Gel Encapsulation Research Articles

Near-infrared and multifunctional fluorescent probe enabled by cyanopyridine cyanine dye for bisulfite recognition and biological imaging

SO2 derivatives, sulfite/bisulfite, are widely employed in both the food processing and drug synthesis industries. Despite their widespread application, excessive levels of sulfite/bisulfite can negatively impact human health. Most probes for detecting sulfite/bisulfite are restricted by their fluorescence within the visible spectrum range and poor solubility in aqueous solution, which limit their use in food testing and biological imaging. Herein, a near-infrared probe comprising of the cyanopyridine cyanine skeleton, 4-((Z)−2-((E)−2-chloro-3-(2-cyano-2-(1-methylpyridine-4(1H)-ylidene)ethylidene)cyclohex-1-en-1-yl)−1-cyanovinyl)−1-methylpyridin-1-ium (abbreviated as CCP), was developed. This probe enables precise quantification of bisulfite (HSO3-) in almost pure buffered solutions, showing a near-infrared fluorescence emission at 784 nm with an impressively low detection limit of 0.32 μM. The probe stands out for its exceptional selectivity, minimal susceptibility to interference, and strong adaptability. The probe CCP utilizes the CC bond to trigger a near-infrared fluorescence quenching reaction with HSO3- via nucleophilic addition, which effectively disrupts the large delocalization within the molecule for accurate HSO3- identification. Moreover, the probe has been successfully applied in detecting HSO3- in various food products and living cells, simplifying the measurement of HSO3- content in water samples. This advancement not only enhances the analytical capabilities but also contributes to ensuring food safety and environmental protection. Environmental ImplicationSO2 derivatives including sulfite/bisulfite, serving dual roles as preservatives and antioxidants, have widespread application across various sectors including food preservation, water sanitation, and the pharmaceutical industry. Despite their widespread application, excessive levels of sulfite/bisulfite can affect human health. Developing methods for precisely and sensitively detecting sulfite/bisulfite in food products and biological samples is important for ensuring food safety and environmental protection. Here, a sensitive near-infrared and multifunctional fluorescent probe in a 99.9 % buffered solution, along with water gel encapsulation, has been successfully applied for the detection of bisulfite in food, authentic water samples, and biological cells.

Use of Silk Fibroin Material Composites for Green, Flexible Supercapacitors.

Within the context of seeking eco-friendly and readily available materials for energy storage, there is a pressing demand for energy storage solutions that employ environmentally sustainable, high-performance, and adaptable constituents. Specifically, such materials are essential for use in wearable technology, smart sensors, and implantable medical devices, whereas, more broadly, their use plays a pivotal role in shaping their efficiency and ecological footprint. Here, we demonstrate an entirely biopolymer-based supercapacitor with a remarkable performance, achieving a capacitance greater than 0.2 F cm-2 at a charge-discharge current of 10 mA cm-2 with 94% capacitance retention after 20,000 cycles. The supercapacitor is composed of three distinct silk fibroin (SF) composite materials, namely, photo-cross-linkable SF (Sil-MA) hydrogel, SF-polydopamine (SF-PDA), and SF bioplastic, to create a gel electrolyte, electrode binder, and encapsulation, respectively. Together, these elements form a mechanically and electrochemically robust skeleton for biofriendly energy storage devices. Moreover, these biomaterial-based supercapacitor devices show stretchability, flexibility, and compressibility while maintaining their electrochemical performance. The biomaterials and fabrication techniques presented can serve as a foundation for investigating various aqueous electrochemical energy storage systems, especially for emerging applications in wearable electronics and environmentally friendly material systems.

Influence of Interfacial Interaction Between Various Metal Substrates and Epoxies on Bonding Reliability Under High Temperture

The shift from gel encapsulation to epoxy encapsulation has been driven by the need to reduce the size of power modules. However, the dissimilar bond between the encapsulation epoxy and substrate is seen as a potential weak point. Previous studies have largely focused on the impact of epoxy materials on package reliability. Our prior research has highlighted the crucial role played by interfacial interactions between copper substrates and epoxy. In this study, we investigate the influence of interfacial interactions between three metal substrates (copper, Ag-plated copper, nickel-plated copper) and epoxy on the reliability of epoxy encapsulation under high temperature. Two types of epoxy (bisphenol A and cycloaliphatic) were used to encapsulate metal substrates. Encapsulated packages were subjected to a high-temperature storage test (HST) at 200°C for 1000 hours, and changes in bonding strength were measured. We then analyzed the fracture surface and bonding interface at the nanoscale. Our results indicate that substrate material has a significant impact on the reliability of epoxy encapsulation. Both epoxies exhibited the highest initial bonding strength with copper, followed by Ag-plated copper and nickel-plated copper. After HST, we found that the catalytic effect of metals caused the epoxy in contact with the metal substrate to decompose. The decomposition was most significant in epoxy in contact with Ag, followed by copper, which resulted in a significant drop in bonding strength. In contrast, epoxy in contact with nickel showed little decomposition and only little change in bonding strength. These findings will greatly benefit power module design.

Effect of transglutaminase on ovalbumin emulsion gels as carriers of encapsulated probiotic bacteria.

The use of emulsion gels to protect and deliver probiotics has become an important topic in the food industry. This study used transglutaminase (TGase) to regulate ovalbumin (OVA) to prepare a novel emulsion gel. The effects of OVA concentration and the addition of TGase on the microstructure, rheological properties, water-holding capacity, and stability of the emulsion gels were investigated. With the addition of TGase and the increasing OVA, the particle size of the emulsion gels decreased significantly (P < 0.05). The gels with TGase exhibited greater water holding, hardness, and chewiness to some extent by forming a more uniform and stable system. After simulated digestion, the survival rate of Bifidobacterium lactis embedded in OVA emulsion gels improved significantly in comparison with the oil-water mixture as a result of the protective effect of the emulsion gel encapsulation. By increasing the OVA content and adding TGase, the rheological characteristics, stability, and encapsulation capability of the OVA emulsion gel could be enhanced, providing a theoretical basis for the use of emulsion gels to construct probiotic delivery systems. © 2023 Society of Chemical Industry.

Electrical Trees of Silicone Gel Encapsulation Materials in Power Electronic Modules Self-Healing Properties and Influencing Factors

Electrical Trees of Silicone Gel Encapsulation Materials in Power Electronic Modules Self-Healing Properties and Influencing Factors

Protein Folding Stability and Kinetics in Alginate Hydrogels.

Proteins are commonly encapsulated in alginate gels for drug delivery and tissue-engineering applications. However, there is limited knowledge of how encapsulation impacts intrinsic protein properties such as folding stability or unfolding kinetics. Here, we use fast relaxation imaging (FReI) to image protein unfolding in situ in alginate hydrogels after applying a temperature jump. Based on changes in the Förster resonance energy transfer (FRET) response of FRET-labeled phosphoglycerate kinase (PGK), we report the quantitative impact of multiple alginate hydrogel concentrations on protein stability and folding dynamics. The gels stabilize PGK by increasing its melting temperature up to 18.4 °C, and the stabilization follows a nonmonotonic dependence on the alginate density. In situ kinetic measurements also reveal that PGK deviates more from two-state folding behavior in denser gels and that the gel decreases the unfolding rate and accelerates the folding rate of PGK, compared to buffer. Phi-value analysis suggests that the folding transition state of an encapsulated protein is structurally similar to that of folded protein. This work reveals both beneficial and negative impacts of gel encapsulation on protein folding, as well as potential mechanisms contributing to altered stability.

Image-Based Gel Encapsulation of Suspended Single Cells for Parallel Single-Cell Screening

Single-cell screening, which has revolutionized the life sciences, is an important method for detecting, separating, or treating specific cells based on desired characteristics. Previously, single cells of interest were manually identified in an image, which required human labor and time. We developed an automated photopolymerization system to encapsulate suspended single cells in approximately 50-µm photo-crosslinkable hydrogel squares. An image was captured, and single cells were selected from grouped cells based on image processing. A generated image was transferred to a digital micromirror device (DMD), and in parallel, target-suspended single cells were encapsulated in gelatin methacryloyl (GelMA) hydrogels. We built a data transfer platform based on a Power Automate Desktop (PAD), completed the data transfer, and projected the processed image onto a sample in 10 s, ensuring a minimum alignment error of 6.2 µm.

Influence of interfacial interaction on the reliability of the bond between encapsulation epoxy and copper substrate

The need for power modules has been promoted by the emergence of electric vehicles. The requirements of small volume, high integrity, and high reliability for the next-generation power module lead to the change of encapsulation method from previous gel encapsulation to epoxy encapsulation. Efforts have been made to enhance epoxy materials, and commercialized high-end epoxy has shown excellent properties, but power module failures still exist. The possible reason may lie in the interfacial interaction between encapsulation epoxy and substrate, which is less noticed previously. This paper seeks to unveil the influence of interfacial interaction on the bonding reliability between encapsulation epoxy and copper substrate. Three reliability tests were performed: high-temperature storage test (HST), temperature cycling test (TCT), and pressure cooker test (PCT). The bonding strength after these reliability tests was evaluated, and the bonding interface and fracture surface were analyzed in a nanoscale. Our study discovered that interfacial interaction plays a vital role in encapsulation reliability. Copper can diffuse into the epoxy and catalyze epoxy thermal oxidative degradation, which results in bonding strength reduction after HST and PCT. The surface structure change caused by copper oxidation after HST and PCT also reduced the bonding strength. These findings will greatly benefit future power module design.

From brain to bone: Harnessing extracellular vesicles released from TBI to enhance osteogenesis by 3D-Printed hydrogel scaffold

The clinical indications reveal that traumatic brain injury (TBI) accelerates the process of limb bone regeneration. However, the mechanisms underlying this phenomenon remain ambiguous. In this inquiry, the activation of endogenous neural stem cells in the hippocampus post TBI led to the secretion of extracellular vesicles (NSC-EV) that targeted bone marrow mesenchymal stem cells, ultimately promoting bone healing. The enrichment of miR-9-5p in NSC-EV facilitated osteogenesis through the activation of the MAP3K3 pathway. We also present a novel hydrogel formulation for clinical application of NSC-EVs by means of ROS-responsive EV delivery. The hydrogel was cross-linked with EVs to create a water-based gel encapsulation, which was applied to a 3D-printed β-TCP scaffold for controlled long-term release that corresponded to those of physiological bone tissue. Our investigation represents the inaugural usage of EVs derived from neural stem cells in bone tissue engineering. These EVs were found to encourage information exchange between the central nervous system and bone tissue regeneration. Our composite scaffold demonstrated impressive bone regeneration qualities in rats with cranial defects, highlighting its potential for pioneering approaches in bone tissue engineering and innovative medical technologies for clinical applications.

Encapsulation of biologically active additives and probiotics by spraying

This article discusses the encapsulation of biologically active additives (BAA) and probiotics by spraying method. Today, a large number of BAA are registered in the country, the issue of rational classification of BAA is relevant. In the production of BAA, the use of plants, fungi and BAA that pose a danger to human life and health is not allowed. Currently, the importance of probiotics for enhancing and maintaining human immunity is emphasized.There are many technologies for encapsulating dietary supplements and probiotics: extrusion, spray drying, spray freezing, addition to the matrix, gel encapsulation, encapsulation in a fluidized bed. Based on the literature review, alginate polymer encapsulation technologies are considered.Sodium alginate was selected as the materials for the experiments. A solution of sodium alginate has been prepared. Capsules obtained from 0.5% sodium alginate are soft, with an inhomogeneous surface, not spherical in shape, which is due to the low viscosity of sodium alginate, the average size was 2,0×10-3м.In an experiment with a concentration of a solution of 1% sodium alginate, it was not possible to obtain capsules by spraying due to the high viscosity. The capsules were obtained by the drip method, had a rounded shape, dense structure, the average size was 3,2×10-3м.

Sulfoaluminate cement-modified straw biochar as a soil amendment to inhibit Pb-Cd mobility in the soil-romaine lettuce system

Biochar is widely used to remediate soil polluted by potentially toxic elements (PTEs), while the effect of a new type of biochar, obtained from modified cement material, on the mobility of Pb and Cd in the soil-plant system is still unknown. In this study, soils doped with sulfoaluminate cement modified biochar (SBC) were characterized using a series of approaches including FTIR, XRD, and XPS, and combined with pot experiments to explore its synergistic effects on the speciation transformation, accumulation, and mobility of both Pb and Cd in a soil-romaine lettuce system in heavily contaminated soils containing 500 mg·kg−1-Pb and 3 mg·kg−1-Cd. The results showed that SBC effectively immobilized Pb and Cd in the soil and that this was achieved through cation exchange, complexation, and gel encapsulation. Moreover, SBC also changed the soil physicochemical properties and indirectly affected the speciation transformation of Pb and Cd. FTIR and XRD analyses revealed that the groups such as –OH, –COOH, SO42−, and SiO32−introduced by SBC stimulated the conversion from the soluble to the residual state of Pb. XPS analysis indicated that, the deviation of the C–O–C, C–OOH, and O–CO peak and the increased in area suggested that organic groups in the SBC were engaged in the immobilization mechanism of Pb and Cd. The transformation of residual Cd in other extractable fractions might be due to either enhanced soil reducibility or competitive adsorption with Pb. In 5% SBC soil, Pb was reduced by 27.69% and 64.84%, and Cd was reduced by 20.45% and 35.87% for shoots and roots of romaine lettuce, respectively. SBC showed a significantly positive correlation with SOM, while SOM showed a highly significantly negative correlation with both Pb and Cd in the roots. In summary, SBC can be strongly recommended as a green amendment to remediate Pb–Cd contaminated soil and to inhibit the mobility to plant.

Failure mechanisms of the bonded interface between mold epoxy and metal substrate exposed to high temperature

The fast development of electric vehicles promoted the development of next-generation power modules. Along with this trend, the encapsulation techniques are also transforming from previous gel encapsulation to epoxy encapsulation because epoxy encapsulation reduces the module size significantly. However, the dissimilar bonding between the epoxy and the metal substrate is a weak part of the entire module. Unlike previous studies, which focused on epoxy properties and thermal stress, we investigated the failure mechanisms between the encapsulation epoxy and the copper substrate under high temperatures by considering the interfacial interaction. A high-temperature storage test (HST) was performed at 200 °C until 1000 h for encapsulated packages. We then measured the bonding strength and identified the fracture path at the nanoscale by SEM, XPS, and ToF-SIMS depth profiling. In addition, the changes in the epoxy were characterized by ATR-FTIR, nanoindentation, and XPS depth profiling. The bonding interface was analyzed with AFM-IR, SEM, EDS, and STEM. We found that the fracture happened inside the epoxy rather than the copper/epoxy interface. More importantly, we found that copper atoms diffused into the epoxy reaching approximately 100 nm. The diffused copper atoms and the long-time high-temperature heating promoted the epoxy pyrolysis, forming a 100 nm thick weak layer at the epoxy side, which is the key reason for the high-temperature failure. Our study provided a fresh understanding of the failure mechanisms of the bonding between encapsulation epoxy and the copper substrate under HST, which will contribute significantly to future power module design and material development.

Content Size-Dependent Alginate Microcapsule Formation Using Centrifugation to Eliminate Empty Microcapsules for On-Chip Imaging Cell Sorter Application.

Alginate microcapsules are one of the attractive non-invasive platforms for handling individual cells and clusters, maintaining their isolation for further applications such as imaging cell sorter and single capsule qPCR. However, the conventional cell encapsulation techniques provide huge numbers of unnecessary empty homogeneous alginate microcapsules, which spend an excessive majority of the machine time on observations and analysis. Here, we developed a simple alginate cell encapsulation method to form content size-dependent alginate microcapsules to eliminate empty microcapsules using microcapillary centrifugation and filtration. Using this method, the formed calcium alginate microcapsules containing the HeLa cells were larger than 20m, and the other empty microcapsules were less than 3m under 4000 rpm centrifugation condition. We collected cell-containing alginate microcapsules by eliminating empty microcapsules from the microcapsule mixture with simple one-step filtration of a 20 m cell strainer. The electrical surface charge density and optical permeability of those cell-encapsulated alginate microcapsules were also evaluated. We found that the surface charge density of cell-encapsulated alginate microbeads is more than double that of cells, indicating that less voltage is required for electrical cell handling with thin alginate gel encapsulation of samples. The permeability of the alginate microcapsule was not improved by changing the reflective index of the medium buffer, such as adding alginate ester. However, the minimized thickness of the alginate gel envelope surrounding cells in the microcapsules did not degrade the detailed shapes of encapsulated cells. Those results confirmed the advantage of alginate encapsulation of cells with the centrifugation method as one of the desirable tools for imaging cell sorting applications.

Synergistic influence of ultrasound and dietary fiber addition on transglutaminase-induced peanut protein gel and its application for encapsulation of lutein

The effects of the combination of ultrasound and dietary fiber (DF) addition on the properties of transglutaminase (TGase) induced peanut protein (PP) gels and its applicability as carrier for lutein were investigated. The combination of ultrasound and DF addition reduced the particle size and increased the zeta potential of PP, leading to the exposure of more hydrophobic and sulfhydryl groups, which contributed to the formation of covalent ε-(γ-glutaminyl) lysine isopeptide bonds, hydrophobic interactions and disulfide bonds during the TGase-induced PP gelation. Ultrasound and DF addition synergistically increased the viscoelasticity and immobilized water of PP gel due to a more compact microstructure, thus improving gel strength and water holding capacity. The improvement of PP gelation properties was related to the unfolding and disordering of protein secondary structure and strong PP-DF interactions. Lutein was encapsulated in PP gels treated with the combination of ultrasound and DF addition. The gel yield, encapsulation efficiency and chemical stability of lutein were enhanced. The ultrasound and DF addition synergistically promoted the sustained and controlled release effect of PP gels on lutein during simulated gastrointestinal digestion due to the reduction in protein loss and swelling properties of gels, while it resulted in a higher release ratio in the intestinal phase than in the gastric phase, which improved the directional release efficiency of lutein during intestinal digestion. Therefore, the synergy of ultrasound and DF addition strengthened PP gels and improved their delivery potential for lutein.

Delivery system for grape seed extract based on biodegradable pectin-Zn-alginate gel particles

Pectin-Zn-alginate gel particles from callus culture pectin with increased linearity and decreased rhamnogalacturonan I branching and degree of methylesterification had a higher gel strength and encapsulation capacity. An increase of the alginate concentration led to an increase in the particle gel strength. The grape seed extract (GSE) loaded and empty particles swelled slightly in the simulated gastric fluid (SGF) and gradually in the intestinal (SIF) fluid. The swelling degrees of the GSE-loaded and empty particles in the simulated colonic fluids (SCF) were decreased in the range SCF-7.0 (pH 7.0 + pectinase) > SCF-5.3 (pH 5.3 + pectinase) > SCF-2.3 (pH 2.3 + pectinase). The FTIR spectra indicated that GSE was embedded in the composite particles. Negligible leakage of GSE in SGF was shown. The increase in GSE release in SIF was due to the decrease in particle gel strength and increased swelling degree. The GSE release in fluids simulating the colon inflammation (SCF-2.3 and SCF-5.3) was similar, and it was lower than that in the SCF-7.0 simulating a healthy colon due to the increased gel strength. The percentage release of GSE increased slightly after exposure to different pH. Pectin-Zn-alginate hydrogel systems may be promising candidates for colon-targeted GSE delivery systems.

Extrusion 3D bioprinting of functional self-supporting neural constructs using a photoclickable gelatin bioink

Many in vitro models of neural physiology utilize neuronal networks established on two-dimensional substrates. Despite the simplicity of these 2D neuronal networks, substrate stiffness may influence cell morphology, network interactions and how neurons communicate and function. With this perspective, three-dimensional (3D) gel encapsulation is a powerful to recapitulating aspects of in vivo features, yet such an approach is often limited in terms of the level of resolution and feature size relevant for modelling aspects of brain architecture. Here, we report 3D bioplotting of rat primary cortical neural cells using a hydrogel system comprising gelatin norbornene (GelNB) and poly (ethylene glycol) dithiol (PEGdiSH). This bioink benefits from a rapid photo-click chemistry, yielding eight-layer crosshatch neural scaffolds and a filament width of 350 µm. The printability of this system depends on hydrogel concentration, printing temperature, extrusion pressure and speed. These parameters were studied via quantitative comparison between rheology and filament dimensions to determine the optimal printing conditions. Under optimal conditions, cell viability of bioprinted primary cortical neurons at day 1 (68 ± 2%) and at day 7 (68 ± 1%) were comparable to the 2D control group (72 ± 7%). The present study relates material rheology and filament dimensions to generate compliant free-standing neural constructs through bioplotting of low-concentration GelNB-PEGdiSH, which may provide a step forward to study 3D neuronal function and network formation.

Lactic acid bacteria: economic propagation, chitinases activity, and enhancing viability by gel encapsulation

Background In a previous study, a lactic acid bacterium, Enterococcus faecium, was locally isolated from Egyptian soil and its ability to inhibit the growth of a test phytopathogen was proven.Objective The study was performed to assess the ability of the tested strain to grow on different media. The produced antifungal agent was investigated. Finally, the strain was encapsulated within different biopolymers to increase its viability.Materials and methods Several byproducts were tested and compared with the standard De Man-Rogosa-Sharpe medium. The antifungal activity was tested using the poisoned food technique. Chromatographic analysis of the fermentation medium was performed using high-performance liquid chromatography. Production of chitinase was confirmed by cultivating the test strain on chitin and estimating the amount of reducing sugars using the Somogyi method. The E. faecium cells were also encapsulated within soy protein isolate-alginate beads, gellan gum discs, and carboxymethyl cellulose beads.Results and conclusion The strain was able to grow on all of the tested byproducts and exerted a potent antifungal activity against Fusarium solani, especially when a very economic medium, mainly composed of whey, was used. High-performance liquid chromatography results confirmed the production of a number of organic acids that contributed in the inhibition of the fungal growth. The study also proved the production of chitinase enzymes, which apparently altered the chitinous layer present in the cell wall of F. solani, causing disintegration of the fungal cells. It was also shown that encapsulation of E. faecium increased its viability in soil as compared with the free uncapsulated strain.

Synthesis, optical, dielectric and thermal property studies of lead mandelate crystals

Lead Mandelate crystals which belong to the class of Metal Organic Frameworks were grown by gel encapsulation technique using chemical reaction method. Powder XRD studies were conducted. The crystalline nature of the grown sample is evident from the XRD data. The grown crystals were characterized by FTIR, Raman and UV–Visible spectroscopy. The FTIR and Raman spectrum confirmed the presence of the various functional groups in the sample. From the UV–Vis studies, it is observed that the sample shows very less absorbance in the entire visible region, which makes it a potential candidate for nonlinear application. The lower cut off wavelength was calculated to be 254 nm. The estimated value of optical bandgap of the grown crystal is 4.42 eV. Thermogravimetric analysis (TGA) was done to study the thermal stability of the grown crystal. The TGA curve establishes that Lead Mandelate crystals have thermal stability upto a temperature of 210 °C. The dielectric studies of the grown crystals conducted at room temperature shows a normal dielectric behavior. The variation of dielectric constant and dielectric loss of the sample with frequency of applied field is studied. Both dielectric constant and dielectric loss is found to decrease with increase in frequency of applied field. The dielectric constant varies in the range between 21.41 and 10.53 for an applied frequency range 0.01Hz–10MHz. The conductivity of the grown crystal is observed to increase with frequency.

Sol–Gel Encapsulation of ZnAl Alloy Powder with Alumina Shell

Additive manufacturing (AM), for example, directed energy deposition (DED), may allow the processing of self-healing metal–matrix composites (SHMMCs). The sealing of cracks in these SHMMCs would be achieved via the melting of micro-encapsulated low melting point particulates (LMPPs), incorporated into the material during AM, by heat treatment of the part during service. Zn-Al alloys are good candidates to serve as LMPPs, for example, when the matrix of the MMC is made of an aluminum alloy. However, such powders should first be encapsulated by a thermal and diffusion barrier. Here, we propose a sol–gel process for encapsulation of a custom-made ZA-8 (Zn92Al8, wt.%) core powder in a ceramic alumina (Al2O3) shell. We first modify the surface of the ZA-8 powder with (12-phosphonododecyl)phosphonic acid (Di-PA) hydrophobic self-assembled monolayer (SAM) in order to prevent extensive hydrogen evolution and formation of non-uniform and porous oxide/hydroxide surface layers during the sol–gel process. Calcination for 1 h at 500 °C is found to be insufficient for complete boehmite-to-γ(Al2O3) phase transformation. Thermal stability tests in an air-atmosphere furnace at 600 °C for 1 h result in melting, distortion, and sintering into a brittle sponge (aggregate) of the as-atomized powder. In contrast, the core/shell powder is not sintered and preserves its spherical morphology, with no apparent “leaks” of the ZA-8 core alloy out of the ceramic encapsulation.

The Thermogel Chronicle─From Rational Design of Thermogelling Copolymers to Advanced Thermogel Applications

ConspectusTemperature responsive supramolecular hydrogels, also known as thermogels, are produced by the self-assembly of amphiphilic copolymers in solution following temperature stimulus. They are a class of high caliber novel materials possessing highly attractive properties such as injectability, ability to undergo temperature controlled reversible sol–gel phase transitions, high biocompatibility, and tunable biodegradability. Much research vigor has been dedicated to designing advanced amphiphilic copolymers and investigating their molecular interactions in order to enhance the properties of the thermogelling systems and expand the scope of their applications. As such, thermogelling systems have since become well established in the field of sustained localized drug or protein delivery and have also been demonstrated as high potential materials for niche applications such as three-dimensional cell culture, wound healing patches, and vitreous endotamponades. Recent developments saw the advent of thermogelling systems with advanced biomedical applications ranging from enhanced cancer therapy to radiology imaging to tissue engineering, and these are usually achieved by the conjugating of biologically relevant molecules such as drugs and peptides to the thermogel copolymer or by incorporating nanoparticles into the thermogel systems. New developments in this field see a shift away from employing traditional synthetic polymers such as polypropylene glycol (PPG) and poly(lactic-co-glycolic acid) (PLGA) to utilizing more advanced nature-derived bioactive molecules and also introducing chiral moieties in the thermogelling copolymer backbone.There are currently a few main types of thermogel copolymers such as diblock, triblock, end-capped, graft, and random multiblock polyurethane thermogels. Among these, our lab is specialized in the synthesis and application of polyurethane multiblock thermogels. These thermogels have the advantage of high molecular weights and enhanced intermolecular hydrogen bonding arising from the urethane groups. These generally allow for the formation of thermogelling systems with higher gel stiffness, resilience, and encapsulation efficiency, allowing these polyurethane thermogels to be well suited for niche applications such as sustained drug delivery and vitreous endotamponades. In this Account, we summarize the fundamental polymeric factors influencing the micellar and bulk polyurethane thermogel properties, provide our group’s insights into the rational design of these thermogels for various advanced applications and finally discuss the future possibilities of thermogelling systems. We speculate that there is still much untapped potential of thermogels in the biomedical field and these can possibly be achieved by designing thermogel copolymers with bioactive moieties and exploring more advanced branched architectures. In addition, we also propose the expansion of thermogels beyond biomedical fields, for which our lab has demonstrated thermogels as electrode contacts for noninvasive plant health monitoring.