Alginate Hydrogel Formulations for Evaluating Staphylococcus Epidermidis Biofilm Growth in Soft Microenvironments

Staphylococcus epidermidis is an opportunistic pathogen that forms biofilms on medical devices such as catheters, prosthetics, and stents. Current in vitro models of biofilm growth do not account for the mechanical environment of the host. Here we evaluate three alginate hydrogel formulations for studying bacterial biofilm growth in soft microenvironments. Additionally, we assess the use of a bacterial growth media reservoir as a nutrient source for bacterial biofilms grown in hydrogels. The mechanical properties of the hydrogels were measured using rheology and bacterial growth within the hydrogels was assessed using confocal microscopy coupled with quantitative image analysis. We determined that alginate hydrogels can be formulated using water or bacterial growth media; however, alginate hydrogel mechanical properties are five times softer when hydrogels are formulated with bacterial growth media. Additionally, a bacterial media reservoir can be utilized as the nutrient source for bacteria grown in hydrogels. Analysis of bacterial growth in hydrogels with a bacterial growth media reservoir showed that bacterial aggregate size was similar in alginate hydrogels across two different stiffnesses, while overall bacterial growth was two times higher in the softer of the two alginate hydrogels. These findings create a basis for using alginate hydrogels in biofilm infection models that mimic the mechanics of the host microenvironment.