Development of alginate-based hydrogels for blood vessel engineering

Vascular diseases are among the primary causes of death worldwide. In serious conditions, replacement of the damaged vessel is required. Autologous grafts are preferred, but their limited availability and difficulty of the harvesting procedures favour synthetic alternatives' use. However, as synthetic grafts may present significant drawbacks, tissue engineering-based solutions are proposed. Herein, tubular hydrogels of alginate combined with collagen type I and/or silk fibroin were prepared by ionotropic gelation using gelatin hydrogel sacrificial moulds loaded with calcium ions (Ca²⁺). The time of exposure of alginate solutions to Ca²⁺-loaded gelatin was used to control the wall thickness of the hydrogels (0.47 ± 0.10 mm-1.41 ± 0.21 mm). A second crosslinking step with barium chloride prevented their degradation for a 14 day period and improved mechanical properties by two-fold. Protein leaching tests showed that collagen type I, unlike silk fibroin, was strongly incorporated in the hydrogels. The presence of silk fibroin in the alginate matrix, containing or not collagen, did not significantly improve hydrogels' properties. Conversely, hydrogels enriched only with collagen were able to better support EA.hy926 and MRC-5 cells' growth and characteristic phenotype. These results suggest that a two-step crosslinking procedure combined with the use of collagen type I allow for producing freestanding vascular substitutes with tuneable properties in terms of size, shape and wall thickness.