Supramolecular Platform Stabilizing Growth Factors

High concentrations of supplemented growth factors can cause oversaturation and adverse effects in <i>in vitro</i> and <i>in vivo</i> studies, though these supraphysiological concentrations are often required due to the low stability of growth factors. Here we demonstrate the stabilization of TGF-β1 and BMP4 using supramolecular polymers. Inspired by heparan sulfate, sulfonated peptides were presented on a supramolecular polymer to allow for noncovalent binding to growth factors in solution. After mixing with excipient molecules, both TGF-β1 and BMP4 were shown to have a prolonged half-life compared to the growth factors free in solution. Moreover, high cellular response was measured by a luciferase assay, indicating that TGF-β1 remained highly active upon binding to the supramolecular assembly. The results demonstrate that significant lower concentrations of growth factors can be used when supramolecular polymers bearing growth factor binding moieties are implemented. This approach can also be exploited in hydrogel systems to control growth factor release

Tough Stimuli-Responsive Supramolecular Hydrogels with Hydrogen-Bonding Network Junctions

Hydrogels were prepared with physical cross-links comprising 2-ureido-4­[1H]-pyrimidinone (UPy) hydrogen-bonding units within the backbone of segmented amphiphilic macromolecules having hydrophilic poly­(ethylene glycol) (PEG). The bulk materials adopt nanoscopic physical cross-links composed of UPy–UPy dimers embedded in segregated hydrophobic domains dispersed within the PEG matrix as comfirmed by cryo-electron microscopy. The amphiphilic network was swollen with high weight fractions of water (<i>w</i>_H₂O ≈ 0.8) owing to the high PEG weight fraction within the pristine polymers (<i>w</i>_PEG ≈ 0.9). Two different PEG chain lengths were investigated and illustrate the corresponding consequences of cross-link density on mechanical properties. The resulting hydrogels exhibited high strength and resilience upon deformation, consistent with a microphase separated network, in which the UPy–UPy interactions were adequately shielded within hydrophobic nanoscale pockets that maintain the network despite extensive water content. The cumulative result is a series of tough hydrogels with tunable mechanical properties and tractable synthetic preparation and processing. Furthermore, the melting transition of PEG in the dry polymer was shown to be an effective stimulus for shape memory behavior

Self-Assembly of Chiral Supramolecular Ureido-Pyrimidinone-Based Poly(ethylene glycol) Polymers via Multiple Pathways

The recently developed supramolecular hydrogelator system based on poly­(ethylene glycols) end-functionalized with ureido-pyrimidinone (UPy) units has been shown to be eminently suitable as a drug delivery vehicle in soft tissues such as the heart and kidney. To understand the assembly behavior of this system in more detail, we here report on the introduction of a stereogenic center. This allowed for the investigation of the self-assembly mechanism of this system by circular dichroism, which showed the presence of helical fibers. Additionally, fluorescence spectroscopy and scattering techniques in combination with cryoTEM showed elongated rod-like structures as the major species, next to spherical micelles. Interestingly, different self-assembly pathways occurred when using two aggregate preparation methods based on different cooling rates. Both positive and negative bisignate Cotton effects were observed only by changing the method of preparation, indicating that the UPy-polymer constructs self-assemble via multiple pathways. A similar phenomenon is observed in biology, which illustrates the versatility of the system. This versatility is key to the optimization of material properties for biomedical applications

Post-Assembly Functionalization of Supramolecular Nanostructures with Bioactive Peptides and Fluorescent Proteins by Native Chemical Ligation

Post-assembly functionalization of supramolecular nanostructures has the potential to expand the range of their applications. We report here the use of the chemoselective native chemical ligation (NCL) reaction to functionalize self-assembled peptide amphiphile (PA) nanofibers. This strategy can be used to incorporate specific bioactivity on the nanofibers, and as a model, we demonstrate functionalization with the RGDS peptide following self-assembly. Incorporation of bioactivity is verified by the observation of characteristic changes in fibroblast morphology following NCL-mediated attachment of the signal to PA nanofibers. The NCL reaction does not alter the PA nanofiber morphology, and biotinylated RGDS peptide was found to be accessible on the nanofiber surface after ligation for binding with streptavidin-conjugated gold nanoparticles. In order to show that this strategy is not limited to short peptides, we utilized NCL to conjugate yellow fluorescent protein and/or cyan fluorescent protein to self-assembled PA nanofibers. Förster resonance energy transfer and fluorescence anisotropy measurements are consistent with the immobilization of the protein on the PA nanofibers. The change in electrophoretic mobility of the protein upon conjugation with PA molecules confirmed the formation of a covalent linkage. NCL-mediated attachment of bioactive peptides and proteins to self-assembled PA nanofibers allows the independent control of self-assembly and bioactivity while retaining the biodegradable peptide structure of the PA molecule and thus can be useful in tailoring design of biomaterials