Hydrogels hold much promise as materials for 3-dimensional printing, however, challenges remain in tailoring the mechanical properties of hydrogels1. Here, we address this by developing mechanically modular hydrogels from rationally designed 3-armed diblock copolypeptides composed of poly(L-glutamate) flanked by sequences of poly(L-tyrosine) or poly(L-valine). Changing outer blocks of the copolypeptides adjusts the stability of the secondary structure, which contributes to drastically different mechanical properties. The diblock copolypeptide hydrogels are then functionalized with methacrylate residues, endowing them with photopolymerization capabilities. The aforementioned properties render them direct ink write (DIW) printable, capable of generating highly stable and well resolved 3D structured objects. Photopolymerization of pendant methacrylate residues affords robust hydrogel materials with modular mechanical toughness based on sequence choice of outer polypeptide blocks. While both hydrogels exhibit contrasting stiffness, they are highly viable as bioink feedstocks for bacteria-laden DIW 3D printing. Hydrogel 3D geometries can be readily printed with high fidelity while maintaining bacteria viability, enabling development of materials capable of harnessing synthetic biology operations. The tunable stiffness of different copolypeptide networks enables control over proliferation and colony formation for embedded E. coli bacteria as demonstrated via isopropyl ß-D-1-thiogalactopyranoside (IPTG) induction of green fluorescent protein (GFP) expression (Figure 1). This translation of molecular structure to network properties highlights the versatility of these polypeptide hydrogel systems with the subsequent biological activity illustrating the future potential of these 3D printed biocomposites.

Tailorable polypeptide-based copolymers for 3D bioprinting of bacteria-laden composites via direct ink writing

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