Abstract
Many pathologies are characterized by poor blood vessel growth and reduced nutrient delivery to the surrounding tissue, introducing a need for tissue engineered blood vessels. Our lab has developed a 3D co-culture method to grow interconnected networks of pericyte-invested capillaries, which can anastamose with host vasculature following implantation to restore blood flow to ischemic tissues. However, if the engineered vessels contain endothelial cells (ECs) that are misaligned or contain wide junctional gaps, they may function improperly and behave more like the pathologic vessels that nourish tumors. The purpose of this study was to test the resistance to permeability of these networks in vitro, grown with different stromal cell types, as a metric of vessel functionality. A fluorescent dextran tracer was used to visualize transport across the endothelium and the pixel intensity was quantified using a customized MATLAB algorithm. In fibroblast-EC co-cultures, the dextran tracer easily penetrated through the vessel wall and permeability was high through the first 5 days of culture, indicative of vessel immaturity. Beyond day 5, dextran accumulated at the periphery of the vessel, with very little transported across the endothelium. Quantitatively, permeability dropped from initial levels of 61% to 39% after 7 days, and to 7% after 2 weeks. When ECs were co-cultured with bone marrow-derived mesenchymal stem cells (MSCs) or adipose-derived stem cells (AdSCs), much tighter control of permeability was achieved. Relative to the EC-fibroblast co-cultures, permeabilities were reduced 41% for the EC-MSC co-cultures and 50% for the EC-AdSC co-cultures after 3 days of culture. By day 14, these permeabilities decreased by 68% and 77% over the EC-fibroblast cultures. Co-cultures containing stem cells exhibit elevated VE-cadherin levels and more prominent EC-EC junctional complexes when compared to cultures containing fibroblasts. These data suggest the stromal cell identity influences the functionality and physiologic relevance of engineered capillary networks.
Highlights
Success within the tissue engineering field continues to be limited due to the inability to form a functional vasculature capable of supplying oxygen and nutrients to sustain tissue growth and metabolism [1,2,3]
This study focuses on the functional differences of capillary networks assembled from endothelial cells (ECs) and these varying mesenchymal cell types as stabilizing pericytes, using permeability as one marker of vessel functionality
Assay Development and Validation During angiogenesis, new capillary sprouts form following initial budding from a source vessel, and become more elongated, branched, and stabilized by supporting pericytes over time
Summary
Success within the tissue engineering field continues to be limited due to the inability to form a functional vasculature capable of supplying oxygen and nutrients to sustain tissue growth and metabolism [1,2,3]. Fabrication of constructs larger than 200 mm in thickness has been mostly unsuccessful, with large, hollow organs or avascular tissues being two exceptions [4] Tissues thicker than this threshold are unable to overcome the limits of diffusion to properly nourish the tissue. One promising option involves the delivery of combinations of pro-angiogenic factors with precise spatial and temporal resolution in order to recruit host vasculature [5] This approach can be limited by the fact that the half-lives of these factors are often very short, thereby limiting their bioactivity, and by the fact that even multiple combinations of factors cannot fully recapitulate the complex milieu of pro-angiogenic factors presented to cells in vivo. Amongst the most recent possible solutions to overcome this hurdle is the idea of creating prevascularized tissues, which contain networks of vessels formed in vitro that can self-organize and anastamose with the host vasculature in vivo shortly after implantation [6,7]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
