WFU Physics Colloquium

TITLE: Single Fiber Nanomechanical Properties of Electrospun Fibers and Modified Fibrin Fibers using Atomic Force Microscopy

SPEAKER: Stephen Baker

TIME: Monday June 8, 2015 at 2:00 PM

PLACE: Room 101 Olin Physical Laboratory

The extracellular matrix is comprised mostly of collagen, the most abundant protein in the body. This protein helps to provide the structural support for various tissues such as skin, bones, muscles, tendons, and even heart valves and blood vessels. Fibrinogen is the most abundant protein found in blood plasma. After exposure to thrombin, it is converted to fibrin, and provides the structural support of a blood clot. In addition to these natural polymers, synthetic polymers can be synthesized outside the body by a process known as electrospinning. This process allows for nanofibers and as a result the macrostructure scaffold to be tailored to specific applications. The mechanical properties of these nanofibers play an important role in determined the overall success for various applications in tissue engineering. We have studied the nanomechanical properties of two natural, collagen and fibrinogen, and one synthetic, poly-ε-caprolactone, group of electrospun fibers that are currently being used for tissue engineering applications. We used a combined atomic force microscopy/ fluorescence microscopy technique to determine the nanomechanical properties of single electrospun fibers and fibrin fibers.

Electrospun fibrinogen fibers, hybrid collagen/fibrinogen fibers, and poly-&epsilon-caprolactone fibers all showed viscoelastic properties. Dry, electrospun fibrinogen fibers proved to be only slightly less extensible than hydrated, electrospun fibrinogen fibers. Hybrid collagen/fibrinogen fibers were as extensible as fibrinogen for dry samples and almost twice as extensible for hydrated samples. Poly-ε- caprolactone fibers had similar extensibility as other dry, single fibers. Total and relaxed moduli were in the 101 MPa range for poly-&epsilon-caprolactone fibers, 10¹-10² MPa range for collagen/fibrinogen fibers, and 10³ MPa range for dry, fibrinogen fibers. All fiber types showed a fast and slow relaxation time as well as strain softening.

Blocking the b-pocket of native fibrinogen fibers showed a decrease in extensibility in a concentration dependent manner. PEGylation of these b-pocket blockers showed an increase in fiber extensibility at higher concentrations suggesting a competition between the PEGylated leg and blocking the b-pocket with respect to clot properties. We also determined that fibrin fibers from older males with cardiovascular disease were more extensible and more elastic than healthy old or healthy young patients.