07 kPa), which facilitates the rapid evaporation of THF and subsequent transformation of THF-rich region into voids. The less volume ratio of DMF and its lower volatility (vapor pressure, 0.36 kPa) should be another key factor to the formation of grooved texture [15]. During the formation of grooves, it is the residual DMF that kept the jet wet, which facilitates the void surface jet to be stretched into a grooved texture. When THF/DMF ratio was 1:1, the formation mechanism should be ascribed to the formation of wrinkled

surface on the jet surface at the early stage of electrospinning and subsequent elongation into a line MGCD0103 purchase surface structure (mechanism II). This hypothesis can be supported by Figure  8I,J,K,L and Figure  9A,B,C,D. In this case, THF and DMF can cooperate well with each other,

the rapid evaporation of THF leads to the formation of semi-solidified shell on the initial jet surface, then the wrinkled surface was formed due to buckling of a cylindrical polymer shell under compressive radial stresses, arising from removal of the solvent from the core of the jet [21], while the residual DMF kept the jet wet, which facilitates the wrinkled surface jets to be stretched into a grooved texture. To find more evidences of the formation mechanism of grooved texture, we also observed the LY2109761 interior structure of PS fibers with different surface morphologies (summarized in Table  2). Figure  3 shows the interior structure Branched chain aminotransferase of PS fibers from 20% (w/v) with various THF/DMF ratios (4:1, 1:1, 0:6, v/v). When THF/DMF ratio was 4:1, the obtained fibers exhibited a heart-shaped cross section and solid interior structure, indicating BI 2536 molecular weight that the formation of single grooved texture should be ascribed to mechanism I. When THF/DMF ratio was 1:1, the obtained fibers have a sawtooth cross section and porous interior structure; the corresponding fibers have a grooved surface.

When THF/DMF ratio was 0:6, the obtained fibers have a circular cross section and porous interior structure, and no wrinkles or grooves can be found on the corresponding fibers surface even though the interior structure was porous, suggesting the indispensible role THF plays during the formation of grooved texture. Table 2 Interior structure of PS fibers with different surface morphologies Concentration (%) THF/DMF ratio Interior structure Cross section Morphology 20 4:1 Solid Heart-like Single grooved 20 1:1 Porous Sawtooth Grooved 20 0:6 Porous Circular Smooth 10 1:1 Porous Sawtooth Grooved 30 1:1 Porous Heart-like Single grooved Figure  4 shows the interior structure of PS fibers from various solution concentrations with THF/DMF ratio 1:1 v/v. When the concentration was equal or less than 25% (w/v), the interior structures were similar to those at 20% (w/v). However, when the concentration was 30% (w/v), the obtained fibers have a heart-shaped cross section and porous interior structure.