Ferrogeles con control remoto de la microestructura mediante campos magnéticos

Abstract

In the last decade, there has been an increasing interest in developing materials that can respond to diverse stimuli. The functionality of these materials is understood as their capacity to alter their physical properties or shape in response to external stimuli. Among these materials, magnetic hydrogels stand out due to their softness, high water content, light weight, mechanical properties, miniaturization potential, controllability without contact, and safe interaction with living tissues and organisms. They are defined as three-dimensional cross-linked polymer networks swollen by water, in which magnetic particles (MPs) are inserted. The polymers and MPs give these materials the ability to respond to different stimuli, such as temperature, pH, chemical compounds, and magnetic fields. These characteristics make them ideal materials for applications related to tissue engineering, bioelectronics, drug delivery, wound dressing, cancer treatment, environmental remediation, soft robots, and soft actuators. The starting hypothesis of this thesis is the possibility of exerting precise control over the microstructure and spatial distribution of MPs in hydrogels by applying mechanical stresses or magnetic fields with adequate spatial modulation. The validity of this hypothesis is based on the results of previous works [Mredha et al., 2018, Lopez-Lopez et al., 2015, Scionti et al., 2013], where the possibility of modifying the hydrogel microstructure by applying external mechanical and magnetic stimuli was shown. In this thesis, hydrogels and ferrogels with precise control of their microstructure and magnetic behavior were prepared. These materials were characterized from a macroscopical point of view via their mechanical properties and magnetic behavior, and from a microscopical point of view using different techniques such as scanning electron microscopy (SEM) and Fourier-Transform Infrared (FT-IR) spectroscopy. In addition, different types of applications in the field of soft actuators and sensors were designed for these ferrogels based on their properties. To summarize, we studied alginate hydrogels with an anisotropic internal structure controlled by a mechanical stress or the alignment of functionalized MPs. Regarding these materials, we demonstrated that the anisotropy was reflected macroscopically, in their mechanical properties, and microscopically, in the arrangement of the polymeric fibers. Subsequently, the analysis focused on semi-interpenetrating polymer network (SIPN) ferrogels based on acrylamide and biopolymers, which showed promising properties for soft robots, actuators, and sensors. These applications demonstrated the potential and versatility of SIPN ferrogels, which can be prepared under different experimental conditions, such as shape, MPs, and polymerization processes, and can sense and actuate under different environmental conditions.