pH-Triggered Silk Fibroin/Alginate Structures Fabricated in Aqueous Two-Phase System

An aqueous two-phase system (ATPS) is a water-in-water biphasic system, which is generally formed by two incompatible polymers. Recently, considerable effort has been dedicated to search for new ATPS polymer pairs to further expand ATPS's applications. In this paper, a new ATPS system based on silk fibroin (SF) and alginate is introduced. A phase diagram was established to show the critical concentrations for the formation of an SF/alginate ATPS. The present system is sensitive to pH stimulus and transformed from an ATPS into a single-phasic system as pH increases above ∼9.5. Circular dichroism, fluorescence emission spectra, hydrodynamic diameter, and ζ-potential data together indicate that the SF chains undergo a dramatic extension as pH is increased, which is the reason underlying the pH-triggered phase transition. As feasible applications of this biphasic system, compartmentalized multiplex immunoassay, controlled encapsulation and release, and hierarchical fiber fabrication were demonstrated using the SF/alginate ATPS.