Abstract
Adaptive hydrogels tailor-made from silk-elastin-like proteins (SELPs) possess excellent biocompatibility and biodegradability with properties that are tunable and responsive to multiple simultaneous external stimuli. To unravel the molecular mechanisms of their physical response to external stimuli in tandem with experiments, here we predict and measure the variation in structural properties as a function of temperature through coarse-grained (CG) modeling of individual and crosslinked SE8Y and S4E8Y molecules, which have ratios of 1:8 and 4:8 of silk to elastin blocks respectively. Extensive structural reshuffling in single SE8Y molecules led to the increased compactness of the structure, whereas S4E8Y molecules did not experience any significant changes as they already adopted very compact structures at low temperatures. Crosslinking of SE8Y molecules at high concentrations impeded their structural transition at high temperatures that drastically reduced the degree of deswelling through extensive suppression of the structural shuffling and the trapping of the molecules in high potential energy states due to inter-molecular constraints. This integrative experimental and computational understanding of the thermal response in single molecules of SELPs and their crosslinked networks should lead to further improvements in the properties of SELP hydrogels through predictive designs and their wider applications in biomaterials and tissue engineering.
Highlights
Protein-based biopolymers manufactured through genetic engineering are one such category of stimuli-responsive hydrogels that are designed through bio-inspiration
Crosslinking of SE8Y molecules at high concentrations impeded their structural transition at high temperatures that drastically reduced the degree of deswelling through extensive suppression of the structural shuffling and the trapping of the molecules in high potential energy states due to inter-molecular constraints
Experimental differential scanning calorimetry (DSC) and dynamics light scattering (DLS) data showed a distinct structural transition temperature, Tt, at 294 K for single SE8Y molecules, beyond which the hydrodynamics radius, RH decreased by 70%
Summary
Protein-based biopolymers manufactured through genetic engineering are one such category of stimuli-responsive hydrogels that are designed through bio-inspiration. Hydrogels derived from silk-elastin-like proteins (SELPs) are notable examples. SELPs are derived from tandemly repeating units of elastin-like (GXGVP) and silk-like (GAGAGS) domains where the elastin-like domains are elastic with dynamic features[4] and the silk-like domains convey mechanical stiffness through the formation of b-sheet secondary structures. An example of the dynamic changes observable in SELPs is the reversible transition in structure, from a soluble protein to a contracted aggregate, around a transition temperature, Tt.[5] The stimuli-response of SELPs can be tuned further by changing the ‘‘X’’ residue located in the elastin-like domain to allow for sensitivity towards changes in pH, ionic strength, and phosphorylation to just name a few options.[6] the naming convention of SELPs helps to broadly clarify the multitude of possible combinations. If the S : E ratio is 1 : 8 and tyrosine (Y) is the ‘‘X’’ amino acid in the elastin block, the resulting molecule is termed as SE8Y
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