150
develop cord-like structures in monolayers and vascularized lumens in 3D microenvironments that can anastomose with host vasculature in vivo.
ECFCs are critical in wound healing/ischemic environments and are found circulating in peripheral blood. These endothelial progenitor cells are advantageous for
patient-specific therapies and have the ability to mature and anastomose with host
vasculature. While patient-specific, these cells are in limited supply circulating in
the peripheral blood, they are initially slow growing, and it takes many passages to
acquire enough cells to perform experiments or use for therapies.
More recently, hESC-EC and hiPSC-EC have been used to make vascular structures in vitro and can anastomose with host vasculature in vivo. hESC-ECs and
hiPSC-ECs have the ability to make lumens in 3D cultures (i.e., hydrogels) and are
responsive to vascular endothelial growth factor (VEGF) and basic fibroblast growth
factor (bFGF) signaling [58, 59]. While phenotypically similar to both mature and
immature endothelial cells, some studies indicate that though hESC-ECs and
hiPSC-ECs may be less responsive to shear stress [135], they retain the ability to be
differentiated into arterial and venous endothelial cells [139].
6.3.3 Fibroblast(-Like) Cells
Developing stable, perfusable vascular networks that can anastomose with host vasculature, to deliver nutrients, increases the capacity to enhance the viability of engineered grafts. Vascular stabilization occurs through the activity of mural cells, i.e.,
pericytes or smooth muscle cells. Several mesenchymal phenotypes (characterized
as being positive for surface markers CD73, CD90, and CD105) have been used to
perform this function [3]. In particular, fibroblasts from the skin, lung, and bladder
have been widely used, though their perivascular characteristics vary with the anatomical site of isolation. Dermal fibroblasts are the most translatable due to the ease
of obtaining them from the skin and their potential to rapidly proliferate and to
express limited perivascular potential. Chen et al. demonstrated vessel development
using normal human lung fibroblasts in co-culture with HUVECs or EPCs. Vessel
development was monitored over 7 days, in the presence of low (0.2 million cells/
mL) or high (two million cells/mL) concentrations of fibroblasts. The higher concentration of normal lung fibroblasts co-cultured with HUVECs or EPCs resulted in
longer vessels, compared to the lower concentration of fibroblasts [15]. CostaAlmeida et al. compared the vessel development of human dermal fibroblasts coupled with HUVECs or blood outgrowth endothelial cells (BOECs). Studies were
completed at 2:1 ratio of EC-FB. Cells were co-cultured for up to 21 days. By day
21, the co-culture of BOECs and NHDF resulted in ~32 capillary-like structures/
mm
2
, while HUVEC and NHDF co-cultures developed ~30 capillary-like structures/mm
2
. The average length of the capillary-like structures decreased from day
14 to day 21 in both groups [21].
Cardiac fibroblasts are specifically derived from the myocardium through biopsy.
This, however, causes damage to the myocardium. Cardiac fibroblasts contribute to
J. Morrissette-McAlmon et al.
develop cord-like structures in monolayers and vascularized lumens in 3D microenvironments that can anastomose with host vasculature in vivo.
ECFCs are critical in wound healing/ischemic environments and are found circulating in peripheral blood. These endothelial progenitor cells are advantageous for
patient-specific therapies and have the ability to mature and anastomose with host
vasculature. While patient-specific, these cells are in limited supply circulating in
the peripheral blood, they are initially slow growing, and it takes many passages to
acquire enough cells to perform experiments or use for therapies.
More recently, hESC-EC and hiPSC-EC have been used to make vascular structures in vitro and can anastomose with host vasculature in vivo. hESC-ECs and
hiPSC-ECs have the ability to make lumens in 3D cultures (i.e., hydrogels) and are
responsive to vascular endothelial growth factor (VEGF) and basic fibroblast growth
factor (bFGF) signaling [58, 59]. While phenotypically similar to both mature and
immature endothelial cells, some studies indicate that though hESC-ECs and
hiPSC-ECs may be less responsive to shear stress [135], they retain the ability to be
differentiated into arterial and venous endothelial cells [139].
6.3.3 Fibroblast(-Like) Cells
Developing stable, perfusable vascular networks that can anastomose with host vasculature, to deliver nutrients, increases the capacity to enhance the viability of engineered grafts. Vascular stabilization occurs through the activity of mural cells, i.e.,
pericytes or smooth muscle cells. Several mesenchymal phenotypes (characterized
as being positive for surface markers CD73, CD90, and CD105) have been used to
perform this function [3]. In particular, fibroblasts from the skin, lung, and bladder
have been widely used, though their perivascular characteristics vary with the anatomical site of isolation. Dermal fibroblasts are the most translatable due to the ease
of obtaining them from the skin and their potential to rapidly proliferate and to
express limited perivascular potential. Chen et al. demonstrated vessel development
using normal human lung fibroblasts in co-culture with HUVECs or EPCs. Vessel
development was monitored over 7 days, in the presence of low (0.2 million cells/
mL) or high (two million cells/mL) concentrations of fibroblasts. The higher concentration of normal lung fibroblasts co-cultured with HUVECs or EPCs resulted in
longer vessels, compared to the lower concentration of fibroblasts [15]. CostaAlmeida et al. compared the vessel development of human dermal fibroblasts coupled with HUVECs or blood outgrowth endothelial cells (BOECs). Studies were
completed at 2:1 ratio of EC-FB. Cells were co-cultured for up to 21 days. By day
21, the co-culture of BOECs and NHDF resulted in ~32 capillary-like structures/
mm
2
, while HUVEC and NHDF co-cultures developed ~30 capillary-like structures/mm
2
. The average length of the capillary-like structures decreased from day
14 to day 21 in both groups [21].
Cardiac fibroblasts are specifically derived from the myocardium through biopsy.
This, however, causes damage to the myocardium. Cardiac fibroblasts contribute to
J. Morrissette-McAlmon et al.