Development of hepatocyte-embedded hydrogel-filled macroporous scaffold cultures using transglutaminase

Recent advancements in enzyme-mediated crosslinkable hydrogels: In vivo-mimicking strategies

Enzymes play a central role in fundamental biological processes and have been traditionally used to trigger various processes. In recent years, enzymes have been used to tune biomaterial responses and modify the chemical structures at desired sites. These chemical modifications have allowed the fabrication of various hydrogels for tissue engineering and therapeutic applications. This review provides a comprehensive overview of recent advancements in the use of enzymes for hydrogel fabrication. Strategies to enhance the enzyme function and improve biocompatibility are described. In addition, we describe future opportunities and challenges for the production of enzyme-mediated crosslinkable hydrogels.

Liver-specific extracellular matrix hydrogel promotes liver-specific functions of hepatocytes in vitro and survival of transplanted hepatocytes in vivo

A solubilized liver-specific extracellular matrix (L-ECM) substratum was obtained by decellularization of porcine liver using Triton X-100 and pepsin treatments. The L-ECM was able to immobilize hepatocyte growth factor at a high efficiency of 87%. L-ECM gelled spontaneously in a physiologically neutral environment. Primary hepatocytes embedded in the L-ECM gel showed a high albumin synthesis activity and ethoxyresorufin-O-deethylase (EROD) activity even at 3 weeks in culture. In addition, the L-ECM gel-embedded hepatocytes implanted subcutaneously into partial hepatectomized rats showed a high survival rate (18%) and formed a large liver tissue-like structure. Their efficiencies of EROD activity and large liver tissue-like structure formation were about twice those of collagen gel-embedded hepatocytes. Based on these results, we clarified the effectiveness of L-ECM gel as a substrate for hepatocyte culture and transplantation.

Base structure consisting of an endothelialized vascular-tree network and hepatocytes for whole liver engineering

Reconstructed liver has been desired as a liver substitute for transplantation. However, reconstruction of a whole liver has not been achieved because construction of a vascular network at an organ scale is very difficult. We focused on decellularized liver (DC-liver) as an artificial scaffold for the construction of a hierarchical vascular network. In this study, we obtained DC-liver and the tubular network structure in which both portal vein and hepatic vein systems remained intact. Furthermore, endothelialization of the tubular structure in DC-liver was achieved, which prevented blood leakage from the tubular structure. In addition, hepatocytes suspended in a collagen sol were injected from the surroundings using a syringe as a suitable procedure for liver cell inoculation. In summary, we developed a base structure consisting of an endothelialized vascular-tree network and hepatocytes for whole liver engineering.

Heparin-conjugated gelatin as a growth factor immobilization scaffold

Tissue engineering requires growth factors, cells and a scaffold to permit effective tissue regeneration. This study aimed to develop a scaffold with a focus on immobilizing growth factors within gelatin. We focused on the extracellular matrix and developed a heparin-conjugated gelatin (Hep-gela). Conjugation was confirmed using the alcian blue assay and X-ray diffraction patterns. The mechanical strength and stability of the Hep-gela gel in protease solution were improved compared with collagen gel. Hep-gela was able to immobilize vascular endothelial growth factor (VEGF) even in the presence of albumin, with an efficiency of 54.2%. Immobilized VEGF promoted proliferation of human umbilical vein endothelial cells. Hep-gela-immobilized VEGF maintained its native biological activity. In summary, Hep-gela has the potential to become an effective material in the field of regenerative medicine.