Microstructured Elastomer-PEG Hydrogels via Kinetic Capture of Aqueous Liquid–Liquid Phase Separation

Journal article, 2018

Heterogeneous hydrogels with desired matrix complexity are studied for a
variety of biomimetic materials. Despite the range of such microstructured
materials described, few methods permit independent control over microstructure
and microscale mechanics by precisely controlled, single-step
processing methods. Here, a phototriggered crosslinking methodology that
traps microstructures in liquid–liquid phase-separated solutions of a highly
elastomeric resilin-like polypeptide (RLP) and poly(ethylene glycol) (PEG) is
reported. RLP-rich domains of various diameters can be trapped in a PEG
continuous phase, with the kinetics of domain maturation dependent on the
degree of acrylation. The chemical composition of both hydrogel phases over
time is assessed via in situ hyperspectral coherent Raman microscopy, with
equilibrium concentrations consistent with the compositions derived from
NMR-measured coexistence curves. Atomic force microscopy reveals that
the local mechanical properties of the two phases evolve over time, even as
the bulk modulus of the material remains constant, showing that the strategy
permits control of mechanical properties on micrometer length scales, of
relevance in generating mechanically robust materials for a range of applications.
As one example, the successful encapsulation, localization, and survival
of primary cells are demonstrated and suggest the potential application of
phase-separated RLP-PEG hydrogels in regenerative medicine applications.