Gel Spun Tubes The latter protocol describes a gel spinning technique where concentrated silk fibroin is extruded onto a rotating mandrel (Fig 4)(Option B). By applying high shear forces as the concentrated silk solution as it is extruded through a small diameter needle, the silk is induced to gel. Further gelation is completed by the addition of methanol once the tube is formed. Due to the nature of the spinning process, gel spun tubes can add texture to the resulting tubes58. Silk tubes can be tailored to individual applications by changing the mandrel size in order to change the inner diameter of the resulting tube, by creating different winding geometries, or by adding a sacrificial polymer such as PEO to create pores58. These tubes have been evaluated for use as vascular conduits and in bioreactor systems2,35. SEM can be used in order to determine tube structure and whether pores were formed (if applicable)58.