Measurement of the flow behavior index of Newtonian and shear-thinning fluids via analysis of the flow velocity characteristics in a mini-channel

Assessing texturometer-derived rheological data for predicting the printability of gummy formulations in SSE 3D printing

Semi-solid extrusion (SSE), an additive manufacturing technique, is gaining significant attention for the printing of thermosensitive drugs. Hydrogels, one of the materials used in SSE, have emerged as a focus in pharmaceutical applications due to their ability to control the release of therapeutic agents spatially and temporally. Understanding the non-Newtonian flow and evaluating the mechanical properties of hydrogel-based materials during extrusion is, however, essential for successful 3D printing. Thus, users often find themselves conducting both rheological and texture profile analyses to characterize the hydrogel. While texturometers are primarily used to evaluate mechanical or sensory properties, viscosity measurements are typically performed using rotational rheometers or viscometers. In this study, we demonstrated how comparable rheological information can be obtained using a texturometer as a capillary rheometer. By preparing similar formulations to a previous study, we compared the rheological data obtained from a rotational rheometer to the data obtained from the texturometer. The means of the parameters obtained by fitting the data from both techniques to the power law model showed insignificant differences. In addition, three clusters were formed based on the flow behaviour and printability of the samples using principal component analysis. Furthermore, the printability was predicted using the samples' consistency and flow indexes, and the regression coefficient was 96.62 and 60.03% for capillary and rotational flow parameters, respectively. This approach thus holds the potential to streamline the time, expertise and equipment required for the rheological characterization of hydrogels for applications in semi-solid extrusion.

Surfactants for stabilization of dermal emulsions and their skin compatibility under UVA irradiation: Diacyl phospholipids and polysorbate 80 result in high viability rates of primary human skin cells

Phospholipids are versatile formulation compounds with high biocompatibility. However, no data on their effect on skin in combination with UVA radiation exist. Thus, it was the aim of this work to (i) develop o/w nanoemulsions (NEs) differing in surfactant type and to investigate their physicochemical stability at different storage temperatures, (ii) establish a standardized protocol for in vitro phototoxicity testing using primary human skin cells and (iii) investigate the phototoxicity of amphoteric phospholipids (S45, S75, E80, S100, LPC80), sodium lauryl ether sulfate (SLES) and polysorbate 80 (PS80). Satisfying systems were developed with all surfactants except S100 due to low zeta potential (-21.4 mV ± 4.69). SLES and PS80-type NEs showed the highest stability after eight weeks; temperature-dependent variations in storage stability were most noticeable for phospholipid surfactants. For phospholipid-based NEs, higher phosphatidylcholine content led to unstable formulations. Phototoxicity assays with primary skin fibroblasts confirmed the lack of UVA-related phototoxicity but revealed cytotoxic effects of LPC80 and SLES, resulting in cell viability as low as 2.7 % ±0.78 and 1.9 % ±1.57 compared to the control. Our findings suggest that surfactants S45, S75 and PS80 are the most promising candidates for skin-friendly emulsifiers in sensitive applications involving exposure to UV light.

Polarisation and rheology characterisation of monoolein/water liquid crystal dynamical behaviour during high-viscosity injector extrusion

HYPOTHESIS

The use of monoolein/water mixtures in serial crystallography experiments using high-viscosity injectors (HVI) results in significant departures from equilibrium behaviour. This is expected to include changes in phase, viscosity, and associated flow behaviour. It should be possible to detect these changes, in-situ, using a combination of polarisation and rheology characterisation techniques.

EXPERIMENTS

A systematic study was performed using monoolein, varying the water content to create a range of mixtures. Injection induced phase changes within the HVI flow were established using real-time cross-polarization measurements. Dynamic flow characteristics and viscosity was characterized by particle tracking and rheology.

FINDINGS

HVI injection induces deformation and phase changes within monoolein (MO)/water mixtures which can be detected through variations in the transmitted intensity during in-situ polarisation studies. The heterogeneity of the extruded sample results in a highly viscous cubic phase in the central region of the stream and a less viscous lamellar-rich phase at the edges adjacent to the walls. The extent of these variations depends on sample composition and injection conditions. Shear-thinning behaviour and increasing heterogeneity in the vicinity of the capillary walls under dynamic flow conditions. This is the first report observing injection induced dynamical behaviour in MO/water mixtures under realistic flow conditions.

Crosslinked carboxymethyl cellulose colloidal solution for cotton thread coating in wound dressing: A rheological study

Cotton thread therapeutic properties as a wound dressing can be enhanced by utilising carboxymethyl cellulose-nanoparticles (CMC/NPs) colloidal solution as a coating solution. Nanoparticles such as graphene oxide (GO), graphene quantum dots (GQD), and silver nanoparticles (AgNP) stability in CMC was investigated through the rheological analysis and UV-Vis spectroscopy of the colloidal solutions. Citric acid (CA) acted as a crosslinker and was utilised to crosslink the colloidal solution with cotton thread. These CMC/NPs coated threads were subjected to mechanical properties and antibacterial activity analysis. Results obtained indicate less nanoparticle agglomeration and were stable in the CMC-based nanofluid. CMC/NPs rheological study suggested that colloidal solutions exhibited shear thinning behaviour and behaved as non-Newtonian fluids with n < 1. Crosslinked CMC/NPs appeared in a gel-like state as the viscoelasticity of the solution increased. Among the colloidal solutions, CMC/AgNP showed the highest enhancement with a significant difference at p < 0.05 in terms of mechanical and antibacterial properties. Consequently, the rheological properties and stability of CMC/NPs might influence the coating solution's appearance and refine the cotton thread's microstructure for a functional wound dressing to be further utilised as a coating solution for antibacterial cotton thread wound dressing material.

Evaluation of Processing Conditions and Hydrocolloid Addition on Functional Properties of Aquafaba

Aquafaba, the cooking water from chickpeas, could replace animal-derived ingredients such as egg whites in systems that require the stabilization of an oil or gas phase. However, little is known about how processing methods and additives affect its functional properties. In this study, aquafaba was prepared via boiling or pressure-cooking at water-to-seed (WSR) ratios of 5:1, 4:1 and 3:1. The effects of preparation method and pH adjustment on viscosity, protein content, solubility and profile were evaluated. Samples were further analyzed for foaming capacity/stability (FC/FS) and emulsifying activity/stability index (EAI/ESI). Foams were also prepared in combination with xanthan gum or hydroxypropyl methylcellulose (HPMC). Solubility was lowest near pH 4 and not affected by cooking method and protein profile was not affected by method or ratio. Samples with pH 3 had high EAI and FS, but low ESI and FC. WSR did not significantly affect interfacial properties. Xanthan gum had a greater effect than HPMC on viscosity and prevented foam liquid drainage for 24 h. While the preparation method affects aquafaba properties, subsequent pH adjustment is of greater relevance for interfacial properties. Foam volumes can be maximized and foam drainage limited by appropriate choice of hydrocolloids and addition levels.

Crosslinking konjac-glucomannan with kappa-carrageenan nanogels: A step toward the design of sacrificial materials

The challenge in designing sacrificial materials is to obtain materials that are both mechanically stable and easily dissolvable. This research aimed to meet this challenge by fabricating a new polymer-nanogel hydrogel based solely on hydrogen bonds between two polysaccharides. The study focused on hydrogels formed from soluble konjac-glucomannan and nanogels synthesized from kappa-carrageenan. This novel hydrogel exhibited self-healing and shear-thinning properties due to its weak physical interactions. The hydrogel dissolved simultaneously with its swelling. Changes in temperature or nanogel concentration, or the addition of potassium ions, altered the swelling and dissolution rates. Furthermore, adding KCl to the as-prepared hydrogel increased its compression and tensile moduli and its strength. The new formulation opens numerous possibilities as a potential sacrificial material for different applications since it is mechanically stable yet rapidly dissolves in physiological conditions without applying high temperatures or using chelating agents.

Quality by Design Assisted Optimization and Risk Assessment of Black Cohosh Loaded Ethosomal Gel for Menopause: Investigating Different Formulation and Process Variables

Black cohosh (Cimicifuga racemosa) (CR) is a popular herb and is medically lauded for ameliorating myriad symptoms associated with menopause. However, its pharmaceutical limitations and non-availability of a patient-compliant drug delivery approach have precluded its prevalent use. Henceforth, the current research premise is aimed at developing an ethosomal gel incorporating triterpene enriched fraction (TEF) obtained from CR and evaluating its effectiveness through the transdermal application. TEF-loaded ethosomes were formulated using solvent injection, optimized and characterised. The optimized ethosomes were then dispersed into a polymeric gel base to form ethosomal gel which was further compared with the conventional gel by in-vitro and ex-vivo experiments. Here, the quality by design (QbD) approach was exploited for the optimization and development of ethosomal gel. The elements of QbD comprising initial risk assessment, design of experimentation (DoE), and model validation for the development of formulation have all been described in detail. The optimized ethosomes (F03) showed a nanometric size range, negative zeta potential and good entrapment. The in vitro release profile of gel revealed a burst release pattern following the Korsmeyer Peppas model having Fickian diffusion. The transdermal flux of ethosomal gel was observed to be more than that of conventional gel. Texture analysis and rheological characterization of the gel, revealed good strength showing shear thinning and pseudoplastic behaviour. The confocal microscope investigation revealed the deeper skin permeation of ethosomal gel than conventional gel. This result was further strengthened by DSC, IR and histological assessment of the animal skin (Wistar rat), treated with the optimized formulation. Conclusively, the implementation of QbD in the formulation resulted in a better understanding of the process and the product. It aids in the reduction of product variability and defects, hence improving product development efficiencies. Additionally, the ethosomal gel was found to be a more effective and successful carrier for TEF than the conventional gel through the transdermal route. Moreover, this demands an appropriate animal study, which is underway, for a stronger outcome.

Numerical and Experimental Analysis of Shear Stress Influence on Cellular Viability in Serpentine Vascular Channels

3D bioprinting has emerged as a tool for developing in vitro tissue models for studying disease progression and drug development. The objective of the current study was to evaluate the influence of flow driven shear stress on the viability of cultured cells inside the luminal wall of a serpentine network. Fluid-structure interaction was modeled using COMSOL Multiphysics for representing the elasticity of the serpentine wall. Experimental analysis of the serpentine model was performed on the basis of a desirable inlet flow boundary condition for which the most homogeneously distributed wall shear stress had been obtained from numerical study. A blend of Gelatin-methacryloyl (GelMA) and PEGDA200 PhotoInk was used as a bioink for printing the serpentine network, while facilitating cell growth within the pores of the gelatin substrate. Human umbilical vein endothelial cells were seeded into the channels of the network to simulate the blood vessels. A Live-Dead assay was performed over a period of 14 days to observe the cellular viability in the printed vascular channels. It was observed that cell viability increases when the seeded cells were exposed to the evenly distributed shear stresses at an input flow rate of 4.62 mm/min of the culture media, similar to that predicted in the numerical model with the same inlet boundary condition. It leads to recruitment of a large number of focal adhesion point nodes on cellular membrane, emphasizing the influence of such phenomena on promoting cellular morphologies.

Towards the Preparation of a Hydrogel from Lyophilisates of the Aloe arborescens Aqueous Extract

Aloe gel is a medicinal raw material with proven pharmacological activity. The health-promoting properties of other species of Aloe upon topical application prompted us to develop a formulation for the topical application of A. arborescence species. As a result of the gel preparation from the aqueous lyophilized extracts of three-year-old leaves of A. arborescence, no changes in the composition of the content of aloins A and aloenin A were found. The potential to neutralize free radicals was tested using DPPH and CUPRAC techniques, which confirmed the anti-radical activity of the lyophilisate. Screening of the inhibition of enzymes, the hyperactivity of which is associated with adverse changes in the skin of a pro-inflammatory nature, was performed. Importantly, using the PAMPA SKIN model, the possibility of the penetration of selected extract compounds (aloin A and aloenin A) through the skin was proven. Then, two formulations were prepared based on sodium alginate and hydroxypropyl methylcellulose (HPMC) and the hydrogels were characterized (rheological analysis, drug release profiles, permeability, and stability studies). HPMC-based hydrogel was the one with a targeted release of active substances and greater stability. Aloe arborescens hydrogel matrices seem to be a promising treatment strategy for inflammatory surface damage based on “green technology” at the stage of extract preparation and development of the drug form for topical application.

Rheological Behavior and Dynamic Mechanical Properties for Interpretation of Layer Adhesion in FDM 3D Printing

Commercial filaments of poly(lactic acid) (PLA) composites with particulate filler, carbon fiber, and copper powder with different contents were fabricated by FDM 3D printing in XZ-direction at bed temperatures of 45 °C and 60 °C. The effects of additives and bed temperatures on layer adhesion, fracture behavior, and mechanical performance of the PLA composites 3D printing were evaluated. Rheological properties informed viscous nature of all filaments and interface bonding in the PLA composites, which improved printability and dimensional stability of the 3D printing. Crystallinity of the PLA composites 3D printing increased with increasing bed temperature resulting in an improvement of storage modulus, tensile, and flexural properties. On the contrary, the ductility of the 3D printing was raised when printed at low bed temperature. Dynamic mechanical properties, the degree of entanglement, the adhesion factor, the effectiveness coefficient, the reinforcing efficiency factor, and the Cole–Cole analysis were used to understand the layer adhesion, and the interfacial interaction of the composites as compared to the compression molded sheets. SEM images revealed good adhesion between the additives and the PLA matrix. However, the additives induced faster solidification and showed larger voids in the 3D printing, which indicated lower layer adhesion as compared to neat PLA. It can be noted that the combination of the additives and the optimized 3D printing conditions would be obtain superior mechanical performance even layer adhesion has been restricted.