Laponite®-From Dispersion to Gel-Structure, Properties, and Applications

Laponite® (LAP) is an intensively studied synthetic clay due to the versatility given by its layered structure, which makes it usable in various applications. This review describes the multifaceted properties and applications of LAP in aqueous dispersions and gel systems. The first sections of the review discuss the LAP structure and the interactions between clay discs in an aqueous medium under different conditions (such as ionic strength, pH, temperature, and the addition of polymers) in order to understand the function of clay in tailoring the properties of the designed material. Additionally, the review explores the aging phenomenon characteristic of LAP aqueous dispersions as well as the development of shake-gels by incorporating LAP. The second part shows the most recent studies on materials containing LAP with possible applicability in the drilling industry, cosmetics or care products industry, and biomedical fields. By elucidating the remarkable versatility and ease of integration of LAP into various matrices, this review underscores its significance as a key ingredient for the creation of next-generation materials with tailored functionalities.

Moldable Tissue-Sealant Hydrogels Composed of In Situ Cross-Linkable Polyethylene Glycol via Thiol-Michael Addition and Carbomers

Moldable tissue-sealant hydrogels were developed herein by combining the yield stress fluidity of a Carbomer and in situ cross-linking of 3-arm PEG-thiol (PEG-SH) and 4-arm PEG-acrylate (PEG-AC). The Carbomer was mixed with each PEG oligomer to form two aqueous precursors: Carbomer/PEG-SH and Carbomer/PEG-AC. The two hydrogel precursors exhibited sufficient yield stress (>100 Pa) to prevent dripping from their placement on the tissue surface. Moreover, these hydrogel precursors exhibited rapid restructuring when the shear strain was repeatedly changed. These rheological properties contribute to the moldability of these hydrogel precursors. After mixing these two precursors, they were converted from yield-stress fluids to chemically cross-linked hydrogels, Carbomer/PEG hydrogel, via thiol-Michael addition. The gelation time was 5.0 and 11.2 min at 37 and 25 °C, respectively. In addition, the Carbomer/PEG hydrogels exhibited higher cellular viability than the pure Carbomer. They also showed stable adhesiveness and burst pressure resistance to various tissues, such as the skin, stomach, colon, and cecum of pigs. The hydrogels showed excellent tissue sealing in a cecum ligation and puncture model in mice and improved the survival rate due to their tissue adhesiveness and biocompatibility. The Carbomer/PEG hydrogel is a potential biocompatible tissue sealant that surgeons can mold. It was revealed that the combination of in situ cross-linkable PEG oligomers and yield stress fluid such as Carbomer is effective for developing the moldable tissue sealant without dripping of its hydrogel precursors.

Injectable, shear-thinning, photocrosslinkable, and tissue-adhesive hydrogels composed of diazirine-modified hyaluronan and dendritic polyethyleneimine

In the present study, we report the first synthesis of diazirine-modified hyaluronic acid (HA-DAZ). In addition, we also produced a precursor polymer solution composed of HA-DAZ and dendritic polyethyleneimine (DPI) that showed strong shear-thinning properties. Furthermore, its viscosity was strongly reduced (i.e., from 5 × 105 mPa s at 10-3 s-1 to 6 × 101 mPa s at 103 s-1), substantially, which enhanced solution injectability using a 21 G needle. After ultraviolet irradiation at 365 nm and 6 mW cm-2, the HA-DAZ/DPI solution achieved rapid gelation, as measured using the stirring method, and its gelation time decreased from 200 s to 9 s as the total concentrations of HA-DAZ and DPI increased. Following UV irradiation, the storage modulus increased from 40 to 200 Pa. In addition, reversible sol-gel transition and self-healing properties were observed even after UV irradiation. This suggests that the HA-DAZ/DPI hydrogel was crosslinked in multiple ways, i.e., via covalent bonding between the diazirine and amine groups and via intermolecular interactions, including hydrogen bonding, electrostatic interactions, and hydrophobic interactions. A lap shear test showed that the HA-DAZ/DPI hydrogel exhibited strong adhesiveness as a fibrin glue following UV irradiation. Finally, the HA-DAZ/DPI hydrogel showed higher tissue reinforcement than fibrin glue in an ex vivo burst pressure test of the porcine esophageal mucosa.

Injectable Extracellular Matrix-Inspired Hemostatic Hydrogel Composed of Hyaluronan and Gelatin with Shear-Thinning and Self-Healing

Injectable ECM-inspired hydrogels composed of hyaluronic acid and gelatin are biocompatible and potentially useful for various medical applications. We developed injectable hydrogels composed of monoaldehyde-modified hyaluronic acid (HA-mCHO) and carbohydrazide-modified gelatin (GL-CDH), "HA/GL gel", whose ratios of HA-mCHO to GL-CDH were different. The hydrogels exhibited gelation times shorter than 3 s. In addition, the hydrogels showed strong shear-thinning and self-healing properties, mainly because of the dynamic covalent bonding of Schiff bases between HA-mCHO and GL-CDH. This hydrogel degraded in the mice's peritoneum for a week and showed excellent biocompatibility. Moreover, the hydrogel showed a higher breaking strength than fibrin glue in the lap shear test of porcine skin. Finally, the hydrogels decreased bleeding to as low as fibrin glue without using thrombin and fibrinogen in a mouse liver bleeding model in both single- and double-barreled syringe administrations. HA/GL gels have the potential for excellent biocompatibility and hemostasis in clinical settings.

Navigating the Solution to Drug Formulation Problems at Research and Development Stages by Amorphous Solid Dispersion Technology

Amorphous Solid Dispersions (ASDs) have indeed revolutionized the pharmaceutical industry, particularly in drug solubility enhancement. The amorphous state of a drug, which is a highenergy metastable state, can lead to an increase in the apparent solubility of the drug. This is due to the absence of a long-range molecular order, which results in higher molecular mobility and free volume, and consequently, higher solubility. The success of ASD preparation depends on the selection of appropriate excipients, particularly polymers that play a crucial role in drug solubility and physical stability. However, ASDs face challenges due to their thermodynamic instability or tendency to recrystallize. Measuring the crystallinity of the active pharmaceutical ingredient (API) and drug solubility is a complex process that requires a thorough understanding of drug-polymer miscibility and molecular interactions. Therefore, it is important to monitor drug solids closely during preparation, storage, and application. Techniques such as solid-state nuclear magnetic resonance (ssNMR), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), Raman spectroscopy, and dielectric spectroscopy have been successful in understanding the mechanism of drug crystallization. In addition, the continuous downstream processing of drug-loaded ASDs has introduced new automated methods for consistent ASD production. Advanced techniques such as hot melt extrusion, KinetiSol, electro spraying, and electrospinning have gained popularity. This review provides a comprehensive overview of Amorphous Solid Dispersions (ASDs) for oral drug delivery. It highlights the critical challenges faced during formulation, the impact of manufacturing variables, theoretical aspects of drug-polymer interaction, and factors related to drug-polymer miscibility. ASDs have been recognized as a promising strategy to improve the oral bioavailability of poorly water-soluble drugs. However, the successful development of an ASD-based drug product is not straightforward due to the complexity of the ASD systems. The formulation and process parameters can significantly influence the performance of the final product. Understanding the interactions between the drug and polymer in ASDs is crucial for predicting their stability and performance.

Prevention of esophageal stenosis via in situ cross-linkable alginate/gelatin powder in a new submucosal exfoliation model in rats

Endoscopic submucosal dissection (ESD) for the treatment of esophageal mucosal lesions often leads to postoperative stenosis, causing difficulty in swallowing, known as dysphagia. In this study, we developed an in situ cross-linkable powder composed of alginate, gelatin, transglutaminase (TG), and calcium chloride ions (Ca2+), which can be administered through a 1.5 m-long and 3.2 mm-diameter endoscopic instrument channel. The powdered mixture of alginate and gelatin quickly formed a hydrogel by absorbing body fluids and was cross-linked by TG and Ca2+, which adhered ex vivo to porcine submucosal layers for over 2 weeks. In addition, we developed a new submucosal exfoliation model in rats that induced severe stenosis, similar to the ESD-induced stenosis models in clinical practice. When administered to the new rat model, the powder system effectively reduced the severity of esophageal stenosis based on body weight change monitoring, anatomical findings, and histological analysis. The body weight of the rats was maintained at the initial weight on postoperative day 14 (POD14), and epithelialization on POD7 and 14 improved to almost 100%. Additionally, collagen accumulation and the number of α-SMA-positive cells decreased due to powder administration. Therefore, these findings indicate that the in situ cross-linkable powder can prevent esophageal stenosis after ESD.

Efficacy of Apremilast Gels in Mouse Model of Imiquimod-Induced Psoriasis Skin Inflammation

Apremilast (APM) is a novel drug for the treatment of psoriasis and psoriatic arthritis. APM is a phosphodiesterase 4 (PDE4) inhibitor, raising intracellular cAMP levels and thereby decreasing the inflammatory response by modulating the expression of TNF-α, IL-17, IL-23, and other inflammatory cytokines. The goal of this study is to develop APM gels as a new pharmaceutical formulation for the treatment of topical psoriasis. APM was solubilized in Transcutol-P and incorporated into Pluronic F127, Sepigel, and carbomer bases at different proportions. All formulations were characterized physiochemically. A biopharmaceutical study (release profile) was performed, and ex vivo permeation was evaluated using a human skin model. A toxicity assay was carried out on the HaCaT cell line. A mouse model of imiquimod-induced psoriasis skin inflammation was carried out to determine its efficacy by histological analysis, RNA extraction, and RT-qPCR assays. APM gel formulations showed good physicochemical characteristics and a sustained release profile. There was no permeation of any gel measured through human skin, indicating a high retained amount of APM on the skin. Cell viability was greater than 80% at most dilution concentrations. APM gels treated the psoriasis mouse model, and it shows a reduction in the proinflammatory cytokines (IL-8, IL-17A, IL-17F, and IL-23). APM gels could be a new approach for the treatment of topical psoriasis.

Prospective applications of two-dimensional materials beyond laboratory frontiers: A review

The development of nanotechnology has been advancing for decades and gained acceleration in the 21st century. Two-dimensional (2D) materials are widely available, giving them a wide range of material platforms for technological study and the advancement of atomic-level applications. The design and application of 2D materials are discussed in this review. In order to evaluate the performance of 2D materials, which might lead to greater applications benefiting the electrical and electronics sectors as well as society, the future paradigm of 2D materials needs to be visualized. The development of 2D hybrid materials with better characteristics that will help industry and society at large is anticipated to result from intensive research in 2D materials. This enhanced evaluation might open new opportunities for the synthesis of 2D materials and the creation of devices that are more effective than traditional ones in various sectors of application.

pH responsive cationic guar gum-borate self-healing hydrogels for muco-adhesion

We developed a new muco-adhesive hydrogel composed of cationic guar gum (CGG) and boric acid (BA). The CGG-BA precursor solution of 0.5-2% w/v concentration exhibited fluidity at low pH (3-5), while gelation occurred within 1 min at physiological pH (7-8) conditions. Scanning electron microscopy and Fourier-transform infrared spectroscopy results confirmed the change in physical and chemical behavior, respectively, with change in pH. The pH-responsive self-healing ability was analyzed through microscopy and rheology. CGG-BA hydrogels showed good self-healing property at pH 7.4. The in vitro biocompatibility test of the hydrogel studied using NIH3T3 and NHEK cells showed that it was non-toxic at concentrations of CGG-BA below 2% w/v. Ex vivo mucoadhesive tests confirmed the hydrogel's potential for use as a muco-adhesive. Burst pressure tests were conducted using pig esophageal mucosa and the results showed that at pH 7.4, 1% w/v CGG-BA self-healable hydrogel resisted about 8 ± 2 kPa pressure, comparable to that of Fibrin glue. This was higher than that at solution (pH 5) and brittle gel (pH 10) conditions. To confirm the good adhesive strength of the self-healable hydrogels, lap shear tests conducted, resulted in adhesive strengths measured in the range of 1.0 ± 0.5-2.0 ± 0.6 kPa, which was also comparable to fibrin glue control 1.8 ± 0.6 kPa. Hydrogel weight measurements showed that 40-80% gel lasted under physiological conditions for 10 h. The results suggest that CGG-BA hydrogel has potential as a pH responsive mucosal protectant biomaterial.

3D Printing of Stretchable, Adhesive and Conductive Ti3C2Tx-Polyacrylic Acid Hydrogels

Stretchable, adhesive, and conductive hydrogels have been regarded as ideal interfacial materials for seamless and biocompatible integration with the human body. However, existing hydrogels can rarely achieve good mechanical, electrical, and adhesive properties simultaneously, as well as limited patterning/manufacturing techniques posing severe challenges to bioelectronic research and their practical applications. Herein, we develop a stretchable, adhesive, and conductive Ti3C2Tx-polyacrylic acid hydrogel by a simple pre-crosslinking method followed by successive direct ink writing 3D printing. Pre-polymerization of acrylic acid can be initiated by mechanical mixing with Ti3C2Tx nanosheet suspension, leading to the formation of viscous 3D printable ink. Secondary free radical polymerization of the ink patterns via 3D printing can achieve a stretchable, adhesive, and conductive Ti3C2Tx-polyacrylic acid hydrogel. The as-formed hydrogel exhibits remarkable stretchability (~622%), high electrical conductivity (5.13 S m−1), and good adhesion strength on varying substrates. We further demonstrate the capability of facilely printing such hydrogels into complex geometries like mesh and rhombus patterns with high resolution and robust integration.