The effects of constant flow bioreactor cultivation and keratinocyte seeding densities on prevascularized organotypic skin grafts based on a fibrin scaffold.

ABSTRACT

Organotypic full-thickness skin grafts (OTSG) are already an important technology for treating various skin conditions and are well established for skin research and development. These obvious benefits are often impaired by the need of laborious production, their noncomplete autologous composition, and, most importantly, their lack of included vasculature. Therefore, our study focused on combining a prevascularized dermal layer with an epidermis to cultivate full-thickness skin grafts incorporating capillary-like networks. It has been shown that prevascularization accelerates ingrowth of tissue-engineered grafts, and it is a prerequisite to circumvent diffusion limits due to graft thickness. To obtain such a graft, we chose a dermal layer incorporating human umbilical vein endothelial cells (HuVEC) amid human dermal fibroblasts within a fibrin-based scaffold, seeded apically with human foreskin keratinocytes (hfKC). Our research investigated the used concept's feasibility, as well as the effect of hfKC addition on the development of a well-connected capillary-like network after approximately 21 days. In addition, we evaluated the utilization of a custom-made constant flow bioreactor for simplified cultivation of these grafts, therefore possibly easing graft production and presumably increasing their cost effectiveness. Skin grafts were assessed by conventional two-dimensional histology. In addition, software-assisted three-dimensional evaluation of the capillary-like structure networks was performed by two-photon laser scanning microscopy (TPLSM) and subsequent image processing was done with ImagePro(®) Analyzer 7.0 software, thereby evaluating its platform technology power in the field of prevascularized skin grafts. All samples showed a capillary-like structure network, but we could report a significant reduction of its total length after 14 days of tri-culture with 5×10(5)/cm(2) seeded hfKC, possibly indicating nutritional deficiencies for this particular high cell density experimental setup. Lower concentrations of hfKC did not affect the formation of the capillary-like structures significantly. The developed bioreactor simplified cultivation of prevascularized OTSG. However, a flow-dependent reduction of capillary-like structures in 1 and 5 mL/min flow conditions occurred. We conclude that our technique for creating prevascularized OTSG is feasible. In addition, TPLSM is well suited for analyzing the prevascularization process. We hypothesize that the handling benefits of our bioreactor can be preserved by using considerably lower flow rates while not impairing the forming of capillary-like structure networks.