The microstructure of Carbopol in water under static and flow conditions and its effect on the yield stress

Hyaluronan-Cholesterol nanogels embedding betamethasone for the treatment of skin inflammatory conditions

Topical application of the glucocorticoid betamethasone (BM) is a common treatment for inflammatory-related skin diseases, such as psoriasis. However, enhancing its bioavailability remains challenging due to poor skin permeability. Herein, we developed and evaluated hyaluronan-cholesterol (HACH) based nanohydrogel systems (NHs) and NHs-Carbopol formulation for dermal delivery of BM. Various parameters were investigated including particle size, surface charge, encapsulation efficiency, in vitro drug release kinetics and stability. The HACH-based NHs demonstrated high encapsulation efficiency, with apparent solubility improved up to 9-fold, small size (∼190 nm) and good stability at 4 ℃ and during long-term storage. Besides, the NHs-Carbopol formulation exhibited excellent rheological properties and an occlusive effect suitable for cutaneous application. Both in-vitro (using Strat-M® membrane) and ex-vivo (using pig ear skin) permeation studies revealed that these formulations significantly improved skin permeation and drug retention in the deeper layers of the epidermis and dermis, making it advantageous for the topical delivery of BM in psoriasis treatment. Moreover, the NHs system demonstrated potential anti-psoriatic activity by downregulating the proinflammatory cytokines in vitro in human keratinocytes (HaCaT cell line) and in an ex vivo 3D skin tissue model (EpiDerm-FT™).

Capillary Flow-MRI: Quantifying Micron-Scale Cooperativity in Complex Dispersions

Strongly confined flow of particulate fluids is encountered in applications ranging from three-dimensional (3D) printing to the spreading of foods and cosmetics into thin layers. When flowing in constrictions with gap sizes, w, within 102 times the mean size of particles or aggregates, d, structured fluids experience enhanced bulk velocities and inhomogeneous viscosities, as a result of so-called cooperative, or nonlocal, particle interactions. Correctly predicting cooperative flow for a wide range of complex fluids requires high-resolution flow imaging modalities applicable in situ to even optically opaque fluids. To this goal, we here developed a pressure-driven high-field magnetic resonance imaging (MRI) velocimetry platform, comprising a pressure controller connected to a capillary. Wall properties and diameter could be modified respectively as hydrophobic/hydrophilic, or within w ∼ 100-540 μm. By achieving a high spatial resolution of 9 μm, flow cooperativity length scales, ξ, down to 15 μm in Carbopol with d ∼ 2 μm could be quantified by means of established physical models with an accuracy of 13%. The same approach was adopted for a heterogeneous fat crystal dispersion (FCD) with d and ξ values up to an order of magnitude higher than those for Carbopol. We found that for strongly confined flow of Carbopol in the 100 μm capillary, ξ is independent of flow conditions. For the FCD, ξ increases with gap size and applied pressures over 0.25-1 bar. In both samples, nonlocal interactions span domains up to about 5-8 particles but, at the highest confinement degree explored, ∼8% for FCD, domains of only ∼2 particles contribute to cooperative flow. The developed flow-MRI platform is easily scalable to ultrahigh field MRI conditions for chemically resolved velocimetric measurements of, e.g., complex fluids with anisotropic particles undergoing alignment. Future potential applications of the platform encompass imaging extrusion under confinement during the 3D printing of complex dispersions or in in vitro vascular and perfusion studies.

Rheology of Gels and Yielding Liquids

In this review, today's state of the art in the rheology of gels and transition through the yield stress of yielding liquids is discussed. Gels are understood as soft viscoelastic multicomponent solids that are in the incomplete phase separation state, which, under the action of external mechanical forces, do not transit into a fluid state but rupture like any solid material. Gels can "melt" (again, like any solids) due to a change in temperature or variation in the environment. In contrast to this type of rheology, yielding liquids (sometimes not rigorously referred to as "gels", especially in relation to colloids) can exist in a solid-like (gel-like) state and become fluid above some defined stress and time conditions (yield stress). At low stresses, their behavior is quite similar to that of permanent solid gels, including the frequency-independent storage modulus. The gel-to-sol transition considered in colloid chemistry is treated as a case of yielding. However, in many cases, the yield stress cannot be assumed to be a physical parameter since the solid-to-liquid transition happens in time and is associated with thixotropic effects. In this review, special attention is paid to various time effects. It is also stressed that plasticity is not equivalent to flow since (irreversible) plastic deformations are determined by stress but do not continue over time. We also discuss some typical errors, difficulties, and wrong interpretations of experimental data in studies of yielding liquids.

Bubble Rupture and Bursting Velocity of Complex Fluids

We analyzed bubble rupture and hole opening dynamics in a non-Newtonian fluid by investigating the retraction process of thin films after inflation at different blowing rates. The experiments were modeled through a dimensional analysis, with the aim of establishing a general approach on the bubble rupture dynamics and discerning the role of viscous, elastic, surface, and inertial forces on the opening velocity, according to the nature of the specific fluid. A new mathematical model, which includes all possible contributions to the hole opening dynamics, was proposed, to the best of our knowledge for the first time. The experimental evidence on the opening velocity as a function of the inflation rate was found to be in good agreement with the prediction of the model. The sensitivity of our modeling was tested by comparing our results with the existing models of retracting velocity.

The Use of Polymer Blends in the Treatment of Ocular Diseases

The eye is an organ with limited drug access due to its anatomical and physiological barriers, and the usual forms of ocular administration are limited in terms of drug penetration, residence time, and bioavailability, as well as low patient compliance. Hence, therapeutic innovations in new drug delivery systems (DDS) have been widely explored since they show numerous advantages over conventional methods, besides delivering the content to the eye without interfering with its normal functioning. Polymers are usually used in DDS and many of them are applicable to ophthalmic use, especially biodegradable ones. Even so, it can be a hard task to find a singular polymer with all the desirable properties to deliver the best performance, and combining two or more polymers in a blend has proven to be more convenient, efficient, and cost-effective. This review was carried out to assess the use of polymer blends as DDS. The search conducted in the databases of Pubmed and Scopus for specific terms revealed that although the physical combination of polymers is largely applied, the term polymer blend still has low compliance.

Parallel-Disk Viscometry of a Viscoplastic Hydrogel: Yield Stress and Other Parameters of Shear Viscosity and Wall Slip

The rheology, i.e., the flow and deformation properties, of hydrogels is generally a very important consideration for their functionality. However, the accurate characterization of their rheological material functions is handicapped by their ubiquitous viscoplasticity and associated wall slip behavior. Here a parallel-disk viscometer was used to characterize the shear viscosity and wall slip behavior of a crosslinked poly(acrylic acid) (PAA) carbomer hydrogel (specifically Carbopol^® at 0.12% by weight in water). It was demonstrated that parallel-disk viscometry, i.e., the steady torsional flow in between two parallel disks, can be used to unambiguously determine the yield stress and other parameters of viscoplastic constitutive equations and wall slip behavior. It was specifically shown that torque versus rotational speed information, obtained from parallel-disk viscometry, was sufficient to determine the yield stress of a viscoplastic hydrogel. Additional gap-dependent data from parallel-disk viscometry could then be used to characterize the other parameters of the shear viscosity and wall slip behavior of the hydrogel. To investigate the accuracy of the parameters of shear viscosity and apparent wall slip that were determined, the data were used to calculate the torque values and the velocity distributions (using the lubrication assumption and parallel plate analogy) under different flow conditions. The calculated torques and velocity distributions of the hydrogel agreed very well with experimental data collected by Medina-Bañuelos et al., 2021, suggesting that the methodologies demonstrated here provide the means necessary to understand in detail the steady flow and deformation behavior of hydrogels. Such a detailed understanding of the viscoplastic nature and wall slip behavior of hydrogels can then be used to design and develop novel hydrogels with a wider range of applications in the medical and other industrial areas, and for finding optimum conditions for their processing and manufacturing.

Mechanistic understanding of the performance of personalized 3D-printed cardiovascular polypills: A case study of patient-centered therapy

The 3D printing has become important in drug development for patient-centric therapy by combining multiple drugs with different release characteristics in a single polypill. This study explores the critical formulation and geometric variables for tailoring the release of Atorvastatin and Metoprolol as model drugs in a polypill when manufactured via pressure-assisted-microextrusion 3D printing technology. The effects of these variables on the extrudability of printing materials, drug release and other quality characteristics of polypills were studied employing a definitive screening design. The extrudability of printing materials was evaluated in terms of flow pressure, non-recoverable strain, compression rate, and elastic/plastic flow. The extrudability results helped in defining an operating space free of printing defects. The Atorvastatin compartment of polypill consisted of mesh-shaped layers while Metoprolol compartment consisted of a core surrounded by a release controlling shell with a hydrophobic septum between the two compartments. The results indicated that both the formulation and geometric variables govern the drug release of the polypill. Specifically, the use of HPMC E3 matrix, and a 2 mm distance between the strands at a weaving angle of 90° were critical in achieving the desired immediate-release profile of Atorvastatin. The core and shell design primarily determined the desired extended-release profile of Metoprolol. The carbopol and HPMC K100 concentration of 1% in the core and 10% in the shell and the number of shell layers in Metoprolol compartment were critical for achieving the desired Metoprolol dissolution. Polymer and Metoprolol content of the shell and shell-thickness affected the mechanical strength of the polypills. In conclusion, the 3D printing provides the flexibility for independently tailoring the release of different drugs in the same dosage form for patient centric therapy, and both the formulation and geometric parameters need to be optimized to achieve desired drug release.

Label-free tracking of whole-cell response on RGD functionalized surfaces to varied flow velocities generated by fluidic rotation

Fluidic flow plays important roles in colloid and interface sciences. Measuring adsorption, aggregation processes and living cell behavior under a fluidic environment with varied flow velocities in a parallel and high-throughput manner remains to be a challenging task. Here a method is introduced to monitor cell response to well-defined flow with varied velocities over an array of label-free resonant waveguide grating (RWG) based optical biosensors. The arrangement consists of a circular well with an array of biosensors at the bottom surface. By rotating the liquid over the biosensor array using a magnetic stirrer bar, flow velocities from zero to a predefined maximum can be easily established over different locations within the biosensor array as characterized in detail by numerical simulations. Cell adhesion and detachment measurements on an Arg-Gly-Asp (RGD) peptide functionalized surface were performed to demonstrate i) measurements at a wide range of simultaneous flow velocities over the same interface; ii) the possibility of parallel measurements at the same flow conditions in one run; and iii) the simple tuning of the employed range of flow velocities. Our setup made it possible to analyze the magnitude and rate of cell detachment at various flow velocities in parallel and determine the critical velocity and force where cells start to detach from the RGD motif displaying biomimetic surface. Furthermore, cellular response to simultaneous mechanical (flow) and chemical stimulation was also investigated using trypsin as a model. This study opens a new possibility to investigate interface phenomena under predefined and conveniently varied flow conditions.

Universal G' ∼ L-3 Law for the Low-Frequency Shear Modulus of Confined Liquids

Liquids confined to sub-millimeter scales have remained poorly understood. One of the most striking effects is the large elasticity revealed using good wetting conditions, which grows upon further decreasing the confinement length, L. These systems display a low-frequency shear modulus in the order of 1-10³ Pa, contrary to our everyday experience of liquids as bodies with a zero low-frequency shear modulus. While early experimental evidence of this effect was met with skepticism and abandoned, further experimental results and, most recently, a new atomistic theoretical framework have confirmed that liquids indeed possess a finite low-frequency shear modulus G', which scales with the inverse cubic power of confinement length L. We show that this law is universal and valid for a wide range of materials (liquid water, glycerol, ionic liquids, non-entangled polymer liquids, isotropic liquids crystals). Open questions and potential applications in microfluidics mechanochemistry, energy, and other fields are highlighted.

Rheological behavior study and its significance in the assessment of application properties and physical stability of phytosome loaded hydrogels

Phytosomes are amphiphilic molecular complexes of substances of plant origin and phospholipids that are considered as active ingredients of dermopharmaceutical and cosmetic formulations of potentially improved efficiency. The study aim was the formulation of carbomer hydrogels with commercially available phytosomes of escin (Escin ß-Sitosterol Phytosome®) (EP) and 18-ß glycyrrhetinic acid (18-ß Glycyrrhetinic Acid Phytosome®) (GP) and evaluation of their application properties and real-time physical stability. Phytosomes incorporation did not significantly affect pH of the hydrogels, which was acceptable for cutaneous application. However, these hydrogels had significantly different organoleptic properties (opaque and softer consistency) compared to the hydrogel without active substance (C) and the hydrogels with pure active substances (E and G) used for comparison. The values of maximum and minimum apparent viscosity and yield stress were significantly lower in phytosome-loaded hydrogels. The results of oscillatory rheological analysis indicated that viscous character prevails in EP and GP hydrogels (elastic modulus (G')˂viscous modulus (G")), while in hydrogels C, E and G elastic properties were more pronounced (G'˃G"). Escin phytosome had greater influence on carbomer gel network strength. Phytosome-loaded hydrogels were physically stable during 24 months of storage under ambient conditions, although the rheological analysis also indicated a potential risk of sedimentation.