ACS Appl Mater Interfaces. 2014 Sep 5. [Epub ahead of print]

Polypeptide Thermogels As a 3D Culture Scaffold for Hepatogenic Differentiation of Human Tonsil-derived Mesenchymal Stem Cells.

Kim SJ, Park MH, Moon HJ, Park JH, Ko DY, Jeong B.

Abstract

Tonsil-derived mesenchymal stem cells (TMSCs) were investigated for hepatogenic differentiation in the 3D matrixes of poly(ethylene glycol)-b-poly(L-alanine) (PEG-L-PA) thermogel. The diblock polymer formed β-sheet based fibrous nano-assemblies in water and the aqueous polymer solution undergo sol-to- gel transition as the temperature increases in a concentration range of 5.0-8.0 wt.%. The cell-encapsulated 3D matrix was prepared by increasing the temperature of the cell-suspended PEG-L-PA aqueous solution (6.0 wt.%) to 37 oC. The gel modulus at 37 oC was about 1000 Pa, which was similar to that of decellularized liver tissue. Cell proliferation, changes in cell morphology, hepatogenic biomarker expressions, and hepatocyte-specific biofunctions were compared for the following 3D culture systems; TMSC-encapsulated thermogels in the absence of hepatogenic growth factors (protocol M), TMSC-encapsulated thermogels where hepatogenic growth factors were supplied from the medium (protocol MGF), and TMSC-encapsulated thermogels where hepatogenic growth factors were coencapsulated with TMSCs during the sol-to-gel transition (protocol GGF). The spherical morphology and size of the encapsulated cells were maintained in the M system during the 3D culture period of 28 days, whereas the cells changed their morphology and significant aggregation of cells was observed in the MGF and GGF systems. The hepatocyte-specific biomarker expressions and metabolic functions were negligible for the M system. However, hepatogenic genes of albumin, cytokeratin 18 (CK-18), and hepatocyte nuclear factor 4α (HNF 4α) were significantly expressed in both MGF and GGF systems. In addition, production of albumin and α-fetoprotein was also significantly observed in both MGF and GGF systems. The uptake of cardiogreen and low-density lipoprotein, typical metabolic functions of hepatocytes, were apparent for MGF and GGF. The above data indicates that the 3D culture system of PEG-L-PA thermogels provides cytocompatible microenvironments for hepatogenic differentiation of TMSCs. In particular, the successful results of the GGF system suggest that the PEG-L-PA thermogel can be a promising injectable tissue engineering system for liver tissue regeneration after optimizing the aqueous formulation of TMSCs, hepatogenic growth factors, and other biochemicals.