Abstract
Multifunctional hydrogels are a class of materials offering new opportunities for interfacing living organisms with machines due to their mechanical compliance, biocompatibility, and capacity to be triggered by external stimuli. Here, we report a dual magnetic- and electric-stimuli-responsive hydrogel with the capacity to be disassembled and reassembled up to three times through reversible cross-links. This allows its use as an electronic device (e.g., temperature sensor) in the cross-linked state and spatiotemporal control through narrow channels in the disassembled state via the application of magnetic fields, followed by reassembly. The hydrogel consists of an interpenetrated polymer network of alginate (Alg) and poly(3,4-ethylenedioxythiophene) (PEDOT), which imparts mechanical and electrical properties, respectively. In addition, the incorporation of magnetite nanoparticles (Fe3O4 NPs) endows the hydrogel with magnetic properties. After structural, (electro)chemical, and physical characterization, we successfully performed dynamic and continuous transport of the hydrogel through disassembly, transporting the polymer–Fe3O4 NP aggregates toward a target using magnetic fields and its final reassembly to recover the multifunctional hydrogel in the cross-linked state. We also successfully tested the PEDOT/Alg/Fe3O4 NP hydrogel for temperature sensing and magnetic hyperthermia after various disassembly/re-cross-linking cycles. The present methodology can pave the way to a new generation of soft electronic devices with the capacity to be remotely transported.
Highlights
Hydrogels, defined as three-dimensional (3D) polymeric networks infiltrated with water, are novel soft materials that have enabled great advances in diverse modern technologies including tissue engineering, drug delivery, biointegrated electronics, and soft robotics.[1−3] Such advances have been made possible, in part, thanks to the similarities in physicochemical properties of hydrogels and biological tissues.[4,5] While the softness and flexibility allow minimizing the mechanical mismatch between hydrogels and tissues, the high water content endows them with a wet and iron-rich environment, which is characteristic of biological systems
Hydrogels are promising components of responsive hybrid materials, which react to chemical or physical stimuli.[8−15] For example, hydrogels with electrical conductivity are emerging as outstanding candidates for a new generation of soft electronics.[10,11]
We have successfully fabricated hydrogels with magnetic and electrical performances integrated into the same system, which can be used as a novel and effective strategy to spatiotemporally transport the hydrogel using magnetic fields
Summary
Hydrogels, defined as three-dimensional (3D) polymeric networks infiltrated with water, are novel soft materials that have enabled great advances in diverse modern technologies including tissue engineering, drug delivery, biointegrated electronics, and soft robotics.[1−3] Such advances have been made possible, in part, thanks to the similarities in physicochemical properties of hydrogels and biological tissues.[4,5] While the softness and flexibility allow minimizing the mechanical mismatch between hydrogels and tissues, the high water content endows them with a wet and iron-rich environment, which is characteristic of biological systems. We repeated the disassembly/re-cross-linking process up to three times and we did not observe any changes in the microstructure, except an increase in the proportion of magnetite NPs (Figure S4) This result suggested that some of the Alg and PEDOT polymeric chains were not recovered with the magnet during this process and remained dispersed in solution (Figure S3). The induced heat can be explained by the following two mechanisms: (i) the eddy current due to the electrical conductivity of the hydrogel and (ii) the hysteresis loss, which has been reported effective for magnetic particles with sizes larger than 100 nm.[57] the change in the plateau temperature can be attributed to the loss of PEDOT and Alg from the hydrogel during re-cross-linking and the increase in the relative content of the magnetite NPs. The thermographic images taken at different times revealed that the heat was homogeneously induced, rather than locally, throughout the entire hydrogel. The utilization of hydrogels where reversible cross-linking is induced by physical (e.g., light, temperature) rather than chemical stimuli, would provide a technology more compatible with biological systems for biomedical applications
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