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High-frequency linear rheology of hydrogels probed by ultrasound-driven microbubble dynamics

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Abstract

Ultrasound-driven microbubble dynamics are central to biomedical applications, from diagnostic imaging to drug delivery and therapy. In therapeutic applications, the bubbles are typically embedded in tissue, and their dynamics are strongly affected by the viscoelastic properties of the soft solid medium. While the behaviour of bubbles in Newtonian fluids is well characterised, a fundamental understanding of the effect on ultrasound-driven bubble dynamics of a soft viscoelastic medium is still being developed. We characterised the resonant behaviour in ultrasound of isolated microbubbles embedded in agarose gels, commonly used as tissue-mimicking phantoms. Gels with different viscoelastic properties were obtained by tuning agarose concentration, and were characterised by standard rheological tests. Isolated bubbles (100–200 μm) were excited by ultrasound (10–50 kHz) at small pressure amplitudes (<1 kPa), to ensure that the deformation of the material and the bubble dynamics remained in the linear regime. The radial dynamics of the bubbles were recorded by high-speed video microscopy. Resonance curves were measured experimentally and fitted to a model combining the Rayleigh–Plesset equation governing bubble dynamics, with the Kelvin–Voigt model for the viscoelastic medium. The resonance frequency of the bubbles was found to increase with increasing shear modulus of the medium, with implications for optimisation of imaging and therapeutic ultrasound protocols. In addition, the viscoelastic properties inferred from ultrasound-driven bubble dynamics differ significantly from those measured at low frequency with the rheometer. Hence, rheological characterisation of biomaterials for medical ultrasound applications requires particular attention to the strain rate applied.

Graphical abstract: High-frequency linear rheology of hydrogels probed by ultrasound-driven microbubble dynamics

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Publication details

The article was received on 16 Dec 2016, accepted on 01 May 2017 and first published on 03 May 2017


Article type: Paper
DOI: 10.1039/C6SM02810A
Citation: Soft Matter, 2017, Advance Article
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    High-frequency linear rheology of hydrogels probed by ultrasound-driven microbubble dynamics

    A. Jamburidze, M. De Corato, A. Huerre, A. Pommella and V. Garbin, Soft Matter, 2017, Advance Article , DOI: 10.1039/C6SM02810A

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