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Permanent fluidic magnets for liquid bioelectronics


Brownian motion allows microscopically dispersed nanoparticles to be stable in ferrofluids, as well as causes magnetization relaxation and prohibits permanent magnetism. Here we decoupled the particle Brownian motion from colloidal stability to achieve a permanent fluidic magnet with high magnetization, flowability and reconfigurability. The key to create such permanent fluidic magnets is to maintain a stable magnetic colloidal fluid by using non-Brownian magnetic particles to self-assemble a three-dimensional oriented and ramified magnetic network structure in the carrier fluid. This structure has high coercivity and permanent magnetization, with long-term magnetization stability. We establish a scaling theory model to decipher the permanent fluid magnet formation criteria and formulate a general assembly guideline. Further, we develop injectable and retrievable permanent-fluidic-magnet-based liquid bioelectronics for highly sensitive, self-powered wireless cardiovascular monitoring. Overall, our findings highlight the potential of permanent fluidic magnets as an ultrasoft material for liquid devices and systems, from bioelectronics to robotics.

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Fig. 1: Creating the PFM and comparing it with traditional magnetic systems.
Fig. 2: Understanding the PFM formation process.
Fig. 3: Characterizing the PFM.
Fig. 4: PFM-based liquid bioelectronics.
Fig. 5: In vivo injectable arrhythmia monitoring.

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Data availability

Source data are provided with this paper. Other relevant information in this study is included in Supplementary Information. Further data are available from the corresponding author upon request.


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We acknowledge the Henry Samueli School of Engineering & Applied Science and the Department of Bioengineering at the University of California, Los Angeles, for the startup support. J.C. acknowledges the Vernroy Makoto Watanabe Excellence in Research Award at the UCLA Samueli School of Engineering, the Office of Naval Research Young Investigator Award (award ID N00014-24-1-2065), NIH Grant (award ID R01 CA287326), the American Heart Association Innovative Project Award (award ID 23IPA1054908), the American Heart Association Transformational Project Award (award ID 23TPA1141360), the American Heart Association’s Second Century Early Faculty Independence Award (award ID 23SCEFIA1157587), the Brain & Behavior Research Foundation Young Investigator Grant (grant number 30944), and the NIH National Center for Advancing Translational Science UCLA CTSI (grant number KL2TR001882). J.C. and T.T. acknowledge the support from Caltech/UCLA joint NIH T32 Training Grant (award ID T32EB027629). S.L. acknowledges support from an NIH Grant (award ID R01 NS126918). We also acknowledge the insightful comments and careful editing from D. Di Carlo and the UCLA Writing Center for a one-on-one personalized writing consultation.

Author information

Authors and Affiliations



J.C. guided the whole research project. X.Z., Y.Z. and J.C. conceived the idea, designed the experiment, analysed the data, drew the figures and composed the paper. J.X., J.L., T.T. and G.C. assisted in device fabrication and testing. S.L., Y.S. and X.Z. performed the in vivo animal study. All authors have read the paper, agreed to its content and approved the submission.

Corresponding author

Correspondence to Jun Chen.

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Competing interests

J.C., X.Z. and Y.Z. have filed a patent related to this work under the US provisional patent application no. 63/596,815 from the University of California, Los Angeles. The authors declare no competing interests.

Peer review

Peer review information

Nature Materials thanks Wei Gao and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–27, Table 1, Notes 1–10 and References.

Reporting Summary

Supplementary Video 1

The 3D ORM network structure in the carrier fluid.

Supplementary Video 2

A continuous magnetic network structure forming in the carrier fluid.

Supplementary Video 3

ORM networks dynamically self-assemble, disassemble and reassemble.

Supplementary Video 4

Separation of PFM droplets in response to an external rotating magnetic field.

Supplementary Video 5

PFM droplet merging in response to the external rotating magnetic field.

Supplementary Video 6

PFM droplet moving under an external magnetic field.

Supplementary Video 7

PFM droplet buoyant in the water responding to the external rotating magnetic field.

Supplementary Video 8

Ferrofluid droplet buoyant in the water responding to the external rotating magnetic field.

Source data

Source Data Fig. 1

Source data for Fig. 1.

Source Data Fig. 2

Source data for Fig. 2.

Source Data Fig. 3

Source data for Fig. 3.

Source Data Fig. 4

Source data for Fig. 4.

Source Data Fig. 5

Source data for Fig. 5.

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Zhao, X., Zhou, Y., Song, Y. et al. Permanent fluidic magnets for liquid bioelectronics. Nat. Mater. 23, 703–710 (2024).

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