A number of strategies exist to design molecular materials based on self-assembled peptides and their derivatives. [1] These include soft materials based on a variety of structural motifs including coiled-coils, [2,3] b-sheets, [4,5] b-hairpins, [6] and peptide amphiphiles. [7][8][9] In these systems, the peptide chains usually contain at least ten amino acids. It has been known for some time that using aromatic components in conjunction with peptides allows the use of much smaller peptides by taking advantage of p-stacking interactions. [10][11][12][13][14][15] One system that has been illustrated is that of N-fluorenylmethoxycarbonyl diphenylalanine (Fmoc-FF) which forms a hydrogel under physiological conditions. This example and other closely related aromatic short peptide derivatives are known to form fibrous hydrogels that have found applications in biological sensing [16] and cell culture. [13,17] Understanding of the supramolecular structures formed by these molecules will aid the rational design of new architectures tailored to the needs of specific biological and non-biological applications. However, to date a complete structure has not been proposed for any member of this class of self-assembly systems. Here we apply a number of spectroscopic techniques to Fmoc-FF and construct a model based on the data obtained comprising a new nanocylindrical molecular architecture based on p-p interlocked b-sheets. Transmission electron microscopy (TEM) and wide angle X-ray scattering (WAXS) was used to confirm the proposed model. Hydrogels of Fmoc-FF were prepared as described previously utilizing a sequential change in pH.[13] As shown in Figure 1a self-supporting gels were formed. The viscoelastic properties of the gels were assessed using oscillatory rheology. Figure 1b shows the mechanical spectrum obtained at room temperature for a Fmoc-FF (20 mmol L -1 ) gel. The storage modulus (G') is found to be approximately an order of magnitude larger than the loss modulus (G''), indicative of an elastic rather than viscous material. Both G' and G'' were found to be essentially independent of frequency over four decades (Fig. 1b). Such rheological behavior is characteristic of solid like gel materials. Light microscopy ( Fig. 1c) revealed a network of fine fibers with microscopic widths. Cryo Scanning Electron Microscopy (cryoSEM) revealed a dense network of flat ribbons with dimensions in the order of tens of nanometers (Fig. 1d). Circular dichroism (CD) was used to investigate the backbone orientation of the dipeptide within the hydrogel. CD analysis of peptide-based supramolecular materials is prone to artifacts. Usually only a narrow concentration range, where the hydrogel forms, can be used reliably to present a detectable CD signal, while showing no or little light scattering ef-

The production of functional molecular architectures through self-assembly is commonplace in biology, but despite advances, it is still a major challenge to achieve similar complexity in the laboratory. Self-assembled structures that are reproducible and virtually defect free are of interest for applications in three-dimensional cell culture, templating, biosensing and supramolecular electronics. Here, we report the use of reversible enzyme-catalysed reactions to drive self-assembly. In this approach, the self-assembly of aromatic short peptide derivatives provides a driving force that enables a protease enzyme to produce building blocks in a reversible and spatially confined manner. We demonstrate that this system combines three features: (i) self-correction--fully reversible self-assembly under thermodynamic control; (ii) component-selection--the ability to amplify the most stable molecular self-assembly structures in dynamic combinatorial libraries; and (iii) spatiotemporal confinement of nucleation and structure growth. Enzyme-assisted self-assembly therefore provides control in bottom-up fabrication of nanomaterials that could ultimately lead to functional nanostructures with enhanced complexities and fewer defects.

We demonstrate that proteases can be used to selectively trigger the self-assembly of peptide hydrogels via reversed hydrolysis.

Nanofibrous materials yielded by the self-assembly of peptides are rich in potential; particularly for the formation of scaffolds that mimic the landscape of the host environment of the cell. Here, we report a novel methodology to direct the formation of supramolecular structures presenting desirable amino acid sequences by the selfassembly of minimalist peptides which cannot otherwise yield the desired scaffold structures under biologically relevant conditions. Through the rational modification of the pK a , we were able to optimise ordered charge neutralised assembly towards in vivo conditions.

Stem cell transplants offer significant hope for brain repair following ischemic damage. Pre-clinical work suggests that therapeutic mechanisms may be multi-faceted, incorporating bone-fide circuit reconstruction by transplanted neurons, but also protection/regeneration of host circuitry. Here, we engineered hydrogel scaffolds to form "bio-bridges" within the necrotic lesion cavity, providing physical and trophic support to transplanted human embryonic stem cell-derived cortical progenitors, as well as residual host neurons. Scaffolds were fabricated by the self-assembly of peptides for a laminin-derived epitope (IKVAV), thereby mimicking the brain's major extracellular protein. Following focal ischemia in rats, scaffold-supported cell transplants induced progressive motor improvements over 9 months, compared to cell- or scaffold-only implants. These grafts were larger, exhibited greater neuronal differentiation, and showed enhanced electrophysiological properties reflective of mature, integrated neurons. Varying graft timing post-injury enabled us to attribute repair to both neuroprotection and circuit replacement. These findings highlight strategies to improve the efficiency of stem cell grafts for brain repair.

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Successful control of stem cell fate in tissue engineering applications requires the use of sophisticated scaffolds that deliver biological signals to guide growth and differentiation. The complexity of such processes necessitates the presentation of multiple signals in order to effectively mimic the native extracellular matrix (ECM). Here, we establish the use of two biofunctional, minimalist self-assembling peptides (SAPs) to construct the first co-assembled SAP scaffold. Our work characterises this construct, demonstrating that the physical, chemical, and biological properties of the peptides are maintained during the co-assembly process. Importantly, the coassembled system demonstrates superior biological performance relative to the individual SAPs, highlighting the importance of complex ECM mimicry. This work has important implications for future tissue engineering studies.

Functionalized N-fluorenylmethyloxycarbonyl self-assembling peptides are biocompatible in vivo, demonstrating their utility as a cell delivery vehicle for tissue engineering.