# Metal Ion-Specific Modulation of Network Connectivity and Defects in Poly(ethylene glycol)–Peptide Conjugate Assemblies and Hydrogels

## TL;DR

This study shows how metal ions can control the structure and properties of self-assembling peptide-polymer materials, making them more stable and responsive.

## Contribution

The novel contribution is demonstrating how specific metal ions modulate the self-assembly and mechanical properties of peptide–polymer conjugates.

## Key findings

- Metal ions like Co2+, Ni2+, Cu2+, and Zn2+ significantly enhance network stability and viscoelastic properties of the hydrogels.
- Coordination geometry of metal ions influences the global assembly and nanofiber morphology of the conjugates.
- Metal coordination improves network recovery and expands the linear viscoelastic region of the hydrogels.

## Abstract

Self-assembling peptide–polymer conjugates offer
a versatile
platform to engineer nanostructures with tunable morphology and functions.
Here we show that alternating phenylalanine–histidine pentapeptide
units, conjugated to a short linear poly­(ethylene glycol), show pH-induced
assembly into β-sheet nanofibers that act as multifunctional
cross-links in the resulting hydrogels. Circular dichroism spectra
demonstrate that the self-assembly is enthalpy driven at low concentrations,
while rheological results suggest that the network connectivity at
high concentrations is compromised by the entropic penalty of chain
stretching. Metal ions (Co2+, Ni2+, Cu2+, Zn2+) enhance secondary structures, with coordination
geometry-dependent change of the global assembly. Common impacts of
metal coordination include orders-of-magnitude higher network stability,
an expanded linear viscoelastic region, and improved network recovery,
all indicative of the fast association of metal complexes. Collectively,
these results highlight the role of metal ions in tuning supramolecular
packing, nanofiber morphology, and consequent hydrogel mechanics in
peptide–polymer conjugate assemblies and their role in modulating
structure–dynamics–property relationships for applications
as stimuli-responsive biomaterials.