Protofibrils within fibrin fibres are packed together in a regular array.

The inner structure of fibrin fibres grown from fibrinogen solution activated by human alpha-thrombin was investigated by means of an Energy Dispersive X-ray Diffraction technique. The experiments show evidence for the well-characterized 22.5 nm repeat distance, which indicates the high order of protofibril arrangement in the longitudinal direction of fibres. The diffraction pattern also manifested a further pronounced peak at 18.1 nm (and its second order reflection at 18.1/ radical 2) demonstrating the existence in fibrin of a high degree of lateral order. The reported results directly confirm, on unperturbed wet samples, that protofibrils closely associate giving rise to a crystalline axial and equatorial packing according to the conclusions of the multibundle model.