Jelena Ostojić

Hydrogels are considered to be a versatile and desirable material, due to their great ability of water retention, flexibility, viscoelasticity, and good mechanical properties. Silk fibroin (SF) is one of the most abundant biopolymers used for preparation of hydrogels. SF hydrogels can be prepared by self-assembly or induced by physical or chemical cross-linking. Self-assembly of SF hydrogels was shown to be favorable due to its simplicity and the potential harmfulness of chemical cross-linking agents. However, it is often very slow and time-consuming process, which is the main drawback and limitation of SF industrial application. In this study, a novel method of preparing SF hydrogels from aqueous dispersions of SF powder is presented. The results showed that the gelation time is significantly reduced when SF hydrogels are prepared from SF dispersions instead of SF solutions, yet both types of hydrogels had similar rheological and viscoelastic properties, within the investigated concentration range. All prepared hydrogels showed thixotropic behavior and the prevailing of storage modulus in comparison to loss modulus.

This study aims to compare and analyse the synthesis of microcapsules stabilized with chitosan/sodium dodecyl sulphate complex according to emulsion preparation methods. For this purpose, 20 % oil-in-water emulsions were obtained in two ways: by emulsifying the oil phase in aqueous solution of chitosan and its mixtures with anionic surfactant (?method I?) and by subsequently dropping chitosan into an already prepared emulsion stabilized by anionic surfactant (?method II?). Good stability, positive zeta potential of the emulsions and uniform droplet size distribution obtained with both methods, enabled the preparation of chitosan-based microcapsules which were separated by spray drying and investigated in terms of yield, moisture content, particle mean diameter and size distribution. The results showed a uniform particle size distribution and approximately equal mean diameters of emulsion droplets (? 8 ?m), i.e., suspension particles (? 5?m), while the microcapsule yields and moisture content for method I were 15 and 1.14 %, and for method II were 1.2 and 2.85 %, respectively. These results indicate that method I may be more suitable for use in the pharmaceutical and food industries for the production of chitosan microcapsules with oil content. The study confirmed that small variations in preparation can lead to large changes in the microencapsulation process and microcapsule structure.

Silk fibroin (SF) is a protein with many outstanding properties (superior biocompatibility, mechanical strength, etc.) and is often used in many advanced applications (epidermal sensors, tissue engineering, etc.). The properties of SF-based biomaterials may additionally be tuned by SF interactions with other (bio)polymers. Being a weak amphoteric polyelectrolyte, SF may form polyelectrolyte complexes (PECs) with other polyelectrolytes of opposite charge, such as poly(acrylic acid) (PAA). PAA is a widely used, biocompatible, synthetic polyanion. Here, we investigate PEC formation between SF and PAA of two different molecular weights (MWs), low and high, using various techniques (turbidimetry, zeta potential measurements, capillary viscometry, and tensiometry). The colloidal properties of SF isolated from Bombyx mori and of PAAs (MW, overlap concentration, the influence of pH on zeta potential, adsorption at air/water interface) were determined to identify conditions for the SF-PAA electrostatic interaction. It was shown that SF-PAA PEC formation takes place at different SF:PAA ratios, at pH 3, for both high and low MW PAA. SF-PAA PEC’s properties (phase separation, charge, and surface activity) are influenced by the SF:PAA mass ratio and/or the MW of PAA. The findings on the interactions contribute to the future development of SP-PAA PEC-based films and bioadhesives with tailored properties.