Viscoelastic and shear-thinning effects of aqueous exopolymer solution on disk and sphere settling

Self-Healing Hydrogel Resulting from the Noncovalent Interaction between Ropivacaine and Low-Molecular-Weight Gelator Sodium Deoxycholate Achieves Stable and Endurable Local Analgesia in Vivo

Regional analgesia based on the local anesthetic ropivacaine plays a crucial role in postoperative pain management and recovery; however, the short duration of analgesia limits its clinical potential. Various drug delivery systems such as microparticles and lipid carriers have been used to prolong the analgesic effect, yet most of them are prone to abrupt release from the site of administration or have poor analgesic effects of less than 48 h, which fail to meet the needs of postoperative analgesia. In this study, a low-molecular-weight gelator sodium deoxycholate-based hydrogel loaded with ropivacaine (DC-ROP gel) was designed for long-acting analgesia. The noncovalent interaction between ropivacaine and sodium deoxycholate helps to improve the stability and sustained release performance of the gel. This internal drug-binding hydrogel also avoids experiencing the burst release effect commonly seen in polymer hydrogels previously reported for the slow release of local anesthetics. DC-ROP gel exhibited the dual advantages of self-healing after compression and long-term controlled release. In mice with inflammatory pain, DC-ROP gel achieved peripheral nerve block for more than 1 week after a single injection. Histological and blood biochemical analyses confirmed that the DC-ROP gel did not produce systemic toxicity, and cytotoxicity experiments demonstrated that the DC-ROP gel resulted in low irritation. These results suggest that DC-ROP gel provides a promising strategy for local anesthetics in long-term postoperative pain management, broadening the potential of bile salt-based low-molecular-weight hydrogels for drug delivery.

Characterization of Liquid Dosage Forms of Atenolol and Enalapril Maleate for Oral and Enteral Feeding Administration

The limited availability of pharmaceutical formulations tailored for cardiovascular diseases in both pediatric and geriatric populations generates the need for compounded dosage forms to guarantee precise dosing and medication adherence. This study aimed to analyze the physicochemical properties and stability of formulations of atenolol and enalapril maleate prepared with a proprietary oral vehicle, SuspendIt®. To this end, palatability, injectability, pH, rheological behavior, and physical, microbiological, and chemical stability over a 180-day storage period at 25 °C and 5 °C were evaluated. Injectability tests confirmed the suitable use of both formulations for administration through enteral feeding tubes. By using a potentiometric electronic tongue, it was confirmed that the SuspendIt® vehicle effectively served as a bitter-blocking strategy for atenolol and enalapril maleate. Adequate stability throughout the storage period was confirmed in terms of the mechanical properties, pH, and effectiveness of the preservative system. The atenolol concentration remained above 90% of the initial amount, while the concentration of enalapril maleate decreased to 88% after 90 days of storage at 25 °C. In summary, the atenolol formulation maintained suitable chemical, physical, and microbiological stability after 180 days at both storage temperatures, while the enalapril maleate formulation remained stable up to 60 days at 25 °C and for 180 days at 5 °C.

Photo-/thermo-responsive bioink for improved printability in extrusion-based bioprinting

Extrusion-based bioprinting has demonstrated significant potential for manufacturing constructs, particularly for 3D cell culture. However, there is a greatly limited number of bioink candidates exploited with extrusion-based bioprinting, as they meet the opposing requirements for printability with indispensable rheological features and for biochemical functionality with desirable microenvironment. In this study, a blend of silk fibroin (SF) and iota-carrageenan (CG) was chosen as a cell-friendly printable material. The SF/CG ink exhibited suitable viscosity and shear-thinning properties, coupled with the rapid sol-gel transition of CG. By employing photo-crosslinking of SF, the printability with Pr value close to 1 and structural integrity of the 3D constructs were significantly improved within a matter of seconds. The printed constructs demonstrated a Young's modulus of approximately 250 kPa, making them suitable for keratinocyte and myoblast cell culture. Furthermore, the high cell adhesiveness and viability (maximum >98%) of the loaded cells underscored the considerable potential of this 3D culture scaffold applied for skin and muscle tissues, which can be easily manipulated using an extrusion-based bioprinter.

Solving urban water microplastics with bacterial cellulose hydrogels: Leveraging predictive computational models

The prevalence of microplastics (MPs) in both urban and aquatic ecosystems is concerning, with wastewater treatment plants being considered one of the major sources of the issue. As the focus on developing sustainable solutions increases, unused remnants from bacterial cellulose (BC) membranes were ground to form BC hydrogels as potential bioflocculants of MPs. The influence of operational parameters such as BC:MPs ratio, hydrogel grinding, immersion and mixing time, temperature, pH, ionic strength, and metal cations on MPs flocculation and dispersion were evaluated. A response surface methodology based on experimental data sets was computed to understand how these parameters influence the flocculation process. Further, both the BC hydrogel and the hetero-aggregation of MPs were characterised by UV-Vis, ATR-FTIR, IGC, water uptake assays, fluorescence, and scanning electron microscopy. These highlights that the BC hydrogel would be fully effective at hetero-aggregating MPs in naturally-occurring concentrations, thereby not constituting a limiting performance factor for MPs' optimal flocculation and aggregation. Even considering exceptionally high concentrations of MPs (2 g/L) that far exceed naturally-occurring concentrations, the BC hydrogel was shown to have elevated MPs flocculation activity (reaching 88.6%: 1.77 g/L). The computation of bioflocculation activity showed high reliability in predicting flocculation performance, unveiling that the BC:MPs ratio and grinding times were the most critical variables modulating flocculation rates. Also, short exposure times (5 min) were sufficient to drive robust particle aggregation. The microporous nature of the hydrogel revealed by electron microscopy is the likely driver of strong MPs bioflocculant activity, far outperforming dispersive commercial bioflocculants like xanthan gum and alginate. This pilot study provides convincing evidence that even BC remainings can be used to produce highly potent and circular bioflocculators of MPs, with prospective application in the wastewater treatment industry.

Enhancement of Self-Healing Efficacy of Conductive Nanocomposite Hydrogels by Polysaccharide Modifiers

The proper design of a polysaccharide/hydrocolloid modifier significantly affects the conductivity, self-healing, and viscoelastic properties of nanocomposite hydrogels. Due to the presence of different functional groups, these hydrogels can participate in the covalent, hydrogen and dynamic bonding of a system. The improvement of interactions in this system can lead to the development of high-performance nanocomposite hydrogels. In this study, resilient, self-healing and self-adhesive conductive nanocomposite hydrogels were produced by multiple and diverse coordination connections between various polysaccharide-based modifiers (Arabic gum, sodium carboxymethyl cellulose, and xanthan), the poly(vinyl alcohol) (PVA) network and different graphene-based fillers. Graphene nanoplatelets (GNP), activated carbon black (ACB), and reduced graphene oxide (rGO) have distinct functionalized surfaces, which were analyzed by X-ray photoelectron spectroscopy (XPS). Furthermore, the introduction of fillers balanced the hydrogels' viscoelastic properties and electrical conductivity, providing the hydrogels with resilience, improved electrical conductivity, and extreme stretchability (5000%). The self-healing properties were analyzed using time-dependent measurements in a shear strain mode using an RSO Rheometer. The improvement in electrochemical and conductivity properties was confirmed by electrochemical impedance spectroscopy (EIS). The obtained conductive nanocomposite hydrogels design opens new possibilities for developing high-performance polysaccharide-based hydrogels with wearable electrical sensors and healthcare monitoring applications.

Drop-of-sample rheometry of biological fluids by noncontact acoustic tweezing spectroscopy

Knowledge of rheological properties, such as viscosity and elasticity, is necessary for efficient material processing and transportation as well as biological analysis. Existing rheometers operate with large sample volume and induce sample contact with container or device walls, which are inadequate for rheological analysis of sensitive fluids limited in availability. In this work, we introduce acoustic tweezing spectroscopy (ATS), a novel noncontact rheological technique that operates with a single 4-6 μl drop of fluid sample. In ATS, a sample drop is acoustically levitated and then exposed to a modulated acoustic signal to induce its forced oscillation. The time-dependent sample viscosity and elasticity are measured from the resulting drop response. The ATS measurements of polymeric solutions (dextran, xanthan gum, gelatin) agree well with previously reported data. The ATS predicts that the shear viscosity of blood plasma increases from 1.5 cP at 1.5 min of coagulation onset to 3.35 cP at 9 min, while its shear elastic modulus grows from a negligible value to 10.7 Pa between 3.5 min and 6.5 min. Coagulation increases whole blood viscosity from 5.4 cP to 20.7 cP and elasticity from 0.1 Pa to 19.2 Pa at 15 min. In summary, ATS provides the opportunity for sensitive small-volume rheological analysis in biomedical research and medical, pharmaceutical, and chemical industries.

Evaluating the influence of particle morphology and density on the viscosity and injectability of a novel long-acting local anesthetic suspension

Proper pain management is well understood to be one of the fundamental aspects of a healthy postoperative recovery in conjunction with mobility and nutrition. Approximately, 10% of patients prescribed opioids after surgery continue to use opioids in the long-term and as little as 10 days on opioids can result in addiction. In an effort to provide physicians with an alternative pain management technique, this work evaluates the material properties of a novel local anesthetic delivery system designed for controlled release of bupivacaine for 72 hours. The formulation utilizes solid-lipid microparticles that encapsulate the hydrophobic molecule bupivacaine in its free-base form. The lipid microparticles are suspended in a non-crosslinked hyaluronic acid hydrogel, which acts as the microparticle carrier. Two different particle manufacturing techniques, milling and hot homogenization, were evaluated in this work. The hot homogenized particles had a slower and more controlled release than the milled particles. Rheological techniques revealed that the suspension remains a viscoelastic fluid when loaded with either particle type up to 25% (w/v) particles densities. Furthermore, the shear thinning properties of the suspension media, hyaluronic acid hydrogel, were conserved when bupivacaine-loaded solid-lipid microparticles were loaded up to densities of 25% (w/v) particle loading. The force during injection was measured for suspension formulations with varying hyaluronic acid hydrogel concentrations, particle densities, particle types and particle sizes. The results indicate that the formulation viscosity is highly dependent on particle density, but hyaluronic acid hydrogel is required for lowering injection forces as well as minimizing clogging events.

Wound dressing adherence: a review

Wound dressing adherence is an important problem that is frequently encountered in wound care, and is associated with both clinical and economic burdens. However, only a few review articles have focused on this issue. The objective of this review was to present a comprehensive discussion of wound dressing adherence, including the mechanism of dressing adherence, adverse consequences (clinical burdens and economic burdens), factors affecting adherence (dressing-, patient- and wound-related factors, and factors related to the wound care procedure), tests to assess dressing adherence (in vitro assay, in vivo assay and clinical trials), and reduction of wound adherence (modification of dressing adherence and special care in particular patients). Accordingly, this review article emphasises an awareness of dressing adherence, and is intended to be an informative source for the development of new dressings and for wound management.

Ag metal interconnect wires formed by pseudoplastic nanoparticles fluid imprinting lithography with microwave assistant sintering

Nanoimprint technology has the advantages of low cost, high precision, high fidelity and high yield. The metal nanoparticle fluid is non-Newtonian fluid, which is used as the imprint transfer medium to realize high fidelity of pattern because of its shear thinning effect. In order to functionalize the metal nanoparticles microstructure, the subsequent sintering step is required to form a metal interconnect wire. Metal interconnect wire with fewer grain boundaries and fewer holes have excellent mechanical and electronic properties. In this paper, the pseudoplastic metal nanoparticle fluid was formed by Ag nanoparticle and precursor solution, and then the thermal diffusion process was completed by microwave sintering after interconnects were embossed. The influence of microwave and thermal atmosphere on the microstructure and performance of Ag Interconnect wires was analyzed and discussed, and the Ag Interconnect wires performance was determined under the influence of time and temperature parameters. In our experiments, the interconnects after microwave sintering can achieve 39% of the conductivity of bulk silver. The microwave sintering module might be integrated as the heat treatment module of the metal micro/nano pattern directly imprint lithography.

Osmotic-controlled release oral tablets: technology and functional insights

In recent years, oral osmotic tablets have sparked a therapeutic paradigm for controlled-release dosage forms due to their intrinsic insensitivity to physiological and physicochemical factors. Despite these benefits, the design of an optimal osmotic technology is precluded by various challenges. These limitations include manufacturing complexity, the lack of understanding of the functional mechanics, and inadequate optimization for the desired bio-performance. This paper systematically reviews the development of an osmotic-driven drug delivery system and the strategy for a zero-order release profile with an emphasis on swellable core technology. We discuss the applicability of the various types of osmotic tablets, their suitability to specific needs, and factors that drive the technology selection. Finally, we review the challenges, opportunities, and future perspectives associated with osmotic tablets.

Effect of Physical Characteristics and Hydrodynamic Conditions on Transport and Deposition of Microplastics in Riverine Ecosystem

Microplastic disposal into riverine ecosystems is an emergent ecological hazard that mainly originated from land-based sources. This paper presents a comprehensive review on physical processes involved in microplastics transport in riverine ecosystems. Microplastic transport is governed by physical characteristics (e.g., plastic particle density, shape, and size) and hydrodynamics (e.g., laminar and turbulent flow conditions). High-density microplastics are likely to prevail near riverbeds, whereas low-density particles float over river surfaces. Microplastic transport occurs either due to gravity-driven (vertical transport) or settling (horizontal transport) in river ecosystems. Microplastics are subjected to various natural phenomena such as suspension, deposition, detachment, resuspension, and translocation during transport processes. Limited information is available on settling and rising velocities for various polymeric plastic particles. Therefore, this paper highlights how appropriately empirical transport models explain vertical and horizontal distribution of microplastic in riverine ecosystems. Microplastics interact, and thus feedback loops within the environment govern their fate, particularly as these ecosystems are under increasing biodiversity loss and climate change threat. This review provides outlines for fate and transport of microplastics in riverine ecosystems, which will help scientists, policymakers, and stakeholders in better monitoring and mitigating microplastics pollution.

Review of Single Bubble Motion Characteristics Rising in Viscoelastic Liquids

The emphasis of this review is to discuss three peculiar phenomena of bubbles rising in viscoelastic fluids, namely, the formation of a cusp, negative wake, and velocity jump discontinuity, and to highlight the possible future directions of the subject. The mechanism and influencing factors of these three peculiar phenomena have been discussed in detail in this review. The evolution of the bubble shape is mainly related to the viscoelasticity of the fluid. However, the mechanisms of the two-dimensional cusp, tip-streaming, “blade-edge” tip, “fish-bone” tip, and the phenomenon of the tail breaking into two different threads, in some special viscoelastic fluids, are not understood clearly. The origin of the negative wake behind the bubbles rising in a viscoelastic fluid can be attributed to the synergistic effect of the liquid-phase viscoelasticity, and the bubbles are large enough; thus, leading to a very long relaxation time taken by the viscoelastic stresses. For the phenomenon of bubble velocity jump discontinuity, viscoelasticity is the most critical factor, and the cusp of the bubbles and the surface modifications play only ancillary roles. It has also been observed that a negative wake does not cause velocity jump discontinuity.

Neat and Aqueous Polyelectrolytes under a Steady-Shear Flow

Materials enabling impact-energy absorption of high-velocity projectiles are of great interest for applications like aerospace. In such a frame, shear thickening fluids were found very useful. Here, we investigated nanorheological properties of neat and aqueous polyelectrolytes of low molecular weights containing poly([2-(methacryloyloxy) ethyl] trimethyl ammonium) as polycations and poly(acrylamide-co-acrylic acid) as polyanions. Results were compared with pure water. We employed nonequilibrium molecular dynamics with the SLLOD algorithm to compute the viscosity at various shear rates. Systems containing polyelectrolytes exhibit shear thickening. The analysis of molecular configurations revealed a strong disruption of the ionic structure and more clusters with smaller sizes on increasing the shear rate. Potential energies showed that shear thickening originates from an increase in intramolecular and van der Waals interactions resulting from the increasing difficultly of polyelectrolyte-based systems to relax at high shear rates. Our method and findings underscore the importance of accounting for the molecular scale in the design of materials absorbing the impact energy efficiently.

Structure-property relationship of a soft colloidal glass in simple and mixed flows

HYPOTHESIS

Under specific conditions, rod-like cellulose nanocrystals (CNC) can assemble into structurally ordered soft glasses (SGs) with anisotropy that can be controlled by applying shear. However, to achieve full structural control of SGs in real industrial processes, their response to mixed shear and extensional kinematics needs to be determined. We hypothesise that by knowing the shear rheology of the CNC-based soft glass and adopting a suitable constitutive model, it is possible to predict the structure-property relationship of the SG under mixed flows.

EXPERIMENTS

We use an aqueous suspension with 2 wt% CNC at 25 mM NaCl to form a structurally ordered SG composed of a CNC network containing nematic domains. We combine rheometry and microfluidic experiments with numerical simulations to study the flow properties of the SG in shear, extension, and mixed flow conditions. Extensional flow is investigated in the Optimised Shape Cross-slot Extensional Rheometer (OSCER), where the SG is exposed to shear-free planar elongation. Mixed flow kinematics are investigated in a benchmark microfluidic cylinder device (MCD) where the SG flows past a confined cylinder in a microchannel.

FINDINGS

The SG in the MCD displays a velocity overshoot (negative wake) and a pronounced CNC alignment downstream of the cylinder. Simulations using the thixotropic elasto-visco-plastic (TEVP) model yield near quantitative agreement of the velocity profiles in simple and mixed flows and capture the structural fingerprint of the material. Our results provide a comprehensive link between the structural behaviour of a CNC-based SG and its mechanistic properties, laying foundations for the development of functional, built-to-order soft materials.

Influence of pycnocline on settling behaviour of non-spherical particle and wake evolution

Settling of non-spherical particles in a stratified fluid exhibits complex dynamics in a low-to-moderate inertia regime. Although this process is involved in a wide variety of phenomena in natural fluid systems, its fundamental mechanisms are still unexplored. Understanding of particle settling in microscale is particularly important to explain challenging problems associated with ecological and biogeochemical processes in the ocean due to the delayed settling of particulate matter at pycnoclines. Here, I explore interactions between disk-shaped particles and a stratified fluid with a density transition. By laboratory experiments, I demonstrate that the settling dynamics of the disk crossing a density transition are tightly coupled with the wake structure evolution, and I observe for the first time in a two-layer ambient configuration a bell-shaped structure that forms on a jet after the wake has detached from the particle. Furthermore, I identify hydrodynamic conditions for the variations of settling velocity and particle orientation instabilities. These findings shed light on particle settling mechanisms necessary to explain dynamics of marine particles such as plankton, faecal pellets, and microplastics and may improve the estimation methods of sedimentation processes in various areas of earth sciences and engineering.