**5. Three-dimensional culture**

In more recent years, three-dimensional cell culture methods have been widely applied and are regarded to have high importance in evaluating the biological processes [12]. Three-dimensional culture systems may simulate the intercellular interactions in regulation of stem cell self-renewal and differentiation [13]. It was shown that a three-dimensional culture enhanced the production of extracellular matrix-related genes when compared with two-dimensional monolayer culture [12].
