Designing peptide / graphene hybrid hydrogels through fine tuning of molecular interactions

A recent strategy that has emerged for the design of increasingly functional hydrogels is the incorporation of nanofillers in order to exploit their specific properties to either modify the performance of the hydrogel or add functionality. The emergence of carbon nanomaterials in particular has provided great opportunity for the use of graphene derivatives (GDs) in biomedical applications. The key challenge when designing hybrid materials is the understanding of the molecular interactions between the matrix (peptide nanofibers) and the nanofiller (here GDs) and how these affect the final properties of the bulk material. For the purpose of this work, three gelling β-sheet forming self-assembling peptides with varying physiochemical properties and five GDs with varying surface chemistries were chosen to formulate novel hybrid hydrogels. First the peptide hydrogels and the GDs where characterised, subsequently the molecular interaction between peptides nanofibres and GDs where probed before formulating and mechanically characterising the hybrid hydrogels. We show how the interplay between electrostatic interactions, that can be attractive or repulsive, and hydrophobic (and π-π in the case of peptide containing phenylalanine) interactions, that are always attractive, play a key role on the final properties of the hybrid hydrogels. The shear modulus of the hydrid hydrogels is shown to be related to the strength of fibre adhesion to the flakes, the overall hydrophobicity of the peptides as well as the type of fibrillar network formed. Finally the cytotoxicity of the hybrid hydrogel formed at pH 6 was also investigated by encapsulating and culturing human mesenchyme stem cells (hMSC) over 14 days. This work clearly shows how interactions between peptides and GDs can be used to tailor the mechanical properties of the resulting hydrogels allowing the incorporations of GD nanofillers in a controlled way and opening the possibility to exploit their intrinsic properties to design novel hybrid peptide hydrogels for biomedical applications.