|Ph.D Student||Regev Omri|
|Subject||Spinnability Issues, Mechanical Properties and|
Biomedical Applications of Electrospun Albumin
|Department||Department of Nanoscience and Nanotechnology||Supervisor||Professor Eyal Zussman|
|Full Thesis text|
Engineered fibers, whose dimensions, mechanical properties and biocompatibility resemble those of the natural fibers of the extracellular matrix, have vast applicative potential in many tissue engineering approaches. In this research, the possibility of fabricating such fibers from globular serum albumin was explored. In order to fabricate albumin fibers, an electrospinning technique was used, wherein a precursor, typically a semi-dilute polymer solution is transformed into solid nanofibers within milliseconds. Solution spinnability presents a major limitation of this method, as fluids undergo large deformations when forming jets, which must elongate and thin without breaking. Comprehensive micro-structural and mechanical studies, of both the precursor solution and resulting fiber, were conducted to determine ideal spinning conditions, and thus control the morphological and mechanical properties of the as-spun albumin fibers.
X-ray scattering measurements of the precursor solution showed that the albumin solution is only spinnable when the protein chain is fully unfolded, as seen following complete reduction of intra-molecular disulfide bonds. In this state, the protein resembles a flexible polymer chain in a random coil conformation. Rheological studies of albumin solutions using shear, extensional, and interfacial rheometry, demonstrated that the unfolded protein molecules at the solution-air interface arranged to form a viscoelastic layer that stabilized the electrospun jet. The electrospun albumin fibers featured stiffness, strength, and a dissipation factor that resembled those of other bio-fibers, such as elastin. Fibers unexpectedly contracted during creep tests, a phenomenon attributed to breakage of disulfide bonds and the tendency of albumin chains to fold into dry molten globule states.
The biocompatibility and biodegradability of electrospun albumin fibers were evaluated in both cell culture and animal study. Albumin fibers proved non-toxic and supported adhesion and spreading of fibroblasts, muscle cells, and endothelial cells in vitro. Fibers evoked a mild inflammatory response throughout the connective tissue of mice and had a half-life of approximately three weeks in vivo, posing a readily applicable alternative to synthetic biomaterials. In addition, short albumin fibers were integrated within a gelatin-based hydrogel, creating an injectable hybrid, in which the hydrogel constituent supplied bulk and cell mobility characteristics, and the fiber constituent provided mechanical strength. Potential applications of these biomaterials include space-filling scaffolds and cell carriers, for the regeneration of soft, yet load-bearing tissues (e.g., heart muscle and cartilage), where the need to enhance the mechanical properties of currently available materials exists.