The Mechanical Properties of Dry, Electrospun Fibrinogen Fibers

Abstract

Due to their low immunogenicity, fibrinogen fibers may be ideal candidates for tissue engineering scaffolds, drug delivery vehicles and other medical devices. However, their mechanical properties are incompletely understood. We have electrospun nanoscopic fibrinogen fibers from a solution of 6% by wt. bovine fibrinogen, 6% minimum essential medium (MEM), and 88% 1,1,1,3,3,3-hexaflouro-2-propanol (HFP). We used a combined atomic force microscopic (AFM)/optical microscopic technique to study the mechanical properties of individual fibers in dry, ambient conditions. Mechanical testing of fibers was done using the AFM to laterally stretch individual fibers suspended over 12 μm wide grooves in a transparent substrate. The optical microscope, located below the sample, was used to monitor the stretching process. Fibers ranging in diameter from 30-200 nm can stretch to 2.34 times their original length before rupturing at a stress of 5.9 GPa. These fibers behave elastically for stretches up to 1.19 times the original length of the fiber. Incremental stress-strain curves were collected to measure the viscoelastic behavior of the individual fibers. The total stretch modulus was 6.0 GPa while the relaxed elastic modulus was 4.1 GPa. While held at constant strain, fibrinogen fibers display a fast and slow relaxation time of 1.5 s and 16 s respectively. Dry electrospun fibrinogen fibers are about 1000 times stiffer than wet electrospun fibrinogen fibers, and nearly as extensible.