The formation of collagen fibrils involves multiple steps starting with gene transcription of collagen. The synthesis of procollagen occurs in the endoplasmic reticulum, followed by post-translational modifications. Procollagen is then secreted into the extracellular space, where enzymes cleave its propeptide extensions, allowing the trimmed molecules to spontaneously assemble into collagen fibrils. This process is known as fibrillogenesis.