Study

What molecular and architectural properties cause strain stiffening and how can it be controlled?

A new type of material recently discovered by our group has been shown to have the unique properties needed to develop a whole new class of cell culture systems. It is based on a fully synthetic, biomimetic, physically cross-linked soft hydrogel derived from helical oligo(ethylene)glycolpolyisocyano-peptides (PIC, Figure 1 Left).

Figure 1: Polymerisation of peptidic isocyanide monomer result in stiff helical betasheet polymers. By varying the functionality, R, R’ Y and X as well as m, the hierarchical assembly can be controlled.

The soft thermo-responsive PIC gels are formed at extremely low polymer concentrations (99.95% water) and possess pore sizes of nanometer dimension (100–250 nm). These unique hydrogels have a fibrous structure that exactly mimics the strain-stiffening behavior of biogels such as actin, collagen and intermediate filaments. In contrast to all other synthetic polymers, the PIC gels stiffen in the biological relevant region, mimicking very closely the mechanical properties of fibrin and collagen; a truly biomimetic synthetic extracellular matrix (sECM).

For this project, in a synthetic/rheological approach, material changes as a function of chemical modification of the PIC polymers will be studied. By modifying the peptide (dipeptides, tripeptides, the chirality, the bulkiness, the tail linkage (ester or amide varying Y, Figure 1), the stiffness and helical pitch of the polymer can be altered and the effect upon the bundling studied. In addition the solubility and ‘stickiness’ will be modified by altering the terminal X group with thiols, azide and acids and butyl, phenyl functions and fluorinated alkyls. Formation is thought to be dependent not only on the molecular properties but also on the nature of the medium and salt effects. The effect of salt and molecular crowding will also be investigated. Ultimately, we would like to know what the structural parameters are that control the onset and gradient of the strain stiffening

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