Evaluation of basement membrane (lamina densa and lamina reticularis) continuity and thickness by means of transmission electron microscopy and light microscopy (reticulin staining). Average thickness of the lamina reticularis was monitored throughout in vitro culture (a, black arrows indicate lamina reticularis). No significant changes were observed in lamina reticularis thickness when analyzing reticulin stainings. The lamina densa remained continuous at all time during the entire cultivation period (up to 96 h) as shown by the transmission electron microscopical images (b-c, black arrows indicate lamina densa). Data are represented as means + SD (error bars).