Over the last decade, synthetically designed scaffolds are emerging as promising biomaterials for tissue engineering applications. In this context, peptide hydrogels are gaining wide attention, owing to their ability to mimic structural and functional complexity of the natural extracellular matrix (ECM). To this end, exploration of minimalistic bioactive peptide sequences for the fabrication of tissue engineering scaffolds provides a competitive edge over the conventional design principles where complex sequences were mainly explored for scaffold formation. In the present study, we explored the self-assembling potential of minimalistic bioactive peptide sequence from tenascin-C protein and its application in supporting cellular viability and proliferation. Tenascin-C is a multimeric protein known to express in adult tissues mainly during tissue injury or remodeling. To the best of our knowledge, the designed octapeptide is the shortest bioactive sequence derived solely from tenascin-C, which is known in the literature to impart specific bioactivity. The short peptide sequence showed high propensity to form a nanofibrous network at physiological pH, which was further entangled to form a macroscopic hydrogel network. Interestingly, the gels were found to be mechanoresponsive and thixotropic which opens up the scope for utilizing them as designer injectable matrices. These novel hydrogels supported the growth and proliferation of cells of both neural and non-neural ECM origin. However, neural cells cultured on these bioactive hydrogels showed normal β-III tubulin expression, highlighting their specific potential to be further explored for tissue engineering applications.

Controlling the self-assembly pathways can be an effective means to create complex multifunctional structures based on a single gelator design. To this direction, an ion mediated approach to control and direct supramolecular structure of the low molecular weight peptide hydrogelator would be an excellent methodology for bottom-up nanofabrication of these advanced functional materials. Our work primarily aims to understand the role of different metal ions as well as anions in modulating the self-assembly of the peptide amphiphiles. Our approach relies on rational incorporation of histidine in the peptide amphiphile, which can impart an ion responsive behavior to the hydrogels. Interestingly, the selfassembly pathway of histidine based dipeptide amphiphile was found to be largely influenced by various metal salts. A gel to sol transition occurred at physiological pH in the presence of Cu 2+ , Ni 2+ and Co 2+ ions, owing to their strong interactions with the histidine, thus shifting the gelation to pH 3.0. However, in the case of Fe 2+ and Mn 2+ , the weak interactions of histidine−metal ion can still hold the gel at physiological pH but gel strength was significantly decreased. Our studies provide a clear insight into this ion-responsive behavior across a wide pH range, which is mainly governed by the stability of a peptide−metal ion complex as per Irving−Williams series. Moreover, anions also influenced the mechanical strength as well as morphology of the nanostructures owing to their differential interaction with water as depicted in the Hofmeister series of anions. This bioinspired approach will provide an elegant strategy for accessing diverse structures, which are "out of equilibrium" and otherwise only accessible through differential molecular design. We envisage that our systematic studies on histidine−metal ion interaction can be an extremely useful methodology, which will pave a way to design and develop the stimuli responsive biomaterials.

Creating diverse nanostructures from a single gelator through modulating the self-assembly pathway has been gaining much attention in recent years. To this direction, we are exploring the effect of modulation of pH as a potential self-assembly pathway in governing the physicochemical properties of the final gel phase material. In this context, we used a classical nongelator with the ionic complementary sequence FEFK, which was rationally conjugated to an aromatic group naphthoxyacetic acid (Nap) at the N-terminal end to tune its gelation behavior. Interestingly, the presence of oppositely charged amino acids in the peptide amphiphile resulted in pH-responsive behavior, leading to the formation of hydrogels over a wide pH range (2.0–12.0); however, their structures differ significantly at the nanoscale. Thus, by simply manipulating the overall charge over the exposed surface of the peptide amphiphiles as a function of pH, we were able to access diverse self-assembled nanostructures within a single gelator domain. The charged state of the gelator at the extreme pH (2.0, 12.0) led to a thinner fiber formation, in contrast to the thicker fibers observed near the physiological pH owing to charge neutralization, thus promoting the lateral association. Such variation in molecular packing was found to be further reflected in the variable mechanical strengths of the peptide hydrogels obtained at different pH values. Moreover, the gelation of the peptide at physiological pH offers an additional advantage to explore this hydrogel as a cell culture scaffold. We anticipate that our study on controlling the self-assembly pathway of the ionic complementary peptide amphiphile can be an elegant approach to access diverse self-assembled materials, which can expand the zone of its applicability as a stimuli-responsive biomaterial.

Multicomponent self-assembly is an emerging approach in peptide nanotechnology to develop nanomaterials with superior physical and biological properties. Inspired by the multicomponent nature of the native extracellular matrix (ECM) and the well-established advantages of co-assembly in the field of nanotechnology, we have attempted to explore the noncovalent interactions among the sugar and peptide-based biomolecular building blocks as an approach to design and develop advanced tissue scaffolds. We utilized TEMPO-oxidized nanofibrillar cellulose (TO-NFC) and a short ionic complementary peptide, Nap-FEFK, to fabricate highly tunable supramolecular hydrogels. The differential doping of the peptide into the TO-NFC hydrogel was observed to tune the surface hydrophobicity, microporosity, and mechanical stiffness of the scaffold. Interestingly, a differential cellular response was observed toward composite scaffolds with a variable ratio of TO-NFC versus Nap-FEFK. Composite scaffolds having a 10:1 (w/w) ratio of TO-NFC and the Nap-FEFK peptide showed enhanced cellular survival and proliferation under two-dimensional cell culture conditions. More interestingly, the cellular proliferation on the 10:1 matrix was found to be similar to that of Matrigel in three-dimensional culture conditions, which clearly indicated the potential of these hydrogels in advanced tissue engineering applications. Additionally, these composite hydrogels did not elicit any significant inflammatory response in Raw cells and supported their survival and proliferation, which further emphasized their ability to form versatile scaffolds for tissue regeneration. This multicomponent assembly approach to construct biomolecular composite hydrogels to access superior physical and biological properties within the scaffold is expected to improve the scope for designing novel ECM-mimicking biomaterials for regenerative medicine.

Neural tissue engineering holds great potential in addressing current challenges faced by medical therapies employed for functional recovery of brain. In this context, self-assembling peptides have gained considerable interest owing...