HydroGuard: a controlled release hydrogel-phage delivery system to combat catheter-associated urinary tract infections

Catheter-associated urinary tract infections (CAUTIs) rank as the fourth-most significant nosocomial infection globally. CAUTIs account for approximately 80% of hospital-acquired urinary tract infections and represent nearly one-third of all device-associated infections. Urinary catheters serve as a hub for bacteria to form highly resistant biofilms containing pathogens, like Enterococcus (E.) faecalis that reduce effectiveness of the immune system and antibiotic treatments. Therefore, tackling biofilm formation at the catheter surface becomes a crucial step in mitigating CAUTIs. We aim to address E. faecalis biofilm formation by engineering HydroGuard: a Gelatin Methacryloyl (Gel-MA)-based hydrogel injected with bacteriophages, to provide targeted, enzyme-triggered antimicrobial activity. Enterococcus faecalis expresses gelatinase (GelE), a zinc metalloprotease that enhances biofilm formation. GelMA is susceptible to GelE-mediated degradation, enabling enzyme-triggered release of bacteriophages that specifically lyse E. faecalis. For a Biosafety Level 1 proof-of-concept experiment with a well-studied host and phage system, we heterologously expressed GelE in Escherichia (E.) coli DH5α to emulate native E. faecalis expression. This system was tested on dynamically grown biofilms, to simulate similar conditions to the urinary tract. Currently, the E. coli system has shown preliminary inhibition when tested against the hydrogel product, however testing of different phage combinations is needed. Mathematical modelling identified hydrogel crosslinking density as a critical tuneable parameter governing therapeutic availability and predicted nonlinear, degradation-dependent phage release profiles. Sensitivity analyses revealed design trade-offs between structural stability and antimicrobial responsiveness. Together, the biofilm, hydrogel, phage-bacteria, and protein design models form a multiscale computational framework that links biofilm development and environmental conditions to enzyme-mediated hydrogel degradation, phage release, and bacterial suppression. Agent-based biofilm simulations captured emergent spatial dynamics under nutrient, flow, and pH constraints, while a coupled predator-prey model investigated phage-bacteria population dynamics within the degrading GelMA matrix. Computational protein design further explored collagen-like peptide motifs with enhanced folding stability and preserved gelatinase cleavage sites, providing a molecular-level approach to tuneable degradation kinetics. This multiscale framework provides predictive insight into how biofilm conditions, hydrogel degradation, and phage availability interact within the proposed system, while the preliminary experimental observations provide supporting evidence for its feasibility. By integrating synthetic biology, tissue engineering, and modelling, HydroGuard offers a novel, non-antibiotic strategy for CAUTI prevention.