Ultrasound And Photoacoustic Imaging To Assess Microvasculature In Tissue Engineered Constructs

Assessment of neovascular growth is essential in various applications related to tissue engineering. However, the process of vascularization from progenitor cells contributing vascular growth is not well understood. Hence, an imaging modality, which is easily applicable, reliable, and capable of quantitative assessment of vascular growth or regression in a three-dimensional environment, is required. In this study, the combined ultrasound and photoacoustic imaging method was applied to assess microvasculature in tissue engineered constructs. Hydrogels that spontaneously promote tube formation from implanted mesenchymal stem cells (MSCs) were imaged. PEGylated fibrin gels, supporting the development of capillary growth were implanted in a Lewis rat. After one week, the rat was euthanized and the gel implants were excised and positioned in water cuvettes for imaging. Ultrasound and photoacoustic images were acquired with single element 25 MHz and 48 MHz focused ultrasound transducers interfaced with a nanosecond pulsed laser source operating at 532 nm wavelength. The 3D ultrasound and photoacoustic image was reconstructed based on hundreds of 2D ultrasound images obtained by mechanically scanning the transducer. The ultrasound and photoacoustic images had good agreement with the vascular structure in the gel samples indicating that the combined ultrasound and photoacoustic imaging is capable of assessing growth of micro blood vessels.