Study of the tunable mechanical and swelling properties of magnetic sensitive calcium alginate nanocomposite hydrogels

Nanocomposite hydrogels were elaborated by the addition of citrated magnetic nanoparticles (MNPs) in sodium alginate aqueous solutions ionically crosslinked by in situ release of calcium ions from calcium carbonate (CaCO₃) with gradual hydrolysis of d-glucono-δ lactone (GDL). The sol-gel transition was studied by time-resolved mechanical spectroscopy (TRMS) in the linear viscoelastic region. The power law frequency dependence of the storage and loss moduli allowed to determine the gelation time (t_g), the power law relaxation exponent (Δ), and the gel stiffness (S) at the critical gel (gel at t_g) for different calcium and MNP concentrations. The effect of an applied magnetic field on these parameters was also studied for the first time. The obtained results show an effect of the concentration of both calcium and MNPs on the kinetics (t_g) and properties at the critical gel (S and Δ) obtaining faster kinetics and harder critical gels for higher calcium and lower MNP concentrations. Moreover, the application of the magnetic field allows to modulate the viscoelastic properties before the gel point, but no effect was observed on the structural properties of the critical gel. Finally, this work highlights how the shear viscoelastic, compressive, and swelling properties of totally gelled nanocomposite hydrogels can be successfully modulated when MNPs are introduced in the calcium alginate matrices with a good agreement between all these properties and with the properties of the critical gels.