Fibrille

Fibrille, in biology, is a slender, elongated structure formed by the assembly of proteins or other polymers into a fibrillar form. The term is the French equivalent of fibril and is used to describe a variety of fibrous elements that contribute to the structure and function of cells and tissues. Fibrils can vary widely in diameter, from a few nanometers to several hundred nanometers, and in length from hundreds of nanometers to micrometers.

Common examples include collagen fibrils in connective tissue, which assemble from collagen molecules into rope-like structures that provide tensile strength; cellulose fibrils in plant cell walls that reinforce the cell wall matrix; and amyloid fibrils, which arise when certain proteins misfold and aggregate into stable cross-beta sheet structures that can deposit in tissues and are associated with disease.

In cells, fibrillar assemblies include cytoskeletal elements such as actin-based fibrils and intermediate filament networks that help maintain shape, enable movement, and organize organelles. Fibrils also form as part of extracellular matrices, where they contribute to mechanical resilience and signaling.

Formation typically proceeds by nucleation of a seed followed by elongation as monomers or oligomers add on. Factors such as pH, ionic strength, temperature, and genetic mutations can influence assembly and stability, and misfolding or aberrant aggregation is linked to disease in several contexts, notably amyloid fibrils.

Study and imaging of fibrils employ electron microscopy, atomic force microscopy, X-ray diffraction, and specific staining techniques. Overall, fibrille is a broad term denoting slender fibrous assemblies that range from structural components to disease-associated aggregates, depending on their composition and context.