Christine R. Carlisle

The mechanical properties of single fibrin fibers

See also Weisel JW. Biomechanics in hemostasis and thrombosis. This issue, pp 1027–9. Carlisle CR, Sparks EA, Der Loughian C, Guthold M. Strength and failure of fibrin fiber branchpoints. This issue, pp 1135–8.

The mechanical properties of individual, electrospun fibrinogen fibers

We used a combined atomic force microscopic (AFM)/fluorescence microscopic technique to study the mechanical properties of individual, electrospun fibrinogen fibers in aqueous buffer. Fibers (average diameter 208 nm) were suspended over 12 microm-wide grooves in a striated, transparent substrate. The AFM, situated above the sample, was used to laterally stretch the fibers and to measure the applied force. The fluorescence microscope, situated below the sample, was used to visualize the stretching process. The fibers could be stretched to 2.3 times their original length before breaking; the breaking stress was 22 x 10 (6)Pa. We collected incremental stress-strain curves to determine the viscoelastic behavior of these fibers. The total stretch modulus was 17.5 x 10 (6)Pa and the relaxed elastic modulus was 7.2 x 10 (6)Pa. When held at constant strain, electrospun fibrinogen fibers showed a fast and slow stress relaxation time of 3 and 55 s. Our fibers were spun from the typically used 90% 1,1,1,3,3,3-hexafluoro-2-propanol (90-HFP) electrospinning solution and re-suspended in aqueous buffer. Circular dichroism spectra indicate that alpha-helical content of fibrinogen is approximately 70% higher in 90-HFP than in aqueous solution. These data are needed to understand the mechanical behavior of electrospun fibrinogen structures. Our technique is also applicable to study other nanoscopic fibers.

The mechanical stress–strain properties of single electrospun collagen type I nanofibers

Knowledge of the mechanical properties of electrospun fibers is important for their successful application in tissue engineering, material composites, filtration and drug delivery. In particular, electrospun collagen has great potential for biomedical applications due to its biocompatibility and promotion of cell growth and adhesion. Using a combined atomic force microscopy (AFM)/optical microscopy technique, the single fiber mechanical properties of dry, electrospun collagen type I were determined. The fibers were electrospun from a 80 mg ml(-1) collagen solution in 1,1,1,3,3,3-hexafluro-2-propanol and collected on a striated surface suitable for lateral force manipulation by AFM. The small strain modulus, calculated from three-point bending analysis, was 2.82 GPa. The modulus showed significant softening as the strain increased. The average extensibility of the fibers was 33% of their initial length, and the average maximum stress (rupture stress) was 25 MPa. The fibers displayed significant energy loss and permanent deformations above 2% strain.

Strength and failure of fibrin fiber branchpoints.

See also Weisel JW. Biomechanics in hemostasis and thrombosis. This issue, pp 1027–9; Liu W, Carlisle CR, Sparks EA, Guthold M. The mechanical properties of single fibrin fibers. This issue, pp 1030–6.

Denaturing of single electrospun fibrinogen fibers studied by deep ultraviolet fluorescence microscopy

Deep ultraviolet (DUV) microscopy is a fluorescence microscopy technique to image unlabeled proteins via the native fluorescence of some of their amino acids. We constructed a DUV fluorescence microscope, capable of 280 nm wavelength excitation by modifying an inverted optical microscope. Moreover, we integrated a nanomanipulator‐controlled micropipette into this instrument for precise delivery of picoliter amounts of fluid to selected regions of the sample. In proof‐of‐principle experiments, we used this instrument to study, in situ, the effect of a denaturing agent on the autofluorescence intensity of single, unlabeled, electrospun fibrinogen nanofibers. Autofluorescence emission from the nanofibers was excited at 280 nm and detected at ∼350 nm. A denaturant solution was discretely applied to small, select sections of the nanofibers and a clear local reduction in autofluorescence intensity was observed. This reduction is attributed to the dissolution of the fibers and the unfolding of proteins in the fibers. Microsc. Res. Tech., 2010.

Single fibrin fiber experiments suggest longitudinal rather than transverse cross-linking: reply to a rebuttal

versely between strands: no. J Thromb Haemost 2004; 2: 394–9. 4 Roska FJ, Ferry JD. Studies of fibrin film. I. Stress relaxation and birefringence. Biopolymers 1982; 21: 1811–32. 5 Roska FJ, Ferry JD, Lin JS, Anderegg JW. Studies of fibrin film. II. Small-angle x-ray scattering. Biopolymers 1982; 21: 1833–45. 6 Mosesson MW. John Ferry and the mechanical properties of crosslinked fibrin. Biophys Chem 2004; 112: 215–18.

Nanomechanics of Electrospun Fibers for Tissue Engineering

Understanding the material properties of the nanofibers comprising electrospun scaffolds for tissue engineering will elucidate the mechanotransduction of cells seeded onto and attached those scaffolds. The overall mechanical properties of any structure built from fibers depend on 1) the architecture, 2) the properties of the constituent single fibers, and 3) the junctions between fibers. All three must be known to design a structure with predictable mechanical properties. We hypothesize that a basic understanding of the nanolevel mechanical properties of individual electrospun fibers will enable accurate prediction of the overall cellular response and bulk mechanical behavior of electrospun tissue scaffolds.Copyright