In nature, collagens exist as triple helical structures in which three polypeptide chains are tightly wrapped around each other. The stability of the triple helical structure, and hence functionality of the collagen, requires hydroxylation of specific proline residues within precursor polypeptide collagen chains by the enzyme prolyl 4-hydroxylase. In the absence of proline hydroxylation, the essential triple-helical conformation of collagen is thermally unstable at well below physiological temperatures.

The production of a synthetic source of human collagen has been attempted using various recombinant production systems. It was found that expression of the collagen gene alone results in unhydroxylated collagen with melting temperatures around 23°C. Even in transgenic systems, such as animals and plants, which rely on endogenous prolyl 4-hydroxylase, the resulting collagen is only partially hydroxylated and still melts below relevant body temperatures.

FibroGen's patented MultiGene Expression System provides the only available method for commercially viable production of human recombinant collagens. FibroGen technology involves the coordinate expression of genes encoding collagen and encoding prolyl 4-hydroxylase, enabling formation of thermally stable, triple helical collagen.