To broaden the application space of engineered living materials (ELMs), their mechanical properties must be improved to be commensurate with contemporary construction materials, such as concrete, wood, and fossil fuel-derived polymeric plastics. Currently, the majority of ELMs make use of soft materials, such as hydrogels, as they are biocompatible and amenable to rapid fabrication methods, such as 3D bioprinting. However, the mechanical stiffness of the resulting materials is very low (e.g., Young’s modulus around 100 kPa) when compared with load-bearing structures from synthetic polymers (in the GPa stiffness range). Whilst some efforts have been made towards mineralising engineered living materials, the resulting composites are often brittle, due to a lack of continuity of a complementary organic matrix around the precipitated inorganic crystal phase. The organic phase is what gives natural bio-inorganic composite materials their remarkable toughness, combining high modulus crystals with elastic biopolymer networks. To recreate these specific structures in an autonomously biomineralizing ELM, a method for controlling the 3D spatial distribution of crystal nucleation sites is required. In this project, we will design fusions of mineral-templating proteins with polysaccharide binding motifs for secretion within varied 3D printable biopolymer hydrogels to achieve in-situ homogenous functionalisation of the matrix.

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Figure 1. Enzyme-mediated biomineralization. Transmission electron microscopy images of a 3D hydrogel before (left) and after (right) mineralization (from Rauner et al. Nature 543, 407–410 2017.)