High frequency rheology of hybrid hydrogels using ultrasound transient elastography

Dynamic ultrasound (US) elastography was developed the last decades to assess elastic properties of living tissues, which helps significantly physicians to characterize pathologies. Compared to classical rheology, these techniques allow then to quantify the mechanical properties of tissues in an unusual frequency range of hundreds of Hertz. In this paper two objectives were investigated: to validate US elastographic measurement by comparing those with classical rheology and to better characterize hybrid hydrogels at high frequency. Hybrid hydrogels were synthetized by radical polymerization of a hydrophilic monomer in presence of water and are highly reproducible materials with adjustable viscoelasticity. Classical rheology experiments were carried out in plane-plane geometry in order to get the elastic moduli G´ and loss moduli G” from 0.01 to 10 Hz. Transient elastography (TE) and Supersonic Imaging (SSI) techniques were used to characterize at high frequency polymers (from 50 to 1200 Hz). Two different hydrogels were tested in US with different concentration of scaterrers (SP2 and SP5). A very good correlation was obtained between each techniques. This paper shows the capability of dynamic US elastography to quantify rheological properties at high frequencies in order to better characterize materials.