TITLE: Ph.D. Thesis Defense: "The Mechanical Properties of Individual Electrospun Fibers & Fibrin Fibers"

SPEAKER: Christine R. Carlisle

TIME: Tuesday, May 4 at 9:00 AM

PLACE: George P. Williams, Jr. Lecture Hall, (Olin 101)

Electrospinning is used to produce collagen and fibrinogen fibers whose mechanical properties are important because of their potential for tissue engineering, due to their biocompatibility. We studied the mechanical properties of individual electrospun collagen and fibrinogen fibers using a combined atomic force microscopy and optical microscopy technique. Using the same technique we also studied the mechanical properties of individual fibrin fibers, a major component of blood clots. The mechanical properties of blood clots have been shown to be related to diseases and disorders yet the mechanisms responsible for their mechanical properties are relatively unknown.

Electrospun type I collagen and electrospun fibrinogen fibers both showed viscoelastic properties. The extensibility of electrospun fibrinogen in buffer is 130% and its average modulus is 10 MPa. Electrospun collagen in ambient conditions has an extensibility of 33% and a bending modulus of 7.5 GPa.

Native crosslinked fibrin fibers have similar properties to electrospun fibrinogen fibers. Crosslinked fibers have an extensibility of 130% and a modulus of 14 MPa. Uncrosslinked fibers are more extensible (226% extensibility) and softer with a modulus of 4 MPa. Fibrin fibers with only alpha crosslinks are as extensible as uncrosslinked fibrin fibers but have a modulus in between crosslinked and uncrosslinked fibrin, of 10 MPa. Alpha crosslinked fibrin fibers have a larger elastic limit, 95% strain, than both uncrosslinked and crosslinked. The study of fibrin branch points showed that crosslinked fibers rupture more often than the joints. Lastly, the technique can be extended to test the properties on individual fibrin fibers from plasma samples. Fibers from patients with type 2 diabetes show no difference in modulus or extensibility when compared with control patient samples.