Self-healing, 3D printed bioinks from self-assembled peptide and alginate hybrid hydrogels

There is a pressing need for new cell-laden, printable, biomaterials that are rigid and highly biocompatible. These materials can mimic stiffer tissues such as cartilage, fibrotic tissue and cancer microenvironments, and thus have exciting applications in regenerative medicine, wound healing and cancer research. Self-assembled peptides (SAPs) functionalised with aromatic groups such as Fluorenyl-9-methoxycarbonyl (Fmoc) show promise as components of these biomaterials. However, the harsh basic conditions often used to solubilise SAPs leads to issues with toxicity and reproducibility. Here, we have designed a hybrid material comprised of self-assembled Fmoc-diphenylalanine (Fmoc-FF) assemblies dispersed throughout a sodium alginate matrix and investigated the influence of different organic solvents as peptide solubilising agents. Bioinks fabricated from peptides dissolved in 1,1,1,3,3,3-Hexafluoro-2-propanol (HFIP) showed improved biocompatibility compared to those made from Dimethyl Sulfoxide (DMSO) peptide stocks, due to the increased volatility and reduced surface tension of HFIP, allowing for more efficient expulsion from the system. Through optimisation of assembly and solvent conditions we can generate hybrid bioinks with stiffnesses up to 8 times greater than sodium alginate alone that remain highly printable, even when laden with high concentrations of cells. In addition, the shear-thinning nature of the self-assembled peptide assemblies gave the hybrid bioinks highly desirable self-healing capabilities. Our developed hybrid materials allow the bioprinting of materials previously considered too stiff to extrude without causing shear induced cytotoxicity with applications in tissue engineering and biosensing.