Nanocomposite-forming solutions based on cassava starch and laponite: Viscoelastic and rheological characterization

Electrochemical Determination of Epinephrine in Pharmaceutical Preparation Using Laponite Clay-Modified Graphene Inkjet-Printed Electrode

Epinephrine (EP, also called adrenaline) is a compound belonging to the catecholamine neurotransmitter family. It can cause neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, Huntington's disease and amyotrophic lateral sclerosis. This work describes an amperometric sensor for the electroanalytical detection of EP by using an inkjet-printed graphene electrode (IPGE) that has been chemically modified by a thin layer of a laponite (La) clay mineral. The ion exchange properties and permeability of the chemically modified electrode (denoted La/IPGE) were evaluated using multi-sweep cyclic voltammetry, while its charge transfer resistance was determined by electrochemical impedance spectroscopy. The results showed that La/IPGE exhibited higher sensitivity to EP compared to the bare IPGE. The developed sensor was directly applied for the determination of EP in aqueous solution using differential pulse voltammetry. Under optimized conditions, a linear calibration graph was obtained in the concentration range between 0.8 µM and 10 μM. The anodic peak current of EP was directly proportional to its concentration, leading to detection limits of 0.34 μM and 0.26 μM with bare IPGE and La/IPGE, respectively. The sensor was successfully applied for the determination of EP in pharmaceutical preparations. Recovery rates and the effects of interfering species on the detection of EP were evaluated to highlight the selectivity of the elaborated sensor.

The Effect of Surface Characteristics of Clays on the Properties of Starch Nanocomposites

In this research, different clays such as laponite and montmorillonite (NaMMT) are used as fillers in the preparation of thermoplastic starch/clay nanocomposites. Thin films are produced by casting and evaporation in a wide composition range, using glycerol as the plasticizer at two different concentrations. The surface energy of clay fillers is measured by inverse gas chromatography (IGC); X-ray diffraction (XRD) and light transmission measurements (UV-VIS) are carried out to characterize the structure of nanocomposites; and mechanical properties and water vapor permeability are also studied. While all the starch/montmorillonite nanocomposites possess intercalated structures, significant exfoliation can be noted in the starch/laponite nanocomposites, mainly at low clay contents. Due to the larger surface energy of montmorillonite, stronger polymer/clay interactions and better mechanical properties can be assumed in starch/NaMMT composites. The smaller surface energy of laponite, however, can facilitate the delamination of laponite layers. Thus, the specific surface area of laponite can be further increased by exfoliation. Based on the results, the better exfoliation and the much larger specific surface area of laponite lead to higher reinforcement in starch/laponite nanocomposites.

Rheological and Viscoelastic Properties of Chitosan Solutions Prepared with Different Chitosan or Acetic Acid Concentrations

Chitosan (Ch) is a partially crystalline biopolymer, insoluble in pure water but soluble in acid solutions. It has attracted interest from researchers to prepare solutions using different acid types and concentrations. This research aims to study both the effect of chitosan (Ch) or acetic acid (Ac) concentrations, at different temperatures, on rheological and viscoelastic properties of Ch solutions. To study the effect of Ch, solutions were prepared with 0.5−2.5 g Ch/100 g of solution and Ac = 1%, whereas to study the effect of Ac, the solutions were prepared with 2.0 g of Ch/100 g of solution and Ac = 0.2−1.0%. Overall, all analyzed solutions behaved as pseudoplastic fluid. The Ch strongly affected rheological properties, the consistency index (K) increased and the index flow behavior (n) decreased as a function of Ch. The activation energy, defined as the energy required for the molecule of a fluid to move freely, was low for Ch = 0.5%. The effect of Ac was less evident. Both K and n varied according to a positive and negative, respectively, parabolic model as a function of Ac. Moreover, all solutions, irrespective of Ch and Ac, behaved as diluted solutions, with G” > G’. The relaxation exponent (n”) was always higher than 0.5, confirming that these systems behaved as a viscoelastic liquid. This n” increased with Ch, but it was insensitive to Ac, being slightly higher at 45 °C.

Rheological and Thermal Study about the Gelatinization of Different Starches (Potato, Wheat and Waxy) in Blend with Cellulose Nanocrystals

The goal of this work was to analyze the effect of CNCs on the gelatinization of different starches (potato, wheat and waxy maize) through the characterization of the rheological and thermal properties of starch–CNC blends. CNCs were blended with different starches, adding CNCs at concentrations of 0, 2, 6 and 10% w/w. Starch–CNC blends were processed by rapid visco-analysis (RVA) and cooled to 70 °C. Pasting parameters such as pasting temperature, peak, hold and breakdown viscosity were assessed. After RVA testing, starch–CNC blends were immediately analyzed by rotational and dynamic rheology at 70 °C. Gelatinization temperature and enthalpy were assessed by differential scanning calorimetry. Our results suggest that CNCs modify the starch gelatinization but that this behavior depends on the starch origin. In potato starch, CNCs promoted a less organized structure after gelatinization which would allow a higher interaction amylose–CNC. However, this behavior was not observed in wheat and waxy maize starch. Insights focusing on the role of CNC on gelatinization yielded relevant information for better understanding the structural changes that take place on starch during storage, which are closely related with starch retrogradation. This insight can be used as an input for the tailored design of novel materials oriented towards different technological applications.

Adsorption-desorption of anthocyanins from jambolan (Syzygium cumini) fruit in laponite® platelets: Kinetic models, physicochemical characterization, and functional properties of biohybrids

This study aims to develop and characterize biohybrids (BH) based on anthocyanins (ACNs) from jambolan (Syzygium cumini) and laponite® (Lap). ACNs from jambolan fruit were extracted using an acidified water solution at pH 1. ACNs were recovered from extract using Lap as adsorbent between 5 °C and 40 °C. There was no significant effect (p > 0.05) of the temperature on the adsorption process of ACNs. Thus, the process was classified as physical adsorption in heterogeneous sites where ACNs were stabilized by means of van der Waals force, π - π force, and hydrogen bonding on the Lap surface. After adsorption, the BH powder appeared to have an amorphous structure and red color. However, the color changed at pH ≥ 7. In addition, the obtained BH showed antioxidant properties and high stability when exposed to visible light irradiation. This research reports new information about the valorization and application of ACNs from jambolan for food industrial applications.

Rheological, physical, and mechanical properties of chicken skin gelatin films incorporated with potato starch

The aim of this study was to investigate the rheological, physical, and mechanical properties of chicken skin gelatin film forming solutions (FFSs) and films incorporated with potato starch. Chicken skin gelatin-based FFSs with various potato starch concentrations (0, 2, 4, 6, 8, and 10%, w/w) were prepared via casting technique. The dynamic viscoelastic properties of FFS were measured, and film characterization in terms of physical and mechanical properties was conducted. Potato starch incorporation with chicken skin gelatin-based FFS resulted in improvement of viscous behavior (G″ > G'). As potato starch concentration increased, the tensile strength, elongation at break, and elastic modulus values of chicken skin gelatin-based films also increased (p < 0.05). Additionally, increasing the concentration of potato starch caused incremental changes in water vapor permeability and melting temperatures (T _m), but a reduction in water solubility (p < 0.05). In addition, the surface smoothness and internal structure of composite films improved via potato starch incorporation. The incorporation of potato starch was also found to provide good barrier properties against ultraviolet and visible light, but did not significantly influence the transparency values of composite films. Overall, chicken skin gelatin film with 6% potato starch concentration incorporation was the most promising composite film, since it was found to exhibit optimal performance in terms of physical properties.

The thiolated chitosan: Synthesis, gelling and antibacterial capability

Chitosan-1-(mercaptomethyl)-cyclopropane acetic acid (CS-MCA) copolymer was synthesized by amino linkage. The obtained copolymer was characterized by FTIR, ¹H NMR, XRD, TGA and SEM. Porous and reticulate morphologies were found on the CS-MCA surface. The effects of pH on the rheological properties of CS-MCA were investigated. On the one hand, the apparent viscosity of CS-MCA indicated a shear-thinning behavior. The graft of MCA enhanced the moduli and the maximum elastic properties were observed at pH = 7.00. The addition of dithiothreitol reduced the viscosity and modulus of CS-MCA hydrogel, and the gelation time, temperature and frequency were obtained in dynamic oscillatory tests. The antibacterial effect of CS-MCA against E. coli was investigated for the inhibition zone and bacterial growth curve. These results showed that CS-MCA had better antibacterial ability than chitosan without modification. Therefore, the rheological behavior and functional activities can be applied for the hydrocolloid gels in food and pharmaceutical applications.

Bioprinting a Synthetic Smectic Clay for Orthopedic Applications

Bioprinting technology has emerged as an important approach to bone and cartilage tissue engineering applications, because it allows the printing of scaffolds loaded with various components, such as cells, growth factors, or drugs. In this context, the bone has a very complex architecture containing highly vascularized and calcified tissues, while cartilage is avascular and has low cellularity and few nutrients. Owing to this complexity, the repair and regeneration of these tissues are highly challenging. Identification of the appropriate biomaterial and fabrication technologies can provide sustainable solutions to this challenge. Here, nanosized Laponite^® (Laponite is a trademark of the company BYK Additives Ltd.) has shown to be a promising material due to its unique properties such as excellent biocompatibility, facile gel formation, shear-thinning property (reversible physical crosslinking), high specific surface area, degrade into nontoxic products, and with osteoinductive properties. Even though Laponite and Laponite-based composite for 3D bioprinting application are considered as soft gels, they may therefore not be thought exhibiting sufficient mechanical strength for orthopedic applications. However, through the merging with suitable composite and, also by incorporation of crosslinking step, desired mechanical strength for orthopedic application can be obtained. In this review, recent advances and future perspective of bioprinting Laponite and Laponite composites for orthopedic applications are highlighted.

Effect of ionic strength on shear-thinning nanoclay-polymer composite hydrogels

Nanoclay-polymer shear-thinning composites are designed for a broad range of biomedical applications, including tissue engineering, drug delivery, and additive biomanufacturing. Despite the advances in clay-polymer injectable nanocomposites, colloidal properties of layered silicates are not fully considered in evaluating the in vitro performance of shear-thinning biomaterials (STBs). Here, as a model system, we investigate the effect of ions on the rheological properties and injectability of nanoclay-gelatin hydrogels to understand their behavior when prepared in physiological media. In particular, we study the effect of sodium chloride (NaCl) and calcium chloride (CaCl2), common salts in phosphate buffered saline (PBS) and cell culture media (e.g., Dulbecco's Modified Eagle's Medium, DMEM), on the structural organization of nanoclay (LAPONITE® XLG-XR, a hydrous lithium magnesium sodium silicate)-polymer composites, responsible for the shear-thinning properties and injectability of STBs. We show that the formation of nanoclay-polymer aggregates due to the ion-induced shrinkage of the diffuse double layer and eventually the liquid-solid phase separation decrease the resistance of STB against elastic deformation, decreasing the yield stress. Accordingly, the stress corresponding to the onset of structural breakdown (yield zone) is regulated by the ion type and concentration. These results are independent of the STB composition and can directly be translated into the physiological conditions. The exfoliated nanoclay undergoes visually undetectable aggregation upon mixing with gelatin in physiological media, resulting in heterogeneous hydrogels that phase separate under stress. This work provides fundamental insights into nanoclay-polymer interactions in physiological environments, paving the way for designing clay-based injectable biomaterials.

Morphology and Structural Properties of Novel Short Linear Glucan/Protein Hybrid Nanoparticles and Their Influence on the Rheological Properties of Starch Gel

Starch nanoparticles were potential texture modifiers. However, they have strong tendency to aggregate and poor water dispersibility, which limited their application. The interaction between glucan (prepared from starch by enzymatic modification) and protein could significantly improve the dispersity of starch nanoparticles and, thus, enhance the rheological properties of food gels. In this work, glucan/protein hybrid nanoparticles were successfully developed for the first time using short linear glucan (SLG) and edible proteins [soy protein isolate (SPI), rice protein (RP), and whey protein isolate (WPI)]. The results showed that the SLG/SPI hybrid nanoparticles exhibited hollow structures, of which the smallest size was approximately 10-20 nm when the SLG/SPI ratio was 10:5. In contrast, SLG/RP nanoparticles displayed flower-like superstructures, and SLG/WPI nanoparticles presented stacked lamellar nanostructures with a width of 5-10 nm and a length of 50-70 nm. In comparison to bare SLG nanoparticles, SLG/SPI and SLG/WPI hybrid nanoparticles had higher melting temperatures. The addition of all nanoparticles greatly increased the storage modulus of corn starch gels and decreased loss tangent values. Importantly, the G' value of starch gels increased by 567% with the addition of flower-like SLG/RP superstructures.