Abstract
Conventional implantable electronic sensors for continuous monitoring of internal tissue strains are yet to match the biomechanics of tissues while maintaining biodegradability, biocompatibility and wireless monitoring capability. Here we present a two-dimensional phononic crystal composed of periodic air columns in soft hydrogel, which was named ultrasonic metagel, and we demonstrate its use as implantable sensor for continuous and wireless monitoring of internal tissue strains. The metagel’s deformation shifts its ultrasonic bandgap, which can be wirelessly detected by an external ultrasonic probe. We demonstrate ex vivo the ability of the metagel sensor for monitoring tissue strains on porcine tendon, wounded tissue and heart. In live pigs, we further demonstrate the ability of the metagel to monitor tendon stretching, respiration and heartbeat, working stably during 30 days of implantation, and we loaded the metagel with growth factors to achieve different healing rates in subcutaneous wounds. The metagel results almost completely degraded 12 weeks after implantation. Our finding highlights the clinical potential of the ultrasonic sensor for tendon rehabilitation monitoring and drug delivery efficacy evaluation.
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Data availability
All data supporting the findings of this study are available in the paper and its Supplementary Information. Source data are provided with this paper.
Code availability
The custom code (MATLAB script) for processing the RF data of echoes acquired by an ultrasound transducer has been deposited to a public database at https://github.com/lostboy520/FFT_Echo_of_Metagel.git (ref. 62).
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Acknowledgements
This work was supported by the National Natural Science Foundation of China (T2350001, 52173280 and 52188102), the China Postdoctoral Science Foundation (2022M711256), the HUST Interdisciplinary Research Project (2023JCYJ044) and the Taihu Lake Innovation Fund for Future Technology, HUST (2023A3).
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Contributions
J.Z., H.T. and Y.T. conceived the concept of the metagel sensor. Y.T. and Y. Yang designed, assembled and tested the metagel strain sensor. Y.T. and H.T. designed and conducted the numerical simulation of the metagel. Y. Yang, N.L. and M.Z. designed and fabricated the metagel implant and bioadhesive hydrogel interface. T.K. and Y.C. designed and characterized the drive and acquisition system of the ultrasonic probe. Y.T., T.K. and Y. Yu analysed the ultrasonic data. Y.T., J.W. and Y. Yang designed and performed the ex vivo experiments. Y. Yang, J.W. and N.L. designed and characterized the metagel’s biodegradability. J.W., Xinqi Liu, Y.T., Y. Yang, Y.C., J.T. and W.C. designed and performed the in vivo experiments and biocompatibility test. Y.T., H.T., J.Z., Y. Yu, Z.Y., N.L. and L.X. contributed to the design of experiments. Y.T., Y. Yang, H.T., L.X., Xurui Liu, Z.Y. and J.Z. prepared the paper with input from all authors.
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Competing interests
J.Z., Y.T., H.T., Y. Yang, Y.C. and T.K. are named as inventors on a patent (CN115752311A) that covers the design and fabrication of the soft structured hydrogel. J.Z., Y.T., H.T., Y. Yang and Y.C. are named as inventors of an ultrasonic monitoring system on a patent (CN115844455A) related to this work. J.Z., Y.T., H.T., Y. Yang, Y.C. and T.K. are named as inventors on patents (CN115844448A) related to this work. The authors declare that they have no other competing interests.
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Nature Biomedical Engineering thanks Nicholas Fang and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Peer reviewer reports are available.
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Supplementary Video 1
Summary video of the ultrasonic implantable metagel strain sensor.
Supplementary Video 2
Flexibility of the metagel strain sensor.
Supplementary Video 3
Echo peak frequency shift of the metagel sensor upon different strains.
Supplementary Video 4
Ex vivo experiment of the metagel strain sensor.
Supplementary Video 5
In vivo experiment of the metagel strain sensor.
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Tian, Y., Yang, Y., Tang, H. et al. An implantable hydrogel-based phononic crystal for continuous and wireless monitoring of internal tissue strains. Nat. Biomed. Eng 9, 1335–1348 (2025). https://doi.org/10.1038/s41551-025-01374-z
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DOI: https://doi.org/10.1038/s41551-025-01374-z
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