Rheological Study of Pluronic/Pluronic Diacrylate Hydrogels Used for Bacteria Encapsulation in Engineered Living Materials

Pluronic (Plu) hydrogels containing Pluronic diacrylate (PluDA) have been used to encapsulate bacteria and yeast in engineered living materials (ELMs). These hydrogels allow regulation of the bacteria growth and prevention of outgrowth by adjusting the PluDA fraction, i.e. the mechanical properties of the hydrogel. Understanding the correlation between matrix mechanics and bacteria growth is relevant for the performance and safety of ELMs. Here we investigate the rheological behavior of 30 wt.% Plu/PluDA hydrogels with increasing PluDA fraction between 0 and 1, which have been used by several groups in ELM design. We present stress relaxation and creep-recovery experiments, and analyze the variation of the critical yield strain/stress, relaxation and recovery parameters of Plu/PluDA hydrogels as function of the covalent crosslinking degree using the Burgers and Weilbull models. This detailed rheological study provides fundamental materials information to a relevant hydrogel model for ELM development. The results will help to validate biophysical models of bacteria growth in Plu/PluDA confinement, beyond the simple association to materials elasticity. The results might also help for machine learning model development in future work.