Abstract

Background: In tissue engineering, scaffolds provide a matrix for cells to attach and proliferate that can be implanted into a tissue defect site. For this purpose, the scaffolds should exhibit a good biocompatibility. Moreover, they should stimulate the fast ingrowth of new blood vessels after implantation in order to guarantee the survival and long-term function of the implanted cells. In the present study, we analyzed in vivo the biocompatibility and vascularization of a novel type of polyurethane scaffolds. These non-toxic scaffolds have been developed for tissue engineering by introducing labile units into the stable polyurethane chains, ensuring an almost frictionless integration into the host tissue due to the elastic material properties of these modified polyurethanes. Materials and Methods: A dorsal skinfold chamber was prepared in 28 balb/c mice for the implantation of three different polyurethane scaffolds (∼3×3×1 mm), i. e. PU-S (n=9), PU-M (n=9) and PU-F (n=10). Using the technique of intravital fluorescence microscopy we repetitively analyzed vascularization of the implants and venular leukocyte-endothelial cell interaction in the surrounding host tissue over a time period of 14 days. Subsequently, incorporation of the scaffolds and leukocyte recruitment was analyzed by histology and immunohistochemistry. Moreover, we performed a WST-1 assay to analyze in vitro the cytotoxicity of the different scaffold types. Results: We could demonstrate by WST-1 assay that all three types of polyurethane scaffords were not cytotoxic. Accordingly, also in vivo the numbers of rolling and adherent leukocytes in venules of the dorsal skinfold chamber were found in a physiological range (∼17–21 cells/min and ∼100–200 cells/mm²) and did not significantly differ between the observation groups. However, implantation of PU-S, PU-M and PU-F induced only a poor angiogenic response with a functional capillary density of only ∼47–60 cm/cm² and ∼3–10 cm/cm² in the border and center zones of the scaffolds at day 14 after implantation. Histology confirmed our intravital microscopic findings. After 14 days, the scaffolds were incorporated in a granulation tissue, which exhibited only a few newly formed blood vessels and infiltrating myeloperoxidase-positive leukocytes. Conclusion: In the present study we could demonstrate that the novel elastic polyurethane scaffolds PU-S, PU-M and PU-F exhibit a good biocompatibility and, thus, may be used to generate tissue constructs which do not induce a strong inflammatory reaction after implantation into patients. However, the scaffolds should be further modified in order to accelerate and improve the process of vascularization.