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W. Qiu and X.-Y. Liu
A (effective loading area of a peptide chain in the β-crystallites), etc. were changed
because of the reeling speed, consequently resulting in modifications in the toughness
of silk fibers. In a similar way, Liu et al. [18] also measured the orientation function
and density of crystallites with varying the reeling speed, and quantitatively studied
the correlation with the mechanical performance of silk fibers (Fig. 6.26e and f).
6.5.4.2 Artificial Spinning of Regenerated Silk Fibroin (RSF) Fiber
Based on Templated Nucleation
Although the above techniques can successfully produce mechanically enhanced
natural silk fibers (neat or composite), the mechanical properties of the obtained silk
fibers still greatly depend on the rearing conditions of the silkworms. With the development of techno-polymer fibers based on petrochemicals, increasing efforts have
been devoted to artificially extruding strong and tough silk fibers from regenerated
silk protein solutions. So far, electro-spinning, dry-spinning, and wet-spinning techniques have been developed to successfully fabricate mechanically enhanced RSF
fibers. Among these techniques, dry-spinning and wet-spinning techniques greatly
bio-mimic the natural silk fiber reeling process in vitro, in which natural fibers are
produced under benign and physiological conditions (i.e., at ambient temperature
and relatively low hydraulic pressures using water as the protein solvent). In particular, the wet-spinning technique, which is performed via the ejection of the spinning
dope solution into a specific coagulation bath, is the most common and versatile
approach; hence, we will comprehensively introduce it within the framework of the
SF molecule crystallization theory in this subsection.
In general, there are two different methods for the reinforcement of artificial
RSF fibers. One involves the control of the spinning process to promote homogeneous SF nucleation kinetics in which neat SF solutions are applied as the feedstock.
The other method involves the addition of specific reinforcement agents or foreign
nanoparticles into the dope solution to extrude composite artificial RSF fibers. By
activating the heterogeneous nucleation of the SF molecules, the nucleation barrier
can be suppressed, thereby increasing the probability of crystallization, which consequently results in a higher crystal density and smaller correlation length of the molecular crystal networks within the composite RSF fibers. Thus, mechanically enhanced
RSF fibers can be synthesized. To date, this method has been successfully used to
fabricate several significantly reinforced composite RSF fibers (or mats).
Figure 6.27 displays a typical procedure and the corresponding experimental
instruments for wet spinning artificial RSF fibers. Priot to wet spinning, the SF
solution was mixed with certain ratios of specific foreign templates and was then
stored for 2 h. Next, the composite RSF solutions were transferred to a steel syringe,
and a high-pressure injection pump was utilized to extrude the solution into a coagulation solution (e.g., aqueous 35% (w/v) (NH 4 ) 2 SO 4 solution) at 20 °C. The fibers
were wound from the coagulation bath over four rollers at an increasing rotating
speed. As a result, a larger external shear force was applied to the as-obtained RSF
W. Qiu and X.-Y. Liu
A (effective loading area of a peptide chain in the β-crystallites), etc. were changed
because of the reeling speed, consequently resulting in modifications in the toughness
of silk fibers. In a similar way, Liu et al. [18] also measured the orientation function
and density of crystallites with varying the reeling speed, and quantitatively studied
the correlation with the mechanical performance of silk fibers (Fig. 6.26e and f).
6.5.4.2 Artificial Spinning of Regenerated Silk Fibroin (RSF) Fiber
Based on Templated Nucleation
Although the above techniques can successfully produce mechanically enhanced
natural silk fibers (neat or composite), the mechanical properties of the obtained silk
fibers still greatly depend on the rearing conditions of the silkworms. With the development of techno-polymer fibers based on petrochemicals, increasing efforts have
been devoted to artificially extruding strong and tough silk fibers from regenerated
silk protein solutions. So far, electro-spinning, dry-spinning, and wet-spinning techniques have been developed to successfully fabricate mechanically enhanced RSF
fibers. Among these techniques, dry-spinning and wet-spinning techniques greatly
bio-mimic the natural silk fiber reeling process in vitro, in which natural fibers are
produced under benign and physiological conditions (i.e., at ambient temperature
and relatively low hydraulic pressures using water as the protein solvent). In particular, the wet-spinning technique, which is performed via the ejection of the spinning
dope solution into a specific coagulation bath, is the most common and versatile
approach; hence, we will comprehensively introduce it within the framework of the
SF molecule crystallization theory in this subsection.
In general, there are two different methods for the reinforcement of artificial
RSF fibers. One involves the control of the spinning process to promote homogeneous SF nucleation kinetics in which neat SF solutions are applied as the feedstock.
The other method involves the addition of specific reinforcement agents or foreign
nanoparticles into the dope solution to extrude composite artificial RSF fibers. By
activating the heterogeneous nucleation of the SF molecules, the nucleation barrier
can be suppressed, thereby increasing the probability of crystallization, which consequently results in a higher crystal density and smaller correlation length of the molecular crystal networks within the composite RSF fibers. Thus, mechanically enhanced
RSF fibers can be synthesized. To date, this method has been successfully used to
fabricate several significantly reinforced composite RSF fibers (or mats).
Figure 6.27 displays a typical procedure and the corresponding experimental
instruments for wet spinning artificial RSF fibers. Priot to wet spinning, the SF
solution was mixed with certain ratios of specific foreign templates and was then
stored for 2 h. Next, the composite RSF solutions were transferred to a steel syringe,
and a high-pressure injection pump was utilized to extrude the solution into a coagulation solution (e.g., aqueous 35% (w/v) (NH 4 ) 2 SO 4 solution) at 20 °C. The fibers
were wound from the coagulation bath over four rollers at an increasing rotating
speed. As a result, a larger external shear force was applied to the as-obtained RSF