# Relation in Alginate-Based Magnetic Suspensions
###### Abstract  
Alginate gels are extensively tested in biomedical applications for tissue regeneration and engineering. In this regard, the modification of alginate gels and solutions with dispersed magnetic particles gives extra options to control the rheo-elastic properties both for the fluidic and gel forms of alginate. Rheological properties of magnetic suspensions based on Na-alginate water solution with embedded magnetic particles were studied with respect to the interfacial adhesion of alginate polymer to the surface of particles. Particles of magnetite (Fe\({}_{5}\)O\({}_{4}\)), metallic iron (Fe), metallic nickel (Ni), and metallic nickel with a deposited carbon layer (Ni@C) were taken into consideration. Storage modulus, loss modulus, and the shift angle between the stress and the strain were characterized by the dynamic mechanical analysis in the oscillatory mode. The intensity of molecular interactions between alginate and the surface of the particles was characterized by the enthalpy of adhesion which was determined from calorimetric measurements using a thermodynamic cycle. Strong interaction at the surface of the particles resulted in the dominance of the \"fluidic\" rheological properties: the prevalence of the loss modulus over the storage modulus and the high value of the shift angle. Meanwhile, poor interaction of alginate polymer with the surface of the embedded particles favored the \"elastic\" gel-like properties with the dominance of the storage modulus over the loss modulus and low values of the shift angle. alginate; ferrogels; magnetic nanoparticles; interfacial adhesion; dynamic mechanical analysis +
Footnote †: journal: Applied  
Acticle  
Gelation in Alginate-Based Magnetic Suspensions  
Favored by Poor Interaction among Sodium Alginate and Embedded Particles  
[PERSON]  
1 Institute of Natural Sciences and Mathematics, Ural Federal University, 19 Mira Str.,  
620002 Yekaterinburg, Russia; [EMAIL_ADDRESS] (E.V.R. ); [EMAIL_ADDRESS] (Y.S.Z. ); [EMAIL_ADDRESS] (N.M.K. ); [EMAIL_ADDRESS] (I.V.B. ); [EMAIL_ADDRESS] (A.Y.Z.) by several monomeric units of adjacent macromolecules and forms a crosslink of the gel networking [1; 2; 3; 4; 5]. The mono/di valent ionic exchange provides the versatility of alginate applications. Thus, the fluidic water solution of sodium alginate can be readily transformed to a certain shape of an elastic gel of calcium alginate by exposure to the solution of simple calcium salts [2; 3; 4; 5; 6]. This feature is widely used in the encapsulation of different bioactive substances in alginate beads for their further in vivo transportation in various medical applications [7; 8]. Alginate gels are extensively tested as scaffolds for cell proliferation and growth [9; 10]. In these applications, the fluid-to-gel transition of alginate driven by the mono/di valent ionic exchange is especially useful for the in vivo tissue regeneration and engineering [11]. Fluidic sodium alginate solution can easily be injected into a living organism and the gelation might then be provided in the desired place of the interior. In this regard, the modification of alginate gels and solutions with dispersed magnetic particles gives extra options to control the rheo-elastic properties both for the fluidic and gel forms of alginate [12]. Several studies on the structure and magneto-rheological properties of alginate ferrogels had been reported [13; 14; 15; 16; 17; 18]. Thus [14; 15], ferrogels filled with iron micron-sized magnetic particles were prepared by the Na+/Ca++ ionic exchange in magnetic suspensions in alginate solution according to the \"internal gelation\" procedure, and their mechanical properties were tested using dynamic mechanical analysis (DMA). It was shown that Ca-alginate ferrogels had substantially higher levels of the storage (elastic) modulus compared to the loss modulus within the linear viscoelastic region, which is the typical behavior of the cross-linked polymeric networks.