Living Materials Approach for In Situ Bio-Polymers Production Using Bacillus Paralicheniformis in Microneedles

Living biomaterials, which integrate live organisms with traditional macromolecular scaffolds, function as "live manufacturers" capable of sensing their environment, synthesizing, and releasing biomolecules while remaining stable under physiological conditions. While systems that produce small biomolecules continue to advance, in situ production and secretion of high-molecular-weight biopolymers remain relatively underexplored. Here, a microneedle (MN) patch system is presented encapsulating Bacillus paralicheniformis (B. paralicheniformis) - a non-pathogenic, Gram-positive bacterium known for its production of γ-polyglutamic acid (γ-PGA). The MNs are designed to painlessly penetrate the stratum corneum and reach the dermis. Bacteria are uniformly distributed within the patch, and their presence has minimal impact on the microneedles' morphology and mechanical integrity. Upon application, B. paralicheniformis is released from the MNs and successfully produced γ-PGA, with molecular weights ranging from 64 to 563 kDa. Growth studies revealed that Luria-Bertani (LB) medium supports optimal bacterial proliferation, while E medium enhances γ-PGA biosynthesis. In vivo studies confirmed that B. paralicheniformis colonized mouse skin following MN administration and secreted γ-PGA without eliciting toxicity or inflammatory responses. Given the increasing therapeutic use of biopolymers and proteins for treating chronic and acute skin conditions, this living bacterial delivery system offers a promising platform for sustainable and symbiotic dermal therapies.