Structural Investigation of a Self-Cross-Linked Chitosan/Alginate Dialdehyde Multilayered Film with in Situ QCM-D and Spectroscopic Ellipsometry

Determining the Characteristics of Ultrathin Polymer Films: A Spectroscopic Ellipsometry Approach

Ellipsometry is a powerful and convenient technique that is widely used to determine the thickness and optical characteristics of polymer thin films. The determination is accomplished by modeling the measured change in the polarization of an electromagnetic wave upon interacting with the thin film. However, due to the strong statistical correlations between the fit parameters in the model, simultaneous determination of the thickness and the refractive indices of optically anisotropic ultrathin films using ellipsometry remains a challenge. Here, we propose an approach that can be used to obtain reliable values of both the thickness and the optical anisotropy of ultrathin polymer films. The approach was developed by performing spectroscopic ellipsometry measurements on thin films of hydrophobic polystyrene and hydrophilic chitosan of thickness between a few tens to a few hundred nm and whose absolute value of the birefringence differed by approximately an order of magnitude. Careful consideration of the characteristics of the root mean squared error of the fits obtained by modeling the ellipsometry data and the statistical correlations between the fit parameters formed the basis of the proposed approach.

Reducing Ice Adhesion to Polyelectrolyte Surfaces by Counterion-Mediated Nonfrozen Hydration Water

Hydrophilic anti-icing coatings can be energy-effective passive solutions for combating ice accretion and reducing ice adhesion. However, their underlying mechanisms of action remain inferential and are ill-defined from a molecular perspective. Here, we systematically investigate the influence of the counterion identity on the shear ice adhesion strength to cationic polymer coatings having quaternary alkyl ammonium moieties as chargeable groups. Temperature-dependent molecular information on the hydrated polymer films is obtained using total internal reflection (TIR) Raman spectroscopy, complemented with differential scanning calorimetry (DSC) and ellipsometry. Ice adhesion measurements show a pronounced counterion-specific behavior with a sharp increase in adhesion at temperatures that depend on the anion identity, following the order Cl- < F- < SCN- < Br- < I-. Linked to the freezing of hydration water, the specific ordering results from differences in ion pairing and the amount of water present within the polymer film. Moreover, similar effects can be promoted by varying the cross-linking density in the coating while keeping the anion identity fixed. These findings shed new light on low ice adhesion mechanisms and may inspire novel approaches for improved anti-icing coatings.

Self-Cross-Linkable Chitosan-Alginate Complexes Inspired by Mussel Glue Chemistry

In this study, mussel-inspired chemistry, based on catechol-amine reactions, was adopted to develop self-cross-linkable chitosan-alginate (Chi-Alg) complexes. To do so, the biopolymers were each substituted with ∼20% catechol groups (ChiC and AlgC), and then four complex combinations (Chi-Alg, ChiC-Alg, Chi-AlgC, ChiC-AlgC) were prepared at the surface and in bulk solution. Based on QCM-D and lap shear adhesion tests, the complex with catechol only on Chi (ChiC-Alg) did not show a significant variation from the control complex (Chi-Alg). Conversely, the complexes with catechol on alginate (Chi-AlgC and ChiC-AlgC) rendered a self-cross-linking property and enhanced cohesive properties.

Schiff base synergized with protonation of PEI to achieve smart antibacteria of nanocellulose packaging films

Microbial growth and reproduction can cause food spoilage. Developing the controlled release packaging films for food is an ideal solution. In this study, polyethyleneimine (PEI) was grafted to cellulose nanofibers (CNF) films by Schiff base, and when the CNF/PEI films were stimulated by pH, PEI released from the CNF/PEI films due to Schiff base hydrolysis, improving the antibacterial efficiency of PEI. Stimulated by acid with pH of 4, the PEI cumulative release rate of the CNF/PEI₈₀₀ and the CNF/PEI₂₀₀₀ films reached to 92.90 % and 87.28 %, respectively. At the same time, the amino groups of PEI protonated by obtaining H⁺, the charge density increased, and PEI molecular chains extended, enhancing the antibacterial activity of films. The Zeta potential value on the surface of the CNF/PEI film increased with the decrease of pH value. Schiff base synergized with protonation of PEI to achieve smart antibacteria of CNF packaging films. The antibacterial rates of the film against L. monocytogenes and E. coli were 94.7 % and 90.6 % at pH 4, but 29.5 % and 23.6 % at pH 8, respectively. The developed films also had good barrier properties of oxygen, visible light and mechanical properties, and had an attractive application prospect in food preservation to control release of antibacterial agent.

Monitoring Cell Adhesion on Polycaprolactone-Chitosan Films with Varying Blend Ratios by Quartz Crystal Microbalance with Dissipation

A detailed understanding of the cell adhesion on polymeric surfaces is required to improve the performance of biomaterials. Quartz crystal microbalance with dissipation (QCM-D) as a surface-sensitive technique has the advantage of label-free and real-time monitoring of the cell-polymer interface, providing distinct signal patterns for cell-polymer interactions. In this study, QCM-D was used to monitor human fetal osteoblastic (hFOB) cell adhesion onto polycaprolactone (PCL) and chitosan (CH) homopolymer films as well as their blend films (75:25 and 25:75). Complementary cell culture assays were performed to verify the findings of QCM-D. The thin polymer films were successfully prepared by spin-coating, and relevant properties, i.e., surface morphology, ζ-potential, wettability, film swelling, and fibrinogen adsorption, were characterized. The adsorbed amount of fibrinogen decreased with an increasing percentage of chitosan in the films, which predominantly showed an inverse correlation with surface hydrophilicity. Similarly, the initial cell sedimentation after 1 h resulted in lesser cell deposition as the chitosan ratio increased in the film. Furthermore, the QCM-D signal patterns, which were measured on the homopolymer and blend films during the first 18 h of cell adhesion, also showed an influence of the different interfacial properties. Cells fully spread on pure PCL films and had elongated morphologies as monitored by fluorescence microscopy and scanning electron microscopy (SEM). Corresponding QCM-D signals showed the highest frequency drop and the highest dissipation. Blend films supported cell adhesion but with lower dissipation values than for the PCL film. This could be the result of a higher rigidity of the cell-blend interface because the cells do not pass to the next stages of spreading after secretion of their extracellular matrix (ECM) proteins. Variations in the QCM-D data, which were obtained at the blend films, could be attributed to differences in the morphology of the films. Pure chitosan films showed limited cell adhesion accompanied by low frequency drop and low dissipation.

Influence of Ionic Strength and Specific Ion Effects on Polyelectrolyte Multilayer Films with pH-Responsive Behavior

Layer-by-layer assembled multilayer films have shown great potential for different applications owing to their responsive behavior. Herein, we systematically investigated the effects of composition, salt concentration, and ion specificity on the pH responsiveness of covalently crosslinked chitosan and alginate dialdehyde multilayer films. The changes in film swelling were measured using ellipsometry from low (0.01 mM) to high (3 M) salt (NaCl or NaSCN) concentrations at pH 3, 6, and 9. The swelling responses to increasing ionic strength matched the swelling responses observed for polyzwitterionic and weak monocomponent polyelectrolyte films and depended on the multilayer composition, pH, and ion specificity. Finally, we used the ellipsometric data to demonstrate that the pH responsiveness of such multilayer films, as measured using a quartz crystal microbalance with dissipation monitoring, strongly depends on the ionic condition under which the responses were measured. We thus show that erroneous conclusions about the pH responsiveness of polyelectrolyte multilayer films can be easily obtained if the ionic environment of the application does not closely resemble the ionic condition under which the pH responsiveness is tested.

Rheological and Self-Healing Behavior of Hydrogels Synthesized from l-Lysine-Functionalized Alginate Dialdehyde

Alginate dialdehyde and l-lysine-functionalized alginate dialdehyde were prepared to provide active aldehyde and l-lysine sites along the alginate backbone, respectively. Different concentrations of substrates and the reduction agent were added, and their influence on the degree of l-lysine substitution was evaluated. An amination reduction reaction (with l-lysine) was conducted on alginate dialdehyde with a 31% degree of oxidation. The NMR confirmed the presence of l-lysine functionality with the degree of substitution of 20%. The structural change of the polymer was observed via FTIR spectroscopy, confirming the formation of Schiff base covalent linkage after the crosslinking. The additional l-lysine sites on functionalized alginate dialdehyde provide more crosslinking sites on the hydrogel, which leads to a higher modulus storage rate than in the original alginate dialdehyde. This results in dynamic covalent bonds, which are attributed to the alginate derivative-gelatin hydrogels with shear-thinning and self-healing properties. The results suggested that the concentration and stoichiometric ratio of alginate dialdehyde, l-lysine-functionalized alginate dialdehyde, and gelatin play a fundamental role in the hydrogel's mechanical properties.

Biodegradable dual stimuli responsive alginate based microgels for controlled agrochemicals release and soil remediation

To meet the growing food demand of increasing world population while reducing the harmful environmental effects of agrochemicals, development of smart nanoformulation is of prime importance. Herein, dual stimuli responsive alginate based microgels (OAlgDP MGs) (≈160 nm) are developed for controlled release of agrochemicals and soil remediation. These microgels are prepared using octyl amine functionalized alginate which is crosslinked by 3, 3'-dithiopropionohydrazide crosslinker providing both hydrazone and disulfide bonds in microgels network. OAlgDP MGs are further loaded with hydrophobic diuron herbicide displaying ≈85 % encapsulation efficiency. Sustained release of diuron is obtained in 2 mM GSH (≈100 % after 380 h) and at pH 5 (≈72 % after 240 h). Furthermore, OAlgDP MGs are nontoxic up to 150 μg/mL against HEK293T cells while their reduced form is capable of capturing the heavy metal ions (Cu²⁺ and Hg²⁺) showing the potential of the developed system for moving toward sustainable agriculture.

Quality assessment of lemon (Citrus aurantifolia, swingle) coated with self-healed multilayer films based on chitosan/carboxymethyl cellulose under cold storage conditions

The polyelectrolyte multilayer self-healing coating film of chitosan and carboxymethyl cellulose (PEM-SH) tended to maintain high sensory quality and control physiological and pathological decay of lemon fruits under cold storage. The PEM-SH film was characterized by ATR-IR, XRD, X-ray photoelectron spectroscopy, SEM analysis, swelling ratio, self-healing, and mechanical characteristics. The 3-layered film (3L) exhibited the optimum barrier properties; WVP: 3.32 ± 0.06 g. mm. k Pa^-1.h^-1.m^-2 and GTR: 0.256 ± 0.032 cc.M^-2.day^-1. The moisture sorption isotherm data were fitted with BET, GAB, and Peleg models and three models showed applicability. The coated fruits exhibit superior features of fruit quality such as reduced weight loss %, respiration rate, and decay symptoms appearance. The 3L-coated fruit showed the lower pectinase enzyme activity (0.689 Ug^-1 FW) up to 60 days. As well as, increased total soluble solids, keeping vitamin C of loss and decreasing percentage acidity of juice up to 60 days.

Applications of oxidized alginate in regenerative medicine

Because of its ideal degradation rate and features, oxidized alginate (OA) is selected as an appropriate substitute and has been introduced into hydrogels, microspheres, 3D-printed/composite scaffolds, membranes, and electrospinning and coating materials. By taking advantage of OA, the OA-based materials can be easily functionalized and deliver drugs or growth factors to promote tissue regeneration. In 1928, it was first found that alginate could be oxidized using periodate, yielding OA. Since then, considerable progress has been made in the research on the modification and application of alginate after oxidation. In this article, we summarize the key properties and existing applications of OA and various OA-based materials and discuss their prospects in regenerative medicine.

Chitosan-based smart hybrid materials: a physico-chemical perspective

Chitosan is one of the most studied cationic polysaccharides. Due to its unique characteristics of being water soluble, biocompatible, biodegradable, and non-toxic, this macromolecule is highly attractive for a broad range of applications. In addition, its complex behavior and the number of ways it interacts with different components in a system result in an astonishing variety of chitosan-based materials. Herein, we present recent advances in the field of chitosan-based materials from a physico-chemical perspective, with focus on aqueous mixtures with oppositely charged colloids, chitosan-based thin films, and nanocomposite systems. In this review, we focus our attention on the physico-chemical properties of chitosan-based materials, including solubility, mechanical resistance, barrier properties, and thermal behaviour, and provide a link to the chemical peculiarities of chitosan, such as its intrinsic low solubility, high rigidity, large charge separation, and strong tendency to form intra- and inter-molecular hydrogen bonds.

Novel Controlled Release Microspheric Soil Conditioner Based on the Temperature and pH Dual-Stimuli Response

A novel type of temperature and pH dual-stimuli-responsive microspheric soil conditioner was prepared for the controlled release of urea. First, poly(N-isopropylacrylamide-co-methacrylic acid) [P(NIPAM-co-MAA)] was synthesized, and the microspheric soil conditioner was prepared on the basis of chitosan-coated P(NIPAM-co-MAA) via the emulsion cross-linking method. The structure and morphology of the microsphere were characterized by Fourier transform infrared spectroscopy, hydrogen nuclear magnetic resonance, polarization optical microscopy, and scanning electron microscopy. The microsphere showed controlled release behavior in different temperature and pH conditions, indicating good stimuli responsiveness. The plant experiment revealed that the microsphere can effectively promote plant growth in acidified soil and high-temperature conditions, and the pH value of acidified soil could be improved. In addition, the microsphere possessed good biodegradation property in the soil. Therefore, the multi-responsive microspheric soil conditioner owns a great potential value to amend soil conditions and promote plant growth in agriculture applications.

Sodium Alginate Cross-Linkable Planar 1D Photonic Crystals as a Promising Tool for Pb2+ Detection in Water

Due to its high toxicity, Pb2+ pollution is a serious threat for human health and environments. However, in situ real-time detection of Pb2+ pollution is difficult and laboratory instruments are usually required. Then, the possibility to monitor water quality without laboratory instruments could lead to the extensive assessment of polluted water sources, especially in rural environments and developing countries where large lead concentrations are often found in surface water. Consequently, new simple colorimetric sensors are highly interesting in the field. In this work we report for the first time disposable polymer planar 1D photonic crystals made of poly (N-vinylcarbazole) as high refractive index medium and sodium alginate as low refractive index and active medium for the detection of Pb2+ in water. The detection relies on the ionic exchange occurring into the alginate matrix. This process effectively induces a physical cross-linking phenomenon, which inhibits water solubilization of the polymer. In turn, this affects the spectral response of the planar 1D photonic crystals modifying its color.

Swelling Behavior, Interaction, and Electrostatic Properties of Chitosan/Alginate Dialdehyde Multilayer Films with Different Outermost Layer

In this study, self-cross-linked chitosan/alginate dialdehyde multilayer films, capped with either alginate dialdehyde (6 layers) or chitosan (7 layers), were fabricated using the layer-by-layer method. The disruption of the electrostatic equilibrium when exposing the fabricated layers to acidic and alkaline conditions causes swelling within the film and independently in the outermost layer, showing dependence on the ionic strength. Spectroscopic ellipsometry and quartz crystal microbalance with dissipation monitoring were employed to examine the swelling behavior. Atomic force microscopy colloidal probe measurements were conducted to assess the surface forces between the multilayer films at different pH and ionic strengths. Finally, the electrostatic properties of the multilayer films were examined at different pH and ionic strengths using zeta potential measurements. The results suggest that stimuli-responsiveness and overall swelling behavior of the polysaccharide multilayer films significantly depend on the outermost layer, an effect that should expectedly become more pronounced the thinner the film becomes.

PPEGMEMA-based cationic copolymers designed for layer-by-layer assembly

We have synthesized three PPEGMEMA-based cationic copolymers with similar amine contents but with systematic variation in the average length of the PEG side chains. The positively charged copolymers were paired with alginate to fabricate layer-by-layer assembled multilayered films. It was demonstrated that the polymeric design, in terms of the systematic variation in the average length of the PEG units, affects the polyelectrolyte multilayer growth mechanism and can be used to tune the structural properties and the water content of the layers. In addition, by partial cross-linking of the amine groups present in the copolymer backbone, disintegration of the film induced by pH changes was prevented. Finally, it was demonstrated how the cross-linked multilayered film can exhibit cationic, zwitterionic and anionic properties depending on the pH value and how these changes are associated with swelling, layer contraction and changes in water content.

PPEGMEMA-based cationic copolymers were synthesized and utilized in a layer-by-layer assembly process to prepare a multilayered film. Film properties were tuned with systematic variation in the average length of the PEG side chains.