Semisolid Systems Research Articles

The effect of Amazonian andiroba oil on antioxidant activity, mechanical, rheological and skin permeation properties of environmentally responsive emulgels

Emulgels are semi-solid systems that can improve the bioavailability of bioactive agents by combining the properties of gels and emulsions in a stable way. The use of bioadhesive systems by combining different polymers can prolong the release of various bioactive agents, such as the oil of Carapa guianensis (andiroba oil; AO), which has been of interest to researchers for years due to its antioxidant properties, antitumor, antibacterial and anti-inflammatory activity. Therefore, the aim of the present work was to evaluate the influence of different amounts of AO on the physicochemical properties of thermoresponsive bioadhesive emulgels composed of Carbopol 974 P® and poloxamer 407. The mechanical, rheological, bioadhesive, skin permeation and antioxidant activity characteristics were analyzed. AO and emulgel systems showed a potential antioxidant effect via different mechanisms. The formulations also displayed important results in terms of textural mechanical, bioadhesiveness, rheological and skin retention characteristics. However, F1 showed more promising results than F2, with differences mainly in softness, bioadhesion and rheology. These results ensure favorable properties for potential use as a topical semi-solid formulation and for therapeutic applications. However, additional studies are necessary to explore their in vitro biological and in vivo performance.

β-carotene and resveratrol loaded glycerol monostearate-based oleogels: Physicochemical characterization at low gelation concentrations

Oleogels are semi-solid systems that can function both as replacers of trans and saturated fats and/or as carriers of lipophilic bioactive compounds. However, bioactive compounds can affect the structure of the oleogel matrix and this effect depends on the properties of such compounds. Therefore, the aim of this study was to develop oleogels loaded with β-carotene (BC) or resveratrol (R), with low concentrations of glycerol monostearate (GMS, 2–5 wt%) and sunflower oil as organic solvent. The gels were characterized by polarized light microscopy, rheological measurements, differential scanning calorimetry, oil binding capacity and Fourier transform infrared spectroscopy. At higher GMS concentrations, stronger oleogels and higher temperatures associated with transitions (sol–gel/gel–sol and crystallization/melting) were observed. The incorporation of bioactive compounds modified the gelation behavior. BC weakened the oleogel structure during the transient molecular organization of GMS, whereas R increased the dynamic moduli. BC also caused slight oil release at lower concentrations, while R improved retention. The high hydrophobicity of BC may be disturbing the solubility balance of the system, while R has phenolic hydroxyl groups that may strengthen hydrogen bonds. However, there were no considerable changes in mechanical properties after storage. We hypothesize that the molecular organization of GMS over time may be masking the modifications that bioactive compounds cause in mechanical properties. In fact, changes in the structure were revealed, as the addition of BC or R changed the morphology of the three-dimensional network crystals. Thus, the results can contribute to the rational choice of system components using low concentrations of oleogelator, as the composition of the bioactive compound exerts influence on the modulation of lipid matrices.

Formulation and Development of herbal Gel containing Cannabis sativa and Azadirachta indica leaves extract for Anti-inflammatory and Anti-bacterial activity

Bacteria are everywhere and play a crucial part in the maintenance of germs that cause illness and disease. Skin infections are anticipated to occur at a rate of 24.6 per 1000 people yearly. The treatment of any skin infections primarily consists of any necessary surgical debridement; nevertheless, injecting an antibiotic directly into a wound has several potential benefits. Topical antibiotic treatment and wound care are recommended. The administration of a therapy may allow treatment with medicines that are not yet available (or safe) for systemic therapy. Gels are semi-solid systems having qualities intermediate between solids and liquids, in which the movement of the dispersing medium is constrained by an interlacing three-dimensional network of particles or solvated macromolecules of the dispersed phase. This study aimed to explore the potential of Cannabis sativa, Azadirachta indica leaves extract as anti-inflammatory and antibacterial agents. The formulation has been developed by solvent casting method. The experiment was conducted using various techniques to measure the effectiveness of each substance individually and in combination. Results showed that Cannabis sativa and Azadirachta indica leaves extract both had strong anti-inflammatory properties, while glycerol demonstrated significant antibacterial activity. When combined, these substances exhibited enhanced anti-inflammatory and antibacterial effects, indicating potential for their use in pharmaceutical and medical applications. Overall, this study highlights the importance of exploring natural products for their therapeutic potential and provides insight into the potential of these substances as novel anti-inflammatory and antibacterial agents.

Metronidazole Modified-Release Therapy Using Two Different Polymeric Systems Gels or Films: Clinical Study for the Treatment of Periodontitis.

This study evaluated the efficacy of semisolid systems (gels) and films containing a combination of metronidazole (MTZ) and metronidazole benzoate after scaling and root-planing (SRP) for periodontitis. In total, 45 patients with stage I or II periodontitis were enrolled and divided into 3 groups: 1-SRP-control; 2-SRP + Film with MTZ; 3-SRP + Gel with MTZ. The pH of gingival crevicular fluid (GCF) before/after treatments, MTZ concentrations, and drug release using high-performance liquid chromatography were investigated. The effects were evaluated by longitudinal monitoring of clinical parameters (probing depth-PD, clinical attachment level-CAL, and bleeding on probing-BP). MTZ and MTZ-benzoate concentrations in the periodontal pocket and pH showed no statistical difference after application. SRP + Gel presented the lowest CAL values. For SRP + Film and SRP + Gel, higher PD values were observed at T0 compared to all groups. A relevant reduction in BP was observed in SRP + Film and SRP + Gel groups at all times compared to T0. Both therapies improved periodontal health compared to SRP alone, reducing PD and BP, and increasing CAL for the gel group, suggesting they are promising for periodontal disease treatment.

A Comparison of Semi-Solid, Liquid, and Temporary Immersion Bioreactor Systems for Effective Plant Regeneration of Gerbera jamesonii “Shy Pink”

Temporary immersion system (TIS) cultures are reported to be superior when compared to semi-solid (SS) and liquid (LQ) cultures for the in vitro plant regeneration of many plant species. In the present study, we used a TIS for plant regeneration of Gerbera jemesonii “Shy Pink” and compared the results with that of SS and LQ cultures. The number of shoots regenerated in the SS, LQ, and TIS cultures was 6.93, 3.13, and 3.03, respectively. The shoots regenerated with the SS and LQ cultures demonstrated 3.33 and 4.22% hyperhydricity, whereas the shoots regenerated with the TIS were healthy even though the number of shoots regenerated was less. The plantlets regenerated with the TIS demonstrated higher values for the number of roots, root length, biomass of the plantlets, leaf length/width, and area compared to the SS and LQ cultures. When the G. jemesonii “Shy Pink” plants were regenerated using the TIS, their levels of photosynthetic pigments were highest. The number of stomata on the abaxial surface of their leaves was 11.40, and the frequency of closed stomata was 59% for the plants regenerated with the TIS. The number of stomata was 21.4 and 14.5 for the plants regenerated with the SS and LQ cultures, respectively. Meanwhile, the frequency of closed stomata was 13% and 15% for the plants regenerated with SS and LQ cultures. Furthermore, G. jemesonii “Shy Pink” showed the highest survival of plants when regenerated in the TIS compared to SS and LQ cultures. The TIS was found to be the most suitable culture system for plant regeneration of G. jemesonii “Shy Pink” compared to SS and LQ cultures.

Technical Considerations, Applications, and Benefits of Organogels in Topical Drug Delivery Systems.

Organogels represent semi-solid systems where an organic liquid phase is entrapped within a three-dimensional network formed by self-assembled, crosslinked, or entangled gelator fibers. These versatile materials find applications in a wide range of fields, including chemistry, pharmaceuticals, cosmetics, biotechnology, and food technology. Notably, in pharmacology, they serve as valuable platforms for drug and vaccine delivery, facilitating the transport of active ingredients through various routes such as transdermal, oral, and parenteral. However, their previous utility as drug delivery systems was hindered by the toxicity associated with the organic solvents used. The pharmacokinetics of medications delivered via organogels are primarily influenced by the distinctive properties of these materials, specifically their "high permeability and poor aqueous solubility," which can impact the bioavailability of the drugs. Organogels can be employed topically or for the controlled release of medications through cutaneous administration and percutaneous absorption, expanding their scope of application beyond conventional drug delivery methods. Organogels hold significant promise as drug delivery vehicles due to their biocompatibility, non-irritating properties, and thermoremanent characteristics. They enable the formulation of diverse drug delivery systems by incorporating both hydrophilic and hydrophobic bioactive compounds within the gel matrix. This comprehensive review offers an overview of organogels, encompassing their nature, synthesis, characterization, and properties. Special attention is directed towards cutting-edge technologies employed in designing organogels as potential controlled delivery systems, with a focus on their emerging therapeutic applications.

Lecithin Organogel: A Promising Carrier for the Treatment of Skin Diseases.

Skin is the largest organ of the human body, as it protects the body from the external environment. Nowadays, skin diseases and skin problems are more common, and millions of people are affected daily. Skin diseases are due to numerous infectious pathogens or inflammatory conditions. The increasing demand for theoretical research and practical applications has led to the rising prominence of gel as a semisolid material. To this end, organogels has been widely explored due to their unique composition, which includes organic solvents and mineral or vegetable oils, among others. Organogels can be described as semisolid systems wherein an organic liquid phase is confined within a three-dimensional framework consisting of self-assembled, cross-linked, or entangled gelator fibers. These gels have the ability to undergo significant expansion and retain substantial amounts of the liquid phase, reaching up to 99% swelling capacity. Furthermore, they respond to a range of physical and chemical stimuli, including temperature, light, pH, and mechanical deformation. Notably, due to their distinctive properties, they have aroused significant interest in a variety of practical applications. Organogels favor the significant encapsulation and enhanced permeation of hydrophobic molecules when compared with hydrogels. Accordingly, organogels are characterized into lecithin organogels, pluronic lecithin organogels, sorbitan monostearate-based organogels, and eudragit organogels, among others, based on the nature of their network and the solvent system. Lecithin organogels contain lecithin (natural and safe as a living cell component) as an organogelator. It acts as a good penetration enhancer. In this review, first we have summarized the fundamental concepts related to the elemental structure of organogels, including their various forms, distinctive features, methods of manufacture, and diverse applications. Nonetheless, this review also sheds light on the delivery of therapeutic molecules entrapped in the lecithin organogel system into deep tissue for the management of skin diseases and provides a synopsis of their clinical applications.

Temporary Immersion Systems in Plant Micropropagation.

Temporary immersion systems (TIS) are technological tools that support plant micropropagation. Given their high efficiency in the in vitro propagation of shoots, a current goal is to update the protocols addressing micropropagation in semisolid culture systems to protocols involving TIS. To this end, different parameters have been evaluated, including TIS types and designs, immersion times, immersion frequencies, and volume of medium per explant, among other characteristics. This has resulted in the improved production of propagules of plants of economic interest and the production of physiologically upgraded plants with high percent survival during acclimatization. TIS are specialized culture flasks that provide countless advantages during the commercial micropropagation of plants.

A REVIEW ARTICLE ON NOVEL DRUG DELIVERY BIGEL

Gel are semisolid systems made up of a gelling agent and a polar liquid solvent. Gels are used in the food, pharmaceutical, and cosmetics industries. They are classified based on their structural and rheological properties. Scientists are looking for new ways to create gels with better properties. Many bigel formulations have been created and altered recently to satisfy the demands of various applications. Bigels ability to deliver both hydrophilic and lipophilic active agents, their water washability after application to the skin, their easy preparation, good stability, and the enrichment of stratum corneums hydration, which results in a cooling and moisturizing effect, are some of their key characteristics that make them useful for controlled drug delivery. Since bigel formulations are a new class of materials, further research into these systems is necessary before they can be used in real-world applications. When synthesizing bigels by combining organogel and hydrogel, several factors are crucial, such as bigel storage. KEY WORDS: Gels, Bigels, Hydrophilic, Lipophilic, Controlled Drug Delivery

Formulation and Evaluation of Herbal Emulgel: A Review Article

Topical Drug Delivery System Drug: The application of a medication containing formulation for the skin in order to treat the cutaneous condition directly is known as topical drug delivery. Factors Affecting Topical Drug Delivery System: Physiological factors are Skin condition, Lipid content, Blood flow, Skin hydration, Skin temperature and Physiochemical factors are partition coefficient, Molecular weight, Drug concentration, Effect on vehicles. Physiology of Skin: Skin consists of Epidermis Dermis Subcutaneous Tissue. Epidermis is composed basically of: Keratinocytes, Melanocytes, Langerhans cells. Introduction: Emulgels are emulsions oil-in-water or water-in-oil that are combined with an emulsifying agent to form gels. Emulgel is made up of two components: Emulsion: An emulsion is a biphasic system made up of two immiscible liquids, which is one of finely and consistently propagated as globules throughout the other to form an emulsion. Gel: According to the U.S.P., gels are semisolid systems made up of a dispersion whether large organic molecules or small inorganic particles that are encased and penetrated by liquid. Characterization and Evaluation of Herbal Emulgel: Physical Appearance, pH, Viscosity study, Spreadability, Total Ash Value, Loss on drying, In-vitro Diffusion Study. Conclusion: The dosage forms are enhancing topical drug delivery of natural drugs for various topical problem.

Edible Gels with Cranberry Extract: Evaluation of Anthocyanin Release Kinetics.

The bioactive compounds found in cranberry fruit are natural antioxidants, and their consumption reduces the risk of diabetes, cardiovascular disease, cancers, and urinary tract infections. Oral gels with cranberry fruit extract are a promising product that can ensure accurate dosage and release of the active compounds and are suitable for people with dysphagia. The aim of this study was to determine the effect of polymeric materials on the dissolution kinetics of cranberry fruit anthocyanins from gel formulations. Gel formulations were prepared using freeze-dried cranberry fruit extract with different gelling excipients: chitosan (G1-G3), sodium carboxymethylcellulose (G4-G6), and sodium carboxymethylcellulose combined with carbomers (G7-G9). The dissolution test showed that the release of anthocyanins from gel formulations G1-G6 and G9 was most intense within the first 10 min, with little change in the anthocyanin content of the acceptor medium afterwards. For the formulations based on carboxymethyl cellulose and carbomers G7 and G8, the amount of anthocyanins released into the acceptor medium gradually increased, which prolonged the release time of the active compounds. The test for the release of anthocyanins from the semi-solid systems through a hydrophilic membrane revealed that within the first hour, the total amount of anthocyanins released from the modeled gel formulations (G1-G9) was within the range of 6.02%-13.50%. The 1% chitosan (G1) gel formulation released the fastest and highest amount of anthocyanins (70% within 6 h). The other formulations showed a slower release of anthocyanins, and after 6 h, the amount of anthocyanins released from formulations G2-G9 was <57%.

(Invited) Microelectrode-Based Diagnosis of Charge Propagation and Redox Transitions in Concentrated Polyoxometallate Electrolyte of Potential Utility for Redox Flow Battery

Concentrated solutions of Keggin-type silicotungstic acid, as well as the system’s single crystals (H4SiW12O40*31H2O) and their colloidal suspensions have been tested using the microelectrode methodology to determine mass-transport, electron self-exchange and apparent (effective) diffusion-type coefficients for charge propagation and homogeneous (electron self-exchange) rates of electron transfers. Silicotungstic acid facilitates proton conductivity, and undergoes fast, reversible, multi-electron electron transfers leading to the formation of highly conducting, mixed-valence (tungsten(VI,V) heteropoly blue) compounds. To develop useful electroanalytical diagnostic criteria, electroanalytical approaches utilizing microdisk electrodes have been adapted to characterize redox transitions of the system and to determine kinetic parameters. Combination of micoroelectrode-based experiments performed in two distinct diffusional regimes: radial (long-term experiment; e.g., slow scan rate voltammetry or long-pulse chronoamperometry) and linear (short-term experiment; e.g., fast scan rate voltammetry or short-pulse chronocoulometry) permits absolute determination of such parameters as effective concentration of redox centers (C0 ) and apparent transport (diffusion) coefficient (Dapp ). The knowledge of these parameters, in particular of [Dapp 1/2 C0 ] seems to be of importance to the evaluation of utility of redox electrolytes for charge storage.While current densities which reflect dynamics of electrochemical processes have an influence on the systems’ current densities, the viscosity of the electrolyte and the mass transport dynamics are also affected by the nature of the redox-active material and its concentration. Trying to develop useful electroanalytical diagnostic approaches, we have successfully utilized microelectrode-based probes, as well as the historical concepts of charge propagation in semi-solid or semi-liquid systems developed for mixed-valence polynuclear materials in order to characterize concentrated redox electrolytes. Among important parameters are concentration of redox centers (C0 ) and apparent transport (diffusion) coefficient (Dapp ). The knowledge of these parameters and, in particular of [Dapp 1/2 C0 ], are crucial when it comes to evaluation of the diffusional-type charge propagation dynamics in the concentrated electrolyte which may reflect both physical mass transport and electron self-exchange (electron-hopping) contributions. Both potential-step (chronocoulometry, chronoamperometry) and cyclic voltammetric experiments utilizing microdisk electrodes have been adapted to characterization (identification of redox transitions and determination of kinetic parameters) of model inorganic redox electrolytes, namely highly-concentrated solutions or colloidal suspensions of Keggin-type polyoxometallate, silicotungstic acid.

Enhanced rheological and tribological properties of nanoenhanced greases by tuning interparticle contacts

HypothesisDespite the wide spectrum of available nanoparticles, their utilization in lubricant and grease formulations remains challenging. To enhance their performance, an improved link between the interparticle contacts, brittleness of the resulting particle network, time-dependent rheology and tribology is required. ExperimentsWe systematically changed interparticle contacts and examined their effect on the colloidal stability, microstructure, rheological and tribological behavior of model greases by investigating four types of nanoclays: montmorillonite (Cloisite Na+), oleic-acid functionalized Cloisite Na+ (OA-Cloisite Na+), organomodified montmorillonite (C20A) and oleic-acid functionalized C20A (C20A-OA). FindingsWe observed a range of behaviors, starting from the lack of colloidal stability in greases derived with Cloisite Na+ and OA-Cloisite Na+ to semi-solid type systems with C20A and C20A-OA. Consistent with previous studies, the rheological and tribological properties of C20A systems scale with nanoclay loadings. Surprisingly, the functionalized C20A-OA system exhibited a delayed transition towards hydrodynamic lubrication, and enhanced lubrication properties, both of which were largely independent of nanoclay loadings. Coupled microstructural investigation and time-dependent rheology reveal that this behavior is governed by increasing repulsive forces, decreasing inter-particle friction between C20A-OA nanoparticles, and faster reorganization of the C20A-OA nanoparticle network under shear. Increased interparticle repulsion enables C20A-OA nanoclays to pass each other under shear and align in direction of shear, which reduces the overall viscosity, while the presence of OA on nanoclays decreases inter-particle friction and particle-steel surface friction.

Green synthesis of organogelators from renewable natural sources for cosmetic and pharmaceutical applications

Organogels are semi-solid systems in which a three-dimensional network, composed by the organgelator fibers, immobilizes an organic liquid phase by twisting around it. They find application in different industrial fields as “soft” materials; their mechanical and chemical properties, together with their rheological behavior, make them excellent candidates in cosmetic and pharmaceutical technologies.The synthesis of organo-gelling agents often suffers of long procedures, unfriendly solvents and reagents, and complex work up. In this research we focused on an ecofriendly solventless synthesis using renewable sources, as starting materials, under microwave activation (MW). Using a simple mixture of reagents in dry media, under acidic conditions, 1,3:2,4-dibenzylidene sorbitol (DBS), a low-molecular-weight gelator, and some derivatives were obtained in good yield in less than ten minutes. The obtained products showed good gelling properties.

Orchid Micropropagation Using Conventional Semi-Solid and Temporary Immersion Systems: A Review.

Orchids, with their astonishingly stunning flowers, dominate the international floricultural market. They are considered prized assets for commercial applications in pharmaceutical and floricultural industries as they possess high therapeutic properties and superior ornamental values. The alarming depletion of orchid resources due to excessive unregulated commercial collection and mass habitat destruction makes orchid conservation measures an extreme priority. Conventional propagation methods cannot produce adequate number of orchids, which would meet the requirement of these ornamental plants for commercial and conservational purposes. In vitro orchid propagation using semi-solid media offers an outstanding prospect of rapidly producing quality plants on a large scale. However, the semi-solid (SS) system has shortcomings with low multiplication rates and high production costs. Orchid micropropagation using a temporary immersion system (TIS) overcomes the limitations of the SS system by reducing production costs and making scaleup and full automation possible for mass plant production. The current review highlights different aspects of in vitro orchid propagation using SS and TIS and their benefits and drawbacks on rapid plant generation.

Micropropagation of Brassavola nodosa (L.) Lindl. using SETIS™ bioreactor

Brassavola nodosa (L.) Lindl. is a tropical epiphytic orchid showing characteristics of interest for the ornamental nursery industry, as well as considered as an endangered species. Problems with traditional propagation methods limit the development of a large-scale commercial production system. The use of micropropagation has been investigated for this species, and the use of liquid in vitro systems showed potential for use of temporary immersion systems, also called temporary immersion bioreactors (TIB) for micropropagation of B. nodosa. This study evaluated the efficiency of the SETIS™ TIBs for the micropropagation of B. nodosa. Explants consisting of young shoots tips measuring between 0.3 and 0.5 cm were collected from 1-yr-old in vitro seedlings of B. nodosa and used for shoot multiplication. Four culture systems were evaluated: a semi-solid in vitro system consisting of 160 mm × 100 mm TP1600 Microbox containing 500 ml semi-solid medium as a control, and a liquid in vitro system consisting of 4 L temporary immersion bioreactor (SETIS™, VERVIT, Belgium) containing 500 ml liquid medium with immersion and aeration frequencies of 2 h, 4 h, and 8 h. For all bioreactor treatments, duration of immersion and aeration was 2 min. Results showed that temporary immersion of B. nodosa explants with a frequency of 2 h and duration of 2 min returned the highest multiplication rates, with 4.6 shoots produced per explant compared with 2.8 shoots per explant in semi-solid agar-based systems. The use of bioreactors also promoted increased growth and development and in vitro rooting, therefore improving survival, and facilitating acclimatization of in vitro-derived plantlets. This is the first study demonstrating a successful protocol for micropropagation of B. nodosa using SETIS™ bioreactors, which could have significant value and impact for the commercial production of this species as well as for conservation purposes. Micropropagation of Brassavola nodosa was achieved using SETIS temporary immersion bioreactors, showing good multiplication rates, increased growth and development and in vitro rooting, thus improving survival and acclimatization ex vitro.

Improving bacoside yield of Bacopa monnieri (L.) Wettst. in temporary immersion system by increasing immersion time and lowering the intervals

Bacopa monnieri (L.) Wettst. or Brahmi has been used in Ayurvedic medicine and currently use as an alternative medicinal herb for several therapeutic healing. Therefore, in vitro mass propagation of B. monnieri for high quality plant production using temporary immersion system (TIS) was necessarily examined. Explants of B. monnieri as regenerated shoots from leaf segments were used to determine the effects of culture system, immersion time and inoculum explant density on growth and bacoside production of B. monnieri. Statistically significant differences in growth and biomass accumulation were observed in the TIS compared with continuous immersion and semi-solid systems. Production of bacoside A, bacopaside II, bacopasaponin C, and total bacoside in B. monnieri obtained from microcontainer cultivation was significantly higher than TIS, whereas total yield of bacosides obtained from different culture systems showed no significant differences. Three immersions per day for 10 min duration promoted growth and biomass accumulation of B. monnieri, while cultivation with 20 explants per container offered optimal inoculum density for large-scale production. Various concentrations and yields of bacoside were obtained from different immersion interval conditions. Reducing immersion duration improved bacoside production. Five explants per container provided the highest bacoside content but yield per container was the lowest.

Ultramicroelectrode Based Approaches to Diagnose Utility of Redox Electrolytes in Flow Batteries

Redox flow batteries are of potential importance to both large scale energy storage and powering the electrical vehicle. Among critical challenges are low volumetric energy density of redox electrolytes, high cost and the maintenance limitations that greatly impede the wide application of conventional flow batteries. In this respect, the redox-active charge-storage material has a significant impact on the performance of a flow battery. The concentration of redox centers and their reaction kinetics have an influence on the available current densities and, thus, the power of the device.Many inorganic and organic electroactive systems have been proposed as alternatives to vanadium species in redox flow batteries. In the study, we explore the concept of highly concentrated solutions of such redox systems as iodine/iodide and poloxometallates of molybdenum and tungsten, and the possibility of optimizing their performance to exhibit high rates of charge propagation. While the iodine/iodide system can be prepared at high concentrations, the polyoxometallates of molybdenum and tungsten can serve as model examples of multi-electron systems for all-liquid redox flow batteries and related fundamental investigations. Reactions in the zinc/iodine (polyiodide) redox flow battery are as follows: Zn → Zn2+ + 2e- (E = −0.76 V vs SHE) at the negative electrode (anode), and 3I- → I3 − + 2e− (E = 0.54 V vs SHE) at the positive electrode (cathode) thus yielding a total theoretical potential output as high as ∼1.3 V. The increase of current density could be achieved not only by reducing the viscosity of the electrolyte, thus accelerating charge-carrier transport, but also – by referencing to our experience with the iodine/iodide couple as charge relay for dye-sensitized solar cells – through improvement of the dynamics of charge propagation in highly concentrated iodine/iodide solution via the catalyzed enhancement of rates of electron self-exchange (hopping) between iodine/iodide (polyiodide) redox species as well as by accelerating the interfacial kinetics at electrodes. This can be realized by choosing appropriate electrode materials and through their activation or modification. The electrochemical activities of the redox couples are usually significantly increased through application of nanostructured functionalized carbons. While dispersed in solutions they can improve electron transfers to the redox sites. The proposed chemistry has been first tested using the microelectrode methodology to determine mass-transport (effectively diffusional) coefficients for charge propagation, heterogeneous and homogeneous (electron self-exchange) rates of electron transfers. Unless catalyzed, both interfacial and bulk (self-exchange) electron transfers involving the iodine/iodide redox system are somewhat complicated; there is a need to break the I-I bond in the I3 -or I2 molecule; it has also been well-established that platinum (e.g. when deposited on the counter electrode) induces electron transfers within the iodine/iodide redox system. As far as heteropolyacids are concerned, they exhibit very strong Brønsted acidity, act as proton conductors, and undergo fast, reversible, multi-electron electron transfers leading to the formation of highly conducting, mixed-valence (e.g. tungsten(VI,V) or molybdenum(VI,V) heteropoly blue) compounds. The polyoxometallate-based redox electrolytes have different chemical identities, and they could be considered as anolytes or catholytes, depending on their redox potentials but, typically, their use would require formation of an asymmetric system with different-type redox species.While dynamics of electrochemical processes has an influence on the systems’ current densities, the viscosity of the electrolyte and the mass transport dynamics are also affected by the choice of the redox-active material and its concentration. Trying to develop useful electroanalytical diagnostic criteria, we are going to extend the historical concepts of charge propagation in semi-solid or semi-liquid systems developed for mixed-valence redox polymers and polynuclear materials to the development of redox electrolytes. Fundamental electroanalytical approaches utilizing ultramicrodisk electrodes and interdigitated arrays will be adapted to characterization of redox electrolytes.

(Invited) Development and Characterization of Polyoxometallate-Based Systems for Aqueous Redox Flow Batteries

Redox flow batteries are of potential importance to both large scale energy storage and powering the electrical vehicle. It is now accepted that flow batteries are the battery technology with the greatest potential to be one of the key elements in the energy transition to a sustainable electricity supply. Among critical challenges are low volumetric energy density of redox electrolytes, high cost and the maintenance limitations that greatly impede the wide application of conventional flow batteries. In this respect, the redox-active charge-storage material has a significant impact on the performance of a flow battery. The concentration of redox centers and their reaction kinetics have an influence on the available current densities and, thus, the power of the device.Many inorganic and organic electroactive systems have been proposed as alternatives to vanadium species in redox flow batteries. In the study, we explore the concept that highly concentrated solutions of the polyoxometallates of molybdenum and tungsten can serve as model examples of multi-electron systems for all-liquid redox flow batteries and related fundamental investigations. Polyoxometallates are polynuclear inorganic materials with well-defined multi-electron reversible electrochemistry and electrocatalytic properties [1]. Among other important characteristics of heteropolyacids are that they exhibit very strong Brønsted acidity, act as proton conductors, and undergo fast, reversible, multi-electron electron transfers leading to the formation of highly conducting, mixed-valence (e.g. tungsten(VI,V) or molybdenum(VI,V) heteropoly blue) compounds. The polyoxometallate-based redox electrolytes have different chemical identities, and they could be considered as anolytes or catholytes, depending on their redox potentials but, typically, their use would require formation of an asymmetric system with different-type redox species. The scope of existing inorganic and organic electroactive materials can be expanded due the possibility of their functionalization and structural modification. Recent developments in the area of the transition-metal-derivatized polyoxometallates are also promising [2] because they imply the feasibility of formation of the bi-redox polyoxmetallate-based electrolytes. In particular, the systems containing such metals as copper, iron, ruthenium, nickel or tin could of interest. Such features as the feasibility of reversible multi-electron redox processes, the improved potential output and cycling performance, sufficiently high solubility and reasonable stability will be examined here. An alternative approach can be based on the preparation of robust zeolite-type cesium salts of polyoxometallates, Cs2.5H0.5PMo12O40, Cs2.5H1.5SiMo12O40, Cs2.5H0.5PW12O40, and Cs2.5H1.5SiW12O40. It is noteworthy that, at certain contents of cesium (or rubidium), these porous salts are characterized by fast charge propagation. They can be considered for application in a form of colloidal suspensions.While kinetics of electrochemical processes has an influence on the systems’ current densities, the viscosity of the electrolyte and the mass transport dynamics are also affected by the choice of the redox-active material and its concentration. Trying to develop useful electroanalytical diagnostic criteria, we are going to extend the historical concepts of charge propagation in semi-solid or semi-liquid systems developed for mixed-valence redox polymers and polynuclear materials to the development of redox electrolytes. Fundamental electroanalytical approaches utilizing ultramicrodisk electrodes and interdigitated arrays will be adapted to characterization of solid suspensions synthesized in a form of stable colloidal solutions utilizing redox active centers capable of exhibiting fast electron transfers according to electron hopping mechanism. Of additional interest is the dynamics of electron transfer at the electrolyte/electrode interface, considered at the molecular and monolayer scales.[1] I.A. Rutkowska, P.J. Kulesza, “Metal Oxide Cluster and Polyoxometallate Supports for Noble Metal Nanoparticles in Efficient Electrocatalysis” in Encyclopedia of Interfacial Chemistry: Surface Science and Electrochemistry, Elsevier, vol. 5, pp 207–216, 2018.[2] J. Goura, B.S. Bassil, J.K. Bindra, I.A. Rutkowska, P.J. Kulesza, N.S. Dalal, U. Kortz, Chemistry - A European Journal 26 (2020) 15821 – 15824.

Method and Critical Aspect of Semisolid Mixing

Semisolid preparations are widely used to deliver drugs through the skin, cornea, rectal tissue, nasal mucosa, vagina, buccal tissue, urethral membrane, and outer ear lining. They can prevent the first-pass metabolism, reduce side effects, provide immediate local effects, and increase patient compliance. However, an improper manufacturing process will produce a system with bad characteristics, one of which is the mixing process. Several conditions that need to be considered, such as vacuum, temperature, humidity, pressure, stirring speed, stirring time, shear stress, the volume of the mixture, and type of impeller, can affect the consistency, size, and dispersion of particle size, homogeneity, porosity, reactivity, and other characteristics that affect the quality of the semisolid system. Therefore, this article discusses the critical aspects of semisolid mixing, the types, principles, and specifications of several mixer tools and impellers, and how they affect the characteristics of semisolid systems. This review concludes that each type of semisolid preparation requires an impeller and mixer with the specifications and mixing conditions that suit the needs in maintaining the stability and quality of the semisolid system.