Ion-Induced Polysaccharide Gelation: Peculiarities of Alginate Egg-Box Association with Different Divalent Cations.

Structural aspects of polysaccharide hydrogels based on sodium alginate and divalent cations Ba2+, Ca2+, Sr2+, Cu2+, Zn2+, Ni2+ and Mn2+ was studied using data on hydrogel elemental composition and combinatorial analysis of the primary structure of alginate chains. It was shown that the elemental composition of hydrogels in the form of freezing dried microspheres gives information on the structure of junction zones in the polysaccharide hydrogel network, the degree of filling of egg-box cells by cations, the type and magnitude of the interaction of cations with alginate chains, the most preferred types of alginate egg-box cells for cation binding and the nature of alginate dimers binding in junction zones. It was ascertained that metal-alginate complexes have more complicated organization than was previously desired. It was revealed that in metal-alginate hydrogels, the number of cations of various metals per C12 block may be less than the limiting theoretical value equal to 1 for completely filled cells. In the case of alkaline earth metals and zinc, this number is equal to 0.3 for calcium, 0.6 for barium and zinc and 0.65-0.7 for strontium. We have determined that in the presence of transition metals copper, nickel and manganese, a structure similar to an egg-box is formed with completely filled cells. It was determined that in nickel-alginate and copper-alginate microspheres, the cross-linking of alginate chains and formation of ordered egg-box structures with completely filled cells are carried out by hydrated metal complexes with complicated composition. It was found that an additional characteristic of complex formation with manganese cations is the partial destruction of alginate chains. It has been established that the existence of unequal binding sites of metal ions with alginate chains can lead to the appearance of ordered secondary structures due to the physical sorption of metal ions and their compounds from the environment. It was shown that hydrogels based on calcium alginate are most promising for absorbent engineering in environmental and other modern technologies.

κ-Carrageenan Hydrogel as a Matrix for Therapeutic Enzyme Immobilization.

During the last few decades, polysaccharide hydrogels attract more and more attention as therapeutic protein delivery systems due to their biocompatibility and the simplicity of the biodegradation of natural polymers. The protein retention by and release from the polysaccharide gel network is regulated by geometry and physical interactions of protein with the matrix. In the present work, we studied the molecular details of interactions between κ-carrageenan and three lipases, namely the lipases from Candida rugosa, Mucor javanicus, and Rhizomucor miehei-which differ in their size and net charge-upon protein immobilization in microparticles of polysaccharide gel. The kinetics of protein release revealed the different capability of κ-carrageenan to retain lipases, which are generally negatively charged; that was shown to be in line with the energy of interactions between polysaccharides and positively charged epitopes on the protein surface. These data create a platform for the novel design of nanocarriers for biomedical probes of enzymatic origin.

Supramolecular Structure and Mechanical Performance of κ-Carrageenan-Gelatin Gel.

In this work, by means of complex physicochemical methods the structural features of a composite κ-carrageenan-gelatin system were studied in comparison with initial protein gel. The correlation between the morphology of hydrogels and their mechanical properties was demonstrated through the example of changes in their rheological characteristics. The experiments carried out with PXRD, SAXS, AFM and rheology approaches gave new information on the structure and mechanical performance of κ-carrageenan-gelatin hydrogel. The combination of PXRD, SAXS and AFM results showed that the morphological structures of individual components were not observed in the composite protein-polysaccharide hydrogels. The results of the mechanical testing of initial gelatin and engineered κ-carrageenan-gelatin gel showed the substantially denser parking of polymer chains in the composite system due to a significant increase in intermolecular protein-polysaccharide contacts. Close results were indirectly followed from the SAXS estimations-the driving force for the formation of the common supramolecular structural arrangement of proteins and polysaccharides was the increase in the density of network of macromolecular chains entanglements; therefore, an increase in the energy costs was necessary to change the conformational rearrangements of the studied system. This increase in the macromolecular arrangement led to the growth of the supramolecular associate size and the growth of interchain physical bonds. This led to an increase in the composite gel plasticity, whereas the enlargement of scattering particles made the novel gel system not only more rigid, but also more fragile.

Modulation of Molecular Structure and Mechanical Properties of κ-Carrageenan-Gelatin Hydrogel with Multi-Walled Carbon Nanotubes.

Hydrogels, three-dimensional hydrophilic water-insoluble polymer networks having mechanical properties inherent for solids, have attracted continuous research attention over a long time period. Here, we studied the structure and properties of hydrogel based on gelatin, κ-carrageenan and CNTs using the combination of SAXS, PXRD, AFM microscopy, SEM and rheology methods. We have shown that the integration of polysaccharide and protein in the composite hydrogel leads to suppression of their individual structural features and homogenization of two macromolecular components into a single structural formation. According to obtained SAXS results, we observed the supramolecular complex, which includes both polysaccharide and protein components associated with each other. It was determined that hydrogel structure formed in the initial solution state (dispersion) retains hydrogel supramolecular structure under its cooling up to gel state. The sizes of dense cores of these polyelectrolyte complexes (PEC) slightly decrease in the gel state in comparison with PEC water dispersion. The introduction of CNTs to hydrogel does not principally change the type of supramolecular structure and common structural tendencies observed for dispersion and gel states of the system. It was shown that carbon nanotubes embedded in hydrogel act as the supplementary template for formation of the three-dimensional net, giving additional mechanical strengthening to the studied system.

Alginate-Based Hydrogel as Delivery System for Therapeutic Bacterial RNase.

To deliver therapeutic proteins into a living body, it is important to maintain their target activity in the gastrointestinal tract after oral administration. Secreted ribonuclease from Bacillus pumilus (binase) has antitumor and antiviral activity, which makes it a promising therapeutic agent. This globular protein of small molecular weight (12.2 kDa) is considered as a potential agent that induces apoptosis of tumor cells expressing certain oncogenes, including colorectal and duodenum cancer. The most important problem of its usage is the preservation of its structure and target activity, which could be lost during oral administration. Here, we developed alginate microspheres reinforced with divalent cations and analyzed the enzyme release from them. Using methods of scanning electron microscopy, measurements of fluorescence, enzyme catalytic activity, and determination of viability of the duodenum adenocarcinoma tumor cell line, we characterized obtained microspheres and chose calcium as a biogenic ion-strengthening microsphere structure. Among such modified additivities as beta-casein, gelatin, and carbon nanotubes introduced into microspheres, only gelatin showed a pronounced increase in their stability and provided data on the prolonged action of enzyme release from microspheres into tumor cell culture medium during 48 h in an amount of about 70% of the loaded quantity.