Effect of particle concentration on the microstructural and macromechanical properties of biocompatible magnetic hydrogels

Abstract

We analyze the effect of nanoparticle concentration on the physical properties of magnetic hydrogels consisting of polymer networks of human fibrin biopolymer with embedded magnetic particles, swollen by a water-based solution. We prepared these magnetic hydrogels by polymerization of mixtures consisting mainly of human plasma and magnetic nanoparticles with OHfunctionalization. Microscopic observations revealed that magnetic hydrogels presented some cluster-like knots that were connected by several fibrin threads. By contrast, nonmagnetic hydrogels presented a homogeneous net-like structure with only individual connections between pairs of fibers. The rheological analysis demonstrated that the rigidity modulus, as well as the viscoelastic moduli, increased quadratically with nanoparticle content following a square-like function. Furthermore, we found that time for gel point was shorter in the presence of magnetic nanoparticles. Thus, we can conclude that nanoparticles favor the cross-linking process, serving as nucleation sites for the attachment of the fibrin polymer. Attraction between the positive groups of the fibrinogen, from which the fibrin is polymerized, and the negative OHgroups of the magnetic particle surface qualitatively justifies the positive role of the nanoparticles on the enhancement of the mechanical properties of the magnetic hydrogels. Indeed, we developed a theoretical model that semiquantitatively explains the experimental results by assuming the indirect attraction of the fibrinogen through the attached nanoparticles. Due to this attraction the monomers condense into nuclei of dense phase and by the end of the polymerization process the nuclei (knots) of the dense phase cross-link the fibrin threads, which enhances the mechanical properties.

Anisotropic magnetic hydrogels: design, structure and mechanical properties

“…As observed in figure 3c, the presence of these clusters of particles resulted in an enhancement of the number of chains linking with a single cluster, which would justify the enhancement observed for isotropic magnetic hydrogels. Note that we presented a theoretical model based on this hypothesis that semiquatitatively predicted the experimental trends for the rigidity modulus as a function of particle concentration [28]. As for the even higher enhancement of the rigidity modulus for anisotropic magnetic hydrogels, its origin must be connected to the presence of the parallel strips observed in figure 3b.…”

“…In fact, once aggregates of peptide-coated particles were built, it was expected that they acted as nuclei of condensation increasing cross-linking between peptide fibrils. Note that in a previous work [28], we showed for fibrin polymer hydrogels that properly functionalized particles acted as nuclei of condensation for the cross-linking of the polymers. The moment of switching off the applied magnetic field (3600 s) was clearly detected by the sharp drop in G in the case of the magnetic hydrogel containing FeNPs@PEG@Fmoc-FF.…”

“…Magnetic fibrin hydrogels presented superior mechanical properties when compared with nonmagnetic hydrogels [28,46,47]. In the particular case of the rigidity modulus (initial slope of the shear stress versus shear strain curves under stationary conditions), the enhancement reached approximately one order of magnitude for a concentration of magnetic nanoparticles as tiny as 0.4 vol.% ( figure 4).…”

Magnetorheology of alginate ferrogels

“…As a consequence, the resulting gel presents a magnetisable character as a bulk. We refer to these systems as magnetic gels (hydrogels when they are water-based) or ferrogels, and from a microscopic point of view they are just suspensions of magnetic nanoparticles in a network of flexible chains swollen by a fluid [26][27][28]. Obviously, ferrogels possess the unique feature among soft matter of being responsive to magnetic fields, which allows not only non-contact manipulation, but also remote modification of their mechanical properties by magnetic fields [25].…”

Mechanical properties of magnetic gels containing rod-like composite particles

“…In these cases, a problem arises because the high density of the particles can favour their gravitational settling during the ferrogel preparation and, in consequence, the resulting gel has a poor homogeneity. This problem can be overcome using core-shell composites (magnetite-polymer, iron-silica) [6,7,10,11], although usually spherical-shaped particles are employed because of the simplicity of the synthesis procedure.…”