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(123b) Synthetic Polypeptide Macromers with Tunable Secondary Structure: Components of a Hydrogel Toolkit for Modeling Cell-Matrix Interactions

Authors: 
Oelker, A. M., Massachusetts Institute of Technology
Hammond, P. T., Massachusetts Institute of Technology

Cellular functions including DNA synthesis, migration, and differentiation are co-regulated by both the stiffness of the extracellular matrix (ECM) and the presence of soluble signaling molecules (growth factors, cytokines, hormones, etc.). The purpose of this research is to synthesize and characterize a set of readily functionalizable synthetic polypeptides with tunable size and secondary structure as part of a hydrogel toolkit for modeling cell-matrix interactions. The polypeptides of interest were synthesized via ring-opening polymerization of N-carboxyanhydride derivatives of γ-propargyl L-and/or D-glutamate. These macromers exhibit low polydispersity and become water soluble after a highly-efficient "click" cycloaddition reaction between the alkyne moieties along the polymer backbone and azide-terminated poly(ethylene glycol) (PEG) chains. Circular dichroism and FTIR spectroscopy data demonstrate that stereoregular polyglutamate (containing only L-glutamate monomers) exhibits α-helix secondary structure in solution, whereas polyglutamate composed of both D and L monomers adopts a random coil conformation. This level of control allows us to design hydrogels with stiff rod-like segments or flexible coil segments, thus possibly impacting mechanical and other physicochemical properties of the gel. The grafted polypeptides form hydrogels upon reaction with a hetero-bifunctional cross-linker (PMPI) and thiol-terminated PEG. We are currently investigating the relationships between polypeptide structure and composition, as well as hydrogel formulation (i.e. mass fraction, cross-link density) on the physicochemical properties of the resulting hydrogels. These characterization data will be used to create a library of hydrogel substrates with systematically and independently varied stiffness, permeability, and ligand presentation for in vitro study of the fundamental parameters of cell-matrix interactions.