Controlling Shape Morphing and Cell Release in Engineered Living Materials

Engineered living materials (ELMs) are a class of materials that incorporate living organisms into biomaterial matrices to derive functions from both living and non-living components. By combining and tuning the properties of both living and non-living components, desired functionalities can be achieved for biosensing, therapeutic, self-healing, and shape-morphing applications. Here, we introduce a method to control the delivery of bacteria from ELMs by varying the cell loadings and matrix stiffnesses. Controlling the long-term delivery of bacteria could potentially be used in biomedical applications to modulate microbial communities within the human body. We fabricate ELMs by encapsulating <i>E. coli</i> DH5α within a non-degradable crosslinked acrylic hydrogel matrix. Growing these ELMs for 1-day results in a volume change of &gt;100%, due to cell proliferation. The forces that drive these shape changes can also release the cells found on or near the surface of the ELMs to the surrounding growth media. When the ELM was introduced to fresh growth media every 24 h for 10 days, the ELM was able to release ~10⁴ colony forming units / mL to the surrounding media within 30 min. Finally, with controlled cell delivery from ELMs, we demonstrated a potential therapeutic material by releasing a probiotic <i>E. coli</i>, asymptomatic bacteriuria (ABU 83972), which could then modulate the proliferation of a uropathogenic E. coli strain, CFT073, <i>in vitro</i>. The ELMs will also be implanted in the urinary bladder of a mouse model and the therapeutic performance will be studied.