The rheological characteristics of pre-spun native silk
protein,
which is stored as a viscous pulp inside the silk gland, are the key
factors that determine the mechanical performance of the endpoint
material: the spun silk fibers. In silkworms and arthropods, microcompartmentalization
was shown to play an important regulatory role in storing and stabilizing
the aggregation-prone silk and in initiating the fibrillar self-assembly
process. However, our current understanding of the mechanism of stabilization
of the highly unstable protein pulp in its soluble state inside the
microcompartments and of the conditions required for initiating the
structural transition in protein inside the microcompartments remains
limited. Here, we exploited the power of droplet microfluidics to
mimic the silk protein’s microcompartmentalization event; we
introduced changes in the chemical environment and analyzed the storage-to-spinning
transition as well as the accompanying structural changes in silk
fibroin protein, from its native fold into an aggregative β-sheet-rich
structure. Through a combination of experimental and computational
simulations, we established the conditions under which the structural
transition in microcompartmentalized silk protein is initiated, which,
in turn, is reflected in changes in the silk-rich fluid behavior.
Overall, our study sheds light on the role of the independent parameters
of a dynamically changing chemical environment, changes in fluid viscosity,
and the shear forces that act to balance silk protein self-assembly,
and thus, facilitate new exploratory avenues in the field of biomaterials.