Size Distribution and Characteristics of Chitin Microgels Prepared via Emulsified Reverse-Micelles

In Situ Viscoelasticity Behavior of Cellulose-Chitin Composite Hydrogels during Ultrasound Irradiation

Composite hydrogels with different cellulose and chitin loading were prepared, and their in-situ viscoelastic properties were estimated under cyclic exposure of 43 kHz and 30 W ultrasound (US) using a sono-deviced rheometer. US transmitted into the hydrogel caused it to soften within about 10 sec, thus causing a decline in the storage modulus (G′) and loss modulus (G″). However, when the US was stopped, the G′ and G″ returned to their initial values. Here, G′ dropped gradually in response to the US irradiation, especially in the first cycle. After the second and third cycles, the decline was much quicker, within a few seconds. When the chitin component in the hydrogel was increased, the drop was significant. FTIR analysis of the hydrogels suggested that the peaks of -OH stretching and amide I vibration near 1655 cm⁻¹ shifted towards lower wave numbers after the third cycle, meaning that the US influenced the hydrogen bonding interaction of the chitin amide group. This repetitive effect contributed to the breakage of hydrogen bonds and increased the interactions of the acetylamine group in chitin and in the -OH groups. Eventually, the matrix turned into a more stabilized hydrogel.

Self-Crosslinked Ellipsoidal Poly(Tannic Acid) Particles for Bio-Medical Applications

Self-crosslinking of Tannic acid (TA) was accomplished to obtain poly(tannic acid) (p(TA)) particles in single step, surfactant free media using sodium periodate (NaIO₄) as an oxidizing agent. Almost monodisperse p(TA) particles with 981 ± 76 nm sizes and −22 ± 4 mV zeta potential value with ellipsoidal shape was obtained. Only slight degradation of p(TA) particles with 6.8 ± 0.2% was observed at pH 7.4 in PBS up to 15 days because of the irreversible covalent formation between TA units, suggesting that hydrolytic degradation is independent from the used amounts of oxidation agents. p(TA) particles were found to be non-hemolytic up to 0.5 mg/mL concentration and found not to affect blood clotting mechanism up to 2 mg/mL concentration. Antioxidant activity of p(TA) particles was investigated by total phenol content (TPC), ferric reducing antioxidant potential (FRAP), trolox equivalent antioxidant capacity (TEAC), total flavanoid content (TFC), and Fe (II) chelating activity. p(TA) particles showed strong antioxidant capability in comparison to TA molecules, except FRAP assay. The antibacterial activity of p(TA) particles was investigated by micro-dilution technique on E. coli as Gram‑negative and S. aureus as Gram-positive bacteria and found that p(TA) particles are more effective on S. aureus with over 50% inhibition at 20 mg/mL concentration attained.

Chitin Hydrogels Prepared at Various Lithium Chloride/N,N-Dimethylacetamide Solutions by Water Vapor-Induced Phase Inversion

Chitin was chemically extracted from crab shells and then dissolved in N,N-dimethylacetamide (DMAc) solvent with lithium chloride (LiCl) at 3, 5, 7, and 10%. The concentrated chitin-DMAc/LiCl solutions were used for the preparation of chitin hydrogels by water vapor-induced phase inversion at 20°C. The coagulation process was investigated while altering the concentration of LiCl in the DMAc solution. The shear viscosity of the chitin solution increased with higher LiCl amounts and decreased when the concentration of LiCl was reduced by adding water to the chitin solution, implying high LiCl concentration delayed the coagulation of chitin solution in the presence of water. The viscoelasticity of the chitin solutions indicated the gel formation intensification was dependent on the dose of LiCl and chitin in the DMAc solution. After the chitin solution was coagulated, the resultant hydrogels had water contents of 387–461% and the tensile strength varied from 285 to 400 kPa when the concentration of LiCl in the hydrogel was adjusted to 3% and 7%, respectively. As for viscoelasticity, the complex modulus of the chitin hydrogels indicated that the increment of the LiCl concentration up to 7% formed the tight hydrogels. Atomic force microscopic (AFM) image revealed the formation of the entanglement network and larger domains of the aggregated chitin segments. However, the hydrogel prepared at 10% LiCl in DMAc solution exhibited weak mechanical properties due to the loose hydrogel networking caused by the strong aggregation of the chitin segments.

Environmentally Friendly Polymers and Polymer Composites

In the last decade, continuous research advances have been observed in the field of environmentally friendly polymers and polymer composites due to the dependence of polymers on fossil fuels and the sustainability issues related to plastic wastes. This research activity has become much more intense in the food packaging industry due to the high volume of waste it generates. Biopolymers are nowadays considered as among the most promising materials to solve these environmental problems. However, they still show inferior performance regarding both processability and end-use application. Blending currently represents a very cost-effective strategy to increase the ductility and impact resistance of biopolymers. Furthermore, different lignocellulosic materials are being explored to be used as reinforcing fillers in polymer matrices for improving the overall properties, lower the environmental impact, and also reduce cost. Moreover, the use of vegetable oils, waste derived liquids, and essential oils opens up novel opportunities as natural plasticizers, reactive compatibilizers or even active additives for the development of new polymer formulations with enhanced performance and improved sustainability profile.