Fibrils

Fibril is a small, elongated, thread-like particle or aggregate made of proteins or other polymers. In biology, fibrils are fundamental building blocks that assemble into larger structures such as fibers, networks, or tissues. They are typically characterized by high length relative to width, insolubility in mild conditions, and a tendency to align along stress directions.

Common biological fibrils include collagen fibrils, which form the fibrous component of connective tissues and bones; cellulose fibrils, which reinforce plant cell walls; amyloid fibrils, formed by misfolded proteins and associated with neurodegenerative diseases; and cytoskeletal fibrils such as actin filaments and other protein filaments that contribute to cell shape, motility, and intracellular transport. In skeletal and cardiac muscle, myofibrils are intracellular bundles of contractile units; while not always called fibrils, they share the same fibrous, organized protein composition.

Fibrils arise by self-assembly or templated polymerization of monomers or protofibrils. Cross-linking and interactions with matrix components increase stability and mechanical strength. The arrangement and diameter of fibrils influence tissue properties such as stiffness and toughness.

Biomaterials research investigates fibrils for their strength, resilience, and failure modes. Abnormal fibrillization, as in amyloid diseases, can be pathogenic. Fibrils also occur in foods and nanomaterials science as natural fibrous proteins and cellulose-based materials.