Abstract
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.
Highlights
Heterogeneous hydrogels with desired matrix complexity are studied for a behavior.[1,2,3,4,5] A variety of evidence suggests that heterogeneity in hydrogels can provariety of biomimetic materials
The resilin-like polypeptide (RLP) were expressed following procedures extensively employed in the Kiick laboratories[56,57,58,59] and were functionalized with acrylamide groups to facilitate the desired on-demand photo-crosslinking of microscale domains
There are 15 lysine residues present in each RLP chain, these are distributed in short (GGKGGKGGKGG) “domains” at regular intervals in the RLP sequence; the close proximity of the lysines in these short domains possibly results in steric hindrance that prohibits complete coupling to all lysines
Summary
The RLP employed in these studies is a 23 kDa polypeptide containing 12 repeats of the putative consensus sequence (GGRPSDSYGAPGGGN) derived from Drosophila melanogaster and 5 repeats of lysine-rich bundles (GGKGGKGGKGG) that can be used for crosslinking or RLP functionalization.[56]. There was no significant change in the gelation time or final plateau storage modulus (Figure 3C, G′ values of 16.5 ± 4.0, 17.1 ± 3.2, and 17.1 ± 5.4 kPa at 0, 5, and 10 min) as a function of the point at which the UV irradiation was applied, suggesting that the extent of phase separation does not alter the bulk mechanical properties of these materials the microstructures are trapped out of equilibrium. In both solutions, the diameters (and distribution of diameters) of the RLP domains increased with time. The difference between the storage moduli in the RLP-rich and PEG-rich phases suggests that the micromechanical properties will be heterogeneous in the microstructured hydrogels, which could be used to selectively and locally promote cell proliferation and/or differentiation within the domains or matrix.[11,13,79]
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