Rheology of magnetic colloids containing clusters of particle platelets and polymer nanofibres

Abstract

<jats:p> Magnetic hydrogels (ferrogels) are soft materials with a wide range of applications, especially in biomedicine because (i) they can be provided with the required biocompatibility; (ii) their heterogeneous structure allows their use as scaffolds for tissue engineering; (iii) their mechanical properties can be modified by changing different design parameters or by the action of magnetic fields. These characteristics confer them unique properties for acting as patterns that mimic the architecture of biological systems. In addition, and (iv) given their high porosity and aqueous content, ferrogels can be loaded with drugs and guided towards specific targets for local (non-systemic) pharmaceutical treatments. The ferrogels prepared in this work contain magnetic particles obtained by precipitation of magnetite nanoparticles onto the porous surface of bentonite platelets. Then, the particles were functionalized by adsorption of alginate molecules and dispersed in an aqueous solution of sodium alginate. Finally, the gelation was promoted by cross-linking the alginate molecules with Ca <jats:sup>2+</jats:sup> ions. The viscoelastic properties of the ferrogels were measured in the absence/presence of external magnetic fields, showing that these ferrogels exhibited a strong enough magnetorheological effect. This behaviour is explained considering the field-induced strengthening of the heterogeneous (particle–polymer) network generated inside the ferrogel. </jats:p> <jats:p>This article is part of the theme issue ‘Patterns in soft and biological matters'.</jats:p>

Magnetically driven in-plane modulation of the 3D orientation of vertical ferromagnetic flakes

“…Another promising application is for the fabrication of shapeadaptable and magnetically actuated materials for robotics or medicine. [59][60][61] Although such materials can be produced using microfibers oriented during 3D printing, employing flakes instead of fibers would increase the possible morphing designs. 62,63 However, 3D printing with magnetically oriented flakes is still time-consuming because each little voxel printed has to be oriented independently before printing the next voxel.…”

Patterns in soft and biological matters

“…The results demonstrate that the appearance of the clusters significantly (more than several times) enhances the viscous and elastic modulus of these systems. The effect of platelet particles clustered with fibre host polymers is studied experimentally in the work of Abrougui et al [40]. The results demonstrate that this internal clustering significantly extends the range of variation of the rheological properties of the composites by applying a magnetic field.…”

The role of thermal diffusion, particle clusters, hydrodynamic and magnetic forces on the flow behaviour of magneto-polymer composites

“…In another work, Mitsumata et al [19] reported a two-order magnitude increase for the storage modulus for magnetic hydrogels consisting of carrageenan and carbonyl iron particles at 30 vol.%. These enhancements of storage modulus for ferrogels were termed as huge or giant, since most magnetic hydrogels exhibited minor changes of only a few per cent under a magnetic field [20,21]. These large increases of the viscoelastic moduli can only be explained by the field-induced migration of particles in weak polymer networks [10].…”