Investigation of Silk Fibroin/Poly(Acrylic Acid) Interactions in Aqueous Solution.

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.

Chitosan/Sodium Dodecyl Sulfate Complexes for Microencapsulation of Vitamin E and Its Release Profile-Understanding the Effect of Anionic Surfactant.

Microencapsulation of bioactive substances is a common strategy for their protection and release rate control. The use of chitosan (Ch) is particularly promising due to its abundance, biocompatibility, and interaction with anionic surfactants to form complexes of different characteristics with relevance for use in microcapsule wall design. In this study, Ch/sodium dodecyl sulfate (SDS) microcapsules, without and with cross-linking agent (formaldehyde (FA) or glutaraldehyde (GA)), were obtained by the spray drying of vitamin E loaded oil-in-water emulsion. All of the microcapsules had good stability during the drying process. Depending on the composition, their product yield, moisture content, and encapsulation efficiency varied between 11-34%, 1.14-1.62%, and 94-126%, respectively. SEM and FTIR analysis results indicate that SDS as well as cross-linkers significantly affected the microcapsule wall properties. The profiles of in vitro vitamin E release from the investigated microcapsules fit with the Korsmeyer-Peppas model (r2 > 0.9). The chemical structure of the anionic surfactant was found to have a significant effect on the vitamin E release mechanism. Ch/SDS coacervates may build a microcapsule wall without toxic crosslinkers. This enabled the combined diffusion/swelling based release mechanism of the encapsulated lipophilic substance, which can be considered favorable for utilization in food and pharmaceutical products.

Study of vitamin E microencapsulation and controlled release from chitosan/sodium lauryl ether sulfate microcapsules.

Potential benefit of microencapsulation is its ability to deliver and protect incorporated ingredients such as vitamin E. Microcapsule wall properties can be changed by adding of coss-linking agents that are usually considered toxic for application. The microcapsules were prepared by a spray-drying technique using coacervation method, by depositing the coacervate formed in the mixture of chitosan and sodium lauryl ether sulfate to the oil/water interface. All obtained microcapsules suspensions had slightly lower mean diameter compared to the starting emulsion (6.85 ± 0.213 µm), which shows their good stability during the drying process. The choice and absence of cross-linking agents had influence on kinetics of vitamin E release. Encapsulation efficiency of microcapsules without cross-linking agent was 73.17 ± 0.64 %. This study avoided the use of aldehydes as cross-linking agents and found that chitosan/SLES complex can be used as wall material for the microencapsulation of hydrophobic active molecules in cosmetic industry.

Interactions of zein and zein/rosin nanoparticles with natural polyanion gum arabic.

The objective of this study was to investigate interactions of zein (Z) and zein/rosin (Z/R) nanoparticles with gum arabic (GA), at different pH. Nanoparticles were firstly prepared by antisolvent precipitation of biopolymers from aqueous ethanol solutions. Nanoparticles suspensions were then dialyzed against water in order to remove ethanol and other impurities, and water suspensions of zein and zein/rosin nanoparticles were obtained. It was shown that composition of nanoparticles affects their surface charge density. Zeta potential of nanoparticles was positive without GA and changed to negative after addition of GA, at all pH tested. SEM analysis proved both Z and Z/R nanoparticles to be spherical and in size around 200 nm. The effect of addition of GA on particle size was determined using dynamic light scattering method. It was found that addition of GA increases size of nanoparticles at pH = 4 and pH = 5.5, from 150 - 220 nm to 250 - 320 nm. However, at pH = 3 it causes aggregation process, and diameter of particles increases up to few micrometres. Isothermal titration calorimetry was used to measure enthalpy changes in reaction between Z or Z/R nanoparticles and GA. Results showed that reaction between GA and Z or Z/R NPs is exothermic at each pH tested, except for Z NPs at pH = 3, where it was endothermic. At presented pHs, Z/R NPs were less charged compared to Z NPs, and their surface get saturated with GA molecules more rapidly. Z NPs showed greater enthalpy change in reaction with GA, compared to Z/R NPs.