Growth of collagen fibrils produced by human osteosarcoma cells: High-resolution scanning electron microscopy

To demonstrate three-dimensionally the process of the collagen fibril growt h, the bottom of culture dishes with human osteosarcoma cells (NOS-1) and t heir extracts were examined by conventional scanning electron microscopy (S ERI), Backscattered electron (BSE) imaging of SEM was also applied to the s pecimens, which were stained with phosphotungustic acid and uranyl acetate. Conventional SEM images showed several stages of collagen fibril assembly. Short collagen fibrils with tapered ends were distributed at the bottom of the dish just beneath and/or around the cultured cells; they were 1 mu m l ong and 20-30 nm in diameter at the thickest middle portion. These fibrils were often twisted and united in a right helical direction, and consequentl y increased in length (5-10 mu m) and diameter (more than 100 nm), In BSE i mages, the periodical bands stained with phosphotungstic acid and uranyl ac etate were visualized throughout the individual fibrils. The banding patter n indicated that the polarity of the collagen molecules was unidirectional; namely, that all molecules were pointed in the same direction throughout t he length of the fibrils.