Increased vasculogenesis of endothelial cells in hyaluronic acid augmented fibrin-based natural hydrogels - from in vitro to in vivo models.

Vascularisation efficiency plays an essential role in the success of bulk transplantation, while biocompatibility and safety are major concerns in clinical applications. Fibrin-based hydrogels have been exploited as scaffolds for their advantages in biocompatibility, degradability and mass transportation in various forms. However, the mechanical strength and degree of vascularisation remain unsatisfactory for clinical usage. An interpenetrating hydrogel was developed by adding hyaluronic acid (HA) to a fibrin-based natural hydrogel. The vasculogenesis of endothelial cells (human umbilical vein endothelial cells, HUVECs) was characterised within the gel using both in vitro and in vivo animal studies. The in vitro vascular morphology analysis showed 17.9 % longer mean tube length and 14.3 % higher average thickness in 7 d cultivation within the HA-supplemented hydrogel. The in vivo results showed 51.6 % larger total tube area, 1.8 × longer average tube length and 81.6 % higher cell number in the HA-supplemented hydrogel compared to the hydrogel without HA. The experimental results demonstrated better vascularisation and cell recruitment in the HA- supplemented hydrogel. The material properties of the hydrogels were also analysed using atomic force microscopy (AFM). The results revealed 3.7 × higher elasticity of the HA-supplemented hydrogel, which provided better mechanical strength and support for easy handling during procedures. With the demonstrated advantages, the developed hydrogels showed promise for exploitation in various practical clinical applications.