LED-Based Photoacoustic Imaging for Monitoring Angiogenesis in Fibrin Scaffolds

Vascularization of engineered constructs is required to integrate an implant within the host blood supply. The ability to noninvasively monitor neovascularization of an implanted construct is ultimately critical for translation. Laser speckle contrast analysis (LASCA), a widely used imaging technique within regenerative medicine, has high spatial resolution but offers limited imaging depth and is only sensitive to perfused blood vessels. As an emerging technology, photoacoustic (PA) imaging can provide centimeters of imaging depth and excellent sensitivity in vascular mapping. PA imaging in combination with conventional ultrasound (US) imaging offers a potential solution to this challenge in regenerative medicine. In this study, we used an LED-based PA-US dual system to image and monitor angiogenesis for 7 days in fibrin-based scaffolds subcutaneously implanted in mice. Scaffolds, with or without basic fibroblast growth factor (bFGF), were imaged on day 0 (i.e., postimplantation), 1, 3, and 7 with both LASCA and PA-US imaging systems. Quantified perfusion measured by LASCA and PA imaging were compared with histologically determined blood vessel density on day 7. Vessel density corroborated with changes in perfusion measured by both LASCA and PA. Unlike LASCA, PA imaging enabled delineation of differences in neovascularization in the upper and the lower regions of the scaffold. Overall, this study has demonstrated that PA imaging could be a noninvasive and highly sensitive method for monitoring vascularization at depth in regenerative applications.