Introduction: Development of tissue grafts and in vitro tissue models is hindered by the lack of vascular networks formation in the engineered constructs. In this study, we used primary human cells to investigate whether hydrogels based on alginate (Alg) blended with silk fibroin (SF) support the spontaneous formation of the tubular networks.
Methods: Alg/SF hydrogels containing normal human dermal fibroblasts were placed in the 24-well plates and cultivated for 14 days. Afterwards, human umbilical vein endothelial cells (HUVEC) loaded with magnetic particles (SPIONs, 3 µg/cm2) were seeded on the hydrogels, in the presence of magnetic field during the first 24 h. The growth of cells was monitored for additional 3 weeks. Metabolic activity of the cells was measured using WST-8 assay. The distribution of HUVECs and fibroblasts was investigated using CD31 or N-Cadherin staining. Two-photon microscopy was used for 3D images and to detect collagen formation (Collagen Iα1 antibody).
Results: Compared with fibroblast only, hydrogels containing both HUVECs and fibroblasts had higher metabolic activity from day 7 of co-culture onwards. HUVECs did not remain on the surface of hydrogels and gradually migrated inside the films. The formation of neo-vessel like structures (N-Cadherin + CD31) was detectable from day 20 of co-culture. Collagen, which is present in all connective tissues and is an indicator of the extracellular matrix (ECM) formation, was detected in the hydrogels at day 20 of fibroblast and HUVEC co-culture.
Conclusions: Alg/SF hydrogels support growth of different vascular cells, as well as the formation of ECM and vessel-like structures. Our initial investigations showed promising results with this highly-biocompatible scaffold, but further efforts are required to produce and validate the vascularized tissue constructs.