| The impressive physical and mechanical properties of natural silk fibers{dollar}sp1{dollar} and the possibility of producing these proteins using biotechnology,{dollar}sp2{dollar} have provided the impetus for recent efforts in both the biosynthesis{dollar}sp{lcub}3,4{rcub}{dollar} and the spinning of these protein based biopolymers.{dollar}sp{lcub}5,6,7{rcub}{dollar} The question still remains: whether fibers spun from solutions with similar chemical makeup can produce fibers with similar structures and therefore with the possibility of improved properties.; Since genetically engineered silk solutions were not readily available, the first objective of this project was to completely dissolve the Bombyx mori cocoon and the Nephila clavipes dragline silk while maintaining the molecular weight integrity of the polymer. The second objective was to develop a system for re-spinning from very small amount of the resulting silk solutions by the process of electrospinning. The third objective was, to produce regenerated silk fibers with diameters that are several orders of magnitude smaller than the original fibers, suitable for direct observation and analysis by transmission electron microscopy and electron diffraction. And finally, to compare these results to structural information obtained from natural (as spun by the organism) fibers to see if the regenerated solutions are able to form the same structure as the original fibers.; Both types of silk fibers were successfully dissolved while maintaining the polymer integrity. Small quantities (25-50 {dollar}mu{dollar}l) of these solutions were used to electrospin fibers with diameters ranging from 8nm-200nm. The fibers were observed by optical, scanning electron, and transmission electron microscopy. These nano fibers showed optical retardation, appeared to have a circular cross-section, and were dimensionally stable at temperatures above 280{dollar}spcirc{dollar}C. Electron diffraction patterns of annealed electrospun fibers of B. mori and N. clavipes showed reflections, demonstrating orientational and semicrystalline order in the material comparable to natural silk.; In addition, electron diffraction was also obtained form extended microtomed single dragline fibers of N. clavipes, and the d-spacings agreed well with thoes obtained from WAXD of dragline fiber bundles. |
