Bone morphogenetic protein-2 (BMP-2) is a potent osteoinductive cytokine that plays a critical role during bone regeneration and repair. In the extracellular environment, sulfated polysaccharides anchored covalently to glycoproteins such as syndecan and also non-covalently to fibronectin fibers have been shown to bind BMP-2 through a heparin-binding domain and regulate its bioactivity. We report here on a synthetic biomimetic strategy that emulates biological BMP-2 signaling through the use of peptide amphiphile nanofibers designed to bind heparin. The supramolecular nanofibers, which integrate the biological role of syndecan and fibronectin, were allowed to form gel networks within the pores of an absorbable collagen scaffold by simply infiltrating dilute solutions of the peptide amphiphile, heparan sulfate, and BMP-2. The hybrid biomaterial enhanced significantly bone regeneration in a rat critical-size femoral defect model using BMP-2 amounts that are one order of magnitude lower than required for healing in this animal model. Using micro-computed tomography, we also showed that the hybrid scaffold was more effective at bridging within the gap relative to a conventional scaffold of the type used clinically based on collagen and BMP-2. Histological evaluation also revealed the presence of more mature bone in the new ossified tissue when the low dose of BMP-2 was delivered using the biomimetic supramolecular system. These results demonstrate how molecularly designed materials that mimic features of the extracellular environment can amplify the regenerative capacity of growth factors.

Regeneration of neural tissues will require regrowth of axons lost due to trauma or degeneration to reestablish neuronal connectivity. One approach toward this goal is to provide directional cues to neurons that can promote and guide neurite growth. Our laboratory previously reported the formation of aligned monodomain gels of peptide amphiphile (PA) nanofibers over macroscopic length scales. In this work, we modified these aligned scaffolds specifically to support neural cell growth and function. This was achieved by displaying extracellular matrix (ECM) derived bioactive peptide epitopes on the surface of aligned nanofibers of the monodomain gel. Presentation of IKVAV or RGDS epitopes enhanced the growth of neurites from neurons encapsulated in the scaffold, while the alignment guided these neurites along the direction of the nanofibers. After two weeks of culture in the scaffold, neurons displayed spontaneous electrical activity and established synaptic connections. Scaffolds encapsulating neural progenitor cells were formed in situ within the spinal cord and resulted in the growth of oriented processes in vivo. Moreover, dorsal root ganglion (DRG) cells demonstrated extensive migration inside the scaffold, with the direction of their movement guided by fiber orientation. The bioactive and macroscopically aligned scaffold investigated here and similar variants can potentially be tailored for use in neural tissue regeneration.

Many naturally occurring peptides containing cationic and hydrophobic domains have evolved to interact with mammalian cell membranes and have been incorporated into materials for non-viral gene delivery, cancer therapy, or treatment of microbial infections. Their electrostatic attraction to the negatively charged cell surface and hydrophobic interactions with the membrane lipids enable intracellular delivery or cell lysis. While the effects of hydrophobicity and cationic charge of soluble molecules on the cell membrane are well known, the interactions between materials with these molecular features and cells remain poorly understood. Here we report that varying the cohesive forces within nanofibres of supramolecular materials with nearly identical cationic and hydrophobic structure instruct cell death or cell survival. Weak intermolecular bonds promote cell death through disruption of lipid membranes, while materials reinforced by hydrogen bonds support cell viability. These findings provide new strategies to design biomaterials that interact with the cell membrane.

Self-assembling peptide materials have been used extensively to mimic natural extracellular matrices (ECMs) by presenting bioactive epitopes on a synthetic matrix. Although this approach can facilitate a desired response from cells grown in the matrix, it lacks the capacity for spatial or temporal regulation of the presented signals. We describe here a photo-responsive, synthetic ECM using a supramolecular platform comprised of peptide amphiphiles (PAs) that self-assemble into cylindrical nanofibers. A photocleavable nitrobenzyl ester group was included in the peptide backbone using a novel Fmoc-amino acid that is compatible with microwave-assisted solid phase peptide synthesis. The placement of the photolabile group on the peptide backbone enabled efficient removal of the ECM-derived cell adhesion epitope RGDS from PA molecules upon exposure to light (half-life of photolysis ~ 1.9 min) without affecting the nanofiber assembly. Fibroblasts cultured on RGDS-presenting PA nanofiber substrates demonstrated increased cell spreading and more mature focal adhesions compared with unfunctionalized and control (RGES-presenting) surfaces, as determined by immunostaining and cell morphological analysis. Furthermore, we observed an arrest in fibroblast spreading on substrates containing a cleavable RGDS epitope when the culture was exposed to light; in contrast, this dynamic shift in cell response was absent when the RGDS epitope was attached to the PA molecule by a light-insensitive control linker. Light-responsive bioactive materials can contribute to the development of synthetic systems that more closely mimic the dynamic nature of native ECM.

We report the construction of DNA nanotubes covalently functionalized with the cell adhesion peptide RGDS as a bioactive substrate for neural stem cell differentiation. Alteration of the Watson–Crick base pairing program that builds the nanostructures allowed us to probe independently the effect of nanotube architecture and peptide bioactivity on stem cell differentiation. We found that both factors instruct synergistically the preferential differentiation of the cells into neurons rather than astrocytes.