Acoustic and mechanical characterisation of a 3D-printable transparent vessel-mimicking material for pre-clinical imaging: comparison with ex-vivo vessels and established clinically-relevant materials

Bisphenol-A-ethoxylate dimethacrylate (BEMA) is an emerging non-cytotoxic, photo-responsive hydrogel that can be used to fabricate microchannel flow systems for use in ultrasound mediated drug delivery research. This study aims to assess the acoustic properties at ultrasound frequencies up to 50 MHz, in addition to the elastic properties of BEMA prior to its use in the fabrication of preclinical flow phantoms. As a comparison, acoustic and mechanical properties of both ex-vivo rat aorta and a series of conventional vessel-mimicking materials were also studied, including polyvinyl alcohol cryogel (1 to 7 freeze–thaw cycles), agar (prepared under IEC standard), and C-Flex®. In this study, BEMA hydrogel exhibited a mean speed-of-sound of 1608.6 ± 8.74 m/s, mean attenuation of 0.64 ± 0.12 dB·cm^-1·MHz^-1 and a median indentation elastic modulus of 425 kPa. In contrast, ex-vivo rat aorta was measured to have mean speed-of-sound of 1533.5 ± 46.9 to 1534.6 ± 38.5 m·s^-1, attenuation at 0.61 ± 0.17 to 0.73 ± 0.20 dB·cm^-1·MHz^-1, for thoracic and abdominal aorta, respectively, and overall median indentation elastic modulus of 7.07 kPa (interquartile range: 4.92 – 10.14 kPa). Given the above results, BEMA hydrogel samples demonstrated high repeatability, however, to realistically mimic vessels, further optimization of the photopolymerization process is required to align the elastic modulus with that measured from vessels.