costs, whereby patients resort to extemporaneous compounding that may further increase the number of adverse events and medical errors. In the management of dysphagia, increasing the bolus viscosity of medication such as fluid gels can be practiced. This study aimed to prepare and characterize the fluid gels as well as to estimate the cost of using fluid gels and compare it to the conventional practice of extemporaneous preparation of thickened liquid. Fluid gels were formulated using gellan gum and determined for physicochemical characteristics and in vitro drug release profile. The cost-based price of the fluid gel was estimated and compared to the cost of administering standard medication as well as administering thickened liquid using thickening powder. Fluid gels exhibited good physicochemical properties with the viscosity within nectar and honey consistency. A similar dissolution profile to the reference was observed for the 0.5% w/v gellan gum fluid gel and exhibiting the Higuchi release model. The price for 100 mL unit of 50 mg/mL paracetamol/acetaminophen and 20 mg/mL ibuprofen fluid gel was estimated to be about USD2.30 and USD2.37, respectively. A dose of 1000 mg paracetamol and 400 mg ibuprofen fluid gel was estimated to be about USD0.46 and USD0.47, respectively, which is lower than the cost of administering the same dose using extemporaneous thickened liquid. Fluid gels could be a cost-effective formulation for delivering medication in patients with dysphagia and can be developed on a profitable scale.

Engineering the Multi-Enzymatic Activity of Cerium Oxide Nanoparticle Coatings for the Antioxidant Protection of Implants

Imbalance of oxidants is a universal contributor to the failure of implanted devices and tissues. A sustained oxidative environment leads to cytotoxicity, prolonged inflammation, and ultimately host rejection of implanted devices/grafts. The incorporation of antioxidant materials can inhibit this redox/inflammatory cycle and enhance implant efficacy. Cerium oxide nanoparticles (CONP) is a highly promising agent that exhibits potent, ubiquitous, and self-renewable antioxidant properties. Integrating CONP as surface coatings provides ease in translating antioxidant properties to various implants/grafts. Herein, we describe the formation of CONP coatings, generated via the sequential deposition of CONP and alginate, and the impact of coating properties, pH, and polymer molecular weight, on their resulting redox profile. Investigation of CONP deposition, layer formation, and coating uniformity/thickness on their resulting oxidant scavenging activity identified key parameters for customizing global antioxidant properties. Results found lower molecular weight alginates and physiological pH shift CONP activity to a higher H2O2 to O2 --scavenging capability. The antioxidant properties measured for these various coatings translated to distinct antioxidant protection to the underlying encapsulated cells. Information gained from this work can be leveraged to tailor coatings towards specific oxidant-scavenging applications and prolong the function of medical devices and cellular implants.

Tailoring Therapeutic Responses via Engineering Microenvironments with a Novel Synthetic Fluid Gel

This study reports the first fully synthetic fluid gel (SyMGels) using a simple poly(ethylene glycol) polymer. Fluid gels are an interesting class of materials: structured during gelation via shear-confinement to form microparticulate suspensions, through a bottom-up approach. Structuring in this way, when compared to first forming a gel and subsequently breaking it down, results in the formation of a particulate dispersion with particles "grown" in the shear flow. Resultantly, systems form a complex microstructure, where gelled particles concentrate remaining non-gelled polymer within the continuous phase, creating an amorphous-like interstitial phase. As such, these materials demonstrate mechanical characteristics typical of colloidal glasses, presenting solid-like behaviors at rest with defined yielding; likely through intrinsic particle-particle and particle-polymer interactions. To date, fluid gels have been fabricated using polysaccharides with relatively complex chemistries, making further modifications challenging. SyMGels are easily functionalised, using simple click-chemistry. This chemical flexibility, allows the creation of microenvironments with discrete biological decoration. Cellular control is demonstrated using MSC (mesenchymal stem cells)/chondrocytes and enables the regulation of key biomarkers such as aggrecan and SOX9. These potential therapeutic platforms demonstrate an important advancement in the biomaterial field, underpinning the mechanisms which drive their mechanical properties, and providing a versatile delivery system for advanced therapeutics.

Physics of agarose fluid gels: Rheological properties and microstructure

Agarose, a strongly gelling polysaccharide, is a common ingredient used to optimize the viscoelastic properties of a multitude of food products. Through aggregation of double helices via hydrogen bonds while cooling under quiescent conditions it forms firm and brittle gels. However, this behavior can be altered by manipulating the processing conditions viz shear. For example, gelation under shear leads to microgel particles with large surface area, which in turn leads to completely different rheological properties and texture. Such fluid gels are shown to play an important role in texture modification of foods and beverages for dysphagia patients. In this study, different concentration of agarose fluid gel (0.5 % wt, 1 % wt and 2 % wt) were considered. Rheological measurements of the microgel particles showed an increase of storage and loss modulus with increasing concentration. However, 1 % wt fluid gel exhibited the lowest viscosity in the low shear range and the shortest LVE range. Furthermore, the effect on the microstructure and size of gel particles were also investigated by using light microscopy and particle size analysis. It was observed that as the concentration of agarose increased the particle size and unordered chains present at the particle surface decreases. Based on our results, we propose specific models suggesting the impact of the particle size, the concentration and the "hairy" projections on the rheological and tribological properties that could help in understanding the differences in characteristics of fluid gels.

Soft κ-carrageenan microgels stabilized pickering emulsion gels: Compact interfacial layer construction and particle-dominated emulsion gelation

HYPOTHESIS

The well-known gelling ability of κ-carrageenan can make aqueous solutions into soft materials, which are crisp and can be mechanically treated into the nano-sized microgel particle (MP) as the building block for constructing the Pickering emulsion gel (PEG). MPs are expected to adhere and further create the network structure in PEGs due to their viscoelastic texture. Herein, properties of PEGs should be possibly altered by using MPs with different pH and ionic strength.

EXPERIMENTS

MPs were prepared by shearing and gelling κ-carrageenan solutions simultaneously. Effects of pH and ionic strength on MPs were formulated, and physical properties of PEGs prepared from corresponding MPs were investigated. The interaction between κ-carrageenan molecules was analyzed by FTIR, and the formation process of the interfacial layer was traced by the interfacial rheological technique.

FINDINGS

The moderate K⁺ could increase the flocculation and hardness of MPs to improve the viscoelasticity of PEGs. Prepared MPs were more favorable for forming PEGs when pH was 8 and 9. The oil fraction impacted physical properties of PEGs slightly. MPs constantly moved to the interface from the continuous phase, forming the compact adsorption layer due to the extrusion of MPs.

Rheology and tribology of starch + κ-carrageenan mixtures

In this study, we investigated the rheological and tribological properties of biopolymer mixtures of gelatinized corn starches (0.5 - 10.0 wt%) and κ-carrageenan (κC) (0.05 - 1.0 wt%). Two different starch samples were used. The first starch (CS1), despite extensive heating and shearing contained "ghost" granules, while the second starch (CS2) had no visible ghost granules after the same gelatinization process as CS1. Apparent viscosity measurements demonstrated that κC + CS1 mixtures were shear thinning liquids, with viscosity values being lower than the corresponding weight average of the values of the individual equilibrium phases at shear rates < 50 s-1 . Tribological results revealed that κC ≥ 0.5 wt% was required to observe any decrease in friction coefficients in the mixed lubrication regime. Starch (CS1) showed an unusual behavior at ≥ 5 wt%, where the friction coefficient decreased not only in the mixed regime but also in the boundary regime, probably due to the presence of the "ghost" granules, as the latter became entrained in the contact region. The CS1 + κC mixtures showed significantly lower friction coefficients than that of pure CS1 and κC in the mixed regime. However, the CS2 + κC mixture (i.e., containing no ghost granules) showed similar behavior to pure κC in the mixed regime, while lower friction coefficients than that of the pure CS2 and κC in the boundary regime. These findings illustrate new opportunities for designing biopolymer mixtures with tunable lubrication performance, via optimizing the concentrations of the individual biopolymers and the gelatinization state of the starch.

Kappa-Carrageenan-Based Dual Crosslinkable Bioink for Extrusion Type Bioprinting

Bioink based 3D bioprinting is a promising new technology that enables fabrication of complex tissue structures with living cells. The printability of the bioink depends on the physical properties such as viscosity. However, the high viscosity bioink puts shear stress on the cells and low viscosity bioink cannot maintain complex tissue structure firmly after the printing. In this work, we applied dual crosslinkable bioink using Kappa-carrageenan (κ-CA) to overcome existing shortcomings. κ-CA has properties such as biocompatibility, biodegradability, shear-thinning and ionic gelation but the difficulty of controlling gelation properties makes it unsuitable for application in 3D bioprinting. This problem was solved by synthesizing methacrylated Kappa-carrageenan (MA-κ-CA), which can be dual crosslinked through ionic and UV (Ultraviolet) crosslinking to form hydrogel using NIH-3T3 cells. Through MA substitutions, the rheological properties of the gel could be controlled to reduce the shear stress. Moreover, bioprinting using the cell-laden MA-κ-CA showed cell compatibility with enhanced shape retention capability. The potential to control the physical properties through dual crosslinking of MA-κ-CA hydrogel is expected to be widely applied in 3D bioprinting applications.

Delivery of synergistic polyphenol combinations using biopolymer-based systems: Advances in physicochemical properties, stability and bioavailability

When consumed at sufficiently high levels, polyphenols may provide health benefits, which is linked to their antidiabetic, antiinflamatory, antimicrobial, antioxidant, antitumor, and hypolipidemic properties. Moreover, certain polyphenol combinations exhibit synergistic effects when delivered together - the combined polyphenols have a higher biological activity than the sum of the individual ones. However, the commercial application of polyphenols as nutraceuticals is currently limited because of their poor solubility characteristics; instability when exposed to light, heat, and alkaline conditions; and, low and inconsistent oral bioavailability. Colloidal delivery systems are being developed to overcome these challenges. In this article, we review the design, fabrication, and utilization of food-grade biopolymer-based delivery systems for the encapsulation of one or more polyphenols. In particular, we focus on the creation of delivery systems constructed from edible proteins and polysaccharides. The optimization of biopolymer-based delivery systems may lead to the development of innovative polyphenol-enriched functional foods that can improve human health and wellbeing.

A gellan-based fluid gel carrier to enhance topical spray delivery

Autologous cell transplantation was introduced to clinical practice nearly four decades ago to enhance burn wound re-epithelialisation. Autologous cultured or uncultured cells are often delivered to the surface in saline-like suspensions. This delivery method is limited because droplets of the sprayed suspension form upon deposition and run across the wound bed, leading to uneven coverage and cell loss. One way to circumvent this problem would be to use a gel-based material to enhance surface retention. Fibrin systems have been explored as co-delivery system with keratinocytes or as adjunct to 'seal' the cells following spray delivery, but the high costs and need for autologous blood has impeded its widespread use. Aside from fibrin gel, which can exhibit variable properties, it has not been possible to develop a gel-based carrier that solidifies on the skin surface. This is because it is challenging to develop a material that is sprayable but gels on contact with the skin surface. The manuscript reports the use of an engineered carrier device to deliver cells via spraying, to enhance retention upon a wound. The device involves shear-structuring of a gelling biopolymer, gellan, during the gelation process; forming a yield-stress fluid with shear-sensitive behaviours, known as a fluid gel. In this study, a formulation of gellan gum fluid gels are reported, formed with from 0.75 or 0.9% (w/v) polymer and varying the salt concentrations. The rheological properties and the propensity of the material to wet a surface were determined for polymer modified and non-polymer modified cell suspensions. The gellan fluid gels had a significantly higher viscosity and contact angle when compared to the non-polymer carrier. Viability of cells was not impeded by encapsulation in the gellan fluid gel or spraying. The shear thinning property of the material enabled it to be applied using an airbrush and spray angle, distance and air pressure were optimised for coverage and viability. STATEMENT OF SIGNIFICANCE: Spray delivery of skin cells has successfully translated to clinical practice. However, it has not yet been widely accepted due to limited retention and disputable cell viability in the wound. Here, we report a method for delivering cells onto wound surfaces using a gellan-based shear-thinning gel system. The viscoelastic properties allow the material to liquefy upon spraying and restructure rapidly on the surface. Our results demonstrate reduced run-off from the surface compared to currently used low-viscosity cell carriers. Moreover, encapsulated cells remain viable throughout the process. Although this paper studies the encapsulation of one cell type, a similar approach could potentially be adopted for other cell types. Our data supports further studies to confirm these results in in vivo models.

Structuring of Hydrogels across Multiple Length Scales for Biomedical Applications

The development of new materials for clinical use is limited by an onerous regulatory framework, which means that taking a completely new material into the clinic can make translation economically unfeasible. One way to get around this issue is to structure materials that are already approved by the regulator, such that they exhibit very distinct physical properties and can be used in a broader range of clinical applications. Here, the focus is on the structuring of soft materials at multiple length scales by modifying processing conditions. By applying shear to newly forming materials, it is possible to trigger molecular reorganization of polymer chains, such that they aggregate to form particles and ribbon-like structures. These structures then weakly interact at zero shear forming a solid-like material. The resulting self-healing network is of particular use for a range of different biomedical applications. How these materials are used to allow the delivery of therapeutic entities (cells and proteins) and as a support for additive layer manufacturing of larger-scale tissue constructs is discussed. This technology enables the development of a range of novel materials and structures for tissue augmentation and regeneration.

Fluid Gels: a New Feedstock for High Viscosity Jetting

Suspensions of gel particles which are pourable or spoonable at room temperature can be created by shearing a gelling biopolymer through its gelation (thermal or ion mediated) rather than allowing quiescent cooling – thus the term ‘fluid gel’ may be used to describe the resulting material. As agar gelation is thermoreversible this type of fluid gel is able to be heated again to melt agar gel particles to varying degrees then re-form a network quiescently upon cooling, whose strength depends on the temperature of re-heating, determining the amount of agar solubilised and subsequently able to partake in re-gelation. Using this principle, for the first time fluid gels have been applied to a high viscosity 3D printing process wherein the printing temperature (at the nozzle) is controllable. This allows the use of ambient temperature feedstocks and by altering the nozzle temperature, the internal nature (presence or absence of gel particles) and gel strength of printed droplets differs. If the nozzle prints at different temperatures for each layer a structure with modulated texture could be created.

Aqueous clay suspensions stabilized by alginate fluid gels for coal spontaneous combustion prevention and control

We have developed aqueous clay suspensions stabilized by alginate fluid gels (AFG) for coal spontaneous combustion prevention and control. Specially, this study aimed to characterize the effect of AFG on the microstructure, static and dynamic stability, and coal fire inhibition performances of the prepared AFG-stabilized clay suspensions. Compared with aqueous clay suspensions, the AFG-stabilized clay suspensions manifest high static and dynamic stability, which can be ascribed to the formation of a robust three-dimensional gel network by AFG. The coal acceleration oxidation experimental results show that the prepared AFG-stabilized clay suspensions can improve the coal thermal stability and effectively inhibit the coal spontaneous oxidation process by increasing crossing point temperature (CPT) and reducing CO emission. The prepared low-cost and nontoxic AFG-stabilized clay suspensions, exhibiting excellent coal fire extinguishing performances, indicate great application potentials in coal spontaneous combustion prevention and control.

Geometric confinement is required for recovery and maintenance of chondrocyte phenotype in alginate

Human articular chondrocytes lose their native phenotype when expanded in traditional monolayer cultures. As a consequence, hydrogel encapsulation has been investigated as a means to maintain the natural phenotype. Alginate has been widely used for cartilage engineering as it has been shown to enable the recovery of a native collagen type II expressing chondrocyte phenotype. This study has evaluated whether the capacity of the materials to maintain/revert the phenotype is due to the composition of the material or the physical entrapment provided by the gel. To achieve this, an alginate “fluid gel” (a shear-thinning structured gel system) was produced of identical chemistry to a traditionally gelled alginate structure. Both were seeded with passaged primary human articular chondrocytes. Chondrocytes in quiescent alginate showed the recovery of the native phenotype and a spherical morphology. Chondrocytes in alginate fluid gel were unable to maintain the recovered phenotype despite having a spherical morphology and were shown to have a lower level of entrapment than those in quiescent alginate. These findings indicate that geometric entrapment is essential for the maintenance of a recovered chondrocyte phenotype in alginate.

Hydrogels for Biomedical Applications: Cellulose, Chitosan, and Protein/Peptide Derivatives

Hydrogels based on polysaccharide and protein natural polymers are of great interest in biomedical applications and more specifically for tissue regeneration and drug delivery. Cellulose, chitosan (a chitin derivative), and collagen are probably the most important components since they are the most abundant natural polymers on earth (cellulose and chitin) and in the human body (collagen). Peptides also merit attention because their self-assembling properties mimic the proteins that are present in the extracellular matrix. The present review is mainly focused on explaining the recent advances on hydrogels derived from the indicated polymers or their combinations. Attention has also been paid to the development of hydrogels for innovative biomedical uses. Therefore, smart materials displaying stimuli responsiveness and having shape memory properties are considered. The use of micro- and nanogels for drug delivery applications is also discussed, as well as the high potential of protein-based hydrogels in the production of bioactive matrices with recognition ability (molecular imprinting). Finally, mention is also given to the development of 3D bioprinting technologies.

Suspended Manufacture of Biological Structures

A method for the production of complex cell-laden structures is reported, which allows high-levels of spatial control over mechanical and chemical properties. The potential of this method for producing complicated tissues is demonstrated by manufacturing a complex hard/soft tissue interface and demonstrating that cell phenotype can be maintained over four weeks of culture.

Functional food microstructures for macronutrient release and delivery

There is a need to understand the role of fat, protein and carbohydrate in human health, and also how foods containing and/or structured using these macronutrients can be designed so that they can have a positive impact on health. This may include a reduction in fat, salt or sugar, the protection and targeted release of micronutrients or active ingredients from/to particular parts of the digestive system, improvement of gastrointestinal health or satiety enhancing properties. Such foods can be designed with various macro- and microstructures that will impact on macronutrient release and delivery. These include simple and double emulsions, the use of Pickering particles and shells, nanoparticles, liposomes, gelled networks, fluid gels and gel particles, foams, self-assembled structures, and encapsulated systems. In order to design foods that deliver these benefits understanding of how these structures behave in the gastrointestinal tract is also required, which should involve utilising both in vitro and in vivo studies. This review aims to draw together research in these areas, by focusing on the current state of the art, but also exciting possibilities for future research and food development.

Nanoparticles combined with growth factors: recent progress and applications

Increasing attention has been focused on the applications of nanoparticles combined with growth factors (NPs/GFs) due to the substantial functions of GFs in regenerative medicine and disease treatments.

Rheology of sheared gels based on low acyl-gellan gum

Sheared gels containing 0.2 wt% low-acyl gellan gum were prepared by different processing protocols using Na(+) or Ca(2+) as gel-promoting ions. Rheology and confocal laser scanning microscopy were used to gain information on the sample structure. Confocal laser scanning microscopy revealed the formation of a heterogeneous microstructure consisting of a dispersion of gel-like clusters. Small amplitude oscillatory shear stress results indicated that their viscoelastic properties had a predominant elastic component. Flow curves exhibited very high viscosities at low shear stress, an apparent yield stress and very shear thinning behaviour, supporting their applications as a stabilizer.

Development of mucoadhesive sprayable gellan gum fluid gels

The nasal mucosa provides a potentially good route for local and systemic drug delivery. However, the protective feature of the nasal cavity make intranasal delivery challenging. The application of mucoadhesive polymers in nasal drug delivery systems enhances the retention of the dosage form in the nasal cavity. Several groups have investigated using low acyl gellan as a drug delivery vehicle but only limited research however, has been performed on high acyl gellan for this purpose, despite its properties being more conducive to mucoadhesion. High acyl gellan produces highly elastic gels below 60°C which make it difficult to spray using a mechanical spray device. Therefore, in this study we have tried to address this problem by making fluid gels by introducing a shear force during gelation of the gellan polymer. These fluid gel systems contain gelled micro-particles suspended in a solution of un-gelled polymer. These systems can therefore behave as pourable viscoelastic fluids. In this study we have investigated the rheological behavior and mucoadhesion of fluid gels of two different types of gellan (high and low acyl) and fluid gels prepared from blends of high and low acyl gellan at a 50:50 ratio. The results demonstrated that by preparing fluid gels of high acyl gellan, the rheological properties were sufficient to spray through a standard nasal spray device. Moreover fluid gels also significantly enhance both high acyl and low acyl gellan mucoadhesion properties.

Preparation and rheological properties of whey protein emulsion fluid gels

The research uses a novel approach to tackle structuring in liquids through shear-gel technology, resulting in advanced material properties.