Directing polymer self-assembly through noncovalent interactions is a powerful way to control the structure and function of nanoengineered materials. Dynamic hydrogen bonds are particularly useful for materials with structures that change over time or in response to specific stimuli. In the present work, we use the supramolecular association of urea moieties to manipulate the morphology, thermal response, and mechanical properties of soft polymeric hydrogels. Urea-terminated poly(isopropyl glycidyl ether)- b -poly(ethylene oxide)- b -poly(isopropyl glycidyl ether) ABA triblock copolymers were synthesized using controlled, anionic ring-opening polymerization and subsequent chain-end functionalization. Triblock copolymers with hydroxy end-groups were incapable of hydrogelation, while polymers terminated with meta -bis-urea motifs formed robust gels at room temperature. Rheometric analysis of the bulk gels, variable-temperature infrared spectroscopy (VT-IR), differential scanning calorimetry (DSC), and small-angle X-ray scattering (SAXS) confirmed the formation of structured hydrogels via association of the meta -bis-urea end-groups. Monourea end-groups did not result in the same regular structure as the meta -bis-urea. In future, the reported hydrogels could be useful for elastomeric, shape-morphing 3D-printed constructs, or as biomimetic scaffolds with precisely tailored porosity and mechanical properties.
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Urea-Modified Self-Assembling Peptide Amphiphiles That Form Well-Defined Nanostructures and Hydrogels for Biomedical Applications
Hydrogen bonding plays a critical role in the self-assembly of peptide amphiphiles (PAs). Herein, we studied the effect of replacing the amide linkage between the peptide and lipid portions of the PA with a urea group, which possesses an additional hydrogen bond donor. We prepared three PAs with the peptide sequence Phe-Phe-Glu-Glu (FFEE): two are amide-linked with hydrophobic tails of different lengths and the other possesses an alkylated urea group. The differences in the self-assembled structures formed by these PAs were assessed using diverse microscopies, nuclear magnetic resonance (NMR), and dichroism techniques. We found that the urea group influences the morphology and internal arrangement of the assemblies. Molecular dynamics simulations suggest that there are about 50% more hydrogen bonds in nanostructures assembled from the urea-PA than those assembled from the other PAs. Furthermore, in silico studies suggest the presence of urea−π stacking interactions with the phenyl group of Phe, which results in distinct peptide conformations in comparison to the amide-linked PAs. We then studied the effect of the urea modification on the mechanical properties of PA hydrogels. We found that the hydrogel made of the urea-PA exhibits increased stability and self-healing ability. In addition, it allows cell adhesion, spreading, and growth as a matrix. This study reveals that the inclusion of urea bonds might be useful in controlling the morphology, mechanical, and biological properties of self-assembled nanostructures and hydrogels formed by the PAs.
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- NSF-PAR ID:
- 10341909
- Date Published:
- Journal Name:
- ACS Applied Bio Materials
- ISSN:
- 2576-6422
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1021/acsabm.2c00158
