The Effect of Hypoxia onIn VitroPrevascularization of a Thick Soft Tissue

Prevascularizing an implantable tissue is one strategy to improve oxygen (O2) transport throughout larger tissues upon implantation. This study examined the role of hypoxia both during (i.e., as a stimulus) and after (i.e., mimicking implant conditions) vascularization of an implantable tissue. Tissues consisted of microcarrier beads coated with human umbilical vein endothelial cells embedded in fibrin. The fibrin was covered with a monolayer of normal human lung fibroblasts (NHLFs), or exposed to conditioned media from NHLFs. Capillary networks developed at 20% or 1% O2 tension for 8 days. In some experiments, tissues were supplemented with vascular endothelial growth factor (VEGF) and basic fibroblast growth factor, whereas in others the tissues prevascularized at 20% O2 were transferred to 1% O2 for 8 additional days. Maximal capillary formation occurred in media conditioned by NHLFs at 20% O2, supplemented with VEGF (concentration >10 pM). Hypoxia (1% O2) did not stimulate basic fibroblast growth factor production and decreased in vitro angiogenesis, despite an increase in endogenous VEGF production. Hypoxia also degraded a preformed capillary network within 4 days. Hence, strategies to prevascularize implantable tissues may not require the physical presence of stromal cells, but will likely require fibroblast-derived growth factors in addition to VEGF to maintain capillary growth.