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Tissue engineering requires the development of three-dimensional water-stable scaffolds. In this study, silk fibroin/chitosan (SFCS) scaffold was successfully prepared by freeze-drying method. The scaffold is water-stable, only swelling to a limited extent depending on its composition. Fourier Transform Infrared (FTIR) spectra and X-Ray diffraction curves confirmed the different structure of SFCS scaffolds from both chitosan and silk fibroin. The homogeneous porous structure, together with nano-scale compatibility of the two naturally derived polymers, gives rise to the controllable mechanical properties of SFCS scaffolds. By varying the composition, both the compressive modulus and compressive strength of SFCS scaffolds can be controlled. The porosity of SFCS scaffolds is above 95% when the total concentration of silk fibroin and chitosan is below 6 wt%. The pore sizes of the SFCS scaffolds range from 100 microm to 150 microm, which can be regulated by changing the total concentration. MTT assay showed that SFCS scaffolds can promote the proliferation of HepG2 cells (human hepatoma cell line) significantly. All these results make SFCS scaffold a suitable candidate for tissue engineering.

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In vivo engineering of hepatic tissue based on primary hepatocytes offers new perspectives for the treatment of liver diseases. However, generation of thick, three-dimensional liver tissue has been limited by the lack of vasculature in the tissue-engineered constructs. Here, we used collagen hydrogel as a matrix to generate engineered hepatic units to reconstitute three-dimensional, vascularized hepatic tissue in vivo. Hepatocytes harvested from Sprague-Dawley rats were mixed with liquid type I collagen, concentrated Dulbecco's modified Eagle's medium (2 x), and hepatocyte maintenance medium to create hepatocyte/collagen hydrogel constructs. The constructs were then dissociated into cylindrical hepatic units (diameter/height: 2000-4000 microm/500-1000 microm). Stacking of hepatic units under the subcutaneous space resulted in significant cell engraftment, with the formation of large fused hepatic system (more than 0.5 cm thickness) containing blood vessels. In contrast, only less cell engraftment could be achieved when hepatocytes were transplanted in a manner of whole constructs. Functional maintenance of the engineered hepatic tissue was confirmed by the expression of liver-specific mRNA and proteins. The engineered hepatic tissue has the ability to respond to the regenerative stimulus. In conclusion, large hepatic tissue containing blood vessels could be engineered in vivo by merging small hepatic units. This approach for tissue engineering is simple and represents an efficient way to engineer hepatic tissue in vivo.