Alignment of magnetic particles in hydrogel matrix: A novel anisotropic magnetic hydrogels for soft robotics

Abstract

Magnetic hydrogels are composed of magnetic particles and hydrogel matrix. In recent years, the magnetic hydrogels have been developed rapidly because they have shown promising applications in drug release and artificial muscle. In this paper, we proposed a study to develop novel anisotropic magnetic hydrogels and investigate their mechanical and sensing properties for possible applications in soft robotics. In preparing the anisotropic magnetic hydrogels, the polyacrylamide (PAAm) hydrogel is chosen as a model hydrogel because of its popular application in soft electronics and ionic conductors. A method of free radicals copolymerization is employed to fill (polyacrylic acid/acrylamide) polymers in preparing anisotropic hydrogels under the magnetic field. Unlike most of the previous studies which incorporated magnetic nanoparticles into hydrogels, we mixed the micro-size carbonyl iron particles (CIPs) with the hydrogel and cured them under a magnetic field to form anisotropic structures within its crosslinking polymer chains. The particles and formed particle chains will not only improve the mechanical properties of the hydrogels but also provide sensing function as the electrical resistance changed from mechanical deformation referred to piezoresistivity. We experimentally evaluated the magnetorheological and the piezoresistive behaviors of the magnetic hydrogels, and demonstrated their potential use in soft robots as flexible touch sensors and variable-stiffness devices.

Hydrogels for Chemical Sensing and Biosensing

“…Li et al developed a novel anisotropic magnetic hydrogel with sensing properties. [69] To create this hydrogel, PAAm, known for its versatile applications, has been chosen as the basic material for the preparation of hydrogels. They employed the free radical copolymerization method by incorporating (polyacrylic acid (PAA)/acrylamide) monomers into the solution.…”

A Comparison Study on the Magneto-Responsive Properties and Swelling Behaviors of a Polyacrylamide-Based Hydrogel Incorporating with Magnetic Particles

“…They found that the mechanical properties of the magnetic hydrogels such as rigidity modulus and the viscoelastic moduli "increased quadratically with nanoparticle content following a square-like function," while these magnetic hydrogels still have high porousness and swelling capacity [37] (p. 13). Recently, we studied the effect of CI on the rheological and piezoresistive behaviors of isotropic and anisotropic magnetic hydrogels [38]. We found that anisotropic magnetic hydrogels have better performance than isotropic magnetic hydrogels, which exhibit noticeable MR effects, excellent mechanical properties, and high piezoresistive behaviors.…”

Magnetic hydrogels with ordered structure for biomedical applications

“…Thus, many efforts have been made to construct bionic structure (such as alignment, orientation and hierarchy) in materials, in order to achieve enhanced physical properties and good biocompatibility ( Shi et al, 2020a ; Reid et al, 2021 ; Xing et al, 2022 ). Magnetic anisotropic hydrogels have been created by utilizing magnetic nanoparticles to construct ordered structures ( Araujo-Custodio et al, 2019 ; Bin et al, 2021 ; Chen et al, 2022a ). Different from the isotropic networks of conventional hydrogels, the magnetic nanoparticles are orderly distributed inside the hydrogels, showing magnetic anisotropy as well as good controllability.…”