Ultrasound-guided photoacoustic imaging-directed re-endothelialization of acellular vasculature leads to improved vascular performance.

As increasing effort is dedicated to investigating the regenerative capacity of decellularized tissues, research has progressed to recellularizing these tissues prior to implantation. The delivery and support of cells seeded throughout acellular scaffolds are typically conducted through the vascular axis of the tissues. However, it is unclear how cell concentration and injection frequency can affect the distribution of cells throughout the scaffold. Furthermore, what effects re-endothelialization have on vascular patency and function are not well understood. We investigated the use of ultrasound-guided photoacoustic (US/PA) imaging as a technique to visualize the distribution of microvascular endothelial cells within an optimized acellular construct upon re-endothelialization and perfusion conditioning. We also evaluated the vascular performance of the re-endothelialized scaffold using quantitative vascular corrosion casting (qVCC) and whole-blood perfusion. We found US/PA imaging was an effective technique to visualize the distribution of cells. Cellular retention following perfusion conditioning was also detected with US/PA imaging. Finally, we demonstrated that a partial recovery of vascular performance is possible following re-endothelialization-confirmed by fewer extravasations in qVCC and improved blood clearance following whole-blood perfusion. STATEMENT OF SIGNIFICANCE: Re-endothelialization is a method that enables decellularized tissue to become useful as a tissue engineering construct by creating a nutrient delivery and waste removal system for the entire construct. Our approach utilizes a decellularization method that retains the basement ECM of a highly vascularized tissue upon which endothelial cells can be injected to form an endothelium. The US/PA method allows for rapid visualization of cells within a construct several cm thick. This approach can be experimentally used to observe changes in cellular distribution over large intervals of time, to help optimize cell seeding parameters, and to verify cell retention within re-endothelialized constructs. This approach has temporal and depth advantages compared to section reconstruction and imaged fluorophores respectively.