Gel Films Research Articles

Chitosan-Based Green Pea (Pisum sativum L.) Pod Extract Gel Film: Characterization and Application in Food Packaging

This work focuses on studying the preparation, characterization (physical, mechanical, optical, and morphological properties as well as antioxidant and antimicrobial activities) and packaging application of chitosan (CH)-based gel films containing varying empty green pea pod extract (EPPE) concentrations (0, 1, 3, and 5% w/w). The experiments revealed that adding EPPE to CH increased the thickness (from 0.132 ± 0.08 to 0.216 ± 0.08 mm), density (from 1.13 ± 0.02 to 1.94 ± 0.02 g/cm3), and opacity (from 0.71 ± 0.02 to 1.23 ± 0.04), while decreasing the water vapour permeability, water solubility, oil absorption ratio, and whiteness index from 2.34 to 1.08 × 10-10 g-1 s-1 pa-1, from 29.40 ± 1.23 to 18.75 ± 1.94%, from 0.31 ± 0.006 to 0.08 ± 0.001%, and from 88.10 ± 0.43 to 77.53 ± 0.48, respectively. The EPPE films had better tensile strength (maximum of 26.87 ± 1.38 MPa), elongation percentage (maximum of 58.64 ± 3.00%), biodegradability (maximum of 48.61% after 3 weeks), and migration percentages than the pure CH-gel film. With the addition of EPPE, the antioxidant and antibacterial activity of the film improved. SEM revealed that as EPPE concentration increased, agglomerates formed within the films. Moreover, compared to control samples, packing corn oil in CH-based EPPE gel films slowed the rise of thiobarbituric acid and peroxide values. As an industrial application, CH-based EPPE films have the potential to be beneficial in food packaging.

Fast determination of electrolyte elements in human blood plasma using surface-enhanced laser-induced breakdown spectroscopy combined with a gel film method

In this work, surface-enhanced laser-induced breakdown spectroscopy combined with a gel film method was used to improve the detection sensitivity and accuracy of electrolyte elements in human blood plasma.

Self-Powered Flexible Multicolor Electrochromic Devices for Information Displays.

The development of self-powered flexible multicolor electrochromic (EC) systems that could switch different color without an external power supply has remained extremely challenging. Here, a new trilayer film structure for achieving self-powered flexible multicolor EC displays based on self-charging/discharging mechanism is proposed, which is simply assembled by sandwiching an ionic gel film between 2 cathodic nickel hexacyanoferrate (NiHCF) and Prussian blue (PB) nanoparticle films on indium tin oxide substrates. The display exhibits independent self-powered color switching of NiHCF and PB films with fast responsive time and high reversibility by selectively connecting the Al wire as anodes with the 2 EC films. Multicolor switching is thus achieved through a color overlay effect by superimposing the 2 EC films, including green, blue, yellow, and colorless. The bleaching/coloration process of the displays is driven by the discharging/self-charging mechanism for NiHCF and PB films, respectively, ensuring the self-powered color switching of the displays reversibly without an external power supply. It is further demonstrated that patterns can be easily created in the self-powered EC displays by the spray-coating method, allowing multicolor changing to convey specific information. Moreover, a self-powered ionic writing board is demonstrated based on the self-powered EC displays that can be repeatedly written freehand without the need of an external power source. We believe that the design concept may provide new insights into the development of self-powered flexible multicolor EC displays with self-recovered energy for widespread applications.

Preparation and characterization of chitosan/Aloe Vera gel film for fresh fruit preservation

Biofilm preservation has become a topic of interest among many scientists. A recent study involved the production of chitosan-based biofilms containing varying amounts of aloe vera gel (5%, 10% and 15% w/w). Evaluation of film formation, water absorption, swelling ratio, solubility, antibacterial ability, colouration, and biodegradability indicated that chitosan film added with 10% aloe vera (CS-10%AV) had the best properties. The study also found that using CS-A10 film to preserve tomatoes helped maintain the fruit’s colour and shape for longer while retaining vitamin C and acids for an extended period.

Preparation and characterization of antioxidant gel foam for preventing coal spontaneous combustion

New antioxidant gel foam is prepared to improve its stability and effectiveness in preventing coal spontaneous combustion. The physicochemical composite inhibitor is prepared by introducing procyanidins into a super absorbent polymer. And then the inhibitor is incorporated into the gel foam (surfactant, foam stabilizer, and gel system), the combined properties of foam, gel and inhibitor are utilized to prevent coal spontaneous combustion. The optimal composition ratio of antioxidant gel foam is obtained by single-factor experiments and response surface methodology. The microstructure of the foam is characterized. The properties of antioxidant gel foam in preventing coal spontaneous combustion are compared and analyzed through cementation, film-forming, and temperature-programmed experiments. The results reveal that the foam properties of the antioxidant gel foam are better when the mass fractions of surfactant, foam stabilizer, gel system, and inhibitor are 0.92 %, 0.49 %, 0.34 %, and 0.55 %, respectively. The inhibitor constitutes a high-water retention skeleton structure of foam wall and stabilizes the platform boundary. The antioxidant gel foam has small bubble size, uniform distribution, and excellent stability. The foam coarsening process is slow, which can fully wet the coal and reduce the coal temperature. Simultaneously, the antioxidant has better cementation and film-forming properties, which can cement the crushed coal and form a complete gel film, blocking the air leakage channels and isolating the contact between the coal and oxygen. Besides, the inhibition effect of antioxidant on coal spontaneous is better than that of water-based foam, polymer-stabilized foam, and ordinary gel foam. It can effectively slow down the oxygen consumption rate, gas production rate, and exothermic intensity during coal oxidation, the inhibition rate at 100 °C is 74.48 %. This study provides an antioxidant gel foam with good foam properties and inhibition effect, which can effectively reduce the oxidation rate of coal and prevent its spontaneous combustion through the physical effects on covering, wetting, and cementing, as well as inhibiting the chemical reaction between coal and oxygen.

Characterization of Hydrogel Films with Reflective Colors Templated by Colloidal Crystals

In this report, we successfully fabricated the temperature-responsive porous gel film by templating the colloidal crystal (CC) film of silica microparticles embedded in a hydrogel matrix of poly(N-isopropylacrylamide) (NIPA). As elevating the temperature from 25 ℃, this porous gel film showed the color changes of Bragg reflection from red to blue, arising from the geometric decrease in the lattice spacing of pores caused by the shrinkage of NIPA gel matrix upon heating process. Such reflection color changes of the porous gel film were found to be fully reversible in the temperature range between 26 ℃ and 33 ℃. Moreover, Fourier transform infrared (FT-IR) spectroscopy and thermal gravimetric analysis (TGA) measurements suggested that the silica microparticles of CC film are thoroughly removed after treatment with hydrofluoric acid, thereby resulting in the formation of porous NIPA gel film without the silica component. This report provides a promising protocol to check the residual silica microparticles in porous gel films by both FT-IR and TGA measurements.

Influence of elapsed time on adsorption equilibrium of water vapor to silica gel film

For adsorption chillers or desiccant systems, thin film adsorbents coated on heat exchanger surfaces contribute to enhance adsorption/desorption rate of vapor, due to low thermal resistance leading to quick exothermic/endothermic heat exchange with external cooling/hot fluid. They enable to downsize adsorbent heat exchanger in systems. In the present study, a silica gel thin film synthesized on aluminum plate was proposed as a novel adsorbent. Pore structure of this new adsorbent changed during 15 months after synthesis: pore diameter enlarging and specific surface area decreasing. Upon this, the influence of time elapsed after synthesis on equilibrium adsorption of water vapor was examined under various adsorbing conditions until 22 months after synthesis. The equilibrium showed S-shape curve characteristics with respect to relative humidity, and decreased monotonously with elapsed time in wide relative humidity range, which was attributed to the pore structure change. Decreasing of equilibrium was not seen after 15 months from synthesis, that is, stabilization was attained. The equilibrium reduction in low relative humidity range was analyzed with the BET equation. Moreover, relative humidity of capillary condensation occurring was compared to the Kelvin equation. Finally, the equilibrium was formulated which reproduced well the measurements over the entire relative humidity range.

Wide-Range Linear Iontronic Pressure Sensor with Two-Scale Random Microstructured Film for Underwater Detection.

A broad linear range of ionic flexible sensors (IFSs) with high sensitivity is vital to guarantee accurate pressure acquisition and simplify back-end circuits. However, the issue that sensitivity gradually decreases as the applied pressure increases hinders the linearity over the whole working range and limits its wide-ranging application. Herein, we design a two-scale random microstructure ionic gel film with rich porosity and a rough surface. It increases the buffer space during compression, enabling the stress deformation to be more uniform, which makes sure that the sensitivity maintains steady as the pressure loading. In addition, we develop electrodes with multilayer graphene produced by a roll-to-roll process, utilizing its large interlayer spacing and ion-accessible surface area. It benefits the migration and diffusion of ions inside the electrolyte, which increases the unit area capacitance and sensitivity, respectively. The IFS shows ultra-high linearity and a linear range (correlation coefficient ∼ 0.9931) over 0-1 MPa, an excellent sensitivity (∼12.8 kPa-1), a fast response and relaxation time (∼20 and ∼30 ms, respectively), a low detection limit (∼2.5 Pa), and outstanding mechanical stability. This work offers an available path to achieve wide-range linear response, which has potential applications for attaching to soft robots, followed with sensing slight disturbances induced by ships or submersibles.

Promoting adsorption performance and mechanical strength in composite porous gel film

Starch is widely used to prepare biodegradable films due to its superior biocompatibility, low immunogenicity, and renewability. In this work, a novel K+/carrageenan porous-starch/casein gel film with high oil absorption was prepared using modified porous starch. Optimal gel stability and uniformity were obtained when adding 10 mg/mL k-carrageenan and 2 mg/mL K+ to 2 mg/mL microgels, with significantly reduced crystallinity and elasticity and increased tensile strength. The concentration of k-carrageenan was the main factor affecting gel strength and the hydrophilic and mechanical properties of the film. In addition, the film-forming solution showed excellent fluidity and spreading typical of non-Newtonian fluids. The film also exhibited a highly porous structure, as visualized by SEM and AFM, in line with a cumulative oil absorption rate of 87.5 % within 20 min, which was significantly higher than that obtained with glutinous rice starch. In conclusion, reinforcement of starch-based microgels as described in this study can maximize the film's adsorption performance and mechanical properties, with promising applications in skin care and beauty products.

Integration of enzyme-encapsulated mesoporous silica between nanohole array electrode and hydrogel film for flow-type electrochemical biosensor.

We herein propose a simple and sensitive electrochemical flow biosensor platform without an external flow device. The sensing unit comprises a platinum nanohole array electrode deposited on a nanoporous track-etched membrane (PtNH/NPM), a packed-layer of glucose oxidase-encapsulated mesoporous silica particles (GOD/MPS), and bovine serum albumin hydrogel film (BSA gel film). This sensing unit was fixed at the open window at the side of the plastic container with internal solution containing NaCl as osmotic reagent. When the sample glucose solution (0.10mL) was pipetted at the sensing unit, a portion of the sample solution (5 μL) was spontaneously transferred into the BSA gel film. The concentration gradient of NaCl between the internal solution and the BSA gel film induced osmotic flow of water toward the internal solution. This osmotic flow assisted delivery of glucose to the GOD/MPS and enzymatically generated H2O2 to the PtNH/NPM. The proposed sensor could be used repeatedly and produced a linear current response for glucose, with a limit of detection of 16μM. These sensor performances confirmed availability of the sensor design utilizing the osmotic flow.

Sol-gel-based porous Ti-doped tungsten oxide films for high-performance dual-band electrochromic smart windows

Dual-band electrochromic smart windows (DESWs) with independent control of the transmittance of near-infrared and visible light show great potential in the application of smart and energy-saving buildings. The current strategy for building DESWs is to screen materials for composite or prepare plasmonic nanocrystal films. These rigorous preparation processes seriously limit the further development of DESWs. Herein, we report a facile and effective sol–gel strategy using a foaming agent to achieve porous Ti-doped tungsten oxide film for the high performance of DESWs. The introduction of foaming agent polyvinylpyrrolidone during the film preparation can increase the specific surface area and free carrier concentration of the films and enhance their independent regulation ability of near-infrared electrochromism. As a result, the optimal film shows excellent dual-band electrochromic properties, including high optical modulation (84.9% at 633 nm and 90.3% at 1200 nm), high coloration efficiency (114.9 cm2 C-1 at 633 nm and 420.3 cm2 C-1 at 1200 nm), quick switching time, excellent bistability, and good cycle stability (the transmittance modulation losses at 633 and 1200 nm were 11% and 3.5% respectively after 1000 cycles). A demonstrated DESW fabricated by the sol–gel film showed effective management of heat and light of sunlight. This study represents a significant advance in the preparation of dual-band electrochromic films, which will shed new light on advancing electrochromic technology for future energy-saving smart buildings.

Evaluation of the optimal dose for maximizing the anti-adhesion performance of a self-degradable dextran-based material

LYDEX, which is a hydrogel composed of aldehyde-functionalized dextran and succinic anhydride-treated ε-poly-L-lysine, was previously developed by our group as a self-degradable adhesive with an excellent functionality. As a result, this hydrogel has been investigated for a wide range of medical applications, including hemostatic agents, sealants, wound dressings for endoscopes, and anti-adhesion materials. Previously, the unique potential of LYDEX to control the in vivo degradation rate depending on its composition was verified for use in anti-adhesion applications. Although the gel thickness also plays a significant role in determining the degradation rate, this issue was not sufficiently investigated in previous studies. Thus, in the current study, the optimal LYDEX dose (film thickness) for maximizing the anti-adhesion material performance was verified using a rabbit colon model and it was confirmed that the gel film thickness affects the degradation period and anti-adhesion effect. The obtained results suggest the potential for designing LYDEX materials suitable for application at a wider range of in vivo treatment sites, which could be extremely valuable for the development and use of novel anti-adhesion materials with adequate hemostatic and sealant performances.

A PEGylated Chitosan as Gel Polymer Electrolyte for Lithium Ion Batteries.

Due to their safety and sustainability, polysaccharides such as cellulose and chitosan have great potential to be the matrix of gel polymer electrolytes (GPE) for lithium-based batteries. However, they easily form hydrogels due to the large numbers of hydrophilic hydroxyl or amino functional groups within their macromolecules. Therefore, a polysaccharide-based amphiphilic gel, or organogel, is urgently necessary to satisfy the anhydrous requirement of lithium ion batteries. In this study, a PEGylated chitosan was initially designed using a chemical grafting method to make an GPE for lithium ion batteries. The significantly improved affinity of PEGylated chitosan to organic liquid electrolyte makes chitosan as a GPE for lithium ion batteries possible. A reasonable ionic conductivity (1.12 × 10-3 S cm-1) and high lithium ion transport number (0.816) at room temperature were obtained by replacing commercial battery separator with PEG-grafted chitosan gel film. The assembled Li/GPE/LiFePO4 coin cell also displayed a high initial discharge capacity of 150.8 mA h g-1. The PEGylated chitosan-based GPE exhibits great potential in the field of energy storage.

High-strength super-hydrophobic double-layered PBO nanofiber-polytetrafluoroethylene nanocomposite paper for high-performance wave-transparent applications

Poly(p-phenylene-2,6-benzobisoxazole) nanofiber (PNF) paper is facing unprecedented challenges in enhancing the interaction between the PNFs and improving its hydrophobicity. In this work, a sol–gel film transformation approach was developed to fabricate high-strength PNF paper. Iron ions formed coordination bonds between PNFs to obtain a preforming three-dimensional, interconnective nanofiber network. Subsequently, polytetrafluoroethylene (PTFE) particles were sprayed onto the surface of the paper, followed by thermal treatment to obtain double-layered PTFE-P/PNF nanocomposite paper. The nanocomposite paper presents incredible tensile strength (271.6 MPa, increased by 52.9%), folding endurance, super-hydrophobicity, and self-cleaning performances. Moreover, it exhibits low dielectric constant (2.06) and dielectric loss tangent (0.0133) values. According to the wave-transparent model for a double-layered dielectric established by Maxwell’s equations, the wave-transparent coefficients of electromagnetic waves incident from both sides of the paper are 97.6% (PNF side) and 96.0% (PTFE/P(S-co-BCB-co-MMA) side), respectively. The PTFE-P/PNF nanocomposite paper possesses great potential in the fields of wave-transparent applications.

Application of traditional Chinese medicine in film drug delivery system.

Film drug delivery systems have the advantages of precise administration, simple process and easy portability, compared with other traditional drug delivery systems such as tablets, capsules, syrups, ointments, etc. The traditional Chinese medicine (TCM) are normally developed in four categories of film agent like patch film, coating, spray film and gel film, which are applied to the treatment of oral ulcers, chronic diseases of lower limbs, burns, scalds, gynecological disease and body care. So the TCM film has great research value and prominent market prospect. In this review, we summarized the research progress of the material composition, pharmaceutical production, clinical application and pharmacology mechanism of various TCM film agents. It may provide a comprehensive reference for further development and utilization of TCM film agents.

Production of Thermoplastic Starch-Aloe vera Gel Film with High Tensile Strength and Improved Water Solubility.

Biodegradable film packaging made from thermoplastic starch (TPS) has low mechanical performance and high water solubility, which is incomparable with synthetic films. In this work, Aloe vera (AV) gel and plasticized soluble potato starch were utilised to improve the mechanical stability and water solubility of TPS. Dried starch was mixed with glycerol and different AV gel concentrations (0% to 50%). The TPS + 50% AV gel (30 g TPS + 15 g AV gel) showed the best improvement compared to TPS alone. When compared to similar TPS films with AV gel added, this film is stronger and dissolves better in water. Mechanical qualities improved the tensile strength and Young’s modulus of the TPS film, with 1.03 MPa to 9.14 MPa and 51.92 MPa to 769.00 MPa, respectively. This was supported by the improvement of TPS water solubility from 57.44% to 46.6% and also by the increase in decomposition temperature of the TPS. This promises better heat resistance. The crystallinity percentage increase to 24.26% suggested that the formation of hydrogen bonding between TPS and AV gel enhanced crosslinking in the polymeric structure. By adding AV gel, the TPS polymeric structure is improved and can be used as a biodegradable food-packaging film.

Bioinspired Collagen/Gelatin Nanopillared Films as a Potential Implant Coating Material.

Collagen-based Sharpey’s fibers are naturally located between alveolar bone and tooth, and they have critical roles in a well-functioning tooth such as mechanical stability, facile differentiation, and disease protection. The success of Sharpey’s fibers in these important roles is due to their unique location, vertical alignment with respect to tooth surface, as well as their micronanofiber architecture. Inspired by these structures, herein, we introduce the use of nanoporous anodic aluminum oxide molds in a drop-casting setup to fabricate biopolymeric films possessing arrays of uniform Collagen:Gelatin (Col:Gel) nanopillars. Obtained structures have diameters of ∼90 nm and heights of ∼300 nm, yielding significantly higher surface roughness values compared to their flat counterparts. More importantly, the nanostructures were parallel to each other but perpendicular to the underlying film surface imitating the natural collagenous structures of Sharpey’s fibers regarding nanoscale morphology, geometrical orientation, as well as biochemical content. Viability testing showed that the nanopillared Col:Gel films have high cell viabilities (over 90%), and they display significantly improved attachment (ca. ∼ 2 times) and mineralization for Saos-2 cells when compared to flat Col:Gel films and Tissue Culture Polystyrene (TCPS) controls, plausibly due to their largely increased surface roughness and area. Hence, such Sharpey’s fiber-inspired bioactive nanopillared Col:Gel films can be used as a dental implant coating material or tissue engineering platform with enhanced cellular and osteogenic properties.

Animal Cellulose with Hierarchical Structure Isolated from Halocynthia aurantium Tunic as the Basis for High-Performance Pressure-Resistant Nanofiltration Membrane.

The structure and transport properties of the new Cellokon-AKH membrane based on animal cellulose obtained from tunic of ascidian Halocynthia aurantium were studied. The results of scanning electron microscopy (SEM), FTIR spectroscopy, and the X-ray diffraction data revealed significant differences in the structure and morphology of upper and lower surfaces of this layered film membrane based on animal cellulose. It was shown that the membrane surface is a network of intertwined cellulose fibers, with both denser and looser areas present on the lower surface compared to the completely uniform morphology of the main part of the upper surface. The hierarchical structure of tunicin-based outgrowths evenly distributed over the upper surface was determined and analyzed. The 3D visual representation of the surface structure was performed with the surface reconstruction technique using scanning electron microscope images. A surface model was calculated from the aligned images based on the photogrammetric approach. The transport properties of samples with different prehistory with respect to ethanol, water, and their mixtures of different compositions were studied depending on the pressure. Representing an alcohol-containing gel film in its original state, as solvents are removed, the membrane transforms into a low-permeability fibrillary organized selective film. The obtained results confirmed the possibility of using Cellokon-AKH (dried form) for the filtration of substances with a molecular weight of more than 600 Da in various media. Further study of this new material will allow to get closer to understanding the structure of the studied seabed inhabitants and to use these natural resources more efficiently.

Characterization and corrosion inhibition studies of protective sol–gel films modified with tannin extracts on low carbon steel

Characterization and corrosion inhibition studies of protective sol–gel films modified with tannin extracts on low carbon steel

Multifunctional Zn-Doped ITO Sol-Gel Films Deposited on Different Substrates: Application as CO2-Sensing Material.

Undoped and Zn-doped ITO (ITO:Zn) multifunctional thin films were successfully synthesized using the sol–gel and dipping method on three different types of substrates (glass, SiO2/glass, and Si). The effect of Zn doping on the optoelectronic, microstructural, and gas-sensing properties of the films was investigated using X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), spectroscopic ellipsometry (SE), Raman spectroscopy, Hall effect measurements (HE), and gas testing. The results showed that the optical constants, the transmission, and the carrier numbers were correlated with the substrate type and with the microstructure and the thickness of the films. The Raman study showed the formation of ITO films and the incorporation of Zn in the doped film (ITO:Zn), which was confirmed by EDX analysis. The potential use of the multifunctional sol–gel ITO and ITO:Zn thin films was proven for TCO applications or gas-sensing experiments toward CO2. The Nyquist plots and equivalent circuit for fitting the experimental data were provided. The best electrical response of the sensor in CO2 atmosphere was found at 150 °C, with activation energy of around 0.31 eV.