Spontaneous Phase Separation Enables Rapid, Polymerization-Free Fabrication of Gels

Hydrogels are cross-linked polymeric networks with wide applications in drug delivery, tissue engineering, biosensing, and environmental remediation. These hydrogels additionally host living cells, small molecules, and biological propagules, which further expand the applications of these materials. However, most, if not all, fabrication methods require covalent modifications. In this work, by deliberately selecting polymers with a known propensity to phase separate and formulating compositions far from the binodal boundary, we demonstrate the propensity of the system to transition directly into viscoelastic liquids or gels. This behavior is demonstrated using a model system of poly(ethylene glycol) (PEG) and dextran (DEX). We carried out rheological studies to provide insights into the viscoelastic behavior of these gels. We systematically characterized the gels through colorimetric assays, FTIR, MALDI-TOF, and thermogravimetric analysis (TGA) to discern the molecular compositions and solvent content of the gels. These experimental findings are supplemented with coarse-grained (CG) simulation insights to investigate the mechanistic origins of phase separation propensity with varying molecular weights of DEX. We utilized coexisting densities in the two phases using CG simulations to predict the role of DEX molecular weight in the partitioning of PEG and DEX in the two phases. Finally, we exploit the fabricated gel's ability to encapsulate live cells, antibiotics, and plant seeds. We anticipate that this ATPS-based fabrication technique will provide a scalable, cross-linker-free route to multifunctional gels, enabling advanced applications in drug delivery and responsive materials.