Self-Growing and Mechanically Tunable Living Materials with <i>Paenibacillus mucilaginosus</i> Extracellular Polymeric Substances

High Resolution Image Download MS PowerPoint Slide Engineered living materials (ELMs) typically embed functional cells in nonliving matrices, limiting growth, remodeling, and long-term adaptation at the material level. Here, we introduce extracellular polymeric substances (EPS) produced by Paenibacillus mucilaginosus as a living carrier matrix for ELMs. P. mucilaginosus EPS possesses suitable rheological behavior, such as shear thinning and elastic recovery, required for extrusion-based fabrication. Its mechanical properties can be further tuned through dynamic covalent cross-linking via boronate ester formation or physical reinforcement with Laponite or xanthan gum. With boronate ester cross-linking (18 mM), the storage modulus increased from 100 to 800 Pa. The inclusion of 0.5 w/v % Laponite further increased the modulus to 1300 Pa. Uniquely, a living matrix comprised of P. mucilaginosus EPS provides a substrate for material growth. As a proof of concept, we manufactured photosynthetic living materials by embedding a photosynthetic cyanobacterium strain, Synechococcus sp. PCC 7002, in the EPS matrix and printed into defined architectures. Both P. mucilaginosus and cyanobacterium PCC 7002 remained viable and grew over 30 days. Matrix outgrowth and microbial colonization enabled the expansion of the living constructs within the printed structure. This work establishes P. mucilaginosus EPS as a candidate living scaffold for self-growing and mechanically tunable ELMs.