Controlling shape morphing and cell release in engineered living materials.

Engineered living materials (ELMs) derive functionality from both a polymer matrix and the behavior of living cells within the material. The long-term goal of this work is to enable a system of ELM-based medical devices with both mechanical and bioactive functionality. Here, we fabricate multifunctional, stimuli-responsive ELMs comprised of acrylic hydrogel matrix and Escherichia coli. These ELMs undergo controlled changes in form and have a controlled release of bacteria from the composite. We hypothesize that the mechanical forces associated with cell proliferation within a covalently-crosslinked, non-degradable hydrogel are responsible for both phenomena. At constant cell loading, increased hydrogel elastic modulus significantly reduces both cell delivery and volume change associated with cell proliferation. ELMs that change volume over 100 % also result in ~10 colony forming units/mL in the growth medium over 2 h after 1 day of growth. At constant monomer feed ratios, increased cell loading leads to significantly increased cell delivery. Finally, these prokaryotic ELMs were investigated for their potential to deliver a probiotic that can reduce the proliferation of a uropathogen in vitro. Controlling the long-term delivery of bacteria could potentially be used in biomedical applications to modulate microbial communities within the human body.